Lecture 5 - Gametogenesis

Question 1

Gamete features

Answer 1

Sperm and ova
Haploid
Product of meiosis
Fuse to form a diploid zygote

Question 2

Gametogenesis

Answer 2

1. Germ cells proliferate by mitosis
2. Become haploid cells by meiosis
3. Cytodifferentiate into mature gametes

Question 3

Sex determining gamete

Answer 3

Sperm

Question 4

Where does spermatogenesis occur?

Answer 4

Seminiferous tubules

Question 5

Spermatogenesis

Answer 5

1. Spermatogonia (germ cells) reside in the basement membrane
2. Divide by mitosis to form 2 primary spermatocytes (spermatogonium)
3. One spermatocyte replaces the spermatogonia and the other one undergoes meiosis I to form 2 secondary spermatocyte (haploid)
4. The 2 secondary spermatocytes undergo meiosis II to form 2 spermatids each

Question 6

Product of spermatogenesis

Answer 6

4 spermatids

Question 7

Difference between spermatogenesis and oogenesis

Answer 7

Spermatogenesis:

• Produces 200 million sperm a day
• 4 spermatids produced each cycle
• Starts at puberty
• Continuous through out adult life
• Motile gametes
• Continuous production
• Disposable cells

Oogenesis:

• Produces 1 ovum per 28 day menstrual cycle
• 1 ovum produced and 3 polar bodies
• Starts in fetus
• Ends at menopause
• Intermittent production
• Non- motile gametes
• 1/400th of reproductive potential each cycle

Question 8

Functions of meiosis

Answer 8

Reduce the chromosome number to 23

Ensures every gamete is genetically unique

Question 9

Meiosis

Answer 9

Only produces eggs and sperm

Produces 4 daughter cells

Question 10

Genetic variation

Answer 10

Arises from:

• Crossing over
• Independent assortment
• Random segregation

Question 11

Why do sperm mature in groups at different stages?

Answer 11

Relatively limited time when women are fertile therefore the male must have a store of mature sperm ready for fertilisation

Question 12

Spermatogenic cycle

Answer 12

Time taken for a group of spermatids to show up again when looking at a specific region of the seminiferous tubules.

Question 13

Spermatogenic wave

Answer 13

Distance between spermatids at the same level of maturation

Question 14

Spermiogenesis

Answer 14

Process whereby spermatids become spermatozoa (mature sperm)

As they reach the epididymis, they remodel, becoming more motile

Question 15

Spermiation

Answer 15

Spermatids realeased into the lumen of the seminiferous tubules

Question 16

Adaptations of sperm

Answer 16

Head - contains nucleus which contains the haploid genetic info

• acrosome - allows fusion with oocyte
• Tail contains many mitochondria to provide ATP for movement
• Tail - motility

Question 17

Seminal vesicle

Answer 17

65% of ejaculation fluid
Contains:
- fructose - energy
- coagulating factors

Question 18

Prostate secretions

Answer 18

25%

Contain proteases

Question 19

Cowper’s gland

Answer 19

Mucus like, alkaline fluid

- neutralise pH of urine

Question 20

Delivery of sperm

Answer 20

1. Seminferous tubules
2. Rete testes
3. Ductuli efferentes
4. Head of epididymis
5. Tail of epididymis
6. Vas deferens
7. Urethra

Question 21

Sperm capacitation

Answer 21

Final maturation where by sperm becomes fertile

1. Removes the glycoprotein and cholesterol layer from the outer sperm membrane
2. Activates sperm signalling pathways
3. Allows sperm to bind to the zona pellucida and initate the acrosome reaction

Question 22

Where does sperm capacitation occur

Answer 22

In the female genital tract

Question 23

In vitro fertilisation

Answer 23

Human sperm for in vitro fertilisation must first be incubated in capacitation media

Question 24

When does a female develop all the potential gametes?

