Chapter 9.
Urinary system
The urinary system is one of the four excretory systems of the body; the other three are the bowels from the digestive system, the skin, and the lungs. The following are the structures of the urinary system: the kidneys (the excretory organs), the ureters (the ducts to the kidney), the bladder (the reservoir for the urine), the urethra (the channel to the outside of the body).
The kidneys lie toward the back of the abdominal cavity, one on each side of the body. Each kidney weights about 5 ounces, and can be described as “bean shaped”. The kidney is about 4 ½ inches long and 2 inches wide, with a thickness of about 1 ¼ inches. The kidneys are embedded in fat for protection. The right kidney is slightly lower than the left kidney. The kidneys have a bountiful blood supply.
The kidneys filter the blood, secrete urine, and absorb needed nutrients. They keep the composition of the blood constant by excreting excess of substances present, or abnormal constituents in the blood. In performing this function, the kidneys excrete water, the end product of metabolism (the work done in the cells), salts and drugs, toxins and chemical substances that may be harmful.
The ureters are ducts that collect the urine secreted by the kidneys and carry it to the urinary bladder. The ureter is a long tube, approximately 10 inches long. One ureter arises from each kidney.
The bladder receives the urine from the kidneys and stores it until it is voided out. It is a peer shaped sack lined with mucous membrane, situated in the pelvic cavity. It lies in front of the rectum in the male, but is separated from the rectum by the uterus in the female.
The urethra is the canal that carries the urine from the bladder to the exterior or outside. It differs in the male and female. The female urethra is a short tube, about 1 ½ inches long, which leaves the base of the bladder and exits just in front of the vagina. The male urethra is about 8 inches long, leaving the bladder to exit at the end of the penis.
Urine is normally clear, yellow or amber colored, and is a sterile liquid. It is usually slightly acid in composition. The amount of urine secreted by a person in good health is approximately 30 to 60 mL per hour. The amount of urine produced by the kidneys is dependent on the amount of fluid intake and fluid loss from the skin by sweat. Urine does not normally contain blood, sugar, protein, acetone, or bile.
Please watch the following videos:
- The Urinary System (about 7 minutes)
- Kidney function and anatomy | Renal system physiology | NCLEX-RN | Khan Academy (about 8 minutes)
Back to Introduction Ch. 8 – Nervous System Ch. 10 – Reproductive System