Reproduction 2 - Control of processes

Question 0

List the hormones secreted by the the anterior pituitary, the cells they are secreted by, target tissue and main action.

Answer 0

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

Question 1

Where does the anterior pituitary arise from? How does this differ from the posterior pituitary?

Answer 1

Rathke’s Pouch - not nervous tissue like the Posterior Pituitary.

Question 2

How do trophic hormones from the hypothalamus reach the anterior pituitary?

Answer 2

Hypophyseal portal vessels

Question 3

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

Answer 3

Gonadotrophin releasing hormone (GnRH)

Question 4

How is GnRH released?

Answer 4

Several groups of hypothalamic neurones secrete GnRH in a pulsatile fashion, with a burst of secretion about once an hour.

Question 5

What influences GnRH release?

Answer 5

GnRH release is under the influence of the brain (Environment via sensory input), body weight and Circulating Hormones

Question 6

Describe (or draw a diagram to show) the influence of circulating sex hormones on both the hypothalamus and anterior pituitary

Answer 6

See diagram

Question 7

What is the action of LH on the testes? What other hormones effect its action?

Answer 7

LH acts on Leydig cells to promote the secretion of Testosterone (4-10mg/day). The effects of LH are enhanced by Prolactin and Inhibin.

Question 8

What is the effect of testosterone on Sertoli cells? What does FSH do?

Answer 8

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.

Question 9

Gonadal steroids fall into two broad categories- what is the deference between determinative and regulatory effects?

Answer 9

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.

Question 10

Name the determinative effects of testosterone

Answer 10

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

Question 11

What are is the effect of oestrogen?

Answer 11

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

Question 12

What is the action of progesterone on oestrogen primed cells

Answer 12

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

Question 13

Name the phases of the menstrual cycle

Answer 13

Follicular
Ovulatory
Luteal

Question 14

What happens during the follicular phase?

Answer 14

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)

Question 15

What happens during ovulatory phase?

Answer 15

o LH surge stimulates ovulation
o surging LH induces progesterone synthesis by granulosa cells
o Brief period of fertility (~3days)

Question 16

Describe the luteal phase

Answer 16

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

Question 17

What happens when there is a sudden fall in oestrogen & progesterone?

Answer 17

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.

Question 18

Describe the secretion of Gonadotrophins and gonadal steroids at the beginning of the menstrual cycle

Answer 18

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

Question 19

Describe what happens around days 12-14 of the menstrual cycle

Answer 19

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

Question 20

What happens to gonadatrophs and gonadal steroids after ovulation

Answer 20

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

Question 21

14 days after ovulation…

Answer 21

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

Question 22

What happens if conception has occurred?

Answer 22

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