When we think of organisms mating, we often think of animals close to us, such as humans, dogs, dragonflies, cats, lizards, or birds. When these animals mate, the egg and sperm meet inside the body rather than outside in the air or water.
Internal fertilisation evolved as a result of the transition to land, because many gametes cannot float through air in the same way they can in water. Though they usually meet in the female, the egg and sperm in some animals meet inside the male. Most sperm are motile, which means they can swim around the body looking for eggs to fuse with.
With internal fertilisation, either sex may have sex organs that aid in the meeting of sperm and egg. In mammals, a penis organ is inserted into the female vagina. Most male insects have a long organ called an aedeagus that functions similarly to a penis. The roles are reversed in a type of insect known as Neotrogla.
What is internal fertilization?
Internal fertilization occurs inside the body. Internal fertilisation animals specialise in the development and protection of an egg. When the offspring is born, it is sometimes encased in an egg, and other times it hatches from an egg before being born. To protect their eggs, reptiles and birds secrete a protective shell that is resistant to water loss and damage.
Except for egg-laying mammals known as monotremes, mammals protect an embryo or fertilised egg within the mother as it develops. This additional protection improves the embryo’s chances of survival by providing it with everything it requires until it is born via live birth. Internally fertilising organisms care for their young for several months to several years after they are born.
What are the types of Fertilization?
The process by which the male and female gametes fuse to form the zygote is known as fertilisation.
Fertilization can be classified into two types:
- External fertilisation: it is a type of fertilisation in which the eggs are fertilised outside of the organism’s body. They are mostly found in wet environments. It is necessary for both the male and female to release their gametes into their surroundings (usually water), a process known as spawning. For example, amphibians and fishes.
- Internal fertilization: The eggs are fertilised within the female reproductive tract in this type of fertilisation. It contributes to the protection of the developing egg. For example: Mammals and birds.
When does fertilization-occur?
Some people believe fertilisation occurs in the uterus because that is where the baby develops. Fertilization, on the other hand, takes place in the fallopian tubes.
Each sperm has a single goal: to find the egg. A sperm cell, on the other hand, must travel a long and difficult path to reach its destination.
It must first travel from the vagina to the cervix, and then through the uterus to the fallopian tubes. If the sperm is lucky enough, it will penetrate the egg and fertilise it.
The newly fertilised egg (now referred to as a zygote) will travel from the fallopian tubes to the uterus. It will hopefully implant in the uterine wall and grow into a fetus there.
Process of fertilization
Fertilization occurs in three stages to ensure that the appropriate egg and sperm find each other and that only one sperm enters the egg: chemotaxis, sperm activation/acrosomal reaction, and sperm/egg adhesion.
Penetration of the corona radiata
The entrance of spermatozoa into corona radiata of egg, a cell coat that covers the egg, is the initial stage of human fertilisation.
The secretion of hyaluronidase enzyme and the mobility of the flagellum allow sperm cells to pass through this first barrier (the tail).
Penetration of the zona pellucida
The ZP must be degraded by more than one sperm cell.
The head of sperm makes contact with the ZP3 receptor in order to get through this second barrier. The acrosome reaction is triggered, resulting in the release of the series of hydrolytic enzymes (contents of acrosome). These enzymes break down the ZP, allowing the sperm cell to pass through.
Fusion of membranes
The creation of the fertilisation cone allows the membranes of egg and sperm to fuse, allowing the sperm’s head to penetrate into the egg. Simultaneously, depolarization and release of cortical granules prevent numerous sperm from entering the uterus.
Symptoms of fertilization
- Pregnancy can be detected in humans within a few days of fertilisation.
- A missed period is the most obvious sign of early pregnancy in humans.
- As a result of the implantation process, bleeding and cramping may occur, and the basal body temperature, which rises slightly during ovulation, remains elevated.
- As the body prepares for parenthood, the breasts begin to grow and become tender; dietary preferences may change as a mechanism for obtaining the proper nutrients; and rapid hormonal changes can cause sickness, fatigue, and mood changes.
Conclusion
Internal fertilisation evolved as a result of the transition to land, because many gametes cannot float through air in the same way they can in water. Though they usually meet in the female, the egg and sperm in some animals meet inside the male. Internal fertilisation animals specialise in the development and protection of an egg. The process by which the male and female gametes fuse to form the zygote is known as fertilisation. Internal fertilization: The eggs are fertilised within the female reproductive tract in this type of fertilisation. It contributes to the protection of the developing egg. It must first travel from the vagina to the cervix, and then through the uterus to the fallopian tubes. If the sperm is lucky enough, it will penetrate the egg and fertilise it.