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chapter 18 18.1 Functions and General Cardiovascular System: Blood 18.4 Hemostasis Composition of Blood 18.4...

chapter 18 18.1 Functions and General Cardiovascular System: Blood 18.4 Hemostasis Composition of Blood 18.4a Vascular Spasm INTEGRATE 18.1a Functions of Blood 18.4b Platelet Plug Formation 18.1b Physical Characteristics of Blood 18.4c Coagulation Phase 18.1c Components of Blood 18.4d Elimination of the Clot 18.2 Composition of Blood 18.5 Development and Aging Plasma of Blood 18.2a Plasma Proteins 18.2b Other Solutes 18.3 Formed Elements in the Blood 18.3a Hematopoiesis 18.3b Erythrocytes INTEGRATE: Concept Overview Recycling and Elimination of Erythrocyte Components 18.3c Leukocytes Module 9: Cardiovascular System 18.3d Platelets Arno Massee/Science Source CAREER PATH Within our bodies is a connective tissue so valuable that donating a portion of it to Blood Bank Technician someone else can save that person’s life. This tissue is regenerated continuously and is A blood bank technician is responsible for responsible for transporting the gases, nutrients, and hormones our bodies need for ­sampling and testing donated blood. This ­testing proper functioning. Losing too much of this tissue can be fatal and yet blood is something involves determining the blood type of the ­donated ­sample and whether the sample con- we frequently take for granted. tains ­infectious agents that can cause serious This valuable connective tissue is blood. Blood is considered a fluid connective tissue diseases (e.g., ­ hepatitis, HIV). The technician because it contains formed elements (red blood cells, white blood cells, platelets) and has a thorough u­ nderstanding of blood composi- dissolved proteins in a liquid ground substance called plasma. Four to six liters of this tion and the importance of matching donor and warm, alkaline, viscous fluid is continuously pumped through our blood vessels. It may recipient blood types prior to a transfusion. This help to think of the circulation of blood as a “fluid conveyor belt” where cells, ions, and individual must always adhere to and practice universal precautions when working with blood. molecules are both continuously added to it and dropped off from it. As a result, the ­(Universal precautions refers to the avoidance composition of blood is ever changing as it is pumped by our heart and makes its of direct contact with a patient’s bodily fluids by continuous journey through our vessels. Because of its intimate contact with the cells of wearing both gloves and safety goggles if there the body, various blood tests can be performed, providing a physician with important is danger of fluid splashing.) information for an accurate diagnosis in assessing the state of our health. In this chapter, we describe the function of blood and the various blood components. Then we examine how these components are formed and function, and discuss hemostasis. Finally, we describe the development and aging of blood. 700  Regulation 18.1 Functions and General Blood participates in the regulation of body temperature, body pH, Composition of Blood and fluid balance: Blood is the specialized fluid that is transported through the ∙∙ Body temperature. Blood helps regulate body temperature. ­cardiovascular (kar′dē-ō-vas′kū-lăr; cardio = heart, vascular = vessels) This is possible because blood absorbs heat from body cells, system, which is composed of the heart and blood ­vessels. Blood especially skeletal muscle, as it passes through blood vessels vessels form a circuit away from the heart and back to the heart that of body tissues. Heat is then released from blood at the body includes the arteries, capillaries, and veins. Arteries transport blood ­surface as blood is transported through blood vessels of the skin away from the heart, whereas veins transport blood toward the heart. (see section 1.6b). Capillaries (kap′i-lār-ēz; ­capillaries = relating to hair) are ­permeable, ∙∙ Body pH. Blood, because it absorbs acid and base from body microscopic vessels between arteries and veins. ­Capillaries serve as cells, helps maintain the pH of cells. Blood contains chemical the sites of exchange between the blood and body tissues; it is at our buffers (e.g., proteins, bicarbonate) that bind and release capillaries that oxygen and nutrients exit the blood, and ­carbon diox- ­hydrogen ions (H+) to maintain blood pH until the excess is ide and cellular wastes enter the blood. eliminated from the body (see section 25.5d). Blood is composed of formed elements (erythrocytes, leuko- ∙∙ Fluid balance. Water is added to the blood from the ­GI tract cytes, and platelets) and plasma. Erythrocytes (ĕ-rith′rō-sīt; erthyros