Anatomy Physiology by Elaine N. Marieb, Katja N. Hoehn
Elaine N. Marieb and Katja Hoehn
Sixth Edition
Questions & Answers from this book
Questions and answers are connected to the referenced book and its available source material.
Chapter 1: The Human Body: An Orientation
What are the three components of a homeostatic control system, and what role does each play?
The three components are the receptor, the control center, and the effector. The receptor is a sensor that detects a stimulus and sends input along the afferent pathway to the control center. The control center sets the set point, analyzes input, and sends output along the efferent pathway to the effector. The effector carries out the response, which feeds back to alter the stimulus and restore the variable toward homeostatic levels.
Name the two subdivisions of the dorsal body cavity and state what each contains.
The two subdivisions are the cranial cavity and the vertebral (spinal) cavity. The cranial cavity, located in the skull, encases the brain, while the vertebral cavity runs within the bony vertebral column and encloses the spinal cord.
Chapter 2: Chemistry Comes Alive
What is the structural difference between a triglyceride and a phospholipid, and how does this difference relate to their functions in the body?
A triglyceride consists of a glycerol backbone with three fatty acid chains attached, making the whole molecule nonpolar. A phospholipid is a modified triglyceride with only two fatty acid chains and a phosphorus-containing polar head group in place of the third fatty acid. Because triglycerides are nonpolar and energy-dense, they are stored as body fat and insulate/protect organs; because phospholipids have both a polar head and nonpolar tail, they are the chief building material for cell membranes.
What is the structural difference between a triglyceride and a phospholipid?
A triglyceride has three fatty acid chains attached to a glycerol backbone, while a phospholipid is a modified triglyceride with only two fatty acid chains and a phosphorus-containing group attached to glycerol. This makes the phospholipid a diglyceride with a polar head and two nonpolar fatty acid tails.
Chapter 4: Tissue: The Living Fabric
What are the five distinguishing characteristics of epithelial tissues?
The five distinguishing characteristics of epithelial tissues are polarity, specialized contacts, support by connective tissue, being avascular but innervated, and the ability to regenerate. Polarity means each epithelium has an apical surface and a basal surface that differ in structure and function. Specialized contacts include tight junctions and desmosomes that bind epithelial cells closely together. Epithelial sheets rest on and are supported by connective tissue, are avascular yet supplied by nerve fibers, and can regenerate rapidly through cell division.
Compare the structure and function of tight junctions, desmosomes, and gap junctions.
Tight junctions are impermeable seals formed when integral proteins in adjacent plasma membranes fuse together, preventing molecules from passing through the intercellular space. Desmosomes are anchoring junctions that use plaques, linker proteins called cadherins, and intermediate filaments to bind cells together into strong sheets that resist mechanical stress. Gap junctions are communicating junctions made of connexons, hollow protein cylinders that form water-filled channels through which ions and small molecules pass from cell to cell.
What are the three main structural elements of connective tissue, and how do ground substance and fibers relate to the extracellular matrix?
The three main structural elements of connective tissue are ground substance, fibers, and cells. Ground substance and fibers together make up the extracellular matrix, which is the largely nonliving material that separates the living cells and gives connective tissue its strength and resilience. Ground substance fills the space between cells and contains the fibers, while the fibers provide support within that matrix.
What are the structural and functional differences between skeletal, cardiac, and smooth muscle tissues?
Skeletal muscle has long, cylindrical, multinucleate fibers with obvious striations; it is voluntary and moves the skeleton. Cardiac muscle has branching, striated, generally uninucleate cells joined at intercalated discs; it is involuntary and pumps blood from the heart. Smooth muscle has spindle-shaped cells with one central nucleus and no striations; it is involuntary and propels substances through hollow organs.
Chapter 7: The Skeleton
What are the five major regions of the adult vertebral column, and how many vertebrae are in each?
