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Phys II Unit II > 2 Hypothalamus And Pituitary Unit > Flashcards

2 Hypothalamus And Pituitary Unit Flashcards

1
Q

The function of the hypothalamus-pituitary unit is to …

A

Coordinate the physiologic response of organs that together maintain homeostasis

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2
Q

Hormones released from the Anterior Pituitary are responsible for…

A 
Metabolism
Growth and development
Reproduction
Lactation
Response to stress

(ACTH, GH, TSH, Prolactin, LH, FSH)

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3
Q

Hormones released from the Posterior Pituitary are responsible for …

A 
Water balance
Parturition and Lactation
Regulation of BP
Cardiac Function
Diuresis

(Oxytocin and Arginine Vasopressin/ADH)

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4
Q

____________ neurons project their axons down the infundibular process and terminate in the posterior pituitary, where they release their hormones into a capillary bed

A

Magnocellular neurons

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5
Q

___________ neurons are the neurovascular link between the hypothalamus and the anterior lobe of the pituitary

A

Parvicellular neurons

They are neurosecretory and project axons to the median eminence, where they secrete releasing hormones

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6
Q

Parvicellular neurons release what?

A

Releasing hormones

RHs flow down the pituitary stalk in the hypothalamo-hypophyseal portal vessels to the anterior pituitary. RHs and inhibiting hormones regulate the secretion of tropic hormones from cell types of the anterior pituitary.

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7
Q

What hormones are released from Magnocellular neurons

A

Oxytocin, ADH, NP (neurophysin)

Originate from Paraventricular nuclei (PVN) and supraoptic nuclei (SON)

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8
Q

What hormones are released from Parvicellular neurons?

A

CRH, TRH, GnRH, GHRH, Somatostatin, DA

These in turn lead to the release of ACTH, TSH, LH/FSH, GH, PRL from anterior pituitary

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9
Q

What is the pituitary hormone and target cell of GHRH?

A

GH (increased synthesis from somatotrophs, 45%) —> Growth via IGF production in liver and energy metabolism

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10
Q

What is the pituitary hormone and target cell of TRH?

A

TSH (increased synthesis from thyrotrophs, 3-5%) —> Growth of thyroid gland and synthesis of T3/T4

Prolactin (increased synthesis from mammotrophs, 10-15%) —> breath development and milk production in mammary glands

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11
Q

What is the pituitary hormone and target cell of Somatostatin?

A

GH and TSH (decreased synthesis)

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12
Q

What is the pituitary hormone and target cell of GnRH?

A

LH (increased synthesis) —> Ovulation and synthesis of estrogen in women, secretion of testosterone from Leydig cells in men

FSH (increased synthesis in gonadotrophs, 15%) —> development of follicle in women, initiation of spermatogenesis in men

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13
Q

What is the pituitary hormone and target cell of CRH?

A

ACTH (increased synthesis from corticotrophs, 15%) —> growth of the adrenal gland and synthesis of corticosteroids

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14
Q

What is the pituitary hormone and target cell of PRF?

A

Prolactin (increased synthesis from lactotrophs) —> breast development and milk production

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15
Q

What is the pituitary hormone and target cell of Dopamine)

A

Inhibits prolactin synthesis (aka PIH)

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16
Q

Where are hormones of the posterior pituitary produced?

A

Synthesized in the hypothalamic neuronal cell bodies of magnocellular neurons, in the supraoptic and paraventricular nuclei

Both OT and ADH are synthesized in the peptide fashion as preprohormones

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17
Q

How big are ADH and Oxytocin?

A

Both are nonapeptides (consist of 9 amino acids)

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18
Q

What are some cool traits of the posterior pituitary hormones (ADH and OT)?

A

Released into fenestrated pituitary capillaries upon stimulation via action potentials

Co-secreted with NEUROPHYSINS

Both have a short plasma half-life of ~8 minutes

Cysteine residues form a disulfide bride that confers its activity. When disulfide bridges are knocked off in the liver, the hormone becomes inactive.

