Human Reproduction: From Gametes to the Reproductive System
Human Reproduction
Reproductive functions are a set of processes by which a living thing produces another living being identical or similar to it, which ensures the continuity of the individual, not as an isolated organism, but as a species.
Asexual vs. Sexual Reproduction
There are two modes of reproduction among living organisms: asexual and sexual. The first requires the participation of an individual and does not require the formation of sex cells. The human species reproduces sexually, so there is one male and one female.
Sexual Reproduction
Sexual reproduction requires specialized forms of reproductive organs: the male and female reproductive tract. These organs produce gametes.
Gametes or Sex Cells
Gametes are special cells that are characterized by having half the number of chromosomes (genetic material) than other cells. This reduction is not causal, then, at the time of fertilization (union of male and female gametes) the sum of chromosomes (genetic material) again gives the typical number of the species. Thus, both the father and the mother give a number of identical genes, and the child will have characteristics of both.
Reducing the number of chromosomes by half is called meiosis and takes place during the process of gametogenesis.
Gametogenesis
Gametogenesis is the process by which gametes are formed. It is produced by meiosis and differentiation.
The cells of our body are diploid, having two sets of repeated chromosomes, some coming from the father and some from the mother. Each pair of repeated chromosomes is called homologous. It is represented by 2n chromosomes, where n is the number characteristic of each species and indicates the chromosome number within each species.
Spermatogenesis
In spermatogenesis, each cell that divides by meiosis produces four sperm. During the process, they lose some of their cytoplasm and form a flagellum. The precursor of the sperm cells is called spermatogonia.
Oogenesis
In oogenesis, each month, a single cell undergoes meiosis and gives only one egg, since the other cells are very small and are not fertile (they are called polar bodies). The egg has increased in size due to the accumulation of reserve substances to nourish the embryo, if fertilized, while it cannot get nutrients from the mother.
The Male Reproductive System
The male reproductive system consists of a set of organs, ducts, accessory glands, and external genitalia.
- Testes: Two small organs located outside the abdominal cavity, are in a pouch of skin called the scrotum. They are the male gonads. The interior contains many seminiferous tubules, where sperm are formed.
- Epididymis: Located below the testicle is a coiled tube located in the anterior part of each testicle. Here, sperm finish maturing.
- Vas deferens: They are long tubes that connect the epididymis to the seminal vesicles.
- Seminal vesicles: Glands attached to the male reproductive system, in which nutrient fluid accumulates that keeps the sperm.
- Prostate: A gland that secretes substances that increase sperm motility.
- Cowper’s glands: Secrete substances that protect the sperm from the acidic urine in the urethra and mucus that lubricates the urethra and the tip of the penis to facilitate copulation.
- Penis: Also called the copulatory organ, it is traversed by the urethra in its entire length. It consists of three cylinders that are spongy and cavernous bodies and, when filled with blood, increase in size and become rigid, causing penile erection. Its final tip is the glans, protected by a piece of skin called the foreskin and may be retracted, leaving it exposed.
The sex cells are an exception, having only one set of chromosomes, so they will have n chromosomes. These cells that only have one set of chromosomes are called haploid. The purpose of gametogenesis is that after fertilization, the new individuals maintain the standard number of chromosomes. The formation of gametes occurs in the gonads or sexual organs: testes in males and ovaries in women.