The Urinary System — Anatomy

All our cells use a variety of proteins in order to function.  When proteins break down, a waste product called “urea” is formed, consisting mainly of nitrogen in the form of ammonia.  The Urinary System gets rid of this. See the Diagram below:

Our two Kidneys are giant filters; every day, about 30-35 gallons of blood pass through them.  The Aorta, our main artery leaving the heart, carries blood down the body, where the Renal Arteries (red, in the diagram) branch off into the Kidneys.  Like all arteries, they spread into narrower sub-branches, finally into one-cell-width capillaries called Glomeruli (one โ€œglomerulusโ€).  Capillaries then transition into veins (blue), eventually to the larger Renal Veins, which take blood to the Vena Cava, then back to the heart.

In the Glomeruli, the bloodโ€™s plasma (clear fluid, without blood cells) enters the million microscopic Nephrons of each Kidney.  The Nephrons in turn filter out urea waste products, while allowing other plasma components like glucose, sodium, potassium, etc. to return to the blood stream.  Urea, in the form of urine then collects in a basin called the Renal Pelvis.  โ€œRenalโ€ is the Latin word for โ€œKidney.โ€

From there, the unwanted urine passes down a tube called the Ureter, and into the Bladder.  The Bladder stores urine, until it fills enough to send a signal to the brain via nerve pathways, saying “full.”   That’s when we can voluntarily decide to relax the Bladder Outlet (its “exit”), whereby we urinate, sending urine out of the body through the Urethra.  The male Urethra is long, running the length of the penis.  The femaleโ€™s is short, less than an inch.  See also Diagrams of the Male Genital System and the Female Genital System.


Various diseases can affect the Urinary System.  In terms of the kidneys, some conditions cause pain, like infections (Pyelonephritis), Kidney Stones, and rare conditions that cause blood clots (Infarcts).  But in these cases, “Kidney Function” (a.k.a. “Renal Function”) almost always remains normal, meaning wastes still get filtered from the blood.  That’s because usually only one kidney is infected; if a kidney gets injured & removed, the other one can do all the work necessary.

On the other hand, there are painless kidney diseases that interfere with or destroy the kidneys’ ability to function well.  One term is Nephropathy, which just means “kidney injury;” it can be caused by long-standing Diabetes, Hypertension, and a whole host of other chronic diseases.  Then there’s Nephritis, also called Glomerulonephritis, which is acute inflammation caused by a wide variety of illnesses, which are usually auto-immune.  Since both Nephropathies and Nephritidies (plural) affect all the nephrons in both kidneys, overall Renal Function declines, sometimes to the point of Kidney Failure requiring dialysis.  Kidney Failure can also come from acute Shock, if blood isn’t getting pumped around for one reason or another (if the shock gets treated, renal function usually returns to normal).

The main disease of the narrow Ureter is a Kidney Stone, which actually doesn’t hurt while it forms in the kidneys, but causes excruciating pain if it flows into a ureter and gets stuck.  The main disease affecting the bladder is a Urinary Tract Infection, commonly abbreviated “UTI” (pronounced letter-by-letter, & not “yoo-tee” or “oo-tee”).  Technically, this could apply to infection of either the bladder or kidney, since both are part of the “urinary tract”.  So we should say โ€œCystitisโ€ when referring to bladder infection, and โ€œPyelonephritisโ€ for kidney infection; however, we all wind up saying “UTI” when we mean the bladder, and “Pyelo” for the kidney.

In men, the prostate gland is located at the bladder outlet; the innermost beginning of the urethra passes through it (not shown above; see Diagram: Male Genital System).ย  Prostates commonly swell with age, beginning around 50, but much more so later on.ย  A swollen prostate gland, called Benign Prostatic Hypertrophy (or “Hyperplasia”), commonly abbreviated BPH, causes lots of urinary symptoms.ย  Worst case is if it swells so much as to produce back-pressure up to the kidneys, causing Nephropathy and eventually Kidney Failure.

Cancer can also occur in the:

  • Kidney (at any age)
  • Bladder (almost only after 50-years-old, especially among smokers)
  • Prostate (usually after 50-60, often older)

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