S3) Gametogenesis Flashcards Preview

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Flashcards in S3) Gametogenesis Deck (56)
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1
Q

What are the starting cells for spermatogenesis and how long are they available for?

A
  • Spermatogonia
  • 70 years
2
Q

Spermatogonia divide by mitosis to give rise to two types of cells.

Identify and describe them

A
  • Ad spermatogonium: reserve stock (resting)
  • Ap spermatogonium: maintain stock (active)

– require different stock because a male always needs sperm on the go as female isn’t always fertile

3
Q

What do ap spermatogonia do?

A

From puberty onwards, ap spermatogonia produce type B spermatogonia which give rise to primary spermatocytes

4
Q

Briefly describe the process of spermatogenesis

A
5
Q

What is spermiation?

A

Spermiation is the release of spermatids into the lumen of seminiferous tubules

6
Q

What is spermiogenesis?

A

Spermiogenesis is when a haploid spermatid differentiates into a spermatozoon

– mainly occurs in the seminiferous tubules

7
Q

Outline the steps involved in spermiogenesis

A

⇒ Spermiation

⇒ Spermatid remodelling (seminiferous tubule)

⇒ Spermatid moves through rete testis and ductuli efferentes and into the epididymis

8
Q

What is the spermatogenic cycle?

A

Spermatogenic cycle is the time taken for reappearance of the same stage (of spermatogenesis) within a given segment of the seminiferous tubule

– each different part appears at different times so you just look at one

9
Q

How long is the spermatogenic cycle in adult humans?

A

16 days

10
Q

What is the spermatogenic wave?

A

Spermatogenic wave is the distance (in the tubule) between the same stage of spermatogenesis

  • along the seminiferous tubule
11
Q

How does the spermatogenic wave move?

A

Waves move in corkscrew-like spirals towards the inner part of the lumen

12
Q

How do spermatids reach the epididymis in the process of spermiogenesis?

A
  • Spermatids are non-motile
  • Transported by Sertoli cell secretions assisted by peristaltic contraction

they learn how to become motile in the epididymis

13
Q

Identify the different structures in the pathway for the delivery of sperm

A

Seminiferous tubules → Rete testis → Ductuli efferentes → Epididymis → Vas deferens → Urethra

this whole process is known as spermiogenesis

14
Q

Identify the contents of seminal vesicle secretions (~70%) and where are they in relation to the journey of the sperm?

A
  • Amino acids
  • Citrate
  • Fructose
  • Prostaglandins
15
Q

Identify the contents of prostate gland secretions (~25%)

A
  • Proteolytic enzymes
  • Zinc
16
Q

What is the function of the bulbourethral gland (<1%)?

A

Secrete mucoproteins to help lubricate and neutralise acidic urine in distal urethra

17
Q

What is the overall contribution of sperm to semen?

A

2-5% of overall volume

18
Q

How many sperm are there per ejaculate?

A

200-500 million

19
Q

Which glands secrete into the urethra?

A
  • Prostate gland
  • Bulbourethral gland
20
Q

Which gland secretes into the vas deferens?

A

Seminal vesicle

21
Q

What is sperm capacitation?

A
  • Sperm capacitation refers to the physiological changes spermatozoa must undergo in order to fertilise an egg
  • The final maturation step for sperm
22
Q

Which three processes are stimulated by the female genital tract?

A
  • Removal of glycoproteins and cholesterol from sperm membrane
  • Activation of sperm signalling pathways
  • Allow sperm to bind to zona pellucida of oocyte
23
Q

When does oocyte maturation begin?

A

Before birth

24
Q

What are oogonia and what do they do?

A
  • Germ cells arise from yolk sac and colonise the gonadal cortex, differentiating into oogonia
  • Oogonia proliferate rapidly by mitosis
25
Q

Describe the arrangement and actions of oogonia by the end of 3rd month

A
  • Arranged in clusters surrounded by flat epithelial cells
  • Majority continue to divide by mitosis but some enter meiosis
26
Q

What are primary oocytes?

A

Primary oocytes are oogonia that have arrested in prophase of meiosis I

27
Q

What is the maximum number of germ cells in the female?

When is this value reached?

A
  • ~7 million germ cells
  • Reached by mid gestation
28
Q

What are primordial follicles?

A

Primordial follicles are surviving primary oocytes which are individually surrounded by a layer of follicular cells

29
Q

What are follicular cells?

