The Lymph and Its Movement through the Body : Part 1

Physiology and Hygiene for Secondary Schools
by Francis M. Walters

(Page 6 of 25)

The blood, it will be remembered, moves everywhere through the body in a system of closed tubes. These keep it from coming in contact with any of the cells of the body except those lining the tubes themselves. The capillaries, to be sure, bring the blood very near the cells of the different tissues; still, there is need of a liquid to fill the space between the capillaries and the cells and to transfer materials from one to the other. The lymph occupies this position and does this work. The position of the lymph with reference to the capillaries and the cells is shown in Fig. 27.

Origin of the Lymph. - The chief source of the lymph is the Plasma of the blood. As before described, the walls of the capillaries consist of a single layer of flat cells placed edge to edge. Partly on account of the pressure upon the blood and partly on account of the natural tendency of liquids to pass through animal membranes, a considerable portion of the Plasma penetrates the thin walls and enters the spaces occupied by the lymph.

The cells themselves also help to form the lymph, since the water and wastes leaving the cells add to its bulk. These mix with the Plasma from the blood, forming the resultant liquid which is the lymph. A considerable amount of the material absorbed from the food canal also enters the lymph tubes, but this passes into the blood before reaching the cells.

Composition and Physical Properties of the Lymph. - As would naturally be expected, the composition of the lymph is similar to that of the blood. In fact, nearly all the important constituents of the blood are found in the lymph, but in different proportions. Food materials for the cells are present in smaller amounts than in the blood, while impurities from the cells are in larger amounts. As a rule the red corpuscles are absent from the lymph, but the white corpuscles are present and in about the same numbers as in the blood.

The physical properties of the lymph are also similar to those of the blood. Like the blood, the lymph is denser than water and also coagulates, but it coagulates more slowly than does the blood. The most noticeable difference between these liquids is that of color, the lymph being colorless. This is due to the absence of red corpuscles. The quantity of lymph is estimated to be considerably greater than that of the blood.

Lymph Vessels. - Most of the lymph lies in minute cavities surrounding the cells and in close relations with the capillaries. These are called lymph spaces. Connecting with the lymph spaces on the one hand, and with certain blood vessels on the other, is a system of tubes that return the lymph to the blood stream. The smallest of these, and the ones in greatest abundance, are called lymphatic. They consist of slender, thin-walled tubes, which resemble veins in structure, and, like the veins, have valves. They differ from veins, however, in being more uniform in size and in having thinner walls.

The lymphatic in different places gradually converge toward, and empty into, the two main lymph tubes of the body. The smaller of these tubes, called the right lymphatic duct, receives the lymph from the lymphatic in the right arm, the right side of the head, and the region of the right shoulder. It connects with, and empties its contents into, the right subclavian vein at the place where it is joined by the right jugular vein.

The larger of the lymph tubes is called the thoracic duct. This receives lymph from all parts of the body not drained by the right lymphatic duct, and empties it into the left subclavian vein. Connection is made with the subclavian vein on the upper side at the place where it is joined by the left jugular vein. The thoracic duct has a length of from sixteen to eighteen inches, and is about as large around as a goose quill. The lower end terminates in an enlargement in the abdominal cavity, called the receptacle of the chyle. It is provided with valves throughout its course, in addition to one of considerable size which guards the opening into the blood vessel.

The lymphatic which join the thoracic duct from the small intestine are called the lacteals. These do not differ in structure from the lymphatic in other parts of the body, but they perform a special work in absorbing the digested fat.

Lymphatic Glands. - The lymphatic glands, sometimes called lymph nodes, are small and somewhat rounded bodies situated along the course of the lymphatic tubes. They vary in size, some of them being an inch or more in length. The lymph vessels generally open into them on one side and leave them on the other. They are not glands in function, but are so called because of their having the general form of glands. They provide favorable conditions for the development of white corpuscles. They also separate harmful germs and poisonous wastes from the lymph, thereby preventing their entrance into the blood.

Relations of the Lymph, the Blood, and the Cells. - While the blood is necessary as a carrying, or transporting, agent in the body, the lymph is necessary for transferring materials from the blood to the cells and vice versa. Serving as a physiological "go between," or medium of exchange, the lymph enables the blood to minister to the needs of the cells. But the lymph and the blood, everything considered, can hardly be looked upon as two separate and distinct liquids. Not only do they supplement each other in their work and possess striking similarities, but each is made in its movements to pass into the vessels occupied by the other, so that they are constantly mixing and mingling. For these and other reasons, they are more properly regarded as two divisions of a single liquid - one which, by adapting itself to different purposes, supplies all the conditions of a nutrient fluid for the cells.

D.C. Heath and Co. - Publishers
Original copyright 1909