(LUSUMA) Reproductive System > S3) Gametogenesis > Flashcards

S3) Gametogenesis Flashcards

(53 cards)

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1
Q

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

A
  • Spermatogonia
  • 70 years
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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)
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3
Q

What do ap spermatogonia do?

A

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

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4
Q

Briefly describe the process of spermatogenesis

A
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5
Q

What is spermiation?

A

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

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6
Q

What is spermiogenesis?

A

Spermiogenesis is when a haploid spermatid differentiates into a spermatozoon

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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

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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

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9
Q

How long is the spermatogenic cycle in adult humans?

A

16 days

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10
Q

What is the spermatogenic wave?

A

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

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11
Q

How does the spermatogenic wave move?

A

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

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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
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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

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14
Q

Identify the contents of seminal vesicle secretions (~70%)

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

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

A
  • Proteolytic enzymes
  • Zinc
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16
Q

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

A

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

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17
Q

What is the overall contribution of sperm to semen?

A

2-5% of overall volume

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18
Q

How many sperm are there per ejaculate?

A

200-500 million

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19
Q

Which glands secrete into the urethra?

A
  • Prostate gland
  • Bulbourethral gland
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20
Q

Which gland secretes into the vas deferens?

A

Seminal vesicle

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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
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22
Q

Which three processes are stimulated by the female genital tract?

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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?

24
Q

What are oogonia and what do they do?

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A
  • Germ cells arise from yolk sac and colonise the gonadal cortex, differentiating into oogonia
  • Oogonia proliferate rapidly by mitosis
25
Describe the arrangement and actions of oogonia by the end of 3rd month
- Arranged in **clusters** surrounded by **flat epithelial cells** - Majority continue to divide by **mitosis** but some enter **meiosis**
26
What are primary oocytes?
**Primary oocytes** are oogonia that have arrested in prophase of meiosis I
27
What is the maximum number of germ cells in the female? When is this value reached?
- ~7 million germ cells - Reached by mid gestation
28
What are primordial follicles?
**Primordial follicles** are surviving primary oocytes which are individually surrounded by a layer of follicular cells
29
What are follicular cells?
**Follicular cells** are the layer of flat epithelial cells that surround individual primary oocytes in late gestation
30
Define follicular atresia
**Atresia** is the degeneration of those ovarian follicles which do not ovulate
31
Describe atresia in females
- **After mid gestation,** many oogonia and primary oocytes degenerate - **By 7th month gestation**, ~5 milion oogonia have degenerated
32
How many oocytes are left by the start of puberty?
~40,000 (most oocytes undergo atresia during childhood)
33
How many oocytes mature each month from puberty onwards?
~15-20 oocytes start to mature each month
34
Identify the 3 stages in oocyte maturation
1. Preantral 2. Antral 3. Preovulatory
35
What happens in the pre-antral stage?
- Primordial follicle grows to form the **primary follicle** - Follicular cells change and proliferate to form a **stratified cuboidal epithelium of granulosa cells**
36
Describe the function of granulosa cells
**Granulosa cells** secrete layer of glycoprotein on oocytes forming the **zona pellucida**
37
What happens in the antral stage?
- **Fluid-filled spaces** appear between granulosa cells - These spaces coalesce to form the **antrum**
38
What induces the preovulatory growth phase?
Surge in LH
39
What happens during the preovulatory stage?
- 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
When does meiosis II occur in oogenesis?
- 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
Which substances stimulate the rapid growth of the follicle?
- Follicle stimulating hormone (FSH) - Luteinising hormone (LH)
42
What is a Graafian follicle?
- A **Graafian follicle** is a mature follicle in the ovary - It is ~2.5cm in diameter
43
What role does LH have in ovulation?
- LH surge increases collagenase activity - Prostaglandins increase response to LH & cause local muscular contractions in ovarian wall
44
What happens to the oocyte in ovulation?
**Oocyte** is extruded & breaks free from ovary
45
How is the corpus luteum formed?
- 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
What does the corpus luteum do?
- Secrete **oestrogen & progesterone** - Stimulates **uterine mucosa** to enter secretory stage in preparation for embryo implantation - **Dies** after 14 days if **no fertilisation** occurs
47
How is the oocyte transported from the ovary?
- Oocyte carried into tube by sweeping movements of **fimbriae** and **mucosal cilia** - Oocyte then propelled by peristaltic muscular contractions of **uterine tube** and by **mucosal cilia**
48
What happens to the corpus luteum if no fertilisation occurs?
- Corpus luteum degenerates - Forms corpus albicans – mass of fibrotic scar tissue - Progesterone production decreases - Menstrual bleeding occurs
49
The corpus luteum does not degenerate if fertilisation occurs. Explain why
Degeneration prevented by **human chorionic gonadotropin**, secreted by developing embryo
50
What role does the corpus luteum have post-fertilisation?
The corpus luteum continues to grow and forms the corpus luteum of pregnancy (**corpus luteum graviditatis**)
51
When does the corpus luteum stop secreting progesterone and why?
Cells continue to secrete **progesterone** until ~ 4th month until the placenta takes over
52
Outline the four steps involved in the ovarian cycle
⇒ 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
Compare and contrast oogenesis and spermatogenesis in terms of the following: - Commencement - Completion - Gamete motility - Daughter cells - Stages - Overall yield
(LUSUMA) Reproductive System
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