Sexual reproduction in Human beings

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Sexual reproduction in Human beings
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Learning outcomes

• Identify on diagrams of the male reproductive
  system and give the functions of testes, scrotum,
  sperm ducts, prostate gland, urethra and penis
• Identify on diagrams of the female reproductive
  system and give the functions of ovaries,
  oviducts, uterus, cervix and vagina
• Compare male and female gametes in terms of size,
  numbers and mobility
• Describe the menstrual cycle with reference to
  the alternation of menstruation and ovulation,
  the natural variation in its length, and the
  fertile and infertile phases of the cycle

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Learning outcomes

• Describe fertilisation and early development of
  the zygote simply in terms of the formation of
  ball of cells which becomes implanted in the wall
  of uterus

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Male reproductive organ
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The male reproductive system

• Testes (testis)
• Organ that produce the gametes and male sex
  hormone (testosterone)
• The testis constantly divide to produce up to
  100,000,000 sperms per day.
• The testis work more efficiently at just below
  body temperature, so they are held outside the
  body in scrotum.

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The male reproductive system

• Storage duct/ epididymis
• Sperms are stored in the storage duct temporarily
  in an inactive form before it enters the sperm
  duct.

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The male reproductive system

• Sperm ducts/ Vas deferens
• Tubes which carry the sperm away from the testes

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The male reproductive system

• Seminal vesicle/ Prostate gland
• Is about the size of the golf ball
• It adds a nutrient fluid and enzyme (seminal
  fluid) in which it activates the sperms to swim
• Sperms seminal fluid semen

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The male reproductive system

• Urethra
• The urethra is a tube that carries both urine and
  semen along the penis to be released from the
  body but at different times.

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The male reproductive system

• Penis
• It is an organ for introducing sperms into the
  female. It contains spongy tissue which fills
  with blood to make the penis firm (an erection).

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QUICK CHECK!

• State the functions of
• Testes
• Scrotum
• Sperm ducts
• Prostate gland
• Urethra
• penis

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Female reproductive organs
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The female reproductive system

• Ovaries
• Female gonads
• Making and releasing the female gametes
• The female releases one ovum every four weeks

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The female reproductive system

• Oviducts/ Fallopian tube
• Are tubes which carry the ova from the ovaries
• They are lined with cilia together with a little
  muscular assistance, help to move the ova gently
  along.
• The egg is fertilized in the oviduct.

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The female reproductive system

• Uterus/ Womb
• A pear shape organ
• The wall contain involuntary muscle
• The embryo develops in the uterus during pregnancy

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The female reproductive system

• Cervix
• Cervix is the neck of the uterus, where the
  uterus joins the vagina.

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The female reproductive system

• Vagina
• it is part of the female system which receives
  the penis during the sexual intercourse
• It is muscular and stretchable

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QUICK CHECK!

• State the functions of
• Ovaries
• Oviducts
• Uterus
• Cervix
• vagina

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Checkpoint 1

• Name the organ/ organs that carry out the
  function
• Store matured sperms
• Carries both sperm and urine
• Produces cells with only half the number of
  chromosome
• Produces the male sex hormone
• Receive sperm
• Egg must be fertilised here for pregnancy to take
  place.

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Female gametes vs male gametes
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Female gametes vs male gametes

• Male gametes
• Released in millions
• Able to swim
• Very small (0.05 mm)
• Very little cytoplasm
• Nucleus contains either an X or a Y chromosome

• Female gametes
• Released one per month
• Unable to move by their own
• Comparatively large (0.1mm in diameter)
• A lot of cytoplasm which contains nourishment for
  the zygote if the ovum is fertilised
• Nucleus always contains an X chromosome

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QUICK CHECK!

• Compare the human male and female gametes in
  terms of
• size,
• numbers and
• Movement
• cytoplasm
• In each case, suggest reasons for the differences
  you describe.

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Human reproductive system

• Menstrual cycle

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Menstrual cycle

• The average menstrual cycle is about 28 days.
• Begins with puberty, ends with menopause.
• Menstrual cycle consists of 4 phases
• a. menstrual phase
• b. proliferative phase
• c. ovulation phase
• d. secretory phase.

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Menstrual cycle

• Menstrul phase (Day 1 5)
• The spongy lining then peel away , damaging the
  blood capillaries. The lining passes out of the
  vagina, together with the blood. Menstrual
  period. It lasts for about 5 days
• Follicles containing ovum develops.

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Menstrual cycle

• Proliferative phase (Day 6 - 11)
• Follicles containing egg cell found in ovaries.
• Day 6, one follicle matures and begins to secrete
  hormone Oestrogen.
• Oestrogen level in blood increases.
• Oestrogen causes the repair and growth of the
  uterine lining. The lining becomes thick and
  spongy with blood vessels.
• High concentration of Oestrogen prevents growth
  and mature of more follicles.

