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USMLE (S1) Endocrinology > Endocrine - Physiology > Flashcards

Flashcards in Endocrine - Physiology Deck (95)
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1
Q

What is the effect of thyrotropin-releasing hormone on pituitary hormone secretion?

A

It stimulates thyroid-stimulating hormone and prolactin secretion

2
Q

What is the effect of dopamine on pituitary hormone secretion?

A

Inhibition of prolactin secretion

3
Q

What is the effect of corticotropin-releasing hormone on pituitary hormone secretion?

A

It stimulates adrenocorticotropic hormone secretion

4
Q

What is the effect of growth hormone-releasing hormone on pituitary hormone secretion?

A

It stimulates growth hormone secretion

5
Q

What is the effect of somatostatin on pituitary hormone secretion?

A

It inhibits growth hormone and thyroid-stimulating hormone secretion

6
Q

What is the effect of gonadotropin-releasing hormone on pituitary hormone secretion?

A

It stimulates luteinizing hormone and follicle-stimulating hormone secretion

7
Q

What is the effect of prolactin on pituitary hormone secretion?

A

It inhibits gonadotropin-releasing hormone, which in turn decreases luteinizing hormone and follicle-stimulating hormone secretion

8
Q

How does prolactin provide negative feedback to its own secretion?

A

High prolactin levels cause increased dopamine synthesis and secretion by the hypothalamus

9
Q

Why might bromocriptine be withheld from a woman who is trying to breast feed?

A

Bromocriptine is a dopamine agonist, and so it inhibits prolactin secretion

10
Q

A woman being treated for schizophrenia complains of breast fullness and amenorrhea; what is the likely cause?

A

Increased prolactin levels secondary to dopamine antagonists (antipsychotics)

11
Q

Why are women less likely to become pregnant when breastfeeding?

A

Prolactin inhibits ovulation via the inhibition of gonadotropin-releasing hormone

12
Q

A woman has had her thyroid surgically removed and is not taking thyroid hormone replacement. She now complains of amenorrhea; what is the likely cause?

A

She has hypothyroidism, which can cause prolactin release and thus amenorrhea

13
Q

How does prolactin affect fertility in men?

A

It decreases spermatogenesis by inhibiting gonadotropin-releasing hormone synthesis and release

14
Q

Which enzyme is responsible for converting cholesterol to pregnenolone?

A

Desmolase

15
Q

Which enzyme catalyzes conversion of testosterone to dihydrotestosterone?

A

5-reductase

16
Q

Adrenocorticotropic hormone has a(n) _____ (inhibitory/stimulatory) effect on desmolase whereas ketoconazole has a(n) _____ (inhibitory/stimulatory) effect on desmolase.

A

Stimulatory; inhibitory

17
Q

What enzyme is responsible for the conversion of pregnenolone to progesterone?

A

3-hydroxysteroid dehydrogenase

18
Q

What is the effect of congenital adrenal enzyme deficiencies on adrenal size?

A

Decreased cortisol production and loss of negative feedback causes increased adrenocorticotropic hormone stimulation leading to bilateral adrenal enlargement

19
Q

Which enzyme catalyzes the conversion of testosterone to estradiol?

A

Aromatase

20
Q

What stimulates aldosterone synthase to convert corticosterone into aldosterone?

A

Angiotensin II stimulates aldosterone synthase

21
Q

A patient has decreased sex hormone and cortisol levels and increased mineralocorticoid levels; what is the diagnosis?

A

17-hydroxylase deficiency

22
Q

What are the symptoms associated with 17-hydroxylase deficiency?

A

Hypertension and hypokalemia (due to increased mineralocorticoids)

23
Q

What is the phenotype of XY males who have 17-hydroxylase deficiency?

A

Pseudohermaphroditism; decreased dihydrotestosterone means that male secondary sex characteristics do not develop

24
Q

Do XY males with 17-hydroxylase deficiency have male or female internal anatomy?

