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Physiology 1 > 8) Capillaries 1 > Flashcards

8) Capillaries 1 Flashcards

1
Q

What are solutes in the body?

A
  • These are substances that are dissolved in body fluids (e.g. oxygen or proteins)
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2
Q

What are the two barriers for solutes in the blood?

A
  • The membrane of cells (between intracellular fluid and extracellular fluid)
  • The capillary membrane (between circulating fluid and extracellular fluid)
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3
Q

Why are concentration gradients continually maintained in solute transport?

A
  • It enables solute exchange between circulating fluid, extracellular and intracellular fluid
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4
Q

How are concentration gradients continually maintained in solute transport?

A
  • Metabolism continually maintains concentration gradients as substances are used up or made
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5
Q

Describe the structure of membranes.

A
  • Consist of two amphipathic phospholipids
  • Phosphate heads projecting outward are polar (hydrophilic)
  • Fatty acid tails projecting inward are non-polar (hydrophobic)
  • They form a bilayer
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6
Q

What type of particles can pass through the membrane?

A
  • Non-polar molecules are able to pass through
  • Polar molecules are unable to pass through due to the hydrophobic nature of the membrane. They have to ravel through proteins or transporters
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7
Q

What are the functions of the cell membrane?

A
  • Provide structure and support
  • Cell-to-cell recognition (e.g. immune system)
  • Controls what enters and leaves the cell (e.g. ion movement in nerves)
  • Regulates cell function (e.g. insulin mediated glucose uptake)
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8
Q

What are the two types of transport of solutes?

A
  • Passive: Movement of molecules down a gradient which does not require energy.
  • Active: Movement of molecules against a gradient which does require energy (ATP)
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9
Q

What are the two types of passive diffusion?

A
  • Simple: straightforward diffusion of particles across the membrane
  • Facilitated: substances which require proteins carriers to help with their diffusion as they are unable to carry out simple passive diffusion
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10
Q

What are the different passive transport processes in the body?

A
  • Diffusion: movement of particles down a concentration gradient
  • Convection: movement of particles down a pressure gradient
  • Osmosis: movement of particles down an osmotic pressure gradient (difference in solute concentration between a membrane which the solutes cannot cross)
  • Electrochemical flux: movement of particles down an electrical and concentration gradient
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11
Q

What are capillaries?

A
  • They connect arterioles to venules and are an extension of the arterioles inner lining
  • They are the smallest blood vessels consisting of a thin layer of endothelial cells and connective tissue membranes
  • They form a semi permeable membrane
  • They supply all tissues in the body but are found in higher density near active tissue
  • Solute exchange in the capillaries depends on passive diffusion as well as fluid exchange along pressure gradients
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12
Q

Why is fluid exchange in the capillaries important?

A
  • It regulates plasma and interstitial fluid volumes
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13
Q

What different factors does rate of solute transport depend on?

A
  • Properties of passive diffusion (e.g. concentration, rate, distance)
  • Properties of solutes and membranes (e.g. Fick’s law)
  • Properties of capillaries (affects movement)

All these factors form one concept called the concept of permeability or how easy it is to cross the membrane

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14
Q

What are the characteristics of passive diffusion?

A
  • Does not require energy (ATP)
  • Random movement of particles from an area of high concentration to an area of low concentration
  • Good for transport of lipid-soluble solutes over very short distances
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15
Q

Why is passive diffusion only suitable for short distances?

A
  • For a short increase in distance we have a large increase in time taken
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16
Q

What properties of solute affect transport?

A
  • Concentration gradient
  • Size of the solute
  • Lipid solubility of solute
17
Q

What properties of membranes affect transport?

A
  • Membrane thickness/composition
  • Aqueous pores in the membrane
  • Carrier-mediated transport
  • Active transport mechanisms
18
Q

What is Fick’s Law?