and lost in numerous ways (including in urine, sweat, and = red, kytes = cell), also known as red blood cells, function to trans- respired air). In addition, there is a constant exchange of fluid port respiratory gases in the blood. Leukocytes (lu′kō-sit; leuko = between the blood plasma in the capillaries and the interstitial white), also known as white blood cells, contribute to defending the fluid surrounding the cells of the body’s t­issues. Blood contains body against pathogens, and platelets help clot the blood and prevent proteins and ions that exert osmotic pressure to pull fluid back blood loss from damaged vessels. Plasma is the fluid portion of blood into the capillaries to help maintain normal fluid b­ alance containing plasma proteins and dissolved solutes. We begin by (see sections 20.3b and 25.1b). ­describing the general functions of blood, its physical characteristics, and its general components. Protection Blood contains leukocytes, plasma proteins, and various molecules 18.1a Functions of Blood that help protect the body against potentially harmful substances. LEARNING OBJECTIVE These substances are part of the immune system, which is described 1. Describe the general functions of blood. in detail in chapter 22. Components of blood, including platelets and plasma proteins, also protect the body against blood loss, as described Blood carries out a variety of important functions as it circulates in section 18.4. throughout the body; these functions can be grouped as transporta- tion, regulation, and protection. WHAT DID YOU LEARN? 1 What are some of the materials that blood transports? Transportation 2 How does blood help regulate body temperature and fluid levels in the body? Blood transports formed elements and dissolved molecules and ions throughout the body. Consider that as blood is transported through 18.1b Physical Characteristics of Blood the blood vessels it transports oxygen from and carbon dioxide to the lungs for gas exchange (see section 23.1a), nutrients absorbed from LEARNING OBJECTIVE the gastrointestinal (GI) tract (see section 26.1b), hormones released 2. List six characteristics that describe blood, and explain the significance of by endocrine glands (see section 17.1a), and heat and waste products each to health and homeostasis. from the systemic cells. Even when you take a medication, it is the blood that delivers it to the cells of your body. Thus, the blood serves Blood is a type of connective tissue (see section 5.2d) that can be as the “delivery system” for the body. ­described based on its physical characteristics, including color, vol- ume, viscosity, plasma concentration, temperature, and pH: ∙∙ Color. The color of blood depends upon whether it is oxygen- INTEGRATE rich or oxygen-poor. Oxygen-rich blood is bright red or almost scarlet. Contrary to popular belief, oxygen-poor blood is not blue; rather, oxygen-poor blood is dark red. The bluish CONCEPT CONNECTION ­appearance of our veins can be attributed to both (a) the fact Recall from sections 1.6b and 6.1d that the amount of heat absorbed and that we can see the blood moving through the superficial veins released through the skin is regulated by the hypothalamus. This in the skin and (b) how light is reflected back to the eye from thermoregulation is accomplished by both (a) stimulating muscle tissue ­different colors. Lower-energy light wavelengths, like red, are contraction to increase the amount of heat generated (e.g., shivering and absorbed by the skin and not reflected back to the eye, but formation of goose bumps) and (b) redistributing blood flow to the dermis higher-energy wave­lengths, like blue, are reflected back to the through vasoconstriction (to retain heat) and vasodilation (to release heat). eye, so the eyes can perceive only the blue coloration from the veins that we see deep to the skin. Chapter Eighteen   Cardiovascular System: Blood 701  ∙∙ Volume. Average volume of blood in an adult is 5 liters (L), Physical Characteristics but can range from 4 to 6 L, depending on the size of the Table 18.1 individual. Sustaining a normal blood volume is essential in of Blood maintaining blood pressure (see section 25.2c). Characteristics Normal Values ∙∙ Viscosity. Blood is about four to five times more viscous than Color Scarlet (oxygen-rich) to dark red (oxygen-poor) water, meaning that it is thicker. Viscosity of blood depends upon the amount of dissolved substances in the blood relative Volume 5 L (average; ranges from 4-6 L) to the amount of fluid; that is, viscosity is increased if the amount of substances—primarily erythrocytes—increases, the Viscosity (relative 4.5–5.5× (whole blood) amount of fluid decreases, or both. to water) ∙∙ Plasma