Human Reproduction

• Gametes are the reproductive cells. The male gamete is called the sperm in many animals, and pollen in many complex plants. The female gamete is called the egg or ovum (Plural: ova).
• Gonads are the reproductive organs that produce gametes and sex hormones. The human male gonad is called the testis (Plural: testes), and the female gonad is the ovary.
• Puberty is the time during teenage years when males start to produce sperm, and females start to release eggs. Puberty usually occurs a couple of years earlier for females than males.

• Menopause is the time when females stop releasing eggs. This usually occurs between 45 to 55 years of age. However, males do not undergo menopause and produce sperm all their lives following puberty.

Human Male Reproductive System

The path that Sperm travel

Testes

Epididymis

Vas Deferens (or Sperm Duct)

Urethra

Parts of the Male Reproductive System

Testis

• There are 2 testes situated in a sac called the scrotum
• Produces sperm in large numbers in seminiferous tubules
• Produce male sex hormone called testosterone which regulates sperm production and secondary sexual characteristics (e.g. hair on face chest armpits and pubic area, deep voice, muscle bulk)

Epididymis

• Stores the large numbers of sperm until they are ejaculated out through the penis

Sperm Duct or Vas Deferens

• Transports sperm from the testis to urethra

Semen - Producing Glands

• Semen is the fluid produced to protect the sperm from dehydration and the acidic environment of the female vagina after sexual intercourse. Semen also allows the sperm to swim more easily.
• Semen - producing glands are Cowper's Gland, the Seminal Vesicles and the Prostate Gland.

Urethra

• This is the tube that normally carries urine from the urinary bladder.
• When semen containing sperm is ejaculated, it also travels out through the urethra, but the prostate gland enlarges to block off any urine from the bladder at that time.

Penis

• The urethra is the tube inside the penis.
• During sexual intercourse, the spongy cells that surround the urethra fill with blood, and the penis becomes firm and erect.

Human Female Reproductive System

The path the Egg travels

Ovary

Oviduct or Fallopian Tube

Uterus or Womb

Cervix

Vagina

Parts of the Female Reproductive System

Ovary

• There are 2 ovaries
• Produces eggs or ova, female sex hormones (oestrogen and progesterone) that regulate the menstrual cycle, pregnancy, and the secondary sexual characteristics (e.g. pubic and underarm hair, breasts, enlarged hips)
• At birth, females have all their eggs formed, but in an immature state
• After puberty and before menopause, one egg is released about every 28 days from each ovary

Oviduct or Fallopian Tube

• Connects between ovary and uterus
• Place where conception or fertilisation of an egg by a sperm occurs

Uterus or Womb

• Strong muscular and elastic organ where an unborn baby develops
• After an egg is released from the ovary, a blood-filled lining develops on the walls of the uterus in preparation for the nourishment of the unborn baby. If no fertilisation of the egg occurs, then this lining passes out through the vagina over several days as 'periods' or menstruation.

Cervix

• The opening between the uterus and the vagina
• During pregnancy, a mucous plug forms across the cervix separating the uterus from the outside to prevent infection of the unborn baby. This plug falls out, and the cervix dilates before the birth of a baby.

Vagina

• Place where the penis is inserted during sexual intercourse
• An elastic and muscular organ that expands during birth to allow for the passage of the baby

Female Menstrual Cycle

• The menstrual cycle begins at puberty and ceases at menopause.
• It takes about 28 days.
• Menstruation is regulated by the female sex hormones, oestrogen and progesterone.
• Menstruation - Menstruation or 'periods' is the release of the blood-filled lining of the uterus if a woman is not pregnant. It begins on Day 1 when menstruation or 'periods' begin, and lasts about 5 days.
• Ovulation is the release of the egg from the ovary between about Days 12 to 16.
• A woman will become pregnant if fertilisation (the joining of the egg and the sperm) occurs several days after ovulation when the egg is in the fallopian tube. During pregnancy, menstruation ceases.
• Role of hormones in the menstrual cycle - The Hypothalamus in the brain stimulates the pituitary gland in the brain to produce the hormone FSH (Follicle-Stimulating Hormone). FSH stimulates the growth of an egg follicle in the ovary. The follicle in the ovary secretes oestrogen which stimulates the repair of the uterus wall after menstruation and it also stimulates the pituitary gland to produce LH (Lutinizing Hormone). This prevents more than one follicle from developing. LH induces ovulation (release of the ovum) and the development of the follicle into the corpus luteum. The corpus luteum secretes progesterone. If a female becomes pregnant, the corpus luteum will secrete gonadotrophin which allows the corpus luteum to continue producing progesterone which stimulates the growth of the uterus wall, by inhibiting LH and FSH. If the woman does not become pregnant, the corpus luteum deteriorates, which leads to less production of progesterone and oestrogen, and menstruation will occur, and another menstrual cycle begins because the lower progesterone and oestrogen levels will stimulate the pituitary gland in the brain to produce FSH.

Oestrus Cycle in other Animals

• Oestrus is a time when a female animal demonstrates the intensity of the sexual urge. She is said to be 'in heat'. Changes in the lining of the vagina and uterus also prepare for the fertilised egg. Oestrus occurs about the time of ovulation. Female cats and dogs have 2 oestrus periods per year, whereas rats can have them every 5 days.

Fertilisation or Conception

• After sexual intercourse, the sperm travels up to join with the egg in the fallopian tube.
• The single-celled fertilised egg is called a zygote.
• 23 chromosomes of the sperm and 23 chromosomes of the egg combine in the zygote's nucleus, so that the developing baby has 46 chromosomes.

Internal and External Fertilisation in Animals

• Internal Fertilisation occurs when the male gamete joins with the female gamete inside an organism (e.g. humans). An advantage is that the survival rate is higher, but the number of offspring is small.
• External Fertilisation occurs when the male gamete joins with the female gamete outside the organism (e.g. fish). This often occurs in a moist environment, many offspring are produced, but there is a low survival rate.

Gestation or Pregnancy

• Gestation in humans lasts about 40 weeks or 9 months
• The first sign that a woman is pregnant is usually absence of menstruation ('no periods')
• After fertilisation in the fallopian tube, the zygote multiplies to form a ball of cells which travels down to the uterus
• The ball of cells (embryo) implants into the wall of the uterus
• At the place where implantation occurs, an organ called the placenta develops
• The umbilical cord grows between the placenta and the unborn baby's navel
• Inside the umbilical cord are blood vessels which provide nutrients and oxygen to the baby, and return wastes such as carbon dioxide back to the mother's bloodstream
• As the baby grows, it is called a foetus
• The foetus is protected by amniotic fluid inside an amniotic sac
• In the ninth month of pregnancy, the foetus turns upside down, and the mother's breasts enlarge ready for milk production

Birth

• At about 9 months, the 'plug' at the cervix releases, the amniotic sac breaks and fluid comes out through the vagina ('breaking of the waters')
• Muscular contractions occur to both dilate the cervix, and 'push' out the baby head first from the uterus
• Further muscular contractions expel the placenta
• The umbilical cord is cut close to the baby's navel
• The mother begins breast milk production
• The mother begins the menstrual cycle again, after the lining of the uterus from the pregnancy has been expelled over several days
• Breech Birth occurs when the baby is born legs first
• Caesarean Birth is the surgical removal of the baby from the mother's uterus
• Twins - Identical Twins (i.e. 2 sisters or 2 brothers) form when one egg and one sperm join, but as the zygote multiplies to form a ball of cells, the ball splits and the 2 embryos implant separately into the wall of the uterus. Non-identical or Fraternal Twins are formed when 2 eggs are fertilised by 2 sperm.