Physiology 2 Block 1 Guyton questions

101. Cortisol and growth hormone are most dissimilar in their metabolic effects on which of the following? A) Protein synthesis in muscle B) Glucose uptake in peripheral tissues C) Plasma glucose concentration D) Mobilization of triglycerides

101. A) Growth hormone and cortisol have opposite effects on protein synthesis in muscle. Growth hormone is anabolic and promotes protein synthesis in most cells of the body, whereas cortisol decreases protein synthesis in extrahepatic cells, including muscle. Both hormones impair glucose uptake in peripheral tissues and, therefore, tend to increase plasma glucose concentration. Both hormones also mobilize triglycerides from fat stores.

102. Infants of mothers who had adequate nutrition during pregnancy do not require iron supplements or a diet rich in iron until about 3 months of age. Why is this? A) Growth of the infant does not require iron until after the 3rd month B) The fetal liver stores enough iron to meet the infant's needs until the third month C) Synthesis of new red blood cells begins after 3 months D) Muscle cells that develop before the 3rd month do not contain myoglobin

102. B) If the mother has had adequate amounts of iron in her diet, the infant's liver usually has enough stored iron to form blood cells for 4 to 6 months after birth. However, if the mother has had insufficient iron, the infant may develop severe anemia after about 3 months of life.

103. Which of the following would least likely be associated with thyrotoxicosis? A) Tachycardia B) Increased appetite C) Somnolence D) Increased sweating E) Muscle tremor

103. C) Thyrotoxicosis indicates the effects of thyroid hormone excess. Thyroid hormone excites synapses. In contrast, somnolence is characteristic of hypothyroidism. Tachycardia, increased appetite, increased sweating, and muscle tremor are all signs of hyperthyroidism.

104. Where does fertilization normally take place? A) Uterus B) Cervix C) Ovary D) Ampulla of the fallopian tubes

104. D) Fertilization of the ovum normally takes place in the ampulla of one of the fallopian tubes.

105. A patient comes to the emergency room and is found to have a slightly below-normal concentration of calcium in the blood (calcium ion activity 5 0.9 mmol/L), a phosphate concentration approximately 50% below normal (HPO42 5 0.5 mmol/L), and undetectable amounts of calcium ion in the urine. Which of the following would one expect to find in this patient? A) Above normal calcitonin concentration in the blood B) Greater than normal parathyroid hormone concentration in the blood C) Suppressed osteoclastic activity in the bone D) Below normal blood pH

105. B) The below-normal plasma calcium concentration in this patient would be expected to strongly stimulate the secretion of parathyroid hormone, which in turn would be expected to increase the rate of excretion of phosphate ions by the kidney and reduce the rate of calcium ion excretion into the urine. There- fore, all the findings can be attributed to a greater than normal parathyroid hormone concentration.

106. Which of the following findings is most likely to oc- cur in a patient who has uncontrolled type 1 diabetes mellitus? A) Decreased plasma osmolality B) Increased plasma volume C) Increased plasma pH D) Increased release of glucose from the liver E) Decreased rate of lipolysis

106. D) Because insulin secretion is deficient in type 1 diabetes mellitus, there is increased (not decreased) release of glucose from the liver. Low plasma levels of insulin also lead to a high rate of lipolysis; increased plasma osmolality, hypovolemia, and acidosis are all symptoms of uncontrolled type 1 diabetes mellitus.

107. Growth hormone secretion would most likely be sup- pressed under which of the following conditions? A) Acromegaly B) Gigantism C) Deep Sleep D) Exercise E) Acute hyperglycemia

107. E) Under acute conditions, an increase in blood glucose concentration will decrease growth hormone secretion. Growth hormone secretion is characteristically elevated in the chronic pathophysiological states of Acromegaly and Gigantism. Deep sleep and exercise are stimuli that increase growth hormone secretion.

108. Two days before the onset of menstruation, secretions of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) reach their lowest levels. What is the cause of this low level of secretion? A) The anterior pituitary gland becomes unresponsive to the stimulatory effect of gonadotropin- releasing hormone (GnRH) B) Estrogen from the developing follicles exerts a feedback inhibition on the hypothalamus C) The rise in body temperature inhibits hypothalamic release of GnRH D) Secretion of estrogen, progesterone, and inhibin by the corpus luteum suppresses hypothalamic secretion of GnRH and pituitary secretion of FSH

108. D) Estrogen and, to a lesser extent, progesterone secreted by the corpus luteum during the luteal phase have strong feedback effects on the anterior pituitary gland to maintain low secretory rates of both FSH and LH. In addition, the corpus luteum secretes inhibin, which inhibits the secretion of FSH.

109. Which of the following would most likely occur in the earliest stages of type II diabetes? A) Increased insulin sensitivity B) High circulating levels of C-peptide C) Decreased hepatic glucose output D) Metabolic acidosis E) Hypovolemia

109. B) The early stages of type II are associated with diminished sensitivity of target tissues to the metabolic effects of insulin, a condition referred to as insulin resistance. Decreased insulin sensitivity tends to increase plasma glucose concentration, in part by promoting hepatic release of glucose. Increased plasma glucose concentration leads to a compensatory in- crease in the secretion of insulin and C-peptide, which is a cleavage product of proinsulin. Metabolic acidosis and hypovolemia occur in type I diabetes but are not present in the early stages of type II diabetes.

110. A baby is born with a penis, a scrotum with no testes, no vagina, and XX chromosomes. This condition is referred to as hermaphroditism. Which of the follow- ing could cause this abnormality? A) Abnormally high levels of human chorionic gonadotropin production by the trophoblast cells B) Abnormally low rates of estrogen production by the placenta C) Abnormally high levels of luteinizing hormone in the maternal blood D) Abnormally high levels of testosterone in the maternal blood

110. D) If a pregnant woman bearing a female child has high blood levels of androgenic hormones early in pregnancy, the child will be born with male genitalia, resulting in a type of hermaphroditism.

111. Which of the following contributes to "sodium escape" in Conn's syndrome? A) Decreased plasma levels of atrial natriuretic peptide B) Increased plasma levels of angiotensin II C) Decreased sodium reabsorption in the collecting tubules D) Increased arterial pressure

111. D) Under chronic conditions, the effects of high plasma levels of aldosterone to promote sodium reabsorption in the collecting tubules are sustained. However, persistent sodium retention does not occur, because of concomitant changes that promote sodium excretion. These include increased arterial pressure and increased plasma levels of atrial natriuretic peptide and decreased plasma angiotensin II concentration.

113. C) Increased plasma levels of cortisol tend to increase plasma glucose concentration and inhibit adrenocorticotropic hormone (ACTH) secretion. Therefore, if cortisol were administered to patients in group 2, the patients in group 1 would have lower plasma glucose concentrations and higher plasma levels of ACTH.

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115. Which of the following metabolic substrates is preferentially metabolized by growth hormone? A) Fats B) Proteins C) Glycogen D) Glucose

115. A) Fats are readily oxidized by growth hormone. In contrast, growth hormone decreases carbohydrate utilization and promotes the incorporation of amino acids into proteins.

116. A man suffers from a disease that destroyed only the motor neurons of the spinal cord below the thoracic region. Which aspect of sexual function would not be possible? A) Arousal B) Erection C) Lubrication D) Ejaculation

116. D) The motor neurons of the spinal cord of the thoracic and lumbar regions are the sources of innervation for the skeletal muscles of the perineum involved in ejaculation.

117. A sustained program of lifting heavy weights will increase bone mass. What is the mechanism of this effect of weightlifting? A) Elevated metabolic activity stimulates parathyroid hormone secretion B) Mechanical stress on the bones increases the activity of osteoblasts C) Elevated metabolic activity results in an increase in dietary calcium intake D) Elevated metabolic activity results in stimulation of calcitonin secretion

117. B) Bone is deposited in proportion to the compressional load that the bone must carry. Continual mechanical stress stimulates osteoblastic deposition and calcification of bone.

118. Levels of transcortin are elevated in a pregnant woman. Which of the following laboratory findings would be expected in this patient? A) Increased total (protein-bound plus free) plasma cortisol concentration B) Increased free (non-protein-bound) plasma cortisol concentration C) Decreased total plasma cortisol concentration D) Decreased free plasma cortisol concentration E) Little or no change in total plasma cortisol concentration

118. A) Cortisol is highly bound to plasma proteins, particularly transcortin. Increased plasma levels of transcortin, such as occur during pregnancy, tend to decrease free cortisol concentration, but feedback results in increased adrenocorticotropic hormone secretion, which stimulates cortisol secretion until free plasma levels of the steroid return to normal levels. Thus, in a steady state, total plasma cortisol concentration (bound plus free) is elevated, but free cortisol concentration is normal.

119. Birth control pills containing combinations of synthetic estrogen and progesterone compounds given for the first 21 days of the menstrual cycle are effective in preventing pregnancy. What is the explanation for their efficacy? A) Prevention of the preovulatory surge of luteinizing hormone secretion from the pituitary gland B) Prevention of development of the ovarian follicles C) Suppressing function of the corpus luteum soon after it forms D) Prevention of normal development of the endometrium

119. A) Administration of either estrogen or progesterone in appropriate quantities during the first half of the menstrual cycle can inhibit ovulation by prevent- ing the preovulatory surge of luteinizing hormone secretion by the anterior pituitary gland, which is essential for ovulation.

120. Which of the following physiological responses is greater for triiodothyronine (T3) than for thyroxine (T4)? A) Secretion rate from the thyroid B) Plasma concentration C) Plasma half-life D) Affinity for nuclear receptors in target tissues E) Latent period for onset of action in target tissues

120. D) In target tissues, nuclear receptors for thyroid hormones have a greater affinity for T3 than for T4. The secretion rate, plasma concentration, half-life, and onset of action are all greater for T4 than for T3.

