2) Origins of the Gametes

Question 1

Describe the process by which germ cells form gametes:

Answer 1

Proliferate by mitosis, genetic reshuffling and reduction to haploid in meiosis

Question 2

What are the functions of meiosis?

Answer 2

Reduce chromosome number to 23

Ensure every gamete is unique

Question 3

By what processes does genetic variation arise?

Answer 3

Crossing over
Random segregation
Independent assortment

Question 4

Which part of the gonad do male germ cells colonise?

Answer 4

Seminiferous cords in medulla

Question 5

Describe the route sperm take in the testis:

Answer 5

Seminiferous tubules -> rete testis -> ductili efferentes -> epididymis

Question 6

Where do spermatozoa develop?

Answer 6

Seminiferous tubules in association with Sertoli cells

Question 7

What does the blood testis barrier separate?

And what is its other function?

Answer 7

Surrounding interstitial tissues and germ cells from seminiferous tubules
Stops sperm being recognised as foreign

Question 8

What cells secrete testosterone and where are they found?

Answer 8

Leydig cells in interstitial tissue

Question 9

What is the name of the cells that are the ‘raw material’ for spermatogenesis?

Answer 9

Spermatogonia

Question 10

What two cells do spermatogonium divide into?

Answer 10

Ad spermatogonium (maintain stock)
Ap spermatogonium (primary spermatocytes)

Question 11

Describe the formation of sperm from primary spermatocytes:

Answer 11

Primary spermatocytes become secondary spermatocytes and then spermatids by meiosis. Spermatids differentiate into sperm

Question 12

What is the spermatogenic cycle?

Answer 12

Time taken for re-appearance of same stage within a given segment of tubule (16 days)

Question 13

What is a spermatogenic wave?

Answer 13

Distance between same stage in a tubule

Question 14

What is spermiogenesis?

Answer 14

Remodelling of spermatids and gaining of motility as they pass to epididymis

Question 15

What allows spermatids to travel to the epididymis?

Answer 15

Sertoli cell secretions and peristaltic contractions

Question 16

What secretions make up semen?

Answer 16

Seminal vesicle
Prostate gland
Sperm (via vas deferens)
Bulbourethral gland

Question 17

What are the seminal vesicle secretions for?

Answer 17

AA, citrate, fructose and prostaglandins

Energy source

Question 18

What are the bulbourethral gland secretions for?

Answer 18

Mucoproteins help lubricate and neutralise acidic urine in distal urethra

Question 19

What is the final maturation step for sperm?

Answer 19

Sperm capacitation

Question 20

What occurs in sperm capacitation?

Answer 20

Conditions in female genital tract stimulate:
Removal of glycoproteins and cholesterol from sperm membrane
Activation of sperm signalling pathways

Question 21

What does sperm capacitation allow?

Answer 21

Allows sperm to bind to zona pellucida of oocyte and initiate acrosome reaction

Question 22

Describe the colonisation by female germ cells:

Answer 22

Colonise gonadal cortex and differentiate into oogonia

Question 23

What stage are primary oocytes in?

Answer 23

Prophase I

Question 24

How are primary oocytes arranged?

Answer 24

Surrounded by flat epithelia cells called follicular cells forming primordial follicle

Question 25

What could be a reason that there is increasing risk of fetal chromosomal abnormalities in older pregnant women?

Answer 25

Primary oocytes remain in resting stage for many years, increasing chance of cell damage

Question 26

Why are there so few oocytes when puberty is reached?

Answer 26

Undergo atresia in late gestation and childhood

Question 27

In what stages do oocytes mature?

Answer 27

Pre-antral, antral and pre-ovulatory

Question 28

What changes occur to follicular cells in the pre-antral stage?

Answer 28

Change from flat to cuboidal before proliferating to produce stratified epithelium of granulosa cells

Question 29

What layers form around the oocyte in the pre-antral stage?

Answer 29

Zona pellucida, granulosa cells, inner and outer theca folliculi

Question 30

What are the granulosa cells surrounding the oocyte called?

Answer 30

Cumulus oophorus

Question 31

What occurs in the antral stage? | What does this development depend upon?

Answer 31

Fluid filled spaces appear in between granulosa cells to from an antrum Development depends upon FSH binding to granulosa cells and LH binding to theca cells

Question 32

What occurs in the pre-ovulatory stage?

Answer 32

Oocyte completes meiosis I forming secondary oocyte (most of cytoplasm) and polar body. Cells enters meiosis II but arrests at metaphase

Question 33

When is meiosis II completed?

Answer 33

If oocyte is fertilised

Question 34

What causes oocyte release?

Answer 34

LH surge increasing collagenase activity and prostaglandins amplifying response and causing local contractions in ovarian wall

Question 35

Describe the formation of the corpus luteum:

Answer 35

Remaining granulosa and theca interna cells become vascularised, develop yellow pigment and change to lutein cells

Question 36

What does the corpus luteum secrete and what effect does this have?

Answer 36

Progesterone and oestrogen under influence of LH | Stimulates uterine mucosa to enter secretory stage in preparation for embryo implantation

Question 37

What causes the oocyte to move into the fallopian tube?

Answer 37

Fimbriae, uterine tube contracting and cilia

Question 38

What happens if there is no fertilisation?

Answer 38

After 14 days, corpus luteum degenerate forming corpus albicans Decreased progesterone = menstrual bleeding

Question 39

What happens to corpus luteum if fertilisation occurs?

Answer 39

Degeneration prevented by human chorionic gonadotropin secreted by embryo Forms corpus luteum graviditatis

Question 40

What happens to progesterone secretion if fertilisation occurs?

Answer 40

Cells of CL secrete progesterone until 4th month where placental secretion becomes adequate

Question 41

What is the effect of FSH in women?

Answer 41

Stimulate follicle growth and maturation

Question 42

What is the effect of LH in women?

Answer 42

Stimulate follicle maturation, ovulation due to surge and promotes corpus luteum development

Question 43

When is the follicular stage of the ovarian cycle?

Answer 43

0-14 days

Question 44

What is the luteal stage of the ovarian cycle?

Answer 44

14-28 days