Urinary System Kidneys: formation of urine -contains the functional unit for filtration = Nephron: -production of urine, absorption of water and salts Ureters: transfer of urine from kidneys to bladder Urethra: transfer of urine from bladder to outside - longer into the male (20 cm vs. 4 cm in the female)

Kidneys 10-12 cm retroperitoneal – behind the peritoneum not part of peritoneal cavity surrounded by three layers of tissue 1. deepest layer = renal capsule – transparent sheet of dense irregular connective tissue 2. middle layer = adipose capsule 3. outer layer = renal fascia divided internally into an outer cortex and an inner medulla medulla consists of 8 to 18 cone-shaped regions called renal pyramids the wider base faces towards the cortex, the narrow region (renal papilla) projects down into a cup-like structure called a minor calyx renal cortex is divided into an outer cortical zone and a deeper juxtamedullary zone the cortex also extends down in between the pyramids to form the renal columns renal lobe = renal pyramid + the overlying renal cortex + ½ the adjacent renal column

kidney URETER URETER BLADDER

Renal Papilla Renal Pelvis URETER Renal Minor Pyramid Calyx Major Cortex Renal Pelvis Renal Medulla URETER

supplied by a renal artery and drained by a renal vein(s) kidney receives 20-25% of the resting cardiac output through the renal arteries (1200mL per minute) renal artery divides into segmental arteries – supply segments of the kidney the segmental arteries give off branches that pass through the renal columns – interlobar arteries at the base on the renal pyramids – between the medulla and cortex – they are called arcuate arteries divisions from the arcuate are called the interlobular arteries (pass between the renal lobes) the afferent arterioles are derived from the interlobular arteries afferent arteriole supplies one nephron and forms the glomerulus (capillary network) drainage of the glomerulus is via the efferent arteriole efferent arteriole forms the peritubular capillary network which surround the upper portions of the nephron an extension of this network covers the lower portion of the nephron – vasa recta the peritubular capillaries form the interlobular veins – arcuate veins – interlobar veins – renal vein Blood supply PCT and DCT surrounded by the peritubular network of capillaries for reabsorption back into the blood, L of H is covered with the vasa recta

The Nephron Path of filtrate: -about one million nephrons -kidneys filter 180 L fluid per day!!!! -each nephron is a renal corpuscle + renal tubules -renal corpuscle: filtering unit consisting of a tangled cluster of capillaries -> glomerulus -tubules: for reabsorption of water and ions leading to final urine volume and composition Interlobular artery Interlobular vein Path of filtrate: - proximal convoluted tubule -> Loop of Henle -> distal convoluted tubule -> collecting duct -> calyces  renal pelvis  ureter

Renal Physiology 1. Glomerular filtration 2. Tubular reabsorption water and most solutes ion the blood plasma move across the glomerular capillaries into the Bowman’s capsule and then into the renal tubule 2. Tubular reabsorption renal tubule cells reabsorb about 99% of the filtered water and many of the solutes return to the blood through reabsorption into the peritubular capillary network reabsorption = return to the blood absorption = entrance of new materials into the blood (e.g. via digestive absorption) 3. Tubular secretion tubular cells also secrete other materials – wastes, drugs, excess ions into the urine this also removes these materials from the blood

Glomerulus glomerulus: capillary tangle derived from afferent arterioles (into) and lead into efferent arterioles (out) surrounded by a glomerular capsule (Bowman’s capsule) – layer of epithelial cells glomerular capsule: site of initial filtration and the first step in the formation of urine consists of visceral and parietal layers visceral layer consists of modified epithelial cells that cover the capillaries = podocytes the endothelial cells of the capillaries have spaces between them the spaces between the endothelial cells + spaces between the podocytes forms a filtration membrane space between the visceral and parietal layers = glomerular capsule

PCT PCT is the site of water reabsorption (PASSIVE) - associated with the ACTIVE reabsorption of sodium ions active transport of Na+ into the blood is by sodium pumps in the cells of the PCT sodium pumped from the cells of the PCT into the blood causes more sodium to diffuse into the cells of the PCT (carries a glucose with it) chloride, bicarbonate and phosphate ions follow Na+ transport = salt reabsorption the active transport of ions into the blood plasma increases osmotic pressure within the blood therefore water moves out of the PCT into the capillaries PASSIVELY! PCT reabsorbs about 70% of filtered Na+, ions and water the apical surface of the PCT epithelium forms microvilli which increases the surface area of this region

