Anatomy and Physiology 2e PDF Download – Betts, Desaix et al. (OpenStax) BS Biology / Health

Anatomy and Physiology 2e is the OpenStax textbook for the two-semester human anatomy and physiology course, written by senior contributing authors including J. Gordon Betts, Peter Desaix, Eddie Johnson and Jody E. Johnson with a large team of contributing authors, and you can download it free as a PDF from the official OpenStax site. Its 28 chapters in six units run from the language of anatomy, chemistry, cells and tissues, through the skin, skeleton, muscles, nerves and hormones, to the heart, blood, immunity, breathing, digestion, metabolism, kidneys and reproduction.

The book is written for life science and allied health students, which makes it a natural fit for BS Biology and health-related degrees. This page gives a summary, key points, a tip, a common mistake and two practice questions for every chapter, plus a study plan, so you know what to read first before you open the official book.

Book Overview

Chapter List

Chapter 1: An Introduction to the Human Body

Unit 1: Levels of Organization · Difficulty: Easy · Key topics: anatomy vs physiology, levels of organization, organ systems, homeostasis, negative feedback, anatomical position, body cavities, medical imaging

The opening chapter separates anatomy, the study of body structure, from physiology, the study of how those structures work, and explains why the two are learned together. It builds the body from six levels of organization and introduces the eleven organ systems. It then covers the functions of human life, the requirements for survival (oxygen, nutrients, suitable temperature and pressure) and homeostasis with its negative and positive feedback loops. The chapter ends with anatomical position, directional terms, body planes and cavities, and the main medical imaging methods.

Key Points:

• The six levels of organization are chemical, cellular, tissue, organ, organ system and organism.
• Metabolism has two halves: anabolism builds molecules and catabolism breaks them down.
• A person survives only minutes without oxygen, several days without water and several weeks without nutrients.
• Every homeostatic loop has four parts: stimulus, sensor, control center and effector.
• Negative feedback reverses a change; positive feedback intensifies it until an end point is reached.
• The three body planes are sagittal, frontal and transverse; the two main cavities are dorsal (posterior) and ventral (anterior).
• Serous membranes have a parietal and a visceral layer around a fluid-filled space: pleura (lungs), pericardium (heart) and peritoneum (abdominopelvic organs).

Memory Tip: Picture a home thermostat. A room that gets too hot is the stimulus, the thermometer is the sensor, the thermostat setting is the control center and the air conditioner is the effector.

Common Mistake: Reading “negative” feedback as “bad” feedback. Negative means the response reverses the change and brings the body back toward its set point.

Important Questions:

• What are the four components of a negative feedback loop? Stimulus, sensor, control center and effector. If a chemical is secreted in excess, sensors activate the control center, which tells the effector (the secreting cells) to reduce output.
• Why is ultrasound the technique of choice for studying fetal growth? Ultrasonography exposes the mother and fetus to no radiation, no radiopharmaceuticals and no magnetic fields, and no medical risks are currently known.

Chapter 2: The Chemical Level of Organization

Unit 1: Levels of Organization · Difficulty: Medium · Key topics: atoms, isotopes, valence shell, ionic and covalent bonds, chemical reactions, enzymes, pH and buffers, carbohydrates, lipids, proteins, nucleotides, ATP

This chapter supplies the chemistry needed for the rest of the book. It starts with elements and atoms, atomic number, mass number, isotopes and the valence shell that makes an atom stable or reactive. It then explains ionic, covalent and hydrogen bonds, the energy changes in chemical reactions and the factors that change reaction rate, including enzymes. The last two sections cover inorganic compounds (water, salts, acids, bases, pH and buffers) and the four organic families: carbohydrates, lipids, proteins and nucleotides such as DNA, RNA and ATP.

Key Points:

• Oxygen, carbon, hydrogen and nitrogen are the most abundant elements in the body and make up more than 95 percent of its mass.
• Atomic number is the number of protons; mass number is protons plus neutrons; isotopes of an element differ in neutrons.
• Ionic bonds attract cations to anions, covalent bonds share electrons, and hydrogen bonds link polar molecules such as water.
• Synthesis reactions build bonds and need energy, decomposition reactions break bonds and release energy, exchange reactions do both.
• pH 7 is neutral and each pH unit is a ten-fold change in hydrogen ions; blood pH stays between 7.35 and 7.45, protected by buffers.
• Dehydration synthesis joins monomers into polymers and hydrolysis splits them; a triglyceride is glycerol plus three fatty acids.
• Proteins are chains of amino acids joined by peptide bonds, and ATP is the body’s basic molecule of energy transfer.

Memory Tip: Atoms want a full valence shell: eight electrons, or two for hydrogen. Keep that octet rule in mind and you can predict whether an atom will donate, accept or share electrons.

Common Mistake: Reading the pH scale backwards. A lower pH means more acidic: lemon juice (pH 2) has 100 times the hydrogen-ion concentration of orange juice (pH 4).

Important Questions:

• Lemon juice has pH 2 and orange juice pH 4. Which is more acidic, and by how much? Lemon juice is one hundred times more acidic, meaning it has a one hundred-fold greater concentration of hydrogen ions.
• How many carbon, hydrogen and oxygen atoms does maltose contain? Twelve carbon, 22 hydrogen and 11 oxygen atoms. Maltose is two glucose molecules (C6H12O6 each) joined by dehydration synthesis, which removes one molecule of water.

Chapter 3: The Cellular Level of Organization

Unit 1: Levels of Organization · Difficulty: Medium · Key topics: cell membrane, diffusion and osmosis, active transport, organelles, DNA replication, transcription, translation, cell cycle, mitosis, stem cells

Chapter 3 tours the cell. It begins with the phospholipid-bilayer cell membrane and the passive and active transport processes that move materials across it, including osmosis. It then describes the cytoplasm and organelles: the endomembrane system (endoplasmic reticulum, Golgi apparatus, lysosomes), mitochondria, peroxisomes and the cytoskeleton. The remaining sections follow genetic information from the nucleus and DNA replication through protein synthesis (transcription and translation) to the cell cycle and mitosis, and finish with cellular differentiation and stem cells.

Key Points:

• The cell membrane is a selectively permeable phospholipid bilayer; only small, nonpolar molecules cross it easily.
• Passive transport (diffusion, facilitated diffusion, osmosis) moves substances down a gradient with no energy; active transport moves them against it using pumps or vesicles.
• Rough ER makes proteins, smooth ER makes lipids and stores ions, the Golgi apparatus modifies and packages, lysosomes digest and mitochondria make ATP.
• DNA replication is semiconservative: each new molecule keeps one original strand and gains one new strand.
• Transcription copies a gene into mRNA; translation reads the mRNA codons at a ribosome while tRNA delivers the amino acids.
• Interphase consists of G1, S and G2; mitosis runs prophase, metaphase, anaphase, telophase and is followed by cytokinesis.
• Stem cells are ranked by potential: totipotent, pluripotent, multipotent, oligopotent and unipotent.

Memory Tip: Use PMAT for mitosis: Prophase, Metaphase, Anaphase, Telophase. For protein synthesis, remember that transcription is a copy job (DNA to RNA, same language) and translation is an interpretation job (RNA to amino acids, new language).

Common Mistake: Mixing up transcription and translation. Transcription makes mRNA from DNA in the nucleus; translation builds the protein from that mRNA at a ribosome.

Important Questions:

• Why is DNA replication called semiconservative? After replication, each daughter DNA molecule is half original (one parent strand) and half newly synthesized, so half of the parent molecule is conserved in each copy.
• What materials can easily diffuse through the lipid bilayer, and why? Only relatively small, nonpolar materials. Large particles do not fit between the packed phospholipids, and polar molecules are repelled by the hydrophobic interior of the bilayer.

Chapter 4: The Tissue Level of Organization

Unit 1: Levels of Organization · Difficulty: Medium · Key topics: epithelial, connective, muscle and nervous tissue, germ layers, cell junctions, glands, collagen, cartilage, inflammation, tissue repair

This chapter shows how cells combine into the four tissue types and how structure fits function. It first defines epithelial, connective, muscle and nervous tissue, the three embryonic germ layers and the membranes that line organs. Separate sections cover epithelium (cell junctions, squamous, cuboidal and columnar shapes, simple versus stratified layers, and glands), connective tissue (fibers, matrix, proper, supportive and fluid types), muscle tissue (skeletal, cardiac, smooth) and nervous tissue (neurons and neuroglia). It closes with inflammation, tissue repair and aging.

Key Points:

• The four tissue types are epithelial, connective, muscle and nervous; all arise from the ectoderm, mesoderm and endoderm.
• Tight junctions seal cells together, anchoring junctions attach them, and gap junctions let small molecules pass between them.
• Epithelia are named by cell shape (squamous, cuboidal, columnar) and layering (simple or stratified); exocrine glands use ducts, endocrine glands release hormones into the blood.
• Connective tissue fibers: collagen is strong, reticular fibers form a supportive mesh, elastin stretches and recoils.
• Hyaline cartilage covers joints, fibrocartilage forms the intervertebral discs and elastic cartilage springs back to shape.
• Skeletal muscle is striated, voluntary and multinucleated; cardiac muscle is striated and involuntary with intercalated disks; smooth muscle is not striated.
• The cardinal signs of inflammation are redness, warmth, swelling and pain.

