Human Reproduction

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Male Reproductive System

  • Seminiferous tubules produce spermatozoa.
  • Seminal vesicles produces secretion to aid sperm mobility.
  • Prostate gland produces alkaline solution to neutralise acidity of urine. 
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Female Reproductive System

  • Ova are passed to the Fallopian tubes which conveys them to the womb, the muscular walls of the uterus are lined with a mucus called the endometrium, supplies blood during pregnancy.
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Spermatogenosis

  • Occurs in the germinal epithelium of the seminiferous tubules:
    -Diploid spermatogonia divide by mitosis to produce primary spermatocytes.
    -These undergo meiosis to form haploid secondary spermatocytes.
    -The second meiosis stage forms spermatids which mature into spermatazoa.
  • In the wall of the seminiferous tubules are Sertoli cells which secrete a fluid which nourishes the spermatids and protects them from the immune system,
  • Interstitial cells produce testosterone. 
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Oogenesis

  • The production of the ova:
    -Oogonia, formed before birth, undergo mitosis to form primary oocytes.
    -The primary oocytes begin meiosis but stop at prophase I.
    -The germinal epethelium also divides to form follicle which surround the primary oocyte and form a primary follicle.
    -At puberty, hormone stimulate follicles to develop further, one a month matures into a mature Graafian follicle.
    -The primary oocyte complete first meiotic divison to form a haploid secondary oocyte and the first polar body.
    -The mature Graafian follicle migrates to the surface of the ovary where it bursts and the secondary oocyte is released - ovulation.
    -The secondary oocyte starts the second meiotic division but arrests at metaphase unless fertilisation takes place; forming a large ovum and a second polar body.
    -Then the ovum and the sperm's nucleus fuse to form a zygote.
    -The Graafian follicle forms corpus luteum which releases hormones during pregnancy but breaks down otherwise. 
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Fertilisation/Acrosome Reaction

  • Internal fertilisation ensures the sperm is deposited into the reproductive tract.
  • The sperm is viable for 48 hours, the ovary 24 hours.
  • Only one sperm penetrates the clear layer of the ovum called the zona pellucida.
  • Sperm can only fertilise once capatation takes place, where the acrosome membrane ruptures and protease enzymes are released which break down the cells around the ovum.
  • The tip of the sperm penetrates the weakened part of the membrane.
  • The nuclei fuse to form the zygote.
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Implantation

  • After fertilisation the zygote divides by mitosis to form the blastocyst which implants itself into the side of the uterus.
  • The outer layer of the blastocyst is called the trophocyst and develops the amnion and the chorion, the second has villi which increase surface area for absorption of nutrients.
  • It also releases hCG which prevents degeneration of the corpus luteum. 
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Sub-Fertility

  • The difficulty to naturally concieve a child:
    -The failure to ovulate which is the abscence or irregular menstrual cycle which can be treated 95% of the time with the drug called clomiphene.
    -A blockage of the Fallopian tubes which requires microsurgery.
  • In vitro Fertilisation:
    -Ovulation is stimulated with hormones, to produce several follicles to form.
    -The oocytes are collected.
    -The male also produces sperm on the same day.
    -The oocyte is placed on the dish and sperm are added to each.
    -They are examined to see which have been fertilised. 
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Pregnancy Testing

  • Use monoclonal antibodies to test for the presence of hCG, only detecting that 'antigen'.
  • Involves detecting the hCG produced by the placenta, and acts as a sign for level of pregnancy.
  • The test relies on coloured latex beads and hCG making them fuse to form a noticable colour change.
     
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