Solute and Fluid exchange

Hannah Tribe
Flashcards by Hannah Tribe, updated more than 1 year ago
Hannah Tribe
Created by Hannah Tribe about 7 years ago


Degree CVS1 Flashcards on Solute and Fluid exchange, created by Hannah Tribe on 04/27/2014.

Resource summary

Question Answer
Many substances are transported around the body in ______ water
What controls what enters and leaves cells? the membrane
What are the features of passive transport? 1. no energy required 2. down a gradient 3. can be simple or facilitated
name 4 different types of passive transport 1. diffusion (concentration gradient) 2. osmosis 3. convection (pressure gradient) 4. electrochemical flux (electrochemical gradient)
What are the features of active transport? 1. requires energy 2. against the gradient
Name the 3 types of capillaries 1. continuous - no gaps (e.g. BBB) 2. fenestrated - small gaps between cells (v. water permeable, in kidneys) 3. discontinuous - large gaps (e.g. sinusoids in liver, spleen)
What controls rate of solute transport? 1. Passive diffusion 2. Fick's Law 3. Lipid solubility of solute 4. Properties of the membrane 5. Presence of intercellular clefts 6. Glycocalyx
What is the equation for time taken for particles to diffuse a certain distance? t = x^2/2D
what are x and D in that equation? x = distance for particle to move D = diffusion coefficient for that solute in a specific medium
What determines D? 1. size/shape of molecule 2. viscosity of the fluid 3. strength of interactions between solute and solvent
What is Fick's Law? Js (mass movement of solute in certain time) = -D x area x (change in concentration)/x
What properties of the membrane affect solute transport? 1. thickness/composition 2. presence of aqueous pores 3. carrier proteins 4. active transport mechanisms
What is the glycocalyx? A layer covering the endothelium acting like a sieve to block proteins passing through
How can Fick's Law be modified for permeability? Js = -P x Am x change in concentration
What is Am? The actual route taken by a solute through a membrane
What are 4 routes of transport for solutes across a membrane? 1. Transcellular 2. vesicles 3. intercellular 4. aquaporins
What is transcellular transport? Through the cell, via simple diffusion or using carrier proteins/channels
What solutes use vesicles? Large, lipophobic proteins
How can solutes travel intercellularly? 1. through gap junctions (small lipophobic) 2. through fenestrations 3. through large gaps (e.g. in inflammation)
What is flow limiting diffusion? Diffusion is very efficient so only flow affects it
How is diffusion limited by flow in alveoli? If flow is slow, O2 diffuses readily into blood at one end of alveoli, but by the time it reaches the other end, some may have diffused out again.
How can rate of diffusion be increased? 1. increase blood flow 2. recruit capillaries 3. change concentration gradient 4. dilate arterioles to increase no. of perfused capillaries
What does an abnormality in fluid exchange result in? Oedema
What 2 pressures act on capillary walls in both directions? 1. hydrostatic pressures 2. osmotic pressures
What is the hydrostatic pressure? the 'push' of a fluid to leave the area it is in (e.g. move out of the vessel)
What is the overall hydrostatic pressure? (Pc - Pi) = Pressure in capillary pushing outwards minus pressure in interstitial fluid pushing in
What is the osmotic pressure and how is it determined? The pull of water back into an area, due to the pull of large proteins
What is the overall osmotic pressure? (πp - πi) = pull of the proteins in the capillary minus pull from interstitial fluid
Jv = Lp x A x [(Pc-Pi) - σ(πp-πi)] This is Starling's principle of fluid exchange, what do Lp and A represent? Lp = 'hydraulic conductance of epithelium' (how leaky it is) A = wall area
What is σ? It is the reflection coefficient. This is the fraction of the osmotic pressure actually exerted (taking into account proteins that travel through the membrane)
In normal capillaries, what is favoured, filtration or absorption? Filtration
What happens in hypovolaemia? (e.g. haemorrhage) Reabsorption is favoured, so that blood volume can be restored
What is the net filtration pressure? = Pc - [ σ(πp - πi) + Pi] = Pc - 13 (approx)
Where does the fluid which is filtered go? Drains into lymphatics - will be drained back into circulation via left subclavian vein)
The lymphatic system contains _______ and _____ _______ to aid flow against ________. valves, smooth muscle, gravity
How is lymph flow helped by skeletal muscle? Lymph vessels surround skeletal muscle. As muscle contracts, it contracts lymph vessels too, to help its return to the great veins.
What are 5 causes of oedema? 1. Increased Pc 2. Decreased πp 3. Increased πi 4. inflammatory response 5. lymphatic problems
How could Pc be increased? DVT or heart failure causing build up of blood
How could πp be decreased? malnutrition or liver disease which prevents the proteins being taken into blood
What can cause lymphatic problems? 1. obstruction of lymph drainage 2. removal of lymphatics after cancer surgery
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