121. A "birth control" compound for men has been sought for several decades. Which of the following would provide effective sterility? A) Substance that mimics the actions of luteinizing hormone B) Substance that blocks the actions of inhibin C) Substance that blocks the actions of follicle- stimulating hormone D) Substance that mimics the actions of gonadotropin- releasing hormone

121. C) Blocking the action of follicle-stimulating hormone on the Sertoli cells of the seminiferous tubules interrupts the production of sperm. Choice C is the only option that is certain to provide sterility.

122. In order for milk to flow from the nipple of the mother into the mouth of the nursing infant, which of the following must occur? A) Myoepithelial cells must relax B) Prolactin levels must fall C) Oxytocin secretion from the posterior pituitary must take place D) The baby's mouth must develop a strong negative pressure over the nipple E) All of the above

122. C) Oxytocin is secreted from the posterior pituitary gland and carried in the blood to the breast, where it causes the cells that surround the outer walls of the alveoli and ductile system to contract. Contraction of these cells raises the hydrostatic pressure of the milk in the ducts to 10 to 20 mm Hg. Consequently, milk flows from the nipple into the baby's mouth.

123. Failure of the ductus arteriosus to close is a common developmental defect. Which of the following would likely be present in a 12-month-old infant with patent ductus arteriosus? A) Below-normal arterial Po2 B) Below-normal arterial Pco2 C) Greater than normal arterial blood pressure D) Lower than normal pulmonary arterial pressure

123. A) If the ductus arteriosus remains patent, poorly oxygenated blood from the pulmonary artery flows into the aorta, giving the arterial blood an oxygen level that is below normal.

124. F) In Cushing's disease, there is a high rate of cortisol secretion, but aldosterone secretion is normal. High plasma levels of cortisol tend to increase plasma glucose concentration by impairing glucose uptake in peripheral tissues and by promoting gluconeogenesis. However, at least in the early stages of Cushing's disease, the tendency for glucose concentration to increase appreciably is counteracted by increased insulin secretion.

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125. The placenta does which of the following? A) Develops from the granulosa cells B) Secretes luteinizing hormone C) Secretes estrogen D) Allows direct mixing of maternal and fetal blood E) None of the above

125. C) The placenta secretes both estrogen and progesterone from the trophoblast cells.

126. Why is osteoporosis much more common in elderly women than in elderly men? A) Men continue to produce testosterone through- out their lifetime, whereas women cease estrogen production after menopause B) Women consume less dietary calcium than men C) Gastrointestinal absorption of calcium is more effective in men than in women D) The bones of women contain less calcium than those of men even before menopause

126. A) Testosterone stimulates the cellular functions of bone that lead to bone formation. Testosterone secretion from the interstitial cells declines with age, but it continues at sufficient levels to stimulate bone formation throughout a man's lifetime. Conversely, estrogen production in women falls to zero after menopause, leaving the bones without the stimulatory effect of estrogen. As a result, osteoporosis is common in women after menopause.

127. When compared with the late-evening values typically observed in normal subjects, plasma levels of both adrenocorticotropic hormone and cortisol would be expected to be higher in which of the following individuals? A) Normal subjects after waking in the morning B) Normal subjects administered dexamethasone C) Patients with Cushing's syndrome (adrenal adenoma) D) Patients with Addison's disease E) Patients with Conn's syndrome

127. A) In healthy patients, the secretory rates of adrenocorticotropic hormone (ACTH) and cortisol are low in the late evening but high in the early morning. In patients with Cushing's syndrome (adrenal adenoma) or in patients administered dexamethasone, plasma levels of ACTH are very low and are certainly not higher than normal early-morning values. In patients with Addison's disease, plasma levels of ACTH are elevated as a result of deficient adrenal secretion of cortisol. The secretion of ACTH and cortisol would be expected to be normal in Conn's syndrome.

128. Which of the following conditions or hormones would most likely increase growth hormone secretion? A) Hyperglycemia B) Exercise C) Somatomedin D) Somatostatin E) Aging

128 B) Exercise stimulates GH secretion. Hyperglycemia, somatomedin, and the hypothalamic inhibitory hormone somatostatin all inhibit GH secretion. GH secretion also decreases in aging.

129. Which blood vessel in the fetus has the highest Po2? A) Ductus arteriosus B) Ductus venosus C) Ascending aorta D) Left atrium

129. B) Blood returning from the placenta through the umbilical vein passes through the ductus venosus. The blood coming from the placenta has the highest concentration of oxygen found in the fetus.

130. A 59-year-old woman has osteoporosis, hypertension, hirsutism, and hyperpigmentation. Magnetic resonance imaging indicates that the pituitary gland is not enlarged. Which of the following conditions is most consistent with these findings? A) Pituitary adrenocorticotropic hormone (ACTH)- secreting tumor B) Ectopic ACTH-secreting tumor C) Inappropriately high secretion rate of corticotropin- releasing hormone D) Adrenal adenoma E) Addison's disease

130. B) Osteoporosis, hypertension, hirsutism, and hyperpigmentation are all symptoms of Cushing's syndrome associated with high plasma levels of ACTH. If the high plasma ACTH levels were the result of either a pituitary adenoma or an abnormally high rate of corticotropin-releasing hormone secretion from the hypothalamus, the patient would likely have an enlarged pituitary gland. In contrast, the pituitary gland would not be enlarged if an ectopic tumor were secreting high levels of ACTH.

131. B) Prolactin secretion is inhibited, not stimulated, by the hypothalamic release of dopamine into the median eminence. Growth hormone is inhibited by the hypothalamic inhibiting hormone somatostatin. The secretion of luteinizing hormone, thyroid stimulating hormone, and adrenocorticotropic hormone are all under the control of the releasing hormones indicated.

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132. I'm Extracellular calcium concentration remains only slightly below normal for many months even when dietary calcium intake is minimal. What accounts for this ability to maintain calcium concentration in the extracellular fluid? A) Only a slight reduction in plasma calcium concentration stimulates large, sustained increases in parathyroid hormone secretion B) Osteoclasts stimulated by high levels of parathyroid hormone remove calcium from the large quantity stored in the bone, thereby maintaining the near-normal extracellular calcium level C) Renal excretion of calcium is greatly reduced under the influence of high concentrations of parathyroid hormone D) All of the above

132. D) During prolonged calcium deficiency, the plasma calcium concentration begins to fall. However, as it falls, parathyroid hormone secretion increases sharply, thereby stimulating osteoclastic degradation of bone and liberating calcium to the extracellular fluid. At the same time, the elevated parathyroid hormone concentration strongly stimulates calcium re- absorption from the tubular fluid of the kidneys and reduces calcium excretion to very low levels.

133. B) Increased heart rate, increased respiratory rate, and decreased cholesterol concentration are all responses to excess thyroid hormone.

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134. During the latter stages of pregnancy, many women experience an increase in body hair growth in a mas- culine pattern. What is the explanation for this? A) The ovaries secrete some testosterone along with the large amounts of estrogen produced late in pregnancy B) The fetal ovaries and testes secrete androgenic steroids C) The maternal and fetal adrenal glands secrete large amounts of androgenic steroids that are used by the placenta to form estrogen D) The placenta secretes large amounts of estrogen, some of which is metabolized to testosterone

134. C) Estrogen secreted by the placenta is not synthesized from basic substrates in the placenta. Instead, it is formed almost entirely from androgenic steroid compounds that are formed in both the mother's and the fetus's adrenal glands. These androgenic com- pounds are transported by the blood to the placenta and converted by the trophoblast cells to estrogen compounds. Their concentration in the maternal blood may also stimulate hair growth on the body.

135. What is the cause of menopause? A) Reduced levels of gonadotropic hormones secreted from the anterior pituitary gland B) Reduced responsiveness of the follicles to the stimulatory effects of gonadotropic hormones C) Reduced rate of secretion of progesterone from the corpus luteum D) Reduced numbers of follicles available in the ovary for stimulation by gonadotropic hormones

135. D) By age 45 years, only a few primordial follicles remain in the ovaries to be stimulated by gonadotropic hormones, and the production of estrogen decreases as the number of follicles approaches zero. When estrogen production falls below a critical value, it can no longer inhibit the production of go- nadotropic hormones from the anterior pituitary. Follicle-stimulating hormone and luteinizing hormone are produced in large quantities, but as the remaining follicles become atretic, production by the ovaries falls to zero.

136. Release of which of the following hormones is an ex- ample of neuroendocrine secretion? A) Growth hormone B) Cortisol C) Oxytocin D) Prolactin E) Adrenocorticotropic hormone

136. C) The secretion of chemical messengers (neuro- hormones) from neurons into the blood is referred to as neuroendocrine secretion. Thus, in contrast to the local actions of neurotransmitters at nerve endings, neurohormones circulate in the blood before producing biological effects at target tissues. Oxytocin is synthesized from magnocellular neurons whose cell bodies are located in the paraventricular and supra- optic nuclei and whose nerve terminals terminate in the posterior pituitary gland. Target tissues for circulating oxytocin are the breast and uterus, where the hormone plays a role in lactation and parturition, respectively.

137. During the week following ovulation, the endometrium increases in thickness to 5 to 6 millimeters. What stimulates this increase in thickness? A) Luteinizing hormone B) Estrogen from the corpus luteum C) Progesterone from the corpus luteum D) Follicle-stimulating hormone

137. C) Progesterone secreted in large quantities from the corpus luteum causes marked swelling and secretory development of the endometrium.

138. A) Several hours after eating a meal (the postabsorptive period), plasma glucose concentration tends to fall. As a result, insulin secretion decreases. Because insulin inhibits hormone sensitive lipase in adipocytes, the activity of this enzyme increases in response to the declining plasma levels of insulin. This leads to increased hydrolysis of triglycerides. A fall in insulin concentration also diminishes glucose uptake in adipocytes, leading to decreased generation of a-glycerol phosphate, which is necessary to form triglycerides from fatty acids. Both of these insulin- induced responses in adipocytes promote release of fatty acids into the circulation. As the postprandial period persists, reductions in plasma glucose concentration stimulate glucagon secretion, which tends to preserve glucose concentration by stimulating glycogenolysis and gluconeogenesis.

