Chemistry - Endocrinology
What effect would a low-salt diet, upright position and diuretics have on the following test results? A. Renin increased, aldosterone increased, hypernatremia, hypokalemia B. Renin increased, aldosterone decreased, hypernatremia, hypokalemia C. Renin decreased, aldosterone decreased, hyponatremia, hyperkalemia D. Renin decreased, aldosterone increased, hyponatremia, hyperkalemia
A. A low-salt diet, upright position and diuretics cause a decrease in effective plasma volume. This decrease stimulates the renin-angiotensin system, which increases aldosterone secretion. Aldosterone promotes sodium retention and potassium loss.
How is the majority of reverse T3 (rT3) made? A. Peripheral deiodination of T4 B. Peripheral deiodination of T3 C. From T3 in the thyroid gland D. From thyroglobulin in th thyroid gland
A. A small amount of reverse T3 (rT3) is made in the thyroid gland, but the majority is made from peripheral deiodination of T4. rT3 varies from T3 in that rT3 contains one iodine atom in the tyrosyl ring and two iodines in the phenolic ring, whereas T3 has two iodines in the tyrosyl ring and one iodine in the phenolic ring. rT3 does not have any physiological action as it is metabolically inactive. However, increased levels of rT3 are associated with nonthyroidal illness (NTI), which also manifests with decreased levels of total T3.
Which of the following hormones initiates its response by binding to cytoplasmic receptors? A. Estradiol B. Epinephrine C. Growth hormone D. Follicle-stimulating hormone
A. At the cellular level, the site of action of the peptide and catecholamine hormones is different from that of the steroid and thyroid hormones. The peptide and catecholamine hormones bring about their effects by combining with receptors on or in the cell membranes of the target cells. In some cases, this binding to the membrane results in activation of adenylate cyclase, which sets in motion the so-called second-messenger mechanism of hormone action. On the other hand, steroid and thyroid hormones act predominantly by diffusing through the target cell membranes and combining with cytoplasmic or nucleic receptors to form a complex that then brings about the hormone's action.
Which of the follwoing would be elevated in the blood in medullary carcinoma of the thyroid? A. Calcitonin B. Thyroxine C. Catecholamines D. Secretin
A. Calcitonin is a calcium-lowering hormone secreted by the parafollicular or C cells of the thyroid. Calcitonin acts as an antagonist to parathyroid hormone (PTH) action on the bone and kidneys. Medullary carcinoma of the thyroid is a neoplasm of the parafollicular cells that usually results in elevated serum levels of calcitonin. If the fasting calcitonin level is within the normal reference interval in a patient with suspected medullary carcinoma, a provacative calcium infusion test is often useful in improving the sensitivity of the test.
Because of infertility problems, a physician would like to determine when a woman ovulates. The physician orders serial assays of plasma progesterone. From these assays, how can the physician recognize when ovulation occurs? A. After ovulation, progesterone rapidly increases B. After ovulation, progesterone rapidly decreases C. Right before ovulation, progesterone rapidly increases D. There is a gradual, steady increase in progesterone throughout the menstrual cycle
A. Progesterone production can be monitored by measuring plasma progesterone or urinary pregnanediol, the major metabolite of progesterone. In the follicular stage of the menstrual cycle, only a small amount of progesterone is secreted. In the luteal stage, or the time from ovulation to menstruation, progesterone levels rapidly increase. Hence, serial assays of plasma progesterone or urinary pregnanediol can be used to identify the time of ovulation. If pregnancy does not occur, progesterone quickly decreases approximately 24 hours before menstruation. If there is no ovulation, then there is no corpus luteum formation and no cyclic rise in progesterone levels.
Which of the following is the major mineralocorticoid? A. Aldosterone B. Cortisol C. Corticosterone D. Testosterone
A. The corticosteroids, produced by the adrenal cortex, may be classified as glucocorticoids or mineralocorticoids. Cortisol is the primary glucocorticoid, and aldosterone is the primary mineralocorticoid. Aldosterone functions as a regulator of salt and water metabolism. Aldosterone promotes water retention and sodium resorption with potassium loss in the distal convoluted tubules of the kidney.
In a patient who is suspected of having pheochromocytoma, measurement of which of the following would be most useful? A. Metanephrine B. Homovanillic acid C. 5-Hydroxyindoleacetic acid D. Homogentisic acid
A. The majority of pheochromocytomas (rare tumors) occur in the adrenal medulla, causing increased secretion of the catecholamines. As a screening test for this disorder, quantification of urinary metanephrine, the methylated product of epinephrine, is suggested because false negatives seldom occur. Follow-up testing should include measurement of urinary vanillylmandelic acid (VMA), because VMA is the primary metabolite of epinephrine and norepinehrine.
