sexual reproduction in humans

• Scrotum

  External sac of skin containing the testes
• Testes

  • Produce sperm by spermatogenesis
  • Produce testosterone
• Epididymis

  Where sperm is stored and will mature to become motile
• Vas Deferens

  Carries sperm towards the penis during ejaculation
• Seminal vesicle

  Secretes fluid into the vas deferens that provides nutrients to the sperm like fructose and amino acids. Helps to neutralise the acidity of any urine remaining in the urethra or in the vaginal tract as it is alkaline.
• Prostate gland

  Secretes fluid, containing zinc ions, into the vas deferens. It is also alkaline so it helps to neutralise the acidity of urine remaining in the urethra and the acidity of the vaginal tract.
• Urethra

  • Transports semen through the penis and out of the body
  • Transports urine from the bladder through the penis and out the body
• Penis

  A specialised organ adapted to transferring semen to the vagina during sexual intercourse
• Semen

  Mixture of sperm (spermatozoa), seminal fluids and prostate fluids.
• Why are the testes contained in an external sac?

  Sperm production is more efficient at a lower temperature than the body
• Ovary

  • Production of gametes (secondary oocytes formed during oogenesis)
  • Produce oestrogen and progesterone
• Fallopian tubes

  Tubes lined with ciliated epithelial cells which transport secondary oocyte to the uterus
• Uterus

  Holds the developing foetus until birth
• Endothelium

  • Inner most layer of the uterus wall
  • Has a good blood supply and builds up every month during menstrual cycle.
  • If there is no implantation of the embryo then the endometrium is shed during menstruation
• Cervix

  • A narrow ring of connective tissues and muscle, it acts as a barrier between the uterus and the outside environment during pregnancy.
  • During pregnancy, a plug of mucous forms in the cervix which helps prevent the entry of pathogens.
• Vagina

  • Where semen is deposited during sexual intercourse and where the foetus will pass out from the uterus during birth
  • Has muscular walls and opens at the vulva
• spermatogenesis

  • occurs in the seminiferous tubules (in the testes)
  • The formation of sperm in the testes
• Stages of spermatogenesis

  1. Starts with Germinal epithelium (2n) which is found in the walls of the seminiferous tubules.
  2. Mitosis occurs producing Spermatogonium (2n), mitosis then occurs 2 more times to form Primary Spermatocytes (2n).
  3. Primary spermatocyte then under goes Meiosis I to produce Secondary spermatocytes (n), then Meiosis II occurs to produce spermatids (n).
  4. Spermatid then matures in the epididymis to become spermatozoa.
• Sertoli cells

  Provide nourishment for spermatids and protection against the males immune system
• Spermatozoa structure

  • Acrosome - contains protease enzymes
  • Mitochondria - spiralled around the microtubules
  • Tail - movement is due to atp produced in the mitochondria around the microtubules
• Oogenesis

  • Occurs in the ovaries
  • Production of ova (ovum)
• Stages of oogenesis

  1. Germinal epithelium undergoes mitosis to form oogonium (2n)
  2. Oogonium then undergoes mitosis to produce a primary oocyte (2n)
  3. Primary oocyte then undergoes meiosis I to produce a secondary oocyte and a first polar body.
  4. Secondary oocyte will undergo meiosis II if fertilisation occurs, producing an ovum (2n) and a secondary polar body (n).
• Secondary oocyte

  Meiosis I of the primary oocyte is completed before ovulation. Meiosis II stops at metaphase II
• Primary follicle

  Primary oocyte surrounded by cells in the ovary
• Secondary follicle

  primary follicle that has developed in response to FSH
• Graafian follicle

  Mature secondary follicle containing a secondary oocyte that is ready for ovulation
• A follicle consists of a ball of diploid cells surrounding an oocyte. The cells of the follicle develop and increase in numbers as the oocyte develops.
• Ovulation

  When the secondary oocyte is being released
• Corpus luteum

  • Development stimulated by LH
  • If fertilisation occurs, it starts secreting progesterone and oestrogen
• Fertilisation

  4 stage process:

  • Capacitation
  • Acrosome reaction
  • Fusion
  • Cortical reaction
• Capacitation

  increases the permeability of the cell membrane in the head of the sperm above the acrosome
• Acrosome reaction

  Releases hydrolase enzymes which digest the zone pellucida
• Zona pellucida

  Jelly like coat secreted by the follicles surrounding the secondary oocyte
• Fusion

  Genetic material of the stem enters the secondary oocyte triggering the completion of meiosis II and the formation of the ovum and secondary polar body.
• Cortical reaction

  Cortical granules fuse with the cell membrane and modify the zone pellucida form the fertilisation membrane preventing polyspermy
• Fertilisation begins with the sperm moving into the fallopian tubes
• Fertilisation ends with the nuclei of the sperm and ovum fusing to form a zygotic nucleus
• Cleavage

  The zygotę undergoes repeated mitotic divisions as it moves down the oviduct to form a ball of cells called a blastocyst.
• Implantation

  Blastocyst moves into the uterus where it attaches and sinks into the endometrium. Cells on the outside of the blastocyst, the trophoblast cells, form trophoblastic vili that penetrate the endometrium. The vili increase the surface area for the absorption of nutrients from the endometrium.
• Formation of the placenta

  Placenta begins to develop from the trophoblast cells