CARDIOVASCULAR SYSTEM OUTLINE 21.1 General Composition and Functions of Blood 638 21.1a Components of Blood 638 21.1b Functions of Blood 638 21 21.2 Blood Plasma 639 21.2a Plasma Proteins 640 21.2b Differences Between Plasma and Interstitial Fluid 640 21.3 Formed Elements in the Blood 640 Blood 21.3a Erythrocytes 641 21.3b Leukocytes 648 21.3c Platelets 650 21.4 Hemopoiesis: Production of Formed Elements 651 21.4a Erythropoiesis 653 21.4b Thrombopoiesis 653 21.4c Leukopoiesis 653 MODULE 9: CARDIOVASCULAR SYSTEM mck78097_ch21_637-655.indd 637 2/14/11 3:54 PM 638 Chapter Twenty-One Blood ithin our bodies is a connective tissue so valuable that donat- Figure 21.2 shows the three components separated by W ing a portion of it to someone else can save that person’s centrifugation, from bottom to top in the test tube: life. This tissue regenerates itself continuously and is responsible for ■ Erythrocytes (ě-rith′rō -sı̄ t; erythros = red, kytes = cell), transporting the gases, nutrients, and hormones our bodies need for sometimes called red blood cells, form the lower layer of the proper functioning. Losing too much of this tissue can kill us, and centrifuged blood. They typically average about 44% of a yet it is something we frequently take for granted. blood sample. This valuable connective tissue is blood. Blood is considered ■ A buffy coat makes up the middle layer. This thin, a fluid connective tissue because it contains cells, a liquid ground slightly gray-white layer is composed of cells called substance (called plasma), and dissolved proteins. In this chapter, leukocytes (or white blood cells) and cell fragments we describe the components of blood, its functions, and how the called platelets. The buffy coat forms less than 1% of a body produces the various types of blood components. blood sample. ■ Plasma is a straw-colored liquid that lies above the buffy coat in the centrifuge tube; it generally makes up about 21.1 General Composition 55% of blood. and Functions of Blood Collectively, the erythrocytes and the components of the Learning Objectives: buffy coat are called the formed elements. It is best not to refer to 1. List and describe the basic components of blood. all of these structures as “cells” because platelets are merely frag- 2. Explain how blood functions in transport, regulation, and ments broken off from a larger cell. The formed elements, together protection. with the liquid plasma, compose whole blood (the substance we most commonly refer to simply as “blood”). Blood is a type of fluid connective tissue (see chapter 4). Blood is about four times more viscous than water, meaning that WHAT DO YOU THINK? it is thicker and more “goopy.” The temperature of blood is about 1°C higher than measured body temperature; thus, if your body ●1 If your body becomes dehydrated, does the plasma percentage in temperature is 37°C, your blood temperature is about 38°C. whole blood increase or decrease? 21.1a Components of Blood 21.1b Functions of Blood Whole blood can be separated into its liquid and cellular components Blood carries out a variety of important functions related to trans- by using a machine called a centrifuge, as shown in figure 21.1 and portation, regulation, and protection. described here: 1. Blood to be sampled is withdrawn from a vein and collected Transportation in a glass tube, called a centrifuge tube. Blood transports numerous elements and compounds throughout 2. The glass tube is placed into the centrifuge, which then spins the body. For example, erythrocytes and plasma carry oxygen it in a circular motion for several minutes. from the lungs to body cells and then transport the carbon diox- 3. The rotational movement separates the blood into liquid ide produced by the cells back to the lungs to diffuse from the and cellular components based on weight, thus allowing body. Blood plasma transports nutrients that have been absorbed these elements to be examined separately. from the GI tract. Plasma also transports hormones secreted Centrifuge Plasma (55% of whole blood) Buffy coat: leukocytes and platelets (<1% of whole blood) Erythrocytes Formed Whole (44% of whole blood) elements blood 1 Withdraw blood into a syringe and 2 Place the tube into a centrifuge and 3 Components of blood separate during place it into a glass centrifuge tube. spin for about 10 minutes. centrifugation to reveal plasma, buffy coat, and erythrocytes. Figure 21.1 Whole Blood Separation. A sample of whole blood is used to determine the ratio of plasma to formed elements. The blood sample is drawn from a vein and placed into a glass tube. After centrifugation, the formed elements in the sample remain packed in the bottom of the centrifuge tube. mck78097_ch21_637-655.indd 638 2/14/11 3:54 PM Chapter Twenty-One Blood 639 Plasma Buffy Coat Water Proteins Other solutes Platelets Leukocytes 92% by weight 7% by weight 1% by weight 150,000-400,000 4,500-11,000 per cubic mm per cubic mm Albumins 58% Electrolytes Globulins 37% Nutrients Fibrinogen 4% Respiratory gases Lymphocytes Regulatory Waste products 