concentration. Although viscosity is a characteristic of Plasma 0.09% whole blood, another important physical characteristic is the concentration plasma concentration, which is the relative concentration of solutes (e.g., proteins, ions) in plasma. This is normally a 0.09% Temperature 38°C (100.4°F) concentration, and it determines whether fluids move into or pH 7.35–7.45 out of the plasma by osmosis as blood is transported through capillaries. For example, when an individual is d­ ehydrated, the plasma becomes hypertonic (see section 4.3b), and fluid moves into the plasma from the surrounding tissues. Additionally, the plasma concentration is used to determine intravenous (IV) 18.1c Components of Blood solution concentrations, which are usually isotonic to plasma. LEARNING OBJECTIVES ∙∙ Temperature. The temperature of blood is almost 1°C (or 2°F) 3. List the three components of a centrifuged blood sample. higher than measured body temperature; thus, if your body 4. Define hematocrit, and explain how the medical definition differs from the ­temperature is 37°C (98.6°F), your blood temperature is about clinical usage. 38°C (100.4°F). Therefore, blood warms areas through which it travels. 5. Name the three formed elements of the blood, and compare their ­relative abundance. ∙∙ Blood pH. Blood plasma is slightly alkaline, with a pH between 7.35 and 7.45. Plasma proteins, like all proteins of the body, have a three-dimensional shape that is dependent upon Centrifuged Blood H+ concentration. If the pH is altered from the normal range, Whole blood, which is both plasma and formed elements, can be plasma proteins become denatured and are unable to carry out separated into its liquid and cellular components by using a their functions (see section 2.8b). ­centrifuge, a device that spins the sample of blood in a tube so that The physical characteristics of blood are summarized in table 18.1. heavier components collect at the bottom. Figure 18.1 shows the resulting three components separated in the test tube. From bottom to WHAT DO YOU THINK? top, these components are as follows: 1 If a woman has 5 L of blood and she donates 1 pint (about 0.5 L), what ∙∙ Erythrocytes form the bottom (inferior) layer of the approximate percentage is she donating: 1%, 5%, 10%, or 15%? Why do centrifuged blood. They typically make up about 44% you think individuals below a certain weight (i.e., less than 110 pounds) are not allowed to give blood? of a blood sample. ∙∙ A buffy coat makes up the thin middle layer. This slightly gray-white layer is composed of both leukocytes and platelets. WHAT DID YOU LEARN? The buffy coat forms less than 1% of a blood sample. ∙∙ Plasma is a pale yellowish liquid that rises to the top in the test 3 Will blood be able to properly carry out its functions if blood pH is significantly altered? Why or why not? tube; it generally makes up about 55% of blood. The percentage of the volume of all formed elements (erythro- cytes, leukocytes, and platelets) in the blood is called the hematocrit (hē′mă-tō-krit, hem′ă-; hemato = blood, krino = to separate). This medical dictionary definition of the true hematocrit differs slightly INTEGRATE from the clinical hematocrit definition, which equates the hematocrit to the percentage of only erythrocytes. (In practice, the true hematocrit and the clinical hematocrit are considered the same.) CONCEPT CONNECTION Hematocrit values vary somewhat and are dependent upon the Recall from section 2.5b that an acid increases the concentration of H+ by age and sex of the individual. A very young child’s hematocrit may releasing it into the solution. Examples include hydrochloric acid (HCl) and vary from 30% to 60%, and that range will narrow to 35% to 50% as carbonic acid (H2CO3). In contrast, a base decreases the concentration of H+ the child becomes older. Adults who produce significant levels of in the solution. Examples include hydroxide ions (OH–) and bicarbonate ions testosterone (typically, males) tend to have a hematocrit ranging (HCO3–). The pH is a measure of the relative amounts of H+ in solution. A buffer between 42% and 56%, whereas in adults who do not have high helps prevent pH changes by binding or releasing excess H+ to maintain the levels of testosterone (typically, females), hematocrits range normal H+ concentration in a solution. from 38% to 46%. Testosterone influences hematocrit by stimulating the kidney to produce the hormone erythropoietin (EPO), which 702 Chapter Eighteen   Cardiovascular System: Blood  Plasma (55% of whole blood) Water Proteins Other solutes 92% by weight 7% by weight 1% by weight Albumins 58% Electrolytes Globulins 37% Nutrients Fibrinogen 4% Respiratory gases Regulatory proteins Waste products