Urinary Functions of the Kidneys main excretion Homeostasis fluid and electrolyte balance Processes Filtering blood plasma Blood volume pressure and osmotic concentration regulation by regulating water output Secreting renin helps increase blood pressure Secreting erythropoietin stimulates production of red blood cells thus supports oxygen carrying capacity of the blood Synthesizing calcitrol help support the blood glucose level by synthesizing glucose from amino acids Waste Materials Useless to body or present in excess to body s needs Metabolic waste waste substance produced by the body Nitrogenous wastes most toxic of metabolic wastes all nitrogen containing compounds ex urea uric acid and creatinine Excretion separation and elimination of wastes from body fluids Carried out by Respiratory system carbon dioxide and small amounts of other gases and water Integumentary system water inorganic salts lactic acid and urea in sweat Digestive system food residue water salts carbon dioxide lipids bile pigments cholesterol other metabolic wastes Urinary system broad variety of metabolic wastes toxins drugs hormones salts hydrogen ions and water Anatomy of Kidney Nephron Renal corpuscle Glomerulus Glomerular capsule Renal tubule PCT Nephron loop DCT collecting duct Different types Cortical close to kidney surface short loops Juxtamedullary closer to medulla longer loops Urine Formation Glomerular filtration filtration of blood makes filtrate Tubular reabsorption removes water and solutes from filtrate returns to blood Tubular secretion removes additional wastes from blood adds to filtrate Water conservation removes water from urine returns to blood Conserves water and concentrates waste in urine Glomerular Filtration process which water and some solutes in blood plasma pass from capillaries of the glomerulus into the capsular space of nephron Glomerulus into capsular space passive and nonselective process hydrostatic Filtration membrane Capillary endothelium fenestrated highly permeable Basement membrane negatively charged gel small molecules only repels neg charge Filtration slits Podocytes look like octopus foot processes legs negatively pressur charged Permeable materials Water electrolytes glucose amino acids nitrogenous wastes and vitamins Non permeable materials Calcium Iron Fatty acids Thyroid hormones and proteins Filtration Pressure Glomerular hydrostatic pressure 60 mmHg higher than other capillaries 15 mmHg because afferent arteriole bigger than efferent arteriole Out Capsular hydrostatic pressure CP 18 mmHg in Colloid Osmotic Pressure COP 32 mmHg proteins etc within blood in Capsular Osmotic Pressure 0mmHg essentially unless kidney disease Net filtration pressure NFP 10 mmHg out Glomerular Filtration Rate GFR Amount of filtrate per minute by kidneys Males 125 ml min 180 L day Females 105 ml min 151 L day Approx 50 60 times more than blood plasma Only 1 2 liters per day of urine output Regulation of GFR If too high fluid too rapid urine output rises dehydration electrolyte depletion If too low fluid too slow reabsorb wastes Homeostatic Mechanisms Adjusted by changes in glomerular BP Renal autoregulation kidneys alter GFR despite high arterial BP Sympathetic control SNS Renin angiotensin mechanism Renal Autoregulation regulation of afferent efferent arterioles Myogenic Mechanism pressure change in renal blood vessels smooth muscle contracts when stretched Increase BP stretches afferent arteriole constricts afferent arteriole Decreases blood flow conversely works other way Tubuloglomerular Feedback glomerulus receives feedback on the status of downstream tubular fluid and adjust filtration to regulate its composition stabilize nephron performance and compensate for fluctuations in BP Juxtaglomerular Apparatus JGA end of nephron loop Mascula Densa end of the loop on side facing arterioles flow or fluid composition secrete messenger to stimulate JGC after stimulate by MD secrete renin which initiates RAA mechanism which raises BP JG cells other side of arteriole constrict or dilate afferent arteriole Mesangial cells chemo mechanoreceptor communication between MD and JGC Sympathetic NS constrict afferent arterioles reduces GFR and urine output redirects blood to heart brain and needed skeletal muscles Adrenal epinephrine constrict afferent arterioles Strenuous exercise or circulatory shock shunts blood away from kidneys indirectly triggers renin angitensin mechanishm stimulating the macula densa cells SNS directly stimulates JG cells to release renin Renin Angiotensin Mechanism collectively raises BP by reducing water loss encouraging water intake and constricting blood vessels Renin released Angiotensin 1 made converted to Angiotensin 2 by Angiotensin converting enzyme Angiotensin 2 stimulates hypothalamus for sense of thirst encouraging water intake afferent efferent arterioles constrict to increase BP posterior pit to secrete ADH for water reabsorption by collecting duct and aldosterone for water and sodium reabsorption by DCT and collecting duct Reabsorption reclaims materials from Nephron to blood peritubular capillaries Secretion removes materials from blood to Nephron peritubular capillaries maintains homeostasis Mechanism of Reabsorption Nephron to Blood Transcellular route through cytoplasm Paracellular route move between cells Methods Primary active transport sodium potassium pump antiport Secondary active transport indirectly by ion gradients SGLT symport Solvent drag solutes follow solvent gradients must be present Proximal Convoluted Tubule reabsorbs most tubular fluid All glucose lactate and amino acids 60 70 of sodium 65 70 of water 90 of bicarbonate 50 of chloride 90 of potassium most other electrolytes Sodium Reabsorption Creates osmotic and electrical gradient to drive reabsorption of water and others Out of tubule into tubule cell facilitated diffusion symport with glucose AA phosphate lactate Antiport with H Into ECF Antiport with Na K pump Into peritubular capillary solvent drag with water Chloride Reabsorption Factors chloride follows sodium water reabsorption Into tubule cell antiport exchange sodium Into ECF symport K Cl Into peritubular capillary solvent drag Glucose Reabsorption No concentration gradient more glucose in cell than tubule Lumen into tubule cell SGLT Tubule cell into ECF facilitated diffusion Into peritubular capillaries solvent drag Transport Maximum maximum rate of absorption when transporters are saturated Limited number of protein