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139. Inhibition of the iodide pump would be expected to cause which of the following changes? A) Increased synthesis of thyroxine (T4) B) Increased synthesis of thyroglobulin C) Increased metabolic rate D) Decreased thyroid-stimulating hormone secretion E) Extreme nervousness

139. B) Inhibition of the iodide pump decreases the synthesis of thyroid hormones but does not impair the production of thyroglobulin by follicular cells. De- creased plasma levels of thyroid hormones result in a low metabolic rate and lead to an increase in thyroid- stimulating hormone (TSH) secretion. Increased plasma levels of TSH stimulate the follicular cells to synthesize more thyroglobulin. Nervousness is a symptom of hyperthyroidism and is not caused by thyroid hormone deficiency.

140. Before implantation, the blastocyst obtains its nutrition from the uterine endometrial secretions. How does the blastocyst obtain nutrition during the first week after implantation? A) It continues to derive nutrition from endometrial secretions B) The cells of the blastocyst contain stored nutrients that are metabolized for nutritional support C) The placenta provides nutrition derived from maternal blood D) The trophoblast cells digest the nutrient-rich endometrial cells and then absorb their contents for use by the blastocyst

140. D) As the blastocyst implants, the trophoblast cells invade the decidua, digesting and imbibing it. The stored nutrients in the decidual cells are used by the embryo for growth and development. During the 1st week after implantation, this is the only means by which the embryo can obtain nutrients. The embryo continues to obtain at least some of its nutrition in this way for up to 8 weeks, although the placenta begins to provide nutrition after about the 16th day beyond fertilization (a little more than 1 week after implantation).

141. Which of the following increases the rate of deposition and decreases the rate of absorption of bone? A) Elevation of parathyroid hormone concentration B) Elevation of estrogen concentration C) Elevation of extracellular hydrogen ion concentration D) Reduction in mechanical stress on the bone

141. B) Elevation of estrogen concentration stimulates osteoblastic activity and reduces the rate of degradation of bone by osteoclasts.

142. Which of the following pituitary hormones has a chemical structure most similar to that of antidiuretic hormone? A) Oxytocin B) Adrenocorticotropic hormone C) Thyroid-stimulating hormone D) Follicle-stimulating hormone E) Prolactin

142. A) Both antidiuretic hormone and oxytocin are pep- tides containing nine amino acids. Their chemical structures differ in only two amino acids.

143. What is the most common cause of respiratory distress syndrome in neonates born at 7 months gestation? A) Pulmonary edema due to pulmonary arterial hypertension B) Formation of a hyaline membrane over the alveolar surface C) Failure of the alveolar lining to form adequate amounts of surfactant D) Excessive permeability of the alveolar membrane to water

143. C) One of the most characteristic findings in respiratory distress syndrome is failure of the respiratory epithelium to secrete adequate quantities of surfactant into the alveoli. Surfactant decreases the surface tension of the alveolar fluid, allowing the alveoli to open easily during inspiration. Without sufficient surfactant, the alveoli tend to collapse, and there is a tendency to develop pulmonary edema.

144. Which of the following steroid hormones is not synthesized to any appreciable degree in the zona fasciculata? A) Aldosterone B) Cortisol C) Corticosterone D) Dehydroepiandrosterone E) Deoxycorticosterone

144. A) The enzyme aldosterone synthase is not present in the zona fasciculata. Consequently, aldosterone is not synthesized in these cells of the adrenal cortex.

145. A 45-year-old woman has a mass in the sella turcica that compresses the portal vessels, disrupting pituitary access to hypothalamic secretions. The secretion rate of which of the following hormones would most likely increase in this patient? A) Adrenocorticotropic hormone B) Growth hormone C) Prolactin D) Luteinizing hormone E) Thyroid-stimulating hormone

145. C) The primary controllers of adrenocorticotropic hormone (ACTH), growth hormone, luteinizing hormone (LH), and thyroid-stimulating hormone (TSH) secretion from the pituitary gland are hypothalamic releasing hormones. They are secreted into the me- dian eminence and subsequently flow into the hypo- thalamic-hypophysial portal vessels before bathing the cells of the anterior pituitary gland. Conversely, prolactin secretion from the pituitary gland is influenced primarily by the hypothalamic inhibiting hormone dopamine. Consequently, obstruction of blood flow through the portal vessels would lead to reduced secretion of ACTH, growth hormone, LH, and TSH, but increased secretion of prolactin.

146. A man who has been exposed to high levels of gamma radiation is sterile due to destruction of the germinal epithelium of the seminiferous tubules, although he has normal levels of testosterone. Which of the following would be found in this patient? A) Normal secretory pattern of gonadotropin- releasing hormone B) Normal levels of inhibin C) Suppressed levels of follicle-stimulating hormone D) Absence of Leydig cells

146. A) Gamma radiation destroys the cells undergoing the most rapid rates of mitosis and meiosis, the germinal epithelium of the testes. The man described is said to have normal testosterone levels, suggesting that the secretory patterns of gonadotropin-releasing hormone and luteinizing hormone are normal and that his interstitial cells are functional. Because he is not producing sperm, the levels of inhibin secreted by the Sertoli cells would be maximally suppressed, and his levels of follicle-stimulating hormone would be strongly elevated.

147. A patient has hypothyroidism due to a primary abnormality in the thyroid gland. Increased plasma levels of which of the following would most likely be reported? A) Cholesterol B) Thyroxine-binding globulin C) Reverse triiodothyronine (RT3) D) Diiodotyrosine E) Iodide

147. A) Increased plasma cholesterol concentration is commonly observed in hypothyroidism.

148. B) In this experiment, the size of the thyroid gland increased because thyroid-stimulating hormone (TSH) causes hypertrophy and hyperplasia of its tar- get gland and increased secretion of thyroid hormones. Increased plasma levels of thyroid hormones inhibit the secretion of thyrotropin-releasing hormone, which decreases stimulation of the pituitary thyrotropes, resulting in a decrease in the size of the pituitary gland. Higher plasma levels of thyroid hormones also increase metabolic rate and decrease body weight.

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149. C) In this experiment, the size of the pituitary and adrenal glands increased because corticotropin-releasing hormone stimulates the pituitary corticotropes to secrete adrenocorticotropic hormone, which in turn stimulates the adrenals to secrete corticosterone and cortisol. Higher plasma levels of cortisol increase protein degradation and lipolysis and, therefore, decrease body weight.

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112. A scientist studying developmental physiology per- forms an experiment in which a substance is given to pregnant rats that give birth to pups that have XY chromosomes but female genital organs. What was the substance given to the rats? A) An antibody that blocked the effect of human chorionic gonadotropin in the embryo and fetus B) A large quantity of estrogen-like compounds C) Follicle-stimulating hormone D) Testosterone

A) In order for a male embryo to develop male genitalia, testosterone must be present in the embryo. Normally, human chorionic gonadotropin (HCG) secreted by the trophoblast cells stimulates testosterone secretion from the testes. Giving an antibody that blocks HCG would prevent testosterone secretion, resulting in the development of female genitalia in a male fetus.

114. A 30-year-old woman reports to the clinic for a routine physical examination. The examination reveals that she is pregnant. Plasma levels of TSH are high but total T4 concentration (protein bound and free) is normal. Which of the following best reflects this patient's clinical state? A) Graves' diseaseB) Hashimoto's disease C) Pituitary tumor secreting TSH D) Hypothalamic tumor secreting TRH E) Patient is taking thyroid extract

B) Circulating levels of free T4 exert biological effects and are regulated by feedback inhibition of TSH secretion from the anterior pituitary gland. Protein bound T4 is biologically inactive. Circulating T4 is highly bound to plasma proteins, especially to thyroid-binding globulin (TBG), which increases during pregnancy. An increase in TBG tends to decrease free T4, which then leads to an increase in TSH secretion, causing the thyroid to increase thyroid hormone secretion. Increased secretion of thyroid hormones persists until free T4 returns to normal levels, at which time there is no longer a stimulus for increased TSH secretion. Therefore, in a chronic steady-state condition associated with elevated TBG, high plasma total T4 (bound and free) and normal plasma TSH levels would be expected. In this pregnant patient, the normal levels of total T4 along with high plasma levels of TSH would indicate an inappropriately low plasma level of free T4. Deficient thyroid hormone secretion in this patient would be consistent with Hashimoto's disease, the most common form of hypothyroidism.

8. A) During exercise, glucose utilization by muscle is increased, which is largely independent of insulin.

In the figure, line D most likely illustrates the influence of which of the following? A) Exercise B) Obesity C) Growth hormone D) Cortisol E) Glucagon

24. B) Secretion of adrenal cortical hormones is deficient in patients with Addison's disease. Consequently, low plasma levels of both aldosterone and cortisol would be reported. As a result of the low plasma levels of aldosterone, plasma potassium concentration would be increased.

24. A patient with Addison's disease

25. E) Patients with Conn's syndrome have tumors of the zona glomerulosa that secrete large amounts of aldosterone. Consequently, plasma levels of aldosterone are elevated, causing hypokalemia. The secretion of cortisol from the zona fasciculata is normal.

25. A patient with Conn's syndrome

83. Which of the following is produced by the trophoblast cells during the first 3 weeks of pregnancy? A) Estrogen B) Luteinizing hormone C) Oxytocin D) Human chorionic gonadotropin E) None of the above

83. D) Human chorionic gonadotropin is secreted from the trophoblast cells beginning shortly after the blastocyst implants in the endometrium.

12. Which of the following could inhibit the initiation of labor? A) Administration of an antagonist of the actions of progesterone B) Administration of luteinizing hormoneC) Administration of an antagonist of prostaglandin E2 effectsD) Mechanically dilating and stimulating the cervix E) Administration of oxytocin

12. C) Antagonism of progesterone's effects, dilation of the cervix, and oxytocin all increase uterine smooth muscle excitability and will facilitate contractions and onset of labor. LH would have no effect. PGE2 strongly stimulates uterine smooth muscle contraction and is formed in increasing rate by the placenta late in gestation.

