Hypothalamo-adenohypophysial system

Question 1

Where is the pituitary located?

Answer 1

base of brain, between hypothalamus and pineal gland

in bony cavity - sella turcica

Question 2

Anatomy of pituitary tumours?

Answer 2

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

Question 3

What surrounds the 3rd ventricle?

Answer 3

hypothalamus

Question 4

What distinguishes the front from the back?

Answer 4

optic chiasma and mammillary bodies

Question 5

What is the anterior adenohypophysis?

Answer 5

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

Question 6

What does the adenohypophysis need to function?

Answer 6

blood supply

Question 7

What is the posterior neurohypophysis?

Answer 7

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

Question 8

What are the hypothalamic nuclei?

Answer 8

neuronal cells bodies bundled functionally

Question 9

What is the region of the median eminence?

Answer 9

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

Question 10

What artery supplies the pituitary?

Answer 10

superior hypophysial artery

Question 11

How does blood exit pituitary?

Answer 11

cavernous sinus –> jugular veins

Question 12

What is the structure of the primary capillary plexus?

Answer 12

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

Question 13

What system exists in the pituitary?

Answer 13

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

Question 14

How is anterior pituitary controlled?

Answer 14

by hormones released in the median eminence by neurones in hypothalamus

Question 15

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

Answer 15

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

Question 16

STEP 2 of hypothalamic control?

Answer 16

HYPOTHALAMIC NEUROSECRETION FROM BLOOD TO CELLS

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

Question 17

STEP 3 of hypothalamic control?

Answer 17

RELEASE OF ADENOHYPOPHYSIAL HORMONE

- adenohypophysial cells release hormones into circulation by exocytosis

Question 18

What controls the anterior pituitary ?

Answer 18

hypothalamus

Question 19

Somatotrophs?

Answer 19

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

Question 20

Lactotrophs?

Answer 20

prolactin

breasts (lactating women), little effect in men

Question 21

Gonadotrophins?

Answer 21

LH and FSH

tested and ovaries (menstrual cycle)

Question 22

Corticotrophs?

Answer 22

ACTH (corticotrophin)

adrenal cortex

Question 23

Thyrotrophs?

Answer 23

thyrotrophin (TSH)

thyroid

Question 24

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

Answer 24

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

Question 25

What do adenohypophysis cells also do?

Answer 25

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

Question 26

What classification of hormones made in the adenohypophysis?

Answer 26

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)

Question 27

What controls adenohypophysial hormones?

Answer 27

hypothalamic hormones

Question 28

Control of somatotrophin?

Answer 28

``` STIMULATE somatotrophin releasing hormone growth hormone releasing hormone INHIBIT somatostatin ```

Question 29

Control of prolactin?

Answer 29

STIMULATE thyrotrophin releasing hormone INHIBIT dopamine

Question 30

Control of thyrotrophin?

Answer 30

STIMULATE | TRH

Question 31

Control of LH and FSH?

Answer 31

STIMULATE Gonadotrophin releasing hormone (GnRH) INHIBIT GnIH

Question 32

Control of corticotrophin (ACTH)?

Answer 32

STIMULATE corticotrophin releasing hormone vasopressin

Question 33

What is special about prolactin?

Answer 33

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

Question 34

Describe the GH axis?

Answer 34

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

Question 35

What is the significance of 2 GH pathways?

Answer 35

GH controls large aspects of metabolism

Question 36

What is the liver in the GH axis?

Answer 36

main GH target and also has an endocrine function

Question 37

Why does GH increase risk of diabetes?

Answer 37

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

Question 38

What stimulates GH production?

Answer 38

``` 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) ```

Question 39

Why do glucogenic amino acids stimulate GH production?

Answer 39

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

Question 40

Explain the action of prolactin?

Answer 40

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

Question 41

What does suckling do?

Answer 41

increase prolactin release | suppression of hypothalamic dopaminergic neurones by suckling

Question 42

What pathway is involved in prolactin regulation?

Answer 42

neuro-endocrine reflex pathway

Question 43

What happens to prolactin when afferent pathway stimulated?

Answer 43

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