1. Renal Physiology

2. Objectives 1-To know the Body Fluid Compartments 2- To know the steps Urine Formation by the Kidneys: I. Glomerular Filtration, Renal Blood Flow, and Their Control 3- Urine Formation by the Kidneys: II. Tubular Processing of the Glomerular Filtrate (reabsorption) 4- Regulation of Extracellular Fluid Osmolarity and Sodium Concentration 5- Renal Regulation of Potassium, Calcium, Phosphate, and Magnesium; Integration of Renal Mechanisms for Control of Blood Volume and Extracellular Fluid Volume 6- Regulation of Acid-Base Balance 7-Kidney Diseases and Diuretics

3. THE URINARY SYSTEM Kidneys Blood supply: Renal arteries and veins Ureter Urinary bladder Urethra

4. Daily Intake of Water (1) it is ingested in the form of liquids or water in the food, about 2100 ml/day (2) it is synthesized in the body as a result of oxidation of carbohydrates, about 200 ml/day. Total intake of about 2300 ml/day highly variable, depending: * on climate, *habits, and*level of physical activity.

5. Daily Loss of Body Water: 1- Insensible Water Loss (700 ml/day) (through respiratory tract and diffusion through the skin). In burns, the rate of evaporation can increase as much as 10-fold, to 3 to 5 L/day.

6. Insensible loss through the respiratory tract averages about 300 to 400 ml/day. As air enters the respiratory tract, it becomes saturated with moisture, to a vapor pressure of about 47 mm Hg, before it is expelled. Because the vapor pressure of the inspired air is usually less than 47 mm Hg, water is continuously lost through the lungs with respiration. Dry feeling in the respiratory passages in cold weather (why)? In cold weather, the atmospheric vapor pressure decreases to nearly 0, causing an even greater loss of water from the lungs as the temperature decreases.

7. 2- Fluid Loss in Sweat(100 ml/day). The volume of sweat normally is about 100 ml/day, but in very hot weather or during heavy exercise, water loss in sweat occasionally increases to 1 to 2 L/hour 3- Water Loss in Feces(100 ml/day) Only a small amount of water (100 ml/day) normally is lost in the feces. This can increase to several liters a day in people with severe diarrhea

8. 4- Water Loss by the Kidneys(1400 ml/day) urine volume can be as low as 0.5 L/day in a dehydrated person or as high as 20 L/day in a person who has been drinking tremendous amounts of water

10. Body Fluid Compartments

11. Multiple Functions of the Kidneys Σ Excretion of metabolic waste products and foreign chemicals Σ Regulation of water and electrolyte balances Σ Regulation of body fluid osmolality and electrolyte concentrations Σ Regulation of arterial pressure Σ Regulation of acid-base balance Σ Secretion, metabolism, and excretion of hormones Σ Gluconeogenesis

12. The Kidneys

13. Physiologic Anatomy of the Kidneys The two kidneys lie on the posterior wall of the abdomen, outside the peritoneal cavity Each kidney of the adult human weighs about 150 grams (size of a clenched fist)

14. Renal Blood Supply Blood flow to the two kidneys is normally about 22 % of the cardiac output, (1100 ml/m).

15. Renal artery → interlobar artery → arcuate artery → interlobular artery → Afferent arterioles → glomerular capillaries → Efferent arterioles → Peritubular capillary → interlobular veins →arcuate veins → interlobar veins → Renal vein.

16. The distal ends of the capillaries of each glomerulus coalesce to form the efferent arteriole, which leads to a second capillary network, the peritubular capillaries, that surrounds the renal tubules.

17. The renal circulation is unique in that it has two capillary beds, the glomerular and peritubular capillaries, which are arranged in series and separated by the efferent arterioles, which help regulate the hydrostatic pressure in both sets of capillaries. High hydrostatic pressure in the glomerular capillaries (about 60 mm Hg) causes rapid fluid filtration, whereas a much lower hydrostatic pressure in the peritubular capillaries (about 13 mm Hg) permits rapid fluid reabsorption.

18. By adjusting the resistance of the afferent and efferent arterioles, the kidneys can regulate the hydrostatic pressure in both the glomerular and the peritubular capillaries, thereby changing the rate of glomerular filtration, tubular reabsorption, or both in response to body homeostatic demands.

19. The Nephron Is the Functional Unit of the Kidney Each kidney in the human contains about 1 million nephrons, each capable of forming urine. The kidney cannot regenerate new nephrons

20. After age 40, the number of functioning nephrons usually decreases about 10% every 10 years; thus, at age 80, many people have 40 % fewer functioning nephrons than they did at age 40. This loss is not life threatening because adaptive changes in the remaining nephrons allow them to excrete the proper amounts of water, electrolytes, and waste products

21. Each nephron contains (1) a tuft of glomerular capillaries called the glomerulus, through which large amounts of fluid are filtered from the blood, and (2) a long tubule in which the filtered fluid is converted into urine on its way to the pelvis of the kidney In each kidney, there are about 250 of the very large collecting ducts, each of which collects urine from about 4000 nephrons.

23. The glomerulus contains a network of branching and anastomosing glomerular capillaries that, compared with other capillaries, have high hydrostatic pressure (about 60 mm Hg). The glomerular capillaries are covered by epithelial cells, and the total glomerulus is encased in Bowman’s capsule. Fluid filtered from the glomerular capillaries flows into Bowman’s capsule and then into the proximal tubule, which lies in the cortex of the kidney.

24. Regional differences in nephron structure: cortical and juxtamedullary nephrons Cortical nephrons Cortical nephrons; they have short loops of Henle that penetrate only a short distance into the medulla. For the cortical nephrons, the entire tubular system is surrounded by an extensive network of peritubular capillaries.

26. Juxtamedullary nephrons Juxtamedullary nephrons ; about 20 to 30 % of the nephrons have glomeruli that lie deep in the renal cortex near the medulla. These nephrons have long loops of Henle that dip deeply into the medulla, in some cases all the way to the tips of the renal papillae. The vascular structures supplying the juxtamedullary nephrons also differ from those supplying the cortical nephrons.

27. For the juxtamedullary nephrons, long efferent arterioles extend from the glomeruli down into the outer medulla and then divided into specialized peritubular capillaries called vasa recta that extend downward into the medulla, lying side by side with the loops of Henle. The vasa recta return toward the cortex and empty into the cortical veins. This specialized network of capillaries in the medulla plays an essential role in the formation of a concentrated urine.