الريفي
18/05/03, 04 :58 04:58:53 AM
The capillaries are small vessels, usually consisting of single endothelial.At times the capillaries seem capable of holding several red blood cells transversely, at other imes the red blood cells appear to pass singly through the capillaries. In a given capillary bed ,there is frequently a stasis of flow in some capillaries and the same time thereis anactive flow in other capillaries. This periodic flow ththrough different capillary beds is thought to have a normal physiological function of increasing nutrition in these areas. Under condition of maximal flow ,the entier capllary may be maximally dilated. Under normal flow conditions ,there may besome gravitational layering of red blood cells, white blood cells, and plasma in the capillaries. Under certain condition , such as acute stress , shock or toxemia, or uncontrolled diabetes, there may be a sludging or congregation of red blood cells in the capillaries. The normal capillary pressure in the systemic circulation is estimated to be approximately 25 mmHg. In contrast , the normal pulmonary capillary pressure is 7 to 10 mmHg. It is estimatedthat the systemic capillary bed, under basal resting condition, has a volume of approximately 5 percent of the total bloodd volume........