63. E) During exercise, glucose uptake by muscle is enhanced, which tends to decrease the blood glucose concentration. Insulin secretion is depressed during exercise, whereas the secretion of glucagon and epinephrine is elevated. Therefore, hepatic glucose uptake is impaired, and the activity of hormone-sensitive lipase is increased.

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1. Seven days after ovulation, pituitary secretion of luteinizing hormone (LH) decreases rapidly. What is the cause of this decrease in secretion? A) The anterior pituitary gland becomes unresponsive to the stimulatory effect of gonadotropin-releasing hormone (GnRH) B) Estrogen from the developing follicles exerts a feedback inhibition on the hypothalamus C) The rise in body temperature inhibits hypothalamic release of GnRH D) Secretion of estrogen and progesterone by the corpus luteum suppresses hypothalamic secretion of GnRH and pituitary secretion of LH E) None of the above

1. D) Estrogen and progesterone are formed in large amounts by the mature corpus luteum that has formed by 7 days following ovulation, causing nega- tive feedback inhibition of LH secretion from the anterior pituitary.

10. A baby is born with a penis, a scrotum with no testes, no vagina, and XX chromosomes. This condition is referred to as hermaphroditism. Which of the follow- ing could cause this abnormality? A) Abnormally high levels of human chorionic gonadotropin production by the trophoblast cells B) The presence of a testosterone-secreting tumor in the mother's right adrenal gland C) Abnormally high levels of luteinizing hormone in the maternal blood D) Abnormally low levels of testosterone in the maternal blood E) Abnormally low rates of estrogen production by the placenta

10. B) Very high concentration of testosterone in a female embryo will induce formation of male genitalia. An adrenal tumor in the mother synthesizing testosterone at a high, uncontrolled rate could produce the masculinizing effect.

100. D) A pituitary tumor secreting growth hormone is likely to present as an increase in pituitary gland size. The anabolic effects of excess growth hormone secretion lead to enlargement of the internal organs, including the kidneys. Because acromegaly is the state of excess growth hormone secretion after epiphyseal closure, increased femur length does not occur.

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11. A young woman is given daily injections of a substance beginning on the 16th day of her normal menstrual cycle and continuing for 3 weeks. As long as the injections continue, she does not menstruate. The injected substance could be which of the following? A) Testosterone B) FSH C) An inhibitor of progesterone's actions D) A prostaglandin E2 inhibitor E) HCG

11. E) HCG has the same stimulatory effect as LH on the corpus luteum. Administration of HCG would cause the corpus luteum to continue to secrete estrogen and progesterone, preventing degradation of the endome- trium and onset of menstruation.

23. In the circulatory system of a fetus, which of the fol- lowing is greater before birth than after birth? A) Arterial Po2 B) Right atrial pressure C) Aortic pressure D) Left ventricular pressure

23. B) Right atrial pressure falls dramatically after the onset of breathing due to a reduction in pulmonary vascular resistance, pulmonary arterial pressure, and right ventricular pressure.

13. Exposure to UV light directly facilitates which of the following? A) Conversion of cholesterol to 25-hydroxycholical- ciferol B) Conversion of 25-hydroxycholicalciferol to 1,25- dihydroxycholicalciferol C) Transport of calcium into the extracellular fluid D) Formation of calcium binding protein E) Storage of vitamin D3 in the liver

13. A) Ultraviolet light absorbed by the skin directly facilitates conversion of cholesterol to 25- hydroxycholesterol.

14. After birth, the pressure in the pulmonary artery decreases greatly. What is the cause of this? A) Systemic arterial pressure increases B) Ductus arteriosus closes C) Left ventricular pressure increases D) Pulmonary vascular resistance decreases

14. D) The pulmonary vascular resistance greatly de- creases as a result of expansion of the lungs. In the unexpanded fetal lungs, the blood vessels are com- pressed because of the small volume of the lungs. Immediately on expansion, these vessels are no longer compressed, and the resistance to blood flow decreases several-fold.

15. If a radioimmunoassay is properly conducted and the amount of radioactive hormone bound to anti- body is low, this would indicate which of the following? A) Plasma levels of endogenous hormone are high B) Plasma levels of endogenous hormone are low C) More antibody is needed D) Less radioactive hormone is needed

15. A) In a radioimmunoassay, there is too little antibody to bind completely the radioactively tagged hormone and the hormone in the fluid (plasma) to be assayed. Thus, there is completion between the labeled and endogenous hormone for binding sites on the anti- body. Consequently, if the amount of radioactive hormone bound to antibody is low, this would indicate that plasma levels of endogenous hormone are high.

16. Spermatogenesis is regulated by a negative feedback control system in which follicle-stimulating hormone (FSH) stimulates the steps in sperm cell formation. What is the negative feedback signal associated with sperm cell production that inhibits pituitary formation of FSH? A) Testosterone B) Inhibin C) Estrogen D) Luteinizing hormone

16. B) The Sertoli cells of the seminiferous tubules secrete inhibin at a rate proportional to the rate of production of sperm cells. Inhibin has a direct inhibitory effect on anterior pituitary secretion of FSH. FSH binds to specific receptors on the Sertoli cells, causing the cells to grow and secrete substances that stimulate sperm cell production. The secretion of inhibin thereby provides the negative feedback control signal from the seminiferous tubules to the pituitary gland.

18. When do progesterone levels rise to their highest point during the female hormonal cycle? A) Between ovulation and the beginning of menstruation B) Immediately before ovulation C) When the blood concentration of luteinizing hormone is at its highest point D) When 12 primary follicles are developing to the antral stage

18. A) The corpus luteum is the only source of progesterone production, except for minute quantities secreted from the follicle before ovulation. The corpus luteum is functional between ovulation and the beginning of menstruation, during which time the concentration of luteinizing hormone (LH) is suppressed below the level achieved during the preovulatory LH surge.

19. Some cells secrete chemicals into the extracellular fluid that act on cells in the same tissue. Which of the following refers to this type of regulation? A) NeuralB) Endocrine C) Neuroendocrine D) Paracrine E) Autocrine

19. D) Paracrine communication refers to cell secretions that diffuse into the extracellular fluid to affect neigh- boring cells.

2. Which of the following is inconsistent with the diagnosis of Graves' disease? A) Increased heart rate B) Exophthalmos C) Increased plasma levels of triiodothyronine (T3) D) Increased plasma levels of thyroxine (T4) E) Increased plasma levels of thyroid-stimulating hormone

2. E) In Graves' disease, thyroid-stimulating immunoglobulins bind to cell membrane receptors, causing the thyroid to produce excessive amounts of thyroid hormones (T3 and T4). As a result of negative feedback, increased plasma levels of T3 and T4 suppress the secretion of thyroid-stimulating hormone. In addition, increased plasma levels of immunoglobulins often cause exophthalmos, and an increased heart rate is a common response to high circulating levels of thyroid hormones.

20. Which of the following pairs is an example of the type of regulation referred to in question 19? A) Somatostatin—growth hormone secretion B) Somatostatin—insulin secretion C) Dopamine—prolactin secretion D) Norepinephrine—corticotropin-releasing hormone secretion E) Corticotropin-releasing hormone -adrenocorticotropic hormone secretion

20. B) The delta cells of the pancreas secrete somatostatin, which inhibits the secretion of insulin and glucagon from the pancreatic beta and alpha cells, respectively. Choice D is an example of neural communication, and the remaining choices are examples of neuroendocrine communication.

21. Estrogen is required for normal reproductive function in the male. Where is the principal site of estrogen synthesis in the male? A) Leydig cells B) Osteoblasts C) Liver cells D) Prostate cells

21. C). Large amounts of estrogen are formed from testosterone and androstanediol in the liver, accounting for as much as 80% of the total male estrogen production.

22. A professional athlete in her mid-20s has not had a menstrual cycle for 5 years, although a bone density scan revealed normal skeletal mineralization. Which of the following facts elicited during the taking of her medical history may explain these observations? A) She consumes a high-carbohydrate diet B) Her grandmother suffered a hip fracture at age 79 C) Her blood pressure is greater than normal D) Her plasma estrogen concentration is very low E) She has been taking anabolic steroid supplements for 5 years

22. E) Anabolic steroids bind to testosterone receptors in the hypothalamus, providing feedback inhibition of normal ovarian cycling and preventing menstrual cycling, as well as stimulation of osteoblastic activity in the bones.

26. D) Aldosterone secretion is elevated when dietary sodium intake is low, but cortisol secretion is normal. Although aldosterone increases the rate of potassium secretion by the principal cells of the collecting tubules, this effect is offset by a low distal tubular flow rate. Consequently, there is little change in either potassium excretion or plasma potassium concentration.

26. A patient on a low-sodium diet

28. Which of the following is greater after birth than before birth? A) Flow through the foramen ovale B) Pressure in the right atrium C) Flow through the ductus arteriosus D) Aortic pressure

28. D) Owing to the loss of blood flow through the placenta, systemic vascular resistance doubles at birth. This increases the aortic pressure as well as the pressure in the left ventricle and left atrium.

29. Parathyroid hormone directly A) controls the rate of 25-hydroxycholicalciferol formation B) controls the rate of calcium transport in the mucosa of the small intestine C) controls the rate of formation of calcium binding protein D) controls the rate of formation of 1, 25-dihydroxy- cholicalciferol E) stimulates renal tubular phosphate reabsorption

29. D) Parathyroid hormone acts in the renal cortex to stimulate the reaction forming 1, 25-dihydroxycholical- ciferol from 25-hydroxycholicalciferol. It has no effects on the other reactions.

30. Which of the following is most likely to produce the greatest increase in insulin secretion? A) Amino acids B) Amino acids and glucose C) Amino acids and somatostatin D) Glucose and somatostatin

30. B) Both amino acids and glucose stimulate insulin secretion. Further, amino acids strongly potentiate the glucose stimulus for insulin secretion. Somatostatin inhibits insulin secretion.

