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Repro > Lecture 5 - Gametogenesis > Flashcards

Lecture 5 - Gametogenesis Flashcards

1
Q

Gamete features

A

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

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2
Q

Gametogenesis

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

Sex determining gamete

A

Sperm

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4
Q

Where does spermatogenesis occur?

A

Seminiferous tubules

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5
Q

Spermatogenesis

A
  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
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6
Q

Product of spermatogenesis

A

4 spermatids

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7
Q

Difference between spermatogenesis and oogenesis

A

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
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8
Q

Functions of meiosis

A

Reduce the chromosome number to 23

Ensures every gamete is genetically unique

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9
Q

Meiosis

A

Only produces eggs and sperm

Produces 4 daughter cells

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10
Q

Genetic variation

A

Arises from:

  • Crossing over
  • Independent assortment
  • Random segregation
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11
Q

Why do sperm mature in groups at different stages?

A

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

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12
Q

Spermatogenic cycle

A

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

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13
Q

Spermatogenic wave

A

Distance between spermatids at the same level of maturation

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14
Q

Spermiogenesis

A

Process whereby spermatids become spermatozoa (mature sperm)

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

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15
Q

Spermiation

A

Spermatids realeased into the lumen of the seminiferous tubules

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16
Q

Adaptations of sperm

A

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
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17
Q

Seminal vesicle

A

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

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18
Q

Prostate secretions

A

25%

Contain proteases

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19
Q

Cowper’s gland

A

Mucus like, alkaline fluid

- neutralise pH of urine

20
Q

Delivery of sperm

A
  1. Seminferous tubules
  2. Rete testes
  3. Ductuli efferentes
  4. Head of epididymis
  5. Tail of epididymis
  6. Vas deferens
  7. Urethra
21
Q

Sperm capacitation

A

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
22
Q

Where does sperm capacitation occur

A

In the female genital tract

23
Q

In vitro fertilisation

A

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

24
Q

When does a female develop all the potential gametes?

A

Before birth

25
Q

Why does the gamete stock decline with age

A

Number primordial follicles decrease due to atresia

26
Q

oogenesis

A

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.
27
Q

Where do germ cells arise from in females

A

In the yolk sac and colonise the gonadal cortex

28
Q

At what month do all oogonia degenerate?

A

7th month of gestation

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

29
Q

Stages of maturation of oocytes

A

Pre-antral
Antral
Pre- ovulatory

30
Q

How many oocytes mature each month after puberty?

A

15 - 20

31
Q

How many oocytes in total remain before puberty

A

40,000

32
Q

Preantral stage

A

Primordial follicle grows

Follicular cells become stratified cuboidal from squamous to produce granulosar cells

The primordial follicle becomes the primary follicle

33
Q

Granulosar cells

A

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

34
Q

Antral stage

A

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

35
Q

Preovulatory stage

A
  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
36
Q

Why are the haploids daughter cells unequal

A

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

37
Q

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

A

23 chromosome

46 chromatids

38
Q

When is meiosis II completed

A

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

39
Q

Graaffian

A

The 1 follicle chosen to mature out of the many that develop

Chosen follicle enters meiosis II just before ovulation

40
Q

Corpus luteum

A

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

41
Q

LH surge

A

Increases collagenase activity

Prostoglandins increase there response

Local muscular contractions in the ovarian wall

42
Q

Oocyte transport

A
  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
43
Q

Corpus albican

A

Mass of fibrotic scar tissue

44
Q

Corpus luteum graviditatis

A

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

45
Q

Average spermatogenic cycle length

A

16 days

46
Q

Granulosa cells surrounding the oocyte

A

Cumulus oophorus

Repro (20 decks)

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