1. CHAPTER 15 THE URINARY SYSTEM

2. Organs of the Urinary System

3. Introduction Functions of the kidneys: The kidneys maintain the purity and constancy of our internal fluids. The kidneys filter gallons of fluid from the bloodstream. The kidneys bear the major responsibility for eliminating wastes from the body. The kidneys regulate the blood’s volume and chemical makeup, so that the proper balance between water and salts and acids and bases is maintained.

4. Introduction Functions of the ureters, the urinary bladder, and the urethra: They provide temporary storage reservoirs for urine. They serve as transportation channels to carry if from one body region to another.

5. Kidneys

6. Structure They are dark red organs with a kidney-bean shape. They are about 12cm long, 6cm wide, and 3cm thick – about the size of a large bar of soap. On top of each kidney is the adrenal gland. 3 main regions of a kidney: Renal Cortex – the outer region Renal Medulla – deep to the cortex; has a striped appearance Renal Pelvis – the medial region

7. Regions of the Kidney

8. Location They lie against the dorsal body wall in the superior lumbar region. They extend from the T12 to the L3 vertebra and receive protection from the lower part of the rib cage. The right kidney is positioned slightly lower than the left because it is crowded by the liver.

9. Blood Supply Approximately ¼ of the total blood supply of the body passes through the kidneys each minute. The arterial supply of each kidney is the RENAL ARTERY

10. Nephrons These are the structural and functional units of the kidneys. They are responsible for forming the urine product. 2 main structures: Glomerulus – a knot of capillaries Renal tubule – surrounds the glomerulus

11. Urine Formation – a result of 3 processes: Filtration – Water and solutes smaller than proteins are forced through the capillary walls and pores of the glomerulus into the renal tubule to form a filtrate. Reabsorption – Water, glucose, amino acids, and needed ions are transported out of the filtrate into the tubule cells and then enter the capillary blood. Secretion – Hydrogen and potassium ions, creatine, and drugs are removed from the blood and secreted by the tubule cells into the filtrate.

12. Characteristics of Urine Urine contains nitrogenous wastes and unneeded substances Fresh urine is usually clear and pale to deep yellow. The normal yellow color is due to a pigment that results from the body’s destruction of hemoglobin. When formed, urine is sterile and its odor is slightly aromatic. Urine pH is slightly acidic – around 6

13. Ureters Structure: Slender tubes that run behind the kidneys to the bladder They are 25 to 30 cm long Function: Are passageways that carry urine from the kidneys to the bladder. Once urine has entered the bladder, it is prevented from flowing back to the ureters

14. Urinary Bladder A smooth, collapsible, muscular sac that stores urine temporarily As urine accumulates, the bladder expands and rises in the abdominal cavity. Its muscular wall stretches, allowing the bladder to store more urine without increasing its internal pressure.

15. Urinary Bladder

16. Urethra Structure: A thin walled tube that carries urine from the bladder to the outside of the body Females = it is about 3 to 4 cm long Males = it is about 20 cm long Function: Females = to carry urine to the body exterior Males = to carry urine and sperm to the body exterior

17. Fluid, Electrolyte, and Acid-Base Balance In 24 hours, the kidneys filter 150 to 180 liters of blood plasma through the glomerulus and only about 1.0 to 1.8 liters of urine are produced Our kidneys can keep our blood composition fairly constant despite wide variations in diet. The kidneys have 4 major roles to play, which keep the blood composition constant: Excretion of nitrogen-containing wastes Maintaining water balance of the blood Maintaining electrolyte balance of the blood Ensuring proper blood pH

18. Maintaining Water and Electrolyte Balance of Blood

19. Body Fluids & Fluid Compartments If you are healthy, water probably accounts for half or more of you body weight. 50% in females 60% in males 75% in babies 45% in elderly Water occupies 3 main locations within the body, called the fluid compartments. About 2/3 of body fluid, intracellular fluid, is found within the living cells. The remainder, extracellular fluid, includes all body fluids outside the cells.

20. The Link Between Water & Salt There is more to fluid balance than just water. The types and amounts of solutes in body fluids are also vitally important to overall body homeostasis. Water and electrolyte balance are tightly linked as the kidneys continuously process the blood. Very small changes in electrolyte balance cause water to move from one compartment to another. This will alter blood volume and blood pressure.

21. The Link Between Water & Salt If the body is to remain properly hydrated, we cannot lose more water than we take in. There are several routes for water to leave the body: Some water vaporizes out of the lungs Some is lost in perspiration Some leaves the body in the stool If large amounts of water are lost, the kidneys compensate by putting out less urine to conserve body water.

22. The Link Between Water & Salt If water intake is excessive, the kidneys excrete generous amounts of urine and a too-full bladder becomes very real. The kidneys regulate electrolyte balance by using antidiuretic hormone: When blood volume drops, blood pressure drops and this decreases the amount of filtrate formed by the kidneys. Cells in the hypothalamus react by becoming very irritable. The result is that nerve impulses are sent to the pituitary gland which releases antidiuretic hormone. This hormone prevents excessive water loss in the urine by traveling through the blood to the kidneys and causing the kidneys to reabsorb more water.

23. Maintaining Acid-Base Balance of Blood For the cells of the body to function properly, blood pH must be maintained between 7.35 and 7.45 If the blood pH rises above 7.45, a person is said to have alkalosis. If the blood pH drops below 7.35, a person is said to have acidosis.

24. Developmental Aspects The kidneys begin to develop in the first few weeks of embryonic life and are excreting urine by the third month. Common urinary system problems in children and young to middle-aged adults are infections caused by fecal microorganisms, sexually transmitted disease-causing microorganisms, and streptococcus.

25. Developmental Aspects Renal failure is an uncommon, but extremely serious, problem in which kidneys are unable to concentrate urine, and dialysis must be done to maintain homeostasis of blood. With age, filtration rate decreases and tubule cells become less efficient at concentrating urine, leading to urgency and frequency. With age, a consequence is bladder shrinkage and loss of bladder tone.