A

Male; these patients still make müllerian inhibitory factor, which leads to development of the male internal reproductive tract

25
Q

What is the phenotype of XX females who have 17-hydroxylase deficiency?

A

Externally female, but they lack secondary sexual characteristics ("sexual infantilism") due to decreased testosterone

26
Q

A patient has increased sex hormones, decreased cortisol and mineralocorticoids, and HYPOtension; what is the diagnosis?

A

21-hydroxylase deficiency

27
Q

What symptoms are associated with 21-hydoxylase deficiency?

A

Masculinization, female pseudohermaphotidism, hypotension, hyperkalemia, salt wasting, increased plasma renin activity, and volume depletion

28
Q

What is the phenotype of XX females who have 21-hydroxylase deficiency?

A

The deficiency shunts precursors to the sex hormone pathway, increasing dihydrotestosterone, which causes masculinization and androgenization of external female genitalia

29
Q

A female infant is born with ambiguous genitalia and is found to be severely hypotensive; what is the diagnosis?

A

21-hydroxylase deficiency causes hyperreninemic hypoaldosteronism and salt wasting, resulting in hypotension and hyperkalemia

30
Q

A patient has increased sex hormones, decreased cortisol, aldosterone, and mineralocorticoids, and has HYPERtension; what is the diagnosis?

A

11-hydroxylase deficiency

31
Q

What are the symptoms associated with 11-hydoxylase deficiency?

A

Masculinization, hypertension

32
Q

Why do patients with a deficiency in 11-hydroxylase have hypertension in the presence of hypoaldosteronism?

A

11-deoxycorticosterone has mineralocorticoid properties and builds up, causing hypertension

33
Q

What is the effect of ketoconazole on steroid synthesis?

A

Ketoconazole inhibits desmolase so that cholesterol is not converted to pregnenolone

34
Q

Androstenedione is converted into _____ in the adrenal zona reticularis and into _____ in the periphery.

A

Testosterone; estrone

35
Q

Name five functions of cortisol.

A

Maintains Blood pressure (by upregulating a-1 receptors on arterioles), decreases Bone formation, antiInflammatory, decreases Immune function, increases Gluconeogenesis, lipolysis, proteinolysis (remember: cortisol is BBIIG)

36
Q

What hormones are involved in regulation of cortisol secretion?

A

Corticotropin-releasing hormone from the hypothalamus stimulates adrenocorticotropic hormone release from the anterior pituitary; adrenocorticotropic hormone then stimulates cortisol production by the adrenal gland

37
Q

In what form is cortisol found in the bloodstream?

A

It is bound to corticosteroid-binding globulin

38
Q

Which cells normally produce parathyroid hormone?

A

Chief cells of the parathyroid glands

39
Q

What is the effect of parathyroid hormone on serum calcium and phosphate?

A

Parathyroid hormone increases the serum calcium level and decreases the serum phosphate level (remember: PTH = Phosphate Trashing Hormone)

40
Q

What effect does parathyroid hormone have on bone?

A

Increased resorption of calcium and phosphate from bone (leading to increases of serum levels of both minerals)

41
Q

What effect does parathyroid hormone have on the kidney?

A

Increased resorption of calcium from distal convoluted tubule, decreased phosphate reabsorption, stimulation of 1 hydroxylase activity

42
Q

How does parathyroid hormone affect calcium absorption in the gut?

A

It stimulates 1-hydroxylase activity in the kidney leading to increased levels of active vitamin D; active vitamin D leads to calcium resorption from the intestines

43
Q

Increased levels of parathyroid hormone would result in what urinary findings?

A

Higher urine phosphate and cAMP levels and lower urine calcium levels

44
Q

What is the major stimulus for the release of parathyroid hormone from the parathyroid glands?

A

Low free serum calcium levels

45
Q

How does parathyroid hormone exert an effect on osteoblasts and osteoclasts?

A

It directly stimulates osteoblast activity and indirectly stimulates osteoclast activity, with a net effect of bone resorption

46
Q

What is the active form of vitamin D?

