Blood and Vascular System

Abstract

Blood (plus lymph), together with connective tissue proper, cartilage and bone, is a type of connective tissue which, as such, arises from the embryonic mesenchyme (see Chapter 5). Blood is a red liquid which functions to transport food, waste products, oxygen, hormones, etc., around the body and thus maintain homeostasis (= equilibrium) of the internal environment. It forms about 7 per cent of the body weight and is composed of the plasma or interstitial substance (=55 per cent of the volume of blood), which contains many salts, enzymes, hormones, etc., in solution, and the cellular components (= 45 per cent of the volume of blood). These include the red blood corpuscles (= erythrocytes), the white blood cells (= leucocytes) and the blood platelets (= thrombocytes). The best way of studying these cells is in a thin blood film which has been stained with a special stain such as Giemsa or Wright’s stain (see Giemsa technique, section 2.1.7(i)).