What is the predominant form of thyroid hormone in the circulation? A. Thyroxine B. Trioodothyronine C. Diiodotyrosine D. Monoiodotyrosine
A. Thyroglobulin is a glycoprotein in which the thyroid hormones are stored in the thyroid gland. When tyrosine residues of the thyroglobulin are iodinated, monoiodotyrosine (MIT) and diiodotyrosine (DIT) are formed. These iodotyrosine residues are not hormones. Triiodothyronine (T3) and thyroxine (T4) are the hormones produced by the thyroid, being formed by the coupling of either MIT or DIT residues. T4 is the predominant form of the thyroid hormones secreted into the circulation, having a concentration in the plasma significantly greater than T3. However, in terms of physiological activity, T3 must be considered because it is four to five times more potent than T4. Thus the overall contribution of T3 to the total physiological effect of the thyroid hormones on the body is very significant.
An elevated level of which of the following hormones will inhibit pituitary secretion of adrenocorticotropic hormone (ACTH)? A. Aldosterone B. Cortisol C. 17 Beta-Estradiol D. Progesterone
B. Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex to secrete cortisol and, to a certain extent, aldosterone. Howeer, aldosterone is also regulated by sodium and potassium levels and, more importantly, by the renin-angiotensin system. Cortisol alone has an inhibitory effect or a negative feedback relationship to ACTH secretion by the pituitary. A low level of cortisol stimulates the hypothalamus to secrete corticotropin-releasing hormone (CRH), which in turn stimulates release of ACTH from the pituitary gland and causes the adrenal cortex to secrete more cortisol. Elevated levels of cortisol reverse this process. ACTH secretion is not inhibited by estrogen or progesterone levels.
What is the major carrier protein of the thyroid hormones in the blood? A. Albumin B. Thyroxine-binding globulin C. Thyroxine-binding prealbumin D. Thyroglobulin
B. Almost all the triiodothyronine (T3) and thyroxine (T4) hormones are reversibly bound to the serum proteins, thyroxine-bbinding globulin (TBG), thyroxine-binding prealbumin (TBPA), and albumin. Most T3 is bound to TBG, whereas 70% of T4 is bound to TBG, 20% to TBPA, and 10% to albumin. T3 has a lower affinity for TBG and TBPA than T4. Thyroglobulin is manufactured and stored int he thyroid follicle and is not released into the circulation.
The presence of a very high titer for antithyroglobulin antibodies and the detection of antithyroid peroxidase antibodies is highly suggestive of what disorder? A. Pernicious anemia B. Hashimoto thyroiditis C. Multinodular goiter D. Thyroid adenoma
B. Antiboides to thyroglobulin (TgAb) and thyroid cell peroxidase (TPOAb) are produced in several thyroid diseases.Very high antibody titers for antithyroglobulin antibodies and the detection of antithyroid peroxidase antibodies are highly suggestive of Hashimoto thyroiditis (a type of hypothyroidism). These antibodies are aldo frequently detected in primary myxedema and Graves disease by means of hemagglutination methods. It should be noted that antithyroid antibodies do occur in othet thyroid diseases, but their prevalence is less. These antibodies have also been detected in 5-10% of the normal population.
Diabetes insipidus is associated with depressed secretion of which of the following hormones? A. Prolactin B. Antidiuretic hormone C. Growth hormone D. Oxytocin
B. Antidiuretic hormone (ADH), also known as vasopressin, is a peptide hormone secreted by the posterior pituitary gland under the influence of three major stimuli: decreased serum osmolality, increased blood volume, or psychogenic factors. ADH increases the renal reabsorption of water by increasing the permeability of the collecting ducts, with the result that body water is retained and urine osmolality increases. Diabetes insipidus is the syndrome that results from decreased secretion of ADH from any cause. Serum levels of ADH can be measured, but usually the measurement of serum and urine osmolality is sufficient to indicate the severity of the disease.
Which of the following is not associated with growth hormone? A. Somatotropin B. Secreted by posterior pituitary C. Hypersecretion results in acromegaly D. Affects lipid, carbohydrate, and protein metabolism
B. Growth hormone (somatotropin) is a polypeptide secreted by the anterior pituitary. It is essential to the growth process of cartilage, bone and a variety of soft tissues. It also plays an important role in lipid, carbohydrate and protein metabolism of adults. During the growth phase of humans, hyposecretion of somatotropin results in dwarfism, whereas hypersecretion, conversely, causes pituitary gigantism. After the growth phase, hypersecretion of somatotropin causes acromegaly. Diagnosis of hypersecretion or hyposecretion of growth hormone usually requires the use of suppression or provacative tests of growth hormone release. Growth hormone levels may be quantified using immunoassay methods, including chemiluminescence immunoassay.
Which of the follwoing is the Hollander insulin test used to confirm? A. Hyperglycemia B. Vagotomy C. Pancreatectomy D. Insulinoma
B. In cases of peptic ulcer, treatment may include surgery that severs the vagus nerve. This severing is known as vagotomy, which, if complete, prevents the secretion of gastrin and HCl by the stomach. The Hollander insulin test is performed to assess the completeness of the vagotomy. If the vagotomy is complete, the hypoglycemia caused by the administration of insulin will not exert its normal stimulatory effect on gastric HCl and pepsinogen secretion.
