Urinary System and Excretion Organs Urine Formation Homeostatic Mechanisms

Path of Urine through the Urinary System Kidneys produce urine Urinary bladder stores urine Urethra passes urine to outside Ureters transport urine

Applying Your Knowledge A.Where is urine stored? B.Which structure passes urine to the outside of the body? C.Which structure transports urine to the bladder? D.Where is urine produced? 1. Ureters 2. Bladder 3. Kidney 4. Urethra

Functions of the Urinary System Excretion: removal of metabolic wastesExcretion: removal of metabolic wastes –Urea: breakdown product of amino acids –Creatinine: breakdown product of creatine phosphate, a high energy molecule in muscles –Uric acid: breakdown product of nucleotides Ammonium from amino acids used for energy

Structure of the Kidney Renal Cortex: outer layerRenal Cortex: outer layer Renal Medulla: inner layerRenal Medulla: inner layer Renal Pelvis: central spaceRenal Pelvis: central space Nephrons are microscopic tubules that produce urine

Structure of the Nephron Glomerular capsule Glomerulus (capillaries) Proximal convoluted tubule Descending limb Ascending limb Loop of the nephron Collecting Duct Peritubular capillary network Distal convoluted tubule

Urine Formation: Glomerular Filtration Formation of a filtrate containing some components from whole bloodFormation of a filtrate containing some components from whole blood Water and small molecules enter glomerular capsule from the glomerulusWater and small molecules enter glomerular capsule from the glomerulus Proteins, cell fragments and cells are excluded from the filtrateProteins, cell fragments and cells are excluded from the filtrate Water, nutrients, salts, nitrogenous wastes enter nephron Cells, cell fragments and proteins remain in the bloodstream

Urine Formation: Tubular Reabsorption Molecules and ions are reabsorbed into the blood, either actively or passivelyMolecules and ions are reabsorbed into the blood, either actively or passively Reabsorption occurs from the proximal convoluted tubule into the peritubular capillary networkReabsorption occurs from the proximal convoluted tubule into the peritubular capillary network Water, nutrients and salts are reabsorbed into the bloodstreamWater, nutrients and salts are reabsorbed into the bloodstream Peritubular capillary network Water, nutrients, salt reenter the bloodstream Nitrogenous waste, excess salts, some water remain in nephron

Urine Formation: Tubular Secretion Substances are actively transported from the blood (peritubular capillary network) into the kidney tubuleSubstances are actively transported from the blood (peritubular capillary network) into the kidney tubule Involves transport of hydrogen ions, creatinine, penicillin and other drugsInvolves transport of hydrogen ions, creatinine, penicillin and other drugs Peritubular capillary network H +, creatinine, drugs enter the nephron

Urine Formation: Water Reabsorption Water is reabsorbed into the bloodstream from all parts of the nephron, and the collecting ductWater is reabsorbed into the bloodstream from all parts of the nephron, and the collecting duct Occurs by osmosis through aquaporins, membrane channel proteinsOccurs by osmosis through aquaporins, membrane channel proteins Controlled byControlled by –Reabsorption of salt –Gradient of NaCl in medulla tissue surrounding the loop –ADH, antidiuretic hormone, released from pituitary when water intake is low, stimulates aquaporin activity in distal convoluted tubule Urine has a lower water concentration than blood release is inhibited by alcohol

Applying Your Knowledge A.Where is glucose returned to the bloodstream? B.Which structure does ADH influence? C.Which structure forms a NaCl gradient to influence water reabsorption? D.Which structure produces a blood filtrate that contains water, nutrients and waste? 1. Distal Convoluted Tubule 2. Glomerular Capsule 3. Loop of the Nephron 4. Proximal Convoluted Tubule 5. Collecting Duct

Urine Formation: Salt Reabsorption Sodium: >99% reabsorbedSodium: >99% reabsorbed – reabsorption in PCT, DCT, collecting duct –active transport in ascending limb of loop of nephron Other reabsorbed or excreted ionsOther reabsorbed or excreted ions –potassium ions –bicarbonate ions –magnesium ions

Hormonal Control of Sodium Reabsorption Angiotensinogen Angiotensin I Angiotensin II If blood pressure decreases Reninsecretes Stimulates sodium reabsorption from DCT, water follows sodium Aldosterone (from adrenal glands) stimulates secretion of constricts blood vessels

Hormonal Control of Sodium Excretion Angiotensinogen Angiotensin I Angiotensin II If blood pressure increases Renin secretes Aldosterone (from adrenal glands) Heart atrial cells Atrial Natriuretic Hormone (ANH) secrete prevents renin secretion X inhibition of secretion XX X Sodium is excreted in urine, water follows

Functions of the Urinary System Maintenance of Water-Salt Balance important for blood pressure and blood volumeMaintenance of Water-Salt Balance important for blood pressure and blood volume –Water reabsorption Loop of the NephronLoop of the Nephron Collecting DuctCollecting Duct –Sodium reabsorption or excretion Proximal convoluted tubuleProximal convoluted tubule Distal convoluted tubuleDistal convoluted tubule

Functions of the Urinary System Maintenance of Acid-Base BalanceMaintenance of Acid-Base Balance –Blood pH is controlled by the bicarbonate buffering system Buffer: substance that resists pH changeBuffer: substance that resists pH change –When lungs release carbon dioxide, H + has been used to produce water, so pH remains about neutral (7.4) bicarbonate ion hydrogen ion carbonic acidcarbon dioxide water

Functions of the Urinary System Maintenance of Acid-Base BalanceMaintenance of Acid-Base Balance –Kidney excretes excess hydrogen ions (H + )excretes excess hydrogen ions (H + ) reabsorbs bicarbonate ions (HCO 3 - )reabsorbs bicarbonate ions (HCO 3 - )

Summary of Urinary System Functions Excretion: removal of metabolic wastesExcretion: removal of metabolic wastes Maintenance of Water-Salt Balance important for blood pressure and blood volumeMaintenance of Water-Salt Balance important for blood pressure and blood volume Maintenance of Acid-Base BalanceMaintenance of Acid-Base Balance Secretion of HormonesSecretion of Hormones –Renin (enzyme) influences secretion of aldosterone from adrenal cortex –Erythropoietin: stimulates red blood cell production

Applying Your Knowledge A.Which one affects activity of aquaporins? B.Which one is made by the kidney in response to decreased blood pressure? C.Which one stimulates red blood cell production? D.Which one stimulates reabsorption of sodium? 1. Aldosterone 2. Antidiuretic Hormone (ADH) 3. Renin 4. Angiotensin II 5. Erythropoietin