The Hypothalamus-Pituitary Complex Flashcards Preview

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

Flashcards in The Hypothalamus-Pituitary Complex Deck (59):
1

What does the HP axis regulate?

The function of the thryoid, adrenal and reproductive glands
Growth, lactation, milk secretion and water metabolism

2

Where is the pituitary?

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

3

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

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

4

What is the key role of the posterior pituitary?

body fluid homeostasis and reproductive function

5

Where are hormones synthesised for secretion by the posterior pituitary?

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

6

What are the pre-prohormones of the posterior pituitary?

preprovasophysin
preprooxyphysin

7

What are Herring Bodies?

Axonal swellings due to the storage of secretory granules

8

What are the main functions of ADH?

Maintenance of normal osmolarity of body fluids
Normal blood volume

9

What are the primary targets of ADH?

Cells lining the distal renal tubule
Principle cells of the collecting ducts in the kidney

10

How does ADH act on the signalling pathways?

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

11

What happens in the presence of ADH?

Urine flow decreases
Urine Osmolality increases

12

What is ADH released in response to?

increased EC fluid osmolality
decreased blood volume and pressure

13

How do osmoreceptive neurons respond to changes in osmolality?

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

14

How is blood volume regulated?

Cardiovascular volume receptors in the atria

15

What is the function of oxytocin?

stimulates the contraction of uterine smooth muscle during labour

16

What is the positive feedback mechanism related to oxytocin?

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

17

How is the anterior pituitary connected to the hypothalamus?

hypophyseal portal circulation

18

What kind of hormones are produced in the anterior pituitary?

tropic

19

What hormones does the anterior pituitary produce?

Prolactin
GH
ACTH
TSH
FSH
LH

20

How are hormones released from the pituitary?

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

21

What are the releasing factors associated with the hormones released?

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

22

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

15-20% - adrenal glands, adipocytes and melanocytes

23

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

3-5% - thyroid gland

24

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

10-15% - Gonads

25

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

40-50% - All tissues, liver

26

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

10-15% - breasts, gonads

27

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

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

28

What is TSH?

a glycoprotein heterodimer composed of an a and b subunit

29

Where does TSH bind?

thyroid epithelial cells with TSH receptors

30

How is TRH released?

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

31

What does T3 negatively feedback on?

the thyrotropes and TRH-producing neurons

32

What is the role of thyroid hormone?

regulates the body energy metabolism
maturation
growth
development

33

What are the main targets for thyroid hormone?

brain, muscle, cardiovascular system and reproductive tissue

34

How does GH act on tissues?

directly on peripheral tissues and indirectly via IGF-1

35

What are the main sites for GH degradation?

Kidney and Liver

36

How is GH secretion regulated?

GHRH stimulates release
Somatostatin inhibits GH and TSH

37

How might b-adrenergic receptors inhibit GH secretion?

stimulate somatostatin which inhibits GH

38

What are the pathological conditions involving GH?

dwarfism, gigantism, acromegaly

39

How is ACTH synthesised?

CRH promotes POMC gene expression which produces ACTH by proteolytic processing

40

What is the role of ACTH?

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

41

What is a-MSH?

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

42

How is ACTH regulated?

CRH, ADH, stress, hypoglycaemia
ADH via inferior hypophyseal artery from pituitary

43

How is ACTH secreted?

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

44

How does cortisol act to negatively regulate ACTH?

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

45

What is Cushing's disease?

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

46

What does increased cortisol secretion do?

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

What regulates LH?

GnRH

48

What regulates FSH?

GnRH and Inhibin cause distinct patterns of LH and FSH secretion

49

When does GnRH preferentially increase LH?

at one pulse per hour

50

When does GnRH preferentially increase FSH?

at 1 pulse per 3 hours

51

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

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

What is the action of LH in men?

stimulates leydig cells to synthesise testosterone

53

What is the action of LH in women?

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

54

What is the function of FSH in women?

stimulates maturation of ovarian follicles

55

what is the function of FSH in men?

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

56

How are FSH and LH regulated?

dopamine, endorphins and prolactin all inhibit GnRH release

57

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

amenorrhea
treat with bromocryptine or surgical removal of tumour

58

What stimulates ovulation?

high plasma estadiol which stimulates GnRH and LH surge

59

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

acts on non-endocrine cells to induce physiological changes
secretion is mainly under inhibitory control by the hypothalamus