CVS: Types of Capillaries Flashcards
Where does most solute and fluid movement occur between cells?
Describe these vessels
Capillaries: Semi-permeable vessels that connect arterioles to venules, 1 endothelial cell thick
Controls solute movement (due to passive/active transport, filtration)
Controls fluid movement (due to pa gradients): e.g. regulation of plasma/interstitial/intracellular fluid
What are the 4 passive transport processes?
What factors affect passive transport?
Diffusion: time taken is directly proportional to distance^2.
Convection: needs a pa gradient
Osmosis: Requires balance of filtration, reabsorption and functioning lymphatics
Electrochemical flux: Requires active and other transport mechanisms to create electrochemical gradients, needs ion channels to provide ion movement across membranes
What properties of a solute can affect transport?
- Concentration gradient
- Size of the solute
- Lipid solubility of solute (lipophilic, lipophobic nature)
What properties of a membrane can affect transport?
- Membrane thickness/composition
- Aqueous pores in the membrane which allow substances to move across
- Carrier-mediated transport- eg channel proteins inside the membrane
- Active transport mechanisms- eg ATPases inside the membrane
Describe and explain Ficks Law
Hay 3 types of capillaries: continuous, fenestrated and discontinuous. Describe continuous capillaries
Continuous capillaries:
- Moderate permeability due to tight gaps between neighbouring cells
- Constant basement membrane
- e.g. blood-brain barrier, creates a v controlled environment
Hay 3 types of capillaries: continuous, fenestrated and discontinuous. Describe fenestrated capillaries
Fenestrated capillaries
- High water permeability
- Solute movement is allowed via fenestration structures (protein pores)
- Basement membrane is broken down and disrupted in some areas only
- Found in places where u need ‘high water turnover’- eg salivary glands, kidney, synovial joints, choroid plexus (cerebrospinal fluid)
Hay 3 types of capillaries: continuous, fenestrated and discontinuous. Describe discontinuous capillaries
- V large fenestration structures and disrupted basement membrane.
- This allows water and many solutes to move in and out, so the most permeable type of capillary
- Found when hay que tener movement of cells eg RBCs in liver, spleen, bone marrow
Use this diagram to explain other properties of capillaries which influence transport
Intercellular cleft: 10-20 nm wide gaps which allow easier movement of solutes across
Glycocalyx: covers endothelium, -ve charged material, acts as sieve for solute permeation and access to transport mechanisms, highly regulated
Caveolae and vesicles: movement of large molecules, e.g. plasma proteins, lipoproteins
What controls diffusion rate?
Increased blood flow increases conc of solutes in capillaries, which increases diff rate, esp for highly membrane permeable solutes, e.g. O2/CO2.
Dilation of arterioles to increase blood flow increases number of capillaries perfused. This increases total SA for diffusion (Fick’s law). Shortens diffusion distance
Fall in interstitial conc (more solute used, metabolism) increases conc difference. Also, metabolism increases blood flow - metabolic hyperaemia increases O2 delivery
What is permeability, and how can we modify Fick’s law to suit it?
All factors affecting diffusion (pores, reduction in area/distance etc) go into one term - permeability (P). Permeability is’how freely a solute crosses a membrane by diffusion’
