Renal Physiology 1 Flashcards
What are the functions of the kidney?
- excretion of waste products of metabolism and foreign chemicals
- Regulation of water balance, osmolality and electrolytes
- Regulation of arterial pressure
- Regulation of acid base balance
- Secretion, metabolism and excretion of hormones
- Erythropoetin production
- 1-25 di-hydroxy-vitamin D3 production
- Gluconeogenesis
How many litres of filtrate enters the proximal tubules daily?
180L
How thick is the nephron?
1 cell
What are the main processes by which substances are transported in the tubules?
- diffusion
- osmosis
- primary and secondary active transport
What is simple diffusion?
Movement of ions/molecules through a membrane opening or intermolecular space with no interaction with other membrane proteins.
Rate is determined by:
- amount of substance
- velocity of kinetic motion
- size of opening in membrane
What is facilitated diffusion?
Requires a carrier protein, which binds chemically with the substance. It “shuttles” the substance across the membrane, enhancing the rate of diffusion. This process can be modified by hormones or drugs.
Occurs via:
- lipid bilayer, if the substance is lipid soluble
- channels that penetrate large transport proteins
What is osmosis?
When there’s a concentration difference for water across a semi-permeable membrane (permeable to water but not the solute) - net movement of water occurs.
What is primary active transport?
- energy consuming process
- sodium is the key molecule
- Na moved out of tubular cell and across the basolateral membrane by Na/K ATPase pump against it’s electrochemical gradient
- sodium then moves from luminal fluid into the tubular cell down it’s electrochemical gradient
- this releases energy for secondary active transport
What is secondary active transport?
Movement of 2 substances at the same time using a protein carrier.
Uses the gradient created by primary active transport as an energy source.
It can co or counter-transport molecules.
How are substances (water or solutes) transported across the tubular epithelial membrane into interstitial fluid?
Either by transcellular (through the epithelial cell membranes themselves) or paracellular (between tubular cells) by diffusion through tight junctions and lateral intercellular spaces - driven by concentration, osmotic or electrical gradients.
How do water and solutes get from the interstitial fluid to the blood?
Through the peritubular capillary walls - mediated by hydrostatic and colloid osmotic forces
What does the sodium potassium ATPase pump on the basolateral membrane of the tubular cell do?
Pumps 3 sodium ions into the interstitial fluid and 2 potassium ions into the tubular cell.
This creates a net positive gradient outside the cell.
Where does paracellular transport occur?
Across tight junctions and intercellular spaces.
What drives paracellular transport?
Osmotic, electrical and concentration gradients.
What is Fick’s Law?
Rate of diffusion across a membrane is proportional to the concentration gradient across that membrane.
