Function Of The Kidneys - Filtration, Reabsorption And Secretion Flashcards
What are the functions of the kidney?
Excrete waste and toxins Regulate blood ionic composition Main blood osmolarity Regulate blood pH Regulate blood pressure Regulate blood glucose Produce hormones
During glomerular filtration which molecules are filtered and which remain in the blood?
Water and low molecular weight molecules are filtered Plasma proteins (and non-protein elements which are bound to them) remain in the blood
What is the equation which related excretion to filtration, reabsorption and secretion?
Excretion = filtration - reabsorption + secretion
What is the term for the bolume of fluid filtered from the glomeruli into the capsule space per unit time?
The glomerular filtration rate
What are the forces influencing the glomerular filtration rate?
Glomerular blood hydrostatic pressure promotes filtration
Blood colloid osmotic pressure and capsular hydrostatic pressure oppose filtration
What is paracellular reabsorption?
A passive process whereby substances pass around tubule epithelial cells via tight junctions and into the interstitial fluid.
What is transcellular reabsorption and how does it occur?
Here reabsorption occurs through tubular cells and into the interstitial fluid. Y active transport, passive diffusion, facilitated transport of cotransport.
What molecules can move by paracellular reabsorption?
Water Calcium Chloride Magnesium Potassium Sodium
Why are some substances removed from the blood by secretion?
Because they are in excess
Because they are harmful substances
To maintain a healthy pH
Where does reabsorption and secretion mainly occur?
The proximal convoluted tubules
Why is the proximal convoluted tubule so highly permeable to water and ions?
Because it has a ‘leaky’ apical membrane on its tubular cells
Approximately how many of the sodium ions in the filtrate are reabsorbed at the proximal convoluted tubule?
Two thirds
By what mechanism is sodium reabsorbed in the proximal convoluted tubule?
Sodium diffuses into the eputhelial cells and is actively pumped out by Na/K-ATPases on the asolateral membrane into the interstitial fluid.
Why is the transport of sodium in the proximal convoluted tubule particularly important?
Because it sets up the electrochemical gradient which drives water reabsorption via osmosis and the reabsorption of other solutes by diffusion
How are nutrients such as glucose, amino acids, lactic acid and water-soluble vitamins reabsorbed in the proximal convoluted tubule?
By facilitated transport with sodium ions
How are bicarbonate ions reabsorbed?
They combine with hydrogen ions to form carbon dioxide and water which can freely pass through the membranes of the tubular cells. Once in the cells they break down into bicarbonate and hydrogen ions again and the bicarbonate ions are transported into the interstitial fluid by sodium/bicarbonate ion transporters.
Which transporter pumps hydrogen ions back into the lumen of the renal tubules so that they can allow the reabsorption of bicarbonate ions?
The hydrogen/sodium ion antiporter
How does the reabsorption of chloride ions help with the reabsorption of other ions?
Chloride ions are negative and so their reabsorption increases the negative charge of the interstitial fluid, and so sets up an electrochemical gradient that allows other positive ions to diffuse into the interstitial fluid
How are small proteins present in the filtrate reabsorbed?
They undergo endocytosis at the apical membrane of the tubule cells and are digested to amino acids which can then be transported across the basolateral membranes of the tubule cells and into the interstitial fluid
Describe the secretion of ammonium ions from the proximal convoluted tubule?
These ions result from the deamination of the amino acid glutamine and then are transported back into the lumen of the tubules bey the hydrogen/sodium ion antiporter which will accept ammonium ions instead of hydrogen ions
Describe the effects of the counter current flows in the loop of Henle.
In the ascending limb there is ion reabsorption without water reabsorption but these ions just sit in the interstitial fluid (because the vasa recta forms hairpin loops)making it hyperosmotic. This hyperosmality drives water reabsorption in the descending limb.
Calcium channels sit on the apical membrane of which part of the renal tubule to assist reabsorption?
The early DCT
Which ions are secreted by the late DCT and collecting tubules of the kidneys?
Potassium ions
Hydrogen ions
Which transport molecule is responsible for the secretion of potassium in the renal tubule?
Na/K-ATPase
