Capillaries I - Solute Exchange Flashcards
What are the two types of transport in the body?
PASSIVE:
the movement of molecules DOWN a gradient
does not require energy
can be simple (O2, CO2) or facilitated (ions, glucose)
ACTIVE:
the movement of molecules AGAINST a gradient
requires energy (uses ATP)
What are the four passive transport processes (including examples of each)?
DIFFUSION:
has a concentration gradient
eg. O2 uptake from the lungs to the blood
CONVECTION:
has a pressure gradient
eg. blood flow from the heart to the blood vessels
OSMOSIS:
has an osmotic pressure gradient
eg. water uptake by cells
ELECTROCHEMICAL FLUX:
has an electrical and concentration gradient
eg. ion flow through the action potential in a nerve
Where does solute and fluid exchange take place?
It takes place in the capillaries. These vessels connect arterioles to venules - they’re an extension of the inner linings of the arterioles.
They are one cell thick and are semi-permeable.
What controls the rate of solute transport?
properties of passive diffusion (eg. rate, distance, concentration)
properties of solutes and membranes (eg. Fick’s Law)
properties of capillaries (affect movement)
List some properties of passive diffusion.
it doesn’t require energy (ATP)
the molecules move randomly
they move from an area of high concentration to low concentration
it’s great for the transport of lipid-soluble solutes over very short distances (eg. O2, CO2)
It can only be a short distance because the time taken (t) for one randomly moving molecule to move a net distance (x) in one specific direction increases with the distance squared.
Since the time increases exponentially, it’s best used for very short distances.
List some properties of solutes and membranes that affect transport.
PROPERTIES OF SOLUTES:
concentration gradient
size of solute
lipid solubility of the solute (lipophilic or lipophobic)
PROPERTIES OF MEMBRANES:
membrane thickness and composition
aqueous pores in the membrane
carrier-mediated transport
active transport mechanisms
What is Fick’s Law and what does it state?
It describes diffusion ie. the movement of a molecule down the concentration gradient.
It states that the solute movement (mass per unit time) can be determined by four factors:
the diffusion coefficient of the solute (the ease of movement through the solvent)
the area
the concentration gradient (C1 - C2)
the distance (between C1 and C2)
List the three types of capillaries and describe them.
CONTINUOUS CAPILLARIES:
moderate permeability, with tight gaps between neighbouring cells
have a constant basement membrane
found in the blood-brain barrier, muscle, skin, fat, connective tissue
FENESTRATED CAPILLARIES:
high water permeability, with fenestration structures throughout the cells (hence a moderate disruption of the membrane)
found in high water turnover tissues, such as salivary glands, kidneys, synovial joints (filled with synovial fluid), anterior eye, choroid plexus (spinal fluid), gut mucosa
DISCONTINUOUS CAPILLARIES:
very large fenestration structures throughout, and a disrupted basement membrane
found where the movement of RBC’s is required, such as the liver, spleen and bone marrow
List some properties of capillaries that affect transport.
INTERCELLULAR CLEFT:
10-20 nm wide
allows solutes and fluids to move through between the cells
CAVEOLAE AND VESICLES:
large pore system
for the movement of proteins across the membrane
GLYCOCALYX:
a negatively charged material that covers the endothelium, blocking solute permeation and access to transport mechanisms
it’s highly regulated
The glycocalyx is very dynamic and can be broken down and remade as required.
What is permeability, and what is its relation with diffusion?
Permeability is the rate of solute transfer by diffusion across a unit area of membrane per unit concentration difference (ie. how freely a solute crosses a membrane).
A porous membrane interferes with the diffusion of lipid insoluble solutes in multiple ways:
a reduction in the area for diffusion (A)
an increased path length through the membrane (x)
restricted diffusion in the pore produces hydrostatic issues (D)
Which is the dominant route of transport: diffusion or filtration?
Diffusion
What increases diffusion rate?
INCREASED BLOOD FLOW:
- increases solutes in capillaries
FALL IN INTERSTITIAL CONCENTRATION:
- increases the concentration difference
RECRUITMENT OF CAPILLARIES:
- dilation of arterioles leads to an increased number of capillaries perfused
