Renal System 2 Flashcards
What substances get filtered?
Anything that is small enough to pass the fenestrate and not blocked by the base membrane
-> ions, glucose, amino acids, nucleic acids, urea, vitamins, peptides…
-> too big: proteins (too big and charged blocked by the base membrane), WBCs, RBCs
also, small molecules bound to proteins are not filtered (like Ca2+ or drugs bound to proteins)
Composition of the newly formed urine:
will be the same as in the blood, except the substances that are too big
f.e. concentration of glucose in the blood is the same as in the urine
What are filtration and secretion?
Filtration: Filtered from the glomerular capillary into the lumen
Secretion: Transported directly from the peritubular capillary into the lumen
What are reabsorption and excretion?
Reabsorption: Taken out of the tubules, and taken back to the blood
Excreted: Stays in the tubules (urine) and goes out
What are the rate the blood is filtered and the rate the ultrafiltrate (new urine) is formed, called?
Glomerular filtration rate (GFR) in ml/min
What determines the rate of GFR?
Starling forces: capillary hydrostatic and oncotic pressure
extra capillary hydrostatic pressure (no oncotic? there is no protein in bowman´s space)
Pressure in the glomerulus + Blood flow in the glomerulus
How can the Starling forces be controlled?
By Vasoconstriction and Vasodilation on afferent or efferent end
Constriction on the afferent end -> lowers blood pressure -filtration rate goes down
Dilation on the afferent end -> increases blood pressure -> filtration goes up
Constriction on efferent end -> increase capillary pressure -> increase the filtration rate
Dilation on efferent end -> the filtration goes down
What is the Filtration rate in a healthy adult?
the rate is the volume per time how much filtrate is formed
normal filtration rate: 125 ml/min
What is the filtration load?
filtration load: mass of a substance that gets filtered over time
filtration rate * concentration of substance
How does reabsorption through tubular epithelial cells occur?
Na+ within the tubular epithelial cells is kept low by the Na-K pump that pumps Na out of the cell (needs ATP) -> because Na concentration is low, Na from the tubular lumen (urine) has a strong tendency to enter epithelial cells and thereby also brings in other substances
-> Secondary active transport (Cotransport)
Why is the maximum reabsorption of glucose at 200 mg/dl?
Because there is a maximum amount of glucose transporter to enable reabsorption
(drug target: glucose transporter is blocked to prevent reabsorption and stay in urine to get excreted in diabetes)
