Anatomy and Physiology Lymphatic System Quiz

Study Notes

Lymphatic System Anatomy

The lymphatic system is a crucial part of the human body, responsible for maintaining fluid balance, absorbing fats and fat-soluble vitamins, and functioning as part of the immune system. It consists of a network of vessels, nodes, and ducts that transport lymph, a fluid that contains nutrients, oxygen, hormones, toxins, and cellular waste products.

Lymph

Lymph is a fluid derived from blood plasma and is pushed out through the capillary wall by pressure exerted by the heart or by osmotic pressure at the cellular level. It contains nutrients, oxygen, and hormones, as well as toxins and cellular waste products generated by the cells. As the interstitial fluid accumulates, it is picked up and removed by lymphatic vessels that pass through lymph nodes, which return the fluid to the venous system.

Lymphatic Vessels

Lymphatic capillaries are blind-ended tubes with thin endothelial walls (only a single cell in thickness). They are arranged in an overlapping pattern, so that pressure from the surrounding capillary forces at these cells allows fluid to enter the capillary. Lymphatic vessels grow progressively larger and form two lymphatic ducts: the right lymphatic duct, which drains the upper right quadrant, and the thoracic duct, which drains the remaining lymphatic tributaries.

Lymphatic vessels have one-way valves to prevent any backflow. The pressure gradients that move lymph through the vessels come from skeletal muscle action, smooth muscle contraction within the smooth muscle wall, and respiratory movement.

Lymph Nodes

Lymph nodes are bean-shaped structures widely distributed throughout the lymphatic pathway, providing a filtration mechanism for the lymph before it rejoins the blood stream. The average human body contains approximately 600-700 lymph nodes, predominantly concentrated in the neck, axillae, groin, thoracic mediastinum, and mesenteries of the GI tract.

Lymph nodes constitute a main line of defense by hosting two types of immunoprotective cell lines, T lymphocytes and B lymphocytes. Lymph nodes have two distinct regions, the cortex and the medulla. The cortex contains follicles, which are collections of lymphocytes. At the center of the follicles is an area called germinal centers that predominantly host B-lymphocytes while the remaining Vessels entering the lymph nodes are called afferent lymphatic vessels and, likewise, those exiting are efferent lymphatic vessels.

Other Lymphatic Tissues

The tonsils, spleen, and thymus glands are also lymphatic tissues. The thymus gland is a lymphatic organ and an endocrine gland that serves as the site of T-lymphocyte maturation, development, and control. The tonsils produce lymphocytes and antibodies, helping to protect against inhaled and swallowed foreign bodies.

The spleen is not part of the connected lymphatic system but is lymphoid tissue. It produces white blood cells and filters the blood to remove microbes as well as old and damaged red blood cells and waste products.