8.24:
Fluid Connective Tissues: Blood and Lymph
Although blood and lymph do not provide mechanical support or structure to other tissues, they connect different organs, deliver nutrients, remove waste, and defend the body from foreign invaders. Thus, blood and lymph are called fluid connective tissues.
Blood contains cells such as erythrocytes, phagocytes, lymphocytes, and platelets suspended in a fluid matrix called plasma.
The red color of blood comes from the oxygen-binding protein hemoglobin in erythrocytes. Phagocytes and lymphocytes are part of the immune system and help fight infection and other diseases.
Platelets, along with fibrous proteins called fibrins, induce blood coagulation.
Blood flows through capillaries and reaches peripheral tissues, surrounded by a network of thin-walled tubes called lymphatic vessels.
The hydrostatic pressure forces surplus fluid out of the capillary walls. This fluid occupies the space around the surrounding tissue cells and is called interstitial fluid.
When it drains back into the lymphatic vessels, it forms the lymph. Lymph resembles plasma but contains fewer proteins and more immune cells.
8.24:
Fluid Connective Tissues: Blood and Lymph
Blood and lymph are fluid connective tissues. They contain cells, also known as formed elements, circulating in a liquid extracellular matrix, the plasma. The formed elements are derived from hematopoietic stem cells in the bone marrow. Blood and lymph connect all vital parts and carry nutrients, oxygen, and other essential molecules like antibodies.
Blood
The blood flows through blood vessels— arteries, capillaries, and veins. Blood plasma is primarily made of proteins, solutes, and water. While plasma forms a significant component of the entire blood volume, the rest of the blood is composed of various formed elements. Erythrocytes or red blood cells (RBCs) are the blood's primary cells. Leukocytes or white blood cells (WBCs) and platelets are the other cells present in the blood.
Nutrients, salts, and wastes are dissolved in the liquid matrix and transported through the body, while the RBCs transport oxygen and carbon dioxide. Other blood cell components also perform specific functions. The WBCs provide an immune response against microbial attacks, and platelets facilitate the blood clotting mechanism.
Lymph
Lymph contains a liquid matrix and WBCs or lymphocytes. Macrophages and lymphocytes (NK cells, B and T cells) are transported from the lymph nodes via lymphatic vessels and capillaries to different body parts and help the organism effectively fight against invading microorganisms. The lymphatic capillaries also deliver fat from the intestine to the bloodstream.
This text is partially adapted from Openstax, Anatomy and Physiology 2e, Section 4.3: Connective Tissue Supports and Protects