The blood circulatory system consists of small tubular structures responsible for carrying blood known as blood vessels. Some intercellular fluid (tissue fluid), however does not re-enter capillaries or veins directly, is picked up by thin-walled blind ended lymph vessels.
Outline the functions and position of the structural components, i.e. vessels, tissues and organs involved in draining of lymph into the blood.
The lymphatic system is a network of vessels, tissues, and organs that works in parallel with the blood circulatory system to drain lymph (the interstitial fluid that is collected across body tissues) back into the bloodstream. Here’s an overview of the structural components and their functions:
1. Lymphatic Capillaries:
- Location: Found throughout most of the body, interspersed among the blood capillaries, except in avascular tissues such as the epidermis and central nervous system.
- Functions: These are the starting points of the lymphatic system, where the excess tissue fluid (also containing proteins, waste products, and other substances) enters the lymphatic system. These capillaries are highly permeable blind-ended tubes that allow fluid and larger molecules to enter but not leave.
2. Lymphatic Vessels:
- Location: Lymphatic capillaries merge to form larger lymphatic vessels, which are found throughout the body parallel to veins.
- Functions: These vessels carry lymph towards the lymph nodes. They have valves to prevent backflow and rely on the contraction of surrounding muscles to move the lymph.
3. Lymph Nodes:
- Location: Lymph nodes are distributed along the courses of the lymphatic vessels. They are predominantly found in the neck, armpits, abdomen, and groin.
- Functions: Lymph nodes act as filters for foreign particles and cancer cells. They contain lymphocytes and macrophages to fight infection and cleanse the lymph before it returns to the bloodstream.
4. Lymphatic Trunks and Ducts:
- Location: Lymphatic vessels converge to form lymphatic trunks, which drain large regions of the body. These trunks then drain into two main ducts: the right lymphatic duct and the thoracic duct.
- Functions: The lymphatic trunks collect lymph from the lymphatic vessels. The right lymphatic duct drains lymph from the right upper quadrant of the body into the right subclavian vein. The thoracic duct, which is the largest lymphatic vessel, collects lymph from the rest of the body and empties it into the left subclavian vein.
5. Thymus:
- Location: Located in the upper anterior part of the chest, behind the sternum and in front of the heart.
- Functions: The thymus is where T-lymphocytes (T cells), a type of white blood cell, mature. It is most active during childhood and atrophies in adulthood.
6. Spleen:
- Location: The spleen is located on the left side of the abdomen, adjacent to the stomach.
- Functions: It filters blood, removes old and damaged red blood cells, stores white blood cells, and produces antibodies. It acts as an immune surveillance organ but is not directly involved in lymph drainage.
7. Tonsils, Peyer’s patches, and the Appendix:
- Location: The tonsils are in the pharynx, Peyer’s patches are in the small intestine, and the appendix is connected to the large intestine.
- Functions: These structures contain lymphoid tissue and contribute to the body's immune response, although they are not directly involved in the drainage of lymph.
The lymphatic fluid ultimately drains back into the circulatory system through the thoracic duct or the right lymphatic duct, completing the cycle of returning interstitial fluid to the bloodstream and maintaining fluid balance in the body.