Human Reproductive Systems

Reproduction in Humans

Human reproduction is the biological process by which new individuals of the same species are produced, ensuring the continuation of the species.

In human reproduction, the two sexes, male and female, generate specialized reproductive cells known as gametes. Sperm, (spermatozoa), are the male gametes, while ova (singular = ovum) or eggs are the female gametes. Fertilization is the process where a sperm unites with an ovum to form a new individual. Following fertilization, the sperm nucleus merges with the ovum, resulting in the formation of a cell called a zygote. This zygote undergoes cell division, eventually developing into an embryo and, subsequently, a fully formed organism.

In humans, males produce millions of sperm, while females produce a smaller number of eggs, typically one per month over approximately 40 years. Normally, only one egg is fertilized at a time; the fertilization of two eggs simultaneously leads to the birth of non-identical twins.

Example:

When a mommy and daddy want to have a baby, they each provide a special cell. The daddy gives a tiny cell called sperm, and the mommy gives a tiny cell called an egg. These cells come together in a process called fertilization, creating a new cell called a zygote.

This zygote then starts dividing and growing, eventually becoming an embryo and later a full-grown baby. The daddy usually has lots of sperm, while the mommy has a smaller number of eggs. Normally, only one egg gets fertilized at a time, but if two eggs are fertilized together, it can result in non-identical twins.

So, in simple terms, human reproduction is when a sperm and an egg join together, leading to the creation of a new life that grows into a baby.

Female Reproductive System

The female reproductive system consists of the ovaries, which produce eggs and hormones, the fallopian tubes that capture and transport eggs, the uterus for nurturing a fertilized egg during pregnancy, the cervix connecting the uterus to the vagina, and the external genitalia (vulva) protecting internal organs, collectively managing the menstrual cycle and facilitating sexual reproduction.

Functions of the Female Reproductive System 

Production of Egg

The production of eggs, also known as ova or oocytes, is a biological process called oogenesis that occurs within the ovaries of females. 

Embryonic Development:

• Females are born with a finite number of immature eggs already present in their ovaries. These immature eggs, or oocytes, are arrested in a state of meiotic division.

Puberty and the Menstrual Cycle:

• During puberty, usually around ages 10 to 14, a girl’s ovaries begin to respond to hormonal signals.
• Each month, under the influence of Follicle follicle-stimulating hormone (FSH) from the pituitary gland, a group of immature follicles starts to grow in the ovaries.

Follicular Development:

• Within these follicles, one oocyte is selected to undergo further development while the others degenerate.
• The selected oocyte begins to undergo meiotic division but pauses at a stage called prophase I.

Ovulation:

• As the menstrual cycle progresses, the dominant follicle containing the selected oocyte continues to grow.
• A surge of Luteinizing Hormone (LH) triggers the completion of meiosis I, leading to the release of a mature egg from the ovary. This process is known as ovulation and typically occurs around the middle of the menstrual cycle.

Formation of Follicle Cells and Zona Pellucida:

• After ovulation, the remaining part of the ruptured follicle transforms into a structure called the corpus luteum.
• The released egg is now enclosed in a protective layer called the zona pellucida, and it is still surrounded by follicle cells.

Journey  through the Oviduct:

• The egg is wafted down the fallopian tube (oviduct) by the movement of cilia and peristalsis.
• If the egg encounters sperm cells in the oviduct and fertilization occurs, the resulting zygote begins to develop into an embryo.

Implantation or Degeneration:

• If fertilization does not occur, the egg, now called an ovum, continues its journey to the uterus.
• The ovum may either implant in the uterus if fertilized or, if unfertilized, it leads to the breakdown of the corpus luteum, triggering the start of a new menstrual cycle.