Chapter 9: Endocrine Physiology

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1

(...) are secreted into the circulation in small amounts and delivered to target tissues, where they produce physiologic responses.

hormones

2

What are the nine classic endocrine glands?

card image
  1. hypothalamus
  2. pituitary
  3. thyroid
  4. parathyroid
  5. adrenal cortex
  6. adrenal medulla
  7. gonads
  8. placenta
  9. pancreas

(The kidney also is considered to be an endocrine gland)

3

Hormones are categorized in one of three classes: (...).

peptides, steroids, or amines

4

Most hormones are classified as peptides; in the nucleus, the gene for the peptide hormone is transcribed into an (...).

mRNA

5

The mRNA for the peptide hormone is transferred to the cytoplasm and translated on the ribosomes to the first protein product, a (...).

preprohormone

6

The signal peptide is removed from the preprohormone in the endoplasmic reticulum, converting the it to a (...).

prohormone

7

The prohormone is transferred to the Golgi apparatus, where it is packaged in (...).

secretory vesicles

8

In the secretory vesicles, proteolytic enzymes cleave peptide sequences from the prohormone to produce the final (...).

hormone

9

The final hormone is stored in (...) until the endocrine cell is stimulated.

card image

secretory vesicles

10

The steroid hormones are cortisol, aldosterone, estradiol and estriol, progesterone, testosterone, and 1,25-dihydroxycholecalciferol, which are derivatives of (...).

cholesterol

11

The amine hormones are catecholamines and thyroid hormones, which are derivatives of the amino acid (...).

tyrosine

12

Adjustments in secretory rates of hormones may be accomplished by (...) mechanisms or by (...) mechanisms.

neural; feedback

13

(...) mechanisms of hormone control are illustrated by the secretion of catecholamines.

neural

14

(...) mechanisms are the most common mechanism of hormone control.

feedback

15

(...) feedback means that some feature of hormone action inhibits further secretion of the hormone.

card image

negative

16

(...) feedback means that the hormone feeds back all the way to the hypothalamic-pituitary axis.

long-loop

17

(...) feedback means that the anterior pituitary hormone feeds back on the hypothalamus.

short-loop

18

(...) feedback means that the hypothalamic hormone inhibits its own secretion.

ultrashort-loop

19

(...) feedback is an uncommon mechanism of hormone control in which some feature of hormone action causes more secretion of the hormone.

card image

positive

20

The primary example of positive feedback is the effect of (...) on the secretion of gonadotropins by the anterior pituitary at the midpoint of the menstrual cycle.

estrogen

21

A second example of hormonal positive feedback is (...), which is secreted by the posterior pituitary in response to dilation of the cervix.

oxytocin

22

The responsiveness of a target tissue to a hormone is expressed in the (...) in which the magnitude of response is correlated with hormone concentration.

dose-response relationship

23

(...) is defined as the hormone concentration that produces 50% of the maximal response.

sensitivity

24

(...) means that the number or the affinity of the receptors for the hormone has decreased.

down-regulation

25

(...) means that the number or the affinity of the receptors for the hormone has increased.

up-regulation

26

The major mechanisms of hormone action on target cells are (1) the (...) mechanism, in which cAMP is the second messenger; (2) the (...) mechanism, in which IP3/Ca2+ is the second messenger; and (3) the (...) mechanism.

adenylyl cyclase; phospholipase C; steroid hormone

27

Insulin and insulin-like growth factors (IGFs) act on their target cells through a (...) mechanism.

tyrosine kinase

28

Several hormones activate (...), in which cyclic guanosine monophosphate is the second messenger.

guanylate cyclase

29

G proteins can be either stimulatory or inhibitory and are called, accordingly, (...).

Gs (stimulatory) or Gi (inhibitory)

30

When no hormone is bound to the receptor, the αs subunit of the Gs protein binds (...); In this configuration, the Gs protein is (...).

GDP; inactive

31

When hormone binds to its receptor in the cell membrane, (...) is released from the αs subunit and is replaced by (...), and the (...) detaches from the Gs protein.

GDP; GTP; αs subunit

32

The αs-GTP complex migrates within the cell membrane and binds to and activates (...).

adenylyl cyclase

33

Activated adenylyl cyclase catalyzes the conversion of adenosine triphosphate (ATP) to (...), which serves as the second messenger.

cAMP

34

cAMP, via a series of steps involving activation of (...), phosphorylates intracellular proteins.

protein kinase A

35

Intracellular cAMP is degraded to an inactive metabolite, (...), by the enzyme (...), thereby turning off the action of the second messenger.

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5′ adenosine monophosphate (5′ AMP); phosphodiesterase

36

With no hormone bound to the receptor, the αq subunit binds (...); In this configuration, the Gq protein is (...).

GDP; inactive

37

When hormone binds to its receptor in the cell membrane, (...) is released from the αq subunit and is replaced by (...), and the (...) detaches from the Gq protein.

GDP; GTP; αq subunit

38

The αq-GTP complex migrates within the cell membrane and binds to and activates (...).

phospholipase C

39

Activated phospholipase C catalyzes the liberation of (...) and (...) from phosphatidylinositol 4,5-diphosphate (PIP2).

diacylglycerol; IP3

40

The IP3 causes the release of (...) from intracellular stores in the endoplasmic or sarcoplasmic reticulum.

Ca2+

41

Ca2+ and diacylglycerol activate (...), which phosphorylates proteins and produces the final physiologic actions.

card image

protein kinase C

42

Some hormones bind to cell surface receptors called (...) that have, or are associated with, enzymatic activity on the intracellular side.

catalytic receptors

43

What are the four types of catalytic receptors?

  1. guanylyl cyclase
  2. serine/threonine kinases
  3. tyrosine kinases
  4. tyrosine kinase–associated receptors
44

Atrial natriuretic peptide (ANP) acts through a (...) mechanism.

receptor guanylyl cyclase

45

Nitric oxide (NO) acts through a (...) mechanism.

cytosolic guanylyl cyclase

46

(...) and (...) phosphorylate serine and threonine in the cascade of events leading to their biologic actions.

Ca2+-calmodulin-dependent protein kinase (CaMK); mitogen-activated protein kinases (MAPKs)

47

(...) have intrinsic tyrosine kinase activity within the receptor molecule; (...) do not have intrinsic tyrosine kinase activity but associate with proteins that do.

