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USMLE® Step 1 > USMLE (S1) Endocrinology > Endocrine - Physiology > Flashcards

Endocrine - Physiology Flashcards

1
Q

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

A

It stimulates thyroid-stimulating hormone and prolactin secretion

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2
Q

What is the effect of dopamine on pituitary hormone secretion?

A

Inhibition of prolactin secretion

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3
Q

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

A

It stimulates adrenocorticotropic hormone secretion

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4
Q

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

A

It stimulates growth hormone secretion

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5
Q

What is the effect of somatostatin on pituitary hormone secretion?

A

It inhibits growth hormone and thyroid-stimulating hormone secretion

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6
Q

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

A

It stimulates luteinizing hormone and follicle-stimulating hormone secretion

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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

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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

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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

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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)

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11
Q

Why are women less likely to become pregnant when breastfeeding?

A

Prolactin inhibits ovulation via the inhibition of gonadotropin-releasing hormone

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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

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13
Q

How does prolactin affect fertility in men?

A

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

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14
Q

Which enzyme is responsible for converting cholesterol to pregnenolone?

A

Desmolase

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15
Q

Which enzyme catalyzes conversion of testosterone to dihydrotestosterone?

A

5-reductase

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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

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17
Q

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

A

3-hydroxysteroid dehydrogenase

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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

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19
Q

Which enzyme catalyzes the conversion of testosterone to estradiol?

A

Aromatase

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20
Q

What stimulates aldosterone synthase to convert corticosterone into aldosterone?

A

Angiotensin II stimulates aldosterone synthase

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21
Q

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

A

17-hydroxylase deficiency

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22
Q

What are the symptoms associated with 17-hydroxylase deficiency?

A

Hypertension and hypokalemia (due to increased mineralocorticoids)

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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

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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