The adult vertebral column has five major regions: cervical, thoracic, lumbar, sacral, and coccygeal. The cervical region has 7 vertebrae, thoracic has 12, lumbar has 5, sacral has 5 fused vertebrae, and the coccyx usually has 4 fused vertebrae.
What are the four major skull sutures and which bones do they connect?
The four major skull sutures are the coronal, sagittal, lambdoid, and squamous sutures. The coronal suture connects the parietal bones to the frontal bone; the sagittal suture connects the two parietal bones at the midline; the lambdoid suture connects the parietal bones to the occipital bone; and the squamous sutures connect each parietal bone to a temporal bone.
Chapter 9: Muscles and Muscle Tissue
How do the T tubules and sarcoplasmic reticulum interact at triads to initiate contraction?
At triads, an electrical impulse travels along the T tubule, which is a deep invagination of the sarcolemma. Integral proteins of the T tubule act as voltage sensors and, when stimulated, cause gated channels in the adjacent terminal cisterns of the sarcoplasmic reticulum to open. This releases Ca2+ into the sarcoplasm, and the rise in intracellular calcium provides the final trigger that initiates contraction.
What is the sliding filament model of contraction?
The sliding filament model states that contraction occurs when thin actin filaments slide past thick myosin filaments toward the center of each sarcomere, increasing their overlap. Neither filament type changes length. Myosin heads bind to actin to form cross bridges, which attach and detach like ratchets to generate tension and pull the thin filaments inward. As sarcomeres shorten, I bands shorten, H zones disappear, Z discs move closer together, and A bands remain the same length.
Chapter 11: Fundamentals of the Nervous System and Nervous Tissue
What are the three groups of intrinsic muscles of the hand, and what are their general functions?
The three groups are the thenar muscles of the thumb's ball, the hypothenar muscles of the little finger's ball, and the midpalmar muscles. They control precise finger movements, with thenar and hypothenar groups flexing, abducting, and opposing their digits, while the midpalmar lumbricals and interossei extend the fingers and the interossei also adduct and abduct the fingers.
What are the three basic functions of the nervous system as described in the chapter?
The three basic functions of the nervous system described in the chapter are receiving information, integrating information, and responding to information.
Chapter 13: The Peripheral Nervous System and Reflex Activity
Chapter 14: The Autonomic Nervous System
What are the three key anatomical differences between the sympathetic and parasympathetic divisions of the autonomic nervous system?
The sympathetic and parasympathetic divisions differ in (1) sites of origin: sympathetic fibers are thoracolumbar, while parasympathetic fibers are craniosacral; (2) relative fiber lengths: sympathetic preganglionic fibers are short and postganglionic fibers are long, whereas parasympathetic preganglionic fibers are long and postganglionic fibers are short; and (3) location of ganglia: sympathetic ganglia lie close to the spinal cord, while parasympathetic ganglia lie within or near the visceral effector organs.
Which cranial nerves carry parasympathetic preganglionic fibers, and what is the distribution of these fibers?
The cranial nerves that carry parasympathetic preganglionic fibers are the oculomotor (III), facial (VII), glossopharyngeal (IX), and vagus (X) nerves. CN III supplies the eye via the ciliary ganglion, controlling pupil constriction and lens bulging for near vision. CN VII supplies the lacrimal and nasal glands and the submandibular and sublingual salivary glands via the pterygopalatine and submandibular ganglia. CN IX supplies the parotid salivary gland via the otic ganglion, while CN X gives rise to about 90% of all preganglionic parasympathetic fibers and distributes widely to thoracic and abdominal organs.
Why does sympathetic activation produce longer-lasting effects than parasympathetic activation?
Sympathetic activation lasts longer because it releases adrenal medullary hormones, norepinephrine and epinephrine, into the blood, which reinforce and prolong sympathetic effects for several minutes until the liver destroys them. In contrast, parasympathetic fibers release acetylcholine, which is quickly destroyed by acetylcholinesterase, producing short-lived, localized effects.