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receptor tyrosine kinases; tyrosine kinase–associated receptors

48

The tyrosine kinase receptor for nerve growth factor (NGF) and epidermal growth factor receptors is a (...) which (...) after binding of ligand.

monomer; dimerizes

49

The tyrosine kinase receptor for insulin and insulin-like growth factor (IGF) is a already a (...).

dimer

50

The tyrosine kinase–associated receptor for growth hormone receptors is noncovalently “associated” with the (...) pathway.

JAK-STAT

51

In contrast to peptide hormones, steroid hormones and thyroid hormones bind to (...) receptors and have a (...) onset of action.

cytosolic (or nuclear); slower (taking hours)

52

The steroid hormone diffuses across the cell membrane, where it binds to a specific (...) that is located in either the cytosol or nucleus.

receptor protein

53

The steroid hormone binds in the (...) of the steroid receptor protein located near the C terminus.

E domain

54

The central (...) of the steroid receptor protein is highly conserved, has two zinc fingers, and is responsible for DNA binding.

card image

C domain

55

The steroid hormone-receptor complex dimerizes and binds (at its C domain) via the zinc fingers to specific DNA sequences, called (...).

steroid-responsive elements (SREs)

56

After binding to the SRE, the hormone-receptor complex has now become a (...) that regulates the rate of transcription of that gene.

card image

transcription factor

57

The posterior lobe (or posterior pituitary) of the hypothalamus is also called the (...).

neurohypophysis

58

The anterior lobe (or anterior pituitary) of the hypothalamus is also called the (...).

adenohypophysis

59

The hypothalamus is connected to the pituitary gland by a thin stalk called the (...).

infundibulum

60

The posterior lobe of the pituitary gland is derived from (...).

neural tissue

61

What are the two hormones secreted by the posterior pituitary?

  1. antidiuretic hormone (ADH)
  2. oxytocin
62

The hormones secreted by the posterior lobe are actually (...); in other words, they are peptides released from neurons.

neuropeptides

63

Although both posterior pituitary hormones are synthesized in both nuclei, ADH is primarily associated with (...) and oxytocin is primarily associated with (...).

supraoptic nuclei; paraventricular nuclei

64

Unlike the posterior lobe, which is neural tissue, the anterior lobe is primarily a collection of (...).

endocrine cells

65

What are the six hormones secreted by the anterior pituitary?

  1. thyroid-stimulating hormone (TSH)
  2. follicle-stimulating hormone (FSH)
  3. luteinizing hormone (LH)
  4. growth hormone (GH)
  5. prolactin
  6. adrenocorticotropic hormone (ACTH)
66

The hypothalamus and anterior pituitary are linked directly by the (...), which provide most of the blood supply of the anterior lobe.

card image

hypothalamic-hypophysial portal blood vessels

67

What are the five major endocrine cell types of the anterior pituitary?

  1. somatotrophs (20%) secrete GH
  2. gonadotrophs (15%) secrete FSH and LH
  3. corticotrophs (15%) secrete ACTH
  4. lactotrophs (15%) secrete prolactin
  5. thyrotrophs (5%) secrete TSH
68

TSH, FSH, and LH are all (...) consisting of two subunits, α and β.

glycoproteins

69

The (...) of TSH, FSH, and LH are identical and are synthesized from the same mRNA.

α subunits

70

The (...) for TSH, FSH, and LH are different and therefore confer the biologic specificity.

β subunits

71

The placental hormone (...) is structurally related to the TSH-FSH-LH family.

human chorionic gonadotropin (HCG)

72

The ACTH family of hormones is derived from a single precursor, (...).

card image

pro-opiomelanocortin (POMC)

73

In (...), POMC and ACTH levels are increased by negative feedback, and because of their MSH activity, skin pigmentation is a symptom of this disorder.

Addison disease (primary adrenal insufficiency)

74

(...) is secreted throughout life and is the single most important hormone for normal growth to adult stature.

growth hormone

75

Growth hormone is synthesized in the somatotrophs of the anterior lobe of the pituitary and also is called (...).

somatotropin

76

Human growth hormone is structurally similar to (...), containing 191 amino acids in a straight-chain polypeptide with 2 internal disulfide bridges.

prolactin

77

Growth hormone is secreted in a (...) pattern, with bursts of secretion occurring approximately every 2 hours.

pulsatile

78

At (...), there is an secretory burst of growth hormone, induced in females by estrogen and in males by testosterone.

puberty

79

(...) and (...) are potent stimuli for growth hormone secretion.

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hypoglycemia; starvation

80

(...) acts directly on somatotrophs of the anterior pituitary to stimulate both synthesis and secretion of growth hormone.

GHRH

81

(...) is also secreted by the hypothalamus and acts on the somatotrophs to inhibit growth hormone secretion.

somatostatin (SRIF)

82

Growth hormone secretion is regulated by negative feedback: (1) GHRH is inhibited by (...); (2) growth hormone is inhibited by (...); (3) somatostatin is stimulated by (...).

card image

GHRH (ultra-short loop); somatomedins; growth hormone and somatomedins

83

The direct actions of growth hormone are mediated by (...) receptors in skeletal muscle, the liver, or adipose tissue.

tyrosine kinase–associated

84

The indirect actions of growth hormone are mediated through the production of (...) in the liver, the most important of which is (...).

somatomedins (or IGFs); somatomedin C (or IGF-1)

85

Somatomedins act on target tissues through IGF receptors that are similar to the insulin receptor, having (...) activity.

intrinsic tyrosine kinase

86

What are the major actions of growth hormone? (3)

  1. diabetogenic or anti-insulin effect
  2. increased protein synthesis and organ growth
  3. increased linear growth
87

Growth hormone deficiency in children causes (...), including failure to grow, short stature, mild obesity, and delayed puberty.

dwarfism

88

One variant of dwarfism is (...), in which growth hormone levels are elevated due to a defect in the growth hormone receptors.

Laron dwarfism

89

Growth hormone excess causes (...) and is most often due to a growth hormone–secreting pituitary adenoma.

acromegaly

90

Before puberty, excessive levels of growth hormone cause (...) because of intense hormonal stimulation at the epiphyseal plates.

gigantism

91

Conditions with excess secretion of growth hormone are treated with (...), which inhibit growth hormone secretion by the anterior pituitary.

somatostatin analogues (e.g. octreotide)

92

(...) is the major hormone responsible for milk production and also participates in the development of the breasts.

prolactin

93

Chemically, prolactin is related to (...), having 198 amino acids in a single-chain polypeptide with 3 internal disulfide bridges.

growth hormone

94

In persons who are not pregnant or lactating, prolactin secretion is tonically inhibited by (...) from the hypothalamus.

dopamine (prolactin-inhibiting factor)

95

Prolactin inhibits its own secretion by increasing the synthesis and secretion of (...) from the hypothalamus.

card image

dopamine

96

(...) and (...) are the most important stimuli for prolactin secretion.

