Session 2 Flashcards
What is the HPG axis?
Hypothalamus-pituitary-gonad axis
Which hypothalamic releasing hormone is associated with the HPG axis?
GnRH
What is the name of the depression in the sphenoid bone in which the pituitary gland is located?
Sella turcica
What other name can be given to the pituitary gland?
Hypophysis
What other names can be given to the anterior pituitary gland?
Pars distalis
Adrenohypophysis
What other name can be given to the posterior pituitary gland?
Pars nervosa
What are the six peptide hormones produced by the anterior pituitary gland?
Prolactin Growth hormone (GH) Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Follicle-stimulating hormone (FSH) Luteinizing hormone (LH)
Which two hormones are secreted by the anterior pituitary in response to GnRH?
LH
FSH
Describe the release of of GnRH from the hypothalamus.
Pulsatile (every 1-3 hours)
Travels to the pituitary via the hypophysial portal system
What is the name given to the cells of the anterior pituitary that secrete FSH and LH?
Gonadotrophs
Which cells of the testis secrete testosterone?
Leydig cells
Which hormone stimulates Leydig cells?
LH
Which hormone stimulates Sertoli cells of the seminiferous tubules?
FSH
What two functions are provided by Sertoli cells?
Increased spermatogenesis
Inhibin secretion
In the male, what feedback effect will testosterone have on the HPG axis?
Negative feedback on the hypothalamus and anterior pituitary gland
Which hormone of the anterior pituitary stimulates theca cells of the ovary and what do they secrete?
LH
Progestins (and androgens)
Which hormones stimulate the granulosa cells of the ovary and what do they secrete?
LH and FSH
Oestrogens
Progestins
Inhibin
In what conditions will oestrogen promote negative feedback on the hypothalamus?
Moderate concentration of oestrogen
In what conditions will oestrogen promote positive feedback on the hypothalamus?
High concentrations of oestrogen AND an absence of progesterone (this causes the LH ‘surge’)
Progesterone increases the inhibitory effects of moderate oestrogen and prevents positive feedback of high oestrogen
Predominantly, the secretion of which hormone is inhibited by inhibin?
FSH (Inhibin has a small inhibitory effect on LH)
In the female, by what mechanisms can oestrogen have both a positive and negative feedback effect on the HPG axis?
Moderate concentrations of oestrogen will cause negative feedback on the HPG axis.
High concentrations of oestrogen, in the absence of progesterone, will cause positive feedback on the HPG.
Which two events does the the menstrual cycle refer to?
Uterine cycle
Ovarian cycle
In the early stage of the menstrual cycle, steroid and inhibin levels are low. The levels of which hormone subsequently rise?
FSH
What is the effect of rising levels of FSH?
Follicular development continues
The follicle is now capable of secreting oestrogen
Inhibin levels rise
When oestrogen is being secreted by the follicle, what feedback effect is seen on the hypothalamus and anterior pituitary?
Positive feedback
What effect is seen as a response to the positive feedback caused by high concentrations of oestrogen?
Increase in LH
What causes the LH surge and what does this trigger?
Rapid rise in circulating oestrodial and inhibin
Ovulation
What are the effects of LH after ovulation?
Luteinisation of the follicle (formation of the corpus luteum)
What is secreted in large quantities by the corpus luteum?
Progesterone (negative feedback on LH secretion)
Oestrogen
Inhibin
After how long will the corpus luteum spontaneously regress in the absence of a further rise in LH?
14 days (after this point a dramatic fall in gonadal hormones will occur, relieving negative feedback and restarting the cycle)
What is secreted by a conceptus that will support the corpus luteum after 14 days?
Human chorionic gonadotropin (HCG is an LH analogue produced by the syncytiotropoblast in the second week of development)
The corpus luteum, supported by placental hCG, produces steroid hormones to support the pregnancy. eventually, what will take over the production of steroid hormones?
Placenta
What are the names given to the two phases of the ovarian cycle?
Follicular phase (more variable in length) Luteal phase (14 days)
Ovulation occurs between the two phases
What are the names given to the three phases of the endometrial cycle?
Menses
Proliferative phase
Secretory phase
What are the physical effects of oestrogen during the follicular phase of the ovarian cycle?
Fallopian tube function Thickening of endometrium Growth & motility of myometrium Thin alkaline cervical mucus Vaginal changes Changes in skin, hair, metabolism
What are the physical effects of progesterone during the luteal phase of the ovarian cycle?
Further thickening of endometrium into secretory form
Thickening of myometrium, but reduction of motility
Thick, acid cervical mucus
Changes in mammary tissue
Increased body temperature
Metabolic changes
Electrolyte changes
