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