1. Transportation. All of the substances essential for cellular metabolism are transported by the circulatory system. These substances can be categorized as follows: a. Respiratory. Red blood cells, or erythrocytes, transport oxygen to the cells. In the lungs, oxygen from the inhaled air attaches to hemoglobin molecules
Chapter Thirteen within the erythrocytes and is transported to the cells for aerobic respiration. Carbon dioxide produced by cell respiration is carried by the blood to the lungs for elimination in the exhaled air.
b. Nutritive. The digestive system is responsible for the mechanical and chemical breakdown of food so that it can be absorbed through the intestinal wall into the blood and lymphatic vessels. The blood then carries these absorbed products of digestion through the liver and to the cells of the body.
c. Excretory. Metabolic wastes (such as urea), excess water and ions, and other molecules not needed by the body are carried by the blood to the kidneys and excreted in the urine.
2. Regulation. The circulatory system contributes to both hormonal and temperature regulation.
b. Temperature. Temperature regulation is aided by the diversion of blood from deeper to more superficial cutaneous vessels or vice versa. When the ambient temperature is high, diversion of blood from deep to superficial vessels helps to cool the body, and when the ambient temperature is low, the diversion of blood from superficial to deeper vessels helps to keep the body warm.
3. Protection. The circulatory system protects against blood loss from injury and against foreign microbes or toxins introduced into the body.
a. Clotting. The clotting mechanism protects against blood loss when vessels are damaged.
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