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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
What is prolactin's role in ovulation?
suppresses ovulation | inhibits synthesis and secretion of GnRH
26
What results in prolactin deficiency? What are the causes?
Inability to lactate Causes: destruction of the entire anterior lobe of the pituitary or selective destruction of the cells that secrete prolactin (lactotrophs)
27
What results in prolactin excess?
Galactorrhea (excessive milk production) and infertility (caused by inhibition of GnRH secretion by prolactin
28
What are the causes of prolactin excess levels?
destruction of hypothalamus or the interruption of hypothalamic-hypophysial tract; loss of tonic inhibition by DA (dopamine) Prolactinomas
29
What can be used to treat prolactin excess?
Bromocriptine (DA receptor agonist) can be used for the treatment of prolactin excess
30
What are the 3 sources of dopamine?
Hypothalamus, posterior lob of pituitary and lactotroph
31
How does the destruction of the hypothalamus cause in INCREASE in prolactin secretion
Dopamine cant be released from the hypothalamus/posterior lobe of the pituitary and thus cant inhibit prolactin secretion.
32
What is panhypopituitarism?
condition of inadequate or absent production of the anterior pituitary hormones
33
What are the causes of panhypopituitarism?
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
What is the most common tumor affecting the HP axis in children and causing hypopituitarism?
Craniopharyngioma
35
What is sheehan syndrome?
Pituitary in pregnancy is enlarge and more vulnerable to infarction
36
Most pituitary tumors are pituitary ________.
Adenomas * most occur spontaneously
37
A pituitary adenoma is classified according to size. Describe the size of macro vs microadenoma
Micro or equal to 1 cm
38
What is the agressiveness of pituitary adenomas ?
nearly all are benign and slow-growing
39
Describe the hormone secretion of pituitary adenomas
Functional: adenomas that release an active hormone, usually an excessive amount Clinically non-functioning adenomas: do not release active hormone
40
What is the most common functional pituitary adenoma?
prolactinoma: overproduces prolactin 60% Acromegaly 20% Cushing's - overproduction of cortisol 10%
41
Pituitary adenomas develop in ____ of patients with MEN 1
25%
42
What is the precursor peptide of ADH?
preprossophysin
43
What is the precursor peptide for oxytocin?
prepro-oxyphysin
44
What is the major hormone concerned with regulating body fluid?
ADH
45
Describe the activation of ADH
In cell bodies of hypothalamus: cleaved from prepropressophysin to propressophysin Cleavage of neurophysins and axoplasmic flow: in axons and becomes ADH
46
What are the triggers of ADH secretion
``` 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
What is the secretion of ADH most sensitive to?
plasma osmolarity changes | An increase in only 1% in osmolarity will increase ADH secretion
48
Urea can pass with water, but _______ cannot
electrolytes
49
What does ADH do in the renal collecting duct?
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
When there is less volume (contraction), how much ADH will be needed with increase in osmolarity?
More ADH secretion (steeper slope) *expansion causes less ADH secretion
51
Describe ADH's role in Diabetes insipidus
Lack of an effect of ADH on renal collecting duct Causes frequent urination Urine diluted
52
Describe Central diabetes insipidus
Lack of ADH Low plasma levels of ADH Results from: damage to pituitary, destruction of the hypothalamus Tx: desmopressin (prevents water excretion
53
Describe nephrogenic DI
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
What is the water deprivation test for DI?
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
What are the results of DI test if normal?
About 300 Osm plasma Urine is 814 Osm Plasma ADH is increased Urine Osm post desmopressing is 815
56
What are the results of DI test if the pt has central DI
Plasma Osm = 342 Urine Osm = 102 Decreased plasma ADH Urine Osm post = 622
57
What are the results of DI test with a nephrogenic DI pt?
Plasma Osm = 327 Urine Osm = 106 Increased Plasma ADH Urine Osm post des = 118
58
Describe SIADH
Excessive secretion of ADH Excessive water retention Hypoosmolarity fails to inhibit ADH release Causes: ectopic ADH with lung cancer, drugs, trauma, CNS disorders,
59
What is the Tx for SIADH?
fluid restriction IV hypertonic saline V2 receptor antagonist Demeclocycline
60
What are the major consequences of pituitary failure
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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