Flashcards in Repro 2.1 Deck (34):
From what embryological structure does the anterior pituitary gland form?
What type of tissue is the anterior pituitary gland?
What type of tissue is the posterior pituitary?
What are trophic hormones?
Hormones which act on other endocrine tissues and promote the secretion of further hormones.
What does the posterior pituitary secrete?
ADH and oxytocin
What do the gonadotrophs secrete?
What do the corticotrophs secrete?
What do the somatotophs secrete?
What do lactotrophs secrete?
How are the secretory cells in the anterior pituitary controlled?
Releasing hormones produced by nerve cells in the median eminence of the hypothalamus which pass to the anterior pituitary in the hypophyseal portal vessels
Why are the hypophyseal portal vessels short?
Concentrated amount of releasing hormone from the hypothalamus to the anterior pituitary gland
What releasing hormone controls the secretion of hormones from gonadotrophs?
Gonadotrophin Releasing Hormone (GnRH) controls the release of FSH and LH. GnRH is released in a pulsatile fashion causing pulsatile release of FSH and LH
What do the gonadotrophins do?
Act on the gonads to influence the production of gametes and to promote the secretion of gonadal steroids - oestradiol and progesterone in females and testosterone in males.
What controls the release of GnRH?
Affected by their connection to other parts of the brain influenced by factors such as body weight and change in environment
What effect does testosterone have on the secretion of GnRH?
Reduces GnRH secretion
What effect does oestrogen have on GnRH?
At intermediate concentrations, oestrogen reduces the secretion of GnRH by reducing the amount secreted per pulse pressure (negative feedback)
At high concentrations without progesterone, oestrogen promotes the release of GnRH producing a 'surge' (positive feedback)
What effect does progesterone have on GnRH secretions?
Progesterone increases the inhibitory effect of oestrogen by reducing the frequency of pulses
It can also inhibits the GnRH surge at high levels of oestrogen
What influences the release of FSH and LH?
GnRH is required for the release of FSH and LH - without GnR, none would be secreted.
Oestrogen at directly effects their release, reducing the amount secreted at intermediate concentrations and at high concentrations promotes it
Inhibin also reduces the amount of FSH secreted in response to GnRH
Where is inhibin produced?
a protein hormone produced by developing follicles in the ovary granulosa cells and seminiferous tubules sertoli cells in the testis
What stimulates the secretion of testosterone?
LH - amount of testosterone secreted for level of LH is relatively constant
How much testosterone does a man secrete each day?
What effect do the gonadotrophins have in the ovary during the astral phase of follicular development?
Cells of the theca interna bind LH
Granulosa cells bind FSH
LH stimulate thecal cells to produce androgens
FSH stimulates the granulosa cells to develop enzymes which convert the androgens to oestrogens
What effect do the gonadotrophins have in the ovary during the pre-ovulatory phase of follicular development?
LH receptors develop in the outer layers of granulosa cells
A surge of LH will stimulate ovulation
What effects do the gonadotrophins have on the corpus lute?
LH stimulates the corpus luteum to secrete progesterone and oestrogen
As the corpus luteum grows more steroids are produced at a given LH concentration
Where does LH bind in the testes?
What enhances the effects of LH in the testes?
Prolactin and Inhibin
What does testosterone do?
Acts on Sertoli cells to promote spermatogenesis and elsewhere in the body to maintain the reproductive system
What effect does FSH have in the male reproductive system?
Maintains Sertoli cells and makes them responsive to testosterone
Why must there constantly be appropriate levels of FSH and LH in the male?
They must produce sperm continually and be ever ready to deliver them to the female
How are constant levels of FSH and LH maintained in the male?
Negative feedback of testosterone on GnRH secretion and it also reduces sensitivity of gonadotrophs to GnRH
How is the rate of spermatogenesis controlled?
If it proceeds too rapidly inhibin levels rise and reduce secretion of FSH by acting on gonadotrophs
What type of rhythm does testosterone follow?
Circadian rhythm - highest in the early morning
What are the categories of the effects of gonadal steroids?
Determinative - qualitative and only partly reversible if at all. Mostly secondary sexual characteristics
Regulatory - highly reversible and rely on continuous hormonal stimulation for their maintenance