Hypothalamo-adenohypophysial System Flashcards
What is the bony shelf that the pituitary is found in?
Sella Turcica
Describe the embryological origin of the pituitary gland.
Adenohypophysis: derived from glandular tissue. Buccal cavity has an extension grows upwards ( in utero) Neurohypophysis: derived from neural tissue.
Which ventricle is the hypothalamus located near?
3rd ventricle
What are the two areas of the brain that are useful anatomical markers for distinguishing the posterior pituitary from the anterior?
Anterior - optic chiasma Posterior - mammillary body
What are hypothalamic nuclei?
They are groups of neuronal cell bodies that can be grouped functionally.
Where is the median eminence?
It is located between the pituitary stalk and the hypothalamus.
Describe the blood supply in the pituitary gland.
The primary capillary plexus is found in the median eminence. It is connected, via the hypothalamo-hypophysial portal system to the secondary capillary plexus in the adenohypophysis. The blood from the secondary capillary plexus drains via the cavernous sinus and out via the jugular veins. NOTE: primary capillary plexus comes from the superior hypophysial artery
What is a key feature of the primary capillary plexus?
The capillary is fenestrated (there are small holes in it)
Describe how the hypothalamus exerts control over the adenohypophysis.
Some neurones from the hypothalamus terminate on the median eminence at the primary capillary plexus. The neurosecretions released by these neurones are hormones that travel via the hypothalamo-hypophysial system to the secondary capillary plexus where they stimulate the secretion of adenohypophysial hormones.
What are the FIVE types of adenohypophysial cells and what hormones do they produce?
Somatotrophs - somatotrophin Lactotrophs - prolactin Gonadotrophs - LH and FSH Thyrotrophs - Thyrotrophin Corticotrophs - corticotrophin (ACTH)
What are the THREE types of adenohypophysial hormone? Give examples of each.
- Protein - somatotrophin + prolactin
- Glycoprotein - FSH + LH + (TSH) thyrotrophin
- Polypeptide - ACTH
- NOTE: Glycoproteins have an alpha chain and a beta chain. They all have the same alpha chain but have different beta chains.
State the EIGHT hypothalamic hormones and the adenohypophysial hormones that they control.
Somatotrophin releasing hormone + somatostatin = somatotrophin Dopamine + Thyrotrophin releasing hormone = prolactin Gonadotrophin releasing hormone + gonadotrophin inhibitory hormone = FSH + LH Thyrotrophin releasing hormone = thyrotrophin Corticotrophin releasing hormone + vasopressin = corticotrophin
State the tissues that the FIVE adenohypophysial hormones act on.
Somatotrophs - most cell (hepatocytes in particular) Prolactin - breasts in lactating women Gonadotrophin - gonads Thyrotrophin - thyroid Corticotrophin - adrenal cortex
Describe the two modes of action of somatotrophin.
Somatotrophin can act directly on tissues by binding to somatotrophin receptors or it can act on hepatocytes and stimulate hepatocytes to produce IGF 1, which is particularly important in growth
What are LH and FSH examples of?
Gonadotrophins
What has a negative feedback effect on somatotrophin?
Somatotrophin itself and somatomedins have a negative feedback effect on somatotrophin production.
What stimulates somatotrophin release?
Sleep, stress, oestrogens, exercise, fasting (hypoglycaemia), amino acids
What is the main effects of prolactin?
MAIN EFFECT: - Prolactin stimulated lactogenesis in the breast Other effects: - effects immune system ( stimulates T cells) - lowers LH release ( pituitary) - upregulates LH receptors in ovaries and testes
What are some other effects of prolactin?
Prolactin is also a natural contraceptive as it inhibits LH release. It also upregulates LH receptors in the gonads. It decreases sexual behaviour and has effects on the immune system.
Describe the neuroendocrine reflex of prolactin.
There are tactile receptors in the nipple that are stimulated by the suckling of the baby and has an afferent pathway to the hypothalamus and stimulates the release of thyrotrophin releasing hormone and inhibits dopaminergic neurones. Prolactin starts the synthesis of milk for the next suckling period.
What are the metabolic Actions on growth hormone ?
- Stimulation of amino acids transport into cells
- Stimulation of protein synthesis
- Increased cartilaginous growth
- Increased lipolysis and fatty acid production
- Decreased glucose utilisation resulting resulting in increased blood concentration
How is growth hormone ( somatrophin) regulated?
ON/OFF Mechanism GHRF (growth hormone releasing hormone) stimulates the release of GH Somatostatin inhibits the release of GH
How is prolactin controlled ?
Dopamine inhibits prolactin secretion TRH stimulates prolactin secretion
How is TSH(thyroid stimulating hormone) regulated ?
TRH ( thyrotropin releasing hormone) stimulates TSH( thyroid stimulating hormone) release
What 2 hormones does GnRH ( gonatrophin releasing hormone) stimulate?
LH(luteinising hormone) FSH (Follicle stimulating hormone)
What 2 hormones stimulate ACTH (corticotrophin)?
CRH (Corticotrophin releasing hormone) Vasopressin (VP)
What are the main somatomedins used to mediate growth?
IGF I
Hat are the target cells of the 6 adenohypophysial hormones?
GH = general body tissue , particularly liver Prolactin= breasts Thyrotrophin = thyroid Gonadotrophins (LH and FSH) = testes( produce testosterone) and ovaries (regulate menstrual cycle) Corticotrophin = adrenal cortex
What are the 2 main parts of the adenohypophysis?
Pars distalis and pars tuberalis
What cells do the neurohypophysis and adenohypophysis derive from?
Adenohypophysis = mouth Neurohypophysis = neural tissue
How are hypothalamic hormones released?
In pulses
Why is it said that somatotrophin has an auto negative feedback loop?
It has negative feedback effects back in the hypothalamus
What inhibits somatotrophin?
Directly -GH + IGF 1 back to the pituitary Indirectly - IGF 1 back to the hypothalamus
Draw the hypothalamo-adenohypophyisial axis for GH
Draw the hypothalamo-adenohypophyisial axis for prolactin
Draw the hypothalamo-adenohypophyisial axis for thyroid hormones
Draw the hypothalamo-adenohypophyisial axis for cortisol
