Flashcards in Repro - control of reproductive processes Deck (67):
What hormones involved in reproduction are produced by the hypothalamus?
GnRH, PRH (prolactin releasing hormone) and PIH (prolactin inhibiting hormone).
What hormones involved in reproduction are produced by the posterior pituitary?
What hormones involved in reproduction are produced by the anterior pituitary?
FSH, LH and prolactin
What hormones involved in reproduction are produced by the testis?
Testosterone, Mullerian inhibiting hormone (MIH) and inhibin.
What hormones involved in reproduction are produced by the ovaries?
Oestrogen, progesterone and inhibin.
What hormones involved in reproduction are produced by the placenta?
Human chorionic gonadotrophin (hCG)
Human placental lactogen (hPL)
Which hormones produced by the anterior pituitary are glycoproteins?
Think: BLT (but using fish not bacon):
FSH, LH and TSH
Which hormones produced by the anterior pituitary are polypeptides?
MSH (melanocyte stimulating hormone)
What type of cell in the anterior pituitary produces FSH and LH?
What type of cell in the anterior pituitary produces ACTH and MSH?
What type of cell in the anterior pituitary produces prolactin?
What is the principle action of FSH?
Growth of the reproductive system
What is the priniciple action of LH?
Sex hormone production
What are the principle actions of ACTH?
Secretion of glucocorticods, mineralocorticoids (though the main regulator of secretion is by angiotensin) and androgens.
What are the main target tissues of growth hormone?
Liver and adipose tissue
What are the principle action of growth hormone?
Promotes growth, lipid and carbohydrate metabolism.
What are the main target tissues of prolactin?
Ovaries and mammary glands.
What are the principle action of prolactin?
Secretions of oestrogen, progesterone and milk production.
What is the effect of testosterone on GnRH secretion?
Reduced GnRH secretion
What secretes GnRH?
Several groups of hypothalamic neurones secrete it in a pulsatile fasion (about one pulse an hour)
What is the effect of intermediate concentration of oestrogen on GnRH secretion?
Reduces secretion - lowers amount secreted per pulse
What is the effect of progesterone on GnRH secretion?
Increases the inhibitory effect of oestrogen - lowers the FREQUENCY of the pulses
What is the effect of oestrogen alone (no progesterone) at high concentrations?
Promotes the release of GnRH producing a surge. Progesterone prevents this.
What secretes inhibin?
1. Developing follicles (granulosa cells) in the ovary
2. Seminiferous tubules (sertoli cells) in the testis
What is the effect of inhibin on the HPG axis?
Inhibin reduces the amount of FSH secreted by the anterior pituitary in response to GnRH.
What is the effect of LH on:
1. The testis
2. The ovaries
1. Binds to Leydig cells to promote the secretion of testosterone
2. Binds to theca interna cells, promoting the release of androgens (mainly androstenedione)
What is the effect of secretion of testosterone from Leydig cells on the testis and body in general?
Testosterone act on sertoli cells promoting spermatogenesis. It also acts elsewhere in the body maintaining the male reproductive system (maintains internal genitalia, metabolic and behavioural effects).
What are the effect of prolactin and inhibin on Leydig cells?
prolactin and inhibin enhance the effects of LH and therefore secretion of testosterone from Leydig cells.
What are the effects of FSH on the testis?
FSH maintain sertoli cells, making them responsive to testosterone.
What is the effect of LH on the ovary in the antral phase?
It binds to theca interna cells, resulting in the release of androgens, primarily androstenedione.
What is the effect of FSH on the ovary in the antral phase?
It binds to granulosa cells, resulting in the production of enzymes which convert androgens to oestrogens.
What happens to the production of oestrogen as the follicle grows?
More oestrogen is produced for a given amount of FSH and LH.
What changes occur to the HPG axis in the preovulatory phase?
1. The follicle has grown and is producing a high amount of oestrogen.
2. LH receptors develop on the outer layers of the granulosa cells
3. High [oestrogen] positively feedback on the HPG axis
4. LH surge produced
What are the effects of the LH surge on the ovary?
1. Stimulates ovulation
2. Follicle size increased - increase in antral volume
3. Collagenase activity is stimulated
4. Rapid changes in the follicle - meiosis restarted and M1 completes and arrests in M2 3 hours prior to ovulation
Why is there not a corresponding FSH surge?
FSH is still inhibited by inhibin.
What is the response of the corpus luteum to LH?
It stimulates it to produces oestrogen and progesterone.
What is the role of progesterone in the luteal phase?
1. Prevents positive feedback due to the high levels of oestrogen present
2. Enhances negative feedback of oestrogen (reducing the pulses of GnRH). The decrease in GnRH this causes prevents new follicles from growing.
What happens as the corpus luteum grows?
More steroids are produced for a given LH level.