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25
What is the phenotype of XX females who have 17-hydroxylase deficiency?
Externally female, but they lack secondary sexual characteristics ("sexual infantilism") due to decreased testosterone
26
A patient has increased sex hormones, decreased cortisol and mineralocorticoids, and **HYPO**tension; what is the diagnosis?
21-hydroxylase deficiency
27
What symptoms are associated with 21-hydoxylase deficiency?
Masculinization, female pseudohermaphotidism, hypotension, hyperkalemia, salt wasting, increased plasma renin activity, and volume depletion
28
What is the phenotype of XX females who have 21-hydroxylase deficiency?
The deficiency shunts precursors to the sex hormone pathway, increasing dihydrotestosterone, which causes masculinization and androgenization of external female genitalia
29
A female infant is born with ambiguous genitalia and is found to be severely hypotensive; what is the diagnosis?
21-hydroxylase deficiency causes hyperreninemic hypoaldosteronism and salt wasting, resulting in hypotension and hyperkalemia
30
A patient has increased sex hormones, decreased cortisol, aldosterone, and mineralocorticoids, and has **HYPER**tension; what is the diagnosis?
11-hydroxylase deficiency
31
What are the symptoms associated with 11-hydoxylase deficiency?
Masculinization, hypertension
32
Why do patients with a deficiency in 11-hydroxylase have hypertension in the presence of hypoaldosteronism?
11-deoxycorticosterone has mineralocorticoid properties and builds up, causing hypertension
33
What is the effect of ketoconazole on steroid synthesis?
Ketoconazole inhibits desmolase so that cholesterol is not converted to pregnenolone
34
Androstenedione is converted into _____ in the adrenal zona reticularis and into _____ in the periphery.
Testosterone; estrone
35
Name five functions of cortisol.
Maintains **B**lood pressure (by upregulating a-1 receptors on arterioles), decreases **B**one formation, anti**I**nflammatory, decreases **I**mmune function, increases **G**luconeogenesis, lipolysis, proteinolysis (remember: cortisol is **BBIIG**)
36
What hormones are involved in regulation of cortisol secretion?
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
In what form is cortisol found in the bloodstream?
It is bound to corticosteroid-binding globulin
38
Which cells normally produce parathyroid hormone?
Chief cells of the parathyroid glands
39
What is the effect of parathyroid hormone on serum calcium and phosphate?
Parathyroid hormone increases the serum calcium level and decreases the serum phosphate level (remember: **PTH** = **P**hosphate **T**rashing **H**ormone)
40
What effect does parathyroid hormone have on bone?
Increased resorption of calcium and phosphate from bone (leading to increases of serum levels of both minerals)
41
What effect does parathyroid hormone have on the kidney?
Increased resorption of calcium from distal convoluted tubule, decreased phosphate reabsorption, stimulation of 1 hydroxylase activity
42
How does parathyroid hormone affect calcium absorption in the gut?
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
Increased levels of parathyroid hormone would result in what urinary findings?
Higher urine phosphate and cAMP levels and lower urine calcium levels
44
What is the major stimulus for the release of parathyroid hormone from the parathyroid glands?
Low free serum calcium levels
45
How does parathyroid hormone exert an effect on osteoblasts and osteoclasts?
It directly stimulates osteoblast activity and indirectly stimulates osteoclast activity, with a net effect of bone resorption
46
What is the active form of vitamin D?
1,25-dihydroxy vitamin D, also called calcitriol
47
Active vitamin D formation is stimulated under which conditions?
Low serum calcium and phosphate and high serum parathyroid hormone levels
48
Low serum calcium levels result in increased _____ secretion, whereas low serum phosphate levels result in increased conversion of _____ in the kidney.
Parathyroid hormone; 25-(OH) vitamin D to 1,25(OH)2 vitamin D
49
Which two organs are the targets for 1,25(OH)2 vitamin D?
The gastrointestinal tract and bone
50
What is the effect of serum magnesium on parathyroid hormone secretion?
Low magnesium leads to decreased parathyroid hormone secretion
51
What are some causes of low magnesium?
Diarrhea, aminoglycosides, diuretics, and alcohol abuse
52
What are the two sources of the precursors for activated vitamin D?
Plants (D2 and sun exposure (D3)
53
In which organ is vitamin D converted to 25-hydroxy vitamin D?
The liver
54
Where is 25-hydroxy vitamin D activated?
The kidney
55
A deficiency of vitamin D in children results in what condition?
Rickets
56
A deficiency of vitamin D in adults results in what condition?
Osteomalacia
57
What effect does vitamin D have on the gut?
It increases the absorption of dietary calcium and phosphate
58
Compare the effect of parathyroid hormone on serum calcium and phosphate levels to that of 1,25(OH)2 vitamin D.
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
What effect does vitamin D have on bone?
Increases resorption of calcium and phosphate
60
Where is calcitonin made?
Parafollicular cells (C cells) of the thyroid
61
Where does calcitonin exert its effect?
Calcitonin decreases calcium resorption from bone
62
What stimulates the secretion of calcitonin?
Increased serum calcium levels
63