When performing parathyroid surgery for adenoma resection, parathyroid hormone is quantified at three points relative to the surgical procedure: baseline prior to incision, second baseline with gland exposure and third sample at post-excision. Which of the following is not correct in assessing the PTH values? A. The second baseline value should be higher than the first baseline B. The first baseline value should be the highest value of the three samples C. The post-excision value should be at least 50% of or lower than the second baseline D. The lack of decrease in the PTH value post-excision indicates possible multigland disease.
B. Measurement of PTH during surgery for adenoma resection of the parathyroid glands assists the surgeon in determining completeness of the resection based on the rapid fall of PTH. At least three samples are needed: first, a pre-incision baseline sample as surgery starts; a second baseline sample following exposure of the gland because PTH will increase with any manipulation of the tissue; and a post-excision sample drawn 10 minutes following gland removal (some surgical protocols may require multiple sampling at 5 minutes, 10 minutes, and 20 minutes post-excision). In general, at 10 minutes post-excision, the PTH level should fall to 50% or less of the pre-incision value at the time of gland resection. If the PTH value remains increased and such a decrease does not occur or if the PTH rises again after what initially appeared to be a decrease, multigland disease or ectopic production need to be investigated.
Plasma renin activity (PRA) measurements are usually made by measuring which of the follwoing using immunoassay? A. Angiotensinogen B. Angiotensin I C. Angiotensin II D. Angiotensin-converting enzyme
B. Renin is a proteolytic enzyme secreted by the juxtaglomerular cells of the kidneys. In the blood, renin acts on renin substrate (angiotensinogen) to produce angiotenin I. An angiotensin-converting enzyme secreted by endothelial cells than converts angiotensin I to angiotensin II. It is the latter that is responsible for the vasoconstrictive action of renin release. Angiotensin III is a product of aminopeptidase on angiotensin II, and the action of angiotensin II and III is directed at modulating aldosterone secretion. Plasma renin activity determined by immunoassay, is assessed by quantifying the amount of angiotensin I produced by the action of renin on angiotensinogen using an initial kinetic assay. In addition, renin can be measured directly by an immunometric-mass assay that utilizes a monoclonal antibody.
Which of the following is the most common cause of the adrenogenital syndrome called congenital adrenal hyperplasia, and which test is used for its diagnosis? A. 17 alpha-Hydroxylase deficiency; progesterone assay B. 21-Hydroxyprogesterone deficiency; 17 alpha-hydroxyprogesterone assay C. 3 Beta-Hydroxysteroid dehydrogenaseisomerase deficiency; 17 alpha-hydroxypregnenolone assay D. 11 Beta-Hydroxylase deficiency; 11-deoxycortisol assay
B. The adrenogenital syndrome, congenital adrenal hyperplasia, is due to a deficiency in specific enzymes needed for the synthesis of cortisol and aldosterone. Because cortisol production is blocked, the pituitary increases its secretion of adrenocorticotropic hormone (ACTH), causing adrenal hyperplasia and hypersecretion of cortisol precursors. There are eight recognized types of inherited enzyme defects in cortisol biosynthesis. The most common type of defect is the lack of 21-hydroxylase, occurring in 95% of the cases. Conversion of 17 alpha-hydroxyprogesterone to 11-deoxycortisol is impaired, causing accumulation of 17 alpha-hydroxyprogesterone, which is metabolized to pregnanetriol. An increased plasma 17 alpha-hydroxyprogesterone level is diagnostic and can be determined by radioimmunoassay. Determinations of serum testosterone and urinary pregnanetriol eleations are also diagnostic of this disorder. Virilization takes place in this syndrome because cortisol precursors are shunted to produce weak androgens [e.g. dehydroepiandrosterone (DHEA) and androstenedione]. These androgens are converted peripherally to testosterone in large-enough amounts to create this condition. The second most common defect is 11 Beta-hydroxylase deficiency. 3 Beta-Hydroxysteroid dehydrogenase-isomerase deficiency and C-17,20-lyase/17 alpha-hydroxylase deficiency are examples of other enzyme defects seen in this disorder. A testicular or adrenal tumor may cause symptoms similar to this syndrome; however, these tumors would be acquired in contrast to congenital disorders.
