Urinary System Don’t break the seal…

Function Removes salts and nitrogenous wastes Maintains the normal concentrations of water and electrolytes Regulates pH and volume of blood fluid Helps control red blood cell production and blood pressure

Kidney Location/Structure Reddish-brown bean shaped organ Located high on posterior wall of abdominal cavity Lateral surface convex, medial side deeply concave Renal sinus formed in depression Hilum provides entrance for blood vessels, nerves, and ureter

Structure cont. Renal pelvis – funnel shaped sac at superior end of ureter Subdivides into major and minor calyces (singular form calyx) Two distinct regions: Renal medulla – inner portion composed of conical masses – renal pyramids Renal cortex – forms a shell around medulla and dips into medulla between renal pyramids forming renal columns

Kidney Function Regulate composition and volume of extracellular fluid Remove metabolic wastes from blood and combine them with water to form urine

Renal Blood Vessels Renal arteries – arise from abdominal aorta, supply blood to kidneys Branch into interlobar arteries Branches branch further and eventually turn into afferent arterioles that lead to nephrons Renal veins – bring blood out of kidneys and connect to inferior vena cava

Blood Supply to the Kidneys

Function of a Nephron Production of filtrate Reabsorption of organic nutrients Reabsorption of water and ions Secretion of waste products into tubular fluid

Nephron Structure Made of renal corpuscle and renal tubule Renal corpuscle – composed of tangled cluster of capillaries called a glomerulus which filters fluid Surrounded by glomerular capsule that receives the fluid the glomerulus filters Renal tubule leads away from glomerular capsule and coils into proximal convoluted tubule

Structure cont. Proximal convoluted tubule (PCT) Loop of Henle Actively reabsorbs nutrients, plasma proteins and ions from filtrate Released into peritubular fluid Loop of Henle Descending limb Ascending limb Each limb has a thick and thin section

Structure cont. Distal convoluted tubule (DCT) Collecting duct Actively secretes ions, toxins, drugs Reabsorbs sodium ions from tubular fluid Collecting duct Where the DCT of all nephrons merge Water is reabsorbed, solutes secreted Empties into minor calyx

Urine Formation Regulating blood volume and composition Excreting waste products Urea Creatinine Uric acid

Urine cont. Glomerular Filtration Tubular Reabsorption Blood pressure causes plasma to be filtered Water and solutes across glomerular capillaries creates a filtrate Tubular Reabsorption The removal of water and solutes from the filtrate for reabsorption back into body Tubular Secretion Transport of solutes from the peritubular fluid into the tubular fluid (stuff body doesn’t need/want) Urine Elimination Waste products from filtrate end up in urine that is expelled from body

Urea and Uric Acid Urea – by-product of amino acid catabolism Enters tubule by filtration Uric acid – product of metabolism of certain organic bases in nucleic acids

Regulation of Urine Concentration and Volume ADH (antidiuretic hormone) stimulates kidney to increase permeability of lining in DCT and collecting duct Water moves rapidly out of these segments by osmosis (water is reabsorbed) Solutes in filtrate become more concentrated (after water is removed from it) When excess water present, ADH secretion decreases Permeability of linings decrease, less water is reabsorbed and more urine is excreted

Urine cont. Urine output of 50-60 mL per hour is normal 30 mL or less could indicate kidney failure

Urine Elimination Ureter Urine in collecting ducts, merge into minor/major calyces, and then into renal pelvis Ureter then carries it to the bladder Muscular walls of ureter propel urine Flap-like fold acts as valve so that urine cannot back up into ureter from bladder

Elimination cont. Urinary Bladder Hollow, stretchable, muscular organ that stores urine and forces it into the urethra Detrusor muscle - smooth muscle controlled by parasympathetic nerve fibers Contraction will cause urine to be expelled into urethra Near neck of bladder can help prevent urine from entering urethra (internal urethra sphincter)

Elimination cont. Urethra Tube that conveys urine from the urinary bladder to the outside

Micturition (Urination) Expulsion of urine from urinary bladder Occurs when detrusor muscle and abdominal muscles contract Requires relaxation of external urethra sphincter (voluntary control) Facts: bladder can hold 600 mL; sensation to pee at 150 mL; urge intensifies at 300 mL or more