How is calcitonin involved in calcium homeostasis?
It opposes the action of parathyroid hormone but is not important in normal calcium homeostasis (remember: calci**TON**in **TON**es down calcium levels)
64
What hormones use the tyrosine kinase signaling pathway?
Insulin, insulin-like growth factor-1, fibroblast growth factor, platelet-derived growth factor, prolactin, growth hormone
65
What hormones use cyclic guanosine monophosphate as a signaling molecule?
Atrial natriuretic peptide, nitric oxide/endothelium-derived relaxing factor (think vasodilators)
66
Except for _____ \_\_\_\_\_ and \_\_\_\_\_, all the hormones of the anterior pituitary utilize the cAMP signaling pathway.
Growth hormone and prolactin
67
Which hormones use steroid receptors in their signaling pathways?
Vitamin D and **PET CAT**: **P**rogesterone, **E**strogen, **T**estosterone, **C**ortisol, **A**ldosterone, **T**3, and T4
68
What hormones use the inositol triphosphate signaling pathway?
Gonadotropin-releasing hormone (**G**nRH), growth hormone-releasing hormone (**G**HRH), **O**xytocin, antidiuretic hormone (**A**DH) (V1 receptor), thyrotropin-releasing hormone (**T**RH); (remember: **GGOAT**)
69
Insulin utilizes the _____ signaling pathway, whereas glucagon increases the concentration of _____ in the cell after binding its receptor.
Tyrosine kinase, cAMP
70
Name the hormones that use the cAMP signaling pathway.
Follicle-stimulating hormone (**F**SH), luteinizing hormone (**L**H), adrenocorticotropic hormone (**A**CTH), thyroid-stimulating hormone (**T**SH), corticotropin-releasing hormone (**C**RH), human chorionic gonadotropin (**h**CG), antidiuretic hormone (**A**DH) (V2 receptor), melanocyte-stimulating hormone (**M**SH), parathyroid hormone (**P**TH), calcitonin, glucagon (remember: **FLAT CHAMP**)
71
Steroid hormones have an (immediate/delayed) onset of action upon binding to a cell.
Delayed; time is required for gene transcription and protein synthesis
72
Why do steroid hormones circulate bound to specific binding globulins?
Steroid hormones are lipophilic and specific binding globulins increase their solubility
73
Do steroid hormones bind receptors found on the cell surface or within the cell?
Steroids bind their receptors within the cell, in the nucleus or the cytoplasm
74
How does the steroid hormone/receptor complex affect cellular physiology?
By binding enhancer-like elements of the DNA, it alters gene expression and protein synthesis
75
What physical finding in a man could suggest increased levels of sex-hormone-binding globulin?
Gynecomastia, due to lower serum free testosterone
76
What physical finding in a woman could suggest decreased levels of sex-hormone-binding globulin?
Hirsutism may result from increased serum free testosterone
77
True or False: All hormones that come from the adrenal cortex are steroids.
TRUE
78
Which iodine-containing hormones in the body control the bodys metabolic rate?
T3 and T4
79
What protein in the plasma binds T3 and T4 for transportation?
Thyroxine-binding globulin
80
What happens to the level of thyroxine-binding globulin during pregnancy and oral contraceptive use?
It is increased as a result of higher estrogen levels
81
What happens to the level of thyroxine-binding globulin during hepatic failure?
It is decreased
82
What cell type in the thyroid produces T3 and T4?
Follicular cells
83
By what mechanism do T3 and T4 affect the basal metabolic rate?
They increase the basal metabolic rate by increasing Na+/K+-adenosine triphosphatase activity
84
What are the four main functions of T3?
The 4 **B**s: **B**rain maturation, **B**one growth, **B**eta-adrenergic effects, **BMR** increase
85
What are the effects of the increased Na+/K+ adenosine triphosphatase activity stimulated by thyroid hormone?
Increased O2 consumption, respiratory rate, and body temperature
86
Which effects of thyroid hormone are similar to those of glucagon?
Increased glycogenolysis, gluconeogenesis, and lipolysis
87
Newborn screening of an infant shows low thyroid hormone levels; what major organ system should you be concerned about?
Central nervous system; thyroid hormones are needed for central nervous system maturation, and a congenital deficiency may cause cretinism
88
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.
Thyrotropin-releasing hormone; thyroid-stimulating hormone
89
How does free T3 exert negative feedback on the hypothalamic-pituitary axis?
Free T3 decreases the sensitivity of the anterior pituitary to thyrotropin-releasing hormone, leading to decreased thyroid hormone production
90
What is the mechanism by which Graves disease causes hyperthyroidism?
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
What are the effects of T3 and T4 on the heart?
Upregulation of the number of 1 receptors causes increased cardiac output, heart rate, stroke volume, and cardiac contractility
92
From which large precursor protein is thyroid hormone derived?
Thyroglobulin
93
What is the role of peroxidase in the production of thyroid hormones?
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
The major hormone product of the thyroid is \_\_\_\_\_, and _____ has greater affinity for thyroid hormone receptors.
T4; T3
95
How do the antithyroid drugs propylthiouracil and methimazole affect thyroid hormone production?
They decrease the formation of monoiodotyrosine and diiodotyrosine

USMLE (S1) Endocrinology (5 decks)

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