Gametogenesis

Question 1

How is genetic variation produced by gametes

Answer 1

Recombination/crossing over

Independent assortment

Random segregation

Question 2

Where does spermatogenesis occur

Answer 2

In the seminiferous tubules of the testes

Sertoli cells are responsible for spermatogenesis

Question 3

What form the blood testis barrier and what is its function

Answer 3

Sertoli cells form the blood testis barrier due to tight junctions between cells

Barrier allows basal and adluminal compartments to exist side by side

Prevents immune response - sperm have large genetic diversity so are recoginsed as foreign by immune system

Question 4

What do spermatogonia divide by mitosis into

Answer 4

Ad spermatogonium - reserve stock

Ap spermatogonium - maintains stock and produces type B spermatogonia which give rise to spermatocytes

Question 5

What is the spermatogenic wave

Answer 5

Distance between groups of spermatids at the same level of maturation

Question 6

What is the spermatogenic cycle

Answer 6

Time taken for reappearance of the same stage within a segment of tubule

Question 7

What is spermiation

Answer 7

Release of sperm into the lumen of seminiferous tubules

Question 8

What is spermiogenesis

Answer 8

Process by which spermatids become spermatozoa

Question 9

How are non-motile spermatozoa transported to the epididymis and when do they become motile

Answer 9

They are transported via sertoli secretions, assisted by peristaltic contractions

Become motile when they reach the epididymis

Question 10

What secretions form semen and what do the secretions contain. How many sperm per ejaculate

Answer 10

Seminal vesicle secretions - amino acids, citrate, fructose, prostaglandins

Prostate secretions - proteolytic enzymes, zinc

Sperm - from vas deferens. 200-500 million per ejaculate

Bulbourethral/cowper gland secretions - mucoproteins that lubricate and neutralise acidic urine

Question 11

What is capacitation

Answer 11

Removal of the top layer of glycoproteins and cholesterol of the outer membranes of the spermatic head

Occurs in female reproductive tract and is final process in maturation of sperm

Question 12

Describe the first part of oogenesis - before the preantral phase

Answer 12

Germ cells settle in ovary, form oogonia and rapidly divide

Oogonia are arranged into clusters surrounded by flat epithelial cells

Oogonia enter meiosis and arrest at prophase I - primary oocytes

Cell death occurs and many oogonia and primary oocytes degenerate to leave the best cells for reproduction

All surviving oocytes enter meiosis I and are surrouned by follicular cells - primordial follicles

Question 13

What are the phases in oogenesis

Answer 13

Preantral phase

Antral phase

Pre-ovulatory phase

Ovulation

Oocyte transport

Question 14

Describe the preantral phase

Answer 14

Primordial follicle grows and follicular cells change from flat to cubiodal

Proliferation occurs to form stratified epithelium of granulosa cells which secrete zona pellucida

Now primary follicle

Question 15

Describe the antral phase

Answer 15

Fluid filled spaces appear between granulosa cells -> coalesce to form antrum - now secondary follicle

Outer fibrous layer develops into theca interna and externa

Question 16

Describe the pre-ovulatory phase

Answer 16

Induced by LH surge

Follicle completes meiosis I

Graafian follicle is chosen to complete ovulation - it enters meiosis II but arrests in metaphase II

Question 17

Describe ovulation

Answer 17

FSH and LH stimulate rapid growth of follicle several days before ovulation - pre-ovulatory phase

Mature follicle now 2.5cm in diameter - graafian follicle

LH surge increases collagenase acitivity while prostaglandins increase response to LH and cause local muscular contraction in ovarian wall

Oocyte extruded and breaks free from ovary

Question 18

Following ovulation what happens to the granulosa and theca interna

Answer 18

They become vascularised and form the corpus luteum which secretes oestrogen and progesterone

This stimulates uterine mucosa to enter secretory stage in preparation for embryo implantation

Question 19

Describe oocyte transport

Answer 19

At ovulation, oocyte is released when follicle ruptures and is caught by fimbriae which sweep over the surface of the ovary shortly before ovulation

Oocyte is carried into the tube and down it - cilia on epithelial lining waft and uterine tube contractions propel oocyte down the tube

Question 20

What happens in the ovary if fertilisation occurs

Answer 20

Implanted embryo releases beta-hCG which maintains corpus luteum until placenta can take over production of progesterone

Corpus luteum continues to grow and forms corpus luteum graviditatis

Question 21

What happens to the corpus luteum if fertilisation does not occur

Answer 21

Corpus luteum degenerates if fertilisation does not occur

It forms the corpus albicans - mass of scar tissue

Progesterone production decreases which precipitates menstral bleeding