Capillaries pt 1 Flashcards
Explain how cell membranes are a barrier to solute transport and the properties of it
-consists of two layers of amphipathic phospholipids
-phosphate head is polar (hydrophilic)
-fatty acid tails is non polar (hydrophobic)
-form bilayer in solution
Give the functions of cell membranes
functions:
1) provide support and protection
2) cell to cell recognition
3) controls what enters or leaves the cell
4) regulates cell function
Describe both active and passive transport
passive transport:
-movement of molecules down a gradient
-does not provide energy
-simple or facilitated diffusion
Active transport:
-movement of molecules against a gradient
-requires energy
Explain the 4 passive transport processes
diffusion:
Concentration gradient
Convection:
Pressure gradient
Osmosis:
Osmotic pressure gradient
Electrochemical flux:
Electrical and concentration gradient
Explain the characteristics and properties of capillaries
Capillaries:
-connect terminal arterioles to venules- extension of inner lining of arterioles
-smallest diameter blood vessels endothelium. 1 cell thick and semi permeable
-higher density in highly active tissues
-solute exchange (electrolytes, 02, glucose, amino acids etc)
-fluid exchange along pressure gradients
Why is passive diffusion only through short distances
Time taken (t) for one randomly moving molecule to move a net distance (x) in one specific direction increases with distance squared.
Essentially this means that more distance means more time to diffuse
what is the equation to represent this
T= x2/ 2D
D= distance
X=net distance
describe fick’s law
Fick’s law- properties of solutes and membranes (polarity and thickness) affecting transport.
What are properties of the solute and properties of the membrane
Properties of the solute:
1) concentration gradient
2) size of the solute
3) lipid solubility of solute
Properties of the membrane:
1) membrane thickness
2) aqueous pores in the membrane
3) carrier mediated transport
4) active transport mechanisms
What 4 factors is solute movement affected by
Js= DA x AC/x
D= diffusion coefficient of solute
A=area
AC= concentration gradient (C1-C2)
X= distance (between C1 and C2)
Explain the characteristics of continuous capillaries, fenestrated capillaries and discontinuous capillaries
Continuous Capillaries:
-moderate permeability, tight gaps between neighbouring cells
-present in blood-brain barrier
-muscle, skin, fat, connective tissue
Fenestrated capillaries:
-high water permeability, contains small pores
-‘high water turnover’ tissues
Discontinuous capillaries:
-very large Fenestration (small pores) structures and disrupted membrane
-RBS in liver, spleen and bone marrow
What are 3 structural features of the capillary walls that can influence solute transfer
Three other structural features of the capillary walls can influence solute transfer:
1) intercellular cleft:
10-20nm wide
2) Caveolae and vesicles:
Large pore system
3) Glycocalyx:
-covers endothelium, negatively charged material
Explain the glycocalyx
the glycocalyx:
-the glycocaly is very dynamic and can be broken down and remade.
-the cells can regulate this and these processes are actively researched.
What is the definition of permeability
Permeability- the rate of solute transfer by diffusion across unit area of membrane per unit concentration difference
Explain how a porous membrane interferes with the diffusion of lipid insoluble solute
a porous membrane interferes with the diffusion of lipid insoluble solute in multiple ways:
-reductio in area for diffusion (A)
-increased path length through membrane (x)
-restricted diffusion in pore produces hydrostatic tissue (D)
Give the equation to represent a modification of Fick’s law for a porous membrane
Js= P x Am/ AC
Js= rate of solute transport
P=permeability
Am= surface area of capillary
AC= concentration gradient
Explain control of diffusion rate in blood flow
More blood brings more solutes, increased blood volume means less time for equilibrium to occur across capillaries so slower diffusion
Explain control of diffusion rate if there is a fall in interstitial concentration
during metabolism, more solute is used up so the concentration difference increases.
Metabolism increases blood flow so increased 02 delivery so increased diffusion
Explain control of diffusion rate by the recruitment of capillaries
-dilation of arterioles leads to increased number of capillaries perfused.
-this increases total surface area and shortens diffusion distance between capillary and cell
-increased diffusion