Memory Tip: Give each tissue one verb: epithelium covers, connective tissue connects and supports, muscle moves, nervous tissue signals. Four verbs recover the four functions.

Common Mistake: Thinking blood is not a tissue. Blood is a fluid connective tissue: cells in a liquid matrix with no supporting fibers.

Important Questions:

• Why does an injury to hyaline cartilage heal more slowly than a bone fracture? Cartilage has no blood vessels, so the cells and nutrients needed for repair reach the injury only by slow diffusion.
• Why does skeletal muscle look striated? The contractile proteins actin and myosin are arranged in regular repeating patterns that appear as stripes under the microscope.

Chapter 5: The Integumentary System

Unit 2: Support and Movement · Difficulty: Easy · Key topics: epidermis layers, melanocytes, dermis, hypodermis, hair, nails, sweat and sebaceous glands, thermoregulation, skin cancer, burns

Chapter 5 treats the skin as an organ system. It describes the epidermis with its layers from stratum basale to stratum corneum, the roles of keratinocytes and melanocytes, the dermis with its papillary and reticular layers, and the fat-storing hypodermis. It then covers hair, nails, and sweat and sebaceous glands. A section on function lists protection, sensation, thermoregulation and vitamin D synthesis, and the chapter ends with skin cancers, burns, scars and common conditions such as acne and eczema.

Key Points:

• Epidermis layers from deep to superficial: stratum basale, spinosum, granulosum, lucidum (when present) and corneum.
• Melanocytes in the stratum basale make melanin, which is passed to keratinocytes to shield them from UV rays.
• The dermis has two layers, papillary and reticular; the hypodermis beneath it stores fat and connects skin to underlying structures.
• Hair and nails are made of dead keratinized cells; sebum moisturizes the skin and sweat cools it.
• The skin protects, senses, regulates temperature and synthesizes vitamin D, which prevents rickets.
• Basal cell and squamous cell carcinoma are highly curable; melanoma, a cancer of melanocytes, is the most dangerous because it can metastasize.
• First- and second-degree burns usually heal quickly; third-degree burns penetrate the full thickness of the skin and can be fatal.

Memory Tip: Read the epidermis from the surface down with “Come, Let’s Get Sun Burned”: Corneum, Lucidum, Granulosum, Spinosum, Basale.

Common Mistake: Assuming the epidermis has its own blood supply. It has none; its cells depend on the dermis beneath them, which is why new cells are made in the deepest layer, the stratum basale.

Important Questions:

• What is the difference between eccrine and apocrine sweat glands? Eccrine glands are found all over the body and release watery sweat. Apocrine glands are larger, lie deeper in the dermis and are associated with hair follicles.
• Why do scars look different from the surrounding skin? Scars are made of collagen and lack the cellular structure of normal skin, so they do not regenerate hair follicles or sweat and sebaceous glands.

Chapter 6: Bone Tissue and the Skeletal System

Unit 2: Support and Movement · Difficulty: Medium · Key topics: bone functions, bone classification, osteons, osteoblasts and osteoclasts, ossification, epiphyseal plate, fractures, calcium homeostasis, PTH and calcitonin

This chapter presents bone as living tissue. It lists the functions of the skeletal system (support, movement, protection, mineral and fat storage, blood cell production) and classifies bones as long, short, flat, irregular or sesamoid. It then looks inside a bone: the diaphysis, epiphyses, periosteum, compact and spongy bone, osteons and the four bone cell types. Later sections cover intramembranous and endochondral ossification, growth at the epiphyseal plate, fracture types and repair, the effects of exercise, nutrition and hormones, and calcium homeostasis.

Key Points:

• The skeleton supports, allows movement, protects organs, stores minerals and fat, and produces blood cells (hematopoiesis in red marrow).
• Bone shapes: long (femur), short (carpals), flat (ribs), irregular (facial bones) and sesamoid (patella).
• Osteoblasts build bone, osteocytes maintain it and osteoclasts resorb it; the matrix is collagen plus hydroxyapatite.
• Compact bone is made of osteons; spongy bone is made of trabeculae and houses red marrow.
• Intramembranous ossification forms bone directly from mesenchyme; endochondral ossification replaces hyaline cartilage; the epiphyseal plate lengthens bones.
• Fracture repair runs through a fracture hematoma, internal and external calli, and finally remodeling.
• Parathyroid hormone raises blood calcium by stimulating osteoclasts; calcitonin lowers it by inhibiting them; normal blood calcium is about 10 mg/dL.

Memory Tip: Use the letters in the names: osteoBlasts Build bone, osteoClasts Cut it down (resorption).

Common Mistake: Treating bone as dead, fixed material. Bone is constantly remodeled, with osteoclasts removing old bone and osteoblasts replacing it, which is how it heals and responds to exercise.

Important Questions:

• How do intramembranous and endochondral ossification differ? In intramembranous ossification, bone develops directly from sheets of mesenchymal connective tissue. In endochondral ossification, bone develops by replacing hyaline cartilage.
• Why did early astronauts lose bone mass in space? Weightlessness removed the mechanical stress of gravity that normally stimulates bone deposition, so bone mass fell. Astronauts now do resistive exercise to load their bones.

Chapter 7: Axial Skeleton

Unit 2: Support and Movement · Difficulty: Hard · Key topics: axial vs appendicular skeleton, skull bones, sutures, cranial fossae, vertebral column, intervertebral disc, ribs and sternum, notochord, fontanelles

Chapter 7 describes the 80 bones of the axial skeleton. It first divides the skeleton into axial and appendicular parts, then examines the skull in detail: the eight brain-case bones, the 14 facial bones, sutures, cranial fossae, sinuses, orbits and the nasal septum. Later sections cover the vertebral column with its regions, curves, special vertebrae and intervertebral discs, and the thoracic cage of 12 pairs of ribs and the sternum. The chapter closes with embryonic development from the notochord and somites, including the fontanelles.

Key Points:

• The axial skeleton has 80 bones (skull, vertebral column, thoracic cage); the appendicular skeleton has 126.
• The brain case has eight bones (paired parietal and temporal; unpaired frontal, occipital, sphenoid and ethmoid); the face has 14.
• Major sutures: sagittal (between parietals), coronal (frontal to parietals), lambdoid (occipital) and squamous (temporal).
• The column has 7 cervical, 12 thoracic and 5 lumbar vertebrae, plus the sacrum (five fused) and coccyx (four fused); C1 (atlas) has no body and C2 (axis) has the dens.
• The thoracic and sacrococcygeal curves are primary; the cervical and lumbar curves develop after birth.
• An intervertebral disc has an outer anulus fibrosus and an inner nucleus pulposus.
• Ribs 1–7 are true ribs, 8–12 are false ribs and 11–12 are floating; the sternum has a manubrium, body and xiphoid process.

Memory Tip: Use the mealtime rule for vertebrae: breakfast at 7, lunch at 12, dinner at 5 gives 7 cervical, 12 thoracic and 5 lumbar.

Common Mistake: Counting the sacrum and coccyx among the 24 vertebrae. The 24 movable vertebrae are the cervical, thoracic and lumbar ones; the sacrum and coccyx are fused bones below them.

Important Questions:

• What are the two divisions of the skeleton? The axial skeleton (80 bones: skull, vertebral column and thoracic cage) and the appendicular skeleton (126 bones: the limbs and the girdles that anchor them).
• How are true, false and floating ribs different? True ribs (1–7) attach directly to the sternum by their own costal cartilage; false ribs (8–12) attach indirectly or not at all; floating ribs (11–12) are short and do not attach to the sternum or another rib.

Chapter 8: The Appendicular Skeleton

Unit 2: Support and Movement · Difficulty: Medium · Key topics: pectoral girdle, clavicle and scapula, humerus, radius and ulna, carpals, pelvic girdle, femur, tibia and fibula, tarsals, limb bud development

This chapter covers the 126 bones of the limbs and girdles. The pectoral girdle (clavicle and scapula) attaches each upper limb to the trunk, and the upper limb contains the humerus, radius, ulna, eight carpals, metacarpals and phalanges. The pelvic girdle section explains the ilium, ischium and pubis of the hip bone and how the two hip bones, sacrum and coccyx form the pelvis. The lower-limb section covers the femur, patella, tibia, fibula and foot bones, and the chapter ends with limb-bud development and ossification centers.

Key Points:

• The pectoral girdle is the clavicle plus the scapula; the clavicle joins the sternum at the sternoclavicular joint and the scapula at the acromioclavicular joint.
• Each upper limb has 30 bones: humerus, radius, ulna, 8 carpals, 5 metacarpals and 14 phalanges.
• Each lower limb has 30 bones: femur, patella, tibia, fibula, 7 tarsals, 5 metatarsals and 14 phalanges.
• The tibia bears the body’s weight; the fibula does not. The patella is a sesamoid bone that protects the quadriceps tendon.
• The hip bone has three regions (ilium, ischium, pubis); the pelvis is the two hip bones plus the sacrum and coccyx.
• The female pelvis is wider, with a larger subpubic angle, as an adaptation for childbirth.
• Limb buds appear at the end of week four; endochondral ossification starts in most limb bones by the twelfth fetal week, while the clavicle ossifies intramembranously.