32. A patient has an elevated plasma thyroxine (T4) concentration, a low plasma thyroid-stimulating hormone (TSH) concentration, and a thyroid gland that is smaller than normal. Which of the following is the most likely explanation for these findings? A) Patient has a lesion in the anterior pituitary that prevents TSH secretion B) Patient is taking propylthiouracil C) Patient is taking thyroid extract D) Patient is consuming large amounts of iodine E) Patient has Graves disease

32. C) If a subject were taking sufficient amounts of exoenous thyroid extract to increase plasma levels of T4 above normal, feedback would cause TSH secretion to decrease. Low plasma levels of TSH would result in atrophy of the thyroid gland. In Graves' disease, the same changes in plasma levels of T4 and TSH would be present, but the thyroid gland would not be atrophied. In fact, goiter is often present in patients with Graves' disease. A lesion in the anterior pituitary that prevents TSH secretion or the taking of propylthiouracil or large amounts of iodine would be associated with low plasma levels of T4.

34. As menstruation ends estrogen levels in the blood rise rapidly. What is the source of the estrogen? A) Corpus luteum B) Developing follicles C) Endometrium D) Stromal cells of the ovaries E) Anterior pituitary gland

34. B) In the non-pregnant female, the only significant source of estrogen is ovarian follicles or corpus luteae. Menstruation begins when the corpus luteum degenerates. Menstruation ends when developing follicles secrete estrogen sufficiently to raise circulating concentration to a level that stimulates regrowth of the endometrium.

33. Extracellular ionic calcium activity will be decreased within 1 min by which of the following? A) Increase in extracellular phosphate ion activity B) Increase in extracellular pH C) Decrease in extracellular Pco2 D) All of the above E) None of the above

34. D) Choices A to C all will shift the mass action balance toward the side favoring association of ionic calcium with phosphate compounds or other anionic compounds, resulting in reduced levels of free ionic calcium.

35. Which of the following anterior pituitary hormones plays a major role in the regulation of a nonendocrine target gland? A) Adrenocorticotropic hormone B) Thyroid-stimulating hormone C) Prolactin D) Follicle-stimulating hormone E) Luteinizing hormone

35. C) The major target tissue for prolactin is the breast, where it stimulates the secretion of milk. The other anterior pituitary hormones (adrenocorticotropic hormone, thyroid-stimulating hormone, follicle-stimulating hormone, and luteinizing hormone) stimulate hormones from endocrine glands.

38. Which of the following would be expected in a patient with a genetic deficiency in 11b-hydroxysteroid dehydrogenase type 2? A) Increased mineralocorticoid activity B) Increased glucocorticoid activity C) Hyperkalemia D) Decreased blood pressure E) Hypoglycemia

38. A) The enzyme 11b-hydroxysteroid dehydrogenase type 2 is present in renal tubular cells and converts cortisol to cortisone, which does not readily bind to mineralocorticoid receptors. When this enzyme is deficient, cortisol, which is present in the plasma in considerably higher concentrations than aldosterone, binds the mineralocorticoids receptor and exerts mineralocorticoid effects. Hyperkalemia and decreased blood pressure reflect mineralocorticoid deficiency.

Which of the following decreases the resistance in the arteries leading to the sinuses of the penis? A) Stimulation of the sympathetic nerves innervating the arteries B) Nitric oxide C) Inhibition of activity of the parasympathetic nerves leading to the arteries D) All of the above

39. B) Nitric oxide is the vasodilator that is normally re- leased, causing vasodilatation in these arteries.

4. After menopause, hormone replacement therapy with estrogen-like compounds is effective in preventing the progression of osteoporosis. What is the mechanism of their protective effect? A) They stimulate the activity of osteoblasts B) They increase absorption of calcium from the gas- gastrointestinal tract C) They stimulate calcium reabsorption by the renal tubules D) They stimulate parathyroid hormone secretion by the parathyroid gland

4. A) Estrogen compounds are believed to have an osteoblast-stimulating effect. When the amount of estrogen in the blood falls to very low levels after menopause, the balance between the bone-building activity of the osteoblasts and the bone-degrading activity of the osteoclasts is tipped toward bone degradation. When estrogen compounds are added as part of hormone replacement therapy, the bone- building activity of the osteoblasts is increased to balance the osteoclastic activity.

40. A patient has a goiter associated with high plasma levels of both thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH). Her heart rate is elevated. This patient most likely has which of the following? A) Endemic goiter B) Hypothalamic tumor secreting large amounts of TRH C) Pituitary tumor secreting large amounts of TSH D) Graves' disease

40. B) A hypothalamic tumor secreting large amounts of TRH would stimulate the pituitary gland to secrete increased amounts of TSH. As a result, the secretion of thyroid hormones would increase, and this would result in an elevated heart rate. In comparison, a patient with either a pituitary tumor secreting large amounts of TSH or Graves' disease would have low plasma levels of TRH because of feedback. Both TRH and TSH levels would be elevated in endemic goiter, but the heart rate would be depressed because of the low rate of T4 secretion.

41. A 40-year-old woman comes to the emergency room with a fracture in the neck of the femur. Radiographs reveal generalized demineralization of the bone in the area. Her plasma calcium ion concentration is significantly greater than normal: 12.2 mg/dL. Which of the following conditions is consistent with this presentation? A) Osteoporosis B) Rickets C) Hyperparathyroidism D) Renal failure

41. C) Demineralization of the bone could be caused by any of the choices, but only an elevated parathyroid hormone concentration would result in both demineralization and elevated plasma calcium concentration. The elevated parathyroid hormone concentration results in overstimulation of the osteoclasts, loss of calcium from bone, stimulation of calcium absorption from the renal tubular fluid and inhibition of calcium excretion, and stimulation of the formation of 1,25-dihydroxycholecal- ciferol, which increases the rate of calcium absorption from the gastrointestinal tract.

42. A man eats a low carbohydrate meal rich in proteins containing the amino acids that stimulate insulin secretion. Which of the following responses accounts for the absence of hypoglycemia? A) Suppression of growth hormone B) Suppression of somatomedin C secretion C) Stimulation of cortisol secretion D) Stimulation of glucagon secretion E) Stimulation of epinephrine secretion

42. D) Consumption of amino acids stimulates both growth hormone and glucagon secretion. Increased glucagon secretion tends to increase blood glucose concentration and thus opposes the effects of insulin to cause hypoglycemia.

43. A 46-year-old man has "puffy" skin and is lethargic. His plasma thyroid-stimulating hormone concentration is low and increases markedly when he is given thyrotropin-releasing hormone. Which of the follow- ing is the most likely diagnosis? A) Hyperthyroidism due to a thyroid tumor B) Hyperthyroidism due to an abnormality in the hypothalamus C) Hypothyroidism due to an abnormality in the thyroid D) Hypothyroidism due to an abnormality in the hypothalamus E) Hypothyroidism due to an abnormality in the pituitary

43. D) Lethargy and myxedema are signs of hypothyroidism. Low plasma levels of thyroid-stimulating hormone indicate that the abnormality is in either the hypothalamus or the pituitary gland. Because the pituitary was responsive to the administration of thyrotropin-releasing hormone (TRH), this suggests that pituitary function is normal and that the hypo- thalamus is producing insufficient amounts of TRH.

44. Which of the following hormones is both synthesized and stored in the pituitary gland? A) Growth hormone (GH) B) GH releasing hormone (GHRH) C) ADHD) Somatostatin E) Somatomedin

44. A) GH and ADH are stored in the anterior and posterior lobes of the pituitary gland, respectively. However, although GH is also synthesized in the (anterior) pituitary gland, this is not the case for ADH. ADH and the hypothalamic releasing (GHRH) and hypothalamic inhibitory hormones (somatostatin) are synthesized in the hypothalamus. Somatomedins are growth factors (small proteins) that stimulate growth in bone and peripheral tissues. One of the most important somatomedins is somatomedin C, which is produced by the liver in response to GH. Somatomedin C stimulates all aspects of bone growth.

47. Giving prostaglandin E2 (PGE2) to a pregnant woman may result in an abortion. What is the best explanation for this finding? A) PGE2 strongly stimulates uterine contraction B) PGE2 causes constriction of the arteries leading to the placenta C) PGE2 stimulates the release of oxytocin from the posterior pituitary D) PGE2 increases the secretion of progesterone from the corpus luteum

47. A) The fetal portion of the placenta releases prostaglandins in high concentrations at the time of labor. This release is associated with deterioration of the placenta. Prostaglandins, especially PGE2, strongly stimuate uterine smooth muscle.

48. During the first few years after menopause, follicle- stimulating hormone (FSH) levels are normally extremely high. A 56-year-old woman completed menopause 3 years ago. However, she is found to have low levels of FSH in her blood. Which of the following is the best explanation for this finding? A) She has been receiving hormone replacement therapy with estrogen and progesterone since she completed menopause B) Her adrenal glands continue to produce estrogen C) Her ovaries continue to secrete estrogen D) She took birth control pills for 20 years before menopause

48. A) After menopause, the absence of feedback inhibition by estrogen and progesterone results in extremely high rates of FSH secretion. Women taking estrogen as part of hormone replacement therapy for symptoms associated with postmenopausal conditions have sup- pressed levels of FSH owing to the inhibitory effect of estrogen.

49. Which of the following pairs of hormones and the cor- responding action is incorrect? A) Glucagon—increased glycogenolysis in liver B) Glucagon—increased glycogenolysis in skeletal muscle C) Glucagon—increased gluconeogenesis D) Cortisol—increased gluconeogenesis E) Cortisol—decreased glucose uptake in muscle

49. B) Glucagon stimulates glycogenolysis in the liver, but it has no physiological effects in muscle. Both glucagon and cortisol increase gluconeogenesis, and cortisol impairs glucose uptake by muscle.