A

Follicular cells are the layer of flat epithelial cells that surround individual primary oocytes in late gestation

30
Q

Define follicular atresia

A

Atresia is the degeneration of those ovarian follicles which do not ovulate

31
Q

Describe atresia in females

A
  • After mid gestation, many oogonia and primary oocytes degenerate
  • By 7th month gestation, ~5 milion oogonia have degenerated
32
Q

How many oocytes are left by the start of puberty?

A

~40,000 (most oocytes undergo atresia during childhood)

  • roughly females have 400 periods so 400 chances too get pregnant
33
Q

How many oocytes mature each month from puberty onwards?

A

~15-20 oocytes start to mature each month

– in the end only one will mature enough to be fertilised

34
Q

Identify the 3 stages in oocyte maturation

A
  1. Preantral
  2. Antral
  3. Preovulatory
35
Q

What happens in the pre-antral stage?

A
  • Primordial follicle grows to form the primary follicle
  • Follicular cells change and proliferate to form a stratified cuboidal epithelium of granulosa cells
36
Q

Describe the function of granulosa cells

A

Granulosa cells secrete layer of glycoprotein on oocytes forming the zona pellucida

37
Q

What happens in the antral stage?

A
  • Fluid-filled spaces appear between granulosa cells
  • These spaces coalesce to form the antrum
38
Q

What induces the preovulatory growth phase?

A

Surge in LH

39
Q

What happens during the preovulatory stage?

A
  • Meiosis I completion results in 2 haploid cells of unequal size
  • One cell receives most of cytoplasm the first polar body receives practically none
40
Q

When does meiosis II occur in oogenesis?

A
  • Before ovulation, cell then enters meiosis II but arrests in metaphase
  • After ovulation, meiosis II is only completed if oocyte is fertilized, otherwise cell degenerates
41
Q

Which substances stimulate the rapid growth of the follicle?

A
  • Follicle stimulating hormone (FSH)
  • Luteinising hormone (LH)
42
Q

What is a Graafian follicle?

A
  • A Graafian follicle is a mature follicle in the ovary that gets released
  • It is ~2.5cm in diameter
43
Q

What role does LH have in ovulation?

A
  • LH surge increases collagenase activity
  • Prostaglandins increase response to LH & cause local muscular contractions in ovarian wall
44
Q

What happens to the oocyte in ovulation?

A

Oocyte is extruded & breaks free from ovary

45
Q

How is the corpus luteum formed?

A
  • After ovulation, remaining granulosa and theca interna cells become vascularized
  • They develop a yellowish pigment and change into lutein cells, which form the corpus luteum
46
Q

What does the corpus luteum do?

A
  • Secrete oestrogen & progesterone
  • Stimulates uterine mucosa to enter secretory stage in preparation for embryo implantation
  • Dies after 14 days if no fertilisation occurs
47
Q

How is the oocyte transported from the ovary?

A
  • Oocyte carried into tube by sweeping movements of fimbriae and mucosal cilia
  • Oocyte then propelled by peristaltic muscular contractions of uterine tube (contract rhythmically) and by mucosal cilia
48
Q

What happens to the corpus luteum if no fertilisation occurs?

A
  • Corpus luteum degenerates
  • Forms corpus albicans – mass of fibrotic scar tissue
  • Progesterone production decreases
  • Menstrual bleeding occurs
49
Q

The corpus luteum does not degenerate if fertilisation occurs.

Explain why

A

Degeneration prevented by human chorionic gonadotropin, secreted by developing embryo

50
Q

What role does the corpus luteum have post-fertilisation?

A

The corpus luteum continues to grow and forms the corpus luteum of pregnancy (corpus luteum graviditatis)

51
Q

When does the corpus luteum stop secreting progesterone and why?

A

Cells continue to secrete progesterone until ~ 4th month until the placenta takes over

52
Q

Outline the four steps involved in the ovarian cycle

A

⇒ Hypothalamic GnRH stimulates anterior pituitary to release FSH and LH

FSH stimulates follicle growth

FSH and LH stimulate follicle maturation

LH surge triggers ovulation & promotes development of the corpus luteum

53
Q

Compare and contrast oogenesis and spermatogenesis in terms of the following:

  • Commencement
  • Completion
  • Gamete motility
  • Daughter cells
  • Stages
  • Overall yield
A
54
Q

what is a primary spermatocyte?

A
  • each forms 4 haploid spermatids
  • the spermatids differentiate into spermatozoa
55
Q

at which point is meiosis II completed In oogenesis

A

at fertilisation.

56
Q

what element of the developing follicle is next to the developing oocyte

A

granuloma cell