A

1,25-dihydroxy vitamin D, also called calcitriol

47
Q

Active vitamin D formation is stimulated under which conditions?

A

Low serum calcium and phosphate and high serum parathyroid hormone levels

48
Q

Low serum calcium levels result in increased _____ secretion, whereas low serum phosphate levels result in increased conversion of _____ in the kidney.

A

Parathyroid hormone; 25-(OH) vitamin D to 1,25(OH)2 vitamin D

49
Q

Which two organs are the targets for 1,25(OH)2 vitamin D?

A

The gastrointestinal tract and bone

50
Q

What is the effect of serum magnesium on parathyroid hormone secretion?

A

Low magnesium leads to decreased parathyroid hormone secretion

51
Q

What are some causes of low magnesium?

A

Diarrhea, aminoglycosides, diuretics, and alcohol abuse

52
Q

What are the two sources of the precursors for activated vitamin D?

A

Plants (D2 and sun exposure (D3)

53
Q

In which organ is vitamin D converted to 25-hydroxy vitamin D?

A

The liver

54
Q

Where is 25-hydroxy vitamin D activated?

A

The kidney

55
Q

A deficiency of vitamin D in children results in what condition?

A

Rickets

56
Q

A deficiency of vitamin D in adults results in what condition?

A

Osteomalacia

57
Q

What effect does vitamin D have on the gut?

A

It increases the absorption of dietary calcium and phosphate

58
Q

Compare the effect of parathyroid hormone on serum calcium and phosphate levels to that of 1,25(OH)2 vitamin D.

A

Parathyroid hormone increases serum calcium levels and decreases serum phosphate levels, whereas 1,25(OH)2 vitamin D increases both calcium and phosphate levels

59
Q

What effect does vitamin D have on bone?

A

Increases resorption of calcium and phosphate

60
Q

Where is calcitonin made?

A

Parafollicular cells (C cells) of the thyroid

61
Q

Where does calcitonin exert its effect?

A

Calcitonin decreases calcium resorption from bone

62
Q

What stimulates the secretion of calcitonin?

A

Increased serum calcium levels

63
Q

How is calcitonin involved in calcium homeostasis?

A

It opposes the action of parathyroid hormone but is not important in normal calcium homeostasis (remember: calciTONin TONes down calcium levels)

64
Q

What hormones use the tyrosine kinase signaling pathway?

A

Insulin, insulin-like growth factor-1, fibroblast growth factor, platelet-derived growth factor, prolactin, growth hormone

65
Q

What hormones use cyclic guanosine monophosphate as a signaling molecule?

A

Atrial natriuretic peptide, nitric oxide/endothelium-derived relaxing factor (think vasodilators)

66
Q

Except for _____ _____ and _____, all the hormones of the anterior pituitary utilize the cAMP signaling pathway.

A

Growth hormone and prolactin

67
Q

Which hormones use steroid receptors in their signaling pathways?

A

Vitamin D and PET CAT: Progesterone, Estrogen, Testosterone, Cortisol, Aldosterone, T3, and T4

68
Q

What hormones use the inositol triphosphate signaling pathway?

A

Gonadotropin-releasing hormone (GnRH), growth hormone-releasing hormone (GHRH), Oxytocin, antidiuretic hormone (ADH) (V1 receptor), thyrotropin-releasing hormone (TRH); (remember: GGOAT)

69
Q

Insulin utilizes the _____ signaling pathway, whereas glucagon increases the concentration of _____ in the cell after binding its receptor.

A

Tyrosine kinase, cAMP

70
Q

Name the hormones that use the cAMP signaling pathway.

A

Follicle-stimulating hormone (FSH), luteinizing hormone (LH), adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), corticotropin-releasing hormone (CRH), human chorionic gonadotropin (hCG), antidiuretic hormone (ADH) (V2 receptor), melanocyte-stimulating hormone (MSH), parathyroid hormone (PTH), calcitonin, glucagon (remember: FLAT CHAMP)

71
Q

Steroid hormones have an (immediate/delayed) onset of action upon binding to a cell.