What are the two broad types of effects that steroid hormones can have?
1. Determinative - effects are qualitative and only partly reversible (if at all) - these are mostly secondary sexual characteristics such as deepening of the voice.
2. Regulatory effects - are highly reversible and rely on continuous hormonal stimulation for their maintenance.
What are some determinative effects of testosterone?
1. Increased size and mass of muscles, vocal chords, bones
2. Deepening of the voice
3. Facial and body hair
4. Increased stature
5. Growth of the penis
What are some regulatory effects of testosterone?
1. Maintenance of male genitalia (prostate, seminal vesicles, vas deferens, epididymis)
2. Metabolic (anabolic) action
3. Behavioural effects (agression, sexual activity)
What are some regulatory effects of oestrogen?
1. Fallopian tube function
2. Thickening of endometrium
3. Growth and motility of myometrium
4. Thin alkaline cervical mucus
5. Vaginal changes
6. Changes in skin, hair, metabolism
7. Calcium metabolism
What are some regulatory effect of progesterone on oestrogen primed cells?
1. Further thickening of the endometrium into secretory form
2. Thickening of myometrium, but reduction of motility
3. Thick, acidic cervical mucus
4. Changes in mammary tissue
5. Increased body temperature
6. Metabolic (mild catabolic) changes
7. Electrolyte changes
List the phases of the menstrual cycle:
1. Follicular phase
2. Pre-ovulatory phase
3. Luteal phase
What happens in the follicular phase of the menstrual cycle?
1. The development of a follicle (group) is stimulated in the ovary
2. The uterus is prepared for sperm transport and implantation of the conceptus
What happens in the pre-ovulatory phase of the menstrual cycle?
1. LH surge stimulate ovulation
2. Brief period of fertility
3. Formation of the corpus luteum
What happens in the luteal phase of the menstrual cycle?
1. LH maintains corpus luteum in the ovary
2. Waiting period to see if the ovum will be fertilised
What happens when the corpus luteum regresses (occurs spontaneously after 14 days if there has not been fertilisation of the ovum)?
1. Sudden fall in oestrogen and progesterone
2. Elaborate secretory epithelium collapses
3. Apoptotic cell death
4. Dead tissue shed as menstrual bleed
5. Spiral arteries contract to reduce bleeding
Why is there an increase in GnRH secretion at the beginning of the menstrual cycle?
It is released from its inhibition by high levels of progesterone and oestrogen.
Why is there a higher secretion of FSH relative to LH at the beginning of the menstrual cycle?
Low inhibin levels have released the selective inhibition of FSH.
What happens to oestrogen levels immediately after ovulation?
Why do new follicles begin to develop ~14 days after ovulation?
The corpus luteum has regressed and therefore GnRH, FSH and LH are released from their inhibition by progesterone and oestrogen.
What happens to the corpus luteum if conception has occurred?
The placenta secretes hCG (human chorionic gonadtrophin) which prevents regression of the corpus luteum, therefore it continues to secrete oestrogen and progesterone until about 12-14 weeks. This maintains suppression of the ovarian cycle.
What happens if testosterone levels rise too much?
Increased negative feedback of hypothalamus and anterior pituitary, therefore decreased secretion of GnRH, FSH and LH -> decrease in production of testosterone by Leydig cells.
What happens if spermatogenesis proceeds too quickly?
Inhibin production by the Sertoli cells increases and therefore increased inhibition of gonadotrophs occurs and decreased secretion of FSH.
Which artery connect the hypothalamus and the anterior pituitary gland?
Superior hypophyseal artery
How is the anterior pituitary gland regulated?
Hypothalamic hypophysiotrophic releasing hormones which travel to the anterior pituitary via the hypohyseal-portal circulation
Which cells in the anterior pituitary gland secrete prolactin?
Which cells in the anterior pituitary secrete MSH?
Pars intermedia cells
Why are hypothalamic releasing hormones released in pulses?
Tied to an internal clock which is synchronised to external signals e.g. light/dark patterns.
What are some notable characteristics of hypothalamic releasing hormones?
1. Stimulate the release of stored hormones
2. Stimulate synthesis of pituitary hormones
3. Stimulate hypertrophy and hyperplasia of target cells
4. Regulate its own receptor
Which hormone released by the hypothalamus stimulates ACTH secretion?
Corticotropin releasing hormone (CRH)
What is another name for prolactin inhibiting hormone?
What type of receptor do FSH and LH bind to in the gonads?
How does the negative feedback of gonadal hormones affect the hypothalamus and anterior pituitary?
It decreases the release of GnRH from the hypothalamus and affects the ability of GnRH to stimulate gonadotropin secretion from the anterior pituitary.
The proliferative phase of the uterine cycle is equivalent to what phase of the ovarian cycle?