Origins Of Gametes

Question 1

After colonising the gonad, germ cells…

Answer 1

Proliferate by mitosis
Reshuffle genetically and reduce to haploid by meiosis
Cytodifferentiate into mature gametes

Question 2

What are the sex chromosomes of the different genders?

Answer 2

XX = female
XY = male

Question 3

Which part of the gonad do the germ cells colonise in males and females?

Answer 3

XY = colonise medulla
XX = colonise cortex

Question 4

Approximately how many gametes has a woman got per lifetime?

Answer 4

400

Question 5

How many sperm do men produce per day?

Answer 5

~ 200 million

Question 6

What are the 2 main functions of meiosis?

Answer 6

Reduce to haploid (chromosome number = 23)

Ensure every gamete is genetically unique

Question 7

What happens to the 4 daughter cells of meiosis in females?

Answer 7

1 becomes the mature oocyte

3 become polar bodies

Question 8

When does crossing over occur?

Answer 8

Prophase 1

Question 9

In meiosis, genetic variation arises from …

Answer 9

Crossing over
Random segregation
Independent assortment

Question 10

Describe crossing over

Answer 10

Exchange of regions of DNA between 2 homologous chromosomes

In prophase 1

Question 11

Describe the passage of sperm from inner testis to vas deferens

Answer 11

Seminiferous tubules > rete testis > ductus efferentes > epididymis (head, body, tail) > vas deferens

Question 12

What do we call male germ cells?

Answer 12

Spermatogonia

Question 13

What is the difference between Ad and Ap spermatogonia?

Answer 13

Ad = maintains stock of spermatogonia 
Ap = gives rise to primary spermatocytes

Question 14

Describe the order of cells from spermatogonium to sperm

Answer 14

Spermatogonium > primary spermatocyte > secondary spermatocyte > spermatid > spermatozoa (sperm)

Question 15

What is the spermatogenic cycle?

Answer 15

Time taken for reappearance of the same stage within a given segment of tubule
(~ 16 days in humans)

Question 16

What is the spermatogenic wave?

Answer 16

The distance between parts in the same stage

Question 17

Define spermiation

Answer 17

Spermatids released into lumen of seminiferous tubules

Question 18

Where does the final stage of spermiogenesis occur?

Answer 18

Epididymis

Question 19

Describe how transport occurs in epididymis

Answer 19

Via Sertoli cell secretions assisted by peristaltic contractions

Question 20

How much semen is there per ejaculate?

Answer 20

2ml

Question 21

What percentage of semen volume comes from the seminal vesicles?

Answer 21

70%

Question 22

What is in the seminal vesicle secretions?

Answer 22

Amino acids
Citrate
Fructose (main energy for sperm)
Prostaglandins

Question 23

What percentage of semen volume comes from the prostate?

Answer 23

25%

Question 24

What is in the prostatic secretions?

Answer 24

Proteolytic enzymes eg. PSA

Zinc

Question 25

What percentage of semen is sperm?

Answer 25

2 - 5%

Question 26

How many sperm are there per ejaculate?

Answer 26

200 - 500 million

Question 27

What percentage of the volume of semen comes from bulbourethral glands?

Answer 27

< 1%

Question 28

What is the other name for bulbourethral glands?

Answer 28

Cowper's glands

Question 29

What is secreted from bulbourethral glands?

Answer 29

Mucoproteins to help lubricate urethra and neutralise acidic urine in distal urethra

Question 30

What is sperm capacitation?

Answer 30

Final maturation step required before sperm become fertile Occurring in the female genital tract Removal of glycoproteins and cholesterol to activate signalling to allow sperm to bind to zona pellucida

Question 31

When are female gametes produced?

Answer 31

All before birth

Question 32

Approximately what age is menopause?

Answer 32

55 years

Question 33

Where do germ cells arise from?

Answer 33

Yolk sac

Question 34

Primary oocytes are arrested in which phase?

Answer 34

Prophase 1

Question 35

How many oocytes remain by puberty?

Answer 35

40,000 | Others have undergone atresia

Question 36

Approximately how many oocytes start to mature every month?

Answer 36

15 - 20

Question 37

What are the 3 stages of maturation an oocyte must pass through?

Answer 37

Pre-antral Natural Pre-ovulatory

Question 38

Describe the pre-antral stage

Answer 38

Primordial follicles begin to grow Surrounding follicular cells get more cuboidal and proliferate Produce a stratified epithelium of granulosa cells which secrete glycoprotein

Question 39

Describe the antral stage

Answer 39

Fluid filled spaces appear between granulosa cells | These coalesce to form the antrum

Question 40

What do we call the granulosa cells surrounding the oocyte directly?

Answer 40

Cumulus oophorus

Question 41

What are the 2 layers of thecal cells?

Answer 41

Outer fibrous | Inner secretory

Question 42

Describe the pre-ovulatory stage

Answer 42

Surge in LH gives growth phase Meiosis I completed Cells enter meiosis II and arrest in metaphase Meiosis II only completed if fertilised

Question 43

Describe ovulation

Answer 43

FSH and LH stimulate rapid growth of follicle Mature follicle 2.5 cm diameter (Graafian follicle) Ruptures to release oocyte - LH surge (to increased collagenase activity)

Question 44

What is the corpus luteum?

Answer 44

Remaining granulosa and theca interna cells become vascularised Develop yellowish pigment and change into lutein cells Secrete oestrogens and progesterone Stimulate uterine mucosa to enter secretory stage - prep for embryo implantation Dies after 14 days if no fertilisation

Question 45

What is the corpus albicans?

Answer 45

When no fertilisation occurs the corpus luteum degenerates forming a mass of fibrotic scar tissue Progesterone production decreases - menstrual bleeding

Question 46

What happens to the corpus luteum if fertilisation occurs?

Answer 46

Degeneration prevented via hCG CL continues to grow and forms the CL of pregnancy Cells continue to secrete progesterone until 4th months until secretion by placenta is adequate

Question 47

What are the main differences between spermatogenesis and oogenesis?

Answer 47

``` 4 spermatids vs 1 ovum 200 million/day vs 1 per 28 day cycle Starts at puberty vs starts in foetus Motile gametes vs non-motile Continues vs ends at menopause ```

Question 48

Why do males have a blood-testis barrier?

Answer 48

To prevent autoimmune attack on sperm (as will be genetically different to the father's cells)