Med Term Chapter 11 Part 1

Lymphatic and Immune Systems Overview

• The lymphatic system consists of vessels, ducts, and trunks that remove interstitial fluid from tissues and return it to the bloodstream.
• It transports dietary lipids and immune cells, primarily lymphocytes derived from bone marrow.
• Primary lymphoid organs (bone marrow, thymus) are sites for lymphocyte development; secondary lymphoid organs (lymph nodes, spleen) are where immune responses occur.

Anatomy of Lymphatic System

• Lymphatic vessels start as open-ended capillaries and progressively merge into larger vessels, emptying into the bloodstream.
• Humans have approximately 500 to 600 lymph nodes situated in regions like the groin, armpits, neck, and abdomen.
• Lymphatic capillaries, found nearly everywhere in the body, do not exist in the CNS, bone marrow, bones, teeth, or cornea.

Fluid Regulation

• Lymph acts as recycled blood plasma, with 20 liters released into interstitial space daily; 17 liters are reabsorbed by blood vessels.
• The lymphatic system returns the excess 3 liters of fluid to circulation, preventing lymphedema caused by blockage or damage to lymphatics.

Lymphatic Vessel Structure

• Larger lymphatic vessels resemble veins, possessing three tunics and one-way valves that give them a beaded appearance.
• Superficial lymphatics typically follow venous pathways, while deep lymphatics align with arteries.
• On the right side, lymph drains into the right subclavian vein via the right lymphatic duct; remaining lymph on the left drains through the thoracic duct into the left subclavian vein.

Primary Lymphoid Organs

• Bone marrow serves as the precursor for all blood cells, including lymphocytes.
• The thymus, located between the sternum and aorta, is critical for T cell maturation with age-related changes termed thymic involution.

Secondary Lymphoid Organs

• Secondary lymphoid organs (lymph nodes, spleen, lymphoid nodules) are the sites where immune responses occur.
• Naïve lymphocytes move from primary organs to wait for antigen encounters in secondary organs.

Lymph Nodes

• Function to filter lymph, removing debris and pathogens; contain dendritic cells and macrophages for pathogen clearance.
• Serve as critical locations for adaptive immune responses involving T cells, B cells, and other immune cells.

Spleen

• Approximately 12 cm long, the spleen is referred to as the "filter of the blood" due to its vascular nature and ability to clear microbes and dying red blood cells.
• Engages in immune responses against blood-borne pathogens.

Lymphoid Nodules

• Comprising dense clusters of lymphocytes, lymphoid nodules lack a surrounding capsule and are prevalent in respiratory and digestive tracts.
• Tonsils, key lymphoid nodules, help develop immunity by responding to oral pathogens; prone to removal if recurrent infections interfere with breathing or swallowing.

Key Terminology

• Immunosenescence: Loss of immune function associated with aging, partly due to thymic involution.
• Lymphedema: Accumulation of interstitial fluid due to lymphatic system damage.

Trivia

• The thymus gland releases thymosin, linking it to endocrine functions, and the spleen can be surgically removed without life-threatening consequences.