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Repro > Gametogenesis > Flashcards

Gametogenesis Flashcards

1
Q

What happens in gametogensis? (4 steps)

A

Germ cells colonise gonad

Then proliferate via mitosis

Become haploid and genetically unique via meiosis

The cytodifferentiate into mature gametes

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2
Q

Gametes and chromosomes

A

Female gametes always contains X chromosome

Male contains X or Y so these are the determinant of the sex of the offspring

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3
Q

Oogenesis vs Spermatogenesis

A

Oogenesis - few gametes, produced once a month (intermittent), 1/400th reproductive potential (women only produce on average 400 eggs in lifetime

Spermatogenesis - 200 million produced PER DAY!!, produced continuously, disposable cells - no limit

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4
Q

What are the two main functions of meisosis?

A

Reduce chromosome number in the gamete to 23 (haploid)

Ensures every gamete is genetically unique

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5
Q

What is involved in meiosis?

A

Two successive divisions

Produces 4 daughter cells (in female this only makes 1 mature oocyte)

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6
Q

When does crossing over occur?

A

Prophase1

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7
Q

Meiossis 1 vs Meiosis 2

A

DNA is replicated first

Meiosis 1 - crossing over, homologous chromosomes line up and are pulled apart - 2 haploid cells (23 chromosomes but with 2 copies so 46 chromatids)

Meiosis 2 - sister chromatids separate, 4 haploid cells with only 1 copy

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8
Q

Chromosome and chromatid number at the end of each meiosis cycle

A

Meiosis 1 result - 23 chromosomes but 46 chromatids

Meiosis 2 - 23 chromosomes, 23 chromatids

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9
Q

How does genetic variation occur in meiosis?

A

Crossing over (exchange of DNA between homologous chromosomes)

Independent assortment (random splitting of different genes into different gametes)

Random segregation (random allele distribution within the 4 gametes)

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10
Q

What structure does crossing over form?

A

Chiasma - crossed homologous chromosomes

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11
Q

Where does spermatogenesis take place initally?

A

Seminiferous tubules

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12
Q

Where does sperm go after seminiferous tubules?

A

Through rete testis and ductilli efferentes to the epididymis (head)

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13
Q

Where are sperm stored?

A

Epididymis

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14
Q

What is created by the sertoli cells and tight junctions within the seminiferous tubules?

A

Blood testis barrier (sertoli cell barrier)

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15
Q

Importance of sertoli cell barrier/blood testis barrier?

A

Seperates basal compartment from Adluminal compartment

If not there mature spermatozoa in adluminal compartment could be seen as ‘non self’ by spermatogonia and attacked by the body

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16
Q

Cycle of a sperm - spermatogenesis

A

Spermatogonium (2n)
(mitosis)

2x primary spermatocyte (2n each)
(meiosis 1)

–> from one primary spermatocyte you get:

2x secondary spermatocyte (1n each)
(meiosis 2)

4x spermatids

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17
Q

What is the process of making spermatids into spermatozoa (sperm)?

A

Spermiogenesis

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18
Q

What are spermatogonia?

A

Raw material for spermatogenesis - they are germ cells

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19
Q

How long are spermatogoniums available for/

A

70 years

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20
Q

What are the 2 types of spermatogonium formed after dividing by mitosis?

A

Ad spermatogonium - dark, resting reserve stock

Ap spermatogonium - pale, active stock, maintain stock and from puberty produce type B spermatogonia –> primary spermatocytes

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21
Q

What happens to primary spermatocytes?

A

They divide by meiosis 1 to form secondary spermatocytes then meiosis 2 to form spermatids

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22
Q

What becomes of each primary spermatocyte?

A

Each forms 4 haploid spermatids with differentiate into spermatozoa (via spermiogenesis)

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23
Q

What is a spermatogenic cycle?

A

time taken for reappearance of the same stage within a given segment of the tubule (time taken for immature sperm to fully mature)

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24
Q

What is a spermatogenic wave?

A

Distance between the same stage (each stage follows orderly sequence along length of tubule)

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25
Q

How do spermatogenic waves move?

A

Corkscrew like movement towards inner lumen (more mature the more internal you go)

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26
Q

What is spermiation?

A

When spermatids are released into the lumen of the seminiferous tubules

27
Q

What happens as spermatids pass down through the lumen of seminiferous tubules?

A

Remodel - pass through rete testis and ductuli efferentes into epididymis to form spermatozoa

28
Q

How do sperm move down seminiferous tubules?

A

They are non motile - transported via sertoli cell secretions and peristaltic contraction to the epididymis

29
Q

Spermiogenesis is?

A

The release of spermatids into lumen of seminiferous tubules

Remodelling of spermatids down seminiferous tubules,

30
Q

What makes up semen?

A

Seminal vesicle secretions - amino acids, citrate, fructose, prostaglandins (70%)

Prostatic secretions - proteolytic enzymes, zinc (25%)

Sperm - 200-500 million per ejaculate (2-5%)

Bulbourethral gland secretions - aka Cowper gland, mucoproteins lubricate and neutralise acidic urine in distal urethra (<1%)

31
Q

What is sperm capacitation?

A

Last step for sperm to become fertile

Female genital tract conditions remove glycoproteins and cholesterol from sperm membrane

Activate sperm signalling pathway

Ultimately allowing sperm to bind to zona pellucida of oocyte and initiate ACROSOME REACTION

32
Q

What significance does sperm capacitation have on IVF?

