Question

Study the flow chart given below. Name the hormones involved at each stage and explain their functions.

Hypothalamus → Pituitary → Ovary → Pregnancy

Hint:

Name GnRH, FSH, LH, oestrogen, progesterone and hCG, hPL, relaxin, with one function each.

Answer 1

Step 1: Hypothalamus:
The hypothalamus secretes Gonadotropin Releasing Hormone (GnRH). GnRH acts on the anterior pituitary and makes it release the gonadotropins.

Step 2: Pituitary:
The anterior pituitary secretes two gonadotropins, FSH and LH.
FSH stimulates the growth of ovarian follicles and the secretion of oestrogen by them.
LH, in a mid-cycle surge, causes ovulation (rupture of the Graafian follicle and release of the ovum). LH then helps form the corpus luteum.

Step 3: Ovary:
Growing follicles secrete oestrogen, which repairs the uterine endometrium and brings about its proliferation.
The corpus luteum secretes progesterone, which makes the endometrium ready for implantation and keeps it that way.

Step 4: Pregnancy:
After fertilisation and implantation, the placenta produces human chorionic gonadotropin (hCG). It keeps the corpus luteum active so that progesterone keeps flowing.
The placenta also secretes oestrogen, progesterone and human placental lactogen (hPL) to maintain pregnancy and prepare the mammary glands. Relaxin from the ovary helps in parturition.

Final Answer:
GnRH (hypothalamus), FSH and LH (pituitary), oestrogen and progesterone (ovary), hCG, hPL, oestrogen, progesterone and relaxin (pregnancy), each with the functions given above.