Memory Tip: In anatomical position the radius is on the thumb side of the forearm, and the tibia is the thick, weight-bearing shin bone on the inner (medial) side of the leg.

Common Mistake: Using “pelvic girdle” and “pelvis” as the same thing. The girdle is a hip bone; the pelvis is the two hip bones together with the sacrum and coccyx.

Important Questions:

• How is the female pelvis adapted for childbirth? It is wider than the male pelvis, with greater distances between the iliac spines and between the ischial tuberosities, and a larger subpubic angle.
• How can an X-ray of a child’s femur show the child’s approximate age? It shows the epiphyseal plates of the secondary ossification centers. Each plate appears and disappears at a different age, so the pattern of open and fused plates indicates age.

Chapter 9: Joints

Unit 2: Support and Movement · Difficulty: Medium · Key topics: fibrous, cartilaginous and synovial joints, synarthrosis, amphiarthrosis, diarthrosis, six synovial types, body movements, shoulder, knee, joint development

Chapter 9 classifies joints structurally (fibrous, cartilaginous, synovial) and functionally by movement (synarthrosis, amphiarthrosis, diarthrosis). It describes the three fibrous joints, the two cartilaginous joints and the parts of a synovial joint, including the capsule, articular cartilage, synovial fluid, ligaments, menisci and bursae. It then defines body movements and the six synovial joint types, studies selected joints such as the shoulder, elbow, hip, knee, ankle, jaw and vertebral column, and ends with joint development from the joint interzone.

Key Points:

• Structural classes are fibrous, cartilaginous and synovial; functional classes are synarthrosis (immobile), amphiarthrosis (slightly mobile) and diarthrosis (freely mobile).
• Fibrous joints: suture (skull), gomphosis (tooth in its socket) and syndesmosis (radius and ulna, tibia and fibula).
• Cartilaginous joints: synchondrosis (hyaline cartilage, such as the epiphyseal plate) and symphysis (fibrocartilage, such as the pubic symphysis and intervertebral discs).
• Every synovial joint has a joint cavity, articular cartilage, an articular capsule and lubricating synovial fluid.
• The six synovial types are plane, hinge, pivot, condyloid, saddle and ball-and-socket; the ball-and-socket has the greatest range of motion.
• The shoulder relies mainly on the four rotator cuff muscles for support, while the knee depends on its menisci and cruciate ligaments.
• A synovial joint cavity forms when cells die at the center of the joint interzone.

Memory Tip: Keep the movement pairs together: flexion and extension, abduction and adduction, medial and lateral rotation. Abduction takes a limb away from the midline; adduction adds it back.

Common Mistake: Assuming the most mobile joint is the strongest. Mobility and stability trade off, which is why the shoulder moves widely but is injured more easily than the sturdy hip.

Important Questions:

• Which structures are found at all synovial joints? A joint cavity filled with synovial fluid, articular cartilage on the bone ends, and an articular capsule lined by a synovial membrane, usually reinforced by ligaments.
• How is the first sternocostal joint classified? Structurally it is a synchondrosis (a cartilaginous joint where hyaline cartilage unites the first rib to the sternum). Functionally it is a synarthrosis, an immobile joint.

Chapter 10: Muscle Tissue

Unit 2: Support and Movement · Difficulty: Hard · Key topics: skeletal, cardiac and smooth muscle, sarcomere, sliding filament model, neuromuscular junction, twitch and tetanus, muscle fiber types, ATP sources, muscle regeneration

Chapter 10 explains how muscle contracts. After comparing skeletal, cardiac and smooth muscle, it describes the connective tissue layers around skeletal muscle and the sarcomere. It then walks through the sliding filament model, from acetylcholine release at the neuromuscular junction to calcium release and ATP-powered cross-bridge cycling. Later sections cover twitch, summation, tetanus and recruitment, the three muscle fiber types, ATP supply, the effects of exercise, the distinct structure and control of cardiac and smooth muscle, and muscle development and regeneration.

Key Points:

• Skeletal muscle is wrapped by the epimysium; perimysium surrounds each fascicle and endomysium surrounds each fiber.
• The sarcomere is the smallest contractile unit: thick filaments are myosin, thin filaments are actin with troponin and tropomyosin.
• Contraction sequence: acetylcholine at the neuromuscular junction, action potential, calcium release from the sarcoplasmic reticulum, tropomyosin shifts, myosin power stroke using ATP.
• ATP comes from creatine phosphate (about the first 15 seconds), anaerobic glycolysis (2 ATP per glucose) and aerobic metabolism (about 36 ATP per glucose).
• Fiber types: slow oxidative resists fatigue, fast oxidative gives more tension, fast glycolytic is powerful but tires quickly.
• Cardiac fibers are branched and joined by intercalated discs with gap junctions and desmosomes; smooth muscle is nonstriated and uses calmodulin and dense bodies.
• Satellite cells repair skeletal muscle, pericytes regenerate smooth muscle, and damaged cardiac muscle is replaced by scar tissue.

Memory Tip: Remember that ATP does two jobs: it powers the power stroke and it lets the myosin head let go of actin. With no ATP the heads stay stuck, which is exactly what rigor mortis is.

Common Mistake: Believing ATP is used only for the pull. Without fresh ATP the myosin head cannot detach, so muscles stiffen instead of relaxing.

Important Questions:

• Why do muscle cells use creatine phosphate rather than glycolysis for the first seconds of contraction? Creatine kinase converts creatine phosphate and ADP into ATP very quickly, faster than glycolysis can generate ATP.
• What happens to a muscle if ATP is completely depleted? Myosin heads cannot detach from actin-binding sites, so the cross-bridges stay stuck and the muscle stiffens, as in a cramp or in rigor mortis.

Chapter 11: The Muscular System

Unit 2: Support and Movement · Difficulty: Hard · Key topics: origin and insertion, prime mover and antagonist, fascicle arrangement, muscle naming, axial muscles, diaphragm, rotator and forearm muscles, quadriceps, hamstrings

Chapter 11 moves from how muscle contracts to which muscles do what. It begins with origins and insertions, the roles of prime mover, synergist, fixator and antagonist, the six fascicle arrangements and lever systems. It then explains how muscles are named from location, shape, size, action and attachments. Region-by-region sections cover the axial muscles of the head, neck, back, abdominal wall, thorax and pelvic floor, the muscles of the pectoral girdle and upper limb, and those of the pelvic girdle and lower limb, such as the quadriceps and hamstrings.

Key Points:

• The origin is the stabilized attachment; the insertion is the attachment on the bone being pulled.
• The prime mover (agonist) produces a movement, synergists assist it, fixators steady the origin and antagonists oppose it.
• Fascicle arrangements are parallel, circular, convergent, pennate, fusiform and triangular; circular muscles act as sphincters.
• Muscle names carry clues: location (tibialis anterior), size (maximus, longus), shape, action (flexor, extensor) and number of heads (biceps, triceps).
• The diaphragm flattens when it contracts, enlarging the pleural cavities so air flows into the lungs.
• The anterior abdominal wall has four pairs of muscles: rectus abdominis, external oblique, internal oblique and transversus abdominis.
• The quadriceps femoris (rectus femoris plus three vastus muscles) extends the knee; the hamstrings (biceps femoris, semitendinosus, semimembranosus) flex it.

Memory Tip: The prefix gives the head count: biceps has two heads, triceps three and quadriceps four.

Common Mistake: Swapping origin and insertion. The origin is the fixed end; the insertion is on the bone that actually moves when the muscle contracts.

Important Questions:

• What is the difference between axial and appendicular muscles? Axial muscles originate on the axial skeleton (head, neck and trunk), while appendicular muscles originate on the bones of the limbs and girdles.
• What roles do agonists, antagonists, synergists and fixators play in a movement? Agonists are the prime movers, antagonists oppose or resist the movement, synergists assist the agonist, and fixators stabilize the muscle’s origin.

Chapter 12: The Nervous System and Nervous Tissue

Unit 3: Regulation, Integration, and Control · Difficulty: Hard · Key topics: CNS and PNS, gray and white matter, neurons, glial cells, resting membrane potential, action potential, graded potentials, synapses, neurotransmitters

Chapter 12 introduces the nervous system and its cells. It divides the system anatomically (central and peripheral) and functionally (sensation, integration, response), and distinguishes gray from white matter, nuclei from ganglia and tracts from nerves. It then describes neurons and the glial cells of the CNS and PNS, follows a pathway from sensory receptor to motor response, and explains the resting membrane potential and the stages of the action potential, including refractory periods and saltatory conduction. It ends with graded potentials, synapses and neurotransmitters.