What are the three possible pathways a preganglionic sympathetic axon can take after reaching a trunk ganglion?
A preganglionic sympathetic axon can synapse in the same trunk ganglion, at the same level. It can ascend or descend the sympathetic trunk to synapse in a trunk ganglion at a higher or lower level. Or it can pass through the trunk ganglion without synapsing, travel via splanchnic nerves, and synapse in a distant collateral (prevertebral) ganglion.
How does the sympathetic innervation of the adrenal medulla differ from typical sympathetic pathways, and why is the adrenal medulla considered a 'misplaced' sympathetic ganglion?
In typical sympathetic pathways, preganglionic fibers synapse in trunk or collateral ganglia on postganglionic neurons that innervate target organs. In the adrenal medulla pathway, some thoracic splanchnic nerve fibers pass through the celiac ganglion without synapsing and instead synapse directly on hormone-producing medullary cells, which release norepinephrine and epinephrine into the blood rather than acting on a local effector. The adrenal medulla is considered a 'misplaced' sympathetic ganglion because embryologically it arises from the same tissue as sympathetic ganglia, so its hormone-releasing cells are viewed as equivalent to postganglionic sympathetic neurons even though they lack nerve processes.
What is the difference between the roles of the hypothalamus and the brain stem reticular formation in autonomic control?
The hypothalamus is the main integration center and overall 'boss' of the autonomic nervous system, directing whether parasympathetic or sympathetic responses dominate. The brain stem reticular formation exerts the most direct influence over autonomic functions, carrying out reflexive control of specific visceral activities such as heart rate, blood vessel diameter, and gastrointestinal functions.
What is autonomic dysreflexia and what triggers it?
Autonomic dysreflexia is a life-threatening condition involving uncontrolled activation of autonomic neurons, usually occurring in people with quadriplegia or other spinal cord injuries above the T6 level. It is typically triggered by a painful stimulus to the skin or an overfilled visceral organ such as the urinary bladder. Blood pressure can skyrocket to dangerous levels, potentially causing a stroke.
Compare and contrast the roles of the parasympathetic and sympathetic divisions of the ANS.
The parasympathetic division is the "rest and digest" system, conserving energy and directing housekeeping activities such as digestion, defecation, and urination. The sympathetic division is the "fight or flight" system, mobilizing the body for activity and emergencies by increasing heart rate, dilating airways, and releasing glucose. The two divisions generally innervate the same visceral organs but produce opposite effects, and both are usually partially active, creating a dynamic antagonism that precisely controls visceral function.
Chapter 15: The Endocrine System
What are the three zones of the adrenal cortex and which hormones does each predominantly produce?
The three zones of the adrenal cortex are the zona glomerulosa, zona fasciculata, and zona reticularis. The zona glomerulosa predominantly produces mineralocorticoids, the zona fasciculata predominantly produces glucocorticoids, and the zona reticularis predominantly produces gonadocorticoids.
How does the hypophyseal portal system ensure that releasing and inhibiting hormones from the hypothalamus reach the anterior pituitary rapidly and without dilution?
The hypophyseal portal system is a direct vascular route consisting of a primary capillary plexus in the infundibulum, hypophyseal portal veins, and a secondary capillary plexus in the anterior lobe. Because these portal veins connect the two capillary beds directly, the releasing and inhibiting hormones travel from the hypothalamus to the anterior pituitary without entering the systemic circulation. This ensures that even minute quantities of hormones reach their target rapidly and without being diluted.
Chapter 16: Blood
How are platelets formed from megakaryocytes?
Platelets form when mature megakaryocytes extend cytoplasmic projections through sinusoid walls in red bone marrow; these projections rupture into the bloodstream, and the plasma membrane around each fragment seals, producing the small, disc-shaped platelets.
How does the body regulate erythropoiesis in response to hypoxia?
