Urinary Tract Overview

The structure of your urinary tract includes: two kidneys, two ureters (tubes leading from the kidneys to the bladder), and the urethra (a tube leading from the bladder to the exterior of the body). Your urinary tract is a little like a plumbing system, with special pipes that allow water and salts to flow through them. Your kidneys make up a filter system for the blood, reabsorbing about 99% of the fluid into the blood, and sending only two to four pints of waste (urine) into the bladder for storage until it can be disposed of. The kidneys allow the blood to keep glucose, salts and minerals after cleansing it of poisonous materials that will be passed out in the urinary tract. Urine is produced in the kidneys and trickles down twenty-four hours a day through two 10-to-12-inch long tubes called ureters, which connect the kidneys to the bladder. The ureters are about one-fourth inch in diameter and their muscular walls contract to make waves of movement to force the urine into the bladder. The bladder is expandable and stores the urine until it can be conveniently disposed of. It also closes openings into the ureters so that urine cannot flow back into the kidneys. The tube through which the urine flows out of the body is called the urethra.

Kidneys

About one-quarter (750-1,000 pints daily) of the blood that is output by the heart is sent to the body's “filter treatment plant,” where it is purified by the kidneys and circulated on to the rest of the body. One to two thousandths (1/1000-2/1000) of the blood flow becomes fluid waste and is sent into the bladder for storage until it can be conveniently expelled. This waste product is called urine. Your kidneys are located about two inches above the body's midline, just below and behind the liver in the upper abdomen and behind the lower ribs. They receive about 120 pints of blood per hour, even if other body systems are shorted. They are the balancers of internal fluids, so if you overeat or over-drink one day and diet the next, or if you have an active, “sweaty” day, your kidneys will compensate and see that these fluctuations in fluid, sodium, and glucose are leveled out. It is important to drink plenty of fluids (preferably, plain water) each day to keep the kidneys in good working order.

Kidney – Blood Connection

The paired kidneys balance the fluid levels of the body. They balance the body's acid/alkaline nature and the concentrations of salts, minerals, and other chemicals. The blood is filtered, purified, cleansed, and adjusted twenty-four hours every day. Hundreds of pints of blood flow through these organs daily, about one-fourth of the heart's output or approximately the body's entire volume. The blood circulates through the kidneys twenty times each hour for purification. About two and one-half pints of this flow becomes urine, although the amount largely depends on our consumption of food and drink, our physical activity, and a few other factors.

Historical Note: The Roman physician, Galen, 2nd Century C.E., believed the kidney was a sieve that filtered out impurities from the system into the urine for disposal. His idea was remarkably accurate, especially when we consider that the role of the heart and circulatory system were not understood until 1500 years later.

Urinary Bladder

Your bladder is a hollow muscular organ that acts as a reservoir for urine. The adult bladder can hold a pint or more of fluid. It lies behind the pubic bone and is protected by the pelvis. The bladder walls are made up of muscle and an inner lining. At the back are two ureters which carry the urine from the kidneys. The bladder collects and stores urine until it can be expelled from the body.

Fun Fact: After birth, when circulation through the placenta stops, only the pelvic portion of the umbilical artery remains patent, becoming the internal iliac and first part of the superior vesicle artery in adulthood. The remainder is converted into a solid fibrous cord called the “medial umbilical ligament,” which extends from the pelvis (centered over your bladder) to the naval, that depression that marks the spot where your umbilical cord was once attached. So, yes, your belly button is still attached to something. Of course, some people I know still claim to not even have a belly button...  J

Urethra

The urethra is a tube that conveys urine from the urinary bladder to the outside of the body. Its wall is lined with mucous membranes and contains a relatively thick layer of smooth muscle tissue. It also contains numerous mucous glands, called “urethral glands,” that secrete mucus into the urethral canal. In females the urethra is only about 1.7 inches (4 cm) long. It passes forward from the bladder, descends below the symphysis pubis, and empties from the labia minor. Its opening is located just above the vaginal opening and about an inch below the clitoris. In males, the urethra functions both as a urinary canal and a passageway for cells and secretions from various reproductive organs; it can be divided into three sections: the prostatic urethra, the membranous urethra, and the penile urethra (lengths obviously vary somewhat). Males have two sphincters in this tube, one at the bladder exit and one just downstream from the prostate gland, while females have only the one at the bladder exit. These sphincter muscles act as backflow prevention devices as well as making sure that we only release the urine by conscious effort - otherwise we'd be dribbling all day long.

Summary so Far

OK, folks, we have covered the digestive tract and the urinary tract. These make up the majority of organs that you affect directly by ingesting food and fluids (along with the bacteria and fungi in those items). We will touch briefly on the remaining organs/systems in the next installment. I'm still trying to assembly the flow chart version of the body, so maybe that will happen about the same time.

A couple things from these brief overviews of your body that should now be planted firmly in your brain: your small intestine does the most toward turning food and drink into something that is put into your blood while your liver and kidneys do the filtering of that blood. When you have problems with these organs/glands, the whole system can go in the toilet (no pun intended). So let's keep those things healthy. A few more newsletters and we're going to share with you just how to do that.

P.S. - Once upon a time, in a land far far away (Orygun), a wise old woman (my mom) once told me, “When you were born, you didn't come with an operating manual. I'm doing the best I can.”  Maybe when this series is done, we can give it to everyone so they will have one available.  Just a thought...