In addition to the force provided by contraction of the ventricular walls, blood is
also driven by the elastic recoil of the arterial walls.
The highest arterial pressure is called the systolic pressure, and the lowest is
called the diastolic pressure.
Pressure on the blood in the arteries can be further increased by vasoconstriction
Structures that ensure that blood flows in only one direction in the veins, are the
valves. When a vein is subjected to pressure, the result is a pump effect. Veins receive
pressure from the arteries, muscular contractions, and gravity. (para 10-34)
Capillary beds are provided with precapillary sphincters and post-capillary
sphincters. The first can stop the flow of blood into the capillaries. When the
postcapillary sphincters close, more fluid flows into the tissue space. (para 10-37)
As it returns to the trunk, cool venous blood is gradually warmed by the arterial
In general, the lymphatic system is a drainage system that picks up tissue fluids
and returns them to the cardiovascular system. These are picked up in the interstitial
A lymph capillary begins with a blind end.
These capillaries join to form lymphatic vessels.
A major collecting vessel of the lymphatic system is the thoracic duct, which
empties into the deep veins of the neck.
The lymph nodes function as sieves for the lymph passing through them.
The lymphocytes are primarily involved in the immune reactions of the body.
An additional circulatory system is the cerebrospinal fluid system.
Two fluid-filled hollow organs are the eyeball and the inner ear. (para 10-45)
End of Lesson 10