The body regulates erythropoiesis through erythropoietin (EPO) secreted mainly by the kidneys. When blood oxygen levels fall, kidney cells become hypoxic, causing hypoxia-inducible factor (HIF) to accumulate, which accelerates EPO synthesis and release. EPO then travels to the red bone marrow, where it stimulates committed erythrocyte precursors to mature more rapidly, increasing RBC production and restoring oxygen-carrying capacity.
Chapter 17: The Cardiovascular System: The Heart
Chapter 18: The Cardiovascular System: Blood Vessels
Chapter 19: The Lymphatic System and Lymphoid Organs and Tissues
Chapter 20: The Immune System: Innate and Adaptive Body Defenses
Chapter 21: The Respiratory System
Why does the pulmonary circulation exhibit vasoconstriction in response to low oxygen levels, and how does this relate to its gas exchange function?
Low oxygen levels in the lungs trigger local vasoconstriction in pulmonary vessels, while high oxygen promotes vasodilation. This directs blood flow toward well-ventilated alveoli and away from collapsed or mucus-blocked air sacs, so blood only reaches functional gas exchange areas.
Why do pulmonary arteries carry oxygen-poor blood and pulmonary veins carry oxygen-rich blood, contrary to the systemic circulation?
Pulmonary arteries carry blood from the right ventricle to the lung capillaries before gas exchange, so that blood is still oxygen-poor. After oxygen moves from the alveoli into the blood and carbon dioxide moves out, the newly oxygen-rich blood drains into venules that form the pulmonary veins, which return it to the left atrium. Thus the reversal is simply because the pulmonary circuit is arranged to deliver deoxygenated blood to the lungs and then carry freshly oxygenated blood away from the lungs, opposite to the direction of oxygen delivery in the systemic circulation.
Chapter 22: The Digestive System
What are the three phases of gastric secretion and what triggers each phase?
The three phases of gastric secretion are the cephalic, gastric, and intestinal phases. The cephalic phase is triggered by the sight, smell, taste, or thought of food, acting through the vagus nerve. The gastric phase is triggered by food in the stomach through distension and chemical stimuli such as partially digested proteins and rising pH. The intestinal phase is briefly stimulated by partially digested food entering the duodenum, and then inhibited by distension, acidity, fat, or hypertonic chyme in the duodenum.
Compare the mucosa of the large intestine with that of the small intestine, and explain how the differences relate to their functions.
The small intestine mucosa has circular folds, villi, and microvilli that greatly increase surface area for digestion and absorption, while the large intestine mucosa has none of these structures because most nutrients have already been absorbed. Instead, the large intestine mucosa is thicker with deeper crypts and abundant goblet cells, producing mucus that eases feces passage and protects the wall from bacteria and irritating acids.
What are the three structural modifications of the small intestine that increase its surface area for absorption?
The small intestine wall has three structural modifications that enlarge its absorptive surface: circular folds, villi, and microvilli. Circular folds are deep permanent folds of the mucosa and submucosa that slow chyme movement. Villi are fingerlike projections of the mucosa containing capillaries and a lacteal. Microvilli are cytoplasmic extensions on absorptive cells that form the brush border.
Describe the sequence of events in the pharyngeal-esophageal phase of swallowing, including the role of the swallowing center and the protective mechanisms that prevent food from entering the respiratory passages.
The pharyngeal-esophageal phase begins when a bolus stimulates tactile receptors in the posterior pharynx, triggering an involuntary swallowing reflex controlled by the swallowing center in the medulla and lower pons. Motor impulses, mainly via the vagus nerves, coordinate the pharyngeal and esophageal muscles. Protective mechanisms include momentary inhibition of respiration, blocking of all routes except the digestive tract, and closure of the epiglottis over the larynx to route food posteriorly into the esophagus.
How do circular folds, villi, and microvilli contribute to the absorptive function of the small intestine?
They amplify the small intestine's surface area enormously, by more than 600 times, creating an absorptive area about equal to 200 square meters. Circular folds slow chyme and make it spiral so nutrients have time to be absorbed, while villi and microvilli provide the detailed surface structures where absorption of digested nutrients into blood and lymph actually occurs.