As a screening test for Cushing syndrome, the physician wishes to see whether a patient exhibits normal diurnal rhythm in his or her cortisol secretion. At what time should the specimens be drawn for plasma cortisol determination? A. 6 AM, 2PM B. 8 AM, 4PM C. 12 noon, 6 PM D. 12 noon, 12 midnight
B. The hypothalamus, which secretes CRH, is sensitive not only to cortisol levels and stress but also to sleep-wake patterns. Thus plasma ACTH and cortisol levels exhibit diurnal variation or circadian rhythm. Cortisol secretion peaks at the time of awakening between 6 AM and 8 AM and then declines to the lowest level between early evening and midnight. After midnight the level again begins to increase. Specimens should be taken at 8 AM and 8PM. The evening cortisol level should be at least 50% lower than the morning result. In 90% of patients with Cushing syndrome there is no diurnal variation. However, absence of the normal drop in the evening cortisol level is not specific for Cushing syndrome. Other conditions, such as ectopic ACTH syndrome, blindness, hypothalamic tumors, obesity, acute alcoholism and various drugs, alter normal circadian rhythm in cortisol secretion. To confirm Cushing syndrome, a dexamethasone suppression test may be performed.
Which of the following tissues does not secrete steroid hormones? A. Ovaries B. Pituitary gland C. Testes D. Adrenal cortex
B. The pituitary gland produces protein hormones such as adrenocorticotropic hormone, thyroid-stimulating hormone, follicle-stimulating hormone, growth hormone and prolactin. Steroid hormones include C21 corticosteroids and progesterone, C19 androgens and C18 estrogens. The mineralo- and gluco-corticosteroids are secreted only by the adrenal glands, but the other steroids listed are secreted by the ovaries, testes, adrenal glands and placenta to a varying extent, depending on the individual's sex.
Once synthesized, the thyroid hormones are stored as a component of thyroglobulin in what area of the thyroid gland? A. Epithelial cell wall of the follicle B. Colloid in the follicle C. Isthmus of the thyroid gland D. Extracellular space of the thyroid gland
B. The thyroid gland is composed of two lobes connected by a structure called the isthmus. The lobes consist of many follicles. The follicle, in the shape of a sphere, is lined with a single layer of epithelial cells. The epithelial cells produce T3 and T4, which are stored as a component of the thyroglobulin. Within the lumen of the follicle is colloid. Thyroglobulin, secreted by the epithelial cells, makes up 90% of the colloid. As the epithelial cells synthesize the thyroid hormones, the hormones are stored in the thyroglobulin molecule. Thyroglobulin is then secreted into the colloid of the follicular lumen. When the thyroid hormones are needed, they are absorbed by the epithelial cells from their storage site, and through proteolysis, the hormones are relased from fragments of the thyroglobulin molecule. T3 and T4 are then secreted by the cells into the blood.
Thyroid-releasing hormone (TRH) is given to a patient. Serum thyroid-stimulating hormone (TSH) levels are taken before and after the injection, and the values are the same - low. This patient probably has which of the following disorders? A. Primary hypothyroidism B. Secondary hypothyroidism C. Tertiary hypothyroidism D. Iodine deficiency
B. To distinguish between a hypothalamic disorder and a disorder of the pituitary gland, thyroid-releasing hormone (TRH) is administered. In the case of a hypothalamic disorder (tertiary hypothyroidism), the TRH administered will cause an increased excretion of pituitary hormone, TSH. However, if the disorder originates in the pituitary gland (secondary hypothyroidism), the administration of TRH will have no effect on the pituitary gland and thus no increased excretion of TSH. Because the values of TSH were low before and remained low after administration of TRH, the disorder is secondary hypothyroidism. Primary hypothyroidism is caused by failure of the thyroid gland itself and is not evaluated by use of the TRH stimulation test. Iodine deficiency would cause high levels of TSH, and administration of TRH is not used to evaluate this disorder.
Which of the following is the most potent estrogen and is considered to be the true ovarian hormone? A. Estriol (E3) B. Estrone (E1) C. 17 Beta-Estradiol (E2) D. 16 Alpha-Hydroxyestrone
C. 17 Beta-Estradiol (E2) is the most potent estrogen. 17 Beta-Estradiol is considered to be the true ovarian hormone because it is secreted almost entirely by the ovaries. In contrast, estrone (E1) is produced from circulating C19 neutral steroids (e.g. androstenedione) and is also synthesized from 17 Beta-estradiol. Estriol (E3) is derived almost exclusively from 17 Beta-estradiol and has little clinical significance except in pregnancy. The measurement of 17 Beta-estradiol is used to evaluate ovarian function.
Which of the following is an autoantibody that binds to TSH receptor sites on thyroid cell membranes, preventing thyroid-stimulating hormone from binding? A. Antithyroglobulin antibodies B. Thyroid antimicrosomal antibodies C. Thyrotropin-receptor antibodies D. Antithyroid peroxidase antibodies
C. Currently, the suggested term for autoantibodies that bind to TSH receptor sites is thyrotropin-receptor antibodies (TRAb). The thyrotropin-receptor antibodies (TRAb) are thyroid-stimulating immunoglobulins (TSI) that are IgG autoantibodies and are able to bind to the thyroid-stimulating hormone (TSH) receptor sites on thyroid cell membranes, thus preventing TSH from binding. These autoantibodies interact with the receptors similarly to TSH, thus stimulating the thyroid to secrete thyroid hormones. Because these autoantibodies do not respond to the negative feedback system as does TSH, hyperthyroidism is the end result. The majority of patients with Graves hyperthyroid disease exhibit high titers of TRAb.
