CVS Different Types of Capillaries, Functions and Solute Movement Flashcards
What are cell memrbanes?
Cell membranes are a barrier to solute transport
What does it mean by semi permeable membrane?
Allow movement of water
What do cell membranes provide?
Provide support and protection
What do cell membranes control?
Controls what enters or leaves the cell – e.g. ion movement in nerves
What do cell membranes regulate?
Regulates cell function – e.g. Insulin-mediated glucose uptake
What layers does the cell membrane consist of?
Consists of two layers of amphipathic
phospholipids
What is the state of phosphate head?
Phosphate head is polar (hydrophilic)
What is the state of fatty acid tail?
Fatty acid tail is non-polar (hydrophobic)
What does a cell membrane form in solution?
Form bilayers in solution
Where does most solute and fluid movement occur?
Most solute and fluid movement occurs at capillaries
How thick is the endothelium of capillaries?
Endothelium only – 1 cell thick
What do capillaries connect?
Vessels that connect arterioles to venules
What is passive movement?
– Movement of molecules DOWN a gradient
Does passive transport require energy?
No
What is active transport?
Movement of molecules AGAINST a gradient
What are the four passive transport processes?
- Diffusion
- Convection
- Osmosis
- Electrochemical flux
How does diffusion work?
Concentration gradient
How does convection work?
Pressure gradient
How does osmosis work?
Osmotic pressure (water) gradient
How does electrochemical flux work?
Electrical and Concentration gradient
e. g. ion flow during an action potential in a nerve
What does convection require?
Requires pressure gradient, functioning heart – appropriate CO etc.
What does osmosis require?
Requires balance of filtration, reabsorption and functioning lymphatics
(see Fluid movement and oedema session)
What does electrochemical flux require?
Requires active and other transport mechanisms to create electrochemical
gradients, needs ion channels to provide ion movement across membranes
What does properties of the solute that affect transport?
-Concentration gradient
-Size of the solute
-Lipid solubility of solute (lipophilic,
lipophobic nature)
What are the properties of the membrane affecting transport?
-Membrane thickness/composition
-Aqueous pores in the membrane
-Carrier-mediated transport
-Active transport mechanisms
What are the 4 factors that determine solute movement?
- D = Diffusion coefficient of solute - how easy it moves through solvent
- Area
- deltaC/x
- x(distance0
Js = - DAdeltaC/x
What are the 3 distinct types of capillaries?
- Continuous capillaries
- Fenestrated capillaries
- Discontinuous capillaries
What are the 3 distinct types of capillaries?
- Continuous capillaries
- Fenestrated capillaries
- Discontinuous capillaries
What is the permeability like for continuous capillaries?
Moderate permeability
How are the gaps like between continuous capillaries?
Tight gaps between neighbouring cells
What type of constant membrane does continuous capillaries have?
Constant basement membrane
What is the permeability like for fenestrated capillaries?
High water permeability
What is the basement membrane like in fenestrated capillaries?
Modest disruption of basement membrane
What structures do discontinuous capillaries have?
Very large fenestration structures
What is the basement membrane
like for discontinuous capillaries?
Disrupted basement membrane
What are the 3 structural features of capillary walls that can influence solute transfer?
- Intercellular cleft
- Glycocalyx
- Caveola-vesicle system
How wide is the intercellular cleft?
10-20 nm wide
What does the glycocalyx cover?
covers endothelium
What does glycocalyx acts as?
acts as sieve for
solute permeation and access to transport mechanisms
What are caveolae and vesicles involved in the movement of?
movement of large molecules,
What processes does glucose transport occur via across membrane from capillaries into tissues?
Glucose transport across membrane from capillaries into tissues
occurs by either passive diffusion or filtration
What is glucose concentration in blood plasma?
Glucose concentration in blood plasma is 1 g / litre
Via what process is the majority of glucose transport into interstitial space?
98% of glucose transport into interstitial space
via passive diffusion
- via GLUT carrier system -
How does increased blood flow increase diffusion rate?
Increases concentration of solutes in capillaries
Less time for equilibration between interstitial spaces and plasma in capillaries
of highly membrane permeable solutes, e.g. O2/CO2
How does a fall in interstitial concentration increase diffusion rate?
Increases the concentration difference
Also, metabolism increases blood flow - metabolic hyperaemia - O2 delivery
How does recruitment of capillaries increase diffusion rate?
Dilation of arterioles - Increased number of capillaries perfused
Increases total surface area A for diffusion (Fick’s law)
Shortens diffusion distance deltax (faster diffusion)
What is permeability?
Permeability is the rate of solute transfer by diffusion
across area of membrane per concentration difference