5. Within minutes following a normal delivery, flow through the foramen ovale decreases dramatically. What is the cause of this change? A) Increased formation of prostaglandin E2 in the endocardium B) Increased rate of flow through the pulmonary artery C) Increased left atrial pressure D) Increased right atrial pressure E) Increased Po2

5. C) Following birth, systemic arterial resistance in- creases dramatically due to loss of the placental vasculature. Consequently, arterial pressure, left ventricular pressure, and left atrial pressure all increase. At the same time pulmonary vascular resistance decreases due to expansion of the lungs, pulmonary artery pressure, right ventricular pressure and right atrial pressure all fall. Blood flow through the foramen is a function of the pressure gradient, which after birth favors flow from the left to the right atrium, but most of the flow is blocked by the septal flap on the septal wall of the left atrium.

50. C) Injection of insulin leads to a decrease in blood glucose concentration. Hypoglycemia stimulates the secretion of growth hormone, glucagon, and epinephrine, all of which have counter regulatory effects to increase glucose levels in the blood.

50.

51. Delayed breathing at birth is a common danger faced by newborn infants. What is a frequent cause of delayed breathing? A) Fetal hypoxia during the birth process B) Maternal hypoxia during the birth process C) Fetal hypercapnia D) Maternal hypercapnia

51. A) Prolonged fetal hypoxia during delivery can cause serious depression of the respiratory center. Hypoxia may occur during delivery because of compression of the umbilical cord, premature separation of the placenta, excessive contraction of the uterus, or excessive anesthesia of the mother.

52. Which of the following hormones is largely unbound to plasma proteins? A) Cortisol B) Thyroxine (T4) C) Antidiuretic hormone D) Estradiol E) Progesterone

52. C) In general, peptide hormones are water soluble and are not highly bound by plasma proteins. Antiduretic hormone, a neurohypophysial peptide hormone, is virtually unbound by plasma proteins. In contrast, steroid and thyroid hormones are highly bound to plasma proteins.

53. A 3-week old infant is brought to the emergency room in a comatose condition. The history reveals that her parents have been feeding her concentrated, undiluted formula for 5 days. (Infant formula preparations are often sold in concentrated forms that must be properly diluted with water before feeding.) The infant's plasma osmolality is 352 mOsm/L (normal is 280 to 300 mOsm/L), and the osmolality of the urine is 497 mOsm/L. What is the ex- planation for the hyperosmotic condition of the plasma?

53. C) Functional development of the kidneys is not complete until about the end of the 1st month of life. The kidneys of a neonate can concentrate urine to only about 1.5 times the osmolality of plasma (in contrast to three to four times plasma osmolality in an adult). If the undiluted formula had a very high osmotic concentration, the neonate would be unable to excrete the solute in sufficiently concentrated urine to prevent the development of hyperosmolality of the plasma.

54. Why is milk produced only after delivery, not before? A) Levels of luteinizing hormone and follicle-stimulating hormone are too low during pregnancy to support milk production B) High levels of progesterone and estrogen during pregnancy suppress milk production C) The alveolar cells of the breast do not reach maturity until after delivery D) High levels of oxytocin are required for milk production to begin, and oxytocin is not secreted until the baby stimulates the nipple

54. B) Although estrogen and progesterone are essential for the physical development of the breast during pregnancy, a specific effect of both these hormones is to inhibit the actual secretion of milk. Even though prolactin levels are increased 10- to 20-fold at the end of pregnancy, the suppressive effects of estrogen and progesterone prevent milk production until after the baby is born. Immediately after birth, the sudden loss of both estrogen and progesterone secretion from the placenta allows the lactogenic effect of prolactin to promote milk production.

56. Which of the following increases the rate of excretion of calcium ions by the kidney? A) Decrease in calcitonin concentration in the plasma B) Increase in phosphate ion concentration in the plasma C) Decrease in the plasma level of parathyroid hormone D) Metabolic alkalosis

56. C) The concentration of parathyroid hormone strongly regulates the absorption of calcium ion from the renal tubular fluid. A reduction in hormone concentration reduces calcium reabsorption and increases the rate of calcium excretion in the urine. The other choices have little effect on or decrease calcium excretion.

6. C) Type 2 diabetes mellitus is characterized by diminished sensitivity of target tissues to the metabolic effects of insulin; that is, there is insulin resistance. As a result, hepatic uptake of glucose is impaired, and glucose release is enhanced. In muscle, the uptake of glucose is impaired.

6. In the figure, which lines most likely illustrate these relationships in a patient with type 2 diabetes? A) A and C B) A and D C) B and C D) B and D

62. D) After eating a meal, insulin secretion is increased. As a result, there is an increased rate of glucose uptake by both the liver and muscle. Insulin also inhibits hormone-sensitive lipase, which decreases hydrolysis of triglycerides in fat cells.

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64. Very early in embryonic development, testosterone is formed within the male embryo. What is the function of this hormone at this stage of development? A) Stimulation of bone growth B) Stimulation of development of male sex organs C) Stimulation of development of skeletal muscle D) Inhibition of luteinizing hormone secretion

64. B) The primary function of testosterone in the embryonic development of males is to stimulate formation of the male sex organs.

65. Which of the following changes would be expected to occur with increased binding of a hormone to plasma proteins? A) Increase in plasma clearance of the hormone B) Decrease in half-life of the hormone C) Increase in hormone activity D) Increase in degree of negative feedback exerted by the hormone E) Increase in plasma reservoir for rapid replenishment of free hormone

65. E) Protein-bound hormones are biologically inactive and cannot be metabolized. Thus, an increase in protein binding would tend to decrease hormone activity and plasma clearance and increase the half-life of the hormone. Free hormone is also responsible for negative feedback inhibition of hormone secretion. There- fore, a sudden increase in hormone binding to plasma proteins would decrease negative feedback. Protein binding of hormones does, however, provide a reservoir for the rapid replacement of free hormone.

66. C) The reduction in hydrogen ion indicated by the elevation in pH increases the concentration of negatively charged phosphate ion species available for ionic combination with calcium ions. Consequently, free calcium ion concentration is reduced.

66. What is the cause of the decrease in calcium ion concentration? A) The increase in arterial pH resulting from the sodium bicarbonate infusion inhibited parathyroid hormone secretion B) The increase in pH resulted in the stimulation of osteoblasts, which removed calcium from the circulation C) The increase in pH resulted in an elevation in the concentration of HPO42, which shifted the equilibrium between HPO42 and Ca11 toward CaHPO4 D) The increase in arterial pH stimulated the formation of 1,25-dihydroxycholecalciferol, which resulted in an increased rate of absorption of calcium from the gastrointestinal tract

67. A 30-year-old woman is breast-feeding her infant. During suckling, which of the following hormonal responses is expected? A) Increased secretion of antidiuretic hormone (ADH) from the supraoptic nuclei B) Increased secretion of ADH from the paraventricular nuclei C) Increased secretion of oxytocin from the paraventricular nuclei D) Decreased secretion of neurophysin E) Increased plasma levels of both oxytocin and ADH

67. C) During suckling, stimulation of receptors on the nipples increases neural input to both the supraoptic and paraventricular nuclei. Activation of these nuclei leads to the release of oxytocin and neurophysin from secretion granules in the posterior pituitary gland. Suckling does not stimulate the secretion of appreciable amounts of ADH.

68. C) In Conn's syndrome, large amounts of aldosterone are secreted. Because aldosterone causes sodium retention, hypertension is a common finding in patients with this condition. However, the degree of sodium retention is modest, as is the resultant increase in extracellular fluid volume. This occurs because the rise in arterial pressure offsets the sodium-retaining effects of aldosterone, limiting sodium retention and permitting daily sodium balance to be achieved.

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69. Why is it important to feed newborn infants every few hours? A) The hepatic capacity to store and synthesize glycogen and glucose is not adequate to maintain the plasma glucose concentration in a normal range for more than a few hours after feeding B) If adequate fluid is not ingested frequently, the plasma protein concentration will rise to greater than normal levels within a few hours C) The function of the gastrointestinal system is poorly developed and can be improved by keeping food in the stomach at all times D) The hepatic capacity to form plasma proteins is minimal and requires the constant availability of amino acids from food to avoid hypoproteinemic edema

69. A) Because the liver functions imperfectly during the first weeks of life, the glucose concentration in the blood is unstable and falls to very low levels within a few hours after feeding.

7. C) In acromegaly, high plasma levels of growth hormone cause insulin resistance. Consequently, there is increased glucose production by the liver and impaired glucose uptake by peripheral tissues.

7. In the figure, which lines most likely illustrate these relationships in a patient with acromegaly? A) A and C B) A and D C) B and C D) B and D

70. Which of the following would be associated with parallel changes in aldosterone and cortisol secretion? A) Addison's disease B) Cushing's disease C) Cushing's syndrome (adrenal tumor) D) A low sodium diet E) Administration of a converting enzyme inhibitor

70. A) In Addison's disease, there is diminished secretion of both glucocorticoids (cortisol) and mineralocorticoids (aldosterone). In Cushing's disease and Cushing's syndrome, cortisol secretion is elevated but aldosterone secretion is normal. A low sodium diet is associated with a high rate of aldosterone secretion but a secretion rate of cortisol that is normal. By inhibiting the generation of ANG II and thus the stimulatory effects of ANG II on the zona glomerulosa, administration of a converting enzyme inhibitor would decrease aldosterone secretion without altering the rate of cortisol secretion.

71. RU486 causes abortion if it is administered before or soon after implantation. What is the specific effect of RU486? A) It binds to luteinizing hormone receptors, stimulating the secretion of progesterone from the corpus luteum B) It blocks progesterone receptors so that progesterone has no effect within the body C) It blocks the secretion of follicle-stimulating hormone by the pituitary D) It blocks the effects of oxytocin receptors in the uterine muscle

71. B) Progesterone is required to maintain the decidual cells of the endometrium. If progesterone levels fall, as they do during the last days of a nonpregnant menstrual cycle, menstruation will follow within a few days, with loss of pregnancy. Administration of a com- pound that blocks the progesterone receptor during the first few days after conception will terminate the pregnancy.

