gametes clara. learning outcomes gmc: p8a : integrate an understanding of the gross anatomical and...
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GAMETES Clara
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Learning Outcomes
• GMC: P8a : Integrate an understanding of the gross anatomical and microanatomical structure of the reproductive systems with their function
• Describe the process of spermatogenesis• Describe the ovarian cycle• Describe the process and control of ovulation• Describe the roles of the hormones of the HPG axis in regulating gamete production
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FIRST THINGS FIRST XY Germ cells induce the testis
XX Germ cells induce the ovary
2 pairs of 22 chromosomes, plus two sex chromosomes = 46 chromosomes
Female gamete = ovum
Male gamete = sperm
Haploid cell = a cell that contains a single set of chromosomes
Diploid cell = a cell that contains two sets of chromosomes
Overall picture :
1. Germ cells colonise the gonad
2. The germ cells proliferate : numbers increase, via mitosis
3. There is a genetic reshuffling within the cells
4. The cells reduce to haploid cells, via meiosis
5. The haploid cells then mature, this is called cytodifferentiation
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MITOSIS AND MEIOSIS
Mitosis = One single cell divides to give two daughter cells, each containing the same number of chromosomes and genetic content as the original cell
Meiosis = one parent replicates and recombines, divides once to give two daughter cells, then divides again creating four daughter cells, each containing half the genetic content of the original parent cell
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SPERMATOGENESIS
XY Germ cell
MitosisSpermatogoni
aMitosis
Spermatocytes
Meiosis
Spermatids(HAPLOID
CELLS)
Maturation
Sperm
Green : Before puberty, Orange : at pubertyEach spermatocyte forms 4 haploid spermatids
SPERMATOGENESIS stimulated by testosterone
SPERMIOGENESIS
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POINT… SHOOT… SCORE!
Semen =
Secretions of seminal vesicle (fructose rich, alkaline fluid & fibrinogen fluid)
Secretions of prostate (seminal fluid: bicarbonate, nutrient citric acid + fibrinolytic)
Sperm
Secretion of bulbo-urethral glands (lubrication)
Semen gets into the vagina via ejaculation.
1.5 – 4 mL may contain > 300M sperm, and 50 lucky boyz will get to the site of fertilisation!
Mixed by emission
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LADIES’ TURN
Oogonia (XX
Germ Cells)
MitosisPrimary
Oocyte (2n) Meiosis I
Secondary Oocyte (1n) + Polar Body
(1n)Meiosis II
Ovum (1n)
Colonise the cortex (outer layers of the gonad)
Surrounded by a single layer of Granulosa Cells, form the Primordia Follicle
The primary oocyte stays in Prophase until Puberty
Meiosis is induced at puberty, thanks to FSH