Urine Formation PDF

Urine Formation Outcome D3, Lesson 2 Review Review What is urea? Where does it come from? Review What is urea? Where does it come from? When excess protein is eaten, it will be converted into sugar Deamination – remove of the amino group from an amino acid This amino g...

Urine Formation Outcome D3, Lesson 2 Review Review What is urea? Where does it come from? Review What is urea? Where does it come from? When excess protein is eaten, it will be converted into sugar Deamination – remove of the amino group from an amino acid This amino group will become ammonia (very toxic) Ammonia is immediately combined with CO2 to form urea Urea gives urine its very distinct smell Review How is urine formed? Four crucial processes: 1. Glomerular filtration – moves water and small solutes from blood plasma to nephron 2. Tubule reabsorption – reabsorbs useful solutes (e.g. sodium) from nephron back into blood 3. Tubular secretion – additional wastes move from blood into nephron 4. Water reabsorption – removes water from nephron and returns it to blood 1. Glomerular Filtration Forces water and dissolved substances out of the blood in the glomerulus and into Bowman’s capsule Blood pressure is four times higher than in other capillary beds within the body Capillaries in glomerulus are extra permeable due to tiny pores in tissue walls Small molecules like water, salts (Na+ and Cl–), glucose, amino acids, hydrogen ions (H+), bicarbonate ions (HCO3–), vitamins, and urea can pass through the capillary walls Large substances like plasma proteins, red blood cells, and platelets cannot pass through, and stay in the bloodstream Now called filtrate 1. Glomerular Filtration Pathway of blood: afferent arteriole  glomerulus  efferent arteriole 1. Glomerular Filtration Filtrate in Bowman’s capsule is very similar blood plasma (minus the plasma proteins) Blood Plasma Glomerular Substance (g/L) Filtrate (g/L) Protein 44.4 0.0 Sodium (Na+) 3.0 3.0 Chloride (Cl–) 3.5 3.5 Glucose 1.0 1.0 Urea 0.3 0.3 2. Tubular Reabsorption About 65% of the filtrate that passes through the length of the proximal tubule and loop of Henle is reabsorbed Reabsorption means leaving the body (nephron) and entering the blood About 1600 L to 2000 L of blood pass through your kidneys everyday From that 180 L of filtrate is formed Without reabsorption, we would need to drink 180 L of water a day to replace what we were excreting, not to mention all of the glucose and nutrients we would be losing as well 2. Tubular Reabsorption Transfer of essential solutes and water from the nephron back into the blood For every 120 mL of filtrate that enters Bowman’s capsule, only 1 mL of urine is made 119 mL are reabsorbed 2. Tubular Reabsorption Proximal Tubule Cells of proximal tubule have many mitochondria Provide energy for active transport of nutrients (ex. glucose and amino acids) and cations (ex. Na+) Anions (ex. Cl–, HCO3–) are electrostatically attracted to cations (like Na+) so they follow them out of the filtrate and into the blood through passive transport (diffusion) Water returns to the blood by osmosis (passive transport) 2. Tubular Reabsorption Loop Of Henle The descending loop of Henle is permeable to water, but only slightly permeable to ions As the descending limb goes deeper into the renal medulla, the ion (salt) concentration in the medulla increases Water moves out of the nephron (towards to hypertonic medulla) and is the reabsorbed by the capillaries As water leaves the filtrate, the concentration of Na+ inside the tubule increases, reaching its maximum concentration at the bottom of the loop 2. Tubular Reabsorption Loop Of Henle As the filtrate goes around the bottom bend of the loop of Henle and starts moving up the ascending limb, the permeability of the tubule changes The thin-walled portion of the ascending limb is now impermeable to water and more permeable to solutes Na+ diffuses from high concentration in the filtrate to low concentration in the blood vessels Anions passively follow cations 2. Tubular Reabsorption Loop Of Henle The thick-walled portion of the ascending limb has the same permeability as the thin-walled portion, but actively transports Na+ out of the filtrate and into the blood vessels Anions passively follow cations The transport of ions out of the ascending limb also helps replenish the salt levels in the medulla At this point, 2/3 of water and filtrate have been reabsorbed 2. Tubular Reabsorption Distal Tubule Reabsorption of Na+ from filtrate into the capillaries depends on the body’s needs Actively transported Anions passively follow cations Ions being reabsorbed decreases the filtrate concentration which triggers water to be reabsorbed via osmosis 3. Tubular Secretion Active transport of substances from the blood into the nephron Opposite flow of absorption Majority of secretion takes place in the distal tubule, but some happens in the proximal tubule Potassium ions (K+) are secreted into the distal tubule Hydrogen ions (H+) are secreted into the proximal and distal tubules to maintain blood pH High H+ concentration = more acidic blood Need to lower acidity by removing H+ from blood Some medications and drugs are secreted into the proximal and distal tubules 4. Water Reabsorption While water has been reabsorbed throughout the nephron, filtrate entering the collecting duct still contains a lot of water The collecting duct (like the loop of Henle) extends deep into the salty medulla This causes osmosis of water out of the nephron and into the capillaries The reabsorption of water in the collecting duct causes the filtrate to become about four times more concentrated by the time it exits the duct Now called urine Summary Water and small substances are filtered out of the blood and into the nephron in the glomerulus Reabsorption of water, nutrients, anions and cation begins in the proximal tubule Water reabsorption occurs in the descending limb of the Loop of Henle. The Loop of Henle extends down into the extremely salty medulla, allowing water to be reabsorbed via osmosis. The ascending limb of the Loop of Henle is not permeable to water Here, salt (NaCl) is reabsorbed through diffusion (in the lower portion) and active transport (in the upper portion). In the distal convoluted tubule, additional water and salt can be reabsorbed if necessary. Secretion of potassium takes place in the distal tubules, as well as H+ and some medications/drugs in the proximal and distal tubules Large amounts of water are reabsorbed in the collecting ducts (as it travels deeper into the salty medulla) and filtrate is concentrated into urine