10-41. COOLING OF ORGANS WITH A HIGH METABOLIC RATE
Certain organs of the body, such as the brain and the liver, have a relatively high
metabolic rate. Because of this, they produce excessive heat. Part of the blood supply
to these organs is specifically designed to remove the excess calories of heat.
10-42. WARMING OF INFLOWING AIR
As blood flows through the arteries of the mucoperiosteum of the nasal
chambers, the inflowing air is warmed.
At the site of an infection or injury, the most common reaction observed is
redness (erythema). This indicates that extra blood and heat are available for healing.
Section VIII. OTHER CIRCULATORY SYSTEMS
10-44. THE LYMPHATIC SYSTEM
In general, the lymphatic system is a drainage system that picks up tissue fluids
and returns them to the cardiovascular system. The tissue fluids are picked up in the
interstitial spaces. They are eventually returned to the veins.
a. Lymphatic Capillaries and Vessels.
(1) Within the tissue spaces, the lymphatic system begins with lymph
capillaries. A lymph capillary begins with a blind end (cul-de-sac).
(2) The capillaries eventually come together to form lymphatic vessels,
which gradually join and become larger and larger. Physiologically, lymphatic vessels
are very similar to veins. Like veins, they have low pressure and possess valves.
(3) The thoracic duct is a major collecting vessel of the lymphatic system
that empties into the deep veins of the neck. It begins in the upper posterior abdomen
with a collection of sacs called the cisterna chyli. The cisterna chyli is a receiving area
for lymph from three other major lymphatic vessels. From the cisterna chyli, the
thoracic duct passes upward through the thorax and into the root of the neck. There, it
empties into the deep veins of the neck.
b. Lymph Nodes. Along the lymphatic vessels at various intervals are small
structures known as lymph nodes. The lymph nodes function as sieves for the lymph
passing through them. In healthy individuals, the lymph nodes usually draw no
attention. However, in chronic diseases, the lymph nodes become enlarged and