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Block 5 > Gametes & HPG Axis > Flashcards

Gametes & HPG Axis Flashcards

1
Q

Define gametes.

A

Specialised halpoid cells allowing us to pass our genes on to the next generation i.e. sperm/ova produced by sexually mature adults in the gonads (testes/ovaries) from specific diploid cells (germ cells) present from the early embryo

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2
Q

What is the difference between a haploid and diploid cell?

A

Haploid: 23 individual chromosomes

Diploid: 23 chromosome PAIRS

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3
Q

What is gametogenesis?

A
  1. Germ cells from early embryonic life migrate to developing gonads at 6 weeks development (time/scale differs between sexes)
  2. They colonise the gonads and:
    - Proliferate by mitosis
    - Reshuffle genetic material
    - Reduce to haploid by meiosis
    - Mature into sperm
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4
Q

What are the steps of mitosis?

A
  1. Interphase (G2): check point on duplicated DNA
  2. Prophase: Centrosomes with spindle poles appear whilst nuclear envelope breaks down
  3. Prometaphase: kinetochore develops from spindle poles and sister chromatids condense
  4. Metaphase: sister chromatids align and attach to kinetochore
  5. Anaphase: sister chromatids separate moving towards poles
  6. Telophase: cleavage furrow due to cytokinesis and 2 new nucleus established
  7. Interphase (G1): 2 identical daughter cells produced
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5
Q

Why is meiosis different to mitosis?

A

DNA is duplicated but then there is 2 divisions/cycles instead of 1 so 4 haploid daughter cells are made with different genetic material to the original cell

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6
Q

What is chiasmata?

A

Joining of genetic material between chromatids due to genetic recombination that occurs in meiosis meaning each gene can be inherited separately

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7
Q

What is spermatogonia?

A

The product of mitotic proliferation of XY germ cells that colonise the medulla of the testes in the early embryo

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8
Q

What happens to spermatogonia at puberty?

A

Spermatic cords hollow out to form seminiferous tubules (~250-750/testis) and the spermatogonia cluster around the edges initially. They are constantly replaced here by mitosis being available under late in life. As maturity and puberty ensue, spermatids are eventually close to the lumen ready to move down the tubule to mature into spermatozoa.

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9
Q

What is the process of sperMATOgenesis?

A

A process that begins at puberty when a group of spermatogonia divide by mitosis a fixed number of times to form a clone of ~64 linked diploid cells called primary spermatocytes. Meiosis cycle 1 produces 2 haploid secondary spermatocytes from each primary one. Meiosis cycle 2 results in 4 haploid spermatids per primary. This process takes 70 days with new spermatogonia groups being recruited every 16 days.

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10
Q

What is the problem with sperm production?

A

There is little quality assurance as it mainly about mass production so even if they have a problem, they will not apoptose

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11
Q

What is sperMIOgenesis?

A

Maturation/remodelling of spermatids in the seminiferous into fully differentiated spermatozoa as they move down the rete testis, efferent duct and epididymis

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12
Q

What are the 4 morphological features of mature spermatozoa?

A
  1. Formation of head containing nucleus and a mid-piece that contains mitochondria
  2. Formation of acrosome from Golgi apparatus
  3. Elongation of 1 centriole to form a tail
  4. Loss of excess cytoplasm
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13
Q

What is the acrosome?

A

A layer surrounding the head of the spermatozoa that contains digestive enzymes that break down the zona pellucida; the glycoprotein layer surrounding the ovum

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14
Q

What are spermatogenic waves?

A

Spermatogenesis occurs in sequential waves along the length of the seminiferous tubules with all stages of the process occurring at the same time in different sections of the tubule

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15
Q

Why is sperm produced continuously?

A

To exploit the time limitations of female fertility

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16
Q

What does semen contain?

A
  1. Seminal vesicle secretions mostly
  2. Prostate secretions
  3. Sperm via vas deferens
  4. Bulbo-urethral gland secretions

Mixed by emission into vagina by ejaculation

17
Q

How much semen does a male produce in each ejaculation?

A

1.4-4ml (>300M sperm but only ~50 get to fertilisation site)

18
Q

What is oogonia?

A

The product of mitotic proliferation of the female XX germ cells that colonise the ovaries cortex

19
Q

How does the numbers of oogonia vary throughout life?

