Capillaries I Flashcards
Why are cell membranes a barrier to solute transport
Difficult to get solutes across hydrophobic centre of the membrane
What controls the rate of solute transport
Properties of passive diffusion, properties of solutes and membranes, and properties of capillaries
What properties of the solute affect transport
Concentration gradient, size of the solute, lipid solubility of solute
What properties of the membrane affect transport
Membrane thickness/composition, aqueous pores in the membrane, carrier-mediated transport, active transport mechanisms
Describe continuous capillaries
Moderate permeability, tight gaps between neighbouring cells
Blood-brain barrier
Muscle, skin, fat, connective tissue
Describe fenestrated capillaries
High water permeability, fenestration structures, modest disruption of membrane
High water turnover tissues e.g. salivary glands, kidney, synovial joints, anterior eye
Describe discontinuous capillaries
Very large fenestration structures, disrupted membrane
When movement of cells is required; RBCs in liver, spleen, bone marrow
What is an intercellular cleft
In between adjacent capillaries, allows solutes and fluids to move through the cells
What are caveolae and vesicles
Substances taken up on one side of the membrane and moved to the other side, from lumen to interstitial space.
What is the glycocalyx
Charged carbohydrate medium at top of endothelial cells. Can be broken down and remade. Blocks solute permeation and access to transport mechanism
What is permability
Rate of solute transfer by diffusion across unit area of membrane per unit concentration difference
Fick’s law for a porous membrane
Js = - P Am deltaC
How does blood flow control diffusion rate
More blood -> More solutes. Increased blood volume means less time for equilibration to occur across capillaries.
How does fall in interstitial concentration control diffusion rate
During metabolism, more solute used up, increasing conc difference. Metabolism also increases blood flow, so more oxygen delivered controlled by arterioles.
How does recruitment of capillaries control diffusion rate
Dilation of arterioles leads to increased number of capillaries perfused which increases total surface area A for diffusion. Shortens diffusion distance between capillary and cell.
