test 8 Flashcards
(42 cards)
Filtration rate =
GFR x Plasma concentration
% of filtered load reabsorbed for:
glucose, bicarb, sodium, chloride, potassium
100% - 87.8% reabsorbed
% of filtered load reabsorbed for:
urea and creatinine
Urea : 50% reabsorbed
Creatinin: 0% all excreted
Tubular Reabsorption - Mechanisms
From tubular lumen into tubular cells = Transcellular path
From tubular lumen into tubular interstitial space = Paracellular path
From interior of cell into tubular interstitial space
From interstitial space into peritubular capillary driven by capillary filtration forces (bulk flow)
Ways of primary active transport movement
Na-K ATPase
Hydrogen ATPase
H-K ATPase
Ca ATPase
Ways of secondary active transport movement: Co-transport
Sodium-glucose
Sodium-amino acids
Secondary active transport: Counter-transport
Sodium-hydrogen
Pinocytosis (requires energy)
Proteins – once in cell broken down to component amino acids and amino acids reabsorbed
Passive transport
Osmotic movement of water
Bulk flow into peritubular capillaries
Sodium pumped out of tubular cells
- into the interstitial spaces while potassium is pumped from interstitial spaces into tubular cells
Na-K ATPase on basolateral sides of tubular epithelial cells
Creates membrane potential -70 mV inside of the cell - a decrease in Na inside of the cell causes Na to move from the lumen to inside of the cell
Sodium follows concentration gradient
Tubular lumen into the tubular cells
Affected by concentration AND electrical gradients
Brush border of proximal tubule luminal membrane creates huge surface area for diffusion
Increases rate of
reabsorption => 20x rate of increase
Sodium quickly moves from interstitial fluid into peritubular capillary with
Water
Sodium reabsorption Enhanced by
- other membrane carrier proteins
Co-transport & countertransport proteins
Most movement of Na is
Passive
Glucose Reabsorption - Luminal (part of the cell in contact with luminal fluid)
Co-transport mechanism tied to sodium gradient from tubular lumen to interior of tubular cells
So efficient that usually removes all filtered glucose
- Two luminal transporters – SGLT2 and SGLT1
SGLT2 and SGLT1
90% glucose reabsorbed via SGLT2 in EARLY PART of proximal tubule
10% reabsorbed in LATER PART of proximal tubule via SGLT1
Glucose Reabsorption - Basolateral (part of the cell in contact with the interstitial fluid)
Two basolateral glucose transporters – GLUT2 and GLUT1
Passive facilitated (no energy required) transport down glucose concentration gradient
GLUT2 early stages of proximal tubule with GLUT1 in the later stages
Bulk flow moves glucose from interstitial spaces into the peritubular capillaries
Amino Acid Reabsorption
- Co-transport mechanism tied to sodium gradient from tubular lumen to interior of tubular cells
Pumps amino acids into the cells
So efficient that usually removes all filtered amino acids
Amino acids diffuse out of the cells into the interstitial spaces following gradient created by co-transport
Bulk flow moves the amino acids from interstitial spaces into the peritubular capillaries
Hydrogen Secretion
- Counter-transport mechanism tied to sodium gradient from tubular lumen to interior of tubular cells
Sodium-hydrogen exchanger is located in brush boarder of the luminal membrane
Is there a max amount of transport of solute?
yes
-depend on the type of transport involved
Maximum tubular reabsorption
Those solutes that depend on a specific transport protein for reabsorption (i.e. glucose, amino acids)
Maximum tubular secretion
Those solutes that depend on a specific transport protein for secretion (i.e. creatinine, para-aminohippuric acid)
Gradient-Time transport
Those solutes that are reabsorbed passively (although some solutes that are actively reabsorbed will this response) (i.e. sodium although mainly driven by Na-K ATPase)
Maximum Active Reabsorption
Occurs when tubular load (amount of solute delivered to tubule) exceeds transport capacity of carrier proteins
