Lymph circulation

The lymphatic system serves as an auxiliary pathway for fluid movement from the interstitial spaces back into the bloodstream. Lymphatic vessels are capable of transporting proteins and larger particulate matter away from tissue spaces. This return of proteins from the interstitial fluid to the blood is crucial for maintaining fluid balance and overall health; its absence would be fatal within approximately 24 hours.

Several factors facilitate lymph flow:

1. Contraction of surrounding skeletal muscles: Muscle movements exert pressure on lymphatic vessels, propelling lymph forward.

2. Movement of body parts: Physical activity and changes in body position help to squeeze lymphatic vessels.

3. Pulsations of adjacent arteries: The rhythmic expansion and contraction of arteries located near lymphatic vessels can assist in lymph movement.

4. External compression: Pressure applied to the body from external sources can also contribute to lymph flow.

5. Rhythmic contraction of large lymphatic vessels: Larger lymph vessels possess contractile abilities that help to propel lymph.

The lymphatic “pump” becomes highly active during exercise, significantly increasing the rate of lymph flow. Conversely, lymph flow is slow or nearly non-existent during periods of rest.

Lymph nodes

These are small, oval or bean-shaped organs situated along the course of lymphatic vessels. Typically, multiple afferent lymphatic vessels carry lymph into a single lymph node, while only one efferent vessel carries lymph out. Lymph fluid may pass through approximately eight nodes before re-entering the blood circulation.

Lymph nodes are comprised of lymphatic tissue, which is densely populated with lymphocytes (immune cells) and macrophages (phagocytic cells), as well as reticular tissue. The reticular tissue forms a network of fibers that provide internal structural support within the node.

Larger lymph nodes are strategically located throughout the body, arranged in both deep and superficial groups. Examples include:

Cervical Lymph nodes: These nodes drain lymph from the head and neck regions.
Axillary Lymph nodes: Located in the armpit, these nodes drain lymph from the upper limbs.
Hilar nodes, aortic nodes, sternal nodes: These nodes are situated in the chest and drain lymph from the thoracic organs and tissues.
Popliteal nodes and Inguinal nodes: These nodes are located in the back of the knee and groin, respectively, and drain lymph from the lower limbs.
Cisterna chyli: This is a sac-like structure that receives lymph from the abdominal and pelvic cavities.

Lymphoid Tissue

This category includes lymphatic glands, commonly known as lymph nodes, as well as other organized collections of lymphatic cells. Specific examples include:

• Pharyngeal tonsils (adenoids): Located near the posterior nasal openings.

• Palatine tonsils: Situated at the back of the mouth.

• Lingual tonsils: Found at the back and sides of the tongue.

• Aggregated lymphoid follicles (Peyer’s patches): Clusters of lymphoid tissue within the small intestine.

Lymphoid tissue is also present in other organs, such as the bone marrow, spleen, liver, lungs, and thymus gland.

Spleen

This is the largest lymphatic organ in the body, positioned in the left upper quadrant (left hypochondriac region) of the abdominal cavity, between the fundus of the stomach and the diaphragm.

The spleen performs two primary functions:

• Destruction of old blood cells: It removes aged or damaged red blood cells from circulation.

• Monitoring the body’s immune system: It contains immune cells that identify and respond to pathogens in the blood.

Essentially, the spleen acts as a blood filter.