Lymphatic & Immune System
Lymph: Definition Lymph is excess tissue fluid contained in lymphatic vessels Consists of (mostly) water and plasma proteins that have leaked out of the capillaries
Semi-independent parts of the lymphatic system Meandering network of lymphatic vessels Lymphoid tissues and organs scattered throughout the body
Functions of the lymphatic system Lymphatic vessels return interstitial fluid and leaked plasma proteins back to the blood Lymphatic capillaries (lacteals) absorb fats/fat soluble vitamins at intestinal villi and transport to the blood The lymphatic system helps defend the body against disease
Lymphatic vessels: 3 types Blind-ended capillaries Lymphatic collecting vessels Trunks and ducts
Blind-ended Capillaries Specially adapted: Highly permeable One-way valves (similar to veins) so lymph only flows towards the heart Valves resist interstitial pressure to remain open Can absorb cell debris, pathogens, cancer cells
Collecting Vessels Similar to veins but have thinner walls and more internal valves Lots of branching networks Anastomose = dividing/branching Travel with the superficial veins in skin Deep vessels travel with arteries Vasa vasorum (vessels of the vessels) supply nutrients to cells
Collecting Vessels Capillaries consist of a single layer of cells and are the only blood vessels that can exchange materials with the interstitial fluid Cells will die if they are not within 1 or 2 cell widths of a capillary The lymphatic system removes excess fluid
Trunks & Ducts Capillaries join to form vessels that merge in the thoracic cavity before entering one of two ducts: Thoracic duct & right lymphatic duct Trunks are formed by joining of the largest collecting ducts and are classified by the regions served Paired lumbar, subclavian, jugular, intestinal
Trunks & Ducts cont’d Lymph is delivered into one of the two large trunks (ducts) Right lymphatic duct Drains right upper arm, the right side of the head and thorax Thoracic duct Drains the rest of the body