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19
Q

Carrier proteins that prevent the diffusion of hormones out of the axons in the posterior pituitary

A

Neurophysins, NP-I and NP-II

NP-I goes with Oxytocin (think you drink your mama’s milk first in life) and NP-II goes with ADH

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20
Q

A defect or lack of neurophysins (specifically NP-II) which leads to the release of ADH at inappropriate levels

A

Central Diabetes Insipidus

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21
Q

What is the physiologic effects of oxytocin in lactating breasts?

A

Stimulates milk ejection (myoepithelial cell contraction)

The suckling of the nipple also stimulates OT release —> afferent sensory signals that elicit an increase in OT in circulation (POSITIVE FEEDBACK)

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22
Q

What is the physiologic effect of oxytocin in the pregnant uterus?

A

Produces rhythmic smooth muscle contraction to induce labor.

Release of OT is stimulated with distention of the cervix as well as the contraction of the uterus during parturition (POSITIVE FEEDBACK)

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23
Q

In addition to controlling lactation and uterine contractions, oxytocin is also…

A

A cardiovascular and cardio metabolic hormone.

Both OT synthesis and receptors (OTR) occur in the heart.

A specific OT-natriuretic peptide-NO axis resides in the heart.

OT causes ANP/BNP release from cardiomyopathy and ANP, in turn, stimulates the release of NO from the vascular endothelium (a cardio-protective system!).

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24
Q

Where are OT, ANP and BNP found in the heart?

A

OT is found in atria and ventricles, but is 3-4x more abundant in atria

ANP is found in atria and ventricle but is more abundant in atria

BNP is found mainly in the ventricles

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25
Q

What does OT respond to in terms of cardiac function?

A

Responds to volume overload to regulate BP

CV effects
• Vasodilation
• Increased NO production
• Negative chronotropic effect (slows heart beat)
• Negative inotropic effect (lessens contraction)

Renal effects
• Natriuresis
• Kaliuresis
• Diuresis
•Decreased plasma volume

Endocrine effects
• Decreased cortisol, aldosterone, renin

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26
Q

OT regulates cardiac function by …

A

Modulating the parasympathetic system and inotropicity

Local OT—> Bradycardia, Negative inotropy, Increased glucose uptake

PItuitary OT —> ANP —> NO Synthesis —> dilation of coronary resistance vessels

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27
Q

In prediabetes, clinical studies show that OT …

A

Increases peripheral glucose uptake by a GLUT4 mechanism but NOT via the insulin receptor pathway —> therapeutic effect of OT?

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28
Q

ADH/AVP is released following…

A

An increase in plasma osmolarity

Osmoreceptors (found in anterior hypothalamus and outside the BBB) have directo contact with the systemic circulation

With dehydration, loss of intracellular water and an increase in plasma Na+ and Cl- is detected by osmoregulators and signal ADH/AVP magnocellular neurons to stimulate release

29
Q

How sensitive are the osmoreceptors that control ADH/AVP release?

A

Release occurs before stimulation of thirst.

Sensitivity of the system is very high - 1% change in osmolarity above the threshold (~280-284 mOsm/L) produces an increase in ADH/AVP release

30
Q

What is the target for ADH/AVP and what does it do?

A

Targets the kidney by acting on a V2 receptor

Water is reabsorbed from distal tubule and collecting duct via aquaporins 1-4

Results in an increase in plasma volume and decrease in osmolarity, and low urine output

31
Q

ADH/AVP is released following a decrease in blood volume, but…

A

It’s not as sensitive to blood volume change as it is to changes in plasma osmolarity. (A decrease in blood volume of 8-10% elicits an increase in ADH release)

A decrease in BP decreases the stretch of the baroreceptors and decreases their rate of firing —> release of ADH/AVP from magnocellular neurons and stimulating thirst center

A decrease in BP is also perceived by the macula dense, resulting in the release of renin —> ang II sensitized the osmoreceptors leading to enhanced ADH/AVP release

32
Q

Secretory rates of GH are about ________ in teens and _______ in adults

A

~700 guys/day for teens, 400 ug/day for adults

Levels are higher in children and teens, reflecting growth

Levels decline with aging, reflecting loss of lean body mass, fitness, protein synthesis, metabolic rate

33
Q

During puberty, when GH levels increase, _______ levels increase in parallel

A

IGF-1 (Insulin-like growth factor)

34
Q

Secretion of GH follows a ________ pattern

A

Diurnal (daily and nocturnal)

Levels remain low during day but increase with sleep (sharp rise at onset, during slow wave sleep, then steady drop throughout sleep time).