Answer 24

Before birth

Question 25

Why does the gamete stock decline with age

Answer 25

Number primordial follicles decrease due to atresia

Question 26

oogenesis

Answer 26

Maturation of an oocyte in the ovary 1. Before birth, germ cells settle in the ovary to form oogonia 2. Oogonia rapidly divide by mitosis 3. Majority continue to dived but some divide by meiosis and arrest at prophase 1 to form primary oocytes until puberty. 4. At birth each primary oocyte is surrounded by folliclar cells - primordial follicles 5. From puberty approx 15-20 oocytes mature each month and go through the preanral, antral and preovulatory phase.

Question 27

Where do germ cells arise from in females

Answer 27

In the yolk sac and colonise the gonadal cortex

Question 28

At what month do all oogonia degenerate?

Answer 28

7th month of gestation All primary oocytes enter prophase I and arrest where they are indiviually surrounded by follicular cells to produce primordial follicles

Question 29

Stages of maturation of oocytes

Answer 29

Pre-antral Antral Pre- ovulatory

Question 30

How many oocytes mature each month after puberty?

Answer 30

15 - 20

Question 31

How many oocytes in total remain before puberty

Answer 31

40,000

Question 32

Preantral stage

Answer 32

Primordial follicle grows Follicular cells become stratified cuboidal from squamous to produce granulosar cells The primordial follicle becomes the primary follicle

Question 33

Granulosar cells

Answer 33

Secrete a layer of glycoprotein on the oocyte forming the zona pellucida

Question 34

Antral stage

Answer 34

Fluid filled spaces appear between granulosa cells. Coalesce to form the antrum. The outer fibrous layer develops into the theca interna and externa Primary follicles form into secondary follicles Several follicles begin to develop with each oovarian cycle but only one reaches maturity and others become atretic

Question 35

Preovulatory stage

Answer 35

1. LH surge (ovulation) 2. Induces preovulatory growth where meiosis I completes and 2 daughter haploid cells are formed of unequal size, a polar body and follicle. 3. The graafian cell is chosen and enters meiosis II and arrests in metaphase II, 3 hours before ovulation

Question 36

Why are the haploids daughter cells unequal

Answer 36

More of the cytoplasm goes to one cell rather than the other (polar body)

Question 37

How many chromosomes and chromatids does the daughter cells have in the preovulatory phase

Answer 37

23 chromosome | 46 chromatids

Question 38

When is meiosis II completed

Answer 38

When oocyte is fertilised, otherwise the cell will degenerate in 24 hours after ovulation

Question 39

Graaffian

Answer 39

The 1 follicle chosen to mature out of the many that develop Chosen follicle enters meiosis II just before ovulation

Question 40

Corpus luteum

Answer 40

The remaining granulosa and theca interna cells become vascularisd to form the corpus luteum after ovulation. Develop yellowish pigment and change into lutein cells/ Secretes oestrogen and progesterone Stimulates uterine mucosa to go into secretory phase If oocyte, not fertilised the corpus luteum degenerates after 14 days to form the corpus albicans

Question 41

LH surge

Answer 41

Increases collagenase activity Prostoglandins increase there response Local muscular contractions in the ovarian wall

Question 42

Oocyte transport

Answer 42

1. Before ovulation, fimbrae sweep over the ovarian surface 2. Uterine tube walls contract rythmically. At ovulation the follicle ruptures 3. Ooctye carried into tubes via fimbrae and cilia 4. oocyte propelled by peristaltic contractions of the tube and cilia 5. If fertlised, reaches the uterine lumen in 3 - 4 days

Question 43

Corpus albican

Answer 43

Mass of fibrotic scar tissue

Question 44

Corpus luteum graviditatis

Answer 44

Corpus luteum continues to grow in pregnancy and secretes progesterone until 4th month

Question 45

Average spermatogenic cycle length

Answer 45

16 days

Question 46

Granulosa cells surrounding the oocyte

Answer 46

Cumulus oophorus