Origin of the Gametes

Question 1

List the main reproductive hormones produced by the Hypothalamus

Answer 1

GnRH - Gonadotrophin Releasing Hormone
PRH - Prolactin Releasing Hormone
PIH - Prolactin Inhibiting Hormone

Question 2

List the main reproductive hormones produced by the

Anterior Pituitary gland

Answer 2

FSH - Follicle Stimulating Hormone
LH - Luteinising Hormone
Prolactin

Question 3

List the main reproductive hormones produced by the Posterior Pituitary gland

Answer 3

Oxytocin

Question 4

List the main reproductive hormones produced by the Testes

Answer 4

Testosterone
Inhibin
MIH - Mullerian Inhibiting Hormone

Question 5

List the main reproductive hormones produced by the Ovaries

Answer 5

Oestrogen
Progesterone
Inhibin

Question 6

List the main reproductive hormones produced by the Placenta

Answer 6

hCG - Human Chorionic Gonadotrophin
hPL - Human Placental Lactogen
Oestrogen
Progesterone

Question 7

Describe the general process of gametogenesis

Answer 7

Germ cells colonise the gonad
Proliferate by mitosis
Undergo Meiosis to become haploid cells
Cytodifferentiate into mature gametes

Question 8

Briefly describe Sertoli cells

Answer 8

Somatic cells of the testis that are essential for the testis formation and spermatogenesis.

They facilitate progression of Germ cells to spermatozoa - controlling the environment milleu in seminiferous tubules

Stimulated by FSH and Testosterone

Question 9

Briefly describe Leydig cells

Answer 9

Produce Testosterone in the presence of LH

Question 10

How does genetic variation occur in meiosis?

Answer 10

Crossing over: the exchange of DNA regions between 2 homologous chromosomes during meiosis

Random segregation: how the chromatids are then distributed into each gamete

Independent assortment

Question 11

Outline the process of Spermatogenesis

Answer 11

Male Primordial Germ cells are known as Spermatogonia
They divide by Mitosis into Primary spermatocytes (Ap Spermatogonium) and Ad spermatogonium (to maintain stock).
Primary spermatocytes undergo Meiosis I to form Secondary spermatocytes (haploid), and Meiosis II to form spermatids.
These then differentiate into Spermatozoa (spermiogenesis).

This process occurs continuously in the walls of the tubules and after spermiogenesis the cytoplasmic bridges are broken down and the sperm are released into the tubule lumen

Question 12

Describe the Spermatogenic cycle

Answer 12

The amount of time it takes for the reappearance of the same stage of the cycle within a given segment of the tube.

Question 13

Describe the Spermatogenic wave

Answer 13

The distance on the tube between parts that are in the same stage of the development process

Question 14

What makes and constitutes Semen?

Answer 14

Seminal vesicle secretions (70%): Amino acids, citrate, fructose, prostaglandins

Secretions of the Prostate (25%): Proteolytic enzymes, Zinc

Sperm (2-5%): 200-500 million per ejaculate

Bulbourethral gland secretions (

Question 15

Describe Sperm capacitation

Answer 15

The final maturation step before sperm become fertile
The conditions in the female genital tract (low vaginal pH) stimulate removal of the glycoproteins and cholesterol from sperm membrane.
This allows sperm to bind to zona pellucida of oocyte and the initiation of the acrosome reaction.

Question 16

Oogenesis: Outline the stages of maturation of oocytes that occur before birth

Answer 16

Germ cells colonise the gonadal cortex where they then differentiate into oogonia.
Oogonia then proliferates rapidly by mitosis
By end of 3rd month: oogonia arranged in clusters surrounded by flat epithelial cells (follicular cells)
Some oogonia start to enter Meiosis and get arrested at Prophase I to form Primary oocytes
By 5th month: germ cells reach a max number (7 million) and cell death (atresia) begins
By 7th month: most oogonia have degenerated, all surviving Primary oocytes have entered Prophase I where they remain arrested until puberty.
Primary oocytes surrounded by follicular cells are known as Primordial follicles.

Question 17

Outline the Preantral stage of oocyte maturation

Answer 17

Stage 1 of oocyte maturation during puberty

As primordial follicles grow, flat follicular cells become stratified cuboidal Granulosa cells…they are now called Primary follicles

Granulosa cells secrete the glycoprotein around the oocyte which makes up the zona pellucida

Question 18

Outline the Antral stage of oocyte maturation

Answer 18

Stage 2 of oocyte maturation during puberty

Fluid filled spaces between Granulosa cells appear and coalesce to form the antrum

Theca folliculi forms around the follicle, developing into an inner and outer layer

• theca interna: vascular, endocrine
• theca externa: outer fibrous capsule

At this point it is known as a Secondary follicle, several of which develop with each ovarian cycle with only one reaching full maturity and the rest becoming atretic.

FSH stimulates Granulosa cells to secrete Oestrogen
LH stimulates Theca cells to secrete androgens which are converted to oestrogens by Granulosa cells

Question 19

Outline the Preovulatory stage of oocyte maturation

Answer 19

Stage 3 of oocyte maturation during puberty

Oestrogen causes receptors for LH to appear on outer Granulosa cells
LH surge stimulates these receptors which induces the preovulatory growth phase
Within 3hrs of the LH surge, the Secondary follicle returns to Meiosis I completing it
It then enters Meiosis II, arresting at Metaphase 3hrs before ovulation

Question 20

Outline oocyte maturation during Ovulation

Answer 20

The secondary follicle is arrested at Meiosis II 3hrs before ovulation

The LH surge stimulates collagenase activity resulting in digestion of collagen fibres surrounding the follicle
Prostaglandins increase in response to LH and cause local muscular contractions in the ovarian wall which extrudes the oocyte
Oocyte breaks free and floats out of the ovary

Meiosis is not completed until fertilisation takes place
Unfertilised cells degenerate 24hrs after ovulation

Question 21

How does the Corpus Luteum form?

Answer 21

Post-ovulation, follicular remains reorganise.
Granulosa and Theca interna cells become vascularised.
And under the influence of LH, these cells develop a yellowish pigment and become known as Lutean cells.`

Life span is 14 days if fertilisation doesn’t take place

Question 22

What is the function of Corpus Luteum?

Answer 22

Secretes Oestrogen and Progesterone to prepare uterine mucosa to enter the ‘secretory’ stage in preparation for implantation

Question 23

What happens to the Corpus Luteum if fertilisation does take place?

Answer 23

Degeneration of the Corpus Luteum is prevented by hCG which is produced by the developing placenta.
CL graviditatis continues to produce progesterone until the 4th month at which point placental progesterone becomes sufficient

Question 24

What is the Corpus Albicans?

Answer 24

When there is no fertilisation…
Corpus Luteum degenerates and forms a mass of fibrotic scar tissue known as the Corpus Albicans.
At this point, the drop in progesterone precipitates menstrual bleeding

Question 25

The function of FSH…

Answer 25

Stimulates the growth and maturation of the Primary follicles, and prevents atresia.
Stimulates Granulosa cells to produce Oestrogen

Question 26

The function of LH…

Answer 26

Maturation of follicles
Promotes development of the Corpus Luteum
Surge stimulates completion of Meiosis I, stimulates production of Progesterone by follicular stromal cells, and also follicular rupture and ovulation.