Capillaries 1 Flashcards
Why do we need to transport solutes and fluids
Metabolism creates a need to transport solutes and fluids. This is in order to supply the body with
oxygen, nutrients, maintain electrolyte balance, and allow hormones to access different cells
amongst other requirements.
Where are the metabolites in the body found
These metabolites is found in a water solution that can be intracellular
(majority) or extracellular fluid.
What can the extracellular fluid be
Extracellular fluid can be interstitial fluid or the fluid in the circulatory
system (plasma) that both have similar compositions. Movement is partly facilitated by concentration
gradients that are generated by metabolism, as well as the membrane barriers to this movement.
What molecules can diffuse through the membrane
Smaller uncharged molecules like oxygen and carbon
dioxide can diffuse across the membrane directly.
Give a mechanism that the cell membrane is involved in
The cell membrane provides support and
protection to the cell and is a way cells recognise each other (e.g. for immunity). It controls what
enters and what leaves the cell thus regulating its function.
As mentioned above, cell membranes selectively facilitate movement through them. This transport
can be active or passive.
What is passive transport
Passive transport is movement of molecules down a gradient that can be
concentration (diffusion), pressure (convection), osmotic (osmosis) or electrical (electrochemical flux)
dependant. This means this process does not require energy. The passive diffusion can be simple
(generally smaller molecules like water and carbon dioxide) or facilitated (generally larger molecules
like ions and glucose).
What is active transport and give examples
Active transport is generally the movement of molecules against a
concentration gradient and is generally used to create a concentration gradient for different
purposes (e.g. ATPase pumps, endocytosis and exocytosis). This process requires energy that is
usually found in the form of ATP.
Where does solute and fluid exchange happen in the body
Solute and fluid exchange in the body occurs at capillaries that are blood vessels of the finest
diameter.
Why are capillaries important
They connect terminal arterioles to venules with every cell of the body reasonably close to
one (especially highly metabolically active cells like brain cells).
Give examples of solute exchange - what exchange is this
Solute exchange occurs across the
capillaries with the molecules involved including oxygen, glucose, amino acids, hormones and drugs.
This movement is facilitated by simple diffusion.
How does the fluid itself move with the solutes and what facilitates this
The fluid itself can move along with the solutes it
contains in bulk movement. This movement is facilitated by pressure gradients that can move
interstitial fluid into plasma or vice versa.
Why is the movement of fluid essential
This movement of fluid is essential to maintaining blood
(maintains blood pressure) and tissue volumes.
What determines the rate of solute transport 3 points
The rate of solute transport is determined by the properties of passive diffusion.
This is dependent
on concentration gradients, distance and rate of movement.
The physical properties of the solutes
involved also determine the rate of solute transport (e.g. Fick’s law) as well as
the properties of the
capillaries across which the movement takes place.
What is passive diffusion based on - when is this suitable
Passive diffusion does not require energy but is
based on the random movement of molecules. The general trend of this movement is that molecules
will move from an area of high to low concentration. This movement is suitable over short distances,
a reason why capillaries cannot be too far from any cells of the body.
Why is passive diffusion suitable across short distances
The reason why this movement
is suitable to short distances only is because it is proportional to the square of time (i.e. time will
increase exponentially with distance). This is why small animals can rely on diffusion whilst larger
animals require a specialised circulatory system.
How is solute transport affected
Solute transport is also affected by properties of the
solute. The concentration gradient will affect the movement (as mentioned before) as well as the size
and lipid solubility (lipophilic or lipophobic) of the solute. Properties of the membrane itself also
affect the movement. Its thickness and composition will affect the movement (e.g. presence of
aqueous pores or channels).
What affects carrier transport
The availability of carriers will also affect active or carrier-mediated
transport.
What does ficks law consider
Fick’s law considers the properties of solutes and membranes affecting transport to
calculate a predicted amount of substance that is transported across a membrane per unit of time mass/unit time or m/t in Js).
What 4 factors affects the amount of substance transported calculated by ficks law
According to Fick’s law, this is determined by 4 factors;
the ease of
movement through the solvent (D),
the surface area for diffusion (A),
the concentration gradient (ΔC)
and the distance (x) (Js = - D A ΔC/x).
In terms of capillaries, this movement across membranes is from inside the capillary through the
walls of the capillary into the interstitial fluid.
What are the three types of capillary
There are broadly 3 types of capillaries in terms of
structure; continuous (upper right), fenestrated (middle right) and discontinuous (lower right).
What is the most and least permeable type of capillary
Discontinuous capillaries are the most permeable type whilst continuous capillaries are the least
permeable type.
What are most capillaries
Most capillaries are continuous. These have moderate permeability dependant on
tight gaps between neighbouring cells and a constant basement membrane.
What is movement across the capillary
Movement across this
capillary can be transcellular or paracellular. However, due to tight junctions between the cells,
paracellular movement is restricted.
Where are junctions between cells and movement restricted
The tightest gaps are found in the brain and this is the basis
behind the blood brain barrier (tightly regulates movement of plasma and interstitial fluid of the
brain).
