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Regulatory Physiology and Pharmacology > The Hypothalamus-Pituitary Complex > Flashcards

The Hypothalamus-Pituitary Complex Flashcards

1
Q

What does the HP axis regulate?

A

The function of the thryoid, adrenal and reproductive glands

Growth, lactation, milk secretion and water metabolism

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2
Q

Where is the pituitary?

A

In a pocket of bone at the base of the brain below the hypothalamus close to the medial eminence
Connected to hypothalamus and is connected by a stalk containing nerve fibres and blood vessels

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3
Q

What are the key features of the anterior and posterior pituitary?

A

Anterior - unique blood supply where releasing factors are secreted into from the hypothalamus
Posterior - blood portal system takes hormones away with direct hormonal secretion from the posterior - not synthesised there however

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4
Q

What is the key role of the posterior pituitary?

A

body fluid homeostasis and reproductive function

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5
Q

Where are hormones synthesised for secretion by the posterior pituitary?

A

Magnocellular neurons secrete directly into pituitary
Paraventricular nuclei - oxytocin
Supraoptic nuclei - ADH

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6
Q

What are the pre-prohormones of the posterior pituitary?

A

preprovasophysin

preprooxyphysin

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7
Q

What are Herring Bodies?

A

Axonal swellings due to the storage of secretory granules

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8
Q

What are the main functions of ADH?

A

Maintenance of normal osmolarity of body fluids

Normal blood volume

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9
Q

What are the primary targets of ADH?

A

Cells lining the distal renal tubule

Principle cells of the collecting ducts in the kidney

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10
Q

How does ADH act on the signalling pathways?

A

Binds to V2Rs on basal side of renal cells
V2R is linked to Gs-cAMP-PKA pathway
Stimulates insertion of Aquaporin 2 to apical membrane
Enhances trans-epithlial flow of water from lumen to renal interstitium

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11
Q

What happens in the presence of ADH?

A

Urine flow decreases

Urine Osmolality increases

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12
Q

What is ADH released in response to?

A

increased EC fluid osmolality

decreased blood volume and pressure

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13
Q

How do osmoreceptive neurons respond to changes in osmolality?

A

Respond to changes by shrinking or swelling
Innervate magnocellular neurons of PVN and SON
Increased osmolality stimulates ADH releases

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14
Q

How is blood volume regulated?

A

Cardiovascular volume receptors in the atria

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15
Q

What is the function of oxytocin?

A

stimulates the contraction of uterine smooth muscle during labour

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16
Q

What is the positive feedback mechanism related to oxytocin?

A

Stretching of the cervix stimulates oxytocin release which in turn facilitates labour further as a neuroendocrine reflex
After birth, stretching of cervix lessens, breaking the cycle

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17
Q

How is the anterior pituitary connected to the hypothalamus?

A

hypophyseal portal circulation

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18
Q

What kind of hormones are produced in the anterior pituitary?

A

tropic

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19
Q

What hormones does the anterior pituitary produce?

A 
Prolactin
GH
ACTH
TSH
FSH
LH
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20
Q

How are hormones released from the pituitary?

A

paravicellular neurosecretory cells secrete releasing factors into the capillaries of the pituitary portal system at the median eminance

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21
Q

What are the releasing factors associated with the hormones released?

A 
CRH - ACTH
TRH - TSH
GHRH - GH
Somatostatin - inhibits GH
GnRH - FSH, LH
PRH - Prolactin
Dopamine - inhibits prolactin
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22
Q

What percentage of cells are corticotrophs and what are their target organs?

A

15-20% - adrenal glands, adipocytes and melanocytes

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23
Q

What percentage of cells are thryotrophs and what are their target organs?

A

3-5% - thyroid gland

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24
Q

What percentage of cells are gonadotrophs and what are their target organs?

A

10-15% - Gonads

25
Q

What percentage of cells are somatotrophs and what are their target organs?

A

40-50% - All tissues, liver

26
Q

What percentage of cells are lactotrophs and what are their target organs?

A

10-15% - breasts, gonads

27
Q

What is the key feature of the feedback regulation in the HP-axis?