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pregnancy; breast-feeding (suckling)

97

What are the major actions of prolactin? (3)

  1. breast development
  2. lactogenesis (milk production)
  3. inhibition of ovulation
98

Prolactin inhibits ovulation by inhibiting the synthesis and release of (...), which accounts for the decreased fertility during breast-feeding.

gonadotropin-releasing hormone (GnRH)

99

Prolactin deficiency can be caused by total destruction of the (...) or selective destruction of (...).

destruction of the anterior pituitary; lactotrophs

100

Prolactin excess can be caused by destruction of the (...) or by prolactin- secreting tumors called (...).

destruction of the hypothalamus; prolactinomas

101

The major symptoms of excess prolactin secretion are (...) and (...).

galactorrhea; infertility

102

Whether the result of hypothalamic failure or a prolactinoma, prolactin excess can be treated by administration of (...), a dopamine agonist.

bromocriptine

103

ADH and oxytocin are homologous (...) (containing nine amino acids) synthesized in the supraoptic and paraventricular nuclei of the hypothalamus.

card image

nonapeptides

104

The ADH neurons have their cell bodies primarily in the (...) nuclei of the hypothalamus.

supraoptic nuclei

105

The oxytocin neurons have their cell bodies primarily in (...) nuclei of the hypothalamus.

paraventricular

106

The peptide precursor for ADH is (...), which comprises a signal peptide, ADH, neurophysin II, and a glycoprotein.

card image

prepropressophysin

107

The precursor for oxytocin is (...), which comprises a signal peptide, oxytocin, and neurophysin I.

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prepro-oxyphysin

108

(...) is the major hormone concerned with regulation of body fluid osmolarity.

ADH (or vasopressin)

109

(...) is the most important physiologic stimulus for increasing ADH secretion.

card image

increased plasma osmolarity

110

(...) is a potent stimulus for ADH secretion which overrides plasma osmolarity.

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hypovolemia

111

What are the major actions of ADH? (2)

  1. increase in water reabsorption
  2. contraction of vascular smooth muscle
112

The receptor for ADH on the principal cells of the kidney is the (...) receptor, which is coupled to (...) via a G protein.

V2; adenylyl cyclase

113

The second messenger for the V2 receptor is (...), which, via phosphorylation steps, directs the insertion of (...) in the luminal membranes.

cAMP; aquaporin 2 (AQP2)

114

The receptor for ADH on vascular smooth muscle is the (...) receptor, which is coupled to (...) via a G protein.

V1; phospholipase C

115

The second messenger for the V1 receptor is (...), which produces (...) of vascular smooth muscle.

contraction; IP3/Ca2+

116

(...) is caused by failure of the posterior pituitary to secrete ADH; the collecting ducts are impermeable to water, and the urine cannot be concentrated.

central diabetes insipidus

117

Central diabetes insipidus is treated with an ADH analogue, (...).

desmopressin (dDAVP)

118

In (...), the posterior pituitary is normal but the principal cells of the collecting duct are unresponsive to ADH due to a defect in the V2 receptor.

nephrogenic diabetes insipidus

119

Nephrogenic diabetes insipidus is treated with (...).

thiazide diuretics

120

In (...), excess ADH is secreted from an autonomous site, such as oat cell carcinoma of the lung.

syndrome of inappropriate ADH (SIADH)

121

SIADH is treated with an ADH antagonist such as (...) or water restriction.

demeclocycline

122

(...) produces milk “letdown” or milk ejection from the lactating breast.

oxytocin

123

The major stimulus for oxytocin secretion is (...); however, (...) also cause milk letdown.

card image

suckling; conditioned responses

124

What are the major actions of oxytocin? (2)

  1. milk ejection
  2. uterine contraction
125

Stimulation of powerful rhythmic contractions of uterine smooth muscle by oxytocin is the basis for its use in inducing (...) and in reducing (...).

labor; postpartum bleeding

126

The two active thyroid hormones are (...) and (...).

card image

triiodothyronine (T3); thyroxine (T4)

127

Thyroid hormones are synthesized by the (...) cells of the thyroid gland.

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follicular epithelial cells

128

The material in the lumen of the follicles is (...), which is composed of newly synthesized thyroid hormones attached to (...).

colloid; thyroglobulin (TG)

129

(...), a glycoprotein containing large quantities of tyrosine, is synthesized on the rough endoplasmic reticulum and the Golgi apparatus of the thyroid follicular cells.

thyroglobulin (TG)

130

(...) is actively transported from blood into the thyroid follicular epithelial cells against both chemical and electrical gradients via (...).

I (iodide); Na+-I cotransport

131

The anions (...) block Na+-I cotransport into follicular cells and interfere with the synthesis of thyroid hormones.

thiocyanate and perchlorate

132

Once I is pumped into the follicular epithelial cell, it is oxidized to (...) by the enzyme (...).

I2 (iodide); thyroid peroxidase

133

Thyroid peroxidase is inhibited by (...), which blocks the synthesis of thyroid hormones.

propylthiouracil (PTU)

134

At the apical membrane, I2 combines with the (...) moieties of TG, catalyzed by thyroid peroxidase, to form (...) and (...).

tyrosine; monoiodotyrosine (MIT); diiodotyrosine (DIT)

135

High levels of I inhibit organification and synthesis of thyroid hormones, which is known as the (...).

Wolff-Chaikoff effect

136

While still part of TG, coupling reactions occur between MIT and DIT; either two molecules of DIT combine to form (...) or DIT combines with MIT to form (...).

thyroxine (T4); triiodothyronine (T3)

137

Iodinated TG is stored in the follicular lumen as (...) until the thyroid gland is stimulated to secrete its hormones (e.g., by TSH).

colloid

138

When the thyroid gland is stimulated, iodinated TG is (...) into the follicular epithelial cells.

endocytosed

139

(...) hydrolyze peptide bonds to release T4, T3, MIT, and DIT from TG.

lysosomal proteases

140

MIT and DIT are deiodinated inside the follicular cell by the enzyme (...), then are incorporated into the synthesis of new TG to begin another cycle.

card image

thyroid deiodinase

141

Most T4 and T3 circulates bound to (...); because only free thyroid hormones are physiologically active, this provides a reservoir of hormones.

thyroxine-binding globulin (TBG)

142

In (...), blood levels of TBG decrease because there is decreased protein synthesis, resulting in a transient (...) in the level of free thyroid hormones.

hepatic failure; increase

143

During (...), high levels of estrogen inhibits hepatic breakdown of TBG, resulting in a transient (...) in the level of free thyroid hormones.

pregnancy; decrease

144

Circulating levels of TBG can be indirectly assessed with the (...), which measures the binding of radioactive T3 to a synthetic resin.

