Vanders Renal Ch4 Flashcards
What are the major morphological components of epithelial tissue?
Lumen, interstitium, apical and basolateral membranes, tight junctions
What is active transcellular reabsorption?
A process where transport mechanisms combine to move substances across epithelial tissues
Define iso-osmotic transport.
Transport where the osmotic pressure of the solute solution remains constant
What is paracellular transport?
Transport that occurs around cells through tight junctions
Differentiate between transcellular and paracellular transport.
Transcellular transport occurs through cells, while paracellular transport occurs around cells
Define channel.
A protein that forms a pore allowing specific solutes to diffuse through
Define transporter.
A protein that binds solutes and undergoes conformational changes to move them across membranes
What is a uniporter?
A transporter that moves a single solute species across a membrane
What is a multiporter?
A transporter that moves two or more solute species across a membrane
What is a symporter?
A multiporter that moves solutes in the same direction
What is an antiporter?
A multiporter that moves solutes in opposite directions
Describe the role of Na-K-ATPase in volume reabsorption in the proximal tubule.
It helps maintain sodium gradients essential for reabsorption
What determines the movement of reabsorbed fluid from the interstitium into peritubular capillaries?
Forces such as hydrostatic pressure and osmotic pressure
Compare Starling forces in glomerular filtration and peritubular capillary absorption.
Glomerular filtration is influenced by capillary hydrostatic pressure, while peritubular absorption is influenced by oncotic pressure
What are Tm and gradient-limited transport?
Tm is the transport maximum; gradient-limited transport occurs when transport rates are limited by concentration gradients
What is diffusion?
The random movement of molecules from an area of higher concentration to lower concentration
How do channels facilitate movement?
By allowing specific solutes to diffuse through them passively
What are aquaporins?
Channels that facilitate the diffusion of water across membranes
What regulates the permeability of channels?
Environmental factors and signaling pathways
What are the three mechanisms for regulating channel and transporter activity?
- Shuttling between membrane and vesicles
- Phosphorylation effects
- Changes in genomic expression
What is facilitated diffusion?
Movement of a solute through a uniporter driven by concentration gradients
What is secondary active transport?
Transport that uses the energy from the movement of one solute down its gradient to move another solute up its gradient
What is primary active transport?
Transport that moves solutes up their electrochemical gradients using ATP hydrolysis
What is the function of the Na-K-ATPase?
To move sodium out of the cell and potassium into the cell against their gradients
What is the primary function of ATPases?
ATPases split ATP to transport solutes across membranes
ATPases have binding sites that alternate between open sides of the membrane.
What is the stoichiometry of the Na-K-ATPase?
Three sodium ions out and two potassium ions in per ATP hydrolyzed
This process is essential for maintaining electrochemical gradients in cells.
What is the role of H-ATPases in cellular transport?
H-ATPases move protons out of cells
They play a critical role in regulating pH.
What do Ca-ATPases transport?
Calcium out of cells
This is important for various cellular functions including muscle contraction.
What are multidrug resistance proteins (MDR)?
Transporters that remove therapeutic drugs from cells
They are also known as ATP-binding cassette proteins.
What is receptor-mediated endocytosis?
A process where a solute binds to a receptor on a cell surface, leading to internalization
This process allows cells to take in specific proteins.
Define transcytosis.
The transport of substances across a cell, remaining intact
Important for immune functions in the kidney.
What is osmosis?
The movement of water from areas of low solute concentration to high solute concentration
This process is driven by the concentration gradient of solutes.
What are osmoles?
Dissolved solutes that displace water
One mole of any dissolved solute is one osmole.
How is osmolarity defined?
The number of osmoles per liter of solution
Commonly expressed in milliunits (mOsm/L).
What is the difference between osmolarity and osmolality?
Osmolarity is per liter of solution; osmolality is per kilogram of water
Values for both are nearly the same in dilute solutions.
What does osmotic pressure theoretically represent?
The pressure needed to prevent water movement by osmosis across a semipermeable barrier
It is numerically equal to real osmolality expressed in pressure units.
What drives water movement across semipermeable barriers?
Osmotic gradients created by solute concentration differences
Water moves towards the solution with higher osmolality.
What is colloid osmotic pressure?
Osmotic pressure due to plasma proteins in the blood
It affects fluid movement across capillary membranes.
What is iso-osmotic reabsorption?
Reabsorption of water and solutes in equal proportions
Occurs primarily in the proximal tubule.
What is the significance of sodium in renal physiology?
Sodium accounts for nearly half of the total solute load in glomerular filtrate
It drives the reabsorption of water and anions.
What is the main mechanism of sodium entry into proximal tubule cells?
Sodium-proton antiporter (NHE3 isoform)
This is a key regulator of sodium excretion.
What happens when water is reabsorbed in the proximal tubule?
Remaining solutes become concentrated
This concentration gradient drives further reabsorption.
What are the steps in sodium and water transport in the proximal tubule?
- Active extrusion of sodium
- Passive entrance of sodium
- Movement of anions
- Osmotic flow of water
- Bulk flow into peritubular capillary
Each step is crucial for maintaining fluid and electrolyte balance.
What happens to solute concentration when two-thirds of water is removed from the lumen?
Increases by a factor of 3
This concentration increase generates a gradient across the tight junctions.
What is the role of tight junctions in solute transport?
Determine permeability to substances
Tight junctions can be leaky or impermeable, affecting solute movement.
What is a key characteristic of gradient-limited systems?
Luminal concentration remains close to interstitial concentration
This occurs due to back leak of substances like sodium.
What are Tm-limited systems characterized by?
Transport rate limited by capacity of transporters
Transporters can become saturated, affecting reabsorption.
What is osmotic diuresis?
Increased urine flow due to high amounts of unreabsorbed solutes
Examples include mannitol and high plasma glucose.
How do kidneys move solutes across membranes?
By multiple transport mechanisms including channels, uniporters, multiporters, and primary active transporters
What drives the movement of water across epithelial barriers?
Osmotic gradients
Water moves from regions of lower to higher osmolality.
What does volume reabsorption involve?
Transport across epithelial membranes and bulk flow driven by Starling forces
What is the effect of water reabsorption on tubular solutes?
Concentrates remaining tubular solutes
This increases the driving force for passive reabsorption.
What limits reabsorptive processes in the kidneys?
Substance back leak (gradient-limited) or transporter saturation (Tm systems)
How much water is approximately reabsorbed when 100 mmol of solutes are reabsorbed iso-osmotically from the proximal tubule?
300 mL
How does most sodium enter proximal tubule cells?
Transcellular diffusion
What do tight junctions in proximal tubule cells permit?
No filtered solutes
They are impermeable to glucose and other solutes.
Where can water move in the proximal tubule?
All of these
Water moves through apical membranes, basolateral membranes, and tight junctions.
What does the secretion of drug X by a Tm-limited system imply?
X cannot easily diffuse by the paracellular route
What do all multiporters do?
Simultaneously move two or more different solute species
