Solute exchange Flashcards
What does the membrane consist of?
Consists of two layers of amphipathic phospholipids
Phosphate head is polar (hydrophilic)
Fatty acid tail is non-polar (hydrophobic)
Form bilayers in solution
What does the cell membrane provide?
Provide support and protection
What is passive transport?
Movement of molecules DOWN a gradient
Does passive transport require energy?
No
What is active transport?
Movement of molecules AGAINST a gradient
Does active transport require energy?
Yes
Passive transport processes(Diffusion)
Concentration gradient
E.g. O2 uptake from lungs into blood
Passive transport processes(Convection)
Pressure gradient
E.g. Blood flow from heart to blood vessels
Passive transport processes(Osmosis)
Osmotic pressure gradient
E.g. Water uptake by cells
Passive transport processes(Electrochemical flux)
Electrical and concentration gradient
E.g. ion flow during an action potential in a nerve
What do capillaries connect?
Connect terminal arterioles to venules
How big are capillaries?
Smallest diameter blood vessels endothelium
1 cell thick, semi-permeable
Where are capillaries found?
Found near every cell in the body
Where is there a higher density of capillaries?
However there is a higher density in highly active tissues (muscles, liver, heart, kidney, brain etc.)
How does blood flow in capillaries?
Fluid exchange (flow down pressure gradients)
Why is diffusion great for transport across 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
What properties of the solute affect transport?
Concentration gradient
Size of the solute
Lipid solubility of solute (lipophilic, lipophobic nature)
What Properties of the membrane affect transport?
Membrane thickness/composition
Aqueous pores in the membrane
Carrier-mediated transport
Active transport mechanisms
Comment on permeability of continuous capillaries
Moderate permeability; tight gaps between neighbouring cells; constant basement membrane
Examples of where continuous capillaries can be found
Blood-brain barrier
Muscle, skin, fat, connective tissue
Comment on permeability of fenestrated capillairies
High water permeability, fenestration structures, modest disruption of membrane
Where are fenestrated capillaries found?
“High water turnover” tissues – e.g. salivary glands, kidney, synovial joints, anterior eye, choroid plexus (cerebrospinal fluid), gut mucosa
What are discontinuous capillaries?
Very large fenestration structures, disrupted membrane
What are three other structural features of capillary walls that influence solute transfer?
Intracellular cleft
Caveolae and vesicles
Glycocalyx
How wide is the intracellular cleft?
10-20nm
What type of system are caveolae and vesicles?
Large pore system
What does glycocalyx cover?
Covers endothelium, negatively charged material
What does glycocalyx block?
Blocks solute permeation and access to transport mechanism
How is glycocalyx regulated?
Highly regulated
Comment on glycocalyx?
It is very dynamic and can be broken down and remade as required
What is permeability?
Permeability is the rate of solute transfer by diffusion across unit are of membrane per unit concentration difference
How does a porous membrane interfere with diffusion of lipid insoluble solute?
A porous membrane interferes with the diffusion of lipid insoluble solute in multiple ways
Reduction in area for diffusion (A)
Increased path length through membrane (x)
Restricted diffusion in pore produces hydrostatic issues (D)
All factors affecting diffusion go into one term – Permeability (P)
What is filtration?
Filtration is going through pores, gaps and fenestrations
What is glucose concentration in plasma?
Glucose concentration in plasma is 1g/litres
What does more blood bring?
More blood brings more solutes
What does increased blood volume mean?
Increased blood volume means less time for equilibration to occur across capillaries
What is flow limited diffusion?
Where there is slow flow in a long capillary
When can flow limited diffusion occur?
Sometime this can occur in sepsis where the blood pressure and flow are low
This can lead to ischaemia
What may cause a fall in interstitial concentration?
During metabolism, more solute is used up thereby increased the concentration difference
What does metabolism increase?
Also, metabolism increases blood flow – there is increased O2 delivery, which is controlled by the arterioles
What does a dilation of arterioles lead to?
Dilation of arterioles leads to increased number of capillaries that are perfused which increases total surface area (A) for diffusion (Fick’s Law)
What does perfusion of capillaries lead to?
shortens diffusion distance between capillary and the cell
What happens during strenuous exercise?
O2 transport from blood to the muscle increases over 40 times
We increase cardiac output (blood flow), use more O2 (fall in tissue concentration) and open up more capillaries (recruitment)