Key Points:

• The CNS is the brain and spinal cord and the PNS is everything else; cell body clusters are nuclei (CNS) or ganglia (PNS), axon bundles are tracts (CNS) or nerves (PNS).
• A neuron receives signals at its dendrites, integrates them at the soma and sends them along its axon; by shape neurons are unipolar, bipolar or multipolar.
• CNS glia: astrocytes (chemical environment, blood-brain barrier), oligodendrocytes (myelin), microglia (phagocytes) and ependymal cells (cerebrospinal fluid). PNS glia: Schwann cells and satellite cells.
• The action potential runs through depolarization (voltage-gated sodium channels), repolarization (potassium leaves) and a brief hyperpolarization.
• No new action potential can start during the absolute refractory period; myelin makes conduction faster by letting the signal jump between nodes of Ranvier (saltatory conduction).
• Graded potentials summate in space and time; an excitatory PSP depolarizes the membrane and an inhibitory PSP hyperpolarizes it.
• At a chemical synapse the signal crosses the synaptic cleft as a neurotransmitter.

Memory Tip: Afferent arrives (sensory signals traveling toward the CNS) and efferent exits (motor signals traveling away from it).

Common Mistake: Confusing graded potentials with action potentials. Graded potentials vary with stimulus strength and fade with distance, while an action potential is all-or-none and travels the whole axon.

Important Questions:

• Multiple sclerosis damages myelin in the CNS. Which cell is the likely target? Oligodendrocytes, because they provide the myelin for axons in the central nervous system.
• What do the terms afferent and efferent mean? Afferent means “toward”: sensory information traveling from the periphery into the CNS. Efferent means “away from”: motor commands traveling out from the CNS.

Chapter 13: Anatomy of the Nervous System

Unit 3: Regulation, Integration, and Control · Difficulty: Hard · Key topics: neural tube, brain regions, cerebral lobes, basal nuclei, spinal cord, circle of Willis, meninges, cerebrospinal fluid, cranial nerves, spinal nerve plexuses

Chapter 13 maps the nervous system. It starts with embryology, in which the neural tube forms from ectoderm, its vesicles become the adult brain regions and the neural crest gives rise to PNS structures. It then describes the four adult brain regions (cerebrum, diencephalon, brain stem, cerebellum), the four cerebral lobes, the basal nuclei and the spinal cord. Later sections cover blood supply and the circle of Willis, the meninges, ventricles and cerebrospinal fluid, and the peripheral nervous system with its ganglia, twelve cranial nerves and spinal nerve plexuses.

Key Points:

• The neural tube forms from ectoderm (front end becomes the brain, back end the spinal cord); the neural crest forms PNS structures and facial cartilage and bone.
• The adult brain has four regions: cerebrum, diencephalon, brain stem and cerebellum; the longitudinal fissure divides the two hemispheres.
• Frontal lobe: motor planning and execution. Parietal: somatosensation. Temporal: hearing and memory. Occipital: vision.
• The circle of Willis keeps the brain perfused if one supplying artery is blocked; the blood-brain barrier isolates the CNS.
• Cerebrospinal fluid is made at the choroid plexuses in the four ventricles, flows into the subarachnoid space and is reabsorbed at the arachnoid granulations.
• The meninges from outside in are dura mater, arachnoid mater and pia mater.
• There are 12 cranial nerves (sensory, motor or mixed); all spinal nerves are mixed and, except the thoracic nerves, pass through plexuses.

Memory Tip: Meninges from the outside in spell DAP: Dura (tough, outermost), Arachnoid (the web-like middle layer), Pia (the delicate layer that clings to the brain).

Common Mistake: Assuming every spinal nerve passes through a plexus. The thoracic spinal nerves do not; they give rise directly to the intercostal nerves.

Important Questions:

• Why can the circle of Willis maintain blood flow to the brain even if one vessel is blocked? Its arteries form a circular connection, so blood arriving from one artery can flow in either direction around the circle and bypass a blockage or narrowing.
• What does the neural crest give rise to? PNS structures such as ganglia, and also the cartilage and bone of the face and cranium.

Chapter 14: The Somatic Nervous System

Unit 3: Regulation, Integration, and Control · Difficulty: Hard · Key topics: special senses, sensory receptors, phototransduction, dorsal column and spinothalamic pathways, optic chiasm, motor cortex, corticospinal tract, extrapyramidal system, reflexes

Chapter 14 follows information through the somatic nervous system. The first section covers the senses (smell, taste, somatosensation, hearing, balance and vision), their receptor types and how stimuli are transduced, from taste buds and the cochlea to the structure of the eye and phototransduction. The second traces sensory pathways to the cortex through the thalamus, contrasting the dorsal column system with the spinothalamic tract. The third follows motor commands from the prefrontal and primary motor cortex down the corticospinal tracts and explains the extrapyramidal system and reflex arcs.

Key Points:

• The special senses are smell, taste, hearing, balance and vision; somatosensation (touch, pressure, vibration, temperature, pain) is a general sense.
• Every sensory pathway except olfaction relays through the thalamus before reaching the cerebral cortex.
• The dorsal column system carries touch and proprioception and crosses in the medulla; the spinothalamic tract carries pain and temperature and crosses in the spinal cord at its level of entry.
• Fibers from the medial retina cross at the optic chiasm, so a pituitary tumor pressing on it causes loss of the lateral visual field.
• The motor stream runs prefrontal cortex, premotor cortex and supplemental motor area, primary motor cortex (Betz cells), corticospinal and corticobulbar tracts, then lower motor neurons.
• The extrapyramidal system (tectospinal, rubrospinal, vestibulospinal, reticulospinal tracts) maintains balance, posture and muscle tone.
• The stretch reflex and the corneal reflex are examples of reflex arcs.

Memory Tip: Pain and temperature cross early: the spinothalamic tract crosses at the spinal level where it enters. Touch and position cross later, in the medulla, via the dorsal columns.

Common Mistake: Assuming a one-sided spinal cord injury removes every sensation on the same side. Because the two tracts cross at different levels, touch can be lost on one side and pain and temperature on the other.

Important Questions:

• Why does a pituitary tumor cause loss of the lateral visual field? As the tumor enlarges it presses on the optic chiasm and disrupts the crossing fibers from the medial retina, which carry information about the lateral visual field.
• Stevia can replace glucose as a sweetener. What does its molecular similarity to glucose mean for taste? Stevia binds the glucose receptor in sweet-sensitive taste buds, so it tastes sweet, but it is not a substrate for ATP-generating metabolism inside cells.

Chapter 15: The Autonomic Nervous System

Unit 3: Regulation, Integration, and Control · Difficulty: Medium · Key topics: sympathetic and parasympathetic divisions, ganglia, norepinephrine and acetylcholine, visceral reflexes, referred pain, hypothalamus, cardiovascular center, autonomic drugs

Chapter 15 explains the autonomic nervous system, the output that regulates internal organs without conscious effort. It contrasts the sympathetic division (fight or flight, thoracolumbar origin) with the parasympathetic division (a restful mode that favors digestion), their two-neuron pathways, ganglia, neurotransmitters and receptors. It then covers visceral reflexes, autonomic tone and referred pain, the role of the hypothalamus, limbic system and medulla in central control, and the effects of drugs, including nicotine, on autonomic function.

Key Points:

• The sympathetic division produces fight or flight and arises from the lateral horn of the thoracolumbar spinal cord; the parasympathetic division produces a restful mode and has a craniosacral origin.
• Both divisions use a two-neuron pathway: a central neuron and a ganglionic neuron, with preganglionic fibers releasing acetylcholine onto nicotinic receptors.
• Postganglionic sympathetic fibers release norepinephrine; postganglionic parasympathetic fibers release acetylcholine.
• The sympathetic system raises heart rate and dilates the pupil; the parasympathetic system lowers heart rate.
• Visceral pain is often felt as referred pain, such as pain in the left shoulder and arm during a heart attack.
• The hypothalamus is the central autonomic structure, and the medullary cardiovascular center regulates heart function and blood pressure.
• Nicotine stimulates both sets of ganglia, but because blood pressure has essentially no parasympathetic input, the net effect is a rise in blood pressure.

Memory Tip: Think S for stress, sprint and spend energy (sympathetic), and P for peaceful and processing food (parasympathetic).

Common Mistake: Treating the two divisions as a simple on-off switch. Both are always active at some level (autonomic tone) and the body balances them; heart rate, for example, sits under parasympathetic tone.

Important Questions:

• Why would the sympathetic system not activate digestion while a lioness hunts? Blood is needed in the skeletal muscles for oxygen supply during the chase, and extra fuel from digestion would not help her as much as that blood flow.
• How do sympathetic and parasympathetic divisions differ at their connection to the target organ? Postganglionic sympathetic fibers release norepinephrine, whereas postganglionic parasympathetic fibers release acetylcholine.

Chapter 16: The Neurological Exam

Unit 3: Regulation, Integration, and Control · Difficulty: Hard · Key topics: localization of function, mental status exam, aphasia, cranial nerve exam, upper vs lower motor neuron signs, reflexes, cerebellar ataxia, stroke and TIA

Chapter 16 applies nervous system anatomy to clinical assessment. It outlines the five parts of the neurological exam, each aimed at a region of the CNS: mental status for the cerebrum, the cranial nerve exam, the sensory and motor exams for the spinal cord and reflexes, and the coordination and gait exam for the cerebellum. It introduces localization of function and the types of stroke. Each later section explains what the tests check and what a deficit points to, such as aphasia, cranial nerve palsies, upper versus lower motor neuron signs and cerebellar ataxia.

