Reproduct Sys (Your Body) (Your Body: How It Works)

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Variations in the reproductive system

The Fix: Feed a second artery into the back side of each arm and leg, by the shoulder blades or buttock, says Rui Diogo, an assistant professor of anatomy at Howard University, in Washington, DC, who studies the evolution of primate muscles. This extra pipe would provide a more direct route from the shoulder to the back of the hand, preventing vessels and nerves from wandering too close to the skin.

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Problem: The photoreceptor cells in the retina of the eye are like microphones facing backward, writes Nathan Lents , an associate professor of molecular biology at the City University of New York. The setup may encourage the retina to detach from its supporting tissue—a leading cause of blindness. It also creates a blind spot where cell fibers, akin to microphone cables, converge at the optic nerve—making the brain refill the hole. Problem: The recurrent laryngeal nerve RLN plays a vital role in our ability to speak and swallow.

It feeds instructions from the brain to the muscles of the voice box, or larynx, below the vocal cords. Theoretically, the trip should be a quick one. But during fetal development, the RLN gets entwined in a tiny lump of tissue in the neck, which descends to become blood vessels near the heart. That drop causes the nerve to loop around the aorta before traveling back up the larynx. Having this nerve in your chest makes it vulnerable during surgery—or a fist fight. While a baby is in utero, develop the RCN after sending that irksome neck lump of vessel tissue to the chest.


Problem: The trachea windpipe and esophagus food pipe open into the same space, the pharynx, which extends from the nose and mouth to the larynx voice box. To keep food out of the trachea, a leaf-shaped flap called the epiglottis reflexively covers the opening to the larynx whenever you swallow. Fix: Take a cue from whales, whose larynx is located in their blowholes. If we moved the larynx into our nose, says German, we could have two independent tubes.

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But we could still communicate in song, as whales do, through vibrations in our nostrils. Problem: The human brain evolved in stages. As new additions were being built, older parts had to remain online to keep us up and running, explains psychologist Gary Marcus in his book Kluge: The Haphazard Evolution of the Mind. A few outcomes: depression, madness, unreliable memories, and confirmation bias. It is situated between the urinary bladder and the rectum. It is about three to five inches long in a grown woman. The muscular wall allows the vagina to expand and contract. The muscular walls are lined with mucous membranes, which keep it protected and moist.

A thin sheet of tissue with one or more holes in it, called the hymen, partially covers the opening of the vagina. The vagina receives sperm during sexual intercourse from the penis. The sperm that survive the acidic condition of the vagina continue on through to the fallopian tubes where fertilization may occur.

The vagina is made up of three layers, an inner mucosal layer, a middle muscularis layer, and an outer fibrous layer. The inner layer is made of vaginal rugae that stretch and allow penetration to occur. These also help with stimulation of the penis. The outer muscular layer is especially important with delivery of a fetus and placenta. The cervix from Latin "neck" is the lower, narrow portion of the uterus where it joins with the top end of the vagina. Where they join together forms an almost 90 degree curve.

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It is cylindrical or conical in shape and protrudes through the upper anterior vaginal wall. Approximately half its length is visible with appropriate medical equipment; the remainder lies above the vagina beyond view.

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It is occasionally called "cervix uteri", or "neck of the uterus". During menstruation, the cervix stretches open slightly to allow the endometrium to be shed. This stretching is believed to be part of the cramping pain that many women experience. Evidence for this is given by the fact that some women's cramps subside or disappear after their first vaginal birth because the cervical opening has widened. The portion projecting into the vagina is referred to as the portio vaginalis or ectocervix.

On average, the ectocervix is three cm long and two and a half cm wide. It has a convex, elliptical surface and is divided into anterior and posterior lips.

Structure of the Male Reproductive System

The ectocervix's opening is called the external os. The size and shape of the external os and the ectocervix varies widely with age, hormonal state, and whether the woman has had a vaginal birth. In women who have not had a vaginal birth the external os appears as a small, circular opening. In women who have had a vaginal birth, the ectocervix appears bulkier and the external os appears wider, more slit-like and gaping. The passageway between the external os and the uterine cavity is referred to as the endocervical canal.

It varies widely in length and width, along with the cervix overall. Flattened anterior to posterior, the endocervical canal measures seven to eight mm at its widest in reproductive-aged women. The endocervical canal terminates at the internal os which is the opening of the cervix inside the uterine cavity.

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During childbirth, contractions of the uterus will dilate the cervix up to 10 cm in diameter to allow the child to pass through. During orgasm, the cervix convulses and the external os dilates.

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The uterus is shaped like an upside-down pear, with a thick lining and muscular walls. Located near the floor of the pelvic cavity, it is hollow to allow a blastocyte, or fertilized egg, to implant and grow. It also allows for the inner lining of the uterus to build up until a fertilized egg is implanted, or it is sloughed off during menses. The uterus contains some of the strongest muscles in the female body. These muscles are able to expand and contract to accommodate a growing fetus and then help push the baby out during labor.

These muscles also contract rhythmically during an orgasm in a wave like action. It is thought that this is to help push or guide the sperm up the uterus to the fallopian tubes where fertilization may be possible. The uterus is only about three inches long and two inches wide, but during pregnancy it changes rapidly and dramatically. The top rim of the uterus is called the fundus and is a landmark for many doctors to track the progress of a pregnancy. The uterine cavity refers to the fundus of the uterus and the body of the uterus. Helping support the uterus are ligaments that attach from the body of the uterus to the pelvic wall and abdominal wall.

During pregnancy the ligaments prolapse due to the growing uterus, but retract after childbirth. In some cases after menopause, they may lose elasticity and uterine prolapse may occur.

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  6. This can be fixed with surgery. Some problems of the uterus include uterine fibroids, pelvic pain including endometriosis, adenomyosis , pelvic relaxation or prolapse , heavy or abnormal menstrual bleeding, and cancer. It is only after all alternative options have been considered that surgery is recommended in these cases.

    This surgery is called hysterectomy. Hysterectomy is the removal of the uterus, and may include the removal of one or both of the ovaries. Once performed it is irreversible. After a hysterectomy, many women begin a form of alternate hormone therapy due to the lack of ovaries and hormone production. At the upper corners of the uterus are the fallopian tubes. There are two fallopian tubes, also called the uterine tubes or the oviducts.

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    Each fallopian tube attaches to a side of the uterus and connects to an ovary. They are positioned between the ligaments that support the uterus. The fallopian tubes are about four inches long and about as wide as a piece of spaghetti. Within each tube is a tiny passageway no wider than a sewing needle.

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