The Excretory System Function Structure Nephron Urine Formation Homeostasis Pathologies

Excretion Excretion The process of separating wastes from bodily fluids and eliminating them The process of separating wastes from bodily fluids and eliminating them The excretory system is responsible for regulating the volume and composition of bodily fluids The excretory system is responsible for regulating the volume and composition of bodily fluids It does this by removing wastes and returning needed substances to the body It does this by removing wastes and returning needed substances to the body

The excretory system consists of 4 main structures The excretory system consists of 4 main structures 1.Kidneys Kidneys 2.Ureters 3.Urinary Bladder Urinary BladderUrinary Bladder 4.Urethra Urethra

The kidney can be divided into 3 main areas The kidney can be divided into 3 main areasareas Renal Cortex Renal Cortex Renal Medulla Renal Medulla Renal Pelvis Renal Pelvis Nephrons span the Renal Cortex and Renal Medulla Nephrons span the Renal Cortex and Renal Medulla Nephrons Nephrons are the functional unit of the kidney Nephrons are the functional unit of the kidney They function to: They function to: 1)Filter various substances from the blood 2)Regulate blood volume and blood pressure 3)Control electrolyte and metabolite balance 4)Maintain blood pH

The Nephron has 3 main regions The Nephron has 3 main regions 1.The Filter 2.The Tubule 3.The Collecting Duct

1. Filtration Capillaries in the glomerulus have large pores that allow water, wastes, and other dissolved substances to pass into Bowman’s Capsule Capillaries in the glomerulus have large pores that allow water, wastes, and other dissolved substances to pass into Bowman’s Capsulepores The pores are small enough to prevent blood cells and large proteins from passing through with the filtrate The pores are small enough to prevent blood cells and large proteins from passing through with the filtrate Filtrate - The fluid and compounds that pass into Bowman’s Capsule Filtrate - The fluid and compounds that pass into Bowman’s Capsule Filtrate The rate of filtration is determined by blood pressure and pore size The rate of filtration is determined by blood pressure and pore size

2. Reabsorption -Proximal Tubule -Most re-absorption of solutes and nutrients occurs here -Active re-absorption of Na +, amino acids, glucose, and + ions -Passive re-absorption of H 2 O (osmosis) and – ions -Descending Loop of Henle -Passive re-absorption of H 2 O by osmosis -Membrane is impermeable to Na +, all ions, and other substances -The hypertonic medulla external to the Loop of Henle causes the re-absorption of H 2 O -The filtrate becomes very concentrated

2. Reabsorption (Con’t) -Ascending Loop of Henle -Active re-absorption of Na + -Adds to the hypertonic medulla environment - Impermeable to H 2 O -Filtrate becomes less concentrated -Distal Tubule -Active re-absorption of Na + -Passive re-absorption of H 2 O and – ions -Collecting Duct -Passive re-absorption of H 2 O -Under nervous control

3. Secretion H + can be actively secreted into the proximal and distal tubule H + can be actively secreted into the proximal and distal tubule K + and drugs can be passively secreted into the distal tubule K + and drugs can be passively secreted into the distal tubule

-The body’s various mechanisms by which it maintains its internal environment despite changes externally -The Excretory System helps to maintain homeostasis through: 1.Water Balance 2.Salt Balance 3.pH Regulation

1.Water Balance Osmoreceptors in the brain detect osmotic pressure Osmoreceptors in the brain detect osmotic pressure Osmoreceptors High osmotic pressure in the blood means it is highly concentrated (ie. Little water = dehydrated) High osmotic pressure in the blood means it is highly concentrated (ie. Little water = dehydrated) ADH (Anti-diuretic hormone) is released from the brain in response to highly concentrated blood ADH (Anti-diuretic hormone) is released from the brain in response to highly concentrated blood ADH acts on the distal tubule and collecting duct and causes more water re-absorption ADH acts on the distal tubule and collecting duct and causes more water re-absorption ADH The result = + blood volume  + blood pressure The result = + blood volume  + blood pressure

2. Salt Balance Na + is regulated by the hormone Aldosterone Na + is regulated by the hormone AldosteroneAldosterone Aldosterone stimulates Na + re-absorption in the distal tubule and collecting duct Aldosterone stimulates Na + re-absorption in the distal tubule and collecting duct Cl - and H 2 O will passively follow Cl - and H 2 O will passively follow The result = + blood volume  + Blood Pressure The result = + blood volume  + Blood Pressure K + is usually secreted as a result of Aldosterone K + is usually secreted as a result of Aldosterone

3. pH Regulation The nephron is also able to secrete H + from the blood into the filtrate in the distal tubule The nephron is also able to secrete H + from the blood into the filtrate in the distal tubule Bicarbonate may also be re-absorbed to counter high blood acidity Bicarbonate may also be re-absorbed to counter high blood acidity

1.Urinary Tract Infection A bacterial or viral infection of the urinary tract, most commonly in the urethra A bacterial or viral infection of the urinary tract, most commonly in the urethra Tx – Anti-bacterial or anti-viral drugs Tx – Anti-bacterial or anti-viral drugs 2.Kidney Stones Kidney StonesKidney Stones Crystalline formations in the urine due to excess Calcium Crystalline formations in the urine due to excess Calcium Tx – Let it pass or use ultrasound shock waves Tx – Let it pass or use ultrasound shock waves 3.Renal Insufficiency A state where the kidneys cannot maintain homeostasis A state where the kidneys cannot maintain homeostasis Tx – Hemodialysis, Peritoneal Dialysis, and Renal Transplant Tx – Hemodialysis, Peritoneal Dialysis, and Renal Transplant