Lecture 26: Microcirculation I and II Flashcards
Microcirculation
Refers to the functions of the smallest blood vessels, capillaries, and neighboring lymphatic vessels
Two functions of microcirculation
- Exchange of nutrients and waste products in the tissue
2. Site of fluid exchange between vascular and interstitial compartments
Blood is delivered to the capillary bed via
arterioles
The degree of constriction or relaxation of the smooth muscle of the arterioles markedly affects
blood flow to the capillaries
Pre-capillary sphincters
Precede some capillaries and help to regulate blood flow
Structure of capillaries
Thin walled and are composed of a single layer of endothelial cells
Capillary pores
- Present between cell junctions
- Permit passage of water soluble substances
What can pass through the lipid bilayer
Lipid soluble substances like O2 and CO2
What must be transported by vesicular transport?
Large molecules such as protein hormones
Three types of capillaries
- Continuous
- Fenestrated
- Sinusoid
Where are continuous capillaries found
Most regions of the body
Fenestrated capillary structure
Contain pores that permit small molecules to filter through without having to pass between clefts
Fenestrated capillaries are found where
In endocrine organs, the glomerulus of the kidneys, and the absorptive areas of intestinal tract
Sinusoid capillary structure
Gaps between adjacent endothelial cells which permit the free exchange of water and solutes as large as plasma proteins
Sinusoid capillaries are found where?
Liver and bone marrow
Are precapillary sphincters innervated?
Nope
What are precapillary sphincters sensitive to?
Local metabolic changes
Do capillaries actively participate in the regulation of blood flow?
Nope, they have no smooth muscle
When a muscle becomes more active,
a greater percentage of pre-capillary sphincters relax simultaneously, which opens up more capillary beds
Concurrent arteriolar vasodilation increases
Blood flow to organs
As a result of more blood flowing through more open capillaries,
The total volume and sa available for exchange increases and the diffusion distance between the cells and an open capillary decreases
Two things that regulate the blood flow through a particular tissue
- Degree of resistance offered by the arterioles in the organ which is controlled by sympathetic activity and local factors
- Number of open capillaries controlled by the action of the same local metabolites on smooth muscle of terminal arterioles and precapillary sphincters
Capillary exchange is accomplished two ways
- Passive diffusion
2. Bulk flow
Passive diffusion
- Down concentration gradient
- Primary mechanism for exchange of individual solutes