Why are the total thyroxine (T4) levels increased in pregnant women and women who take oral contraceptives? A. Inappropriate iodine metabolism B. Changes in tissue use C. Changes in concentration of thyroxine-binding globulin (TBG) D. Changes in thyroglobulin synthesis
C. Due to increased protein synthesis, the binding capcity of thyroxine-binding globulin (TBG) is increased in situations such as pregnancy and administration of oral contraceptives. The increased total thyroxine (total T4) levels in these situations do not reflect the functional state of the thyroid gland. It is important when interpreting total T4 levels to take into consideration situations such as these. Free T4 is not affected by variations in thyroxine-binding proteins and better reflects the metabolic state that is euthyroid. However, use of the thyroid hormone binding ratio (THBR), which measures the unoccupied binding sites of TBG, in conjunction with the free and total T4 levels permits a better interpretation of thyroid function. By this process it can be seen where the primary change occurs, whether in the level of or in TBG-binding capcity.
When do the highest levels of gonadotropins occur? A. During the follicular phase of the menstrual cycle B. During the luteal phase of the menstrual cycle C. At the midpoint of the menstrual cycle D. Several days prior to ovulation
C. During the menstrual cycle, follicle-stimulating hormone (FSH) levels decrease in the later part of the follicular stage. Luteinizing hormone (LH) gradually increases during the follicular stage. At midcycle, both FSH and LH levels spike. Following this spike, in the luteal stage or second half of the menstrual cycle, FSH and LH levels gradually decrease. In post-menopausal women the ovaries stop secreting estrogens. In response the gonadotropins, FSH and LH, rise to their highest levels. The reason is the feedback system between estrogen secretion by the gonads and the secretion of releasing factors by the hypothalamus; a decreased estrogen level causes increased secretion of FSH-releasing factor and LH-releasing factor.
What would be an example of ectopic hormone production? A. Prolactin production by pituitary tumors B. Calcitonin production by thyroid tumors C. Growth hormone production by lung tumors D. Cortisol production by adrenal tumors
C. Ectopic hormones are hormonal substances produced by benign and malignant tumors derived from tissues that do not normally secrete those hormones. Examples of ectopic hormone production would be ACTH production by oat cell carcinoma of the lung and growth hormone production by bronchogenic carcinomas of the lung. Cortisol and growth hormone are normally secreted by the adrenal gland and anterior pituitary gland, respectively. Ectopic hormones are not in all cases chemically identical to the native hormone but may be similar enough to cross-react in immunoassay methods for the native hormone.
Zollinger-Ellison syndrome is characterized by an elevated blood level of which of the following? A. Trypsin B. Pepsin C. Gastrin D. Cholecystokinin-pancreozymin
C. Gastrin is the designation given to a family of protein hormones produced by the mucosal cells of the gastic antrum. Once secreted, gastrin is carried in the blood to the fundic cells, causing release of hydrochloric acid. Serum gastrin levels are markedly elevated in the Zollinger-Ellison syndrome, a neoplastic proliferation of the non-beta cells of the pancreatic islets. Gastrin levels may also be elevated in pernicious anemia, duodenal ulcer disease, and gastric ulcer disease.
In a patient with suspected primary hyperthyroidism associated with Graves disease, one would expect the following laboratory serum results: free thyroxine (FT4) ____, thyroid hormone binding ratio (THBR)____, and thyroid-stimulating hormone (TSH)____. A. Increased, decreased, increased B. Increased, decreased, decreased C. Increased, increased, decreased D. Decreased, decreased, increased
C. Graves disease is a name given to a diffusely hyperactive thyroid that produces thyrotoxicosis. Thyrotoxicosis results from elevated levels of thyroid hormone; therefore, laboratory results for free thyroxine (FT4) and free triiodothyronine (FT3) would be increased, thyroid hormone binding ratio (THBR) increased, and thyroid-stimulating hormone (TSH) decreased. In hyperthyroidism, the THBR is increased because thyroxine-binding globulin (TBG) is saturated with endogenous T4. TSH levels are decreased because of the negative-feedback control of the thyroid hormones on the anterior pituitary.
