Flashcards in 2.1 Deck (40):
Where is the pituitary gland located?
Immediately beneath the hypothalamus in the pituitary fossa
Two names for ant pit
Where does the ant pit arise
From Rathke's pouch - not nervous tissue
How does ant pit connect to the hypothalamus?
Superior hyphyseal artery
What hormones does ant pit produce?
Prolactin, GH, TSH, FSH, LH, ACTH
Two names for the post pit
How can you tell the difference between the adenohypophysis and the neurohypophysis in histology
Ant pit stains darker and post pit stains lighter
What is the post pit derived from
Nervous tissue, outgrowth of hypothalamus
What does the post pit secrete
How does it connect to the hypothalamus?
Hypothalmic neurones pass through the neural stalk addend in the post pit.
What are the glycoproteinhormones that the ant pit secretes? Cell type producing these?
FSH - gonadotrophs
LH - gonadotrophs
What are the polypeptide hormones that the ant pit secretes? Cell type producing these?
ACTH - corticotrophs
GH - somatotrophs
Prolactin - lactotrophs
What 3 repro hormones doe stye hypothalamus produce?
Gonadotrophin releasing hormone GnRH
Prolactin inhibiting hormone (dopamine)
Prolactin releasing hormone
What hormones do the testes and ovaries secrete?
How is gonadotrophin secretion controlled by the hypothalamus?
Ant pit secretion is controlled by hypophysiotrophic releasing/inhibitory hormones produced by neurosecretory neurones in the hypothalamus.
These pass to the ant pit via the hypophyseal portal circulation.
Arterial blood in hypothalamus picks up the reeling hormones and moves into hypophyseal portal circulation.
Why does the hypothalamus not need to secrete much releasing hormone?
Goes into hypophyseal portal circulation only to ant. pit. which means it doesn't get diluted due to direct blood supply.
Give characteristics of hypothalamic releasing hormones.
Secretion in pulses according to internal clock.
Synchronised with external signals.
Act on specific receptors.
Transduce signals via second messengers.
Stimulate synthesis and release of pituitary hormones.
Stimulate hyperplasia and hypertrophy of target cells.
Regulates own receptor.
Describe GnRH secretion and therefore FSH and LH release.
Burst of secretion once an hour..
What circulating hormones feedback on GnRH secretion?
- Reduces secretion
Oestrogen at Intermediate conc.
- Reduces secretion so lowers the amount secreted per pulse.
- Increases the inhibitory effect of moderate oestrogen by lowering the frequency of pulses.
Oestrogen alone at high conc.
- Promotes release of GnRH producing LH surge.
- Progesterone prevents positive feedback of high oestrogen.
What are the actions of FSH and LH
- Oe and Pro in females
-Test in males
What else influences GnRH secretion?
What kind of receptors do LH/FSH bind to?
GsPCR on gonads
What is the function of inhibin?
Reduce the amount of FSH secreted in response to GnRH.
Secretion related to developing gametes - more gametes developed, more inhibit released.
Draw HPG axis in males
What is the action of LH in males?
Stimulate testosterone secretion from leydig cells.
What hormones enhance the effect of LH?
Prolactin and Inhibin
Describe the action of testosterone.
Acts on sertoli cells to promote spermatogenesis.
Acts to maintain the male repro tract.
What does FSH do in males?
Maintains setoli cells making them responsive to testosterone.
Stimulate sertoli cells to produce androgen binding globulin, which keeps testosterone in the seminiferous tubules, and inhibit, which helps support spermatogenesis.
Describe the operation of the whole HPG axis in males
Male must constantly produce sperm.
This requires constant appropriate levels of FSH, LH and testosterone, achieved by negative feedback.
If testosterone levels rise, this inhibits GnRH secretion so reduced LH/FSH so reduced testosterone and spermatogenesis.
If spermatogenesis proceeds to rapidly, inhibit levels rise.
This reduces secretion of FSH by acting on gonadotrophs in ant pit.
Testosterone is affected by
Circadian rhythm - highest in morning
What are the 3 phases of the menstrual cycle?
What cells do LH and FSH bind to in the ovaries? What are their function in the astral phase?
LH --> Theca interna --> produce andtrogens (androstenedione)
FSH --> Granulosa cells --> produce enzymes to convert androgens to oestrogen
Describe oestrogen secretion in the antral phase
As follicle grows, more oestrogen is produced for given amount of LH/FSH.
Oestrogen at low levels exerts a negative feedback on gonadotrophin release.
What are the functions of oestrogen in the astral phase?
Fallopian tube function
Thickening of endometrium
Growth and motility of myometrium
Thick alkaline cervical mucus
Describe the pre-ovulatory stage.
Follicle has grown and is producing a high amount of oestrogen --> Positive feedback enhancing LH release.
LH receptors develop on outer layers of granulosa cells.
LH surge produce:
Weakens theca externa with increased collagenase activity.
FSH is still inhibited by inhibin --> LH increases more.
Describe the luteal phase.
Remains of follicle reorganise into corpus luteum.
LH stimulates corpus luteum to secrete progesterone and oestrogen.
Progesterone prevents high oestrogen from producing GnRH surge by enhancing negative feedback.
Also reduces frequency of GnRH pulses.
As corpus luteum grows, more steroids are produced for given [LH]
What are the actions of progesterone on oestrogen primed cells?
Further thickening of endometrium into secretory form.
Thickening o myometrium.
Thick, acid cervical mucus.
Changes in mammary tissue.
Increased body temp.
What happens to the HPG axis after menopause?
Oestrogen secretion dramatically reduces.
FSH levels rise dramatically
LH levels rises
GnRH levels rise
As negative feedback is reduced..
Why, after monpause, do FSH levels rise more than LH levels?
No inhibit from ovary so selective inhibition of FSH by inhibit no longer occurs allowing FSH to rise.
Give the determinative effects of testoterone
Increase size and mass of muscles, vocal cords, bones
Deepening of voice
Facial and body hair
Growth of penis.