Lecture 4 Reabsorption and Secretion Flashcards
What percentage of plasma is filtered into the bowman’s capsule from the glomerulus
20%
What happens when carriers maximum transport capacity in exceeded
Excess substrate enters the kidneys
Up to how many mmoles/l will the be absorbed in man before it appears in the urine
10mmoles/l
if plasma glucose os 15mmoles/l how much will be absorbed and how much will be excreted
10 mmoles/l absorbed
5 moles/l secreted
What levels of sulphate and phosphate lead to saturation and excretion
Normal levels
What is the most abundant ion in the ECF
Na+
Where does majority of Na+ ion resorption occur
Proximal tubule
How is Na+ reabsorbed
• Not reabsorbed by a Tm mechanism, but by active transport, which establishes a gradient for Na+ across the tubule wall.
Moves Na+ into blood and K+ into cell to create a gradient for Na+ to passively move into the tubule cells across the luminal surface
Why does the proximal tubule cells brush border have a high permeability to Na+ ions
Enormous surface area offered by the microvilli and larger number of Na+ ion channels
The active transport of Na+ leads to the movement of what other components
Cl- (passie) and H2O (osmosis)
Permeable solutes are reabsorbed by diffusion as the fluid volume in the lumen has decreased
What percentage of urea is absorbed
50%
Remainder stays in tubule
The tubular membrane is impermeable to
Inulin and mannitol
What substances share the same carrier molecule as Na+ (symport)
Glucose
Amino acids
Tubular secretion in the peritubular lumen is important for ___
Elimination of potentially harmful substances
The amount of solute secreted can be calculated by
Amount filtered - amount reabsorbed + amount secreted
What is the normal ECF level of K+
4mmoles/l
What are the consequences of Hyperkalaemia
reduced resting membrane potential of excitable cells and eventually ventricular fibrillation and death
What are the consequences of Hypokalaemia
increase in resting membrane potential hyperpolarise muscle, cardiac cells cardiac arrhythmias and eventually death
What hormone regulates the secretion of K+
Aldosterone
An increase in potassium in ECF stimulates what
Aldosterone release which circulates to the kidneys to stimulate increase in renal tubule cell K+ secretion
