FERTILIZATION IN ANIMALS
What is fertilization in animals? Fertilization is preceded by copulation in which the erect penis is inserted into the vagina. This leads to ejaculation of semen. The sperms swim through the female’s genital tract to the upper part of the oviduct.
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The head of the sperm penetrates the egg after the acrosome_ releases lytic enzymes dissolve the egg membrane. The tail is left behind. Sperm nucleus fuses with that of the ovum and a zygote is formed.
A fertilization membrane forms around the zygote which prevents other sperms from penetrating the zygote.
Implantation:
After fertilization the zygote begins to divide mitoticaly as it moves towards the uterus. It becomes embedded in the wall of the uterus a process called implantation. By this time the zygote is a hollow ball of cells called blastocyst or embryo.
In the uterus the embryo develops villi which project into uterus for nourishment later the villi and endometrium develop into placenta.
Embryonic membranes
Embryonic membranes develop around the embryo. The outermost membrane is the chorion which forms the finger-like projections (chorionic villi) which supply nutrients to the embryo. The amnion surrounds the embryo forming a fluid filled cavity within which the embryo lies. Amniotic cavity is filled with amniotic fluid.
This fluid acts as a shock absorber and protects the foetus against mechanical injury. It also regutates temperature. The chorionic villi, allantois together with the endometrium from the placenta. The embryo is attached to the placenta by a tube called umbilical cord which has umbilical vein and artery.
The maternal blood in the placenta flows in the spaces lacuna and surrounds capillaries from umbilical vein and artery. The umbilical cord increase in length as the embryo develops.
Role of placenta
Protection
Maternal blood and foetal blood do not mix. This ensures that the pathogens and toxins from maternal blood do not reach the foetus. The placenta allows maternal antibodies to pass into the foetus, providing the foetus with immunity.
Nutrition
The placenta facilitates the transfer of nutrients from maternal blood to foetus.
Excretion
Placenta facilitates the removal of nitrogenous wastes from the foetus’ blood to maternal blood.
Gaseous exchange
Oxygen from the maternal blood diffuses into the foetal blood while carbon (IV) oxide from foetal blood diffuse into maternal blood.
Production of hormones
Placenta produces progesterone and oestrogen.
Evaluation
- What are the steps of fertilization in animals?
- Where does fertilization occur in animals?
- What animals use fertilization?
- What type of fertilization and how it happens in the animal?
- What are the 7 steps of fertilization?
- What is fertilization process?
- How does fertilization take place in hen?
- Do all mammals internally fertilize?
- How do animals fertilize eggs?
- What is reproduction in animals?
See also
METHODS OF FRUIT AND SEED DISPERSAL