The basis of reproduction is that the man provides sperm and the woman provides eggs. The sperm and eggs each carry the genetic material of the parents and are combined together through fertilization to form a new life.
Sperm are produced in the seminiferous tubules of the testicles. After the development of male puberty, the testicles have the ability to continuously produce sperm. Adult testicles weigh 10 to 20 grams, and each gram of testicular tissue can produce approximately 10 million sperm per day. After the age of 40, the ability to produce sperm gradually weakens, but people aged 60 to 70 and even some 90-year-olds still have the ability to produce sperm. Therefore, the childbearing age of men is significantly longer than that of women.
Eggs develop from primordial oocytes in the ovary. After a woman reaches puberty, she releases one mature egg, sometimes two, every menstrual cycle. A woman releases approximately 400 eggs in her lifetime, with a maximum of 500 eggs. The development of eggs originates from the fetal period, forms during adolescence, and develops during the childbearing period, which lasts for decades. The eggs of older pregnant women have a higher chance of developing abnormalities over decades. Around the age of 55, women enter menopause, and their ovaries lose their ability to ovulate, thus losing their reproductive function.
How sperm are formed
Male reproductive cells are called sperm. Sperm is produced in the seminiferous tubules of the testicles, and its formation takes more than two and a half months.
According to the cytological characteristics of spermatogenic cells, it is divided into 3 stages.
(1) Spermatogonia divide and proliferate and produce spermatocytes:In the formation of sperm During the process, it undergoes two mature divisions.
The first mature division is from primary spermatocytes to secondary spermatocytes. This division, called meiosis, reduces the number of chromosomes in the cell by half. There are 23 pairs of chromosomes in primary spermatocytes, including 22 pairs of autosomes and 1 pair of sex chromosomes. In a pair of sex chromosomes, one is the X chromosome and the other is the Y chromosome. When the primary spermatocyte divides, the 23 pairs of chromosomes are evenly distributed into the two secondary spermatocytes, that is, there are 23 chromosomes in each secondary spermatocyte.
Since sex chromosomes are divided into X and Y, one secondary spermatocyte after division contains the X chromosome, while the other secondary spermatocyte contains the Y chromosome.
(2) Spermatocytes undergo meiosis to form haploid sperm cells:The second division is made by secondary sperm The mother cell divides into sperm cells. After this division, each chromosome splits into two again, and the chromosomes of the entire cell are divided into two groups and then distributed into each sperm cell. Therefore, the chromosomes in the sperm cells are the same as those in the secondary spermatocytes. Two secondary spermatocytes divide into four sperm cells, each of which has 23 chromosomes. Two sperm cells contain Y chromosomes and the other two sperm cells contain X chromosomes.
(3) Sperm cells become sperm: Sperm cells no longer divide, but undergo morphological changes Become sperm. The sperm is shaped like a tadpole. The structure of sperm: It consists of four parts: acrosome, head, middle body and tail. The head of the sperm is condensed from the nucleus of the sperm cell. While the other parts are formed from the cytoplasm. The head of the sperm contains genetic material (chromosomes). The acrosome contains proteins that help sperm pass through the thick outer layer of the egg. The middle part of the body contains energy substances needed for sperm movement. The long tail helps the sperm swim nimbly. Sperm can survive in the epididymis for several months and in the female reproductive tract for 1 to 3 days. The ability to fertilize eggs can only last about 20 hours.
How eggs are produced
The egg is the largest cell in the human body and is also the mother cell unique to women that produces new life.
(1) When a woman is still in her mother’s womb, her small ovaries already have millions of oocytes, and each oocyte is wrapped in a primordial follicle. , properly stored, and came to the human world. Generally speaking, a woman can have a total of 400 to 500 eggs in her lifetime that can mature and be excreted outside the ovaries waiting for fertilization.
(2) At puberty, the pituitary gland secretes gonadotropins to cause oocytes to begin to develop, but only one primordial follicle matures every month (up to two), and the eggs stored inside are discharge.
(3) The mature egg waits for fertilization by sperm in the ampulla of the fallopian tube. If it does not meet the sperm to form a fertilized egg after 48 hours, it will begin to die naturally.
(4) One month later, another egg will mature and be released, and the same process will be repeated. Usually, the left and right ovaries take turns to ovulate.
This article is provided by Baidu Reading and is excerpted from \”Three Months Before Pregnancy – Pregnancy Preparation Period\” Author: Wang Liru