Bovine biology series
Part - 16 Lymph
Of the primary body fluids, blood receives most of the attention. Blood is the fluid responsible for transporting food to our cells and carrying waste products away. But there is another fluid, which serves a wide variety of functions, and it is lymph.
An odd name. The word "lymph" is derived from the Latin word "lympha", which means water goddess, or water. The name may have been used to describe the clear-like fluid of the abdominal cavity by early investigators, hence the name lymph assigned to this watery-appearing fluid.
There are two common examples that may help us right from the start thinking about lymph. The first is the accumulation of edema (from the Greek word "oidema" meaning swelling) in the udder, belly or brisket of a fresh cow. This is lymph. This is fluid that accumulates because the movement of skeletal muscle is not sufficient to move this fluid along towards its point of discharge, the circulatory system, and then the kidney system and finally urine output. Gravity is (partially) responsible for the accumulation to be clinically expressed here. Physiologically, lymph accumulates because of the tremendous increase in blood flow to the udder in response to the hormones prolactin (initiation of milk syntheses) and progesterone and other corticosteroids (initiation of udder secretory tissue formation). The by-products of the blood, such as discarded blood cells, are gathered in the lymph, increasing its volume and therefore we see it as edema.
The second example is the bloated belly of a child suffering from malnourishment, primarily severe protein malnourishment. In a growing child, the body is not only maintaining itself but also developing muscle and bone mass (as well as brain tissue). We call that growth, of course, and it is directed in large part by somatic growth hormone. When the diet of this youngster is deficient in protein, the body sacrifices blood protein. These proteins found in the blood are broken down into their amino acids complements, carried to the cells and used for self maintenance (Homeostasis). Growth is slowed or stopped, of course. As the blood proteins are reduced, blood osmotic pressure is reduced, and accordingly the volume (amount) of lymph is increased. Since lymph is primarily found in the abdominal cavity, i. e. the belly and chest, then this fluid accumulates here. Thus we see in this child the accumulation of lymph around the belly, the sickening expression of a bloated belly, the result of a body saving itself by searching for protein in the bloodstream so that somatic - body cells can live.
As an aside here is the remarkable ability of the body to save itself.....to a point. The inherit genetic code, that which has survived and developed over tens of thousands of generations in living matter, is first and foremost attendant to saving the body. All else becomes secondary. This is called homeostasis.
These are two examples of lymph, the watery-like fluid expressed clinically in two very different physiological situations. But there is a point that is reached, physiologically, when the body can deal with lymph and accumulate it until the circulatory system drains it away. Beyond that point, however, and the lymphatic system is overwhelmed and death may result.
Let's take a closer look at this fluid.
When we think of lymph we should define the term interstitial fluid. The term "interstitial" (from the Latin word "interstitium") refers to the space between essential parts of an organ or cell. Thus lymph is defined as the fluid occupying the spaces between cells and organs in the body. In terms of volumes, the body is about 65-70% water. Of that volume, 15% is interstitial fluid. It is this 15% that is primarily lymph. For a 1350-pound cow, then, about 918 pounds of her is water, and 138 pounds (17 gallons) is lymph.
Lymph resembles water in that it is clear, transparent and usually almost colorless. If the lymph is found around the digestive tract at the lower portion of the abdominal cavity, it will like contain absorbed fats [these fats - lipids are transported to the circulatory system - blood], exhibiting a milky color. It differs from blood in that red blood cells are not present and its protein content is lower. Lymph has a specific gravity of 1.01 - 1.02, thus being just slightly heavier than water but not as heavy as blood (1.04 - 1.06). The pH of lymph is alkaline, at 7.5, slightly higher than blood plasma at a pH of 7.4.
Lymph is comprised of water, of course, but has large molecular weight serum proteins, such as albumin’s, globulin’s and fibrinogens, salts, urea, glucose and some cells very important to the immune systems.....lymphocytes. The lymphocytes are formed in the lymph nodes.
Lymph is the dumping ground for molecules that have served the role as end products of digestion, urea is a good example, or as a transitory fluid holding large molecular weight proteins, the serum globulin’s, etc., until they can be put back into the circulatory system and directed towards their final destination.
Lymph is a fluid serving another role. It accumulates the spilled blood that is emptied next to a cell by a capillary, but due to pressure and gradient differences not all of it can be cycled into and out of the cell itself. So the interstitial fluid is there, bathing the cells and collecting this spillage. The lymph fluid is moved via smooth muscle movement through the vessel system of the lymphatic system, dumping this watery fluid into the blood system at two locations near the neck - shoulders. These are the thoracic duct or the right lymph node. It is here that a filtering process occurs, in which metabolites and especially bacteria are collected.
It is here, then, that the body filters out harmful bacteria and even cancers that may harm the body. The effluent from these ducts is dumped back into the circulatory system and it is cleansed of harmful stuff keeping us from harms way.
We will examine the lymphatic system, and the lymph nodes in detail next month, then begin a journey into immunity, of which the lymphatic system plays an important role.
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