A

the ability of hypothalamic releasing hormones to provide negative feedback on the system

28
Q

What is TSH?

A

a glycoprotein heterodimer composed of an a and b subunit

29
Q

Where does TSH bind?

A

thyroid epithelial cells with TSH receptors

30
Q

How is TRH released?

A

according to diurnal rhythm and regulated by various stresses i.e. starvation

31
Q

What does T3 negatively feedback on?

A

the thyrotropes and TRH-producing neurons

32
Q

What is the role of thyroid hormone?

A

regulates the body energy metabolism
maturation
growth
development

33
Q

What are the main targets for thyroid hormone?

A

brain, muscle, cardiovascular system and reproductive tissue

34
Q

How does GH act on tissues?

A

directly on peripheral tissues and indirectly via IGF-1

35
Q

What are the main sites for GH degradation?

A

Kidney and Liver

36
Q

How is GH secretion regulated?

A

GHRH stimulates release

Somatostatin inhibits GH and TSH

37
Q

How might b-adrenergic receptors inhibit GH secretion?

A

stimulate somatostatin which inhibits GH

38
Q

What are the pathological conditions involving GH?

A

dwarfism, gigantism, acromegaly

39
Q

How is ACTH synthesised?

A

CRH promotes POMC gene expression which produces ACTH by proteolytic processing

40
Q

What is the role of ACTH?

A

to regulate the stress response by regulating the adrenal cortex and the synthesis of adrenocorticosteroids

41
Q

What is a-MSH?

A

the first 13 aa in ACTH which stimulate melanocytes and can darken skin when ACTH is over-produced

42
Q

How is ACTH regulated?

A

CRH, ADH, stress, hypoglycaemia

ADH via inferior hypophyseal artery from pituitary

43
Q

How is ACTH secreted?

A

according to circadian rhythm although can be altered by jetlag
Stress both neurogenic and systemic stimulate ACTH secretion

44
Q

How does cortisol act to negatively regulate ACTH?

A

negatively feedback on pituitary reducing POMC expression and hypothalamus reducing pro-CRH gene expression and CRH release

45
Q

What is Cushing’s disease?

A

a benign tumour of the pituitary gland that produces a large amount of ACTH causing adrenal glands to produce elevated levels of cortisol

46
Q

What does increased cortisol secretion do?

A

causes a tendency:
weight gain characteristically in centripetal fat distribution
wasting of extremities, bruising easily and healing poorly
buffalo humo
moon face
high BP, severe fatigue and muscle weakness

47
Q

What regulates LH?

A

GnRH

48
Q

What regulates FSH?

A

GnRH and Inhibin cause distinct patterns of LH and FSH secretion

49
Q

When does GnRH preferentially increase LH?

A

at one pulse per hour

50
Q

When does GnRH preferentially increase FSH?

A

at 1 pulse per 3 hours

51
Q

What are the different feedback mechanisms for LH and FSH in men and women?

A

men - testosterone on pituitary and hypothalamus
women - progesterone on pituitary and hypothalamus
oestrogen on FSH and LH secretion
Inhibin negatively feedsback on FSH in men and women

52
Q

What is the action of LH in men?

A

stimulates leydig cells to synthesise testosterone

53
Q

What is the action of LH in women?

A

acts on theca cells to produce testosterone which is converted to oestrogen by granulosa cells

54
Q

What is the function of FSH in women?

A

stimulates maturation of ovarian follicles

55
Q

what is the function of FSH in men?

A

supports the function of the sertoli cells which support aspects of sperm cell maturation

56
Q

How are FSH and LH regulated?

A

dopamine, endorphins and prolactin all inhibit GnRH release

57
Q

What can overproduction of prolactin cause and how might this be treated?

A

amenorrhea

treat with bromocryptine or surgical removal of tumour

58
Q

What stimulates ovulation?

A

high plasma estadiol which stimulates GnRH and LH surge

59
Q

How is prolactin different from other endocrine cells in the anterior pituitary?

A

acts on non-endocrine cells to induce physiological changes

secretion is mainly under inhibitory control by the hypothalamus

Regulatory Physiology and Pharmacology (14 decks)

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