The word vessel generally makes one think of blood vessels, and the word blood brings to mind the color red. Yet there exists another system of vessels carrying white fluid and undertaking awesome functions at least as important as those of blood vessels. This system is employed for a number of very interesting functions – functions that are critical to human health. This system is the lymphatic system.
1. Absorption of blood in tissue spaces and the prevention of edemas
Capillary vessels are responsible for bringing blood to the body’s tissues. Let’s consider our capillaries like a hose we use for watering the garden. Just like vegetables would die if deprived of water, our cells would die if blood is not pumped from the engine called the heart to the organs, tissues, and eventually to cells.
But our capillaries do more than just water our cells; they also clean them. Nutrients such as sugar and fats abound in the part of the capillary where it connects to the tissue, but their amount decreases at the end, where the capillary leaves the tissue. Oxygen decreases, while carbon dioxide increases. Waste matter produced by cells like urea, uric acid, and creatinine are low in arterial blood but high in venous blood. So our capillaries do not just feed the body but also clear it of waste.
The amount of fluids carried in and out of the tissues by capillaries is approximately the same, a phenomenon called the “Starling equation” after the scientist who first defined it. Yet detailed calculations show that the amounts are not perfectly equal, and the fluids given by capillaries are far more than those they take away. To put it simply, the blood in our vessels decreases every second, and tissue fluids between cells increases. The decrease in blood is about 2 ml every minute, which adds up to 2-3 liters a day. Lymph vessels function like vacuums, sucking the extra fluid and then discharging it back into blood vessels. All the lymph vessels in the body flow into the blood vessels at the heart, thus blending the white blood with the red blood. If it were not for lymph vessels, human life would be shorter than a day. Edemas form in the related organs of people who lack lymph vessels from birth or whose lymph vessels are blocked or removed after surgery. This system has the vital task of recycling proteins and fluids that normally escape into tissues.
2. Keeping the germs and cancer away
Our body is lined with the skin on the outside and inner-skin, called mucosa, on the inside. The structure of the skin makes up the first layer of protection against germs, which cannot penetrate the skin if it is intact. If the integrity of the skin is compromised, germs can penetrate into the tissue fluid between the cells. They can enter the body through a break on the skin, a tear caused by scratching, a surgery incision, or even during a tooth extraction or injection.
Lymph vessels take in these germs as they absorb tissue fluid. The first stop is lymph nodes to get rid of possible germs in the fluid. Lymph nodes are located in several locations: the groin, around the intestines, behind the tongue, in the oral cavity, in the armpits, under the chin, behind the ears, in the neck, and in several other places. Lymph fluid (white blood) is taken through narrow passages, where it is contacted by macrophages, or cells specialized in hunting germs. Macrophages swallow up, digest, and kill the germs through a special process called phagocytosis.
Cancer cells can break off, spread across the body, and cause new cancers elsewhere. Like germs, a free cancer cell first enters tissue fluid, where it is absorbed into the vessel and then carried to the lymph node. The macrophages in the lymph node swallow and break up cancer cells like they do with germs. Macrophages are also assigned with the task of sending a message to lymphocytes, cells that protect us from germs and cancer, and waking them up.
3. Absorption of fats
Absorption, in the intestines, happens either by blood circulation or lymph circulation. Proteins and carbohydrates are absorbed by blood vessels, while fats are absorbed by lymph vessels. Absorption of fats is another important function of lymph circulation.
Why do proteins (amino acids) and carbohydrates (glucose, galactose, fructose) as well as minerals and water enter the blood stream, while fats go into the lymph vessels? This is a pertinent question. Nutrients absorbed into the blood start their journey in the part of the intestines called vena porta and are carried by veins into the liver, where they are preprocessed and then transferred into the blood. The fats, on the other hand, skip the liver and are transferred directly into the blood. If fats were sent to the liver first, they would cause fatty liver syndrome and then increase the risk of cirrhosis. Extra fat is certain to harm the liver. This harm is prevented by the transport of fats straight to fatty tissues.
4. Generation of negative pressure necessary for breathing
The cavity around the lungs under the rib cage is called the pleura, or chest cavity, where there is a tiny amount of an oily fluid that enables the lungs to expand and contract smoothly. This fluid is constantly secreted into the cavity through the blood vessels and absorbed constantly through the lymph vessels. In other words, the cavity is vacuumed regularly by the lymphatic vessel system, hence a negative pressure in the cavity. As is known, positive pressure pushes, while negative pressure pulls. We can breathe thanks to negative pressure, which is made possible with the lymphatic vessel system.
In some abnormal circumstances, this extremely important negative pressure disappears and even becomes positive, which prevents the person from breathing. It is a grace the right and left lungs have been created with the ability to work independently from each other. If one side happens to fail, the other can take over.
This abnormality is called pneumothorax, which is caused when the lungs are punctured from inside or the chest cavity is pierced from the outside because of such factors as an accident or stabbing. It takes both surgery and a long period of treatment to recover from pneumothorax.
There is not a single structure or function in the human body that is not full of wonders.