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Description
Flashcards by Hannah Tribe, updated more than 1 year ago
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Created by Hannah Tribe
almost 10 years ago
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| 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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