Functions Removes wastes Regulate normal concentrations of water and electrolytes Regulates pH and body fluid volume Helps regulate RBC production Helps regulate blood pressure

Part of the System Part of the System Kidneys Ureters Urinary bladder Urethra

Kidney Red-brown, bean-shaped organ Located on either side of vertebral column high in abdominal cavity

Kidney Functions Regulate composition, volume, and pH of extracellular fluid Formation of urine Secrete erythropoietin to control RBC production Role in activation of vitamin D Secrete renin to regulate blood volume and pressure

Kidney Structure Concave side leads to hollow cavity called renal sinus Entrance is called the hilum Entering through hilum: Renal artery and renal vein Lymphatic vessels Nerves Ureter

Kidney Structure Ureter expands into renal pelvis in the renal sinus Renal pelvis subdivides into major calyces Major calyces subdivide into minor calyces Renal papillae - projection of renal sinus wall with openings into the minor calyces Surrounding renal sinus: Renal medulla- striated renal pyramids Renal cortex- granular shell with renal columns dipping into renal medulla

Blood flow to Kidneys Renal artery carries 15-30% of cardiac output to kidney Blood flow sequence: Renal artery  Interlobular arteries  Afferent arterioles  Glomerular capillaries  Efferent arterioles  Peritubular capillaries  Enters venous system  Leaves through renal vein

Nephrons Functional unit of kidney About 1 million nephrons PER kidney Composed of renal corpuscle/cortex and renal tubules/medulla

Renal corpuscle/cortex Glomerular capillaries form tangled structure called glomerulus Thin-walled sac, glomerular capsule, is surrounded by capillaries Renal tubule is connected to capsule

Renal Tubule/medulla Proximal convoluted tubule  Descending limb of the loop of Henle  Ascending limb of the loop of Henle  Distal convoluted tubule  Collecting duct  Minor calyces Kidney animation

Juxtaglomerular Apparatus Location of secretion of renin Apparatus is composed of two types of cells: 1) densely packed cells called the macula densa in the distal convoluted tubule 2) juxtaglomerular cells in the afferent and efferent arterioles

Steps of Urine Formation Steps of Urine Formation 1) Glomerular filtration Filter substances out of the blood plasma 2) Tubular reabsorption Substances in tubule are reabsorbed into plasma 3) Tubular secretion Substances are secreted into tubule

Glomerular Filtration Produced 180 liters of filtrate every 24 hours Plasma is forced out of the gomerular capillary due to blood pressure Glomerular capillary is more permeable than other capillaries due to tiny openings called fenestrae Podocytes Cells that cover the capillaries and don’t allow plasma proteins to leave the capillary Glomerular capsule receives glomerular filtrate

Filtration Pressure Pressure is kept high by the two capillary bed structure Pressure overcomes osmotic pressure and hydrostatic pressure in the capsule Net filtration pressure takes into account all three factors (usually remains positive favoring filtration)

Rate of Filtration Controlled by diameter of blood vessels Afferent: Constriction , Dilation  Efferent: Constriction , Dilation  Controlled by colloid osmotic pressure Plasma Protein Concentration: inversely proportional to filtration rate Controlled by hydrostatic pressure Fullness of capsule: inversely proportional to filtration rate

Regulation of Filtration Rate Sympathetic nervous system Control rate by changing diameter of arterioles Atrial natriuretic peptide Hormone secreted by heart when blood volume is to high Increases filtration rate

Regulation of Filtration Rate (cont) Renin is secreted when: Afferent arterioles sense blood pressure drop Response to sympathetic stimulation Macula densa senses decrease in Cl, K, and Na in distal tubule Renin converts angiotensinogen to angiotensin I Angiotensin I is converted to angiotensin II Angiotensin II constricts efferent arteriole and increases secretion of aldosterone Look back at Ch 11 for function of aldosterone!

Tubular Reabsorption Substances are moved out of the tubule by: Diffusion, osmosis, and active transport Proximal tubule Glucose, amino acids, creatine, lactic acid, uric acid, ascorbic acid, phosphate, sulfate, calcium, potassium, and sodium moved by active transport Water moved by osmosis

Bicarbonate (HCO 3 - ) - is the most important buffer in the blood -prevents blood from becoming too acidic

Tubular Reabsorption (cont) Sodium is actively transported Negatively charged ions are moved using passive transport Water follows by osmosis due to concentration difference Sodium and water reabsorption continues along sections of the loop of Henle and distal tubule

Tubular Reabsorption (cont) Limited transport capacity- only limited number of carriers for transport If concentration is below renal plasma threshold, carriers can reabsorb all If concentration is above renal plasma threshold, some of the substance will be left in urine

Tubular Secretion Secretion of: Penicillin Creatinine Histamine Hydrogen ions Potassium ions

Regulation of Urine Volume and Concentration Regulation of Urine Volume and Concentration Aldosterone: Increase Na reabsorption and K secretion ADH: Makes distal tubule and collecting duct more permeable to water

Urea and Uric Acid Urea Part of filtrate; 50% is excreted in urine Uric acid All but a small amount is reabsorbed

Urine Final composition varies: Contains urea, some uric acid, some amino acids, and electrolytes Should not contain plasma proteins or blood Volume of urine: Usually between 0.6 and 2.5 liters PER day

Ureter Carries urine from kidney to bladder Layers of wall: Mucous coat- inner layer Muscular layer- smooth muscle Fibrous coat- outer layer Peristalsis moves urine towards bladder Flap of the mucous coat covers opening to bladder and prevents backflow of urine into ureter

Urinary Bladder Hollow, expandable, muscular organ Trigone triangular shaped part of the bladder with an opening at each corner (ureters and neck of bladder leading to ureter) Four layers to walls: Mucous coat (transitional epithelium) Submucous layer (connective tissue and elastic fibers) Muscular Coat (detrusor muscle and sphincters) Serous coat (parietal peritoneum on one side and connective tissue on the other)

Urethra Tube leading from bladder to outside Longer in males than females Urethral glands Secrete mucous into the canal

Micturition When bladder becomes full internal urethral sphincter relaxes External urethral sphincter is voluntary muscle Micturition reflex- detrusor muscle and muscles in abdomen and pelvic floor contract forcing urine into urethra Kidney/Urinary System review

Seinfeld