Human Reproduction

• Gonad


  An organ that produces sex cells in animals
• Testes development


  1. Develop inside the body at first

  2. Descend into the scrotum a few weeks before birth
• Testes are kept at slightly lower than body temperature (35°C) which is the ideal temperature for sperm production
• Seminiferous tubules


  • Inside the testes, lined with sperm producing cells
  • Cells between the tubules produce the hormone testosterone
• Epididymis


  All the seminiferous tubules join to form the epididymis, where sperm mature and are stored
• Sperm transport


  1. Epididymis leads to the sperm duct (vas deferens)

  2. Sperm duct brings sperm to the urethra
• Urethra


  Responsible for carrying sperm and urine out of the body
• Seminal fluid


  Produced by glands in the male reproductive system, nourishes the sperm and provides a medium in which to swim
• Glands in the male reproductive system

  • Seminal Vesicle
  • Prostate Gland
  • Cowper's Gland
• Functions of main parts of male reproductive system


  • Testis: Produces sperm and testosterone
  • Epididymis: Matures and stores sperm
  • Sperm duct: Carries sperm from the epididymis to the urethra
  • Seminal vesicles, Cowper's gland and Prostate gland: Produce seminal fluid which feeds the sperm and allows them to swim
  • Urethra: Allows the passage of either urine or sperm
  • Penis: Places sperm inside the body of a female
  • Scrotum: Keeps testes at a lower temperature (35°C), the optimum temperature for Meiosis to occur
• Sperm structure


  • Head: Acrosome (contains digestive enzymes), Nucleus (contains 23 chromosomes)
  • Middle: Collar (contains mitochondria)
  • Tail: Flagellum (allows sperm to swim)
• Role of meiosis in sperm and egg production

  1. Sperm and egg producing cells are diploid (46 chromosomes)

  2. They divide by meiosis to form sperm and egg cells, each with a haploid number of chromosomes (23)

  3. Sperm nucleus and egg nucleus combine in fertilisation to form a diploid zygote (46 chromosomes)

  4. Zygote grows by mitosis division ensuring each new cell has a diploid number of chromosomes
• Testosterone


  The male hormone responsible for the development of primary and secondary male sexual characteristics
• Male secondary sexual characteristics

  • Growth of pubic, facial and body hair
  • Enlargement of larynx and 'breaking' of the voice
  • Increased muscular development and bone development
  • A growth spurt at puberty
  • An increased secretion of sebum in the skin
• Structure of the female reproductive system

  • Fallopian tube (Oviduct), Funnel, Ovary, Ovarian Ligament, Uterus, Lining of uterus (endometrium), Wall of uterus, Cervix, Vagina, Vulva
• Functions of main parts of female reproductive system

  • Ovary: To produce the egg (ova) and the hormones oestrogen and progesterone
  • Fallopian tube (oviduct): Catches the egg from the ovary and transports it to uterus, site of fertilisation
  • Uterus: Site of implantation, holds the developing embryo, has a lining (endometrium) enriched with blood vessels to nourish the embryo, forms the placenta
  • Vagina: Allows entry of sperm and exit of baby at birth
• The ovary


  • Produces the eggs and female hormones
  • All the eggs in an ovary are present at birth
  • After puberty 20 eggs mature each month, only one will be released from the ovary - the rest will die
• The fallopian tube (oviduct)

  • Muscular and approx 12cm long
  • Funnels at the tip catch the egg after it is released from the ovary
  • The egg is moved along the tube by cilia and muscular peristalsis
  • The egg is either fertilised or dies in the fallopian tube
• The uterus (womb)


  • Muscular structure approximately the size of your fist
  • Outer wall made of involuntary muscle
  • Inner lining is called the endometrium, this thickens each month with cells and blood vessels to nourish the embryo
  • The cervix separates the uterus from the vagina
• The vagina


  Elastic muscular tube 10cm long, allows entry of sperm and is the birth canal for the exit of a baby, lined with cells that produce mucous to protect against pathogens
• Oestrogen and progesterone


  The female hormones
• Secondary female characteristics caused by oestrogen and progesterone at puberty


  • The maturing and enlargement of the breasts
  • The widening of the pelvis to allow for birth
  • The growth of pubic and underarm hair
  • A growth spurt
• The menstrual cycle


  1. Day 1-5: Blood from the womb lining is shed from the body

  2. After day 5 the lining of the uterus repairs and builds up again

  3. Fertile period

  4. Ovulation occurs on Day 14

  5. Implantation may happen

  6. If fertilisation has not occurred the cycle begins again with the breakdown of the endometrium
• Inside the ovary


  • Potential egg
  • Developing Graafian follicle - secretes oestrogen
  • Graafian follicle now changes to the Corpus luteum which secretes progesterone
  • Egg is released from ovary (ovulation)
• Insemination


  1. Contractions of uterus and fallopian tubes move the sperm to the fallopian tubes within 5 minutes

  2. If an egg is present it releases chemicals to attract the sperm (chemotaxis)
• Fertilisation


  1. Fertilisation usually occurs in the fallopian tube

  2. A number of sperm may reach the egg at the same time

  3. The acrosome releases enzymes to digest the egg membrane

  4. The sperm loses its tail and the head enters the egg

  5. The sperm and egg nuclei fuse to form a zygote

  6. A chemical reaction at the membrane prevents other sperm cells entering
• Implantation


  1. Implantation is the embedding of the fertilised egg into the lining of the uterus, 6-9 days after fertilisation

  2. By this time the zygote has grown into an embryo

  3. After implantation the placenta forms

  4. During implantation a membrane called the amnion develops around the embryo, secreting amniotic fluid which acts as a shock absorber
• Placenta


  Acts as an endocrine gland, allowing exchange of nutrients, oxygen, antibodies, wastes, carbon dioxide and water between mother's blood and embryo's blood
• Birth


  1. The hormones oestrogen and progesterone are produced throughout pregnancy firstly by the corpus luteum (3 months) and then by the placenta

  2. Immediately before birth the placenta stops making progesterone, the walls of the uterus begin to contract

  3. The pituitary gland releases the hormone oxytocin, causing further contractions of the uterus, labour has now begun

  4. Umbilical cord is cut
• Lactation


  The secretion of milk from the mammary glands, triggered by the release of prolactin by the pituitary gland
• Breastfeeding is better than bottle feeding because colostrum and breastmilk provides the baby with essential antibodies protecting it against infection, and has the ideal balance of nutrients for the baby
• Infertility


  The inability of a couple to achieve conception
• Male infertility disorders


  • Low sperm count
  • Low sperm mobility
  • Endocrine gland failure
• Causes of low sperm count

  • The persistent use of drugs such as alcohol, cigarettes and anabolic steroids
  • Abnormalities in sperm production or obstruction of the tubes through which sperm travels
  • Stress
• Treatments for low sperm count

  • A change in diet
  • A change in lifestyle e.g. stopping alcohol consumption, smoking
  • A reduction in stress levels
• Female infertility disorders


  • Blockage of the Fallopian Tube
  • Endocrine gland failure
• Blockage of the fallopian tubes


  • Fragments of the uterus lining may spread to the fallopian tube
  • Inflammation as a result of infection
• Treatment for blocked fallopian tubes

  In-vitro fertilisation (I.V.F.)