72. Following ejaculation, arterial blood flow into the corpora cavernosa decreases back to the normal resting level resulting in the flaccid state. What is the best ex- planation for this decrease in blood flow? A) Systemic arterial pressure decreases due to absence of sexual stimulation B) The level of sympathetic stimulation to the arterioles supplying the corpora cavernosa decreases C) Resistance of the arterioles supplying the corpora cavernosa increases D) Formation of nitric oxide in the endothelial cells of the arterioles supplying the corpora cavernosa is stimulated by the increase in parasympathetic nervous system activity E) Resistance of the venules draining the sinuses of the corpora cavernosa increases

72. C) The only true choice is the increase in arteriolar resistance in the vasculature supplying the corpora (C). The others will tend to maintain erection (B, D, E). (A), reduction in arterial pressure, will have a negligible effect.

73. Which of the following decreases the rate of urinary excretion of calcium ions by the kidney? A) Increase in calcitonin concentration in the plasma B) Decrease in phosphate ion concentration in the plasma C) Increase in the plasma level of parathyroid hormone D) Metabolic acidosis E) Increase in calcium ion activity in the plasma

73. C) Parathyroid hormone strongly stimulates calcium ion absorption from the tubular fluid, decreasing calcium excretion. The other choices have either no effect or tend to increase calcium excretion.

74. A 55-year-old man has developed the syndrome of in- appropriate antidiuretic hormone secretion due to carcinoma of the lung. Which of the following physiological responses would be expected? A) Increased plasma osmolality B) Inappropriately low urine osmolality (relative to plasma osmolality) C) Increased thirst D) Decreased secretion of antidiuretic hormone from the pituitary gland

74. D) An inappropriately high rate of antidiuretic hormone (ADH) secretion from the lung promotes excess water reabsorption, which tends to produce concentrated urine and a decrease in plasma osmolality. Low plasma osmolality suppresses both thirst and ADH secretion from the pituitary gland.

75. During pregnancy, the uterine smooth muscle is quiescent. During the 9th month of gestation the uterine muscle becomes progressively more excitable. What factors contribute to the increase in excitability? A) Placental estrogen synthesis rises to high rates B) Progesterone synthesis by the placenta decreases C) Uterine blood flow reaches its highest rate D) Prostaglandin E2 synthesis by the placenta decreases E) Activity of the fetus falls to low levels

75. B) Very high plasma concentration of progesterone maintains the uterine muscle in a quiescent state during pregnancy. In the final month of gestation the concentration of progesterone begins to decline, in- creasing the excitability of the muscle.

76. E) During sodium depletion, the renin-angiotensin system is activated, and the high levels of circulating angiotensin II stimulate the adrenal glands to secrete increased amounts of aldosterone. In contrast, angiotensin II has no effect on cortisol secretion, and sodium depletion is associated with normal plasma levels of cortisol. Consequently, reducing plasma levels of angiotensin II by administering an ACE inhibitor would decrease plasma aldosterone to normal levels but would have no effect on plasma cortisol concentration. Because high plasma levels of aldosterone pro- mote sodium retention, reducing aldosterone levels by administering an ACE inhibitor would tend to produce a natriuresis and a decrease in arterial pressure. In time, the opposing effects of reduced arterial pressure and aldosterone secretion on sodium excretion would offset each other, and sodium balance would eventually be achieved at a lower arterial pressure.

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77. A 20-year-old woman is not having menstrual cycles. Her plasma progesterone concentration is found to be minimal. What is the explanation for the low level of progesterone? A) LH secretion rate is elevated B) LH secretion rate is suppressed C) FSH secretion rate is suppressed D) No corpus luteum is present E) High inhibin concentration in the plasma has sup- pressed progesterone synthesis

77. D) The corpus luteum is the only source of progesterone, and if she is not having menstrual cycles no corpus luteum is present.

78. Before the preovulatory surge in luteinizing hormone, granulosa cells of the follicle secrete which of the following? A) Testosterone B) Progesterone C) Estrogen D) Inhibin

78. C) Follicle-stimulating hormone stimulates the granulosa cells of the follicle to secrete estrogen.

79. E) In response to increased blood levels of glucose, plasma insulin concentration normally increases during the 60-minute period following oral intake of glucose. In type 1 diabetes mellitus, insulin secretion is depressed. In contrast, in type 2 diabetes mellitus, insulin resistance is a common finding and, at least in the early stages of the disease, there is an abnormally high rate of insulin secretion.

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80. D) In Cushing's syndrome, high plasma levels of cortisol impair glucose uptake in peripheral tissues, which tends to increase plasma levels of glucose. As a result, the insulin response to oral intake of glucose is enhanced.

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81. Neonates that are kept in 100% oxygen incubators for several days become blind when they are removed from the incubator, a condition referred to as retrolental fibroplasia. What is the explanation for the loss of sight? A) The high concentration of oxygen stimulates the growth of fibrous tissue into the retina B) Thehighconcentrationofoxygencausesruptureof blood vessels in the retina, resulting in fibrous in- filtration of the vitreous humor C) The high concentration of oxygen retards the growth of blood vessels in the retina, but when the oxygen therapy is stopped, the fall in oxygen concentration stimulates an overgrowth of blood vessels in the retina and vitreous humor, which later become densely fibrous and block the light from the pupil D) The high concentration of oxygen destroys the retinal neurons

81. C) Too much oxygen in the incubator stops the growth of new blood vessels in the retina. Then when oxygen therapy is stopped, an overgrowth of blood vessels occurs, with a great mass of vessels growing all through the vitreous humor. Later the vessels are re- placed by a mass of fibrous tissue, causing permanent blindness.

82. Which of the following hormones activate enzyme- linked receptors? A) ADH B) Insulin C) ACTH D) PTH E) Aldosterone

82. B) In general, protein hormones cause physiological effects by binding to receptors on the cell membrane. However, of the four protein hormones indicated, only insulin activates an enzyme-linked receptor. Aldosterone is a steroid hormone and enters the cytoplasm of the cell before binding to its receptor.

84. Which of the following findings is most likely in a patient who has myxedema? A) Somnolence B) Palpitations C) Increased respiratory rate D) Increased cardiac output E) Weight loss

84. A) Somnolence is a common feature of hypothyroidism. Palpitations, increased respiratory rate, increased cardiac output, and weight loss are all associated with hyperthyroidism.

85. At birth, a large, well-nourished baby is found to have a plasma glucose concentration of 17 mg/dL (normal is 80 to 100 mg/dL) and a plasma insulin concentration twice the normal value. What is the explanation for these findings? A) Neonate suffered from in utero malnutrition B) Mother was malnourished during pregnancy C) Mother is diabetic, with poorly controlled hyperglycemia D) Mother is obese

85. C) An infant born of an untreated diabetic mother will have considerable hypertrophy and hyperfunction of the islets of Langerhans in the pancreas. As a consequence, the infant's blood glucose concentration may fall to lower than 20 mg/dL shortly after birth.

86. Which of the following stimulates the secretion of parathyroid hormone (PTH)? A) Increase in extracellular calcium ion activity above the normal value B) Increase in calcitonin concentration C) Respiratory acidosis D) Increased secretion of PTH-releasing hormone from the hypothalamus E) None of the above

86. E) A to D would not stimulate PTH secretion: (A) (increase in Ca concentration) suppresses PTH secretion; (B) (calcitonin) has little to no effect on PTH secretion; (C) (acidosis) would increase free Ca in the extracellular fluid, thereby inhibiting PTH secretion; and there is no such thing as (D) (PTH-releasing hormone).

87. A 40-year-old woman is placed on a high-potassium diet for several weeks. Which of the following hormonal changes is most likely to occur? A) Increased secretion of dehydroepiandrosterone B) Increased secretion of cortisol C) Increased secretion of aldosterone D) Increased secretion of adrenocorticotropic hormone E) Decreased secretion of corticotropin-releasing hormone

87. C) Potassium is a potent stimulus for aldosterone secretion, as is angiotensin II. Therefore, a patient consuming a high-potassium diet would exhibit high circulating levels of aldosterone.

89. If a woman hears her baby cry, she may experience milk ejection from the nipples even before the baby is placed to the breast. What is the explanation for this? A) The sound of the hungry baby's cry elicits secretion of oxytocin from the posterior pituitary, which reaches the breast and causes contraction of the myoepithelial cells B) The sound of the hungry baby's cry causes a reflex relaxation of the myoepithelial cells, allowing the milk to flow C) The sound of the hungry baby's cry elicits a surge of prolactin from the anterior pituitary, which promptly stimulates milk production from the breast D) The sound of the hungry baby's cry elicits sympathetic nervous system discharge that causes con- traction of the myoepithelial cells

89. A) Neural projections from higher centers of the brain to the hypothalamus can elicit the secretion of oxytocin into the blood from the posterior pituitary gland. Upon reaching the breast, oxytocin stimulates contraction of the myoepithelial cells, forcing milk from the alveoli and ducts to the nipple.

9. One treatment for erectile dysfunction requires the injection of a substance into the corpora cavernosa of the penis. The injection of which of the following causes an erection? A) Norepinephrine B) A substance that inhibits formation of nitric oxide C) Thromboxane A2, which is a vasoconstrictor prostaglandin D) Angiotensin II E) None of the above

9. E) Erection requires dilation of the vascular smooth muscle of the resistance vessels leading to the corpora cavernosa. All of the substance listed are vasoconstrictors and would prevent erection.

90. Which of the following hormones is not stored in its endocrine-producing gland? A) T4 B) PTH C) Aldosterone D) ACTH E) Insulin

90. C) Steroid hormones are not stored to any appreciable extent in their endocrine producing glands. This is true for aldosterone, which is produced in the adrenal cortex. In contrast, there are appreciable stores of thyroid hormones and peptide hormones in their endocrine-producing glands.