What are the three layers of the muscularis externa in the stomach wall, and how does the oblique layer contribute to stomach function?
The stomach's muscularis externa contains the usual outer longitudinal and middle circular layers of smooth muscle, plus an incomplete inner layer of oblique smooth muscle fibers. The oblique layer helps the stomach pummel and physically break down food by jackknifing the stomach into a V shape, which provides propulsive action in the pyloric region and ram food into the small intestine.
How does the stomach's lining protect itself from the acidic gastric juice it produces?
The stomach lining protects itself by building a mucosal barrier: a thick coating of bicarbonate-rich mucus, tight junctions that seal epithelial cells together, and rapid replacement of damaged surface cells by dividing stem cells.
What are the functions of the parietal, chief, mucous neck, and enteroendocrine cells in gastric glands?
The source identifies parietal cells as HCl-producing cells, chief cells as secreting pepsinogen and lipases, and enteroendocrine cells as releasing chemical messengers such as histamine, serotonin, somatostatin, and gastrin. However, it does not describe a function for mucous neck cells.
Chapter 23: Nutrition, Metabolism, and Energy Balance
Why does carbohydrate deficiency lead to incomplete fat oxidation and ketone body formation?
Carbohydrate deficiency causes lipolysis to accelerate as the body tries to use fats for energy, but acetyl CoA from fat oxidation can enter the citric acid cycle only when sufficient carbohydrate intermediates are present. When carbohydrates are deficient, those intermediates are instead converted to glucose to fuel the brain, so fat oxidation is incomplete and acetyl CoA accumulates. The liver then converts the accumulating acetyl CoA into ketone bodies through ketogenesis.
Compare the energy yield from the oxidation of fats versus carbohydrates, and explain why fats are considered the body's most concentrated source of energy.
Fats yield about 9 kcal per gram, whereas carbohydrates yield about 4 kcal per gram. Fat catabolism produces roughly twice as much energy per gram as carbohydrate oxidation, and fats contain very little water, making them the body's most concentrated source of stored energy.
Chapter 24: The Urinary System
How does antidiuretic hormone (ADH) regulate water reabsorption in the collecting ducts?
ADH makes the principal cells of the collecting ducts more permeable to water by triggering insertion of aquaporin water channels into their apical membranes. The number of aquaporins inserted, and therefore the amount of water reabsorbed by osmosis, is determined by how much ADH is present. This ADH-dependent movement is called facultative water reabsorption; when ADH levels are low, the collecting ducts remain relatively impermeable to water. ADH also promotes urea reabsorption in the deep medullary collecting duct, which strengthens the medullary osmotic gradient and supports concentrated urine production.
How do macula densa cells detect changes in GFR and what is their role in the tubuloglomerular feedback mechanism?
Macula densa cells detect changes in GFR by acting as chemoreceptors that monitor the NaCl concentration of filtrate entering the distal convoluted tubule. Because filtrate NaCl concentration varies with flow rate, a high GFR produces high NaCl levels, which triggers the macula densa to release vasoconstrictor chemicals that constrict the afferent arteriole and lower GFR. Conversely, a low GFR produces low NaCl, which inhibits those signals, causing afferent arteriole vasodilation and raising GFR. This tubuloglomerular feedback helps keep GFR relatively constant over a wide range of blood pressures.
Chapter 26: The Reproductive System
What are the phases of the uterine (menstrual) cycle and what happens in each?
The uterine (menstrual) cycle has three phases. The menstrual phase (days 1–5) sheds the functional layer of the endometrium with bleeding. The proliferative phase (days 6–14), driven by rising estrogens, rebuilds the functional layer. The secretory phase (days 15–28), driven by progesterone from the corpus luteum, prepares the endometrium for embryo implantation.
Describe the process of spermatogenesis, including the roles of sustentocytes and the blood-testis barrier.