T3 resin uptake test

145

The major secretory product of the thyroid gland is (...), which is the less active form of thyroid hormone.

T4

146

In the target tissues, the enzyme (...) converts T4 to T3 by removing one atom of I2 from the outer ring of the molecule.

5′-iodinase

147

The target tissues also convert a portion of the T4 to an inactive form, (...), by removing one atom of I2 from the inner ring of the molecule.

reverse T3 (rT3)

148

(...) inhibits 5′-iodinase in tissues such as skeletal muscle, thus lowering O2 consumption and basal metabolic rate.

starvation

149

(...) acts on the thyrotrophs of the anterior pituitary to stimulate synthesis and secretion of TSH.

TRH

150

(...) regulates the growth of the thyroid gland (i.e. a trophic effect) and the secretion of thyroid hormones.

card image

TSH

151

TSH secretion is regulated by two reciprocal factors: (1) (...) stimulates the secretion of TSH; (2) (...) inhibits the secretion of TSH by down-regulating the TRH receptor.

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TRH; thyroid hormone (i.e. free T3)

152

The actions of TSH on the thyroid gland are initiated when TSH binds to a membrane receptor, which is coupled to (...) via a G protein.

adenylyl cyclase

153

Activation of adenylyl cyclase generates (...), which serves as the second messenger for TSH.

cAMP

154

The TSH receptor on the thyroid cells also is activated by (...), which are antibodies to the TSH receptor.

thyroid-stimulating immunoglobulins

155

(...), a common form of hyperthyroidism, is caused by increased circulating levels of thyroid-stimulating immunoglobulins.

Graves disease

156

The first step in the action of thyroid hormones in target tissues is (...).

conversion of T4 to T3 by 5′-iodinase

157

Once T3 is produced inside the target cells, it binds to a (...).

nuclear receptor

158

The T3-receptor complex then binds to a (...) on DNA, where it stimulates (...).

thyroid-regulatory element; DNA transcription

159

A vast array of new proteins are synthesized under the direction of thyroid hormones, including (...).

Na+-K+ ATPase

160

What are the major effects of thyroid hormones? (5)

card image
  1. increase BMR
  2. increase metabolism
  3. increase in cardiac output
  4. stimulate growth and bone development
  5. essential for normal maturation of the CNS
161

Thyroid hormones increase oxygen consumption in all tissues except (...) by inducing the synthesis and increasing the activity of (...).

brain, gonads, and spleen; Na+-K+ ATPase

162

The cardiac effects of thyroid hormones are explained by the fact that they induce the synthesis of (...).

β1-adrenergic receptors

163

Many of the effects of thyroid hormones on BMR, heat production, heart rate, and stroke volume are similar to those produced by catecholamines via (...) receptors.

β-adrenergic

164

The most common form of hyperthyroidism is (...), an autoimmune disorder characterized by increased circulating levels of (...).

Graves disease; thyroid-stimulating immunoglobulins

165

The diagnosis of hyperthyroidism is based on symptoms and measurement of increased levels of (...).

T3 and T4

166

If the cause of hyperthyroidism is a disorder of the thyroid gland, then TSH levels will be (...).

decreased

167

If the cause of hyperthyroidism is a disorder of the hypothalamus or anterior pituitary, then TSH levels will be (...).

increased

168

What are the symptoms of hyperthyroidism? (10)

  1. increased basal metabolic rate
  2. weight loss
  3. negative nitrogen balance
  4. increased heat production
  5. sweating
  6. increased cardiac output
  7. dyspnea (shortness of breath)
  8. tremor, muscle weakness
  9. exophthalmos
  10. goiter
169

Treatment of hyperthyroidism includes (...), which inhibits the synthesis of thyroid hormones, surgical removal of the gland, or radioactive ablation with (...)

propylthiouracil: 131I

170

The most common cause of hypothyroidism is (...) in which antibodies may either frankly destroy the gland or block thyroid hormone synthesis.

autoimmune destruction (thyroiditis)

171

The diagnosis of hypothyroidism is based on symptoms and a finding of decreased levels of (...).

T3 and T4

172

If the cause of hypothyroidism is a disorder of the thyroid gland, then TSH levels will be (...).

increased

173

If the cause of hypothyroidism is a disorder of the hypothalamus or anterior pituitary, then TSH levels will be (...).

decreased

174

What are the symptoms of hypothyroidism? (10)

  1. decreased basal metabolic rate
  2. weight gain
  3. positive nitrogen balance
  4. decreased heat production
  5. cold intolerance
  6. decreased cardiac output
  7. hypoventilation
  8. myxedema
  9. drooping eyelids
  10. goiter
175

In some cases of hypothyroidism, (...) develops, in which there is edema due to accumulation of osmotically active mucopolysaccharides in interstitial fluid.

myxedema

176

When the cause of hypothyroidism is a defect in the thyroid, a (...) develops from the unrelenting stimulation of the thyroid gland by TSH.

goiter

177

If hypothyroidism occurs in the perinatal period and is untreated, it results in an irreversible form of growth and mental retardation called (...).

cretinism

178

Treatment of hypothyroidism involves thyroid hormone replacement therapy, usually (...).

T4 (levothyroxine)

179

Which of the following conditions are associated with goiter?

  1. Graves disease
  2. TSH-secreting tumors
  3. factitious hyperthyroidism (ingestion of T4)
  4. autoimmune thyroiditis
  5. TSH deficiency
  6. I deficiency
  1. In Graves disease, high levels of thyroid-stimulating immunoglobulins have a trophic effect on the thyroid gland to produce goiter.
  2. In cases of TSH-secreting tumors, increased levels of TSH will have a trophic effect on the thyroid gland to produce goiter.
  3. In factitious hyperthyroidism, increased thyroid hormones cause decreased TSH by negative feedback and there is no goiter
  4. In autoimmune thyroiditis, decreased thyroid hormones cause increased TSH by negative feedback and produces goiter.
  5. In cases of TSH deficiency, decreased levels of TSH cause decreased thyroid hormone secretion and no goiter.
  6. In I deficiency, decreased synthesis of T4 and T3 increases TSH secretion by negative feedback to produce goiter.
180

The (...), which is in the inner zone of the adrenal gland that comprises 20% of the tissue, is of (...) origin and secretes (...).

adrenal medulla; neuroectodermal; catecholamines

181

The (...), which is in the outer zone of the adrenal gland that comprises 80% of the tissue, is of (...) origin and secretes (...).

adrenal cortex; mesodermal; adrenocortical steroids

182

The innermost zone of the adrenal cortex, called the (...), and the middle zone, called the (...), synthesize and secrete (...) and (...).

zona reticularis; zona fasciculata; glucocorticoids; adrenal androgens

183

The outermost zone of the adrenal cortex, called the (...), secretes (...).

card image

zona glomerulosa; mineralocorticoids

184

All of the steroids of the adrenal cortex are chemical modifications of a basic steroid nucleus, which is illustrated in the structure of (...).