In a patient suspected of having primary myxedema, one would expect the following serum results: free thyroxine (FT4) _____, thyroid hormone binding ratio (THBR) ____, and thyroid-stimulating hormone (TSH) ____. A. Decreased, increased, decreased B. Increased, increased, decreased C. Decreased, decreased, increased D. Increased, decreased, increased
C. Hypothyroidism is a systemic disorder in which the thyroid gland does not secrete sufficient thyroid hormone. Myxedema is commonly used synonymously for hypothyroidism. Hypothyroidism can result from various diseases. If the disease affects the thyroid itself, it is referred to as primary hypothyroidism. If there is TSH deficiency of the pituitary gland, it is termed secondary hypothyroidism. Tertiary hypothyroidism is caused by hypothalamic failure that results in a decreased secretion of thyrotropin-releasing hormone. Thyroid failure in the newborn is termed cretinism. The free T4 level and the thyroid hormone binding ratio (THBR) are decreased because of inadequate secretion of hormones. Since the thyroid hormones are low in concentration, the feedback mechanism to the anterior pituitary gland is triggered to increase production of TSH.
Durine pregnancy in the second trimester, human chorionic gonadotropin (hCG) levels_____ and progesterone and estriol levels _____. A. Increase, increase B. Increase, decrease C. Decrease, increase D. Decrease, decrease
C. In pregnant women the level of human chorionic gonadotropin (hCG) is highest during the first trimester, then it stabilizes to a lower level during the rest of the pregnancy. In the first trimester, the level of pregnanediol is slightly higher than that found in nonpregnant women during the luteal phase of the menstrual cycle. As pregnancy progresses, the placenta secretes more progesterone, which peaks midway into the third trimester and then levels off. It should be noted that pregnanediol is a biologically inactive metabolite of progesterone hat is sometimes measured in urine. After the second month of pregnancy, estriol levels steadily increase as the placenta takes over estrogen production.
What does the concentration of urinary free cortisol mainly reflect? A. Total serum cortisol B. Conjugated cortisol C. Unbound serum cortisol D. Protein-bound serum cortisol
C. Only very small quantities, normally less than 2%, of the total adrenal secretion of cortisol appear in the urine as free cortisol. The majority of cortisol is either metabolized in various tissues or conjugated in the liver and excreted. It is only the serum unconjugated cortisol not bound to cortiocotropin binding globulin (CBG) or the conjugated cortisol that can be cleared by glomerular filtration in the kidney. Therefore, the measurement of free cortisol in the urine is a sensitive reflection of the amount of unbound cortisol in the serum. It is not a reflection of the amount of conjugated cortisol or the serum total cortisol, but, rather, only the increased cortisol production that is not accompanied by an increase in serum levels of CBG.
Of which of the following is 5-hydroxyindoleacetic acid (5-HIAA) the primary metabolite? A. Epinephrine B. Norepinephrine C. Serotonin D. Prolactin
C. Serotonin (5-hydroxytryptamine or 5-HT) is synthesized from tryptophan in a variety of tissues, with the majority found in the argentaffin (enterochromaffin) cells of the intestine. Abdominal carcinoid is a metastasizing tumor of those cells and is associated with excessive production of serotonin. Serotonin in the blood is found almost exclusively in the platelets and is rapidly oxidized in the lungs to 5-hydroxyindoleacetic acid (5-HIAA), its major urinary metabolite. Urinary levels of 5-HIAA may also be increased by eating foods such as bananas and avocados, which are rich in serotonin; by the use of certain drugs such as the phenothiazines; and by carcinoid tumors.
The secretion of which of the following is controlled by growth hormone? A. Growth hormone-releasing hormone B. Corticotropin-releasing hormone C. Somatomedin D. Somatostatin
C. Somatomedins, insulin-like growth factors I and II, is the designation given to a family of small peptides whose formation in the liver is under the control of growth hormone. The somatomedins exhibit similar activity as insulin and are active in stimulating many aspects of cell growth, particularly that of cartilage. Blood levels of somatomedin have been determined by radioimmunoassay methods, and acromegalic adults have been shown to have significantly elevated levels in comparison with normal adults.
The adrenal medulla secretes which of the following in the greatest quantity? A. Metanephrine B. Norepinephrine C. Epinephrine D. Dopamine
C. The adrenal medulla produces 80% epinephrine and 20% norepinephrine (noradrenalin). Metanephrine is a metabolite of epinephrine. Dopamine, a catecholamine, is a precursor of norepinephrine. Norepinephrine is converted to epinephrine by an enzyme, N-methyltransferase, which is present almost exclusively in the adrenal medulla. A tumor of the chromaffin tissue, called a pheochromocytoma, secretes excessive amounts of epinephrine. Ninety percent of pheochromocytomas are in the adrenal medulla. The increrased levels of epinephrine from the pheochromocytoma cause hypertension. Although hypertension caused by a pheochromocytoma is rare, a correct diagnosis is very important because pheochromocytoma is one of the few causes of hypertension that is curable by surgery.
