26) The renal system

• The renal system is involved in filtering metabolic waste and excess ions in the blood
• What are all the different functions of the kidney?

  - Removal of metabolic waste

  - Regulation of osmosis

  - Regulation of electrolytes

  - Control pH

  - Blood pressure regulation

  - Hormone productuon

  - Gluconeogenesis
• What are three waste products formed by the renal system?


  1. UREA (by product of protein catabolism when they are hydrolysed to amino acids)

  2. URIC ACID

  3. CREATININE
• Why is it important that blood volume and pressure is regulated in the body?

  - Cell function and metabolism

  - Temperature regulation

  - Electrolyte balance

  - Waste removal

  - Digestion

  - Brain function
• What is osmoregulation?

  The control of solute concentrations and water balance
• What is the osmolarity of blood plasma normally kept at?

  290 to 300 mOsm/L
• What are the Kidneys functions:

  - Filters the blood - filtrate flows into nephron

  - Reabsorbs precious molecules (glucose, amino acids)

  - Secretes waste product/drugs into the urine from the blood

  - Excretes urine
• What are the two different types of nephron?

  - Juxtamedullary nephron

  - Corticol nephron
• What is the macula densa?

  Part of the Juxtamedullary nephron that monitors filtrate osmolarity and blood pressure
• What is the vasa recta?

  Capillary network that supplies blood to the medulla

  • highly permeable to solute and water
  • Form hair pin loops next to the loop of henle
• What are the three basic processes in the nephron?

  1. Glomerular filtration - filtration of water and solutes form blood plasma into the Bowmans capsule

  2. Tubular reabsorption - reabsorption of valuable solutes and water

  3. Tubular secretion -secretion of solutes from blood to tubule
• What are the cell types in the kidney?

  - Epithelial cells

  - Immune cells

  - Renal intersitium

  - Endothelial cells
• Where does the flow of blood occur during ultrafiltration?

  Aorta --> Renal Artery --> Interlobar artery --> afferent arteriole --> glomerular capillaries
• What makes up the ultrafiltration membrane?


  1. Endothelial cells of the capillary

  2. Glycocalyx - negatively charged to repel proteins

  3. Glomerular basement membrane - collagen

  4. Podocytes - specialised epithelial cells
• What is the function of the glomerular basement membrane?

  - Maintains the integrity of the glomerulus

  - Allows water and small molecules through, blood cells and protein stay in the blood
• What are the 8 stages of the nephron?

  1. Renal artery

  2. Glomerulus

  3. Bowmans capsule

  4. PCT

  5. Loop of henle

  7. Distal convoluted tubule

  8. Collecting ducts

  
• What is the function of the proximal convoluted tubule?

  Reabsorption of substances back into the bloodstream
• What processes allow reabsorption of solutes:

  - Diffusion

  - Active transport

  - Facilitated co-transport

  
• How does co-transport occur in the proximal convoluted tubule?

  1. Sodium moves down its concentration gradient through a glucose co-transporter

  2. Uses the energy to move glucose with it against its concentration gradient

  3. Glucose leaves the cell via glucose channels (passive diffusion)

  4. Many solutes (eg amino acids) are reabsorbed with the help of sodium in the PCT

  5. Sodium increases in the cell and needs to be pumped out via Na+/ K+ pumps

  6. Sodium moves against its concentration gradient into the interstitium needing ATP

  7. Keeps intracellular sodium low and allows movement across the apical surface

  
• What are the three things that the PCT secretes?

  1. Organic acids and bases (eg bile salts)

  2. Hydrogen ions

  3> Drugs/ toxins
• How does the loop of henle work?

  1. THE DESCENDING LIMB

  - The descending limb contains lots of channels called aquaporins

  - Not many ion channels

  - Water leaves by osmosis via the aquaporin channels

  - Reabsorbed into base recta

  - The filtrate increases in conc as it descends

  - Filtrate is same as interstitial fluid

  
  

  2. THE ASCENDING LIMB

  - Not permeable to water (no aquaporins)

  - Has lots of sodium and chloride channels (ATPase)

  - Ions diffuse down conc gradient into interstitial fluid
• What is counter-current multiplication?

  • Using passive exchange of solute and water to generate an osmotic gradient between the descending and ascending limbs of the loop of henle
  • This allows reabsorption of water from the tubular fluid and produce concentrated urine.
• Describe the distal convoluted tubule:

  - Impermeable to water

  - More sodium in the tubular fluid

  - Sodium moves down its conc gradient via various channels ie cotransporters
• What is the distal convoluted tubules response to aldosterone?

  - increase in reabsorption of Na+ and H2O

  - Increased blood volume/ pressure
• What is the distal convoluted tubules response to ADH?

  Increases aquaporins in the collecting duct
• What is osmolarity?

  Concentration of solutes in a solution
• How is the hypothalamus involved in water regulation?

  Osmoreceptors in the hypothalamus monitor the osmolarity of the blood