Excretory System
You've already learned that solid food wastes pass out of your dog via the large intestines. Wastes from water and many metabolic processes leave via the excretory system. This system is led by the kidneys, which work with the ureters, bladder, and urethra.
Kidneys and Ureters
The kidneys are the prime organs of the excretory system. Your dog has two, one on each side, tucked up in front of the hind legs near the spinal column. They are bean-shaped (as in kidney beans!) and are real workhorses. The kidneys remove metabolic wastes and toxins from the blood while taking up some of the fluid and any nutrients that pass through them. Kidneys can concentrate urine or dilute it, depending on how much your dog is drinking and if there are any health problems. Urine made by the kidneys is then passed down tubes, the ureters, to the bladder.
Dogs may be born with congenital kidney defects, or the kidneys may be damaged by toxins or infection. Dogs with kidney problems may vomit as a result of toxin buildup, or they may drink a lot with excessive urination or no urine production at all. About two-thirds of the kidneys must be damaged before your dog shows signs of illness. Dogs can survive very well with just one healthy kidney at work.
Bladder and Urethra
The bladder is a pouch that receives the urine flowing from the kidneys via the ureters. The bladder collects and holds urine until the amount is big enough to stimulate your dog to urinate. Obviously, in a puppy, that's not very much! Older dogs can often hold their urine much longer, but as they lose muscle tone with age they need to relieve themselves more often.
Dalmatians have a unique uric acid metabolism that predisposes them to developing urinary tract stones in the kidney or bladder. These stones can cause urinary blockages, especially in males. Miniature schnauzers are susceptible to a different type of bladder stone. Special diets may help to prevent stones in these breeds.
Bladder problems that dogs can have include loss of muscle tone, hormonal influences, infections, cancer, and even developing bladder stones. Stones are often diet related and may require surgery or a special diet.
The urethra is the membranous passageway for urine from the bladder out via the vagina or penis. This is usually a trouble-free area of the excretory system, though stones can block the urine flow.