Key Points:

• The exam has five parts: mental status (cerebrum), cranial nerves, sensory, motor, and coordination and gait (cerebellum).
• Localization of function: the location of damage matches the function that is lost.
• An ischemic stroke is a blocked blood supply and a hemorrhagic stroke is bleeding; a transient ischemic attack (TIA) resolves within 24 hours.
• Wernicke’s area handles language comprehension (damage causes receptive aphasia); the medial temporal lobe, including the hippocampus, is essential for forming memories.
• The Rinne and Weber tests separate conductive from sensorineural hearing loss.
• Spasticity, hyperreflexia and a Babinski sign point to upper motor neuron damage; flaccid paralysis and fasciculations point to lower motor neuron damage.
• The cerebellum compares motor commands with sensory feedback; damage causes ataxia (poorly coordinated movement).

Memory Tip: Upper motor neuron damage sends tone and reflexes up (spastic, brisk reflexes); lower motor neuron damage lets them fall low (flaccid, weak reflexes).

Common Mistake: Dismissing a TIA because the symptoms disappeared. The only difference from a stroke is duration (under 24 hours); it signals the same blood-flow problem.

Important Questions:

• How is a TIA different from a stroke? The main difference is time. If the effects of the cerebrovascular event last longer than 24 hours it is a stroke; if they resolve sooner it is classed as a transient ischemic attack.
• A patient looks puzzled when asked “What is your name?” Which language area is likely damaged, and what is the aphasia called? Wernicke’s area, which supports comprehension of language; the condition is receptive aphasia.

Chapter 17: The Endocrine System

Unit 3: Regulation, Integration, and Control · Difficulty: Medium · Key topics: hormone classes, cAMP second messenger, hypothalamus and pituitary, thyroid, parathyroid and calcium, adrenal glands, pancreas, insulin and glucagon, stress response

Chapter 17 compares neural and endocrine communication, then covers the hormone classes (amine, peptide and steroid), their receptors and second messengers such as cAMP and IP3. It goes gland by gland: the hypothalamus and pituitary (two posterior and six anterior hormones), thyroid, parathyroids, adrenals, pineal gland, gonads and placenta, and the endocrine pancreas with insulin and glucagon. It closes with organs that have secondary endocrine roles, such as the heart, stomach and kidneys, and with development and aging of the endocrine system.

Key Points:

• Hormones are amino acid derivatives (amines, peptides, proteins) or steroids made from cholesterol; lipid-soluble ones use intracellular receptors, water-soluble ones use membrane receptors and second messengers such as cAMP.
• The posterior pituitary releases oxytocin and ADH; the anterior pituitary makes GH, TSH, ACTH, FSH, LH and prolactin under hypothalamic control.
• The thyroid makes T3 and T4, which need iodine and set basal metabolism; iodine deficiency can cause goiter.
• Parathyroid hormone is released when blood calcium is low; high calcium inhibits PTH and triggers calcitonin from the thyroid.
• The adrenal medulla releases epinephrine and norepinephrine (short-term stress); the cortex releases aldosterone, cortisol and androgens, with cortisol driven by CRH and ACTH (long-term stress).
• Insulin from beta cells lowers blood glucose; glucagon from alpha cells raises it; diabetes mellitus is characterized by high blood glucose.
• The pineal gland releases melatonin in low light; the heart (ANP), kidneys (EPO) and gut (gastrin, secretin, CCK) have secondary endocrine functions.

Memory Tip: The posterior pituitary only stores and releases hormones made by hypothalamic neurons (oxytocin and ADH), while the anterior pituitary manufactures its own six hormones.

Common Mistake: Treating insulin and glucagon as partners that do the same job. They are opposites: insulin lowers blood glucose after a meal and glucagon raises it when glucose is low.

Important Questions:

• How do endocrine and exocrine glands differ? Endocrine glands are ductless and release hormones into the surrounding fluid, from which they enter the blood. Exocrine glands release their secretions through a duct onto a surface or into a cavity.
• How do insulin and glucagon differ? Insulin, made by beta cells in response to high blood glucose, increases glucose uptake and storage. Glucagon, made by alpha cells in response to low blood glucose, raises blood glucose, for example by breaking down glycogen.

Chapter 18: The Cardiovascular System: Blood

Unit 4: Fluids and Transport · Difficulty: Medium · Key topics: plasma and formed elements, hemopoiesis, hemoglobin, leukocytes, platelets, hemostasis, coagulation, ABO and Rh blood groups

Chapter 18 describes blood as a fluid connective tissue. It covers blood’s functions, physical traits and composition (plasma, red cells, white cells and platelets) and shows how hemopoiesis builds each formed element from stem cells in red bone marrow. Separate sections cover erythrocytes and the structure and recycling of hemoglobin, the leukocyte classes and platelets, and the three steps of hemostasis from vascular spasm to fibrin clot. The chapter ends with ABO and Rh blood typing, transfusion reactions and hemolytic disease of the newborn.

Key Points:

• Blood is plasma (over 90 percent water, plus albumin, globulins and fibrinogen) and formed elements (erythrocytes, leukocytes and platelets).
• Hemopoiesis starts in red bone marrow: myeloid stem cells give rise to most formed elements and lymphoid stem cells to lymphocytes; erythropoietin and thrombopoietin are growth factors.
• Hemoglobin is four globin proteins plus heme, which holds iron; erythrocytes live about 120 days and heme breaks down into bilirubin.
• Neutrophils are the most abundant leukocytes and the first responders to bacterial infection; lymphocytes make up 20–30 percent of leukocytes.
• Hemostasis has three steps: vascular spasm, platelet plug formation and coagulation (a fibrin clot).
• A thrombus is a clot that stays attached to a vessel wall; an embolus is a thrombus that has broken free.
• ABO types are A, B, AB and O; plasma holds preformed antibodies against the antigens a person lacks; Rh-negative mothers can form anti-Rh antibodies against an Rh-positive fetus.

Memory Tip: Remember leukocytes from most to least abundant with “Never Let Monkeys Eat Bananas”: Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils.

Common Mistake: Calling platelets cells. Platelets are fragments of megakaryocytes, which is why the book groups everything as “formed elements” rather than “blood cells”.

Important Questions:

• A patient’s hematocrit is 42 percent. About what percentage of the blood is plasma? About 58 percent, since the buffy coat (leukocytes and platelets) is less than 1 percent of the sample.
• What are the three steps of hemostasis? Vascular spasm, formation of a platelet plug, and coagulation, in which clotting factors produce a fibrin clot.

Chapter 19: The Cardiovascular System: The Heart

Unit 4: Fluids and Transport · Difficulty: Hard · Key topics: heart chambers and valves, coronary circulation, conducting system, ECG, cardiac cycle, heart sounds, cardiac output, stroke volume, heart development

Chapter 19 explains the heart as a pump. It covers the heart’s position in the pericardial sac, its wall layers, chambers, valves and coronary circulation, and traces blood through the pulmonary and systemic circuits. It then describes the conducting system (SA node, AV node, bundle of His, Purkinje fibers), the long plateau of contractile-cell action potentials and what the ECG waves show. Later sections follow the 0.8-second cardiac cycle and heart sounds, the control of heart rate, stroke volume and cardiac output, and the early embryonic development of the heart.

Key Points:

• The heart wall has three layers (epicardium, myocardium, endocardium) and sits in a pericardial sac with lubricating serous fluid.
• The right side pumps blood to the lungs (pulmonary circuit) and the left side to the body (systemic circuit); the pulmonary circuit has lower pressure because it is shorter and offers less resistance.
• The impulse travels SA node, internodal pathways, AV node, bundle of His, bundle branches and Purkinje fibers; the AV node delay lets the atria finish emptying first.
• ECG: the P wave is atrial depolarization, the QRS complex is ventricular depolarization and the T wave is ventricular repolarization.
• The cardiac cycle lasts about 0.8 seconds; the first heart sound (lub) is the AV valves closing and the second (dub) is the semilunar valves closing.
• Cardiac output equals heart rate times stroke volume, and stroke volume equals end diastolic volume minus end systolic volume.
• The heart is the first organ to function: it forms from mesoderm about day 18–19 and begins beating about day 21–22.

Memory Tip: Valves in the order blood meets them: “Try Pulling My Aorta” for Tricuspid, Pulmonary, Mitral (bicuspid), Aortic.

Common Mistake: Assuming arteries always carry oxygen-rich blood and veins oxygen-poor blood. The pulmonary arteries carry oxygen-poor blood to the lungs, and the pulmonary veins return oxygen-rich blood to the left atrium.

Important Questions:

• Why is the plateau phase so important to cardiac muscle function? It prolongs the refractory period, preventing further impulses from spreading prematurely, so the muscle has time to contract fully and pump blood effectively.
• How does the delay at the atrioventricular node help the heart work? It gives the atrial muscle time to contract and push blood into the ventricles before the impulse is conducted to the lower chambers.

