Lymphatic system

The lymphatic system is the anatomical structure that transports lymph. It bears some similarities with the circulatory system, but the liquid that is transported is not blood, but lymph. It is not a closed system, it begins in the body tissues, continues through the lymphatic vessels that progressively increase in size until they converge in the thoracic duct or in the right lymphatic duct, both flow into the venous system at the point of union between the vein subclavian and internal jugular vein, each on one side. The lymphatic system constitutes the second network for transporting body fluids, some authors consider it as a part of the circulatory system. Lymph is a whitish-colored, transparent-looking liquid that runs through the lymphatic vessels and generally lacks pigments. It is produced from excess fluid that leaves the blood capillaries into the interstitial space and is collected and transported by the lymphatic capillaries that drain to larger lymphatic vessels.

The lymphatic system was discovered in the 17th century by Thomas Bartholin and Olaus Rudbeck independently, although Bartholin was the first to publish it.

Function

The main functions of the lymphatic system are:

• Interstitial fluid drainage: The lymphatic system captures the excess of interstitial fluid found between the cells and returns it to the blood.
• Fat transport: Most of the fats that are absorbed in the intestine from food are transported by the lymphatic system to the blood. The cells that form the intestinal wall (enterocites) absorb fats from food and synthesize complex particles called quilomicrons, mainly constituted by triglycerides. Chilomicrons are released into the intercellular space, where they enter the lymph vessels that transport them to the venous system through the chest duct.
• Immunity Response: T lymphocytes, B lymphocytes and macrophages present in lymph nodes and other lymphoid organs recognize and remove foreign substances and potential pathogenic microorganisms.

Formation of lymph

The wall of the lymph vessels contains smooth muscle that when contracted propels the lymph.

Lymph comes from interstitial or intercellular fluid, that is, from the fluid found in the tissues in the small spaces between cells. In humans, it is estimated that between 2 and 3 liters are produced per day, most of which is discharged into the venous system through the thoracic duct. The protein concentration of interstitial fluid in most tissues is around 2 g/dL, very similar to that of lymph. However, the lymph that originates from the wall of the intestine and the liver has a higher protein concentration that can reach 6 g/dL.

The lymphatic system also absorbs a large amount of fat from the digestion of food, in such a way that after a copious meal the lymph can contain up to 2% fat. Because bacteria and microorganisms can take advantage of the lymphatic ducts to invade the body, they get in the way of lymph nodes containing large numbers of defensive cells called lymphocytes, which destroy invading microorganisms. Lymphatic circulation is possible because the duct system is equipped with small valves that prevent the fluid from returning, on the other hand, the largest vessels have a layer of smooth muscle that, when contracted, propels the content in the correct direction towards the mouth. in the venous system.

Formation and circulation of the lymph from the interstitial fluid.

Limph circulation

Scheme showing the drained areas through the right lymphatic duct and the chest duct.

It begins in small lymphatic capillaries whose wall is made up of cells attached to each other by button-like junctions that allow interstitial fluid to pass through to enter the lumen of the vessel. The lymphatic capillaries unite forming a network of ducts that lead to vessels of greater diameter, finally all the lymph produced by the body ends up in only two ducts, the right lymphatic duct that drains the upper right half of the body and the thoracic duct, from bigger size, for the rest of the body. Both drain into the venous system, at the junction of the subclavian vein and the internal jugular vein on each side. The small lymphatic vessels on their way to the venous system pass through the lymph nodes in which there are large numbers of lymphocytes and other cells of the immune system.

When the lymphatic vessels cannot fulfill their purpose due to obstruction, the phenomenon known as lymphedema occurs, which consists of a swelling that is usually especially intense in the lower limbs. In severe lymphedema, the extremities accumulate so much fluid that they can double their diameter, making bodily movement extremely difficult.

Lymphoid tissues and organs

A type of connective tissue in which the predominant cells are lymphocytes is called lymphoid or lymphatic tissue. Lymphocytes are responsible for the specific immune response, they are produced in the primary lymphoid organs from where they migrate to the secondary lymphoid organs. There are two main types of lymphocytes: T lymphocytes and B lymphocytes. The body produces about 1 billion new lymphocytes every day.

The primary lymphoid organs are the bone marrow and the thymus; in them lymphoid cells are generated and differentiate into mature B lymphocytes and mature T lymphocytes. Secondary lymphoid organs include lymph nodes, spleen, and mucosa-associated lymphoid tissue; in these tissues, B and T lymphocytes come into contact with the pathogens and their antigens, activating and multiplying.

The different lymphoid organs are interconnected by blood vessels and lymphatic vessels, so that a unitary, intertwined and well-connected system is formed. These vessels carry immune system cells of which the central type is the lymphocyte.

• Bone medulla. The bone marrow fulfills the function of hematopoiesis, that is, to produce all the cells that make up the blood. Among these are the lymphocytes, which are a type of leucocyte. Of these lymphocytes, the B (B) lymphocytes MarrowThey mature here.
• Timo. The thymus fulfills the function of maturating T (T) lymphocytes.
• Bazo. The spleen has the function of filtering the blood and cleaning it in altered cell forms.
• Lymphal Gang. They are small accumulations of lymphoid tissue wrapped by a capsule that interpose in the path of lymphatic vessels. In the human organism there are between 500 and 1000. Each of them has aferent lymphatic vessels that penetrate the lymph and efferent by which it comes out. They are often grouped forming ganglion chains.
• Lymphoid tissue associated with mucosa. It includes additions of lymphoid tissue that are located near the mucosa of the respiratory system and digestive system. It is also called MALT for its English initials. It includes amygdala palatin, amygdala faríngea and Peyer's plates in the intestine.

lymph nodes in the abdomen and inguinal region of a woman

Lymph nodes are interposed among vessels carrying lymphatic

lymph nodes in the abdomen and inguinal region of a male

Diseases of the lymphatic system

The most common manifestations of diseases of the lymphatic system are:

• Adenopathy. It is swelling and inflammation of a lymph node that increases its normal size.
• Linphedema. It is a type of edema caused by obstruction or malfunction of lymph vessels.
• Linfangitis. inflammatory process of lymphatic ducts, usually of infectious origin.
• Lymphoma. It is a type of cancer that originates in the lymph tissue.