Sexual Reproduction

• Chromosomes


  2 sister chromatids joined by a centrometre
• Mitosis 


  G1 - new organelles made and energy reserves built up

  Interphase - S - synthesis - DNA copied

  G2 - PMAT
• Mitosis


  Early prophase - condense and untangle, coil into 'X', centrioles move towards poles.

  Late prophase - Nuclear envelope breaks down and nucleolus disappears.

  Metaphase - Spindle forms, chromosomes align at the equator attached to microtubules via centrometre.

  Anaphase - Spindle fibres shorten, centromeres divide and chromatids are pulled towards opposite poles.

  Telophase - Chromatids reach poles and become indistinct by uncoiling, the nuclear envelope reforms, nucleolus reforms and spindle disintegrates.
• Meiosis I


  No interphase

  Early prophase - condense and untangle, coil into 'X', centrioles move towards poles.

  Late prophase - homologous pair up to bivalent pairs and chiasma formation - crossing over to swap alleles.

  Metaphase - chromosomes line up with equator

  Anaphase - each homologous pair pulled to either poles (random assortment of homologous pairs)

  Telophase
• Meiosis II


  Prophase

  Metaphase - sometimes Chiasma formation

  Anaphase - centromeres divide allowing microtubules of the spindles to pull the chromatids to opposite poles (random assortment of chromatids)

  Telophase - 4 cells - all genetically different (haploid)
• Male anatomy:

  • Vas deferens - sperm duct
  • Seminal vesicle - secretes mucus and prostate fluid to mix with sperm
  • Epididymis - sperm collects here
  • Testes - where testosterone is made in the seminiferous tubules
  • Urethra - where sperm leaves
  • Scrotum
  • Penis
  • Bladder
  • Prostate gland
• Female anatomy:

  • Cervix
  • Vagina
  • Uterus
  • Ovary - oocytes mature
  • Fallopian tube - cilia lining wafts 2nd oocyte along
  • Endometrium - membrane supplied well with blood
  • Bladder in front
• Spermatogenesis: (male gametogenesis)


  Forms in the seminiferous tubules.

  • Germinal epithelium
  • Fluid filled lumen
  • Interstitial cells (makes testosterone)
  • Blood capillaries
• Spermatogenesis


  1. Occurs in testes to form sperm

  2. Cells move from outside towards the centre of the seminiferous tubule, becoming more mature

  3. Diploid (2n) germinal epithelial cells divide by mitosis to produce spermatogonia (2n)

  4. Spermatogonia divide many times by mitosis and increase in size to form primary spermatocytes (2n)

  5. Primary spermatocytes (2n) divide by meiosis I to produce secondary spermatocytes (n)

  6. Secondary spermatocytes undergo meiosis II to make spermatids (n)

  7. Spermatids (n) differentiate and mature into spermatozoa (n)
• Sertoli cells


  • Provide spermatozoa with nutrients and protect from immune system
• Interstitial cells


  • Secrete testosterone
• Mitosis 


  PMAT

  
• Meiosis 


  Stages 1 and 2

  
• Male reproductive system

  
• Female Reproductive system

  
• Spermatogenesis: (grows on Sertoli cells - nurse cells)

  1. Spermatogonia (2n) - mitosis
  2. Primary spermatocyte (2n) - meiosis I - early
  3. Secondary spermatocyte (n) - meiosis II - split
  4. Spermatids (n) - meiosis II - differeniate and mature into...
  5. Spermatozoa (sperm cells) (n) - maturation

  
• Oogenesis explanation:

  1. Oogonium (2n) forms from germinal epithelium - mitosis
  2. Primary oocyte (2n) and primary follicle develops - early prophase meiosis I - holds until sexual maturity
  3. Follicle matures (1 month) produced FSH (produces oestrogen)
  4. Secondary oocyte (n) and polar body (n) - continutes meiosis II. Primary follicle develops Graafian follicle
  5. Graafian follicle forms a blister on the ovary surface
  6. LH and FSH reach max, follicle reaches the surface and bursts releasing the secondary oocyte (n) - ovulation - meiosis II

  
• Oogenesis explanation - continued:

  1. If sperm meets, meiosis II completed forming ovum (n) and 2nd polar body (n).
  2. Corpus luteum forms and produces progesterone to hold endometrium together after fertilisation.