Chapter 20: The Cardiovascular System: Blood Vessels and Circulation

Unit 4: Fluids and Transport · Difficulty: Medium · Key topics: vessel tunics, arteries and veins, blood pressure, resistance, capillary exchange, baroreceptors, renin-angiotensin-aldosterone, shock, circulatory pathways, fetal circulation

Chapter 20 follows blood after it leaves the heart. It compares the three tunics and the types of arteries, capillaries and veins, then explains blood flow, resistance and blood pressure (systolic, diastolic, pulse and mean arterial pressure) and the exchange of fluid across capillary walls by filtration and reabsorption. It describes how neural, hormonal and local controls regulate pressure, including hypertension and circulatory shock. The chapter finishes with the major arteries and veins of the pulmonary and systemic circuits, blood vessel development and fetal circulation.

Key Points:

• Arteries, arterioles, venules and veins have three tunics (intima, media, externa); capillaries have only a tunica intima.
• Arterioles are resistance vessels; veins have larger lumens, thinner walls and valves, and act as capacitance vessels.
• Pulse pressure is systolic minus diastolic pressure; mean arterial pressure is roughly diastolic plus one third of pulse pressure (for 130/85: 45 and 100 mm Hg).
• Arterial pressure depends on cardiac output, compliance, blood volume, blood viscosity and vessel length and diameter.
• Capillary hydrostatic pressure drives filtration at the arterial end; blood colloid osmotic pressure drives reabsorption at the venous end.
• Pressure is controlled by the medullary cardiovascular centers and baroreceptors, by hormones (epinephrine, ADH, the renin-angiotensin-aldosterone system, ANH) and by local autoregulation.
• Fetal shunts are the foramen ovale, ductus arteriosus and ductus venosus; the umbilical vein brings oxygen-rich blood and the umbilical arteries carry waste away.

Memory Tip: Arteries carry blood Away from the heart. At a capillary, hydrostatic pressure pushes fluid out at the arterial end and colloid osmotic pressure pulls it back in at the venous end.

Common Mistake: Thinking capillaries have the same wall layers as arteries. A capillary has only a one-cell-thick tunica intima, which is exactly what makes exchange possible.

Important Questions:

• Why are arterioles called resistance vessels? Their lumen is very narrow (about 30 micrometers or less), which slows blood flow, and they can constrict or dilate to change resistance and so adjust blood pressure.
• A patient’s blood pressure is 130/85. What are the pulse pressure and mean arterial pressure? Pulse pressure is 130 − 85 = 45 mm Hg, which is normal. Mean arterial pressure is 85 + one third of 45 = 100 mm Hg.

Chapter 21: The Lymphatic and Immune System

Unit 4: Fluids and Transport · Difficulty: Hard · Key topics: lymph and lymphoid organs, innate immunity, inflammation, complement, T cells and MHC, B cells and antibodies, hypersensitivity, autoimmunity, transplantation

Chapter 21 covers the lymphatic and immune systems together. It starts with lymph vessels, nodes and the primary and secondary lymphoid organs, then describes innate defenses: barrier defenses, inflammation, phagocytes, complement and interferons. Two long sections explain the adaptive response, with T cells (MHC presentation, selection in the thymus, helper, regulatory and cytotoxic types) and B cells (activation, plasma cells and five antibody classes). The chapter ends with responses to different pathogens, immunodeficiency, hypersensitivity and autoimmunity, and transplantation and cancer immunology.

Key Points:

• Lymphatic vessels return interstitial fluid to the blood and carry dietary lipids and immune cells; valves keep lymph flowing one way.
• Primary lymphoid organs (bone marrow, thymus) produce and mature lymphocytes; secondary organs (lymph nodes, spleen, MALT) are where immune responses are mounted.
• Innate immunity is fast but not specific (barriers, inflammation, phagocytes, complement, interferons); adaptive immunity is specific and builds memory.
• T cells recognize antigen only when it is presented on MHC molecules; they mature in the thymus and come as helper, regulatory and cytotoxic types.
• B cells mature in bone marrow and become plasma cells that secrete antibodies in five classes: IgA, IgD, IgE, IgG and IgM.
• Complement damages bacteria and fungi, interferons and cytotoxic T cells handle viruses, and eosinophils attack worms.
• Hypersensitivities are overactive responses, autoimmune disease is a breakdown of tolerance, and transplants are matched by MHC (tissue typing).

Memory Tip: B cells mature in Bone marrow and T cells mature in the Thymus; the first letter tells you where to look.

Common Mistake: Treating innate and adaptive immunity as separate systems. They cooperate: the innate response prepares and guides the adaptive response and keeps working alongside it.

Important Questions:

• Describe two early induced immune responses and the pathogens they affect. Interferons are made by virally infected cells and tell neighbouring cells to make antiviral proteins. C-reactive protein is made by the liver and opsonizes certain bacteria.
• Where do T cells and B cells develop, and how do T cells recognize antigen? B cells develop in the bone marrow and T cells in the thymus. T cells recognize only processed antigen displayed in the binding groove of an MHC molecule.

Chapter 22: The Respiratory System

Unit 5: Energy, Maintenance, and Environmental Exchange · Difficulty: Medium · Key topics: conducting and respiratory zones, lungs and pleura, Boyle’s law, lung volumes, Dalton and Henry laws, oxygen transport, carbon dioxide transport, acclimatization

Chapter 22 explains how the body takes in oxygen and removes carbon dioxide. It describes the conducting zone (nasal cavity, pharynx, larynx, trachea, bronchi) and the respiratory zone of alveoli, then the lobes, pleura and blood supply of the lungs. Later sections cover the mechanics of breathing (pressure gradients, Boyle’s law, lung volumes, neural control), gas exchange governed by Dalton’s and Henry’s laws, oxygen and carbon dioxide transport in blood, adjustments for exercise and altitude, and the embryonic development of the lungs.

Key Points:

• The conducting zone moves, warms, humidifies and filters air; the respiratory zone (alveoli) is where gas exchange happens.
• The pharynx has three parts (nasopharynx, oropharynx, laryngopharynx), and the epiglottis closes over the trachea during swallowing.
• The right lung has three lobes and the left lung two; the pleura has visceral and parietal layers around the pleural cavity.
• Air flows down a pressure gradient; by Boyle’s law, gas pressure falls when volume rises, so enlarging the thorax draws air in.
• Dalton’s law: each gas in a mixture exerts its own partial pressure; Henry’s law: the amount of gas that dissolves depends on its partial pressure. Oxygen moves from alveoli into blood and carbon dioxide the other way.
• Each hemoglobin molecule binds up to four oxygen molecules; carbonic anhydrase in red cells helps carry carbon dioxide as bicarbonate.
• Chronic exposure to high altitude increases circulating erythrocytes, and type II alveolar cells begin making surfactant during fetal development.

Memory Tip: Boyle’s law in one line: larger volume, lower pressure. When the diaphragm flattens and the chest expands, pressure inside falls below atmospheric pressure and air rushes in.

Common Mistake: Thinking the lungs themselves pull in air. The lungs are passive; the diaphragm and intercostal muscles change the volume of the thorax and the pressure gradient does the rest.

Important Questions:

• What would happen if the epiglottis were injured? Food or drink could enter the trachea when swallowing, because the epiglottis normally closes over the trachea as the pharynx moves upward.
• How do the right and left lungs differ? The right lung has three lobes and is shorter because the liver lies beneath it. The left lung has two lobes and a cardiac notch that makes room for the heart.

Chapter 23: The Digestive System

Unit 5: Energy, Maintenance, and Environmental Exchange · Difficulty: Medium · Key topics: alimentary canal, wall layers, six digestive activities, swallowing, gastric glands, villi and microvilli, liver and bile, pancreatic juice, nutrient absorption

Chapter 23 follows food from mouth to anus. It begins with the alimentary canal, the accessory organs, the four wall layers and the enteric nervous system, then lists the six digestive activities and their neural and hormonal control. Separate sections cover the mouth, pharynx and esophagus (teeth and swallowing), the stomach (gastric glands, acid and chyme), the small and large intestines (villi, microvilli, segmentation, gut bacteria) and the liver, pancreas and gallbladder. The final section details chemical digestion and absorption of carbohydrates, proteins, lipids and nucleic acids.

Key Points:

• The alimentary canal is mouth, pharynx, esophagus, stomach, small intestine and large intestine; accessory organs are the teeth, tongue, salivary glands, liver, pancreas and gallbladder.
• The wall has four layers (mucosa, submucosa, muscularis, serosa); the enteric nervous system is intrinsic and the autonomic nervous system extrinsic.
• The six activities are ingestion, motility, mechanical digestion, chemical digestion, absorption and defecation.
• In swallowing the soft palate rises, the larynx elevates and the epiglottis folds over the glottis; an adult has 32 teeth.
• Parietal cells make hydrochloric acid and intrinsic factor, chief cells make pepsinogen and G cells make gastrin; the stomach stores food as acidic chyme.
• The small intestine (duodenum, jejunum, ileum) completes digestion and absorbs nearly all nutrients; circular folds, villi and microvilli raise its surface area about 600-fold.
• Bile emulsifies fats; pancreatic juice buffers acid and supplies enzymes; fats travel as micelles then chylomicrons into lacteals.

Memory Tip: Think of two highways: water-soluble nutrients such as sugars and amino acids take the blood highway to the liver, while fats, packaged as chylomicrons, take the lymph highway through the lacteals.

Common Mistake: Believing the stomach does most of the digesting and absorbing. It starts protein digestion and stores chyme, but the small intestine completes digestion and absorbs almost all nutrients.

