When a fertilized egg does implant, a hormone called human chorionic gonadotropin hCG begins to be produced in the uterus. This is the hormone that a pregnancy test measures.
It prevents the uterine lining from being shed, so the woman does not have a period. Other signs such as breast changes and nausea occur in a woman's body, also meaning that pregnancy has begun. Author: Healthwise Staff. This information does not replace the advice of a doctor. Healthwise, Incorporated, disclaims any warranty or liability for your use of this information.
Your use of this information means that you agree to the Terms of Use. Learn how we develop our content. They produce oocytes eggs for fertilisation and they produce the reproductive hormones, oestrogen and progesterone. The function of the ovaries is controlled by gonadotrophin-releasing hormone released from nerve cells in the hypothalamus which send their messages to the pituitary gland to produce luteinising hormone and follicle stimulating hormone.
These are carried in the bloodstream to control the menstrual cycle. The ovaries release an egg oocyte at the midway point of each menstrual cycle. Usually, only a single oocyte from one ovary is released during each menstrual cycle, with each ovary taking an alternate turn in releasing an egg.
A female baby is born with all the eggs that she will ever have. This is estimated to be around two million, but by the time a girl reaches puberty, this number has decreased to about , eggs stored in her ovaries.
In the ovary, all eggs are initially enclosed in a single layer of cells known as a follicle, which supports the egg. Over time, these eggs begin to mature so that one is released from the ovary in each menstrual cycle. As the eggs mature, the cells in the follicle rapidly divide and the follicle becomes progressively larger.
Many follicles lose the ability to function during this process, which can take several months, but one dominates in each menstrual cycle and the egg it contains is released at ovulation. As the follicles develop, they produce the hormone oestrogen. Once the egg has been released at ovulation, the empty follicle that is left in the ovary is called the corpus luteum. This then releases the hormones progesterone in a higher amount and oestrogen in a lower amount.
These hormones prepare the lining of the uterus for potential pregnancy in the event of the released egg being fertilised. About once a month, during ovulation, an ovary sends a tiny egg into one of the fallopian tubes.
Unless the egg is fertilized by a sperm while in the fallopian tube, the egg leaves the body about 2 weeks later through the uterus — this is menstruation. Blood and tissues from the inner lining of the uterus combine to form the menstrual flow, which in most girls lasts from 3 to 5 days.
A girl's first period is called menarche MEH-nar-kee. It's common for women and girls to have some discomfort in the days leading to their periods.
Premenstrual syndrome PMS includes both physical and emotional symptoms that many girls and women get right before their periods, such as:. PMS is usually at its worst during the 7 days before a girl's period starts and disappears after it begins. Many girls also have belly cramps during the first few days of their periods caused by prostaglandins, chemicals in the body that make the smooth muscle in the uterus contract.
These involuntary contractions can be dull or sharp and intense. It can take up to 2 years from menarche for a girl's body to develop a regular menstrual cycle. During that time, her body is adjusting to the hormones puberty brings. On average, the monthly cycle for an adult woman is 28 days, but the range is from 23 to 35 days.
If a female and male have sex within several days of the female's ovulation, fertilization can happen. When the male ejaculates when semen leaves the penis , a small amount of semen is deposited into the vagina. Millions of sperm are in this small amount of semen, and they "swim" up from the vagina through the cervix and uterus to meet the egg in the fallopian tube.
It takes only one sperm to fertilize the egg. About 5 to 6 days after the sperm fertilizes the egg, the fertilized egg zygote has become a multicelled blastocyst. A blastocyst BLAS-tuh-sist is about the size of a pinhead, and it's a hollow ball of cells with fluid inside. The blastocyst burrows itself into the lining of the uterus, called the endometrium.
The hormone estrogen causes the endometrium en-doh-MEE-tree-um to become thick and rich with blood. Progesterone, another hormone released by the ovaries, keeps the endometrium thick with blood so that the blastocyst can attach to the uterus and absorb nutrients from it.
This process is called implantation. As cells from the blastocyst take in nourishment, another stage of development begins. In the embryonic stage, the inner cells form a flattened circular shape called the embryonic disk, which will develop into a baby. The outer cells become thin membranes that form around the baby. The cells multiply thousands of times and move to new positions to eventually become the embryo EM-bree-oh. If the egg does not become fertilized, the lining of the uterus endometrium is shed during menstruation.
The average menstrual cycle lasts 28 days. The cycle starts with the first day of one period and ends with the first day of the next period. The average woman ovulates on day At this time, some women have minor discomfort in their lower abdomen, spotting, or bleeding, while others do not have any symptoms at all.
A woman is generally most likely to get pregnant fertile if she has sex a few days before, and during ovulation. Menstruation is one part of a woman's cycle when the lining of the uterus endometrium is shed. This occurs throughout a woman's reproductive life.
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