Reproduction 2 - Control of processes Flashcards
List the hormones secreted by the the anterior pituitary, the cells they are secreted by, target tissue and main action.
Follicle Stimulating Hormone (FSH) -Gonadotrophs, Glycoprotein
Gonads, Growth of reproductive system
Luteinising Hormone (LH) - Gonadotrophs, Glycoprotein, Gonads, Sex hormone production
Thyroid Stimulating Hormone (TSH) - Thyrotrophs, Glycoprotein, Thyroid Gland, Secretion of thyroid hormones
ACTH - Corticotrophs, Polypeptide, Adrenal Gland, Secretion of glucocorticoid, mineralocorticoid and androgens
Melanocyte Stimulating Hormone (MSH) - Corticotrophs, Polypeptide
Melanocytes in Skin and Hair, Production and release of melanin
Growth Hormone - Somatotrophs, Polypeptide
Liver, adipose tissue, Promotes growth, lipid and carbohydrate metabolism
Prolactin, Lactotrophs, Polypeptide, Ovaries, mammary glands
Secretions of oestrogen, progesterone, milk production
Where does the anterior pituitary arise from? How does this differ from the posterior pituitary?
Rathke’s Pouch - not nervous tissue like the Posterior Pituitary.
How do trophic hormones from the hypothalamus reach the anterior pituitary?
Hypophyseal portal vessels
The main reproductive anterior pituitary hormones, FSH and LH are produced by one cell type, the Gonadotrophs, name the one releasing hormone that controls this
Gonadotrophin releasing hormone (GnRH)
How is GnRH released?
Several groups of hypothalamic neurones secrete GnRH in a pulsatile fashion, with a burst of secretion about once an hour.
What influences GnRH release?
GnRH release is under the influence of the brain (Environment via sensory input), body weight and Circulating Hormones
Describe (or draw a diagram to show) the influence of circulating sex hormones on both the hypothalamus and anterior pituitary
See diagram
What is the action of LH on the testes? What other hormones effect its action?
LH acts on Leydig cells to promote the secretion of Testosterone (4-10mg/day). The effects of LH are enhanced by Prolactin and Inhibin.
What is the effect of testosterone on Sertoli cells? What does FSH do?
Testosterone in turn acts on Sertoli cells to promote spermatogenesis, along with acting elsewhere in the body to maintain the male reproductive system.
FSH maintains Sertoli cells, making them responsive to Testosterone.
Gonadal steroids fall into two broad categories- what is the deference between determinative and regulatory effects?
Determinative effects are qualitative and only partly reversible (if at all) – these are mostly secondary sexual characteristics such as deepening of the voice.
Regulatory Effects are highly reversible, and rely on continuous hormonal stimulation for their maintenance.
Name the determinative effects of testosterone
o Increase size and mass of muscles, vocal cords, bones o Deepening of the voice o Facial and body hair o Increased stature o Growth of the penis
What are is the effect of oestrogen?
o Fallopian tube function o Thickening of endometrium o Growth and motility of myometrium o Thin alkaline cervical mucus o Vaginal changes o Changes in skin, hair, metabolism o Calcium metabolism
What is the action of progesterone on oestrogen primed cells
o Further thickening of endometrium into secretory form
o Thickening of myometrium, but reduction of motility
o Thick, acid, cervical mucus
o Changes in mammary tissue
o Increased body temperature
o Metabolic (mild Catabolic) changes
o Electrolyte changes
Name the phases of the menstrual cycle
Follicular
Ovulatory
Luteal
What happens during the follicular phase?
o Gonadotrophins
FSH binds to granulosa cells
LH binds to theca cells
Stimulate follicle development (Cohort of follicles mature but only one becomes dominant (graffian))
Theca cells produce androgens; granulosa cells convert them to oestrogen
o Gonadal steroids - oestrogen stimulates
Fallopian tube function, thickening of endometrium, thin alkaline cervical mucus, vaginal changes, changes in skin hair and metabolism, calcium metabolism (
Uterus is prepared for sperm transport and implantation of the conceptus)
What happens during ovulatory phase?
o LH surge stimulates ovulation
o surging LH induces progesterone synthesis by granulosa cells
o Brief period of fertility (~3days)
Describe the luteal phase
o Formation and maintenance of corpus luteum in the ovary
o Luteal cells make large amounts of oestrogen, inhibin & progesterone
o progesterone prevents oestrogen stimulating another LH surge
o negative feedback on GnRH pulses –> baseline LH & FSH
o Waiting to see if there is a pregnancy
What happens when there is a sudden fall in oestrogen & progesterone?
o The elaborate secretary epithelium of the endometrium collapses
o Apoptotic cell death
o Dead tissue shed as menstrual bleed.
o Spiral arteries contract to reduce bleeding.
Describe the secretion of Gonadotrophins and gonadal steroids at the beginning of the menstrual cycle
o Oestrogen, Progesterone, Inhibin levels low
o GnRH secretion is released from inhibition
o LH and FSH rise, FSH more as low Inhibin levels release FSH from selective inhibition at the pituitary
FSH, followed by LH causes Follicles to Grow:
o Oestrogen and Inhibin secretion rises
o FSH secretion is selective inhibited by Inhibin at the pituitary
o Rising Oestrogen leads to stimulation of GnRH and hence LH secretion
Describe what happens around days 12-14 of the menstrual cycle
o +’ve feedback of rising Oestrogen stimulates an LH surge
▪ Precise timing may be influenced by environmental factors
o LH surge produces ovulation
o Oestrogen levels fall dramatically
o Corpus Luteum forms
What happens to gonadatrophs and gonadal steroids after ovulation
o LH promotes Oestrogen and Progesterone secretion from Corpus Luteum
o As Corpus Luteum grows, more steroids are secreted
o Rising Oestrogen does not positively feedback on LH because Progesterone levels are also rising
14 days after ovulation…
o In the absence of pregnancy the Corpus Luteum regresses spontaneously
o Progesterone and Oestrogen levels fall
o Triggering a menstrual bleed
o Relieves inhibition on GnRH, FSH and LH, triggering the development of new follicles and the beginning of a new cycle
What happens if conception has occurred?
o The implanted embryo develops a placenta, which secretes Human Chorionic Gonadotrophin (hCG)
o hCG prevents the regression of the Corpus Luteum
o Continues to secrete Oestrogen and Progesterone
o Supports early weeks of pregnancy (Until about 12-14 weeks)
o Maintains suppression of the ovarian cycle