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cholesterol

185

The (...), represented by cortisol, have a ketone group at carbon 3 (C3) and hydroxyl groups at C11 and C21.

glucocorticoids

186

The (...), represented by aldosterone, have a double-bond oxygen at C18.

mineralocorticoids

187

The (...), represented in the adrenal cortex by dehydroepiandrosterone (DHEA) and androstenedione, have a double-bond oxygen at C17.

androgens

188

The layers of the adrenal cortex are specialized to synthesize and secrete particular steroid hormones; the basis for this is the presence or absence of (...).

enzymes that catalyze modifications of the steroid nucleus

189

The precursor for all adrenocortical steroids is (...).

cholesterol

190

The enzymes catalyzing the conversion of cholesterol to active steroid hormones require (...), molecular oxygen, and NADPH.

cytochrome P-450

191

A flavoprotein enzyme called (...) and an iron-containing protein called (...) are intermediates in the transfer of hydrogen from NADPH to the cytochrome P-450 enzymes.

adrenodoxin reductase; adrenodoxin

192

The first step in the synthesis of all adrenocortical steroid hormones, conversion of cholesterol to pregnenolone, is catalyzed by (...).

cholesterol desmolase

193

Cholesterol desmolase, the rate-limiting enzyme in adrenocortical steroid hormone synthesis pathway, is stimulated by (...).

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ACTH

194

The major glucocorticoid produced in humans is (...), which is synthesized in the (...).

cortisol; zonae fasciculata and reticularis

195

Cortisol is not the only steroid in the pathway with glucocorticoid activity; (...) is also a glucocorticoid.

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corticosterone

196

(...) inhibits 11β-hydroxylase, the last step in cortisol synthesis.

metyrapone

197

(...) inhibits several steps in the pathway including cholesterol desmolase, the first step.

ketoconazole

198

(...) are androgenic steroids produced in the (...).

DHEA and androstenedione; zonae fasciculata and reticularis

199

Adrenal androgens have a ketone group at C17, thus they are also called (...).

17-ketosteroids

200

The major mineralocorticoid in the body is (...), which is synthesized only in the (...).

aldosterone; zona glomerulosa

201

The addition of the enzyme (...) in the zona glomerulosa allow the conversion of corticosterone to aldosterone.

aldosterone synthase

202

Aldosterone is not the only steroid with mineralocorticoid activity; (...) and (...) also have mineralocorticoid activity.

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11-deoxycorticosterone (DOC); corticosterone

203

The synthesis and secretion of steroid hormones by the adrenal cortex depend on the stimulation of cholesterol desmolase by (...).

ACTH

204

The zonae fasciculata and reticularis, which secrete glucocorticoids and androgens, are under the exclusive control of the (...).

hypothalamic-pituitary axis

205

The zona glomerulosa, which secretes mineralocorticoids, depends on ACTH for the first step in steroid biosynthesis, but otherwise it is controlled via the (...).

renin-angiotensin-aldosterone system

206

An impressive feature of the regulation of cortisol secretion is its (...) nature and its (...) pattern.

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pulsatile; diurnal (daily)

207

The secretion of glucocorticoids by the zonae fasciculata/reticularis is regulated exclusively by the (...).

hypothalamic-pituitary axis

208

(...) acts on the corticotrophs by an adenylyl cyclase/cAMP mechanism to cause secretion of ACTH into the bloodstream.

CRH

209

(...) activates cholesterol desmolase in the adrenal cortex and up-regulates transcrption of its own receptor.

ACTH

210

ACTH has a (...) secretory pattern that drives a parallel pattern of cortisol secretion.

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pulsatile and diurnal

211

Negative feedback is exerted by cortisol at three points in the hypothalamic-pituitary axis: (1) it directly inhibits (...); (2) it indirectly inhibits CRH secretion by effects on (...); (3) it inhibits the action of CRH on the (...).

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CRH secretion; hippocampal neurons; anterior pituitary

212

The (...) test is based on the negative feedback effects of cortisol on the CRH-ACTH axis.

dexamethasone suppression

213

When a low dose of dexamethasone is given to a healthy person, it inhibits (...).

ACTH secretion

214

The major use of the dexamethasone suppression test is in persons with (...).

hypercortisolism

215

If the cause of hypercortisolism is (...), a low dose of dexamethasone does not suppress cortisol secretion but a high dose of dexamethasone does.

ACTH-secreting tumor

216

If the cause of hypercortisolism is an (...), then neither low-dose nor high-dose dexamethasone suppresses cortisol secretion.

adrenal cortical tumor

217

The major con­trol of aldosterone secretion is via the (...).

renin–angiotensin II–aldosterone system

218

The mediator of mineralcorticoid secretion is (...), which increases the synthesis and secretion of aldosterone by stimulating cholesterol desmolase and aldosterone synthase.

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angiotensin II

219

(...) is the enzyme that catalyzes the conversion of angiotensinogen to angiotensin I, which is inactive.

renin

220

(...) catalyzes the conversion of angiotensin I to angiotensin II, which then acts on the zona glomerulosa to stimulate aldosterone synthesis.

angiotensin-converting enzyme (ACE)

221

Increases in serum (...) concentration increase aldosterone secretion.

