These muscles are able to expand and contract to accommodate a growing fetus and then help push the baby out during labor. When a woman isn't pregnant, the uterus is only about 3 inches 7. At the upper corners of the uterus, the fallopian tubes connect the uterus to the ovaries. The ovaries are two oval-shaped organs that lie to the upper right and left of the uterus. They produce, store, and release eggs into the fallopian tubes in the process called ovulation av-yoo-LAY-shun.
There are two fallopian fuh-LO-pee-un tubes, each attached to a side of the uterus. Within each tube is a tiny passageway no wider than a sewing needle. At the other end of each fallopian tube is a fringed area that looks like a funnel. This fringed area wraps around the ovary but doesn't completely attach to it. When an egg pops out of an ovary, it enters the fallopian tube. Once the egg is in the fallopian tube, tiny hairs in the tube's lining help push it down the narrow passageway toward the uterus.
The ovaries OH-vuh-reez are also part of the endocrine system because they produce female sex hormones such as estrogen ESS-truh-jun and progesterone pro-JESS-tuh-rone. Sexual reproduction couldn't happen without the sexual organs called the gonads.
Most people think of the gonads as the male testicles. But both sexes have gonads: In females the gonads are the ovaries, which make female gametes eggs. The male gonads make male gametes sperm. When a baby girl is born, her ovaries contain hundreds of thousands of eggs, which stay inactive until puberty begins. At puberty, the pituitary gland in the central part of the brain starts making hormones that stimulate the ovaries to make female sex hormones, including estrogen.
The secretion of these hormones causes a girl to develop into a sexually mature woman. Toward the end of puberty, girls begin to release eggs as part of a monthly period called the menstrual cycle. 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. After about 8 weeks, the embryo is about the size of a raspberry, but almost all of its parts — the brain and nerves, the heart and blood, the stomach and intestines, and the muscles and skin — have formed.
During the fetal stage, which lasts from 9 weeks after fertilization to birth, development continues as cells multiply, move, and change. It gets oxygen and nourishment from the mother's blood via the placenta pluh-SEN-tuh. This disk-like structure sticks to the inner lining of the uterus and connects to the fetus via the umbilical um-BIL-ih-kul cord.
The amniotic fluid and membrane cushion the fetus against bumps and jolts to the mother's body. Pregnancy lasts an average of days — about 9 months.
When the baby is ready for birth, its head presses on the cervix, which begins to relax and widen to get ready for the baby to pass into and through the vagina.
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