Fluid Connective Tissues: Blood and Lymph

Fluid connective tissues, including blood and lymph, lack mechanical support but connect different organs, deliver nutrients, remove waste, and defend the body from foreign invaders. Blood contains cells suspended in plasma, while lymph resembles plasma but contains fewer proteins and more immune cells. Both tissues circulate formed elements derived from hematopoietic stem cells in bone marrow.

Blood contains erythrocytes (red blood cells) that transport oxygen via hemoglobin, phagocytes and lymphocytes that fight infection as part of the immune system, and platelets that induce blood coagulation with fibrous proteins called fibrins. Each cell type performs specific functions essential for oxygen transport, immune defense, and clotting.

Hydrostatic pressure forces surplus fluid out of capillary walls into the space around tissue cells, creating interstitial fluid. When this fluid drains back into lymphatic vessels, it becomes lymph. Lymph circulates through a network of thin-walled lymphatic vessels and lymph nodes, transporting immune cells and fat from the intestine to the bloodstream.

Blood plasma is the liquid extracellular matrix composed primarily of proteins, solutes, and water. It forms a significant portion of total blood volume and serves as the medium in which formed elements circulate. Nutrients, salts, and wastes dissolve in plasma and are transported throughout the body.

Lymph contains lymphocytes, macrophages, and natural killer cells transported from lymph nodes via lymphatic vessels and capillaries to different body parts. These white blood cells help the organism effectively fight invading microorganisms and provide immune response against microbial attacks throughout the body.

Blood flows through capillaries surrounded by a network of thin-walled lymphatic vessels. Hydrostatic pressure in capillaries forces fluid into interstitial spaces around tissue cells. Lymphatic capillaries then collect this fluid, which becomes lymph and circulates back to the bloodstream, creating a continuous exchange between blood and lymph.

Lymph resembles plasma but contains fewer proteins and more immune cells than blood. While blood plasma contains a higher concentration of proteins and various formed elements including erythrocytes and platelets, lymph is enriched with lymphocytes and macrophages that support immune function throughout the body.