K+

222

What are the major actions of glucocorticoids? (7)

  1. stimulation of gluconeogenesis
  2. anti-inflammatory effects
  3. suppression of immune response
  4. maintain vascular responsiveness to catecholamines
  5. inhibition of bone formation
  6. increases in glomerular filtration rate (GFR)
  7. effects on CNS (e.g decreased REM sleep)
223

Glucocorticoids are essential for survival during (...) because they stimulate these gluconeogenic routes.

fasting

224

Cortisol interferes with the body's inflammatory response by (1) inducing synthesis of (...), an inhibitor of phospholipase A2; (2) inhibiting production of (...), and proliferation of T lymphocytes; and (3) inhibiting release of (...) and (...) from mast cells and platelets.

lipocortin; interleukin-2 (IL-2); histamine; serotonin

225

Aldosterone has three actions on the late distal tubule and collecting ducts:

  1. It increases (...) reabsorption.
  2. It increases (...) secretion.
  3. It increases (...) secretion.

Na+; K+; H+

226

Renal cells contain the enzyme (...), which converts high-affinity cortisol to low affinity cortisone to prevent it from dominating mineralocorticoid receptors.

11β-hydroxysteroid dehydrogenase

227

In (...), there is increased synthesis of adrenal androgens leading to masculinization in females and suppression of gonadal function in both males and females.

adrenogenital syndrome

228

In the adrenogenital syndromes, due to the overproduction of adrenal androgens, there will be increased urinary levels of (...).

17-ketosteroids

229

Cortisol promotes gluconeogenesis; therefore, excess levels produce (...) and deficits produce (...) upon fasting.

hyperglycemia; hypoglycemia

230

Aldosterone causes increased K+ secretion by the renal principal cells; thus excess causes (...) and deficiency causes (...).

hypokalemia; hyperkalemia

231

Because adrenal androgens have testosterone-like effects, in females, overproduction causes (...) and deficits result in (...).

masculinization; loss of pubic hair and libido

232

(...) is commonly caused by autoimmune destruction of all zones of the adrenal cortex, resulting in decreased synthesis of all adrenocortical hormones.

Addison disease (primary adrenocortical insufficiency)

233

Addison disease also is characterized by (...), particularly of the elbows, knees, nail beds, nipples, and areolae and on recent scars.

hyperpigmentation

234

Hyperpigmentation in Addison disease is a result of increased levels of (...).

ACTH (contains the α-MSH fragment)

235

Conditions of (...) occur when there is insufficient CRH or insufficient ACTH.

secondary adrenocortical insufficiency

236

(...) is the result of chronic excess of glucocorticoids due to overproduction by the adrenal cortex or exogenous administration.

Cushing syndrome

237

(...) is characterized by excess glucocorticoids, in which the cause is hypersecretion of ACTH from a pituitary adenoma.

Cushing disease

238

What are the symptoms of Cushing syndrome? (8)

  1. hyperglycemia
  2. muscle wasting (increased proteolysis)
  3. increased lipolysis and thin extremities
  4. central obesity, round face, buffalo hump
  5. poor wound healing
  6. osteoporosis, and
  7. striae (caused by a loss of connective tissue)
  8. virilization and menstrual disorders in females
239

The (...), in which a synthetic glucocorticoid is administered, can distinguish between Cushing syndrome and Cushing disease.

dexamethasone suppression test

240

In (...), because the tumor functions autonomously, cortisol secretion is not suppressed by either low- or high-dose dexamethasone.

Cushing syndrome

241

In (...), ACTH and cortisol secretion are suppressed by high-dose dexamethasone but not by low-dose dexamethasone.

Cushing disease

242

Treatment of Cushing syndrome includes administration of drugs such as (...), which block steroid hormone biosynthesis.

ketoconazole or metyrapone

243

Because of its different etiology, treatment of Cushing disease involves (...).

surgical removal of the ACTH-secreting tumor

244

(...) is caused by an aldosterone-secreting tumor.

Conn syndrome (primary hyperaldosteronism)

245

Treatment of Conn syndrome consists of administration of an aldosterone antagonist such as (...), followed by surgical removal of the tumor.

spironolactone

246

The most common enzymatic defect in the steroid hormone biosynthetic pathways is deficiency of (...), which belongs to a group of disorders called (...).

21β-hydroxylase; adrenogenital syndrome

247

Without 21β-hydroxylase, the adrenal cortex is unable to convert progesterone to (...) or 17-hydroxyprogesterone to (...).

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DOC; 11-deoxycortisol (the adrenal cortex does not synthesize mineralocorticoids or glucocorticoids)

248

In 21β-hydroxylase deficiency, steroid intermediates will accumulate above the enzyme block and be shunted toward production of (...).

adrenal androgens (causes virilization in females)

249

In 21β-hydroxylase deficiency, elevated ACTH (via negative feedback) has a trophic effect on the adrenal cortex; thus the other name for this disorder is (...).

congenital adrenal hyperplasia

250

A less common congenital abnormality of the steroid hormone biosynthetic pathway is deficiency of (...).

17α-hydroxylase

251

Without 17α-hydroxylase, pregnenolone cannot be converted to (...) and progesterone cannot be converted to (...).

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17-hydroxypreg­nenolone; 17-hydroxyprogesterone (neither gluco­corticoids nor adrenal androgens will be produced)

252

In this 17α-hydroxylase deficiency, steroid intermediates accumulate to the left of the enzyme block and will be shunted toward production of (...).

mineralocorticoids (causes hypertension, hypokalemia, and metabolic alkalosis)

253

The endocrine cells of the pancreas are arranged in clusters called the (...), which compose 1% to 2% of the pancreatic mass.

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islets of Langerhans

254

The β cells compose 65% of the islet and secrete (...).

insulin

255

The α cells compose 20% of the islet and secrete (...).

glucagon

256

The delta (δ) cells compose 10% of the islet and secrete (...).

somatostatin

257

The remaining cells of the pancreatic islets secrete (...).

pancreatic polypeptide

258

Insulin is synthesized and secreted by the (...).

β cells

259

Insulin is a peptide hormone consisting of two straight chains designated as the (...) and (...).

A chain; B chain

260

The synthesis of insulin is directed by a gene on (...), a member of a superfamily of genes that encode related growth factors.

chromosome 11

261

The mRNA directs ribosomal synthesis of (...), which contains four peptides: a signal peptide, the A and B chains of insulin, and a connecting peptide (C peptide).

preproinsulin

262

The signal peptide is cleaved from preproinsulin early in the biosynthetic process, yielding (...)

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proinsulin

263

Proinsulin is packaged in secretory granules on the Golgi apparatus, during which, proteases cleave the connecting peptide, yielding (...).

insulin

264

The secretion of (...) is the basis of a test for β cell function in persons with type I diabetes mellitus who are receiving injections of exogenous insulin.

C peptide (It is packaged with insulin and released in equimolar quantities)

265

The most important factor influencing the secretion of insulin by β cells is (...)