Important Questions:

• Why does segmentation occur, and peristalsis slow, in the small intestine? Most digestion and absorption happen there, and segmentation together with slower peristalsis slows the movement of chyme, giving time for these processes.
• What does bile do? The bile salts and phospholipids in bile emulsify large lipid globules into tiny droplets, a necessary step for fat digestion and absorption.

Chapter 24: Metabolism and Nutrition

Unit 5: Energy, Maintenance, and Environmental Exchange · Difficulty: Medium · Key topics: catabolism and anabolism, ATP, glycolysis, Krebs cycle, electron transport chain, beta-oxidation, ketone bodies, urea cycle, absorptive and postabsorptive states, heat exchange, vitamins and minerals

Chapter 24 covers how the body uses food. It defines metabolism as the sum of catabolic and anabolic reactions and explains the role of ATP and oxidation-reduction reactions. It then follows carbohydrate metabolism (glycolysis, the Krebs cycle, the electron transport chain and gluconeogenesis), lipid metabolism (beta-oxidation, ketone bodies, lipogenesis) and protein metabolism (digestion, transamination and the urea cycle). Later sections explain the absorptive, postabsorptive and starvation states, energy and heat balance, and nutrition, vitamins and minerals.

Key Points:

• Metabolism is catabolism (breakdown, releasing energy for ATP) plus anabolism (synthesis, using ATP); NAD and FAD carry electrons in oxidation-reduction reactions.
• Glycolysis turns glucose into pyruvate, NADH and ATP; with oxygen pyruvate enters the Krebs cycle, without oxygen it becomes lactate.
• The electron transport chain and ATP synthase (oxidative phosphorylation) make most of the ATP; gluconeogenesis builds new glucose.
• Beta-oxidation breaks fatty acids into acetyl CoA; excess acetyl CoA forms ketone bodies or is used for lipogenesis.
• Protein digestion starts with HCl and pepsin; pancreatic trypsinogen and chymotrypsinogen are activated in the intestine; nitrogen waste enters the urea cycle.
• In the absorptive state insulin promotes glucose uptake and glycogen storage; in the postabsorptive state glucagon triggers glycogen breakdown.
• Core temperature is held near 36.5–37.5 °C by the hypothalamus; heat moves by conduction, convection, radiation and evaporation.

Memory Tip: Match the four heat-exchange modes to everyday pictures: conduction is touching a cold floor, convection is a breeze, radiation is warmth from a heater and evaporation is sweat drying.

Common Mistake: Imagining that the body stores ATP for later. Cells hold only a small ATP pool; surplus energy is kept as glycogen and fat and ATP is regenerated continuously.

Important Questions:

• How is glucose metabolized to yield ATP? Glucose is oxidized in glycolysis to pyruvate, which is processed through the Krebs cycle to produce NADH, FADH2, ATP and carbon dioxide; the NADH and FADH2 then drive ATP production.
• What are the three metabolic states of the body? The absorptive (fed) state, the postabsorptive (fasting) state and starvation. Metabolism switches between the first two every day; starvation is rare in well-nourished people.

Chapter 25: The Urinary System

Unit 5: Energy, Maintenance, and Environmental Exchange · Difficulty: Hard · Key topics: urine characteristics, ureters, bladder and micturition, nephron structure, glomerular filtration, tubular reabsorption, countercurrent multiplier, renin-angiotensin-aldosterone, ADH, diuretics

Chapter 25 follows urine from filtration to excretion. It starts with the physical characteristics of urine, then the ureters, bladder, urethra and micturition reflex, and the gross and microscopic anatomy of the kidney with its nephrons, filtration membrane and juxtaglomerular apparatus. The physiology sections explain glomerular filtration rate, tubular reabsorption and secretion, the countercurrent concentration of urine, and the control of renal blood flow by myogenic, tubuloglomerular and hormonal mechanisms. The chapter ends with fluid regulation, diuretics and the kidneys’ role in homeostasis.

Key Points:

• Normal urine has a pH of 4.5–8.0 and at least 400–500 mL a day is needed to clear wastes; white blood cells in urine suggest infection.
• The kidneys receive about 25 percent of cardiac output and each holds about 1.3 million nephrons, of which about 15 percent are juxtamedullary.
• The nephron runs from renal corpuscle (glomerulus and Bowman’s capsule) to proximal tubule, loop of Henle, distal tubule and collecting duct.
• Filtration is driven mainly by glomerular hydrostatic pressure; about 99 percent of filtered water is reabsorbed, 90 percent of it before the collecting ducts.
• Renin converts angiotensinogen to angiotensin I, lung ACE makes angiotensin II (a vasoconstrictor), and angiotensin II stimulates aldosterone release.
• ADH inserts aquaporin water channels into collecting duct cells; natriuretic peptides from the atria increase sodium excretion and lower blood pressure.
• The kidneys complete the activation of vitamin D and make erythropoietin, and share pH regulation with the lungs and blood buffers.

Memory Tip: Follow the filtrate with C-P-L-D-C: Capsule, Proximal tubule, Loop of Henle, Distal tubule, Collecting duct.

Common Mistake: Crediting ADH with most of the water recovery. About 90 percent of filtered water is recovered before the collecting ducts; ADH fine-tunes only the last 10 percent.

Important Questions:

• Why are bladder infections more common in people with a female urinary tract? The female urethra is shorter, so bacteria have less distance to travel to reach the bladder.
• How does urine differ in diabetes mellitus and diabetes insipidus, though both give large volumes? Diabetes mellitus produces urine containing glucose; diabetes insipidus produces very dilute urine with low osmolarity and low specific gravity.

Chapter 26: Fluid, Electrolyte, and Acid-Base Balance

Unit 5: Energy, Maintenance, and Environmental Exchange · Difficulty: Medium · Key topics: fluid compartments, edema, water balance, ADH, electrolytes, aldosterone, buffer systems, blood pH 7.35-7.45, acidosis and alkalosis

Chapter 26 explains how the body keeps its fluids, ions and pH steady. It describes the intracellular and extracellular fluid compartments, how water and solutes move between them and what causes edema. It then covers water balance (thirst, ADH, dehydration), the six key electrolytes and the disorders caused by too much or too little of each, and the role of aldosterone. The last two sections explain the buffer systems that hold blood pH between 7.35 and 7.45, the roles of the lungs and kidneys, and metabolic and respiratory acidosis and alkalosis.

Key Points:

• Body fluid is divided into intracellular fluid (ICF) and extracellular fluid (ECF, including interstitial fluid and plasma); osmotic and hydrostatic pressures move fluid between compartments.
• Most water enters through the digestive tract, about 10 percent is metabolic water from aerobic respiration, and urine is the largest route of loss.
• ADH helps the body retain water by increasing water reabsorption in the kidneys.
• Aldosterone and angiotensin II control sodium and potassium exchange in the collecting tubule; PTH, calcitriol and calcitonin regulate calcium and phosphate.
• Blood pH stays between 7.35 and 7.45, held by buffers such as proteins, hemoglobin, phosphates and the bicarbonate system.
• The lungs remove carbon dioxide and the kidneys remove hydrogen ions to maintain acid-base balance.
• Acidosis is blood pH below 7.35 and alkalosis is above 7.45; each can be metabolic (bicarbonate) or respiratory (carbon dioxide) in origin.

Memory Tip: Name an acid-base disorder by its source: respiratory means carbon dioxide, metabolic means bicarbonate. Expect the other system to compensate, so the kidneys help with respiratory problems and the lungs with metabolic ones.

Common Mistake: Expecting plasma sodium and chloride to be equal because plasma is electrically neutral. Plasma also contains other negative ions such as bicarbonate and proteins, so sodium is higher.

Important Questions:

• Why must water intake equal water output? Any imbalance in water entering or leaving the body creates an osmotic imbalance that harms cell and tissue function.
• What does ADH do in the renal collecting tubules? It moves aquaporin water channel proteins into the membranes of the epithelial cells lining the collecting tubules, so more water is reabsorbed into the blood.

Chapter 27: The Reproductive System

Unit 6: Human Development and the Continuity of Life · Difficulty: Medium · Key topics: gametes and gonads, spermatogenesis, semen, oogenesis, folliculogenesis, ovarian and menstrual cycles, SRY, Wolffian and Mullerian ducts, puberty

Chapter 27 covers the reproductive systems. The first section follows sperm production in the seminiferous tubules, the duct system and accessory glands that form semen, and the hormonal control by GnRH, FSH, LH and testosterone. The second describes the ovarian reproductive system, including the ovaries, uterine tubes, uterus, vagina and mammary glands, oogenesis and folliculogenesis, and the hormonal changes of the ovarian and menstrual cycles. The last section covers the embryonic development of the reproductive organs (the SRY gene, Wolffian and Müllerian ducts) and the changes of puberty.

