Blood and Lymph Systems : The Classical World

Introduction

The blood and lymph systems provide all parts of the body with a steady supply of oxygen and nutrients, removal of metabolic wastes, and protection against invasive organisms.

The blood system is a true circulatory system, with the blood being pumped out by the heart and returned to the heart, whereas the lymph originates in the soft tissues of the body and travels one-way through its own channels until it ultimately empties into the veins. Hence we speak of the blood flowing out through the arteries and arterioles and back through the venules and veins, with the microscopic capillaries being the link between the arterioles and venules. Lymph is transported from the soft tissues by capillaries, lymph vessels, and lymph ducts before emptying into the veins.

The iron-containing balls of protein in the red cells, hemoglobin, give the distinctive red color to the blood, and transport oxygen, which they gather from the lungs at inhalation, to the rest of the body, and return carbon dioxide to the lungs for exhalation. White blood cells, leukocytes, protect the body from harmful foreign substances and remove cellular debris.