A

Delayed; time is required for gene transcription and protein synthesis

72
Q

Why do steroid hormones circulate bound to specific binding globulins?

A

Steroid hormones are lipophilic and specific binding globulins increase their solubility

73
Q

Do steroid hormones bind receptors found on the cell surface or within the cell?

A

Steroids bind their receptors within the cell, in the nucleus or the cytoplasm

74
Q

How does the steroid hormone/receptor complex affect cellular physiology?

A

By binding enhancer-like elements of the DNA, it alters gene expression and protein synthesis

75
Q

What physical finding in a man could suggest increased levels of sex-hormone-binding globulin?

A

Gynecomastia, due to lower serum free testosterone

76
Q

What physical finding in a woman could suggest decreased levels of sex-hormone-binding globulin?

A

Hirsutism may result from increased serum free testosterone

77
Q

True or False: All hormones that come from the adrenal cortex are steroids.

A

TRUE

78
Q

Which iodine-containing hormones in the body control the bodys metabolic rate?

A

T3 and T4

79
Q

What protein in the plasma binds T3 and T4 for transportation?

A

Thyroxine-binding globulin

80
Q

What happens to the level of thyroxine-binding globulin during pregnancy and oral contraceptive use?

A

It is increased as a result of higher estrogen levels

81
Q

What happens to the level of thyroxine-binding globulin during hepatic failure?

A

It is decreased

82
Q

What cell type in the thyroid produces T3 and T4?

A

Follicular cells

83
Q

By what mechanism do T3 and T4 affect the basal metabolic rate?

A

They increase the basal metabolic rate by increasing Na+/K+-adenosine triphosphatase activity

84
Q

What are the four main functions of T3?

A

The 4 Bs: Brain maturation, Bone growth, Beta-adrenergic effects, BMR increase

85
Q

What are the effects of the increased Na+/K+ adenosine triphosphatase activity stimulated by thyroid hormone?

A

Increased O2 consumption, respiratory rate, and body temperature

86
Q

Which effects of thyroid hormone are similar to those of glucagon?

A

Increased glycogenolysis, gluconeogenesis, and lipolysis

87
Q

Newborn screening of an infant shows low thyroid hormone levels; what major organ system should you be concerned about?

A

Central nervous system; thyroid hormones are needed for central nervous system maturation, and a congenital deficiency may cause cretinism

88
Q

The hypothalamus releases _____, which stimulates the pituitary to release _____, which in turn stimulates the production of T3 and T4 from follicular cells in the thyroid.

A

Thyrotropin-releasing hormone; thyroid-stimulating hormone

89
Q

How does free T3 exert negative feedback on the hypothalamic-pituitary axis?

A

Free T3 decreases the sensitivity of the anterior pituitary to thyrotropin-releasing hormone, leading to decreased thyroid hormone production

90
Q

What is the mechanism by which Graves disease causes hyperthyroidism?

A

Graves disease is an autoimmune disorder in which antibodies toward the thyroid-stimulating hormone receptor in the thyroid stimulate the production of thyroid hormones, independent of regulation by thyroid-stimulating hormone

91
Q

What are the effects of T3 and T4 on the heart?

A

Upregulation of the number of 1 receptors causes increased cardiac output, heart rate, stroke volume, and cardiac contractility

92
Q

From which large precursor protein is thyroid hormone derived?

A

Thyroglobulin

93
Q

What is the role of peroxidase in the production of thyroid hormones?

A

I- is oxidized to I2 by peroxidase then combines with thyroglobulin to make monoiodotyrosine and diiodotyrosine; peroxidase couples monoiodotyrosine and diiodotyrosine to make T4 and T3

94
Q

The major hormone product of the thyroid is _____, and _____ has greater affinity for thyroid hormone receptors.

A

T4; T3

95
Q

How do the antithyroid drugs propylthiouracil and methimazole affect thyroid hormone production?

A

They decrease the formation of monoiodotyrosine and diiodotyrosine