A

In vitro, sperm must be incubated in capacitation media to make them fertile

33
Q

What happens to the female stock of gametes?

A

start off with stock before birth

declines as you age due to atresia - very selective on which eggs are kept

then menopause = 0 eggs

34
Q

How do oocytes mature?

A

Before birth - germ cells (from yolk sac) colonise gonadal cortex and differentiate into oogonia (oogonium if single)

35
Q

What happens to oogonia after they colonise gonads?

A

Proliferate via mitosis - by 3rd month oogonia arrange in clusters and are surrounded by flat epithelia

36
Q

What happens to the clusters of oogonia surrounded by flat epithelial cells?

A

Majority continue to divide, some enter meiosis 1 - BUT arrest in prophase 1

37
Q

What are the oogonia called that have entered meiosis 1 but arrested in prophase 1?

A

Primary oocytes

38
Q

What happens as the oocytes continue to proliferate?

A

Max number reached by mid gestation (7 million)

Cell death begins, many oogonia and primary oocytes degenerate (via atresia)

39
Q

What happens to oogonia after cell death via atresia?

A

Majority have degenerated

All remaining oogonia have entered meiosis 1 so are primary oocytes and are surrounded by flat epithelial cells called FOLLICULAR CELLS

40
Q

What is it called when primary oocytes are surrounded by follicular cells (flat epithelia)?

A

Primordial follicle

41
Q

What happens to oocytes from now until puberty?

A

Arrest in prophase 1, many still undergo atresio until 40,000 ish remain at puberty

42
Q

What happens to oocytes from puberty onwards?

A

15-20 oocytes start maturing each month by passing through 3 stages

43
Q

3 stages of oocyte maturation

A

Pre-antral
Antral
Preovulatory

44
Q

Describe pre-antral stage

A

Primordial follicle grows, follicular (flat) epithelium changes to cuboidal and proliferate to form stratified epithelium of granulosa cells

45
Q

What do granulosa cells do?

A

Secrete glycoprotein on oocyte to form zona pellucida

46
Q

What does the primordial follicle become at the end of pre-antral stage?

A

Primordial follicle
–>
Growing follicle
–>
Primary follicle

47
Q

Describe antrum stage

A

Fluid filled spaces appear between granulosa cells
Coalesce/join to form antrum

Secondary follicle is formed

48
Q

Layers of secondary follicle

A

Outer fibrous (theca externa)

Inner secretory (theca interna)

Granulosa cells

Granulosa cells surrounding follicle - Cumulus oophorus

49
Q

What induces the pre-ovulatory stage?

A

Surge in LH

50
Q

What happens in pre-ovulatory stage?

A

Meiosis 1 is complete = 2 haploid daughter cells of unequal size (23 chromosomes, 46 chromatids, one cell has more cytoplasm)

51
Q

What happens to these 2 haploid daughter cells from follicle?

A

One enters meiosis 2 but arrests in metaphase (3 hours before ovulation)

The other, smaller cell becomes first polar body

52
Q

When is meiosis 2 completed for oocyte?

A

Only completed if oocyte is fertilised, otherwise cell degenerates 24 hrs after ovulation

53
Q

What stimulates growth of follicle prior to ovulation?

A

FSH and LH

54
Q

What is mature follicle called?

A

Graafian follicle

55
Q

What does LH surge cause?

A

Increase in collagenase activity, prostaglandins increase and cause local muscular contractions in ovarian wall

= oocyte extruded and breaks free from ovary

56
Q

What is the corupus luteum?

A

Granulosa cells remaining and theca interna cells become vascularised

develop yellowish pigment and become lutein cells which form corpus luteum

57
Q

What does corpus luteum do?

A

Secrete oestrogen and progesterone

These stimulate uterine mucosa to enter secretory stage and prep for embryo implantation

  • Dies after 14 days if no ferilisation
58
Q

How is the oocyte transported?

A

Before ovulation, fimbriae sweep over ovary surface

Uterine tube rhythmically contracts

Fimbrae sweeps and oocyte is carried into tube

Oocyte propelled by peristalsis (muscular contractions) and cilia in mucosa

59
Q

What happens to corpus luteum if no fertilisation occurs?

A

Corpus luteum degenerates
Forms mass of fibrotic scar tissue - corpus albicans

Progesterone decreases = menstrual bleeding

60
Q

What happens to corpus luteum if fertilisation occurs?

A

Degeneration is prevented by human chorionic gonadotrophin secreted by embryo

forms corpus luteum of pregnancy - corpus luteum graviditatis

secrete progesterone until 4th month

61
Q

Whathormones influence the ovarian cycle?

A

GnRH (gonadotrophin releasing hormone) from hypothalamus

Anterior pituitary releases FSH and LH

Follicles grow from FSH and mature with FSH and LH

LH surge = ovulation and development of corpus luteum

62
Q

When are the other 2 polar bodies formed of eggs?

A

After fetilisation - 1 polar body

1st polar body (from before fertilisation) divides into 2 polar bodies

63
Q

What is oocyte called once fertilised?

A

Ovum and then Zygote once diploid

64
Q

Spermatogenesis vs Oogenesis

A

1 oocyte per 28 days, 200 million sperm per day

4 spermatids, 1 ovum with 3 polar bodies

male - starts at puberty, female starts in fetus

male - continues throughout life, female ends at menopause

Sperm are motile, egg are non motile

All stages of meiosis are complete in males testes, in females last stage of meiosis occurs after fertilisation in oviduct

Repro (22 decks)

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