20–40% proteins <1% Neutrophils 50–70% Erythrocytes Monocytes 2–8% Erythrocytes 4.2–6.2 million per cubic mm Eosinophils Basophils 1–4% 0.5–1% Figure 21.2 Whole Blood Composition. Whole blood contains plasma (average = about 55%) and formed elements (average = about 45%). (The percentages presented in this figure are average numbers of cells, and the numbers for components of the buffy coat represent average ranges. A cubic millimeter of blood is equivalent to a microliter [μL] of blood.) by the endocrine glands. Finally, plasma carries some waste blood pressure drops to unhealthily low levels, and the tissues products from the cells to organs such as the kidneys, where swell with excess fluid. To maintain a balance of fluid between these waste products are removed. the blood and the interstitial fluid, blood contains molecules (such as salts and some proteins) to prevent excess fluid loss from the Regulation plasma. Blood regulates many body functions including body temperature. Plasma absorbs and distributes heat throughout the body. If the Protection body needs to be cooled, the blood vessels in the dermis dilate and Leukocytes help guard against infection by mounting an immune dissipate the excess heat through the integument. Conversely, when response if a pathogen or an antigen (an′ti-jen; anti = opposite, the body needs to conserve heat, the dermal blood vessels constrict, gen = producing) (a substance perceived as foreign to the body) is and the warm blood is shunted to deeper blood vessels in the body found. Antibodies (an′tē -bod-ē ; body = main part), which are mol- (see chapter 5) . ecules that can bind to antigens until a leukocyte can completely Blood also helps regulate pH levels in the body’s tissues. The kill or remove the antigen, are transported in plasma. In addition, term pH is a measure of how acidic or alkaline a fluid is. A neutral platelets and blood proteins protect the body against blood loss by pH (neither acidic nor alkaline fluid, such as water) is measured forming blood clots. at exactly 7, while acidic fluids (e.g., orange juice) are between 0 and 7, and alkaline fluids (e.g., milk) are between 7 and 14. Blood WHATW DID YOU LEARN? plasma contains compounds and ions that may be distributed to ●1 Erythrocytes make up what average percentage of whole blood? the fluid bathing cells within the tissues (interstitial fluid) to help maintain normal tissue pH. In addition, blood plasma pH is con- ●2 What are the protective functions of the blood? tinuously regulated to try to maintain a value of 7.4, which is the pH level required for normal cellular functioning. If the blood pH falls below 7.4 to 7.0, the condition called acidosis results, and the central nervous system is depressed; coma and death could occur. 21.2 Blood Plasma If the blood pH rises above 7.4 to 7.8, alkalosis results, character- Learning Objective: ized by a hyperexcited nervous system and convulsions. 1. Outline the components of plasma. Blood maintains normal fluid levels in the cardiovascular system and prevents fluid loss. A constant exchange of fluid takes Blood plasma is a complex mixture of water, proteins, and place between the blood plasma and the interstitial fluid. If too other solutes (table 21.1). When the blood cells, platelets, and much fluid is absorbed into the blood, high blood pressure results. clotting proteins are removed from plasma, the remaining fluid is If too much fluid escapes the bloodstream and enters the tissues, termed serum (ser′um; whey). mck78097_ch21_637-655.indd 639 2/14/11 3:54 PM 640 Chapter Twenty-One Blood Table 21.1 Composition of Blood Plasma Plasma Component (Percentage of Plasma) Functions WATER (~92% OF PLASMA) Acts as the solvent in which formed elements, solutes, and wastes are suspended PLASMA PROTEINS (~7% OF PLASMA) Albumin (~58% of plasma proteins) Regulates water movement between the blood and interstitial fl uid (and thus the viscosity of blood); transports some fatty acids and hormones Globulins (~37% of plasma proteins) Alpha-globulins transport lipids and some metal ions Beta-globulins transport iron ions and lipids in bloodstream Gamma-globulins are antibodies that immobilize pathogens (bacteria, viruses, etc.) Fibrinogen (~4% of plasma proteins) Helps with blood clotting Regulatory proteins (<1% of plasma proteins) Consists of enzymes, proenzymes, and hormones OTHER SOLUTES (~1% OF PLASMA) Electrolytes (e.g., sodium, potassium, calcium, chloride, iron, Help establish and maintain membrane potentials, maintain pH balance, and bicarbonate, and hydrogen) regulate osmosis Nutrients (e.g., amino acids, glucose, cholesterol, vitamins, fatty acids) Energy source Respiratory gases Oxygen and carbon dioxide Wastes (breakdown products of metabolism) (e.g., lactic acid, Waste products are transported to the liver and kidneys where they can be removed creatinine, urea, bilirubin, ammonia) from the blood Water is the most abundant compound in plasma, making up interstitial fluid (the type of extracellular fluid that bathes the about 92% of plasma’s total volume.