Anatomy & Physiology

Anatomy & Physiology Study Guide

©2018 Achieve Page 233 18.8 Chapter Eighteen Review An introduction to the cardiovascular system: • The cardiovascular system enables the rapid transport of nutrients, respiratory gases, waste products, and cells within the body. Blood has several important tasks and unique physical characteristics: • Blood is a specialized fluid connective tissue. Its functions include transporting dissolved gases, nutrients, hormones, and metabolic wastes; regulating the pH and ion composition of interstitial fluids; restricting fluid losses at injury sites; defending the body against toxins and pathogens; and regulating body temperature by absorbing and redistributing heat. • Blood contains plasma and formed elements—red blood cells (RBCs), white blood cells (WBCs), and platelets. The plasma and formed elements constitute whole blood, which can be fractionated for analytical or clinical purposes. • Hemopoiesis is the process of blood cell formation. Circulating stem cells divide to form all types of blood cells. • Whole blood from any region of the body has roughly the same temperature, viscosity, and pH. Plasma, the fluid portion of blood, contains significant quantities of plasma proteins: • Plasma accounts for 46–63 percent of the volume of blood; 92 percent of plasma is made of water. • Plasma is different from interstitial fluid regarding its oxygen and carbon dioxide levels and the concentrations and kinds of dissolved proteins. • The three major kinds of plasma proteins are albumins, globulins, and fibrinogen. • Albumins constitute about 60 percent of plasma proteins. Globulins constitute roughly 35 percent of plasma proteins; they include antibodies (immunoglobulins), which attack foreign proteins and pathogens, and transport globulins, which bind ions, hormones, and other compounds. • Fibrinogenmolecules are converted to fibrin in the clotting process. The removal of fibrinogen from plasma leaves a fluid called serum. • The liver synthesizes and supplies more than 90 percent of the plasma proteins. Red blood cells, formed by erythropoiesis, contain hemoglobin that can be recycled: • Red blood cells account for slightly less than half of the blood volume and 99.9 percent of the formed elements. The hematocrit value indicates the percentage of whole blood occupied by formed elements and is commonly reported as the volume of packed red cells (VPRC). • Each RBC is a biconcave disc, providing a large surface-to-volume ratio. This form permits RBCs to stack, bend, and flex. • Red blood cells lack most organelles, including mitochondria and nuclei, keeping only the cytoskeleton. They degenerate after about 120 days in the bloodstream. • Molecules of hemoglobin (Hb) account for more than 95 percent of the proteins in RBCs. Hemoglobin is a globular protein formed from two pairs of polypeptide subunits. Each subunit of 368