70% of total daily secretion occurs during sleep, released in pulsatile bursts

35
Q

GH secretion is greater in _________ women

A

Premenopausal (before ovulation: effect of estradiol)

Testosterone also amplifies the secretion of GH in males

The pattern and frequency of pulse release is the same for males and females

36
Q

The principle regulators of GH release are…

A

GH-releasing hormone (GHRH) and somatostatin

GHRH acts on somatotrophs to induce transcription, synthesis, and release of GH and proliferation of somatotrophs

GHRH binds to G protein-coupled receptor —> activating adenylate cyclase and PKA —> phosphorylation of CREB —> activation and increased transcription of the PIT-1 gene —> PIT-1 activates transcription of GH gene

Somatostatin produces inhibitory effect through binding to a Gi protein-coupled somatostatin receptor —> decreased adenylate cyclase —> inhibition of CREB and PIT-1

37
Q

Proteins/factors that are the ultimate intracellular targets of GHRH to allow for production of GH

A

CREB (cAMP response element binding protein)

PIT-1 (pituitary-specific transcription factor)

38
Q

Factors that stimulate GH release

A 
HYPOglycemia*****
Decreased FFAs
ARGININE*****
Fasting/starvation/exercise
Stress
SLEEP**** 
Thyroid hormone
Adrogens
Ghrelin
39
Q

Factors that inhibit GH release

A 
HYPERglycemia
Increased FFAs
Obesity
Aging
GH
IGF-1
40
Q

________ is used clinically to evaluate GH status

A

Arginine

Given intravenously, it suppresses somatostatin release allowing GH to be secreted unopposed.

Insulin challenges are also used (to induce hypoglycemia, another release stimulating factor)

41
Q

DIRECT physiologic effects of GH

A

Direct effects on cellular responses by binding to a GH receptor at target tissues

42
Q

INDIRECT physiologic effects of GH

A

Indirect effects by stimulating the production of hepatic IGF-1, a mediator of GH’s effect on tissues

43
Q

Direct actions of GH related to muscle

A

GH is a protein anabolic hormone

Increases amino acid uptake and incorporates it into protein

Enhances cell proliferation and represses protein degradation

Produces positive nitrogen balance - muscle wasting, normal to aging, is in part caused by lower GH secretion

44
Q

Direct actions of GH related to adipose tissue

A

GH activates hormone-sensitive lipase and mobilizes lipids for energy use by tissues during fasting

45
Q

Direct actions of GH related to carbohydrate metabolism

A

GH alters carb metabolism by a secondary increase in FFAs —> decreasing glucose uptake by muscle and adipocytes

GH stimulates hepatic gluconeogenesis (b/c it wants to produce glucose)

Net effect is an increase in glucose and subsequent rise in plasma insulin. GH may induce a diabetogenic effect - meaning GH antagonizes the action of insulin, and may lead to diabetes with over-secretion of GH

46
Q

Why do patients with acromegaly and gigantism often co-present with diabetes?

A

B/c the overproduction of GH induces a diabetogenic effect, antagonizes the action of insulin, with a net effect of increasing blood glucose

The diabetes is unrelated to pancreatic function

47
Q

_____ promotes growth of bones, soft tissue, and visceral growth, the indirect actions of GH.

A

IGF-1

Sex steroids, insulin, and thyroid hormones regulate IGF-1 production in the liver

48
Q

IGF are proteins but must be bound to _____ to be transported in the plasma

A

Binding proteins

IGF-1 is transported bound to IGF-BP (BP1-6 are synthesized in the liver in response to GH)

49
Q

_______ is the major transporter for IGF-1, binding ~80% of IGF-1

A

IGF-BP3

50
Q

After GH increases production of IGF1 and IGFBP3 in the liver, what do they do?