  
• Spermatozoon structure:

  • Acrosome - contains proteases to digest cells of corona radiata and zona pellucida
  • Midpiece - many mitochondria for ATP for movement
  • Tail - move in circular motion
  • Centriole - where microtubules that make the axial filament start

  
• Egg structure:

  • Lysosomes - made by golgi to break down food before implantation into the wall of the uterus and placenta is formed.
  • Lipid droplets - food store
  • First polar body - meiosis I
  • Secondary oocyte - egg
  • Corona radiata - follicle cells
  • Zona pellucida - jelly secreted by follicles - allows entry of sperm.

  
• Fertilisation - form embryo from first mitotic division:

  • Sperm responds to chemicals produced by oocyte and swim through the uterus into the oviduct
  • Oocyte only viable for 24 hours after ovulation
  • Sperm viable for a few days (12-24 hours most fertile)
  • Cortical reaction - protein receptors cause jelly (zona) to harden and stop other sperms entering.
  • Acrosome reaction - releasing proteases to digest cells in corona radiata to allow sperm head to touch the zona pellucida. (acrosin hydrolyses this so sperm touches the oocyte.
  • Nuclei of ovum and sperm fuse to form a zygotic nucleus.

  
• Fertilisation - selection process


  Sperms knocked out due to acidic pH and antibodies fighting off the sperm till the 'fittest' sperm isn't knocked out and fertilises the egg.
• Implantation or Embryo development:

  Zygote continues to divide by mitosis down the oviduct forming balls of cells (morula) by day 3 through the process, cleavage. By day 7, blastocyst forms with an outer layer of cells called the trophoblast. This develops protrusions called trophoblastic villi. Endometrium thickens allowing implantation of the blastocyst to occur by day 8-10. (from the fallopian tube to the endometrium)

  
• Capacitation in fertilisation


  Cholesterol and glycoproteins removed, covering sperms acrosome making the membrane more fluid, only several hours after the sperm is deposited
• The menstrual cycle:

  1. Hormones low so menstruation occurs.
  2. FSH increases to cause the follicle in the ovary to be stimulated.
  3. The outer layer of the follicle produces lots of oestrogen.
  4. Endometrium thickens.
  5. Oestrogen levels trigger hypothalamus to let out LH.
  6. LH levels spike so pituitary gland releases oocyte for fertilisation and forms the corpeus luteum
  7. The corpus luteum increases progesterone levels.
  8. If fertilised, placenta takes over progesterone, keeps endometrium together and no period.
  9. If not fertilised, progesterone levels drop, endometrium breaks down, period, cycle repeats.

  
• Pregnancy:

  • Amniotic sac - shock absorber and maintains temperature
  • Temperature low during abstinence, high during ovulation
  • If temperature goes back to normal - not pregnant
  • Developing embryo secretes HCG (GnRH) which maintains the corpus luteum for first 16 weeks, Placenta secretes progesterone and oestrogen. FSH and LH inhibited. Progesterone suppresses uterine wall's ability to contract. Oestrogen stimulates growth of the uterus to accomodate and stimulate growth and development of the mammary glands. Causes breast development for feeding.
• Pregnancy Test


  Tests GnRH in urine by binding to mobile antibodies at test line to attach to antigens that form a positive line. Excess antibodies attach to control area to show test has worked (control line).
• Placenta - absorbing surface:

  • Large surface area
  • Thin walls (permeable)
  • Moist
  • Good blood supply
• Placenta:

  • Oxygen disassociation curve - fetal haemoglobin has a higher affinity for oxygen
  • Makes progesterone
  • Filters some harmful substances (not nicotine/alcohol)
  • Fetal alcohol syndrome - carbon monoxide causes brain damage
  • Acts as a barrier between maternal circulation as a higher blood pressure
  • Antibodies can cross through placenta to protect fetus
• Roles of structures

  Chorion develops from trophoblast forming larger chorionic villi which acquire capillaries and embed into the endometrium. They are supplied by the developing umbilical artery and vein to form the placenta.

  
• Birth:

  1. Before birth, oestrogen levels rise and progesterone decreases so uterine wall can now contract.
  2. Posterior pituitary gland secretes oxytocin, stimulating contractions which stimulate more oxytocin - positive feedback
  3. Anterior pituitary gland releases prolactin to stimulate production of milk by mammary glands and oxytocin triggers the milk release (contraction of milk ducts)
  4. May create an infant-mother-bond