1. Urinary System Chapter 15

3. Kidney Functions The main functional organs of the urinary system are the kidneys. The kidneys dispose of wastes and excess ions. They regulate blood volume and water/salt, acid/base balance. In the process, the kidneys produce urine

4. Kidney Structure Each kidney has a medial indentation called a hilus, where the ureters, blood vessels and nerves enter. Each kidney is surrounded by a renal capsule and encased in a protective layer of fat called the adipose capsule.

5. Kidney Structure The outermost region of the kidney is the renal cortex. The inner region is the renal medulla, which contains the medullary pyramids separated by the Medial to the hilus is the renal pelvis which is continuous with the ureter leaving the hilus. Extensions of the pelvis called calyces collect urine which continually drains from the pyramids.

7. Blood Supply The kidneys continuously cleanse the blood and adjust its composition. Approximately ¼ of the total blood supply passes through the kidneys each minute.

8. Nephrons Each kidney contains over a million nephrons, the functional units responsible for forming the urine. Nephrons have two main parts, the glomerulus- a knot of capillaries, and the renal tubule.

9. Nephrons The cup-shaped end of the renal tubule that surrounds the glomerulus is called the Bowman’s capsule. Peritubular capillaries cling to the length of the renal tubule where they receive solutes and water from the tubule cells as those substances are reabsorbed from the filtrate traveling through the tube.

11. Urine Formation Urine formation is the result of three processes, filtration, reabsorption and secretion.

12. Filtration The functional “filter” of the urinary system is the Glomerulus. Because the afferent arteriole serving the glomerulus is greater in diameter than the efferent arteriole leaving it, the blood pressure in the glomerulus is extraordinarily high. This forces fluid and solutes (smaller than proteins) into the bowman’s capsule.

13. Reabsorption 99% of the filtrate forced through the glomerulus is returned to the blood by the peritubular capillaries. Tubule cells begin taking up needed substances from the filtrate and passing them to the peritubular capillaries. The peritubular capillaries are specialized for absorption.

14. Waste When the body uses amino acids, nucleic acids, or a few other substances for energy it results in nitrogenous byproducts, such as urea and uric acid. During reabsorption these products are left behind in the proximal convoluted tubule.

15. Secretion Some substances that were not already present in the filtrate can still make it into the tubules for excretion. In secretion, some substances move from the blood in the peritubular capillaries into the tubule cells (like reabsorption in reverse)

16. Urine Urine is water, plus solutes. The amount and types of solutes vary depending largely on diet and body metabolism. Urine usually contains potassium ions, sodium, urea, uric acid, creatinine, ammonia, bicarbonate ions and various other ions depending on blood composition..

18. Urine Urine is water, plus solutes. The amount and types of solutes vary depending largely on diet and body metabolism. Urine usually contains potassium ions, sodium, urea, uric acid, creatinine, ammonia, bicarbonate ions and various other ions depending on blood composition. Remember: the whole point of urine formation is to help the body regulate blood composition to maintain homeostasis.

19. Urine 150-180 Liters of blood plasma go through the kidneys a day. In that same time only 1-2 liters of urine is produced. Filtrate contains everything that blood plasma does except the proteins. By the time the filtrate reaches the collecting ducts it has lost most of its water, and almost all its nutrients and necessary ions.

20. Fluid, Electrolyte, and Acid-Base Balance