Fertilisation in humans:
- Fertilisation is the union (fusion) of the male and the female gamete nuclei to form a zygote.
Humans undergo internal fertilization.
- This is a type of fertilisation where the nuclei of the female cells unite with that of the male one inside the female’s body.
- This takes place when there introduction of semen in the female organs during the time of ovulation.
Ovulation is a process where the ovary releases a mature ovum into the oviduct.
- Ovulation takes place every 12-14 days from the day of menstruation.
- 2-3 hundred million sperms are introduced in the vagina in one ejaculation but only one is required to fertilise an ovum.
- The act of inserting the penis into the vagina which results in the accumulated semen being ejaculated into the vagina is called copulation (mating).
- A released human ovum is estimated to live for 12- 24 hrs. while a sperm can live in a female reproductive organ for 2-3 days.
- When the nucleus of the sperm and ovum unite, a zygote is formed.
- A zygote is a developing embryo between fertilisation to 8 weeks.
- A foetus is a developing embryo between 8 weeks to birth.
- In animals like rats, rabbits, dogs, pigs etc. many ova are relesed and are fertilised by a corresponding number of sperms.
- This is the monthly shedding of blood by the uterine walls whenever an ovum is not fertilised.
- Usually, during ovulation, the walls of the uterus are thickened with layers of cells onto which the fertilised ovum attaches.
- But if the ovum is not fertilised, the uterus walls break and shed off the blood, mucus and unwanted cells.
- Menstruation occurs once in every 28 days.
- It lasts about 3-5 days.
- Implantation is a process where a fertilised ovum attaches itself onto the uterine lining.
- After implantation, we say conception has taken place and that confirms pregnancy.
- This is a period from fertilisation to birth.
- In man, it lasts 9 months.
3. Common indicators of pregnancy.
- monthly menstrual periods stop.
- breasts enlarge.
- morning sickness especially in the 2nd and 3rd month of pregnancy.
- enlargement of the belly.
- cervix closes.
- movement of the baby can be felt.
Events in pregnancy.
- The fertilised ovum develops finger-like structures (villi) into the uterus.
- The part with the villi develops into a specialised organ called a placenta.
- The uterine lining under the influence of Oestrogen and progesterone develop rich supply of blood vessels to facilitate exchange of materials between the mother’s and the foetus’ blood.
- Dissolve oxygen, glucose, amino aids and salts from the mothers uterine blood pass to the embryo while the carbondioxide and other nitrogenous wastes pass in the opposite direction through the umbilical cord.
- A water sack called an amnion, which cushions it from damage, surrounds the embryo.
Human foetus in the uterus.
Functions of different parts.
- Umbilical cord: contains an artery and a vein through which materials are conducted to and from the foetus.
- An amnion: holds the amniotic fluid.
- Amniotic fluid: cushions the foetus from damage.
- The placenta:
- acts as a food store and wastes.
- prevents the mother’s hormones from reaching the foetus.