Capillaries I: Solute Exchange Flashcards
Describe the structure of the cell membrane
- Consists of two layers of amphipathic phospholipids.
- Phosphate head is polar (hydrophilic).
- Fatty acid tails is non-polar (hydrophobic).
- Form bilayers in solution.
List functions of the cell membrane
- Provide support and protection
- Cell-to-cell recognition – eg. immune system
- Controls what enters or leaves the cell – e.g. ion movement in nerves
- Regulates cell function – eg. Insulin-mediated glucose uptake
Describe Passive transport
- Movement of molecules DOWN a gradient
- Concentration / Pressure / Osmotic / Electrical
- Does not require energy
- Simple (O2/CO2) or facilitated (ions, glucose)
Describe Active transport
- Movement of molecules AGAINST a gradient
- Requires energy (uses ATP) eg. ATP-dependent pumps, endocytosis, exocytosis
List the different types of passive transport and give examples
- Diffusion Concentration gradient eg. O2 uptake from lungs into blood - Convection Pressure gradient eg. blood flow from heart to blood vessels - Osmosis Osmotic pressure gradient eg. water uptake by cells - Electrochemical flux Electrical and concentration gradient eg. ion flow across cell membranes
Describe Capillaries
- Connect terminal arterioles to venules -
extension of inner lining of arterioles. - Smallest diameter blood vessels endothelium,
- 1 cell thick, semi-permeable.
- Found near every cell in the body but higher
density in highly active tissue (muscles, liver,
heart, kidney, brain etc)
List factors that affect the rate of solute transport
- Properties of passive diffusion
eg. concentration, rate, distance - Properties of solutes and membranes
eg. Fick’s law - Properties of capillaries
affect movement
List the properties of passive diffusion
- Does not require energy (no ATP).
- Molecules move randomly.
- Move from area of high to low concentration.
- Great for transport of lipid-soluble solutes over very short distances, eg. O2, CO2.
Why is passive diffusion good for transporting lipid-soluble solutes over short distances ?
- Time taken (t) for one randomly moving molecule to move a net distance (x) in one specific direction increases with the distance squared
- t = x^2/ 2D
- D = diffusion coefficient for molecule within the medium
eg. D for O2 in water and O2 in air are different
List the properties of solutes affecting transport
- Concentration gradient
- Size of the solute
- Lipid solubility of solute (lipophilic, lipophobic nature)
List the properties of membranes affecting transport
- Membrane thickness/composition
- Aqueous pores in the membrane
- Carrier-mediated transport
- Active transport mechanisms
How do you calculate how much of a substance is transported per time?
Js = -D * A * concentration gradient/ x
D = Diffusion coefficient of solute – ease of movement through solvent
A = Area
ΔC = concentration gradient (C1-C2)
x = distance (between C1 and C2)
*It has a negative value = flowing ‘down’ a concentration gradient
List 3 different types of capillaries
- Continuous capillaries
- Fenestrated capillaries
- Discontinuous capillaries
Describe Continuous capillaries
- Moderate permeability; tight gaps between
neighbouring cells; constant basement membrane - Blood-brain barrier
- Found in muscle, skin, fat, connective tissue
Describe Fenestrated capillaries
- High water permeability, fenestration structures,
modest disruption of membrane - Found in ‘High water turnover’ tissues eg. salivary glands, kidney, synovial joints, anterior eye, choroid plexus (cerebrospinal fluid), gut mucosa