Secretion of hormones by the anterior pituitary may be controlled by the circulating levels of hormones from the respective target gland, as well as hormones secreted by what organ? A. Posterior lobe of the pituitary gland B. Intermediate lobe of the pituitary gland C. Hypothalamus D. Adrenal medulla
C. The hypothalamus produces releasing factors or hormones that affect the release and synthesis of anterior pituitary hormones. The releasing hormones could have a stimulatory effect, as in the case of luteinizing hormone-releasing hormone (LH-RH), or an inhibitory effect, as in the case of prolactin-inhibiting factor (PIF). The posterior lobe of the pituitary acts only as a storage area for vasopressin and oxytocin, which are manufactured in the hypothalamus. The posterior lobe of the pituitary gland does not affect any feedback control on the anterior lobe. The intermediate lobe secretes beta-melaninophore-stimulating hormone, which acts on the skin. It also does not affect any control over the anterior lobe. The adrenal medulla secretes catecholamines, which are not involved in any feedback mechanism to the pituitary gland.
A 30-year-old woman is admitted to the hospital. She has truncal obesity, buffalo humpback, moon face, purple striae, hypertension, hyperglycemia, increased facial hair, acne and amenorrhea. The physicain orders endocrine testing. The results are as follows: Urine free cortisol - increased Serum cortisol (8AM) - increased Plasma ACTH - decreased Dexamethasone suppression test: Overnight low dose- no suppression of serum cortisol High dose- no suppression of serum cortisol What is the most probable diagnosis? A. Pituitary adenoma B. Ectopic ACTH lung cancer C. Adrenocortical carcinoma D. Addison disease
C. The probable diagnosisis Cushing syndrome caused by adrenocortical carcinoma. In adrenocortical carcinoma, the urinary free cortisol and the serum cortisol levels would be elevated and the plasma ACTH level would be decreased. The carcinoma produces excess cortisol that, because of the feedback loop, turns off pituitary production of ACTH. Neither the low-dose dexamethasone suppression test nor the high-dose test is able to suppress cortisol production. Because dexamethasone is a cortisol analogue, it would normally suppress ACTH and cortisol levels in a healthy individual. All these data support primary adrenal dysfunction caused by an adrenal carcinoma. If the elevated cortisol level was due to a pituitary adenoma or ectopic ACTH lung cancer, the ACTH level would also be increased. Addison disease is caused by hypofunction of the adrenal cortex.
Which of the following is not quantified in the triple test for Down Syndrome? A. Alph1-Fetoprotein B. Unconjugated estriol C. Progesterone D. Human chorionic gonadotropin
C. The triple test for Down syndrome includes quantification of alpha1-fetoprotein (AFP), unconjugated estriol (uE3), and human chorionic gonadotropin (hCG) in the maternal serum. These measurements should be done between 16 and 18 weeks gestation, and they are useful in detecting neural tube defects and Down syndrome. In Down syndrome, the AFP and uE3 levels are low, whereas the hCG level is elevated. These test results are related to gestational age and are expressed as a multiple of the median (MoM), meaning the maternal serum result is divided by the median result of the corresponding gestational population.
Which of the following compounds is not a precursor of the estrogens? A. Progesterone B. Testosterone C. Cholesterol D. Aldosterone
D. Acetate, cholesterol, progesterone and the male sex hormones testosterone and androstenedione all serve as precursors for the synthesis of estrogens. The major pathway for conversion of testosterone to estradiol is in the ovaries. The major pathway for conversion of androstenedione to estrone is outside the ovaries.
A patient is suspected of having Addison disease. His symptoms are weakness, fatigue, loss of weight, skin pigmentation, and hypoglycemia. His laboratory tests show low serum sodium and chloride, elevated serum potassium, and elevated urine sodium and chloride levels. The serum cortisol level is decreased and the plasma ACTH is increased. To make a definitive diagnosis, the physician orders an ACTH stimulation test, and serum cortisol levels are measured. If the patient has primary hypoadrenocortical function (Addison disease), what would be the expected level of serum cortisol following stimulation? If the patient has hypopituitarism and secondary hypoadrenocortical function, what would be the expected level of serum cortisol following stimulation? A. Increase from baseline; decrease from baseline B. Decrease from baseline; increase from baseline C. Slight increase from baseline; no change from baseline D. No change from baseline; slight increase from baseline
D. For differentiation of primary and secondary adrenal dysfunction, stimulation or suppression tests that depend on the feedback mechanism between cortisol and ACTH are performed. In the ACTH stimulation test, a patient with a low baseline serum cortisol level is given ACTH. The level of cortisol will increase slightly if the problem lies with the anterior pituitary gland, thus secondary adrenal insufficiency. This increase will be less than normal and may be somewhat delayed due to atrophy of the adrenal cortex as a result of the primary pituitary dysfunction. If the serum cortisol level does not change from baseline, the dysfunction is with the adrenal cortex, thus primary adrenal insufficiency.