A
  • How much of a substance is transported per unit time
  • Js = -D A (deltaC/x)
    Js : solute movement (mass per unit time)
    D: diffusion coefficient of solute (ease of movement through solvent/cell membrane)
    A: area
    deltaC: Concentration gradient (C1-C2)
    x: distance
    It is negative as it is flowing “down” a concentration gradient
19
Q

What is the structure of capillaries?

A
  • Consists of a single layer of endothelial cells which are enclosed in a basement membrane made up of connective tissue
  • There is also a membrane lining the lumen of the endothelial cells facing the inside
20
Q

What are the two methods of transport out of the capillaries?

A
  • Through the cell by diffusing across the cell membrane, across the cytoplasm and out the other side
  • In between the cells by squeezing between the gaps found around endothelial cells
21
Q

What are the three types of capillaries?

A
  • Continuous
  • Fenestrated
  • Discontinuous
22
Q

Describe the structure of continuous capillaries.

A
  • Moderately permeable with tight gaps between neighbouring cells which restricts movement of solute between cells so movement across cells has to occur
  • They have uninterrupted basement membranes
  • The tightness of gaps can vary between different parts of the body. In the blood-brain we find the tightest gaps between endothelial cells.
23
Q

Describe the structure of fenestrated capillaries?

A
  • They have bigger gaps (fenestrations) between endothelial cells
  • They have some disruption of basement membrane
  • They are found in areas where lots of water is moved (e.g. kidneys) as they have a high water permeability
24
Q

Describe the structure of discontinuous capillaries

A
  • Very large gaps (fenestration) between endothelial cells which allow movement of solutes between the cells
  • They also have very disrupted basement membranes
  • They are found in the transport of RBCs in the liver
25
Q

What are the different structural features of capillaries that can affect solute transfer?

A
  • Intracellular cleft: The gap between endothelial cells. Only accessible by smaller solutes
  • Caveolae and vesicles: Large pore system which uses endocytosis and exocytosis to transport larger solutes across the endothelial cells.
  • Glycocalyx: Covers the luminal (internal) surface of the endothelium which can be formed and reformed. It is negatively charged and blocks solute diffusing out of the lumen. It is highly regulated
26
Q

What is permeability?

A
  • The rate of solute transfer by diffusion across a membrane (how freely a solute crosses a membrane)
  • A porous membrane can interfere with diffusion of insoluble solutes.
  • Factors that affect diffusion are grouped into one term called permeability
27
Q

What is Fick’s Law for a porous membrane?

A
  • Js = -P Am delta C

Js: Rate of solute transport
P: Permeability (involving pore size, length and diffusion coefficient)
Am: Surface area of capillary involved
deltaC: Concentration gradient

28
Q

What are the family of transporters that transport glucose?

A
  • GLUT transporters
29
Q

What is filtration?

A
  • Filtration is the bulk movement of water and its dissolved solutes.
  • Filtration occurs through pores such as gaps or fenestrations.
30
Q

What is the dominant route of transport for glucose?

A
  • Majority of glucose is transported into interstitial space via passive diffusion through GLUT transporters
  • A small minority of glucose is filtered
31
Q

How do we control the rate of diffusion?

A
  • Blood flow: More blood means more solutes which replenish the solutes that have been used. This means the concentration gradient is regularly maintained and there is less time for equilibrium to occur across capillaries
  • Fall in intestinal concentration: During metabolism more solute is used up which increases the concentration gradient. Metabolism also improves blood flow
  • Recruitment of capillaries: Dilation of arterioles causes an increase in the number of capillaries perfused and hence increases the total surface area for diffusion due to Fick’s law. This also shortens the diffusion distance between the capillary and the cell
32
Q

What is flow limited diffusion?

A
  • Diffusion that occurs where there is slow flow in long capillaries
  • This means there is little diffusion over the rest of the vessel as solutes diffuse at proximal (closer to the arteriole side) sections
33
Q

What is equilibrate mean?

A
  • Equalisation of the concentration gradient

Physiology 1 (64 decks)

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