URINARY SYSTEM

URINARY SYSTEM

The organs, tubes, muscles, and nerves that work together to create, store, and carry urine are the urinary system. The urinary system includes two kidneys, two ureters, the bladder, two sphincter muscles, and the urethra.

Kidney and urinary system parts and their functions:

• Two kidneys. This pair of purplish-brown organs is located below the ribs toward the middle of the back. Their function is to remove liquid waste from the blood in the form of urine; keep a stable balance of salts and other substances in the blood; and produce erythropoietin, a hormone that aids the formation of red blood cells. The kidneys remove urea from the blood through tiny filtering units called nephrons. Each nephron consists of a ball formed of small blood capillaries, called a glomerulus, and a small tube called a renal tubule. Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.
• Two ureters. These narrow tubes carry urine from the kidneys to the bladder. Muscles in the ureter walls continually tighten and relax forcing urine downward, away from the kidneys. If urine backs up, or is allowed to stand still, a kidney infection can develop. About every 10 to 15 seconds, small amounts of urine are emptied into the bladder from the ureters.
• Bladder. This triangle-shaped, hollow organ is located in the lower abdomen. It is held in place by ligaments that are attached to other organs and the pelvic bones. The bladder's walls relax and expand to store urine, and contract and flatten to empty urine through the urethra. The typical healthy adult bladder can store up to two cups of urine for two to five hours.
• Two sphincter muscles. These circular muscles help keep urine from leaking by closing tightly like a rubber band around the opening of the bladder.
• Nerves in the bladder. The nerves alert a person when it is time to urinate, or empty the bladder.
• Urethra. This tube allows urine to pass outside the body. The brain signals the bladder muscles to tighten, which squeezes urine out of the bladder. At the same time, the brain signals the sphincter muscles to relax to let urine exit the bladder through the urethra. When all the signals occur in the correct order, normal urination occurs.

 

RELATIONSHIP

The urinary system, like all body systems, does not work alone. It has an interdependent relationship with the endocrine system, the circulatory system, the musculoskeletal system and the nervous system. The adrenal glands are also part of the endocrine system and secrete a chemical that allows the kidneys to effectively regulate fluids in the body. This process is directly related to blood pressure and the circulatory system. The urinary system is also closely related to the circulatory system by virtue of the processes of cleaning the blood of the waste, eliminating the excess of liquids and generally keeping other fluids in balance. The nervous and musculoskeletal systems also play a role. They work in concert with the urinary system to regulate the release of urine. Children still in diapers have yet to develop these systems in their entirety. The bladder is a muscle that can expand and contract as needed to accommodate or expel urine. When the bladder is full, the nervous system receives messages that it is time to leave. The muscles of the bladder and urethra help us to "hold" when there is no bathroom in sight.

Summary of the Urinary System. The urinary system removes waste from the body. It is also important for keeping the body in homeostasis (balance) by controlling the composition and volume of blood. The organs of the urinary system are the two kidneys, the two ureters, the bladder and the urethra.