Urinary System Contributes to Homeostasis Summary Chapter 15 Excretion processes that remove wastes and excess materials from the body Digestive system excretes food residues and wastes produced by the liver Respiratory system lungs excrete carbon dioxide Integumentary system skin excretes water salt Urinary system kidneys excrete nitrogenous wastes excess solutes and water Kidneys regulate body water levels Excess water is excreted Output varies from 2 1 2 liter day to 1 liter hour Kidneys regulate nitrogenous wastes and other solutes Nitrogen from amino acids is made into urea in liver and transported to kidney as waste Other solutes regulated by kidneys Sodium chloride potassium calcium hydrogen ions creatinine Organs of the Urinary System Kidneys Principal organ of urinary system Cortex outer portion of the kidney Medulla inner region of the kidney Ureters Urinary Bladder Stores urine 600 1 000ml Urethra Carries urine from the body Two Sphincters control urination Transport urine form the kidneys to the bladder Nephrons Produce Urine Nephron functional unit of the kidney Tubule Associated blood supply 1 million nephrons per kidney Each nephron consists of a long thin hollow tube tubule plus associated blood supply Role of nephrons remove approximately 180 liters of fluid from the blood daily and return most of it minus the wastes that are excreted Tubule Filters Fluid and Reabsorbs Substances Nephron Structure Glomerular Capsule cuplike end of nephron tubule surrounding glomerulus network of capillaries This is where filtration occurs Proximal Tubule extends from glomerular capsule to renal medulla Loop of Henle Distal Tubule Collecting Duct shared by several nephrons empties into renal pelvis Special Blood Vessels Supply the Tubule Renal artery supplies the kidney Blood vessels associated with tubules Arterioles Capillaries Afferent enters the glomerular capsule Efferent leaves the glomerular capsule Glomerular network within the glomerular capsule Peritubular surround proximal and distal tubule Vasa recta parallels the loop of Henle Formation of Urine Three Basic Processes Glomerular filtration movement of protein free solution of fluid and solutes from blood into the glomerular capsule Tubular reabsorption return of most of the fluid and solutes into the blood Tubular secretion addition of certain solutes form the blood into the tubule Glomerular Filtration Filters Fluid from Capillaries Filters protein free plasma fluid from capillaries into glomerular capsule Large volume filtration yet highly selective Impermeable to large proteins and cells Filtration is driven by high blood pressure in glomerular capillaries Rate of filtration Resting rate under local chemical control Stress causes sympathetic nervous system to reduce blood flow to kidneys Tubular Reabsorption Returns Filtered Water and Solutes to Blood 100 of filtered glucose amino acids and bicarbonate and 50 of urea are reabsorbed Most tubular reabsorption occurs in proximal tubule Reabsorption of sodium begins the process Sodium moved by active transport from tubule cells to interstitial fluid and diffuses to capillaries Chloride passively accompanies sodium balanced charge Water reabsorbed with salts Water moves through aquaporins water channels Movement of sodium provides energy to transport glucose and amino acids into renal tubule Glucose amino acids then diffuse to the interstitial fluid Tubular Secretion Removes Other Substances from Blood Involves the movement of materials form the peritubular capillaries or vasa recta to the tubule Purpose Regulation of chemical levels in body Excretion of harmful chemicals Substances secreted Penicillin cocaine marijuana pesticides preservatives hydrogen ions ammonium potassium Producing Dilute Urine Excreting Excess Water Kidneys respond to excess water by excreteing it Mechanism Distal tubule is impermeable to water NaCL is reabsorbed without the concurrent reabsorption of water Producing Concentrated Urine Conserving Water Too little water can lead to lower blood volume declining blood pressure risk of dehydration of body cells Kidneys respond by conserving water and producing a more concentrated urine Mechanism Mediated by ADH antidiuretic hormone from the posterior pituitary gland ADH increases permeability of the collecting ducts to water and increases conservation of water Urination Depends on a Reflex Micturition reflex Responds to stretch receptors in bladder wall Internal urethral sphincter Smooth muscle External urethral sphincter Skeletal muscle under voluntary control Brain can override the micturition reflex and control the timing of urination Voluntary control becomes increasingly difficult as the bladder gets very full Kidneys Maintain Homeostasis in Many Ways Maintain water balance Adjust blood volume and blood pressure Aldosterone renin ANH help maintain salt balance in order to control blood volume Maintain acid base balance and blood pH Regulate red blood cell production via erythropoietin Activate an inactive form of vitamin D Water Balance Determines Blood Volume and Blood Pressure Involves the kidneys hypothalamus and posterior pituitary gland Negative feedback loop regulates solute concentration of the blood Involves increasing or reducing ADH secretion which will modify water reabsorption of kidneys Involves increasing or decreasing thirst Diruretic increases the formation and excretion of urine Lasix furosemide medication that reduces blood volume and blood pressure Caffeine inhibits sodium reabsorption Alcohol inhibits ADH release Aldosterone Renin and ANH Control Blood Volume Aldosterone release is stimulated indirectly by decreased blood volume or blood pressure Decreased blood volume blood pressure cause release of renin from juxtaglomerular apparatus Renin converts angiotensin I to angiotensin II Angiotensin II stimulates adrenal cortex to release aldosterone Aldosterone increases sodium reabsorption by distal tubules and collection ducts Angiotensin II also a potent vasocontrictor increases blood pressure ANH atrial natriuretic hormone released by atria in response to stretching due to high blood volume inhibits Na reabsorption Kidneys Help Maintain Acid Base Balance and Blood pH Blood pH must stay between 7 35 and 7 45 pH regulated by kidneys buffers lungs Role of kidneys in pH maintenance Reabsorption of filtered bicarbonate Excretion of acid as ammonium Erythropoitein Stimulates Production of Red Blood Cells Decrease in amount of