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Endocrine - MSI Spring > Hypothalamic-Pituitary relationships > Flashcards

Hypothalamic-Pituitary relationships Flashcards

1
Q

How is the anterior pituitary connected to the hypothalamus?

A

by hypothalamic-hypophysial portal vessels

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2
Q

Do hypothalamic hormones appear in the systemic circulation in high concentration?

A

No

They appear in high concentration in the hypothalamic-hypophysial portal vessels

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3
Q

What are the connections between the hypothalamus and anterior lobe ?

A

Via median eminence and portal system: Neural and endocrine

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4
Q

What are the connections between the hypothalamus and posterior lobe?

A

neural axons via neuro-hypophyseall stalk

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5
Q

ACTH has melanocyte-stimulating hormone activity. Explain the clinical relevance

A

Increase blood levels of MSH can cause skin pigmentation

Addison disease ACTH levels increase, Skin pigmentation is a symptom

POMC-> ACTH + Y-lipotropin + B-Endorphin

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6
Q

Describe the HPA axis

A

Major hormones: CRH->ACTH
Target organs: medulla and cortex adrenal gland
peripheral hormone: aldosterone, cortisol, sex horm
Regulations: stress - neurogenic (fear) or systemic (surgery)

Hypothalamus has the ability to reset the set point in response to stress

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7
Q

Describe the HPT axis

A

TRH->(PKC mechanism) TSH->(PKA mechanism) thyroid gland->T3/T4

Regulation: stress - physical, starvation, infection inhibits TRH secretion

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8
Q

Describe the HPG axis

A

GnRH->(Ca, PKC, other) FSH and LH->gonands and thyroid(PKA mech.) ->estrogen and testosterone

Regulation: stress inhibits via inhibin
Puberty promotes

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9
Q

What stimulates GH secretion?

A

Decreased blood glucose levels: ghrelin->GH release

Secreted in pulsatile pattern every 2 hours

GHRH->GH

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10
Q

What is the lifetime pattern of growth hormone secretion?

A

Peaks at puberty then declines

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11
Q

What are the direct and indirect effects of growth hormone?

A

Direct: effect on tissues like skeletal muscle, liver, adipose tissue
Indirect: mediated by the production of somatomedins in the liver (IGF-1)

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12
Q

What are the actions of growth hormone?

A

Diabetogenic effect
Increased Protein synthesis and organ growth
Increased linear growth

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13
Q

The diabetogenic effect directly results in what actions of GH?

A

Body not using glucose but using fats
Results in increase in blood insulin levels from liver, skeletal m, adipose tissue
Leads to insulin resistance
Decrease in glucose uptake and utilization
Increase in lipolysis in adipose tissue (ketogenic)

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14
Q

what is the hypophysial stalk?

A

physical connection between hypothalamus and (posterior) pituitary gland

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15
Q

What inhibits the release of growth hormones from the anterior pituitary?

A

Target tissues release somatomedins which directly inhibits

Somatomedins also stimulate the hypothalamus to secrete somatostatin which inhibits the anterior pituitary

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16
Q

Describe the action of Growth hormone from the indirect effect of somatomedins

A

Stimulate synthesis of DNA, RNA, and proteins

Protein synthesis and organ growth: increase uptake of aa
Increase linear growth: Increase metabolism in cartilage-forming cells and chondrocytes proliferation

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17
Q

What are causes of growth hormone deficiency ?

A

Decrease secretion of GHRH - hypothalamic
Decrease in GH secretion - 1* deficiency
- failure to generate somatomedins
GH or somatomedin resistance - receptor deficiency

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18
Q

What does growth hormone excess cause?

A

acromegaly
Before puberty: gigantism
After puberty: increase organ size, extremities size, insulin resistance, glucose intolerance

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19
Q

What is excessive growth hormone in the body usually caused by?

A

GH- secreting pituitary adenoma

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20
Q

What are conditions with excess secretion of GH treated with ?

A

somatostatin analogues like octreotide

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21
Q

With combined actions of progesterone and estrogen, what role does prolactin play in breast development?

A

At puberty: stimulate proliferation and branching of mammary ducts

During pregnancy: stimulates growth and development of the mammary alveoli

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22
Q

What role does prolactin play in lactogenesis?

A

Induces synthesis of lactose, casein, and lipids

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23
Q

Why does lactation not occur during pregnancy even though prolactin levels are high?

A

High levels of estrogen and progesterone down-regulate prolactin receptors

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24
Q

How is inhibition of lactation released at birth?

A

Estrogen and progesterone levels drop precipitously, when this occurs lactogenesis is stimulated

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25
Q

What is prolactin’s role in ovulation?

A

suppresses ovulation

inhibits synthesis and secretion of GnRH

26
Q

What results in prolactin deficiency? What are the causes?

A

Inability to lactate

Causes: destruction of the entire anterior lobe of the pituitary or selective destruction of the cells that secrete prolactin (lactotrophs)

27
Q

What results in prolactin excess?

A

Galactorrhea (excessive milk production) and infertility (caused by inhibition of GnRH secretion by prolactin

28
Q

What are the causes of prolactin excess levels?

A

destruction of hypothalamus or the interruption of hypothalamic-hypophysial tract; loss of tonic inhibition by DA (dopamine)

Prolactinomas

29
Q

What can be used to treat prolactin excess?

