Circulatory lecture notes

Revision as of 22:35, 17 February 2010 by 149.166.10.188 (Talk)

Vasculature

All vessels except capillaries have:
- smooth muscle cells so they can undergo constriction or dilation
- innervation that can control the constriction / dilation.
Veins, in general, have much larger diameters.
The artery has some layers.
- Throughout these layers are elastic fibers.
- The endothelial cells that line the inside of the artery are bunched up so they can expand outward and then spring back forward.
Veins have some layers
- These include the outer and inner layers of smooth muscle.
- There are no elastic fibers.
All three arteries, veins, and capillaries have:
- An endothelial layer, a basement membrane (on which the endothelial layer sits).
Arteries and veins both have:
- Smooth muscle (except that arteries have larger layers of smooth muscle).
Only arteries have:
- Two elastic layers between the smooth muscle and the basement membrane.
- These are important for handling pressure.
Only the veins have:
- One way valves.
In the arteriole, the smooth muscle layer has become very thing.
Veins progress from capillaries as small venules, medium sized venuoles, and veins.

When you have an increased stroke volume, it is handled by the expansion of the arteries.
- As you lose expansion ability, then the whole system pressure is increased, including backward pressure. This will cause problems with the afterload.

Blood pressure measurement:
- Close off artery.
- Release pressure until you hear a sound, this is systolic pressure.
- Release more until you hear nothing, this is the diastolic pressure.

Nature of the wall changes:
- Elasticity decreases, muscle decreases.
Next level is known as the muscular or distributing arteries.
- These can change how much blood gets to the muscles.
- Uses vasoconstriction / dilation.

Resistance to flow is inversely proportional to the radius raised to the fourth power.
Flow is proportional to the pressure divided by the resistance.
Flow is proportional to the pressure times the resistance raised to the fourth power.
Take home: change the radius a little, change the resistance and flow a lot (in opposite directions).

Smalles of these is a single smooth muscle cells surrounding the endothelial lining of the vessel.
Not much bigger than the capillary, but can still change diameter.
There are both neuronal control and small molecule control that can change arteriole flow.
This is where diameter changes will help to direct blood away from the skin if cold.

There are arteriole systems that can bypass the capillaries. When closed it will increase the pressure in the capillaries.

Very thin wall, with a basement membrane.
Very small diameter.
Not all capillaries are the same.
Water, O2, Co2 just diffuse.
There are intercellular clefts and pinocytic vesicles which can be used to move stuff across the membrane.
You can move things across the endothelial membranes.
You can move stuff through fenestrations; these are ares of membrane that do not have cytoplasm behind them that are adjacent to the endothelial cells. Think of them as a window into the extracellular space.
Some capillaries don't let much through, like those in the brain.
Some capillaries let lots thorugh, like the kidney and the intestinal tract.
- There will be more endo and exo cytosis.
- There will be fenestrations.
There are some like the liver, bone, and lymphoid capillaries that have to move stuff.

While there is smooth muscle, there is much less control.
There are thinner walls.
There is less pressure.
61% of the blood in an at rest, healthy person, is found in the systemic venous system.
- Only 18% in systemic arterial system.