What is the difference between a follicle and an egg?

Ever since we took biology class, we have known that we are the product of the union of our parents' sperm and egg. However, due to shyness, people know very little about this aspect, and many people don’t even know what these two things are. In fact, eggs are unique to the female body, so what are follicles? Today, let us understand what eggs are and what are the differences between them and follicles.

1. The relationship between the egg and the follicle

Under the influence of sex hormones, only one oogonia matures each month. The mature oogonia undergoes meiosis to form four daughter cells, one of which is called an egg and the other three are called polar bodies (which eventually degenerate and disappear).

The human ovaries produce egg cells, which contain many primordial germ cells, namely oogonia. Women generally produce only one egg cell each month, and in very rare cases, two or more. The oogonia and the surrounding follicular cells together form an ovarian follicle, which gradually matures and releases the egg cell.

The ovum (egg) is the reproductive cell of female organisms. Both animals and seed plants produce eggs. In higher organisms, eggs are produced by the ovaries. All mammals have immature eggs in their ovaries when they are born, and the number of eggs does not increase after they mature. When the egg and sperm combine and fertilize, a fertilized egg is formed, marking the beginning of a new life. Some animals (such as birds) fertilize internally, while others (such as most fish) fertilize externally.

2. Egg formation time

The formation of eggs must first go through the shedding of the endometrium. The shedding of the endometrium is cyclical, once a month, and it is affected by the cyclical changes in ovarian endocrine secretions. Each time the endometrium is shed, the follicles in the ovaries begin to develop. Under the influence of the estrogen they secrete, the endometrium begins to grow and thicken again. The endometrium at this time is called the proliferative phase.

Around the middle of the menstrual cycle, to be exact 14 days before the next menstrual period. The follicle in the ovary ovulates (taking a 28-day cycle as an example, the ovulation day is the 14th day). After ovulation, the follicle forms a corpus luteum, which can secrete estrogen and progesterone. These hormones act on the endometrium, making it thicker, the blood vessels more curved and congested, and the glands thicker and expanded to secrete a lot of nutrients. The endometrium at this time is called the secretory phase.

If the egg released this month is not fertilized, the corpus luteum in the ovary will degenerate, the production of estrogen and progesterone will decrease, the endometrium will not receive the support of estrogen and progesterone, and it will atrophy and collapse. The blood vessels in the endometrium will spasm and contract, and finally rupture and bleed. The endometrial layer will peel off from the uterine cavity and be discharged through the vagina. This is menstruation. In women of childbearing age, this change repeats itself unless they become pregnant, so it is called the menstrual cycle. It can also be understood that menstruation is a manifestation of failure of fertilization after ovulation once a month.