Key Points:

• The gonads (testes and ovaries) make gametes and hormones; gametes are haploid because they are produced by meiosis.
• Spermatogenesis in the seminiferous tubules runs spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids and then spermatozoa; sperm mature in the epididymis and leave through the ductus deferens.
• Semen is formed by secretions of the seminal vesicle (about 60 percent of the volume, rich in fructose), the prostate and the bulbourethral glands.
• Follicles develop from primordial to primary, secondary and tertiary; one dominant follicle survives each ovarian cycle while the rest undergo atresia.
• Oocyte meiosis is completed only if a sperm penetrates the oocyte.
• FSH stimulates follicle growth; granulosa and theca cells make estrogen, and high estrogen triggers negative feedback on the hypothalamus and pituitary.
• The SRY gene on the Y chromosome triggers testis development; testosterone from Leydig cells promotes the Wolffian duct, and without it the Müllerian duct forms female structures.

Memory Tip: Trace the sperm path with SEVEN UP: Seminiferous tubules, Epididymis, Vas deferens, Ejaculatory duct, (N)othing, Urethra, Penis.

Common Mistake: Believing oogenesis is finished at ovulation. The second meiotic division is completed only if a sperm penetrates the oocyte.

Important Questions:

• Why do mature gametes carry only one set of chromosomes? Each gamete must combine with another to form a fertilized egg, the first cell of a new individual, which needs a complete set of chromosomes.
• What special features do sperm have that somatic cells lack? Sperm are haploid with very little cytoplasm, a head with a compact nucleus capped by an enzyme-filled acrosome, and a mid-piece full of mitochondria that power movement.

Chapter 28: Development and Inheritance

Unit 6: Human Development and the Continuity of Life · Difficulty: Medium · Key topics: fertilization, blastocyst and implantation, embryonic membranes, placenta, gastrulation, fetal circulation, labor, lactation, genotype and phenotype, Mendelian inheritance

The final chapter follows a human life from conception to inheritance. It covers fertilization (capacitation, the acrosomal and cortical reactions), embryonic development from cleavage and the blastocyst through implantation, the embryonic membranes, placenta, gastrulation and organogenesis, and the fetal period with its circulatory shunts. Later sections describe the changes of pregnancy, labor and birth, the infant’s adjustments at birth, lactation, and patterns of inheritance, including genotype and phenotype, Mendel’s principles, Punnett squares and autosomal and X-linked disorders.

Key Points:

• Only a few hundred of the hundreds of millions of sperm reach the oocyte; capacitation improves their motility and prepares the acrosome, and the cortical reaction after entry helps block polyspermy.
• Early development runs zygote, cleavage, morula, blastocyst (inner cell mass plus trophoblast) and implantation in the uterine wall.
• The four embryonic membranes are the amnion, yolk sac, allantois and chorion; chorionic villi form the fetal part of the placenta.
• Gastrulation forms the three germ layers, neurulation begins the central nervous system, and the fetal period runs from week 9 to birth.
• Three fetal shunts (ductus venosus, foramen ovale, ductus arteriosus) bypass the semifunctional liver and lungs; the newborn’s first breath closes them.
• Estrogen, progesterone and hCG maintain pregnancy; falling progesterone and uterine stretch prompt labor; suckling triggers oxytocin and the let-down reflex.
• Genotype is the alleles a person carries and phenotype is their expression; Mendel’s crosses of heterozygotes gave a 3:1 dominant to recessive ratio.

Memory Tip: Remember the early stages as a ladder: the morula is a solid “mulberry” ball of cells, the blastocyst is a hollow ball with an inner cell mass, and the gastrula has three germ layers.

Common Mistake: Treating genotype and phenotype as the same thing. A heterozygous carrier of a recessive allele can have the same phenotype as a dominant homozygote.

Important Questions:

• Why is folate recommended for everyone who might become pregnant? Folate, a B vitamin, is important for the healthy formation of the embryonic neural tube, which forms in the first weeks after conception.
• What is the benefit of shunts in the fetal circulation? The shunts bypass the fetal lungs and liver, giving these semifunctional organs just enough oxygenated blood for their needs and sending the rest to where it is needed more.

Download Anatomy and Physiology 2e PDF (Free)

Anatomy and Physiology 2e is free from its official publisher, OpenStax. Click the button below to open the official OpenStax book page, where you can download the complete PDF or read every chapter online in your browser.

How to Study This Book

Anatomy and Physiology 2e has 28 chapters grouped by the authors into six units: Levels of Organization (Chapters 1 to 4), Support and Movement (5 to 11), Regulation, Integration, and Control (12 to 17), Fluids and Transport (18 to 21), Energy, Maintenance, and Environmental Exchange (22 to 26), and Human Development and the Continuity of Life (27 and 28). It was written for the two-semester anatomy and physiology course, and many courses split it after Chapter 17, but the book does not mark the split, so follow your own syllabus.

Treat Chapters 1 to 4 as the foundation, not as an introduction to skim. Chapter 1 gives the anatomical terms, planes and body cavities that every later chapter assumes, plus homeostasis and feedback loops. Chapter 2 supplies the chemistry behind pH and buffers (used again in Chapters 22 and 26) and the energy molecules behind Chapter 24. Chapter 3 gives membrane transport, which returns in the kidney chapter, and Chapter 4 gives the four tissue types that the organ-system chapters build on.

In the Support and Movement unit, read in order. Chapter 6 (bone tissue) comes before the skeleton chapters, and Chapter 10 (how muscle contracts) comes before Chapter 11 (which muscles do what). Chapters 7, 8 and 11 are the most memorization-heavy in the book, with long lists of bones, landmarks and muscles, so study them with diagrams, a few regions at a time, and use the book’s pronunciation guide for the Latin and Greek terms.

Chapter 12 is the key to the whole control unit: the resting potential, action potential and synapse explained there return in the heart (Chapter 19) and in muscle contraction (Chapter 10). Read Chapter 13 (structures) before Chapter 14 (sensory and motor pathways) and Chapter 15 (autonomic control). Chapter 16, the neurological exam, applies those chapters to clinical cases, so it is optional if your course is not clinical. Chapter 17 links back to calcium in Chapter 6 and forward to the kidney (25) and reproduction (27).

The fluid and exchange units form chains. Read Chapters 18, 19 and 20 in that order (blood, heart, vessels). Chapter 21 builds on the white blood cells of Chapter 18 and the inflammation of Chapter 4. In the next unit, Chapter 22 (respiration) and Chapter 26 (fluid and acid-base balance) share the carbon dioxide and pH story, Chapter 24 (metabolism) builds on Chapters 2 and 23, and the kidney chapter (25) is easier after Chapters 20 and 26.

The end-of-chapter material is large: 142 Interactive Link questions, 714 Review questions and 370 Critical Thinking questions, 1,226 in all. According to the preface, students get answers to the odd-numbered questions through the Student Solution Manual on the Student Resources page, while even-numbered answers go only to instructors. Student resources also include guided lecture notes. The chapters are also rich in feature boxes, such as Homeostatic Imbalances, Diseases, Disorders, Aging and Career Connections, which are worth reading because they connect structure and function to real conditions.

This is a textbook, not a dissection manual or an atlas, and it is written for life science and allied health students rather than for medical specialists. It introduces diseases through its feature boxes but does not replace a pathology, pharmacology or clinical anatomy text. If you plan to go further in medicine or physiotherapy, use it as the base and add those subject books later.

Used In These Programs

This book is used for the two-semester Anatomy and Physiology course in BS Biology and in allied health programs. Browse all Anatomy and Physiology books or all Biology books.

Who Should Read This

Anatomy and Physiology 2e is written for a first- or second-year university student taking the two-semester human anatomy and physiology course, which in Pakistan usually means a BS Biology student or a student in an allied health program. It assumes no earlier anatomy and physiology and builds its own foundation in the first four chapters, but it moves quickly and relies on school-level biology and chemistry, so students who need a refresher can start with the Biology 1st Year FSc book and, for the chemistry in Chapter 2, the Chemistry 1st Year FSc book. It is a good fit for readers who learn well from diagrams, clinical examples and plenty of self-check questions. It is not a substitute for a lab manual, an atlas or a clinical text.

Applicable Universities

This book is useful for students at Pakistani universities offering BS Biology and allied health programs with an anatomy and physiology course, including University of the Punjab, University of Karachi, Quaid-i-Azam University, COMSATS, Dow University of Health Sciences, University of Health Sciences Lahore, Riphah International University, and other HEC-recognized institutions.

FAQs

Related Books

• Biology 1st Year Book – Punjab Board FSC (college biology groundwork for the cell, tissue and organ-system chapters)
• Biology 2nd Year Book – Punjab Board FSC (homeostasis, support and movement, coordination and reproduction topics that this book covers in depth)
• Biology Class 10 English Medium – Punjab Board PCTB (a school-level view of human body systems to read before the detailed chapters)
• Chemistry 1st Year Book – Punjab Board FSC (the atoms, bonding and solutions behind Chapter 2)

Anatomy and Physiology 2e gives BS Biology and health science students a complete, free two-semester guide to the human body, from cells to inheritance. Browse more Biology books or the Chemistry books that go with them.

Anatomy and Physiology 2e, by J. Gordon Betts, Peter Desaix, Eddie Johnson, Jody E. Johnson, Oksana Korol, Dean Kruse, Brandon Poe, James A. Wise, Mark Womble, Kelly A. Young and contributing authors. OpenStax, Rice University. Free under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International licence (CC BY-NC-SA 4.0). Access for free at https://openstax.org/details/books/anatomy-and-physiology-2e