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Endocrinology > Hypothalamo-adenohypophysial system > Flashcards

Hypothalamo-adenohypophysial system Flashcards

1
Q

Where is the pituitary located?

A

base of brain, between hypothalamus and pineal gland

in bony cavity - sella turcica

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2
Q

Anatomy of pituitary tumours?

A

may protrude out towards the brain and go through bone if very malignant
tumour generally constrained by walls of bony cavity

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3
Q

What surrounds the 3rd ventricle?

A

hypothalamus

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4
Q

What distinguishes the front from the back?

A

optic chiasma and mammillary bodies

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5
Q

What is the anterior adenohypophysis?

A

glandular tissue
in buccal cavity (pharyngeal region of mouth)
extension grows upwards
secretory cells

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6
Q

What does the adenohypophysis need to function?

A

blood supply

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7
Q

What is the posterior neurohypophysis?

A 
nervous tissue (nerve axons, terminals)
mainly made of axons 
cell bodies in hypothalamus
moves down from developing hypothalamus
fuse and lose contact with buccal cavity
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8
Q

What are the hypothalamic nuclei?

A

neuronal cells bodies bundled functionally

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9
Q

What is the region of the median eminence?

A

area between the top of the pituitary stalk and hypothalamus
= mass of capillaries receiving blood from the superior hypophysial artery
some axons terminate here

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10
Q

What artery supplies the pituitary?

A

superior hypophysial artery

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11
Q

How does blood exit pituitary?

A

cavernous sinus –> jugular veins

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12
Q

What is the structure of the primary capillary plexus?

A

fenestrated
neurones from hypothalamic nuclei terminate on walls of plexus
median eminence outside blood brain barrier therefore holes to allow diffusion of substances

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13
Q

What system exists in the pituitary?

A

hypothalamo-hypophysial portal system

primary plexus feeds blood down portal vessels running through pituitary stalk and terminate in adenohypophysis where the secondary plexus is located

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14
Q

How is anterior pituitary controlled?

A

by hormones released in the median eminence by neurones in hypothalamus

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15
Q

What is STEP 1 of hypothalamic control via hypothalamo-hypophysial portal system?

A

HYPOTHALAMIC SECRETION

  • activated hypothalamic neurones release hormones from nerve endings in ME into primary plexus capillaries
  • portal system carries chemical to anterior pituitary
  • hormones released in PULSES
  • PLEXUS IS FENESTRATED TO ALLOW ENTRY OF NEUROSECRETIONS
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16
Q

STEP 2 of hypothalamic control?

A

HYPOTHALAMIC NEUROSECRETION FROM BLOOD TO CELLS

  • hormones bind to target cells in anterior pituitary
  • stimulates their function
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17
Q

STEP 3 of hypothalamic control?

A

RELEASE OF ADENOHYPOPHYSIAL HORMONE

- adenohypophysial cells release hormones into circulation by exocytosis

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18
Q

What controls the anterior pituitary ?

A

hypothalamus

19
Q

Somatotrophs?

A

somatotrophin (GH)
general body tissues (childhood, puberty)
liver –> somatomedins (IGF I and II)

20
Q

Lactotrophs?

A

prolactin

breasts (lactating women), little effect in men

21
Q

Gonadotrophins?

A

LH and FSH

tested and ovaries (menstrual cycle)

22
Q

Corticotrophs?

A

ACTH (corticotrophin)

adrenal cortex

23
Q

Thyrotrophs?

A

thyrotrophin (TSH)

thyroid

24
Q

What is the process of production of the hormones of the adenohypophysis?

A

made as prohormones
cleaved enzymatically to give bioactive hormone
stored in secretory granules and released by exocytosis

25
Q

What do adenohypophysis cells also do?

A

undefined function
or produce molecules with para or autocrine effects
(POMC –> ACTH + pro-gMSH +bLPH)

26
Q

What classification of hormones made in the adenohypophysis?

A

most proteins - GH (191), prolactin (199)
middle glycoproteins
- same a subunit different b subunit that determines characteristics (thyrotrophin has B subunit of 110), (LH and FSH 115)
least are polypeptides (corticotrophin 39)

27
Q

What controls adenohypophysial hormones?

A

hypothalamic hormones

28
Q

Control of somatotrophin?

A 
STIMULATE
somatotrophin releasing hormone
growth hormone releasing hormone
INHIBIT
somatostatin
29
Q

Control of prolactin?

A

STIMULATE
thyrotrophin releasing hormone
INHIBIT
dopamine

30
Q

Control of thyrotrophin?

A

STIMULATE

TRH

31
Q

Control of LH and FSH?

A

STIMULATE
Gonadotrophin releasing hormone (GnRH)
INHIBIT
GnIH

32
Q

Control of corticotrophin (ACTH)?

A

STIMULATE
corticotrophin releasing hormone
vasopressin

33
Q

What is special about prolactin?

A

it is under tonic inhibition by dopamine to keep in normal range

34
Q

Describe the GH axis?

A

adenohypophysis –> somatotrophin (GH)
this directly binds to body tissues

or GH binds to hepatocytes in liver and stimulates production of hormones (somatomedins IGF I and II)
these have an indirect effect on body tissues

both pathways stimulate AA transport into the cell to cause muscle and protein synthesis

35
Q

What is the significance of 2 GH pathways?

A

GH controls large aspects of metabolism

36
Q

What is the liver in the GH axis?

A

main GH target and also has an endocrine function

37
Q

Why does GH increase risk of diabetes?

A

increase gluconeogenesis
stimulate lipolysis and increase fatty acid production
increase cartilaginous growth and somatic cell growth
decrease glucose use and increase blood glucose

38
Q

What stimulates GH production?

A 
sleep (stage III, IV)
stress
oestrogens
exercise
fasting (hypoglycaemia is a biological stresser) - GH functions to increase blood glucose so is stimulated
amino acids (arginine)
39
Q

Why do glucogenic amino acids stimulate GH production?

A

after meal there is increased amino acids movement into cells to increase protein synthesis at a nuclear level

40
Q

Explain the action of prolactin?

A

causes breast lactogenesis post-partum
inhibit LH release from pituitary (natural contraceptive so that mother not pregnant whilst suckling)
increase LH receptors in gonads
decrease sexual behaviour
enhance immune system (stimulate T cells)
steroidogenesis
renal Na and water reabsorption

41
Q

What does suckling do?

A

increase prolactin release

suppression of hypothalamic dopaminergic neurones by suckling

42
Q

What pathway is involved in prolactin regulation?

A

neuro-endocrine reflex pathway

43
Q

What happens to prolactin when afferent pathway stimulated?

A

dopaminergic neurones inhibited
TRH stimulated
lactrotrophs release prolactin
suppression of hypothalamic dopaminergic neurones by suckling

Endocrinology (13 decks)

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