91. A young woman comes to the emergency room with a vertebral compression fracture. Radiographs of the spine indicate generalized demineralization. She is vegetarian, does not smoke or drink alcohol, has normal plasma potassium concentration of 5.4 mEq/L, sodium concentration of 136 mEq/L, plasma calcium concentration is 7.0 mg/dL. Her vitamin D3 value is several times greater than normal, although her 1,25-dihydroxycholecalciferol concentration is at the lower limit of detectability. She has been in renal fail- ure for the last 5 years and undergoes hemodialysis three times each week. What is the cause of her low 1,25-dihydroxycholecalciferol level? A) Metabolic acidosis B) Metabolic alkalosis C) She is unable to form 1,25-dihydroxycholecalciferol because of her extensive kidney disease D) She is being dialyzed with a dialysis fluid without calcium E) She is not receiving calcium supplements

91. C) 1,25-dihydroxycholecalciferol is formed only in the renal cortex. Extensive renal disease reduces the amount of cortical tissue, eliminating the source of the active calcium regulating hormone, 1,25-dihydroxycholecalciferol.

92. A neonate develops a jaundice condition with a bilirubin concentration of 10 mg/dL on day 2 (normal is 3 mg/dL at 2 days old). The neonatologist can be confident that the condition is not erythroblastosis fetalis if which of the following is true? A) Bilirubin concentration rises no further B) Hematocrit falls only slightly C) Mother, father, and neonate are all Rh-negative D) Mother has no history of hepatic dysfunction

92. C) In order for erythroblastosis fetalis to occur, the baby must inherit Rh-positive red blood cells from the father. If the mother is Rh-negative, she then becomes immunized against the Rh-positive antigen in the red blood cells of the fetus, and her antibodies destroy fetal red blood cells, releasing large quantities of bilirubin into the fetus's plasma.

93. Which of the following findings would likely be re- ported in a patient with a deficiency in iodine intake? A) Weight loss B) Nervousness C) Increased sweating D) Increased synthesis of thyroglobulin E) Tachycardia

93. D) Because iodine is needed to synthesize thyroid hormones, the production of thyroid hormones is impaired if iodine is deficient. As a result of feedback, plasma levels of thyroid-stimulating hormone increase and stimulate the follicular cells to increase the synthesis of thyroglobulin. This results in a goiter. Increased metabolic rate, sweating, nervousness, and tachycardia are all common features of hyperthyroidism, not hypothyroidism due to iodine deficiency.

94. Before intercourse, a woman irrigates her vagina with a solution that lowers the pH of the vaginal fluid to 4.5. What will be the effect on sperm cells in the vagina? A) Metabolic rate will increase B) Rate of movement will decrease C) Formation of prostaglandin E2 will increase D) Rate of oxygen consumption will increase

94. B) Sperm cell motility decreases as pH is reduced below 6.8. At a pH of 4.5, sperm cell motility is significantly reduced. However, the buffering effect of sodium bicarbonate in the prostatic fluid raises the pH somewhat, allowing the sperm cells to regain some mobility.

95. B) A protein meal stimulates all three of the hormones indicated.

95

96. Men who take large doses of testosterone-like androgenic steroids for long periods are sterile in the reproductive sense of the word. What is the explanation for this finding? A) High levels of androgens bind to testosterone receptors in the Sertoli cells, resulting in overstimulation of inhibin formation B) Overstimulation of sperm cell production results in the formation of defective sperm cells C) High levels of androgen compounds inhibit the secretion of gonadotropin-releasing hormone by the hypothalamus, resulting in the inhibition of luteinizing hormone and follicle-stimulating hormone release by the anterior pituitary D) High levels of androgen compounds produce hypertrophic dysfunction of the prostate gland

96. C) Testosterone secreted by the testes in response to luteinizing hormone (LH) inhibits hypothalamic secretion of gonadotropin-releasing hormone (GnRH), thereby inhibiting anterior pituitary secretion of LH and follicle-stimulating hormone. Taking large doses of testosterone-like steroids also suppresses the secretion of GnRH and the pituitary gonadotropic hormones, resulting in sterility.

97. A 30-year-old woman is administered cortisone for the treatment of an autoimmune disease. Which of the following is most likely to occur? A) Increased adrenocorticotropic hormone secretion B) Increased cortisol secretion C) Increased insulin secretion D) Increased muscle mass E) Hypoglycemia between meals

97. C) Steroids with potent glucocorticoid activity tend to increase plasma glucose concentration. As a result, insulin secretion is stimulated. Increased glucocorticoid activity also diminishes muscle protein. Because of feedback, cortisone administration leads to a de- crease in adrenocorticotropic hormone secretion and, therefore, a decrease in plasma cortisol concentration.

98. The function of which of the following is increased by an elevated parathyroid hormone concentration? A) Osteoclasts B) Hepatic formation of 25-hydroxycholecalciferol C) Phosphate reabsorptive pathways in the renal tu- bules D) All of the above

98. A) An increase in the concentration of parathyroid hormone results in the stimulation of existing osteoclasts and, over longer periods, increases the number of osteoclasts present in the bone.

99. Which of the following statements about peptide or protein hormones is usually true? A) They have longer half-lives than steroid hormones B) They have receptors on the cell membrane C) They have a slower onset of action than both steroid and thyroid hormones D) They are not stored in endocrine-producing glands

99. B) In general, peptide hormones produce biological effects by binding to receptors on the cell membrane. Peptide hormones are stored in secretion granules in their endocrine-producing cells and have relatively short half-lives because they are not highly bound to plasma proteins. Protein hormones often have a rapid onset of action because, unlike steroid and thyroid hormones, protein synthesis is usually not a prerequisite to produce biological effects.

46. In controlling aldosterone secretion, angiotensin II acts on which of the following structures? A) Zona glomerulosa B) Zona fasciculata C) Zona reticularis D) Adrenal medulla

A) The cells of the zona glomerulosa secrete most of the aldosterone. These cells have receptors for angiotensin II, which is a major controller of aldosterone secretion.

31. In order for male differentiation to occur during embryonic development, testosterone must be secreted from the testes. What stimulates the secretion of testosterone during embryonic development? A) Luteinizing hormone from the maternal pituitary gland B) Human chorionic gonadotropin C) Inhibin from the corpus luteum D) Gonadotropin-releasing hormone from the embryo's hypothalamus

B) Human chorionic gonadotropin also binds to luteinizing hormone receptors on the interstitial cells of the testes of the male fetus, resulting in the production of testosterone in male fetuses up to the time of birth. This small secretion of testosterone is what causes the fetus to develop male sex organs instead of female sex organs.

17. During the 12-hr period preceding ovulation, which of the following is true? A) The plasma concentration of estrogen is rising B) A surge of luteinizing hormone is secreted from the pituitary C) The surge occurs immediately after the formation of the corpus luteum D) The surge is followed immediately by a fall in the plasma concentration of progesterone E) The number of developing follicles is increasing

B) Ovulation will not take place unless a surge of LH precedes it. Immediately prior to ovulation the number of follicles is decreasing due to normal attrition of all but one follicle, and consequently estrogen synthesis by the ovary is decreasing. Progesterone synthesis is stimulated by the LH surge.

61. In a normal young man, what is the maximum pressure that can be achieved within the corpora cavernosa during a sexual experience? A) 20to40mmHg B) 60to80mmHg C) 150 to 250 mm Hg D) 400 to 600 mm Hg

C) Arterial resistance leading into the corpora cavernosa is greatly reduced during erection, while venous resistance leading from the sinuses is extremely high due to compression of the veins against the fibrous tis- sue surrounding the sinuses. Therefore, pressure in the sinuses during erection is at least equal to systolic arterial pressure. However, contraction of the skeletal muscles in the floor of the perineum that overlies portions of the corpora cavernosa can compress the sinuses, increasing the pressure to levels that are substantially higher than systolic pressure.

Which of the following statements about antidiuretic hormone is true? A) It is synthesized in the posterior pituitary gland B) It increases salt and water reabsorption in the col- collecting tubules and ducts C) It stimulates thirst D) It has opposite effects on urine and plasma osmolality.

D) Antidiuretic hormone (ADH) increases the permeability of the collecting tubules and ducts to water, but not to sodium, which in turn increases water reabsorption and decreases water excretion. As a result, urine concentration increases, and the retained water dilutes the plasma. ADH is synthesized in the supraoptic and paraventricular nuclei of the hypothalamus and has no direct effect on the thirst center.

37. A female athlete who took testosterone-like steroids for several months stopped having normal menstrual cycles. What is the best explanation for this observation? A) Testosterone stimulates inhibin production from the corpus luteum B) Testosterone binds to receptors in the endometrium, resulting in the endometrium's failure to develop during the normal cycle C) Testosterone binds to receptors in the anterior pituitary that stimulate the secretion of follicle- stimulating hormone (FSH) and luteinizing hormone (LH) D) Testosterone inhibits the hypothalamic secretion of gonadotropin-releasing hormone and the pituitary secretion of LH and FSH

D) The cells of the anterior pituitary that secrete LH and FSH, and the cells of the hypothalamus that secrete gonadotropin-releasing hormone, are inhibited by both estrogen and testosterone. The steroids taken by the woman caused sufficient inhibition to result in cessation of the monthly menstrual cycle.

60. If a woman has a tumor secreting large amounts of estrogen from the adrenal gland, which of the follow- ing will occur? A) Progesterone levels in the blood will be very low B) Her luteinizing hormone secretion rate will be to- tally suppressed C) She will not have normal menstrual cycles D) Her bones will be normally calcified E) All of the above

E) Choices A to D are true: LH secretion will be sup- pressed (B) by the negative feedback effect of the estrogen from the tumor; consequently, she will not have menstrual cycles (C); since she will not have normal cycles, no corpus luteae will develop so no progesterone will be formed (A). The high levels of estrogen produced by the tumor will provide stimulation of osteoblastic activity to maintain normal bone activity (D).

45. A man is taking a number of medications, one of which appears to be interfering with the emission phase of the sexual act. Which of the following medications could cause this problem? A) A medication that prolongs the duration of action of nitric oxide B) A medication that blocks the smooth muscle receptors for nitric oxide C) A medication that increases the release of nitric oxide D) A testosterone-like androgen compound E) An inhibitor of beta-adrenergic nervous system receptors

E) Emission is elicited by reflexes mediated by the beta-adrenergic nervous system. Beta adrenergic antagonists interfere with the reflex. None of the other choices is involved.