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Menstrual cycle

• Ovulation Phase (Day 12 - 15)
• On Day 12 13, rapid increase in Oestrogen
  level.
• Triggers ovulation (1 mature follicle releases a
  ovum) on Day 14.
• The remains of the mature follicle secretes
  hormone progesterone and little oestrogen.

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Menstrual cycle

• Secretory Phase (Day 16 - 28)
• The remains of the mature follicle secretes
  hormone progesterone and little oestrogen.
• Progesterone maintains the uterine lining by
  causing it to thicken further and be supplied
  with blood vessels.
• The thickened lining also begins to secrete
  nutrients and mucus to prepare for an embryo to
  be implanted.
• High level of progesterone ensures no new
  follicles mature. (ref to the pill)

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Menstrual cycle

• Secretory Phase (Day 16 - 28)
• If the ovum (egg cell) is not fertilised, the
  remains of the mature follicle will last for
  about 10 12 days, then degenerates.
• Secretion of progesterone and oestrogen stops
• The drop in hormone levels causes the uterine
  capillaries to rupture.
• Follicles are not inhibited anymore.

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If Fertilisation takes place ....

• Secretory Phase (Day 16 - 28)
• Embryo embeds/implants itself in the uterine
  lining.
• Causes the remains of the follicle to continue
  secreting progesterone.

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Menstrual cycle

• The fertile period is from day 11 to day 17,
  because ovulation has occurred. Ovum can survive
  for 2 days and allowing for the possible survival
  of sperms in the oviduct.
• The rest of the time is considered infertile
  period.

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Factors affecting menstrual cycle

• Severe Stress
• malnutrition
• Mental fatigue
• Severe Illness
• These factors can alter or stop the menstrual
  cycle

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Summary
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Reproduction

• Fertilization and development of embryo

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Fertilization

• The egg released is surrounded by a few layers of
  follicle cells.
• The sperm swim toward the egg in the oviduct, it
  will release enzymes that digest the follicle
  cells. Only one sperm enters the egg.
• The fusion of the nuclei to form the zygote is
  called fertilization.
• Fertilization occurs in oviduct.

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Development of embryo

• The zygote passes along the oviduct to the
  uterus, assisted by action of cilia, and it
  begins to divide by mitosis to form a hollow ball
  of cells called embryo.
• The embryo becomes embedded in the uterine
  lining. This is called implantation.

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Development of embryo
placenta Finger like projections (villi) to provide large surface area for diffusion Allow dissolved food substances (glucose, amino acid, mineral salts) and oxygen to diffuse from mother blood to the embryo Allow metabolic waste (urea and carbon dioxide) to diffuse from embryo to mothers blood Allow the antibodies to diffuse to the embryo Produce progesterone
umbilical cord Contain umbilical vein and two umbilical arteries bring dissolved oxygen and nutrients by the umbilical vein to the foetus removing waste via umbilical arteries.
amniotic fluid Provide the buoyancy to the foetus, thus protect it from shock and mechanical injuries Maintains a relatively constant environment for the foetus.
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Development of embryo

• The exchange of the material between the foetus
  and the placenta.

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Exchange of materials across the placenta

• Mother to fetus
• Oxygen
• Glucose
• Amino acids
• Vitamins, minerals
• Alcohol, nicotine, many other drugs
• Viruses
• antibodies

• Fetus to mother
• Carbon dioxide
• Urea
• Other metabolic waste

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Development of embryo

• The time between conception and birth is nine
  months.
• The nine months is known as the gestation period.
• At the end of the gestation period, contraction
  of the uterus walls causes the rupture of the
  amniotic sac.
• The birth of the baby is followed by the ejection
  of the placenta.

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Thinking room?

• How are identical twins come about? Why do they
  always - look alike and same sex?

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IVF

• A woman with blocked oviducts cannot have a baby
  in the normal way but can now have a test-tube
  baby. A doctor, using a fine tube through the
  body wall, sucks up several eggs from the ovary,
  puts them in a dish and mixes them with sperm.
  The eggs are then kept for a few days before they
  are put back into the womans uterus via the
  cervix.
• Describe what can normally happen in the oviduct.
• Why does the doctor get the eggs from the ovary
  through the body wall and not through the vagina
  and uterus?
• Why must the sperms be mixed with eggs before
  they are put back in the woman?
• Why do you think the eggs are kept for a few days
  before they are put back into the uterus?
• Why is the term test-tube baby inaccurate?