Hiyah guys! Thanks for all of your support for this blog. Today my article is about how animals and humans reproduce in two ways. Note that this article is recommended for only adults and should not be read by children or teens below 18. If any child reads this article I am not to be blamed for my blog does not have any special restrictions because it is a free version. Note that the content I have written is censored to an extent to avoid any controversy. Please note that whatever you read here is a form of knowledge, It is nothing to be disgusted of as it is biology and in biology you have to read all of this. Please don’t report my blog. Feel free to comment and tell any errors that might be on my article. Thank You!
Asexual reproduction in Animals
In my previous articles you had read about mitosis and meiosis. In my article about plant reproduction you had learned that Asexual reproduction does not involve any gamete cells (sperm and ovum are gamete cells). Also the Asexual reproduction only has one parent involved in it meaning that the new born animal or a plant is identical to its parent and has the same gene as its parent. Asexual reproduction is not common in animals and is definitely not found in humans. Some animals like the Hydra reproduce Asexually. How this works is that Hydra starts the reproduction process with mitosis. A bulge grows out of the body of the Hydra and This bulge grows to a greater extent until it separates from the parent and forms a new animal. This covers one example of Asexual reproduction in animals.
Reproduction in Humans/Animals
Every human/animal (almost every animal) reproduce their species by sexual reproduction. This revolves around meiosis. This means the gametes are involved in this. The gametes are the sperm cells and the ovum (egg). Mainly these two gametes are found in different individuals. Now for the sperm to fertilize the egg a process called mating should occur (this will not be discussed).
In males (This paragraph is not written with the intention of offense), the glands called testes (singular: testis), which are covered by scrotum, produce the hormone testosterone as well as produce sperm cell by dividing by meiosis. When the sperms are produced they are sent through the sperm duct (Vas deferens) which passes through the seminal vesicle and the prostrate gland where it joins the urethra and then extends into the penis. On top of the penis is an erector tissue which may fill with blood which makes the penis erect and stiff for mating. When the sperms pass through the seminal vesicle and the prostrate gland it mixes with the substances produced by these glands. These substances produced have nutrients in it which provide a source of energy for the sperm and also has enzymes which simulates it to move. The mixed substance is then called semen.
In females (this paragraph is not written with the intention of offense), the glands involved are the ovaries (singular: ovary). Ovaries produce the cell ovum (egg) which is the size of a dot or full-stop at the end of this sentence and can be seen by a naked eye. There is a funnel right by the each of the ovary. This funnel is the part of the oviduct which extends and enters the uterus or womb. The neck of the uterus is called the cervix. Below the cervix is the vagina and the part opening to the outside is called the vulva (again, this is not an offense). The funnel shaped opening of the oviduct helps an ease for the ovum to enter the oviduct where the sperm merges with it and forms a zygote.
FSH and LH
Follicle stimulating hormone (FSH) and Luteinising hormone (LH) are two hormones formed by the pituitary gland. The FSH, in male, is responsible for the production of the sperm. While the LH in a male is responsible for the release of the hormone testosterone which develops the secondary sex features such as “breaking” of voice and growth of hair in pubic area, in armpits, and growth of facial hair.
In a female, the FSH causes the production of the ovum/egg and is responsible for the production of the hormone estrogen which develops the secondary sex features of the female which are almost the same as the male. The LH causes the ovulation and helps in growth of the follicle.
Ovulation is the process of production of ovum. It occurs in the middle of the menstruation cycle . Ovary has a structure in it which is called a follicle. This follicle has many cells that have the tendency to become ovum/eggs. The pituitary gland secretes a hormone called the Follicle Stimulating Hormone (FSH). This stimulates the follicle to grow an egg each month. As the follicle grows it reaches the outside of the ovaries and bursts open releasing the ovum to the funnel shaped oviduct opening. The LH turns follicle into corpus luteum which produces the hormone progesterone which reduces the amount of FSH and Lutienising Hormone (LH) in a female body. The ovum is produced every month.
Menstruation is the discharge of blood from the uterus. The monthly discharge of blood from the uterus is called a menstruation cycle. But, however, menstruation lasts days, weeks or even months. However, after fertilization the menstruation cycle ends indicating pregnancy. But when no fertilization occurs, the corpus luteum breaks down and the amount of progesterone released reduces. The uterus sheds again and the cycle begins again.
When the ovum is released it enters the funnel and into the oviduct. When the ovum is fertilized by the sperm cell the corpus luteum starts to secrete progesterone which reduces the LH and FSH level in the body. The progesterone thickens the uterus lining and makes it spongy and fills it with blood. This prepares the uterus to meet the embryo and the menstruation period stops. As mentioned above, if no fertilization takes place then the menstruation continues and the corpus luteum breaks down.
The sperm cell structure as shown has a flagellum which helps it to move and has a group of mitochondria in its middle piece which breakdown the nutrients in the semen to supply energy for movement. The head of the sperm cell has a nucleus with a haploid number of chromosomes and on top of it is acrosome which has enzymes in it to break down the outer membrane of the ovum.
The egg structure as shown has a layer of follicle cells on its outer part due to the bursting of the follicle during ovulation. The ovum has an outer membrane which protects it from mechanical injury and under it is another membrane. The inner part of the cell has a cytoplasm and a nucleus with the haploid number of chromosomes.
When the sperms meet the egg in the oviduct a sperms cell breaks the outer membrane of the ovum and passes through the inner membrane. The nucleus of the sperm cell merges with the nucleus of the ovum and creates a new nucleus with a diploid number of chromosomes. This merged nucleus is called the zygote. The ovum then forms the fertilization membrane which does not allow any other sperm cell to enter the ovum. In a matter of days the zygote performs cell division by mitosis and on the fifth day forms the embryo. The embryo has a layer around it called amnia which altogether is called the amniotic sac. The layer is not a membrane. It produces the amniotic fluid which lubricates the embryo allowing it to move and protects the embryo by acting as a shock absorbent.
The embryo moves to the uterus lining and sets on its wall which has cilia on it. This phase is called implantation. The embryo continues its cell division and soon is recognizable as a forming baby. After this phase the embryo is called a fetus until its birth. As the embryo grows it moves to the uterus cavity. Above the uterus cavity is an organ formed called the placenta. It is made of embryonic tissue and the tissues of the uterus lining. The placenta takes the role of the corpus luteum and produces the hormone progesterone. The fetus is attached to the placenta by an umbilical cord. It provides blood to the fetus which has nutrients in it.
The umbilical cord and the placenta has blood vessels in it. The mother’s blood vessel also reaches here. The blood of the mother and the fetus is not mixed because of a membrane dividing them. But many mineral and nutrients and other important substances mixed into the blood of the fetus through diffusion, osmosis and active transport.
These important substances are:
- Nutrients and minerals such as carbohydrates, protein, fat etc. to provide energy. Fiber is also supplied to the blood of the fetus for avoiding constipation. The fiber does not digest but helps in movement of waste products.
- Antibodies are also diffused into the fetus which provide a small protection for the baby. After a few months or weeks the baby is vaccinated to further strengthen the immunity system.
- Respiratory products such as oxygen are essential for the fetus to survive because the fetus cut off of air of the environment. The carbon dioxide in the fetus is diffused in to the mother’s blood capillaries which is exhaled out of the body.
- The urea of the fetus is also diffused into the mother’s capillaries which is then excreted out of the body.
- The progesterone is not diffused into the fetus but rather is a function of the placenta. The placenta produces this hormone to maintain the thickness of the uterus.
With this I end my article. Thank you for reading.