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ACEM Primary Written > Endocrinology: Physiology - Hypothalamic and pituitary function > Flashcards

Endocrinology: Physiology - Hypothalamic and pituitary function Flashcards

1
Q

What is the hypothalamus (structurally)?

A

Anterior end of diencephalon lying below hypothalamic sulcus, in front of interpeduncular nuclei

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2
Q

How does the hypothalamus communicate with the anterior pituitary?

A

Via vascular connections (portal hypophysial vessels)

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3
Q

How does the hypothalamus communicate with the posterior pituitary?

A

Via neural connections

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4
Q

Where do the anterior and posterior pituitary arise from embryologically?

A

Anterior: pouch of Rathke (evagination from roof of pharynx)
Posterior: evagination of floor of third ventricle

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5
Q

What type of tissue composes most of the posterior pituitary?

A

Made up in large of axon endings arising from cell bodies in the supraoptic and paraventricular nuclei, and passing to the posterior pituitary via the hypothalamohypophysial tract

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6
Q

What hormones are secreted by the posterior pituitary?

A

Vasopressin
Oxytocin

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7
Q

What hormones are secreted by the anterior pituitary?

A

TSH
ACTH
FSH
LH
Prolactin
GH

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8
Q

Five regulatory functions of the hypothalamus

A
  1. Temperature regulation
  2. Neuroendocrine control
  3. Appetite behaviours
  4. Defensive reactions (fear, rage)
  5. Control of body rhythms
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9
Q

Eight hormones under neuroendocrine control of the hypothalamus

A
  1. Catecholamines
  2. Vasopressin
  3. Oxytocin
  4. TSH via TRH
  5. ACTH and B-LPH via CRH
  6. GH via somatostatin and GRH
  7. FSH and LH via GnRH
  8. Prolactin via PRH and PIH
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10
Q

What three “appetitive behaviours” are under hypothalamic control?

A
  1. Thirst
  2. Hunger
  3. Sexual behaviour
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11
Q

In what three organs is vasopressin produced?

A

CNS
Gonads
Adrenal cortex

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12
Q

In what two organs is oxytocin produced?

A

CNS
Thymus

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13
Q

What is the effect of hypothalamic control on prolactin secretion?

A

Predominantly inhibitory

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14
Q

What are the two physiologic effects of oxytocin?

A
  1. Induce contraction of myoepithelial cells lining breast ducts to induce milk ejection
  2. Induce contraction of uterine smooth muscle (enhanced by oestrogen, inhibited by progesterone) -> role in labour
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15
Q

Six hypophysiotropic hormones

A
  1. TRH
  2. CRH
  3. GnRH
  4. GRH
  5. Somatostatin
  6. PIH
    (postulated that PRH also exists)
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16
Q

From what part of the hypothalamus are the hypophysiotropic hormones secreted?

A

Median eminence

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16
Q

What pituitary hormones are released in response to TRH?

A

TSH
Prolactin

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17
Q

Release of which two pituitary hormones is inhibited by somatostatin?

A

TSH
GH

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18
Q

What is the function of B-LPH?

A

Unknown

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19
Q

What is Kallmann syndrome?

A

Congenital abnormality in the olfactory pathways which prevents the normal migration of GnRH neurons up the olfactory nerve
Presents as hypogonadotropic hypogonadism and anosmia

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20
Q

What is the normal morning oral temperature and how does this change throughout the day?

A

Normal morning oral temperature 36.3-37.1°C
Regular circadian fluctuation of 0.5-0.7°C
Lowest at 0600, highest in the evenings

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21
Q

What is the temperature of the scrotum?

A

Tightly regulated at 32°C

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22
Q

What is the relationship between rectal, oral and core temperature?

A

Rectal reflects core
Oral 0.5°C lower than rectal

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23
Q

What is the difference in basal temperature between children and adults?

A

Children typically 0.5°C higher

24
Q

What happens to basal temperature during ovulation?

A

Increases

25
Q

What are the three main mechanisms of heat production, and which is the major source of heat?

A
  1. Muscular activity (major heat source)
  2. Food intake
  3. Basic metabolic processes
26
Q

What are the four main mechanisms of heat loss and what % does each account for at 21°C?

A
  1. Radiation and conduction (70%)
  2. Vaporisation of sweat (27%)
  3. Respiratory (2%)
  4. Urination and defecation (1%)
27
Q

Which part of the pituitary regulates the response to heat, and which to cold?

A

Anterior pituitary responds to heat
Posterior pituitary responds to cold

28
Q

Five afferents to hypothalamus for body temperature information

A
  1. Skin
  2. Deep tissues
  3. Spinal cord
  4. Extrahypothalamic brain
  5. Hypothalamus itself
29
Q

What are the temperature thresholds for different temperature-regulating responses?

A

37°C: sweating, vasodilation
36.8°C: vasoconstriction
36°C: non-shivering, thermogenesis
35.5°C: shivering

30
Q

At what body temperature is the ability to spontaneously return temperature to normal lost?