A

Numbers peak at 7M by mid-gestation but then they start to die and are not replaced so about 2M remain at the end of gestation and they all enter meiosis before birth so females develop their entire stock of potential gametes before birth

20
Q

What is the process of oogenesis?

A

When meiosis stops before birth, a diploid primary oocyte is surrounded by a single layer of granulosa cells in a primordial follicle and from puberty, each month 1 or 2 primary oocytes complete development to form a mature ovum. Meiotic division resumes at ovulation (start of short fertility period of 24-36hrs) producing 1 haploid secondary oocyte and 1st polar body in cycle 1 and one mature haploid ovum and the 2nd polar body in cycle 2. Polar bodies are discarded.

21
Q

What is the requirement for successful fertilisation?

A

Effective transfer of viable male and female gametes to the right place at the right time

22
Q

What are the 3 requirements for successful reproduction?

A
  1. Fertilisation
  2. System of support for conceptus, embryo and then foetus in the female
  3. Birth at the right time
23
Q

What is the hypothalamus?

A

Dominant part of endocrine system that regulates the function of several hormonal axes:

  1. HPA
  2. HPG
  3. HPG
24
Q

What are the hormones of the Hypothalamus-Pituitary-Gonadal (HPG) axis?

A

H: GnRH

P: Ant - FSH, LH and prolactin + Post - oxytocin

G: oestrogen, progesterone, testosterone and inhibin

25
Q

What are the 6 hypothalamic releasing hormones and their relevant peptide hormones produced by the anterior pituitary gland in decreasing order of amount?

A 
GHRH -> GH
CRH -> ACTH
GnRH -> LH/FSH 
PIH/DA -> prolactin
TRH -> TSH
26
Q

What is the role of oxytocin?

A

Labour and lactation

27
Q

What is gonadotrophin releasing hormone (GnRH) and what does it do?

A

Decapeptide produced by cleavage of pre-pro-GnRH with a short T1/2 of < 10mins produced by the post-pubertal hypothalamus by pulsatile release every 1-2hrs transferred along pituitary stalk and acts on membrane receptors w/ IC signal transduction via 2nd messengers producing glycoprotein gonadotrophic hormones FSH and LH

28
Q

How does the release of gonadotrophin hormones change over life?

A

Low levels after birth with levels rising during puberty when pulsatile GnRH production begins

29
Q

What do gonadotrophin hormones do to the male reproductive system?

A

LH/FSH target Leydig cells and Sertoli cells lining the semiuniferous tubles of the testes. Leydig cells produce testosterone in response. Sertoli cells produce inhibin in response and support the developing sperm pushing them towards the tubule lumen ready for release. These hormones also support the 2ndary sexual characteristics of males.

30
Q

What is testosterone and what does it do?

A

Steroid hormone of the androgen family produced by Leydig cells that migrates to the seminiferous tubules, is converted to dihydrotestosterone (more active) by Sertoli cells, binds to androgen receptors in Sertoli cells to:

  • Stimulate sperm production
  • Secondary sex characteristics/libido
31
Q

What occurs in the female reproductive cycle overall?

A
  1. Follicle grows, oestrogen rises and there is -ve feedback to HP
  2. Dominant follicle with very high oestrogen levels and +ve feedback to HP
  3. LH surge occurs disrupting the dominant follicle so ovulation occurs
  4. Progesterone is high and exhibits -ve feedback
32
Q

What are the phases of the uterine cycle?

A

Days 0-7: menses
Days 7-14: proliferative phase
Days 14-28: secretory phase

33
Q

What are the 2 phases of the ovarian cycle?

A
  1. Follicular (days 0-14)

2. Luteal (days 14-28)

34
Q

What occurs post-ovulation?

A

Disrupted follicle forms corpus luteum and LH stimulates this to secrete progesterone and oestrogen which increase more as it expands negatively feeding back to HP - corpus luteum and therefore, oestrogen/progesterone production wane after 14 days if pregnancy does not occur

35
Q

What are the 5 roles of oestrogen?

A
  1. Increases muscular contraction in uterine tubes and uterus to facilitate sperm passage
  2. Proliferation of uterine lining to prepare for implantation
  3. Cervical mucus thinning and alkalizing to allow sperm entry
  4. Breast development at puberty and in pregnancy
  5. Affects female body fat distribution, hair, genitals and supports bone growth

Block 5 (29 decks)

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