Loop of Henle active transport of Na+ continues through the loop of Henle and DCT descending loop of Henle is quite permeable to water but impermeable to solute movement salt reabsorption in the ascending limb determines how much water is reabsorbed from the descending limb ascending loop is the opposite – permeable to salt (salt pumped out of the urine back into the blood plasma) Na+ is pumped out of the cell into the blood causes more Na+ to diffuse into the cell – carries with it Cl- and K+ ions

DCT and Collecting Duct DCT and collecting duct are normally impermeable to water !!!! the DCT and CD become permeable upon action of hormones two types of cells found in the collecting duct: principal cells – contain receptors for ADH and aldosterone also found in the DCT binding of ADH to the principal cell increases the synthesis of aquaporins aquaporins form water “pores” in the principal cell – more water reabsorption aldosterone increases the synthesis of Na/K pumps – for more salt reabsorption intercalated cells – play a role in the homeostasis of blood pH pump H+ ions into the urine the H+ ions combine with ammonia to form ammonium urine is slightly acidic and smells like ammonia

Urinary System Function 1. Excretion of Metabolic Wastes: nitrogenous wastes -Urea: by-product of amino acid metabolism -produced when ammonia + carbon dioxide -reclaim urea from bottom section of collecting duct -Creatinine: produced by breakdown of creatine phosphate (high energy molecule reserve of muscles) -Uric acid: by-product of nucleotide breakdown -insoluble and ppts in the blood, concentrates in joints - gout 2. Water-Salt balance of blood: water is reabsorbed into blood from the PCT, the descending Loop of Henle & from the DCT collecting duct -reclaim salt from the ascending portion of Loop of Henle -release of anti-diuretic hormone by pituitary: increase reabsorption of water 3. Acid-Base balance of blood: reabsorption of bicarbonate ions from urine into the blood increases levels in blood (decreases carbonic acid levels) -movement of hydrogen ions from blood into the nephron, combines with ammonia to form ammonium (NH4+)

4. Secretion of hormones: release of renin by kidneys which leads to release of aldosterone by adrenal glands (reabsorption of salts by kidneys) -release of erythropoietin by kidneys (stimulates RBC production) -activation of vitamin D produced by the skin

WATER BALANCE -average intake - 2.5 L (60% from drinking water, 30% from moist foods, 10% byproduct of metabolism) -regulation of intake - thirst center within the hypothalamus e.g. as body loses water - osmoreceptors within the thirst center detects increase in osmotic pressure within the ECF – tells us to drink to decrease OP into normal range -drinking distends the stomach which inhibits signalling from the thirst center PLUS osmotic pressure becomes normal again -water is lost through urine, feces and sweat plus respiration and skin evaporation -2.5 L of water must be lost for water balance -60% lost in urine, 6% in feces, 6% in sweat, 28% evaporation from skin and lungs -primary means of controlling output is through urine production

Water Balance -extracellular fluids/ECF: blood plasma, interstitial fluids, CSF, lymph etc…. -intracellular fluids/ICF: cytosol -of the 40 liters of water in the average male - 37% is ECF and 63% is ICF -blood pressure and osmotic pressure control the movement of fluid between ECF and ICF e.g. blood pressure causes the movement of fluid out of the capillaries into the interstitial spaces of the tissue (between cells) – some will move into the cells and become cytosol -BUT osmotic pressure causes fluids to leave the cells and tissues and enter the capillaries -dehydration: blood plasma loses water (becomes concentrated) - increases osmotic pressure/OP of the plasma -OP increase is detected by osmoreceptors in hypothalamus -posterior pituitary gland releases anti-diuretic hormone (ADH) -ADH causes distal convoluted tubule and collecting duct to increase water reabsorption back into blood and OP comes back down to normal – urine volume drops -excess water intake: plasma less concentrated - decrease in OP -osmoreceptors signal to the post. pituitary- decreases ADH release and nephrons decrease water reabsorption – urine volume goes up