A

28°C

31
Q

What body temperatures are survivable without permanent ill effects?

A

21-24°C

32
Q

Five secretory cell types in the anterior pituitary by percentage. What other cell types are in the pituitary?

A

Secretory cells:
1. Somatotropes (50%)
2. Lactotropes (10-30%)
3. Gonadotropes (20%)
4. Corticotropes (10%)
5. Thyrotropes (5%)

Others:
1. Folliculostellate cells (regulate growth and function of secretory cells
2. Pluripotent stems cell (responsible for pituitary plasticity over lifetime)

33
Q

How much of growth hormone circulates in bound form?

A

50%

34
Q

Normal plasma level of growth hormone (bound and unbound)

A

<3ng/dL

35
Q

Half-life of GH

A

6-20mins

36
Q

Where is growth hormone metabolised?

A

Liver

37
Q

What type of receptor is the growth hormone receptor?

A

Cytokine receptor (extracellular, transmembrane, and intracellular portions -> downstream intracellular signalling cascade)

38
Q

Seven direct and four indirect effects of growth hormone

A

Direct:
1. Increased Ca+ intestinal absorption
2. Na+/K+ retention
3. Lipolysis (increased free fatty acids)
4. Protein synthesis (increased PO43-, decreased Ur and AAs)
5. Decreased sensitivity to insulin
6. Epiphysial growth
7. IGF-1 release

Indirect via IGF-1:
1. Antilipolytic activity
2. Insulin-like activity
3. Protein synthesis
4. Epiphysial growth

39
Q

What are the effects of GH-stimulated increased protein synthesis on biochemistry?

A

Increased phosphate and nitrogen balance
Decreased blood urea nitrogen and circulating amino acids

40
Q

What is the role of IGF-II?

A

Somatomedin which regulates growth during foetal development

41
Q

Describe the feedback control seen with GH

A

GH inhibits GRH release from hypothalamus
IGF-1 inhibits GH release from anterior pituitary, and stimulates somatostatin release from hypothalamus

42
Q

What broad groups of factors increase GH secretion?

A
  1. Actual or threatened decrease in substrate available for intracellular energy production
  2. Conditions in which certain amino acids are increased
  3. Stressful stimuli
  4. Certain hormones
43
Q

Fifteen factors which stimulate growth hormone secretion

A
  1. Hypoglycaemia
  2. 2-deoxyglucose
  3. Fasting
  4. Exercise
  5. Going to sleep
  6. Increase in certain AAs (e.g. Arginine)
  7. Protein meal
  8. Ghrelin
  9. Glucagon
  10. Vasopressin
  11. Oestrogens and androgens
  12. L-Dopa and a-adrenergic agonists
  13. Dopamine receptor agonists
  14. Stressful stimuli
  15. Pyrogens
44
Q

Six factors which inhibit growth hormone secretion

A
  1. Glucose
  2. FFAs
  3. REM sleep
  4. Cortisol
  5. Medroxyprogesterone
  6. GH and IGF-1
45
Q

Half-life of FSH

A

170mins

46
Q

Half-life of LH

A

60mins

47
Q

Half-life of prolactin

A

20mins

48
Q

What is prolactin inhibiting hormone?

A

Dopamine

49
Q

What type of receptors are FSH and LH receptors?

A

GPCRs

50
Q

What kind of receptor is the prolactin receptor?

A

Cytokine receptor

51
Q

Two effects of FSH

A
  1. Stimulate Sertoli cells in testes to maintain spermatogenic epithelium
  2. Early growth of ovarian follicle
52
Q

Five effects of LH

A
  1. Tropic for Leydig cells (produce testosterone in testes)
  2. Maturation of ovarian follicles and oestrogen secretion from them
  3. Initial formation of corpus luteum
  4. Progesterone secretion
  5. Ovulation
53
Q

What is the effect of prolactin on FSH/LH?

A

Inhibits
Prevents ovulation

54
Q

Five factors that increase prolactin secretion

A
  1. Exercise
  2. Stress
  3. Nipple stimulation
  4. Pregnancy (peaks at parturition)
  5. Chlorpromazine and other dopamine receptor blockers
55
Q

Two factors that decrease prolactin secretion

A
  1. L-dopa and dopamine agonists (e.g. bromocriptine)
  2. Prolactin (negative feedback loop)
56
Q

What is Sheehan syndrome?

A

Hypopituitarism caused by pituitary infarct and necrosis as a result of shock secondary to massive postpartum haemorrhage
Vascular supply to anterior pituitary is already vulnerable, and moreso in pregnancy as the pituitary is enlarged

57
Q

Three causes of hypopituitarism?

A
  1. Infarct (e.g. Sheehan syndrome)
  2. Tumour
  3. Suprasellar cyst (compression)

ACEM Primary Written (150 decks)

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