Capillaries I Flashcards
What does metabolism create?
→ A need to transport solute and fluids
a need for gaseous and nutrient exchange.
The metabolism going on in cells is generating concentration gradients that facilitate this movement
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)
Facilitated is where a transporter or channel is required but no external energy the movement is still due to a gradient. Same with the GLUT transporters.
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
pO2 within the lungs versus bound O2 in 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
eg. K+ is high in the cell so will diffuse out of cell due to concentration gradient
The concentration gradient is stronger than the electrical gradient that will draw K+ into the cell so there is net change
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
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 eg. eg. concentration, rate- rate at which a substance can move in the medium, distance
→Properties of solutes and membranes eg. Fick’s Law
→ 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
Depends on molecules moving randomly
What are properties of the solute that affect transport?
→ Concentration gradient
→ size of solute
→ Lipid solubility of solute- lipids tend to cross quickly
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-
flowing ‘down’ a concentration gradient
What are the three types of capillaries?
→ Continuous capillaries
→ Fenestrated capillaries
→ Discontinuous capillaries
What are properties of continuous capillaries?
→Moderate permeability
→Tight gaps between neighbouring cells- so most movement is through diffusion between cells
→ constant basement membrane
What are properties of fenestrated capillaries?
→ High water permeability
→ Fenestration structures
→ modest disruption of the membrane
→‘High water turnover’ tissues eg. salivary glands, kidney, synovial joints, anterior eye, choroid plexus (cerebrospinal fluid), gut mucosa
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
incredibly leaky so large molecules and some cells such as rbc and immune cells out.
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
so large protein molecules can’t pass through
What are the caveolae + vesicles?
→ large pore systems
What is the glycocalyx?
→ Covers the endothelium
→ -vely charged carbohydrate carbohydrate
→ Blocks solute permeation and access to transport mechanism
→ highly regulated- acts as additional barrier
→ 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
maintains interstitial fluid
How does 98% of glucose get transported?
into the interstitial space via passive diffusion
→ via GLUT transporter by passive diffusion because capillaries permeate every part of the body
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
By having more capillaries, it means more tissues are not far from diffusion
During strenuous exercise how much does O2 transport to the muscle increase by?
40x
What is the equation for
X^2/2D
D= coefficient. The diffusion coefficient is different for different media as the solute moves differently in different media
x=distance
t= time taken for molecule to move a net distance
How do large lipophobic proteins, lipophilic, and small lipophobic glucose travel across membrane?
Large lipophobic proteins= big gaps in inflammation, transcellular and vesicles
Lipophilic= transcellular
small lipophobic, glucose= intercellular, intracellular
water= fenestral route, water channels
What is pericyte?
are multi-functional mural cells of the microcirculation that wrap around the endothelial cells that line the capillaries and venules throughout the body.
Pericytes are embedded in basement membrane, where they communicate with endothelial cells
What are the capillary layers?
lamina densa
lamina rara
