Reproductive system 3 - Regulation by Reproductive hormones

Question 1

What is the Regulation of Reproductive Hormone Secretion: Male reproductive System?

Answer 1

1) GnRH stimulates secretion of LH and FSH from anterior pituitary

2) LH stimulates testosterone secretion from Leydig Cells

3) FSH stimulates Sertoli cells to increase spermatogenesis

4) Testosterone
- Stimulates Sertoli cells
- Development of reproductive organs

5) Testosterone: negative effect on Hypothalamus and Pituitay
Sertoli cells secrete inhibin – negative feedback

Question 2

What does the female reproductive cycle consist of?

Answer 2

ovarian cycle
- series of event that precede and follow oocyte maturation
- controls oogenesis

uterine cycle
- preparation of uterus to receive ovum

[medicated by reproductive hormones]

Question 3

What are the 4 stages of the female reproductive system?

Answer 3

Menses > Follicular Phase > Ovulation > Luteal Phase

Question 4

Ovarian cycle

Answer 4

• each ovarian cycle = up to 20 primordial follicles are activated to begin the maturation process > usually one reaches full maturity, reminder regress

Question 5

what are the 3 phases of ovarian cycle?

Answer 5

1) Follicular phase - development of Graafian follicle

2) Ovulatory phase - release of mature follicle

3) Luteal phase - formation of corpus luteum

Question 6

Ovarian and endometrial cycle

Answer 6

Proliferative (follicular) phase:
secondary follicles mature
Granulosa cells secrete oestrogens
Oestrogen: causes the epithelial cells of the endometrium to divide rapidly.
endometrium thickens

Secretory (Luteal) phase:
the corpus luteum begins to secrete progesterone and smaller amounts of oestrogen.
Progesterone: causes the cells of the endometrium to become larger and to secrete a small amount of fluid.
Fullest development of endometrium
If no fertilisation – corpus luteum degenerates – progesterone drops

Question 7

What axis is ovarian and endometrial cycle controlled by?

Answer 7

FHS and LH (from anterior pituitary)

Question 8

Summary: Female Reproductive System

Answer 8

Gonadotropin releasing hormone (GnRH) ( Hypothalamus)
Stimulates secretion of LH and FSH from Anterior pituitary
Luteinizing hormone (LH)
Causes follicles to complete maturation; causes ovulation; causes the ovulated follicle to become the corpus luteum
Follicle-stimulating hormone (FSH)
Causes follicles to begin development
Oestrogen (from follicles and corpus luteum)
Proliferation of endometrial cells
Progesterone (from corpus luteum
Enlargement of endometrial cells / maintenance of pregnant state

Question 9

Feed back mechanisms: overall

Answer 9

Oestrogen
Postive feedback before ovulation,
resulting in increased LH and FSH secretion;
Negative feedback (with progesterone) on the hypothalamus and anterior pituitary after ovulation, resulting in decreased LH and FSH secretion

Progesterone
Negative feedback (with oestrogen) on the hypothalamus and anterior pituitary after ovulation, resulting in decreased LH and FSH secretion

Question 10

Hormonal control of the reproductive cycle - Follicular Phase

Answer 10

• Oestrogen (developing follicles) stimulates GnRH secretion from hypothalamus
• GnRH triggers FSH and LH
• FSH stimulates oestrogen secretion at an increasing rate from the developing follicles.
• This positive-feedback loop produces a series of larger and larger surges of FSH and LH secretion

Question 11

Hormonal control of the reproductive cycle - Ovulation

Answer 11

• Ovulation occurs in response to the large increases in LH levels
• about day 14 of the menstrual cycle
• This large increase in LH is also responsible for the development of the corpus luteum

Question 12

Hormonal control of the reproductive cycle - Luteal Phase

Answer 12

• Corpus luteum begins to secrete progesterone and oestrogen
• Progesterone : cells of the endometrium to become larger
• Negative Feedback: Together, progesterone and oestrogen act on the hypothalamus and anterior pituitary gland to inhibit GnRH, LH, and FSH secretion.
• LH and FSH levels decline
  No stimulation of follicles
• Corpus luteum degenerates - Lower progesterone

Question 13

Hormonal control of the reproductive cycle - Menses

Answer 13

Oestrogen and progesterone secretion is low

In response to declining progesterone levels, the endometrial lining of the uterus sloughs off, resulting in menses

The rate of LH remains low, and

the rate of FSH secretion increases as progesterone levels decline (negative feedback released)

Stimulates development of follicles

Start to release oestrogen

Question 14

Alternatively Fertilisation

Answer 14

The egg lives for 12-24 hrs

Takes 5 days to reach Uterus
- Fertilisation must occur in uterine tube

Endometrial development continues
- Progesterone production

Question 15

How does fertilisation happen?

Answer 15

hCG from pituitary and later placenta maintains corpus luteum

Oestrogen and progesterone levels maintained
Endometrium doesn’t break down

Subsequently Placenta takes over progesterone and oestrogen production