Capillaries I - Solute exchange Flashcards
What does metabolism create?
→ A need to transport solute and fluids
What do cell membranes consist of?
→ Phosphate head (Polar)
→ Fatty acid tail (non-polar)
What do cell membranes form?
→ Bilayers in solution
What are the functions of cell membranes?
→ Provide support and protection
→ Cell-to-cell recognition
→Controls what enters and leaves the cell
→ Regulates cell function
What are properties of Passive transport?
→ Movement of molecules down a gradient
→ Concentration/pressure/osmotic/electrical
→ Does not require energy
→ Simple (O2/CO2) or facilitated (ions/glucose)
What are properties of Active transport?
→Movement of molecules against a gradient
→ Requires energy (uses ATP)
What gradient does diffusion use and give an example
→ concentration gradient
→ O2 uptake from the lungs into the blood
What gradient does convection use and give an example
→Pressure gradient
→ blood flow from heart to blood vessels
What gradient does osmosis use and give an example
→ Osmotic pressure gradient
→ Water uptake by cells
What gradient does electrochemical flux use and give an example
→ Electrical and concentration gradient
→ Ion flow during an action potential in a nerve
Where does solute and fluid exchange occur?
→ At capillaries
What do capillaries connect?
→ Connect terminal arterioles to venules
→ Extension of inner lining of an arteriole
How thick are capillaries?
→ 1 cell thick
Where are capillaries found?
→ found near every cell in the body
→higher density in highly active tissues (muscles, liver, heart, kidneys, brain)
What is the function of capillaries?
→ Solute exchange
→ Fluid exchange
→ Regulation of plasma and interstitial fluid
What controls the rate of solute transport?
→Properties of passive diffusion
→Properties of solutes and membranes
→ Properties of capillaries
What are properties of passive diffusion?
→Does not require any energy
→ molecules move randomly
→ Move from areas of high to low concentrations
→ transport of lipid soluble solutes over short distances
What are properties of the solute that affect transport?
→ Concentration gradient
→ size of solute
→ Lipid solubility of solute
What are properties of the membrane that affect transport?
→ Membrane thickness/ composition
→ Aqueous pores in the membrane
→ Carrier mediated transport
→ Active transport mechanisms
What is Fick’s law?
→solute movement (mass per unit time) can be determined by four factors:
→the diffusion coefficient of the solute (the ease of movement through the solvent)
→the area
→the concentration gradient (C1 - C2)
→ the distance (between C1 and C2)
What value does Fick’s law have down a concentration gradient?
→ a negative value
What are the three types of capillaries?
→ Continuous capillaries
→ Fenestrated capillaries
→ Discontinuous capillaries
What are properties of continuous capillaries?
→Moderate permeability
→Tight gaps between neighboring cells
→ constant basement membrane
What are properties of fenestrated capillaries?
→ High water permeability
→ Fenestration structures
→ modest disruption of the membrane
Where are fenestrated capillaries found?
→ in high water turnover tissues
→ salivary glands, kidneys, synovial joints, anterior eye, choroid plexus, gut mucosa
Where are continuous capillaries found?
→ blood-brain barrier
→ Muscle, skin, fat, connective tissue
What are properties of discontinuous capillaries?
→ Very large fenestration structures
→ disrupted membrane
Where are discontinuous capillaries found?
→ When the movement of cells is needed
→ RBCs in liver, spleen + bone marrow
How wide is the intercellular cleft?
→ 10-20nm wide
What are the caveolae + vesicles?
→ large pore systems
What is the glycocalyx?
→ Covers the endothelium
→ -vely charged
→ Blocks solute permeation and access to transport mechanism
→ highly regulated
→ dynamic and can be broken down and remade as required
What is permeability?
→ Permeability is the rate of solute transfer by diffusion across a unit area of membrane per unit concentration difference
(ie. how freely a solute crosses a membrane).
How does a porous membrane interfere with the diffusion of lipid insoluble solutes?
→ a reduction in the area for diffusion (A)
→an increased path length through the membrane (x)
→ restricted diffusion in the pore produces hydrostatic issues (D)
What is filtration?
→going through gaps, pores and fenestrations
→ as fluid moves through the dissolved glucose goes with it
What is the glucose concentration in plasma?
→ 1g/liter
What is the total volume of plasma filtrate flowing into tissues per day?
→ 8 liters
What is the maximum filtration of glucose per day?
→ 8g/day
What does filtration transport account for?
→ 2% of glucose transport
How does 98% of glucose get transported?
→ into the interstitial space via passive diffusion
→ via GLUT transporter
How does blood flow control diffusion rate?
→More blood brings more solutes
→ Increased blood volume means less time for equilibration to occur across capillaries
What is flow limited diffusion?
→ slow flow in a long capillary
→ O2/CO2 equilibrate over the proximal section and there is little diffusion across the rest of the vessel
When can flow limited diffusion occur and what can this lead to ?
→ In sepsis when blood pressure and flow are low
→ can lead to ischaemia
How can a fall in interstitial concentration affect diffusion rate?
→More solute is used up
→ increases the concentration difference
→metabolism increases blood flow
→Increased O2 delivery controlled by arterioles
How can recruitment of capillaries affect diffusion rate?
→ Dilation of arterioles leads to more perfused capillaries
→ Increases total SA for Fick’s Law
→ Shortens diffusion distance between capillary and cell
During strenuous exercise how much does O2 transport to the muscle increase by?
40x
