blood vessels

Pericytes- contractile stem cells that can generate new vessels or scar tissue, stabilize the capillary wall, and help control capillary permeability.

Capillary structures

Continuous capillary- (least permeable and most common): abundant in skin, muscles, lungs and CNS.

Continuous capillaries in the body have intercellular clefts between endothelial cell. However, in the brain capillaries and epithelial cells lack intercellular clefts and have tight junctions around their perimeter. (This creates the blood brain barrier)

Fenestrated capillary- (fenstrations aka pores) increase permeability. Occur in areas of active filtration (e.g kidney) Or absorption (e.g small intestine) And areas of endocrine hormones, secretion.

Sinusoid capillaries- (most permeable in limited locations): occur in liver, bone marrow, spleen, and adrenal Medulla. Has large intercellular clefts and fenestrations (pores).

local chemical conditions and arteriolar vasomotor Nerve fibers regulate the amount of blood entering a capillary bed.

Vascular shunt directly connects terminal arterials to post capillary venule via metarteriole and a throughfare channel so blood can bypass capillaries.

precapillary sphincter acts as valve to regulate blood flow into capillary. Controlled by local chemical conditions.