Nephron Function and Urine Formation Ms. Kula December 1, 2014 Biology 30S
The Role of the Nephron In order for the body to properly function and maintain homeostasis, the amount of dissolved substances in the blood must remain at fairly constant levels Nephrons, the functional units within the kidneys, remove wastes as well as excess amounts of certain dissolved substances
Major Processes of Urine Formation FILTRATION REABSORPTION SECRETION
Filtration The Bowman s capsule is the membrane that filters the fluid coming into the kidney through the renal artery
Afferent arteriole Efferent arteriole
Filtration The afferent arteriole supplies blood to the glomerular capillaries This blood in the glomerulus contains filterable and non-filterable components
Filtration Blood pressure pushes the filterable components out of the capillaries where they enter the Bowman s capsule, this fluid is called filtrate The filtrate contains water, nitrogenous waste, nutrients, and salts Filtrate leave the Bowman s capsule and enters the proximal convoluted tubule
Filtration The non-filterable components of blood consist of blood cells, platelets, and plasma proteins Blood exits the glomerulus through the efferent arteriole and flows through the peritubular capillaries
Afferent arteriole Water Nitrogenous Waste Salts Nutrients Blood cells Platelets Plasma Proteins Efferent arteriole
Reabsorption The peritubular capillaries surround the proximal tubule, loop of Henle, and the distal tubule As the filtrate moves throughout the above tubules, certain dissolved substances move from the filtrate back into the capillaries. This occurs by both active and passive transport
Reabsorption In the Proximal Convoluted Tubule Cells in the proximal tubule are filled with mitochondria which produce energy for active transport into the blood Salts and nutrients are reabsorbed Examples of salt ions: Na+ Cl- Examples of nutrients: Glucose, Amino Acids
Reabsorption In the Proximal Convoluted Tubule The proximal tubule is highly permeable to water After the ions and nutrients have been reabsorbed, the concentration of water is higher in the filtrate than in the peritubular capillaries Water moves out of the filtrate by osmosis back into the blood
Reabsorption In the Loop of Henle Water and salt are reabsorbed from the Loop of Henle The descending and bottom part of the loop is very permeable to water, but not so much to salts and other dissolved substances
Reabsorption In the Loop of Henle The ascending portion of the loop moving towards the distal tubule is where salt is actively pumped into the capillaries The ascending loop is not permeable to water After flowing through the Loop of Henle, the filtrate can now be considered urine
Reabsorption In the Collecting Duct As urine moves through the collecting duct, the high salt concentration of the medulla tissue allows for even more water to be reabsorbed into the blood
Secretion Some substances are secreted from the blood through the peritubular capillaries into urine as it travels through the distal convoluted tubule These substances include: Hydrogen ions, uric acid, creatinine, ammonia, and drugs
Secretion Secretion occurs by active transport The cells lining the distal convoluted tubule are filled with mitochondria, which produce energy for active transport
Urine from the collecting duct gathers in the renal pelvis of the kidney and sent via the ureter to be stored in the urinary bladder.
Change in Concentrations Dissolved Substances Arterial Blood Postglomerular Blood Filtrate Urine Venous Blood Urea 30 0 30 1800 15 Uric Acid 4 0 4 50 3.6 Glucose 100 0 100 0 98 Salts 900 0 900 2300 850 Proteins 8000 9000 0 0 8020