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glucose

266

The β cell membrane contains (...), a specific transporter for glucose that moves glucose from the blood into the cell by facilitated diffusion

GLUT2

267

Once inside the cell, glucose is phosphorylated to glucose-6-phosphate by (...), and glucose-6-phosphate is subsequently oxidized.

glucokinase

268

Oxidation of glucose-6-phosphate generates (...), which appears to be the key factor that regulates insulin secretion.

ATP

269

When ATP levels inside the β cell increase, the ATP-sensitive (...) channels close, which depolarizes the β cell membrane.

K+

270

The depolarization of the β cell caused by closure of the K+ channels opens voltage-sensitive (...) channels.

Ca2+

271

Increases in intracellular Ca2+ concentration within the β cell causes exocytosis of the (...)-containing secretory granules

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insulin

272

Oral glucose is a more powerful stimulant for insulin secretion than intravenous glucose because it stimulates the secretion of (...).

glucose-dependent insulinotropic peptide (GIP)

273

(...) activates a Gq protein coupled to phospholipase C, which leads to a rise in intracellular Ca2+, causing exocytosis of insulin.

glucagon

274

(...) inhibits the insulin-releasing mechanism that glucagon stimulates.

somatostatin

275

(...) treat type II diabetes mellitus by stimulating insulin release from β cells by closing the ATP-dependent K+ channels.

sulfonylureas (e.g. tolbutamide, glyburide)

276

The insulin receptor is a tetramer composed of two (...) and two (...), joined by disulfide bonds.

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α subunits; β subunits

277

The (...) of the insulin receptor have intrinsic tyrosine kinase activity.

β subunits

278

Insulin binds to the (...) of the tetrameric insulin receptor, producing a conformational change in the receptor.

α subunits

279

The conformational change in the α subunits of the insulin receptor activates tyrosine kinase in the β subunits, which (...) presence of ATP.

autophosphorylate

280

Activated (...) on the β subunits phosphorylates several other proteins or enzymes that are involved in the physiologic actions of insulin.

tyrosine kinase

281

Insulin (...) its own receptor by decreasing the rate of synthesis and increasing the rate of degradation of the receptor.

down-regulates

282

What are the major actions of insulin? (4)

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  1. decreases blood glucose concentration
  2. decreases blood fatty acid and ketoacid concentrations
  3. decreases blood amino acid concentration
  4. promotes K+ uptake into cells by stimulating Na+-K+ ATPase
283

The hypoglycemic action of insulin is the result of (1) it increasing glucose transport into target cells by increasing (...) (2) it promoting (...) in the liver and in muscle and inhibiting (...); (3) it inhibiting gluconeogenesis by increasing the production of (...).

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GLUT4; glycogenesis; glycogenolysis; fructose 2,6-bisphosphate

284

Insulin also appears to have a direct effect on the hypothalamic (...) center independent of the changes it produces in blood glucose concentration.

satiety

285

(...) is caused by destruction of β cells, often as a result of an autoimmune process.

type I (insulin-dependent) diabetes mellitus

286

The increased levels of ketoacids in type I diabetes mellitus cause a form of metabolic acidosis called (...).

diabetic ketoacidosis (DKA)

287

In diabetes mellitus, the nonreabsorbed glucose in the renal tubules acts as an osmotic solute in urine, producing (...).

osmotic diuresis

288

(...) is often associated with obesity and is caused by down-regulation of insulin receptors in target tissues and insulin resistance.

type II (non–insulin-dependent) diabetes mellitus

289

(...) can be used to treat type II diabetes mellitus by stimulating pancreatic insulin secretion, while (...) up-regulate insulin receptors on target tissues.

sulfonylureas (e.g. tolbutamide or glyburide); biguanides (e.g. metformin)

290

Glucagon is synthesized and secreted by the (...) of the islets of Langerhans.

α cells

291

The major factor stimulating the secretion of glucagon is (...).

decreased blood glucose concentration

292

Glucagon secretion also is stimulated by the ingestion of protein, specifically by the amino acids (...) and (...).

arginine; alanine

293

Another factor stimulating glucagon secretion is (...), which is secreted from the gastrointestinal tract when protein or fat is ingested.

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cholecystokinin (CCK)

294

The glucagon receptor is coupled to (...) via a G protein and second messenger is (...).

adenylyl cyclase; cAMP

295

What are the major actions of glucagon? (2)

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  1. increases blood glucose concentration
  2. increases blood fatty acid and ketoacid concentrations
296

Glucagon increases the blood glucose concentration by (1) stimulating (...) and inhibiting (...); and (2) by increasing gluconeogenesis by decreasing the production of (...).

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glycogenolysis; glycogenesis; fructose 2,6-bisphosphate

297

Pancreatic somatostatin is secreted by the (...) of the islets of Langerhans.

δ cells

298

Pancreatic somatostatin inhibits secretion of (...) via paracrine actions.

insulin and glucagon

299

The total Ca2+ concentration in blood is normally 10 mg/dL; (...) amounts to 50% of total Ca2+ and it is the only form that is biologically active.

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free, ionized Ca2+

300

(...) is a decrease in the plasma Ca2+ concentration, which produces symptoms of hyperreflexia, spontaneous twitching, muscle cramps, and tingling and numbness.

hypocalcemia

301

Specific indicators of hypocalcemia include the (...), or twitching of the facial muscles elicited by tapping on the facial nerve, and the (...), which is carpopedal spasm upon inflation of a blood pressure cuff.

Chvostek sign; Trousseau sign

302

(...) is an increase in the plasma Ca2+ concentration, which produces symptoms of constipation, polyuria, polydipsia, hyporeflexia, lethargy, coma, and death.

hypercalcemia

303

Changes in plasma (...) concentration alter the total Ca2+ concentration in the same direction.

protein

304

Changes in plasma (...) concentration alter the ionized Ca2+ concentration by changing the fraction of complexed Ca2+.

anion

305

(...) abnormalities alter the ionized Ca2+ concentration by changing the fraction of Ca2+ bound to plasma albumin.

acid-base

306

In (...), there is more H+ in blood to bind to albumin, leaving fewer sites for Ca2+ to bind, thus the free ionized Ca2+ concentration (...).

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acidemia; increases

307

In (...), there is less H+ in blood to bind to albumin, leaving more sites for Ca2+ to bind, thus the free ionized Ca2+ concentration (...).

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alkalemia; decreases

308

What three organ systems are involved in Ca2+ homeostasis?

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bone, kidney, and intestine

309

The (...) of the parathyroid glands synthesize and secrete PTH.

chief cells

310

PTH secretion is regulated by plasma (...) concentration; when it decreases to less than (...), PTH secretion is stimulated.