The placenta secretes numerous hormones both protein and steroid. Which of the following hormones is not secreted by the placenta? A. Human chorionic gonadotropin (hCG) B. Estrogen C. Human placental lactogen (HPL) D. Luteinizing hormone (LH)
D. Luteinizing hormone (LH) is secreted only by the anterior pituitary. A protein hormone, human chorionic gonadotropin (hCG), appears soon after conception and is thus used for early detection of pregnancy. Human placental lactogen (HPL), also a protein hormone, is produced only by the placenta and is measurable between the seventh and ninth weeks. HPL steadily increases throughout pregnancy and peaks near term. Analysis of HPL for placental dysfunction has been successful; however, it is not widely used for this purpose. During pregnancy the placenta is the main source of estrogen and progesterone. Both hormones are needed for the maintenance of pregnancy.
A 4-year-old female presents with a palpable abdominal mass, pallor, and petechiae. Based on family history, clinical findings, and the patients physical examination, neuroblastoma is suspected. Which of the following does not support such a diagnosis? A. Increased blood dopamine levels B. Increased blood epinephrine levels C. Increased urinary homovanillic acid D. Decreased urinary vanillylmandelic acid
D. Neuroblastoma is a solid malignant tumor found in the medulla of the adrenal gland, or it may arise from the extra-adrenal sympathetic chain. More commonly the disease occurs in children under the age of 5 years. Metastasis may occur to the liver, bone, bone marrow or brain. Neuroblastoma is characterized by tumor production of epinephrine, norepinephrine and dopamine, so all three hormones will be increased in the blood. The end product of dopamine metabolism is homovanillic acid (HVA). The end product of the catecholamines, epinephrine and norepinephrine, is vanillylmandelic acid (VMA). Both HVA and VMA will be excreted in excess in the urine.
Which of the following functions as an inhibiting factor for somatotropin release? A. Gonadotropin-releasing hormone B. Growth hormone-releasing hormone C. Somatomedin D. Somatostatin
D. Somatostatin is also known as growth hormone-inhibiting hormone (GHIH). Somatostatin is a 14-amino-acid peptide that is secreted by the hypothalamus and is an inhibitor of growth hormone (somatotropin) secretion by the pituitary. It is also secreted by a variety of other organs and is a powerful inhibitor of insulin and glucagon secretion by the pancreas. Somatostatin can be measured by immunoassay methods, but its concentration in the peripheral circulation is extremely low, making it likely that its action is mostly at or near the site of secretion.
Which of the following is the most potent androgen? A. Androstenedione B. Dehydroepiandrosterone C. Androsterone D. Testosterone
D. Testosterone is the most potent of the body's androgens. One of the major functions of the testes s to produce testosterone. It is metabolized to the 17-ketosteroids, etiocholanolone and androsterone, but testosterone is not itself a 17-ketosteroid. The 17-ketosteroids, dehydroepiandrosterone (DHEA), androsterone, and androstenedione, all have androgenic properties but are much weaker than testosterone.
What percentage decrease in plasma of urinary estriol, in comparison with the previous day's level, is considered significant during pregnancy? A. 5 B. 10 C. 25 D. 40
D. The concentration of estriol in maternal plasma or in a 24-hour sample of maternal urine is often used as an indicator of fetal distress or placental failure. A single value of either serum or urine estriol has relatively little value unless it can be related accurately to the gestational week. When sequential estriol determinations are made during pregnancy, a pattern of stable or steadily falling values may indicate a problem pregnancy. For serum or urine estriols, any individual value that is 30-50% less than the previous value or the average of the previous 3 days' values is significant.
During pregnancy, estriol is synthesized in the placenta from ____ formed in the ____. A. Estrasiol, mother B. Estradiol, fetus C. 16 alpha-Hydroxy-DHEA-S, mother D. 16 alpha-Hydroxy-DHEA-S, fetus
D. The formation of estriol during pregnancy involves mainly the fetoplacental unit. Dehydroepiandrosterone sulfate (DHEA-S) and its 16 alpha-hydroxy-DHEA-S derivative are formed mainly by the fetal adrenal glands and to a lesser degree by the liver. The fetus possess 16 alpha-hydroxylase activity, which is needed to convert dehydroepiandrosterone sulfate (DHEA-S) to 16 alpha-hydroxy-DHEA-S. The 16 alpha-hydroxy-DHEA-S compound is metabolized by the placenta to estriol. The placenta lacks certain enzymes needed for the conversion of simple precursors such as acetate, cholesterol and progesterone to estrogens. Thus, the placenta must rely on immediate precursors produced in the fetus. In the case of estriol, the placenta utilizes the 16 alpha-hydroxy-DHEA-S precursor made in the adrenal glands of the fetus. The latter compound crosses into the placenta, which takes over with the necessary enzymes to complete the synthesis of estriol. This estriol produced in the placenta is rapidly reflected in the maternal plasma and far exceeds maternal synthesis of estriol. Thus measurement of estriol in the maternal blood or urine is a sensitive indicator of the integrity of the fetoplacental unit. A defect in either the fetus or the placenta will be reflected by a decrease in estriol production.
