Lesson 1, Topic 1
In Progress


April 11, 2024

Learning Objective: Analyze the role of blood and the components found in the blood.
      The average body holds 10 to 12 pints of blood. The heart circulates the blood through the circulatory system more than 1000 times every day. More than 70,000 miles of passageways, most of which are narrower than human hair, carry blood throughout the body. The blood is contained in a closed system of vessels. The largest is the aorta, and the smallest are the capillaries. The capillaries are only one cell layer thick, and their thin, permeable walls allow certain substances to move back and forth between blood vessels and surrounding tissue. The circulating blood contains more than 25 trillion cells, and every second the body replaces 8 million old red blood cells (RBCs) with 8 million new RBCs.

Role of Blood in the Body
Learning Objective: Describe the role of blood in the body.
      The circulating blood supplies the body’s cells with nutrients and oxygen. The blood also distributes enzymes, hormones, and other chemicals needed for the regulation of body activities. In addition, the blood functions to maintain body temperature, keep body fluids in balance, and maintain pH. Maintaining a constant internal environment is called homeostasis.

Whole Blood
Learning Objective: Describe the components in blood.
      Whole blood is composed of visible-formed elements suspended in plasma (a clear, yellow liquid). Plasma makes up approximately 55% of blood by volume. The remaining 45% consists of the following visible cellular elements: erythrocytes (RBCs), leukocytes (WBCs), and thrombocytes (platelets). The characteristics of blood and cellular components are reviewed in Chapter 25.

      Plasma is the highly complex liquid that transports the formed elements plus other substances, such as plasma proteins, throughout the body to every cell. Plasma proteins include albumin, the clotting proteins prothrombin and fibrinogen, and immunoglobulins. Plasma also transports nutrients (carbohydrates, fats, and amino acids), hormones, enzymes, mineral salts, gases, and waste products.
Plasma is composed of approximately 90% water, 9% protein, and 1% other chemical substances. The liquid portion of the blood in the body is plasma. In blood samples drawn for testing or other purposes, the body plasma must have an added anticoagulant to remain part of the whole blood. The liquid that remains after blood has clotted is called serum.