How does oogenesis occur

This is why fraternal twins run in families. However, only women ovulate. Moms pregnant with twins complain of more back pain, sleeping difficulties, and heartburn than moms who are carrying one child.

Moms pregnant with twins also have a higher rate of maternal anemia and a higher rate of postpartum hemorrhage bleeding after delivery. The best time to have this ultrasound is at weeks of pregnancy. This is usually when your health professional can say for sure how many fetuses, placentas and amniotic sacs there are.

A previous pregnancy — or, better yet, previous multiple pregnancies — may increase your chances of having twins. In fact, according to the , women between the ages of 35 to 40 with four or more children are three times more likely to have twins than a woman under 20 without children.

Elevated Beta-hCG Levels You cannot conclusively distinguish a single pregnancy from twins on a urine pregnancy test. That said, you may have a very early positive pregnancy test if you are carrying twins. Most parents expect to experience sleepless nights when their twins are babies. However, many pregnant moms are surprised by how difficult it is to get proper rest during their pregnancy with multiples.

Physical discomfort and anxiety can produce occasional restlessness or even full-blown insomnia. Between 7 and 9 hours of sleep each day is recommended at the age most women find themselves pregnant.

Genetics and quality of sleep can affect these numbers, but this is a good general guideline for how much shut-eye is needed. Most women experience sleep problems during pregnancy. Pregnant women tend to get more sleep during their first trimesters hello, early bedtime but experience a big drop in the quality of their sleep. It turns out that pregnancy can make you feel exhausted all day long.

It can also cause insomnia at night. Many women feel tired in early pregnancy. Some pregnant women notice this fatigue even as early as one week after conception, making this one of the first noticeable signs of pregnancy. The fluid-filled spaces between granulosa cells merge together to form a central fluid-filled space called the antrum.

These are referred to as secondary follicles. Those secondary follicles develop during each monthly cycle under the influence of follicle-stimulating hormone and luteinizing hormone. LH surge induces this stage and meiosis-I complete here. Inside the follicle are formed two haploid cells of unequal sizes.

A polar body forms one of the daughter cells which receives less cytoplasm. This cell is not involved in the development of an ovum. The secondary oocyte is known as the other daughter cell. Meiosis-II occurs in the two daughter cells. The polar body replicates to form two polar bodies whereas the secondary oocyte arrests in the meiosis-II metaphase stage. Oocyte formation occurs in ovaries. To form a follicle each oocyte is neighbored by follicle cells. As the menstrual cycle begins, primary oocytes begin to grow larger, and the number of follicle cells increases, causing the follicle to grow larger too.

Some nursing oocytes usually degenerate and leave one follicle only to mature. Fraternal twins, which are genetically distinct, can be born here. The primary oocyte begins its primary meiotic division when a follicle reaches maturity and becomes secondary oocyte. Shortly after, in the Fallopian tube, the follicle splits and secondary oocytes are released even though the second meiotic division has not occurred.

That release from ovaries of a secondary oocyte is known as ovulation. On fertilization Meiosis-II is complete. This produces a third polar structure.

Part of the uterus, called the cervix, protrudes into the top of the vagina, which functions as the birth canal. The vagina is a muscular tube that serves several purposes.

It allows menstrual flow to leave the body, is the receptacle for the penis during intercourse, and serves as the vessel for the delivery of offspring. It is lined by stratified squamous epithelial cells to protect the underlying tissue. Spermatogenesis and oogenesis are both forms of gametogenesis, in which a diploid gamete cell produces haploid sperm and egg cells, respectively.

Gametogenesis, the production of sperm and eggs, takes place through the process of meiosis. The production of sperm is called spermatogenesis and the production of eggs is called oogenesis. Oogenesis occurs in the outermost layers of the ovaries. As with sperm production, oogenesis starts with a germ cell, called an oogonium plural: oogonia , but this cell undergoes mitosis to increase in number, eventually resulting in up to one to two million cells in the embryo.

A primary oocyte begins the first meiotic division, but then arrests until later in life when it will finish this division in a developing follicle. This results in a secondary oocyte, which will complete meiosis if it is fertilized.

The cell starting meiosis is called a primary oocyte. This cell will begin the first meiotic division, but be arrested in its progress in the first prophase stage. At the time of birth, all future eggs are in the prophase stage.

At adolescence, anterior pituitary hormones cause the development of a number of follicles in an ovary. This results in the primary oocyte finishing the first meiotic division. The cell divides unequally, with most of the cellular material and organelles going to one cell, called a secondary oocyte, and only one set of chromosomes and a small amount of cytoplasm going to the other cell. This second cell is called a polar body and usually dies.

A secondary meiotic arrest occurs, this time at the metaphase II stage. At ovulation, this secondary oocyte will be released and travel toward the uterus through the oviduct. If the secondary oocyte is fertilized, the cell continues through the meiosis II, completing meiosis, producing a second polar body and a fertilized egg containing all 46 chromosomes of a human being, half of them coming from the sperm.

Spermatogenesis occurs in the wall of the seminiferous tubules, with stem cells at the periphery of the tube and the spermatozoa at the lumen of the tube. Immediately under the capsule of the tubule are diploid, undifferentiated cells. These stem cells, called spermatogonia singular: spermatagonium , go through mitosis with one offspring going on to differentiate into a sperm cell, while the other gives rise to the next generation of sperm. Spermatogenesis : During spermatogenesis, four sperm result from each primary spermatocyte, which divides into two haploid secondary spermatocytes; these cells will go through a second meiotic division to produce four spermatids.

Meiosis begins with a cell called a primary spermatocyte. At the end of the first meiotic division, a haploid cell is produced called a secondary spermatocyte. This haploid cell must go through another meiotic cell division. The cell produced at the end of meiosis is called a spermatid.

Four sperm result from each primary spermatocyte that goes through meiosis. Stem cells are deposited during gestation and are present at birth through the beginning of adolescence, but in an inactive state.

During adolescence, gonadotropic hormones from the anterior pituitary cause the activation of these cells and the production of viable sperm.

This continues into old age. Privacy Policy. Skip to main content. Animal Reproduction and Development. Search for:. Human Reproductive Anatomy and Gametogenesis. Male Reproductive Anatomy The male reproductive system is a series of organs and glands that produce sperm, fluids, hormones, and enable the ejaculation of sperm. Learning Objectives Diagram the structures of human male reproductive anatomy.

Key Takeaways Key Points The male gonads, or testes, produce sperm within the seminiferous tubules; the sperm are housed here until they are nearly mature, at which point they enter the epidydimis for full maturation.

The testes are housed in the scrotum, an external sac that keeps the sperm at a temperature lower than that of the body. At ejaculation, sperm leave the epidydimis and enter the vas deferens, a duct which carries the sperm out of the body through the urethra, along with the fluids of various glands of the male reproductive system. The seminal vesicles produce a thick fluid that is alkaline in order to protect sperm from the acidic nature of the female vagina; it also contains sugars to nourish the sperm.

The prostate gland produces the force necessary to push the sperm out of the epididymis at ejaculation, while the bulbourethral gland emits a fluid just prior to ejaculation that neutralizes acid from any urine left over in the urethra.

During sexual arousal, the spongy tissue inside the penis the corpus spongiosum fills with blood, causing the penis to become erect and hard; after ejaculation, the blood flows back out of the penis, leaving it flaccid.