Blood vessels

• Blood is classified as a connective tissue and consists of two main components: plasma, which is a clear extracellular fluid, and formed elements, which are made up of the blood cells (red and white blood cells) and platelets.
• Tissue fluid consists of a water solvent containing sugars, salts, fatty acids, amino acids, coenzymes, hormones, neurotransmitters, as well as waste products from the cells.
• Arteries, capillaries and veins have different wall thicknesses, lumen sizes, permeabilities, valves, types of blood, and pressures.