XV. Urinary System The urinary system, also known as the renal system, produces, stores and eliminates urine, the fluid waste excreted by the kidneys. The kidneys make urine by filtering wastes and extra water from blood. Urine travels from the kidneys through two thin tubes called ureters and fills the bladder. When the bladder is full, a person urinates through the urethra to eliminate the waste. Parts: Two kidneys. This pair of purplish-brown organs is located below the ribs toward the middle of the back. Their function is to: o Remove waste products and drugs from the body o Balance the body's fluids o Release hormones to regulate blood pressure o Control production of red blood cells 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. 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. Functions: The accessory organs of the urinary system include liver, skin, lungs, and large intestine. The major functions of the urinary system are the following: 1. Excretion – kidneys are the major excretory organs of the body. They remove waste products, many of which are toxic, from the blood. Most waste products are metabolic by-products of cells and substances absorbed from the intestine. 2. Regulation of blood volume and pressure. The kidneys play a major role in controlling the extracellular fluid volume in the body producing either a large volume of dilute urine or a small volume of concentrated urine. Consequently, blood volume and blood pressure are regulated by kidneys. 3. Regulation of the concentration of solutes in the blood. The kidneys help regulate the concentration of the major molecules and ions such as glucose, sodium, calcium and etc. 4. Regulation of extracellular fluid pH. Kidneys secrete variable amount of Hydrogen to help regulate extracellular fluid pH. 5. Regulation of red blood cell synthesis. Kidneys secrete a hormone, erythropoietin, which regulates the synthesis of red blood cells in bone marrow. 6. Vitamin D synthesis. The kidneys play an important role in controlling blood levels of calcium by regulating the synthesis of vitamin D. Self Help: https://www.hopkinsmedicine.org/health/wellness-and-prevention/anatomy-of-the-urinarysystem Fig. 42: The Urinary System Urine Formation: Waste is excreted from the human body mainly in the form of urine. Our kidneys play a major role in the process of excretion. Constituents of normal human urine include 95 percent water and 5 percent solid wastes. It is produced in the nephron which is the structural and functional unit of the kidney. Urine formation in our body is mainly carried out in three phase’s namely glomerular filtration, Reabsorption and Secretion. Self Help: https://byjus.com/biology/urine-formation-osmoregulation/ https://youtu.be/805VoHIIQCs
