2) Control of Reproductive Processes Flashcards
What hormones does the hypothalamus produce?
Gonadotrophin releasing hormone (GnRH)
Prolactin releasing hormone (PRH)
Prolactin inhibiting hormone (PIH)
What hormone does the posterior pituitary produce?
Oxytocin
What hormones does the anterior pituitary produce?
Follicle stimulating hormone (FSH)
Luteinising hormone (LH)
Prolactin
What hormones do the testes produce?
Testosterone
Inhibin
Mullerian inhibiting hormone (MIH)
What hormones do the ovaries produce?
Oestrogen
Progesterone
Inhibin
What hormones does the placenta produce?
Human chorionic gonadotrophin (hCG)
Human placental lactogen (hPL)
Oestrogen
Progesterone
Where does the anterior pituitary arise from?
Rathke’s pouch
What type of tissue does the posterior pituitary arise from?
Nervous tissue
Which hormones do the gonadotrophs secrete?
FSH - growth of reproductive system
LH - sex hormone production
Which hormones are secreted by corticotrophs?
ACTH - secretion of glucocorticoid, mineralocorticoid & androgens
MSH - Melanocyte stimulating hormone, production & release of melanin
Thyroid stimulating hormone is released by which type of cell?
Thyrotrophs
What do somatotrophs secrete?
Growth hormone - Promotes growth, lipid & carbohydrate metabolism
What do lactotrophs secrete?
Prolactin - secretions of oestrogen, progesterone, milk production
Which hormone controls the release of FSH & LH?
Gonadotrophin releasing hormone (GnRH)
produced in hypothalamus
travels to anterior pituitary
via hypophyseal portal vessels
What reduces GnRH release?
Testosterone Oestrogen intermediate concentration - lowers amount secreted per pulse Progesterone - increases inhibitory effect of oestrogen - lowers frequency of pulses
What increases GnRH release?
Oestrogen ALONE at high concentrations
- promotes GnRH surge
- progesterone prevents this
What is the function of Inhibin?
Reduces the amount of FSH secreted in response to GnRH
Acts on anterior pituitary
Which cells produce inhibin?
Developing follicles (granulosa cells) in ovary Seminiferous tubules (sertoli cells) in testis
What is the effect of LH in the testes?
Acts on Leydig cells
Promote secretion of testosterone
LH effects enhanced by Prolactin & Inhibin
What are the actions of testosterone?
Acts on Sertoli cells to promote spermatogenesis
Acts in the body to maintain male reproductive system
What is the effect of FSH in the testes?
Maintains sertoli cells, makes them responsive to testosterone
During the antral phase of follicular development, what is the role of FSH & LH?
LH binds to theca interna cells, produce androgens
FSH binds to granulosa cells, produce enzymes - androgens > oestrogen
During the pre-ovulatory phase of follicular development, what is the role of FSH & LH?
Follicle producing high amount of oestrogen LH receptors develop on granulosa cells [High] oestrogen +vely feeds back LH surge Stimulates ovulation FSH still being inhibited by Inhibin
During the luteal phase of follicular development, what is the role of FSH & LH?
LH stimulates corpus luteum,
Produces oestrogen & progesterone
Progesterone prevents +ve & enhances -ve feedback
Prevents new follicles developing, decreases FSH
What are the 2 broad effects of gonadal steroids (testosterone)?
Determinative effects - qualitative, only partly reversible
Regulatory effects - highly reversible, rely on continuous hormonal stimulation
What are the determinative actions of testosterone?
Increase muscle size & mass, vocal cords, bones Deepening of voice Facial & body hair Increased stature Growth of penis
What are the regulatory actions of testosterone?
Maintenance of male internal genitalia
Metabolic (anabolic) action
Behavioural effects - aggression, sexual activity
What are the actions of oestrogen?
Fallopian tube function Thickening of endometrium Growth & motility of myometrium Thin alkaline cervical mucus Vaginal changes Changes in skin, hair & metabolism Calcium metabolism
What are the actions of progesterone on oestrogen primed cells?
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 (mild catabolic) changes
Electrolyte changes
List the phases of the menstrual cycle
Menses 0-5
Follicular phase 5-14
Ovulation 14
Luteal phase 14-28
What happens during the follicular phase?
Stimulation of development of follicle in ovary
Uterus prepared for sperm transport & implantation of conceptus
Steady rise of oestrogen
What happens during pre-ovulation/ovulation?
LH surge stimulates ovulation
Brief period of fertility
Formation of corpus luteum
Rapid drop in oestrogen
What happens during the luteal phase?
LH maintains corpus luteum in ovary
Wait to see if there’s a pregnancy
Actions of progesterone on oestrogen primed cells (increased progesterone)
What happens when there is a sudden fall in progesterone & oestrogen levels? (usually around day 28)
Secretory epithelium of endometrium collapses
Apoptotic cell death
Dead tissue shed as menstrual bleed
Spiral arteries contract to reduce bleeding
Describe the hormonal changes during the beginning of the menstrual cycle
Oestrogen, progesterone & inhibin levels low
GnRH secretion is released from inhibition
LH & FSH rise, FSH more as low Inhibin levels release FSH from selective inhibition at the ant. pituitary
Describe the hormonal changes during days 12-14 of the cycle
+ve feedback of rising oestrogen stimulates an LH surge
LH surge produces ovulation
Oestrogen levels fall dramatically
Corpus Luteum forms
Describe the hormonal changes after ovulation
LH promotes oestrogen & progesterone secretion from corpus luteum
As corpus luteum grows, more steroids are secreted
Rising oestrogen does not +vely feedback on LH because progesterone levels also rising
Describe the hormonal changes 14 days after ovulation
Absence of pregnancy CL regresses
Progesterone & oestrogen fall - menses
Relieves inhibition on GnRH, LH & FSH - development of new follicle
What hormonal changes take place if conception has occurred?
Implanted embryo develops placenta - secretes hCG
hCG prevents regression of CL
CL secretes oestrogen & progesterone
supports early weeks of pregnancy (up to 12-14)
How is testosterone release regulated by feedback?
Testosterone rise: GnRH inhibited, reduced LH & FSH
LH & FSH reduced further by testosterone reducing sensitivity of gonadotrophs to GnRH
Testosterone levels fall back
