Kidney Function Excretory Function Filters blood plasma, eliminates waste, returns useful chemicals to blood Homeostatic Functions (Endocrine System) Osmoregulatory Function Regulates osmolarity of body fluids Regulates blood volume and pressure Secretes renin, activates angiotensin, aldosterone controls BP, electrolyte balance Secretes erythropoietin, controls RBC count Regulates PCO2 and acid base balance Gluconeogenesis
Excretory -- Formation of Urine Filter and Excrete toxins, metabolic waste products, excess ions, organic acids, and nitrogenous wastes. Uric acid: results from the catabolism of nucleic acids Urea: derived from the breakdown of amino acids Proteins amino acids NH2 removed forms ammonia which the liver converts to urea Creatinine: derived from The breakdown of creatine phosphate ( a molecule in muscle that stores energy used in the synthesis of ATP) The main waste products excreted in urine are the nitrogenous compounds.
Kidney Urine Formation Filtration Blood with all materials enters the glomerular capillaries Small molecules pass from the capillaries into the capsular space sodium (Na +) H2O glucose potassium (K+) nitrogenous wastes These molecules are filtered by cell membranes based on size and charge Renal Corpusle
Kidney Filtration Membrane Fenestrated endothelium Fenestrated endothelium of the glomerular capillaries 70-90nm pores exclude blood cells Basement membrane (main molecular filter) Basement membrane (main molecular filter) Proteoglycan gel, negative Proteoglycan gel, negative charge excludes molecules charge excludes molecules > 8nm (ex. Proteins) > 8nm (ex. Proteins) Filtration slits Filtration slits Podocyte ( cells of the viseral layer of the glomerular capsule ) arms have pedicels with negatively charge with negatively charge filtration slits filtration slits Renal Corpusle
The Juxtaglomerular apparatus: senses BP in the afferent arteriole
Reabsorption in the Proximal Convoluted Tubule Mechanisms Leakage or Diffusion through tight junction Active transport Secondary active transport-- antiport Facilitated diffusion Diffusion through membrane channel Solvent Drag: H2O absorb by osmosis and drags solute along with it Pinocytosis Peritubular capillary Epithelial cellsTubular Fluid
Additional waste materials enter the tubule from the interstitial fluid by the same mechanisms which facilitated reabsorption. Waste removal urea, uric acid, bile salts, ammonia, catecholamines, many drugs Acid-base balance secretion of hydrogen and bicarbonate ions regulates pH of body fluids Primary function of nephron loop water conservation, also involved in electrolyte reabsorption Secretion into the Proximal Convoluted Tubule and Nephron Loop
Urine Physical Characteristics Physical Characteristics –Color: due to urochromate (pigment released in hemoglobin catabolism) –Odor: Ammonia, due to bacterial metabolism –pH: ~6.0 (acidic) that varies with diet –Specific gravity: more dense than distilled water Chemical Characteristics Chemical Characteristics –95% water, 5% solutes –Urea: Nitrogenous wastes from catabolism of Amino Acids, creatine phosphate, etc.