A

Bromocriptine (DA receptor agonist) can be used for the treatment of prolactin excess

30
Q

What are the 3 sources of dopamine?

A

Hypothalamus, posterior lob of pituitary and lactotroph

31
Q

How does the destruction of the hypothalamus cause in INCREASE in prolactin secretion

A

Dopamine cant be released from the hypothalamus/posterior lobe of the pituitary and thus cant inhibit prolactin secretion.

32
Q

What is panhypopituitarism?

A

condition of inadequate or absent production of the anterior pituitary hormones

33
Q

What are the causes of panhypopituitarism?

A

Problems that affect the pituitary gland and either reduce or destroy its function or interfere with hypothalamic secretion of the varying pituitary-releasing hormones

34
Q

What is the most common tumor affecting the HP axis in children and causing hypopituitarism?

A

Craniopharyngioma

35
Q

What is sheehan syndrome?

A

Pituitary in pregnancy is enlarge and more vulnerable to infarction

36
Q

Most pituitary tumors are pituitary ________.

A

Adenomas

  • most occur spontaneously
37
Q

A pituitary adenoma is classified according to size. Describe the size of macro vs microadenoma

A

Micro or equal to 1 cm

38
Q

What is the agressiveness of pituitary adenomas ?

A

nearly all are benign and slow-growing

39
Q

Describe the hormone secretion of pituitary adenomas

A

Functional: adenomas that release an active hormone, usually an excessive amount

Clinically non-functioning adenomas: do not release active hormone

40
Q

What is the most common functional pituitary adenoma?

A

prolactinoma: overproduces prolactin 60%

Acromegaly 20%
Cushing’s - overproduction of cortisol 10%

41
Q

Pituitary adenomas develop in ____ of patients with MEN 1

A

25%

42
Q

What is the precursor peptide of ADH?

A

preprossophysin

43
Q

What is the precursor peptide for oxytocin?

A

prepro-oxyphysin

44
Q

What is the major hormone concerned with regulating body fluid?

A

ADH

45
Q

Describe the activation of ADH

A

In cell bodies of hypothalamus: cleaved from prepropressophysin to propressophysin

Cleavage of neurophysins and axoplasmic flow: in axons and becomes ADH

46
Q

What are the triggers of ADH secretion

A 
decreased blood pressure: baroreceptors 
Decrease arterial stretch due to low blood volume: atrial stretch receptors 
Increased osmolarity: osmoreceptors 
Increased angiotensin II 
Sympathetic stimulation 
Dehydration

All to sensory neurons and interneurons -> hypothalamus

47
Q

What is the secretion of ADH most sensitive to?

A

plasma osmolarity changes

An increase in only 1% in osmolarity will increase ADH secretion

48
Q

Urea can pass with water, but _______ cannot

A

electrolytes

49
Q

What does ADH do in the renal collecting duct?

A

Through G protein V2 receptors, it increases cAMP via Adenylate cyclase activity
That Activates PKA
which increases the amount of aquaporin-2 causing more water to be reabsorbed

50
Q

When there is less volume (contraction), how much ADH will be needed with increase in osmolarity?

A

More ADH secretion (steeper slope)

*expansion causes less ADH secretion

51
Q

Describe ADH’s role in Diabetes insipidus

A

Lack of an effect of ADH on renal collecting duct
Causes frequent urination
Urine diluted

52
Q

Describe Central diabetes insipidus

A

Lack of ADH
Low plasma levels of ADH
Results from: damage to pituitary, destruction of the hypothalamus
Tx: desmopressin (prevents water excretion

53
Q

Describe nephrogenic DI

A

Kidneys unable to respond to ADH (increase in plasma ADH)
Caused by drugs like lithium and chronic disorders like polycistic kidney disease

Desmopressin tx does not work

54
Q

What is the water deprivation test for DI?

A

Allow fluids overnight before test and give breakfast w/ no fluids
Weigh patients
Allow no fluid for 8 hr.
Every 1-2 hr: weigh
Stop of weight drops by >5% initial bw
Patient empties bladder: measure volume and osmolarity (stop if >300)

If results suggest DI, let pt drink and administer desmopressin
measure volume and osmolarity

55
Q

What are the results of DI test if normal?

A

About 300 Osm plasma
Urine is 814 Osm
Plasma ADH is increased
Urine Osm post desmopressing is 815

56
Q

What are the results of DI test if the pt has central DI

A

Plasma Osm = 342
Urine Osm = 102
Decreased plasma ADH
Urine Osm post = 622

57
Q

What are the results of DI test with a nephrogenic DI pt?

A

Plasma Osm = 327
Urine Osm = 106
Increased Plasma ADH
Urine Osm post des = 118

58
Q

Describe SIADH

A

Excessive secretion of ADH
Excessive water retention
Hypoosmolarity fails to inhibit ADH release

Causes: ectopic ADH with lung cancer, drugs, trauma, CNS disorders,

59
Q

What is the Tx for SIADH?

A

fluid restriction
IV hypertonic saline
V2 receptor antagonist
Demeclocycline

60
Q

What are the major consequences of pituitary failure

A

GH: short children
FSH/LH: infertility, hypogonadism, menstrual irregularity and reduce sperm
TSH: hypothyroidism
ACTH: Loss of pigmentation hypoadrenalism
ADH: diabetes insipidus

Endocrine - MSI Spring (15 decks)

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