2 - Hypothalamo-adenohypophysial system Flashcards
What is another name for the pituitary?
the hypophysis
Where is the hypothalamus?
just above the pituitary
What is the embryological origin of the adenohypophysis?
derived from glandular tissue
- a few weeks after conception, the Buccal cavity has an extension that starts to grow upwards
What is the embryological origin of the neurohypophysis?
derived from neural tissue
- a few weeks after conception, there is downwards movement of tissue from the developing hypothalamus
How do the 2 parts of the pituitary come together during development?
the 2 (different) tissues fuse and lose contact with the buccal cavity
What are nuclei in the hypothalamus?
clusters of cell bodies (neuronal somas) with an axon sticking out
What mainly makes up the neurohypophysis?
nerve axons
Where do the axons that stem from the nuclei terminate?
most terminate in the neurohypophysis, but some terminate in the median eminence
What is the median eminence?
Where does its blood supply come from?
a mass of capillaries receiving blood from the superior hypophysial artery
Describe the hypothalamus-hypophysial portal circulation?
What is involved and how does the blood travel through it?
PRIMARY CAPILLARY PLEXUS
- neurones coming from the hypothalamic nuclei terminate here
- blood from here feeds down into portal vessels which run down through the pituitary stalk to terminate within the adenohypophysis (the secondary capillary plexus)
SECONDARY CAPILLARY PLEXUS
- blood from here drains via the cavernous sinus and out via the jugular veins
Where are the primary and secondary capillary plexuses?
primary - the the median eminence
secondary - the anterior pituitary
What type of capillaries make up the primary capillary plexus?
fenestrated capillaries
since the median eminence lies outside the blood-brain barrier
What chemicals are released from the neurones that terminate in the median eminence?
hormones (they travel in the blood to the sedentary capillary plexus in the AP, and stimulate it to release hormones)
List the 5 adenohypophysial hormones?
somatotrophin (growth hormone) prolactin thyrotrophin LH and FSH ACTH (corticotrophin)
For somatotrophin (growth hormone):
1) What adenohypophysial cell releases it?
2) What is the hypothalamic hormone that stimulates its release?
3) What is the hypothalamic hormone that inhibits its release?
4) What is its target cell?
1) somatotrophs
2) Somatotrophin Releasing Hormone/growth hormone releasing hormone (GHRH)
3) somatostatin
4) targets general body tissues, especially the liver
For prolactin:
1) What adenohypophysial cell releases it?
2) What is the hypothalamic hormone that stimulates its release?
3) What is the hypothalamic hormone that inhibits its release?
4) What is its target cell?
1) lactotrophs
2) Thyrotrophin Releasing Hormone (TRH)
3) dopamine
NOTE: dopamine is the main regulating hormone
4) breasts (of lactating women)
For Thyroid Stimulating Hormone:
1) What adenohypophysial cell releases it?
2) What is the hypothalamic hormone that stimulates its release?
3) What is its target cell?
1) thyrotrophs
2) TRH (thyrotrophin releasing hormone)
3) thyroid
For LH and FSH:
1) What adenohypophysial cell releases them?
2) What is the hypothalamic hormone that stimulates their release?
3) What is the target cell?
1) gonadotrophs
2) Gonadotrophin Releasing Hormone (GnRH)
3) testes (men) and ovaries (women)
For ACTH:
1) What adenohypophysial cell releases it?
2) What is the hypothalamic hormone that stimulates its release?
3) What is its target cell?
1) corticotrophs
2) Corticotrophin Releasing Hormone (CRH) and Vasopressin
3) adrenal cortex
Give an example of hormone production from a prohormone?
POMC—–>ACTH + Pro-MSH
MSH = mealnocyte stimulating hormone
What stimulates the release of prolactin?
Thyrotrophin Releasing Hormone
it is controlled by the production of thyrotrophin from the AP
List the hypothalamic hormones that are dominant over their counterpart
- somatotrophin releasing hormone/GHRH is dominant over somatostatin
- dopamine is dominant over TRH (thyrotrophin releasing hormones)
- GnRH is dominant over its inhibitory counterpart
What stimulates somatotrophin (non-hormones)?
GHRELIN hypoglycaemia amino acids stress sleep oestrogens exercise
What are the inhibitors of somatotrophin (non hormone)?
IGF 1
- direct - to pituitary
- indirect - to the hypothalamus
somatotrophin also has its own negative feedback effects
