The Excretory System: Urine Formation … eww

The Excretory System Mammals must excrete many different wastes in order to remove toxic substance from the body The wastes form as a result of the metabolic processes of the body and degeneration of cells (ie. urea, ammonia, CO2, lactic acid, etc.) Much of the excretory system flows through the kidneys

Kidneys Part of excretory system, controlled by nervous and endocrine system Weighing ~0.5 kg each, kidneys may hold as much as 25% of the body’s total blood volume at any given time Involved in the production of urine

Kidneys Stabilize internal environment by: regulating water content (osmoregulation) eliminating poisonous by-products of biological reactions regulating ion concentration Mechanisms of Regulation: diffusion/osmosis forced filtration active transport

Nephron Each kidney contains over 1 million slender tubules called nephrons The functional units of the kidney

Nephron Structure Glomerulus: High-pressure capillary bed The site of blood filtration Bowman’s Capsule: Funnel-like structure ‘Beginning’ of the nephron Each nephron has its own independent blood supply (renal arterioles and veins)

Nephron Structure Components not entering capsule: Blood proteins Blood Cells Platelets

Nephron Structure Proximal Tubule: Re-absorption of molecules important to the blood Loop of Henle: Concentration of urine (solutes to be excreted)

Nephron Structure Distal Tubule: Final re-absorption and secretion of molecules Collecting Duct Collection of urine from multiple nephrons Joins with the ureters; ultimately the bladder

Urine Formation Accomplished by 3 functions of the nephron: Forced filtration of blood from the afferent arteriole into the glomerulus, and through Bowman’s capsule under high pressure proteins, blood cells and platelets are too large to pass through & stay in the blood sodium chloride, glucose, amino acids, ions enter the nephron

Urine Formation Re-absorption of most fluids and solutes from the filtrate back into the blood for every 120 mL of fluids filtered, only 1 mL becomes urine many solutes are removed from the nephron into the capillary beds surrounding the convoluted tubules passive transport moves Na+, Cl- and HCO3 active transport moves glucose and amino acids an osmotic gradient is created by the solutes in the capillary bed, drawing water out of the nephron (in all tubules but the ascending Loop of Henle)

Urine Formation Secretion moves wastes from blood into the distal tubule of the nephron Urea, uric acid, ammonia, excess ions, minerals, drugs, etc. moved by active transport

How it all works:

How it all works: YouTube Link: http://www.youtube.com/watch?v=vNvZaGcLzEo

Lab Exercise Comparing Solutes in the Plasma, Nephron & Urine Activity: 7.5.1 - p.363