Spermatogenesis in the seminiferous tubules begins when spermatogonia divide by mitosis; one daughter cell stays at the basal lamina as a stem cell, while the other becomes a primary spermatocyte. After moving into the adluminal compartment, the primary spermatocyte undergoes meiosis I and II to form haploid spermatids, which then differentiate into sperm through spermiogenesis. Sustentocytes (Sertoli cells) support and nourish the developing cells, and their tight junctions form the blood-testis barrier that prevents sperm antigens from entering the bloodstream and triggering an immune response.
How does the ovarian cycle coordinate with the uterine cycle, and what hormonal events trigger ovulation?
The ovarian cycle and uterine cycle are coordinated by ovarian hormones. The follicular phase of the ovarian cycle overlaps the uterine menstrual and proliferative phases, while the luteal phase corresponds to the uterine secretory phase. Ovulation is triggered by a midcycle LH surge that occurs when high estrogen levels from the dominant follicle exert positive feedback on the anterior pituitary. This LH surge causes follicle rupture and formation of the corpus luteum.
Why does the corpus luteum degenerate at the end of the ovarian cycle if fertilization does not occur, and what are the consequences for hormone levels?
When fertilization does not occur, LH blood levels fall, and because LH is the stimulus for luteal activity, the corpus luteum begins degenerating about 10 days after ovulation and eventually becomes a scar called the corpus albicans. As it degenerates, its output of progesterone and estrogens ends, so blood levels of these ovarian hormones drop sharply near the end of the cycle. This decline removes the negative feedback blockade of FSH and LH secretion, so a new ovarian cycle can begin.
What are the functions of sustentocytes (Sertoli cells) in spermatogenesis?
Sustentocytes (Sertoli cells) act as nurse cells that support and regulate spermatogenesis. They nourish spermatogenic cells, remove their debris, and move them toward the tubule lumen. They also form the blood-testis barrier via tight junctions, secrete testicular fluid, phagocytize faulty cells and excess cytoplasm, and produce chemical mediators such as inhibin and androgen-binding protein.
Describe the phases of the ovarian cycle and the hormonal changes that occur during each phase.
The ovarian cycle has two phases: the follicular phase and the luteal phase. During the follicular phase, FSH stimulates follicle growth and estrogen secretion, and the dominant follicle is selected; high estrogen levels eventually cause an LH surge around day 14. The LH surge triggers ovulation and transforms the ruptured follicle into the corpus luteum. During the luteal phase, the corpus luteum secretes progesterone and some estrogens, which inhibit FSH and LH; if pregnancy does not occur, the corpus luteum degenerates and hormone levels fall, allowing the cycle to restart.
Describe the sequence of events in the ovarian cycle, including the roles of FSH and LH.
The ovarian cycle has a follicular phase (days 1-14) and a luteal phase (days 14-28). In the follicular phase, FSH stimulates vesicular follicles to grow and secrete estrogens, while LH stimulates thecal cells to supply androgens that are converted to estrogens; one follicle becomes dominant. The resulting high estrogen level triggers an LH surge, which causes the dominant follicle's primary oocyte to complete meiosis I and leads to ovulation around day 14. The LH surge also converts the ruptured follicle into the corpus luteum, whose progesterone and estrogen maintain the uterine lining until it degenerates if no pregnancy occurs.
Describe the three phases of the uterine (menstrual) cycle, including the days each occurs and the hormonal influences driving each phase.
The uterine cycle has three phases: menstrual (days 1-5), proliferative (days 6-14), and secretory (days 15-28). Low estrogen and progesterone levels allow endometrial shedding in the menstrual phase, rising estrogens rebuild the endometrium in the proliferative phase, and progesterone from the corpus luteum prepares the secretory endometrium for implantation. If no pregnancy occurs, corpus luteum degeneration lowers progesterone, causing the functional layer to slough off around day 28 and the cycle to restart.
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