reproduction in humans

• male reproductive system consists of

  sperm duct, prostate gland, urethra, penis, testis, scrotum
• the testes produces sperm and male sex hormones like testosterone
• male hormones are responsible for the development and maintenance of the secondary sexual characteristics in males
• scrotum, where the testes lay, is outside the main body cavity so that it is at a slightly lower temperature than body temperature for sperm to develop properly
• the sperm consists of the head, middle piece and tail (flagellum)
• the head of the sperm contains a large nucleus which carries a halpoid set of chromosomes
• the middle piece of the sperm contains numerous mitochondria which provides energy for the sperm to swim towards the egg
• the tail of the sperm allows the sperm to be motile, to swim towards the egg through its beating movement
• the sperm travels:

  testis -> sperm duct -> urethra -> outside of the body
• the female reproductive system consists of

  ovary, oviduct, uterus, cervix, vagina
• the ovary produce ova (eggs) and hormones like oestrogen and progesterone
• the female sex hormones are responsible for the development and maintenance of the secondary sexual characteristics in females
• the inner surface of the oviduct is lined with cilia which helps to move the egg along the oviduct due to its movement
• the uterus has elastic muscular walls which contract to push the fetus out during birth
• the embryo is implanted on the uterine lining
• difference between structure of male and female gametes

  • male has a head, middle piece and a tail while female is spherical in shape
  • male has nucleus containing either X or Y chromosome while female has nucleus containing one X chromosome only
  • male is 60 micro m long with diameter of 2.5 micro m for the head while female diameter is 120 to 150 micro m
• difference between motility of male and female gametes

  male has a tail that enables it to swim towards the oviduct while female is due to the movement of cilia along the oviduct and peristalsis of the oviduct wall
• difference between numbers of male and female gametes

  a large number of sperm is released per ejaculation while only one egg is released per month, with both ovaries producing about 500 mature eggs
• what are the stages in the menstrual cycle?

  menstruation, after menstruation, ovulation, after ovulation
• what happens during menstruation?

  the uterine lining and unfertilised egg break down and are shed with some blood
• what happens after menstruation ?

  the ovary produces a hormones called oestrogen which causes the uterine lining to repair and thicken. high oestrogen concentration leads to ovulation
• what happens during ovulation ?

  an ovary releases an egg into the oviduct
• what happens after ovulation ?

  the ovary produces a hormone called progesterone, which prevents ovulation and further development of eggs and causes the uterine lining to thicken further, preparing it for the implantation and growth of the embryo.

  oestrogen production decreases and if no fetilisation occurs, progesterone production decreases, and the uterine lining breaks down and the whole cycle repeats
• what days do menstruation occur?

  day 1 to 5
• what day does ovulation occur ?

  day 14
• how long does the menstrual cycle last ?

  28 days
• what happens if no fertilisation occurs ?

  • the egg breaks down
  • blood progesterone levels decrease
  • on the 28th day without progesterone, the uterine lining begins to break down
  • the whole cycle repeats
• what happens if fertilisation occurs ?

  • the fertilised egg becomes a zygote which develops into an embryo
  • the ovary secretes progesterone and oestrogen, causing the maintenance and thickening of uterine lining for the implantation of the embryo
  • the embryo embeds itself in the uterine lining until a str5ucture called the placenta is formed
  • the ovary continues to secrete progesterone and oestrogen until the placenta is able to take over the production of the 2 hormones
• the egg can survive in the oviduct for up to 24 hours
• the sperm can survive in the female reproductive system for about 3 - 5 days
• the fertile period is between day 10 to 15 of the menstrual cycle
• fertilisation is the process by which the nucleus of the male gamete fuses with the nucleus of the female gamete to produce a zygote
• what are the 3 stages of embryo development ?

  implantation, development of the placenta, development of the amniotic sac
• describe the process of implantation during embryo development

  • the cilia lining the inner surface of the oviduct sweeping the fertilised egg together with the peristaltic movements in the wall of the oviduct helps move the fertilised egg to the uterus
  • the zygote divides by mitosis to form a ball of cells called the embryo, using the energy provided by nutrients store in the egg.
  • eventually, the embryo becomes embedded in the uterine lining. this is called implantation and it usually occurs 7 days after fertilisation
• it takes about 5 days for the embryo to reach the uterus and it may float freely in the uterus for about 2 days
• describe the process of development of the placenta

  • after implantation, villi, which contain the blood capillaries of the embryo begin to grow from the embryo into the uterine lining
  • the villi and the uterine lining make up the placenta
  • a tube known as the umbilical cord attaches the embryo to the placenta
• describe the development of the amniotic sac

  • a membrane called the amniotic sac begins to develop at about the same time as the placenta
  • the amniotic sac encloses the embryo in the amniotic cavity, which is filled with amniotic fluid
  • about 10 to 12 weeks after fertilisation, all major organs are formed and the embryo is known as the fetus
• what are the functions of the placenta ?

  • it allows oxygen and dissolved food substances, such as glucose, amino acids and mineral salts, to diffuse from the maternal blood into the fetal blood
  • it allows metabolic waste or excretory products, such as urea and carbon dioxide, to diffuse from the fetal blood into the maternal blood
  • it allows the protective antibodies to diffuse from the maternal blood into the fetus to protect the fetus against certain diseases
  • it produces oestrogen and progesterone which maintain the uterine lining in a healthy state during pregnancy
• what are the functions of the umbilical cord ?

  it contains:

  • 2 umbilical arteries that transport deoxygenated blood and metabolic waste products from the fetus to the placenta
  • 1 umbilical vein that transports oxygenated blood and food substances from the placenta to the fetus
• what are the functions of amniotic fluid ?

  • it supports and cushions the fetus before birth. it is a shock absorber, and because it cannot be compressed, it protects the fetus against physical injury
  • it allows the fetus a certain degree of movement, which promotes muscular development
  • during birth, it lubricates and reduces friction in the birth canal