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Ca2+; 10 mg/dL

311

The parathyroid cell membrane contains (...) that are linked, via a G protein to phospholipase C.

Ca2+ sensing receptors

312

Chronic (...) causes (...), which is characterized by increased synthesis and storage of PTH and hyperplasia of the parathyroid glands.

hypocalcemia; secondary hyperparathyroidism

313

Chronic (...) causes decreased synthesis and storage of PTH, increased breakdown of stored PTH, and release of inactive PTH fragments into the circulation.

hypercalcemia

314

(...) has parallel, although less important, effects on PTH secretion as Ca2+.

Mg2+

315

The receptor for PTH is coupled, via a G protein, to (...).

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adenylyl cyclase

316

In bone, PTH receptors are located only on (...).

osteoblasts

317

Initially and transiently, PTH causes (...) by a direct action on osteoblasts.

increased bone formation

318

In a second, long-lasting, indirect action on osteoclasts, PTH causes (...), mediated by (...) released from osteoblasts.

increased bone resorption; cytokines

319

PTH inhibits (...) reabsorption in the proximal convoluted tubule.

phosphate (causes phosphaturia)

320

The cAMP generated in cells of the proximal tubule is excreted in urine and is called (...).

nephrogenous or urinary cAMP

321

The phosphaturic action of PTH is critical because otherwise the phosphate resorbed from bone would (...).

complex Ca2+ in ECF

322

PTH stimulates (...) reabsorption in the proximal convoluted tubule.

Ca2+

323

PTH does not have direct actions on the small intestine, although indirectly it stimulates intestinal Ca2+ absorption via (...).

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activation of vitamin D

324

Primary hyperparathyroidism is most commonly caused by (...).

parathyroid adenomas (tumors)

325

In primary hyperparathyroidism, (...) results from increased bone re­­sorption, increased renal Ca2+ reabsorption, and increased intestinal Ca2+ absorption.

hypercalcemia

326

In primary hyperparathyroidism, (...) results from decreased renal phosphate reabsorption and phosphaturia.

hypophosphatemia

327

Persons with primary hyperparathyroidism are said to have "(...)."

“stones, bones, and groans” (stones from hypercalciuria, bones from increased bone resorption, and groans from constipation)

328

In secondary hyperparathyroidism, the parathyroid glands are stimulated to secrete excessive PTH secondary to (...), which can be caused by (...).

hypocalcemia; vitamin D deficiency or chronic renal failure

329

(...) is a relatively common, inadvertent consequence of thyroid surgery or parathyroid surgery.

hypoparathyroidism

330

In hypoparathyroidism, (...) results from decreased bone resorption, decreased renal Ca2+ reabsorption, and decreased intestinal Ca2+ absorption.

hypocalcemia

331

In hypoparathyroidism, (...) results from increased phosphate reabsorption.

hyperphosphatemia

332

Patients with (...) have hypocalcemia and hyperphosphatemia; however, circulating levels of PTH are increased rather than decreased.

pseudohypoparathyroidism

333

Pseudohypoparathyroidism is an inherited autosomal dominant disorder in which the (...) for PTH in kidney and bone is defective.

Gs protein

334

Some malignant tumors secrete (...), which is structurally homologous with the PTH secreted by the parathyroid glands, with all the same physiologic actions.

PTH-related peptide (PTH-rp)

335

Humoral hypercalcemia of malignancy is treated with (...), which inhibits renal Ca2+ reabsorption, and inhibitors of bone resorption such as (...).

furosemide; etidronate

336

(...) is an autosomal dominant disorder characterized by decreased urinary Ca2+ excretion and increased serum Ca2+ concentration.

familial hypocalciuric hypercalcemia (FHH)

337

FHH is caused by inactivating mutations of (...) in the parathyroid glands and the thick, ascending limb of the kidney.

Ca2+ sensing receptors

338

Calcitonin is synthesized and secreted by the (...) of the thyroid gland.

parafollicular or C cells

339

The major stimulus for calcitonin secretion is (...).

increased plasma Ca2+ concentration

340

The major action of calcitonin is to (...), which decreases the plasma Ca2+ concentration.

inhibit bone resorption

341

(...) in conjunction with PTH, is the second major regulatory hormone for Ca2+ and phosphate metabolism.

vitamin D

342

Vitamin D in the form of (...) is provided in the diet and is produced in the skin from cholesterol.

cholecalciferol

343

Cholecalciferol is physiologically inactive; it is hydroxylated in the liver to form (...), which also is inactive.

25-hydroxycholecalciferol

344

In the kidney, 25-hydroxycholecalciferol (1) can be hydroxylated at C1 to produce (...), the active form, or (2) can be hydroxylated at C24 to produce (...), which is inactive.

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1,25-dihydroxycholecalciferol; 24,25-dihydroxycholecalciferol

345

C1 hydroxylation of 25-hydroxycholecalciferol in the kidney is catalyzed by the enzyme (...).

1α-hydroxylase

346

1α-hydroxylase activity is stimulated by(1) decreased plasma (...) concentration, (2) increased circulating levels of (...), and (3) decreased plasma (...) concentration.

Ca2+; PTH; phosphate

347

The overall role of 1,25-dihydroxycholecalciferol is to increase the plasma concentration of (...) to promote (...).

Ca2+ and phosphate; mineralization of new bone

348

In the intestine, 1,25-dihydroxycholecalciferol induces the synthesis of a vitamin D–dependent Ca2+-binding protein called (...).

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calbindin D-28K

349

The actions of 1,25-dihydroxycholecalciferol on the kidney are parallel to its actions on the intestine—it stimulates (...).

Ca2+ and phosphate reabsorption

350

In bone, 1,25-dihydroxycholecalciferol acts synergistically with PTH to stimulate (...).

bone resorption (“old” bone is resorbed to provide Ca2+ and phosphate so that “new” bone can be mineralized)

351

In children, vitamin D deficiency causes (...), a condition in which insufficient amounts of Ca2+ and phosphate are available to mineralize the growing bones.

rickets

352

In adults, vitamin D deficiency results in (...), in which new bone fails to mineralize, resulting in bending and softening of the weight-bearing bones.

osteomalacia

353

(...) occurs when the kidney is unable to produce the active metabolite, 1,25-dihydroxycholecalciferol.

vitamin D resistance

354

Vitamin D resistance can be caused by the congenital absence of 1α-hydroxylase or, more commonly, by (...).

chronic renal failure

355
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...

356
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...

357
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...

358
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...

359
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...