The body consists of several organ systems. While they all have their unique functions, each is dependent on the other to maintain homeostasis. Part of this process is the removal of waste products such as carbon dioxide and urea. While our lungs take care of the former—a byproduct of respiration—our urinary system prevents soluble wastes from accumulating in the blood. Like most of our organ systems, it also plays other roles, all of which help preserve a healthy balance within the body.
The urinary system consists of the kidneys, ureters, urethra, and bladder. Together, they maintain homeostasis by removing waste products from the body. To do this, they filter blood and produce urine, then excrete this liquid by-product out of the body. In healthy individuals, the body produces between three and eight cups of urine every day; the exact amount depends on kidney function and fluid intake.
The kidneys are two bean-shaped organs that sit below the ribs. Found on both sides of the spine, they filter blood, regulate blood pressure, and produce a hormone that aids the formation of red blood cells. The ureters are narrow tubes that take urine from the kidneys to the bladder. The bladder is a muscular sac in the lower abdomen. The expandable organ’s main function is to store urine from the kidneys. In a healthy individual, the bladder can store up to two cups of urine comfortably. Then a duct, the urethra, excretes urine from the body. Urination occurs when the brain signals the bladder muscles to relax and contract.
The primary function of the urinary system is to eliminate urea—a waste product of metabolism—from the body. In addition to that, it the system maintains electrolyte balance, which plays a role in regulating blood pressure and blood volume. Furthermore, the urinary system works with the lungs to control blood pH.
The kidneys remove urea and other harmful particles from the blood through nephrons—functional units that filter the blood. These tiny filters contain a cluster of blood capillaries called the glomerulus, which works in tandem with the renal tubule to produce urine. There are approximately one million nephrons in each kidney.
Made up of smooth muscle fibers, the ureters propel urine from the kidneys to the bladder by constantly contracting and relaxing. Once it enters the bladder, the pressure from the urine squeezes the end of the ureters, which prevents the liquid from going back up into the kidneys; this is important for preventing infection.
The bladder is a distensible organ capable of stretching significantly to accumulate large amounts of urine. It contains four layers, the outermost of which is made up of blood vessels and fibrous tissue, and detrusor muscles that contract for the release of urine. A urinary sphincter prevents urine from leaking out of the bladder.
Nerve signals go back and forth between the brain and the bladder; this pathway is ultimately responsible for normal voiding. If the nerves are damaged, the smooth muscles of the bladder may not be able to contract or relax at the appropriate time—this often leads to urinary incontinence. While there are no specific medications for the condition, some drugs can enhance or reduce the bladder’s contractions.
While they are quite similar, there are a couple of differences between the male and female urinary systems. In females, the reproductive system is entirely separate from the ureter, bladder, and urethra. In contrast, in men, the urethra passes through the center of the prostate gland—an organ responsible for secreting seminal fluid. The length of the urethra is also different in men and women. While it is eight inches long in males, it is only two inches in females; this is why women tend to be more prone to urinary tract infections.
Several disorders affect the urinary system—the kidneys, ureters, urethra, or bladder. Some examples include urinary tract infections, kidney stones, urethritis, incontinence, cystitis, and benign prostatic hyperplasia. While these conditions occur in people of all ages, they are generally more common among the older population.
Keeping the urinary tract healthy helps prevent infection. More specifically, individuals should drink plenty of fluids, exercise regularly, maintain a healthy weight, limit caffeine and alcohol, and quit smoking. Pelvic floor exercises can also help strengthen the muscles that control the bladder. People should also avoid holding in urine for extended periods of time, as this tends to increase the chance of infection.
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