A

CHONDROCYTES increase amino acid uptake, protein synthesis, RNA/DNA synthesis, collagen, chondroitin sulfate, and cell size/number —> INCREASE LINEAR GROWTH

MUSCLE increase amino acid uptake and protein synthesis —> INCREASE LEAN BODY MASS

TISSUE/ORGANS increase protein synthesis, RNA/DNA synthesis, and cell size/number —> INCREASE ORGAN SIZE AND FUNCTION

51
Q

GHRH can suppress its own release through…

A

An ultrashort feedback loop

52
Q

GH can feedback to suppress GHRH release and exerts an _________ inhibitory effect on somatotrophs

A

Autocrine

53
Q

In both fed and fasting situations, the plasma GH levels are …

A

Increased

However, the effects are opposing - abundance of food favors anabolic/growth states, while scarcity of food favors catabolic state

54
Q

In the fed state, when protein and energy intake are both ample _________ is favored

A

Protein synthesis

Protein intake —> increased GH, IGF, and insulin —> protein synthesis and growth but no change in caloric storage

GH facilitates insulin action to promote growth

55
Q

In the fed state, when carbs alone are ingested, ________ is favored

A

Storage

CHO intake —> decreased GH (b/c hyperglycemia inhibits release), no change in IGF and increased insulin —> no change in protein synthesis or growth but increased caloric storage

56
Q

In the fasted state, ____________ is favored

A

Glucose sparing

Fasting —> increased GH (b/c hypoglycemia promotes release), decreased IGF and decreased insulin —> caloric mobilization, decreased protein synthesis and growth

The GH released in response to hypoglycemia enhance lipolysis, increase hepatic gluconeogenesis, and decrease peripheral glucose uptake

57
Q

In addition to increased GH due to hypoglycemia, fasting causes what other hormone level changes?

A

Decreased insulin, increased glucagon, and increased cortisol

Together with the GH, the increased cortisol promotes production of IGF-BP3 —> further limits the availability to IGF-1 to tissues. This is one mechanism by which growth is diverted by GH under fasting conditions

58
Q

Dwarfism is also classified as a form of _________

A

Hypopituitarism

The term panhypopituitarism is used to describe a deficiency in more than one anterior pituitary hormone (ie Thyroid, ACTH)

59
Q

The most frequent cause of hypopituitarism is …

A

Traumatic injury, such as that linked to surgery, or MVAs.

60
Q

Blood loss or hypoperfusion of the pituitary gland or stalk, or ischemic damage during postpartum period that can lead to pituitary insufficiency

A

Sheehan Syndrome

61
Q

_______ results from GH deficiency before puberty

A

Dwarfism

Well-proportioned bodies and normal intelligence

If deficiency is limited GH, can have a normal life span

May appear “pudgy” b/c of loss of GH-induced lipolysis

62
Q

GH resistant individuals with genetic defect in expression of the GH receptor in the liver —> Normal to high serum GH levels but NO IGFs in response to GH

A

Laron dwarf

Also have failure to produce IGF-BPs

63
Q

Type of dwarfism with normal serum GH levels, but do not exhibit the normal rise in IGFs with puberty

A

African Pigmy

Not as severe as Laron dwarfism

Partial defect in GH receptors and do not totally lack the IGF response to GH

64
Q

________ occurs with GH hypersecretion after the epiphyses closes in adults

A

Acromegaly

Caused primarily by a tumor of the somatotrophs. IGF-1 levels are elevated.

Favors appositional growth of bone and soft tissue deformities (not linear growth)

Visceral enlargement, enlarged hands and feet, and decreased fat content

Propensity to be diabetic. Very slow in onset

65
Q

How is Acromegaly treated?

A

Surgery

Octreotide (somatostatin analogues)

Dopamine analogues

GH receptor antagonists (if PRL is co-secreted)

66
Q

Why might you see gynecomastia and lactation in patients with acromegaly?

A

If prolactin and mammosomatotrophs are involved as well

Treat with GH-receptor antagonists

67
Q

Excess GH secretion before puberty resulting in increased linear growth because of stimulation of epiphyseal plates

A

Gigantism

Typically a pituitary involvement - tumor growth eventually compresses other components of the anterior pituitary, decreasing secretion of other hormones

Frequently manifests with hyperinsulinemia and glucose intolerance or diabetes

68
Q

Typical cause of death for patients with gigantism

A

Cardiac hypertrophy

Phys II Unit II (9 decks)

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