Lecture 1 + 2 - 2018 Flashcards
What does the hypothalamus do?
It secretes hormones involved in: fluid balance, smooth muscle contraction, and the control of hormone secretion by the anterior pituitary gland.
What does the pituitary gland do?
It secretes multiple hormones that regulate: endocrine activities of the adrenal cortex, thyroid gland, reproductive organs and a hormone that stimulates melanin production.
Describe the embryonic development of the hypothalamus?
The hypothalamus came from the diencephalon which came from the forebrain.
Describe the embryonic development of the anterior pituitary gland?
It is derived from the ectoderm of the primitive mouth cavity, it develops into two parts:
- Pars distalis.
- Pars tuberalis.
Describe the embryonic development of the posterior pituitary gland?
It is a downward externsion of the floor of the brain (hypothalamus). It becomes the pars nervosa.
Describe the hormonal feedback control of the hypothalamus and anterior pituitary?
There is a stimulus which affects the hypothalamus, it causes the hypothalamus to release hormones which act on the anterior pituitary which release hormones that act on the gonads which can release hormones to act on target tissues.
What is the purpose of feedback loops?
They are to amplify or inhibit the final hormone that acts on the target tissue.
e.g. Oestrogen acts back on the hypothalamus to stop the release of FSH and LH (negative feedback).
What is the posterior boundary of the hypothalamus?
Mamillary bodies and midbrain.
What is the anterior boundary of the hypothalamus?
Anterior commissure and lamina terminalis.
What is superior boundary of the hypothalamus?
Thalamus.
What is the inferior boundary of the hypothalamus?
Pituitary gland.
What is the neurohypophysis?
It is what forms the posterior pituitary. It is made up of the: median eminence, hypothalamo-hyophyseal tract, stalk and posterior lobe.
What does the posterior pituitary release?
- Oxytocin.
2. ADH (antidiuretic hormone).
Describe the blood supply to the hypothalamus and anterior pituitary gland?
Blood foes from the top of the stalk to the pituitary (flow of blood is not all one way). The superior and inferior hypophyseal artery come off the internal carotid artery.
Describe the blood supply from the superior hypophyseal artery? (for ant.pit)
The superior hypophyseal artery comes in at the top of the pituitary and feeds the capillary bed and upper infundibulum. It then runs to the pars distalis (portal vessels). The trabecular artery comes from the superior hypophyseal artery and goes into the lower capillary bed.
Describe the blood supply from the inferior hypophyseal artery?
The inferior hypophyseal artery comes in through the posterior pituitary and feeds vessels into the lower capillary bed.
Where do short axons go to? (for ant.pit)
Upper capillary bed.
Where do long axons go to? (for ant.pit)
Lower capillary bed.
What hormones does the anterior pituitary release?
- LH (lutenising hormone).
- FSH (follicle stimulating hormone).
- TSH (thyroid stimulating hormone).
- GH (growth hormone).
- Prolactin.
- ACTH (adrenocortioctrophic hormone).
What hormones does the hypothalamus release?
- GnRH (gonadotropin releasing hormone).
- Dopamine (inhibits prolactin).
- Somatostatin (inhibits GH).
- GHRH (growth hormone releasing hormone).
- CRF (Corticotropin releasing hormone).
- TRH (thyrotropin releasing hormone).
- PRF (prolactin releasing factor).
What can cells of the pars distalis (ant pit) be classified as?
Chromotrophs (don’t stain) and chromophils (stain):
- Acidophils.
- Basophils.
Describe the staining of acidophils?
Acidophils are stained orange, because they are negatively charged and indicate proteins. Acidophils are made up of
- Somatotrophs (secrete GH).
- Lactotrophs (secrete prolactin).
Describe the staining of basophils?
Basophils are stained purple because they are positively charged and indicate glycoproteins. They are made up of:
- Gonadotrophs (secrete LH, FSH).
- Thyrotrophs (secrete TSH).
- Corticotrophs (secrete ACTH).
What happens in pregnancy?
There is marked proliferation of acidophils (prolactin).
What happens in acromegaly (in terms of staining)?
There is excess GH, so there is marked orange staining (lots of acidophils).
What happens in cushings syndrome (in terms of staining)?
There is excess ACTH, so there is marked purple staining (lots of basophils).
Describe the secretion of growth hormone and the feedback control of it?
The hypothalamus releases GHRH which acts on the ant pit, the ant pit then releases GH. GH acts on epithelia, adipose tissue and the liver. The liver produces somatomedins (IGF-1 - insulin growth factor 1) which stimulate growth of skeletal muscle, cartilage and other tissues. Somatomedins also inhibit GHRH (in the hypothalamus), thus it can’t act on the ant pit. The somatomedins also stimulate somatostatin (GHIH) which inhibits the ant pit and stops GH from being released.
What does prolactin do?
Regulates milk production.
What does oxytocin?
Regulates milk lactation.
Describe the feedback loop for prolactin?
Prolactin has a positive feedback loop, where the more that is made the more it is produced (prolactin acts back on the hypothalamus - PRF). Dopamine is secreted in the median eminence and acts on the ant pit to inhibit prolactin production.
Describe the hormonal control of the male HPO axis?
- Hypothalamaus secretes GnRH.
- GnRH acts on the ant pit which causes it to secrete FSH and LH.
- FSH acts on the sertoli cells (testes), which causes them to stimulate spermatogenesis and inhibin to be released.
- LH acts on leydig cells (testes) to release testosterone which acts on sertoli cells.
- Inhibin inhibits the ant pit from releasing FSH.
- Testosterone
Describe the hormonal control of the female HPO axis?
- Hypothalamus secretes GnRH.
- GnRH acts on the ant pit which causes it to secrete FSH and LH.
- FSH and LH act on the ovaries which cause the release of oestrogen and progesterone.
- Progesterone inhibits FSH and LH (at pit level) and GnRH (at hypothalamus level).
- Estrogen has both negative and positive feedback loops on FSh and LH.
