BLOOD
Blood Functions
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Transports
1.
2.
3.
4.
5.
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Dissolved gasses
Nutrients
Waste products to lungs and kidneys
Enzymes
Hormones from endocrine organs
Regulates
1. pH
2. Electrolyte concentration of body fluids
3. Body temperature
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Restricts fluid loss
Defends pathogens and toxins
Overview of Blood Circulation
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Blood leaves the heart via arteries that branch repeatedly
until they become capillaries
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Oxygen (O2) and nutrients diffuse across capillary walls and enter tissues
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Carbon dioxide (CO2) and wastes move from tissues into the blood
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Oxygen-deficient blood leaves the capillaries and flows in veins to the heart
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This blood flows to the lungs where it releases CO2 and picks up O2
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The oxygen-rich blood returns to the heart
Composition of Blood
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Blood is the body’s only fluid tissue
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It is composed of liquid plasma and formed elements
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Formed elements include:
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Erythrocytes, or red blood cells (RBCs)
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Leukocytes, or white blood cells (WBCs)
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Platelets
Physical Characteristics and Volume
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Blood is a sticky, opaque fluid with a metallic taste
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Color varies from scarlet (oxygen-rich) to dark red (oxygen-poor)
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The pH of blood is 7.35–7.45
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Temperature is 38C, slightly higher than “normal” body temperature
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Blood accounts for approximately 8% of body weight
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Average volume of blood is 5–6 L for males, and 4–5 L for females
Distribution
Blood transports:
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Oxygen from the lungs and nutrients from the digestive tract
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Metabolic wastes from cells to the lungs and kidneys for elimination
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Hormones from endocrine glands to target organs
Regulation
Blood maintains:
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Appropriate body temperature by absorbing and
distributing heat
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Normal pH in body tissues using buffer systems
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Adequate fluid volume in the circulatory system
Protection
Blood prevents blood loss by:
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Activating plasma proteins and platelets
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Initiating clot formation when a vessel is broken
Blood prevents infection by:
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Synthesizing and utilizing antibodies
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Activating complement proteins
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Activating WBCs to defend the body against foreign invaders
Blood Plasma
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Plasma accounts for 55 % of the volume of whole blood.
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92% of plasma is water, the rest consists of electrolytes and dissolved organic compounds.
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The exchange of dissolved materials occurs by diffusion across the walls of capillaries.
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The dissolved concentration of gases, nutrients, and waste products differs, depending on the region
sampled and the metabolic state of the tissue and individual.
Blood plasma contains over 100 solutes, including:
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Proteins – albumin, globulins, clotting proteins, and others
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Nonprotein nitrogenous substances – lactic acid, urea, creatinine
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Organic nutrients – glucose, carbohydrates, amino acids
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Electrolytes – sodium (Na+), potassium (K+), calcium (Ca++), chloride (Cl-), bicarbonate (HCO3-)
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Respiratory gases – oxygen and carbon dioxide
The Plasma Proteins:
1. Albumin, the most abundant plasma protein, contributes to the osmotic pressure of the blood and provides
a transport mechanism for specific insoluble or valuable materials in the blood.
2. Globular proteins are important in binding and transporting hormones, lipids (lipoproteins), and metal ions.
The immunoglobulins (antibodies) are proteins that attack foreign proteins and pathogens.
3. Under the proper stimulation, fibrinogen molecules aggregate to form large insoluble strands of fibrin that
establish the basis for a blood clot. The removal of fibrinogen from plasma leaves a fluid called serum.
Formed Elements
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Erythrocytes, leukocytes, and platelets make up the formed elements
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Only WBCs are complete cells
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RBCs have no nuclei or organelles, and platelets are just cell fragments
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Most formed elements survive in the bloodstream for only a few days
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Most blood cells do not divide but are renewed by cells in bone marrow
Erythrocytes (RBCs)
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Biconcave discs & anucleate allow for a huge surface area to volume ratio
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Hematocrit – percentage of RBCs out of the total blood volume. (Ave) 46 adult
men & 42 adult women.
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There are roughly 5 million RBCs in each microliter of blood; they transport
oxygen and carbon dioxide, and have large surface-to volume ratios.
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Red blood cells account for slightly less than half the blood volume.
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Erythrocytes are unable to perform normal maintenance operations and usually degenerate after
about 120 days in the circulation.
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Each red blood cell contains molecules of hemoglobin (Hgb), a globular protein formed from four
subunits. Each subunit contains a single molecule of heme, which can reversibly bind oxygen.
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Heme molecules bind to oxygen when plasma concentrations are high; the oxygen is released when
plasma concentrations decline.
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Carbon dioxide molecules can be bound to the globin portion of the hemoglobin molecule.
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Damaged or expired red blood cells are recycled by phagocytes. The proteins are disassembled into
amino acids, and the iron gets bound to transferrins for transport to the bone marrow and liver. The
heme units are not recycled, but removed from the circulation by the liver and excreted in the bile.
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Agglutinogens A, B, and D (Rh) on the exposed surfaces of the red blood cells determine an
individual's blood type. Agglutinins within the plasma will react with red blood cells bearing different
agglutinogens.
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Anti-Rh agglutinins are only synthesized after an Rh-negative individual becomes sensitized to the Rh
agglutinogen. (During pregnancy)
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Testing for compatibility involves the determination of blood type and a cross-match test.
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Standard blood typing detects the A, B, and D (Rh) agglutinogens. The most common blood type used
for transfusion is O-negative (universal donor).
AB-positive (Universal recipient)
Hemoglobin (Hgb)
Hemoglobin is composed of:
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The protein globin, made up of two alpha and two beta chains, each bound to a heme group
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Each heme group bears an atom of iron, which can bind one to oxygen molecule
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Each hemoglobin molecule can transport four molecules of oxygen
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Oxyhemoglobin – hemoglobin bound to oxygen
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Oxygen loading takes place in the lungs
• Deoxyhemoglobin- hemoglobin after oxygen diffuses into tissues (reduced Hgb)
Carboxyhemoglobin – hemoglobin bound to carbon dioxide
•
•
Carbon dioxide loading takes place in the tissues
The fetus forms HbF, which has a higher affinity for oxygen than adult hemoglobin
Production of Blood Cells
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Hematopoiesis – blood cell formation
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Hematopoiesis occurs in the red bone marrow of the:
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Axial skeleton and girdles
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Epiphyses of the humerus and femur
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Hemocytoblasts give rise to all formed elements
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Circulating stem cells give rise to embryonic blood cells which migrate into the liver, spleen, thymus,
and bone marrow.
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Hemocytoblasts divide to give rise to several populations of stem cells. The divisions of these cells
produce the various blood cells throughout life.
Erythropoiesis
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Erythropoiesis primarily occurs within red marrow of the sternum, vertebrae, skull, scapulae, pelvis,
and proximal limb bones.

Red blood cell formation increases under erythropoietin stimulation. This hormone is released from
the kidneys when they are not receiving adequate supplies of oxygen.
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Erythropoiesis is hormonally controlled and depends on adequate supplies of iron, amino acids, and B
vitamins
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Stages in red blood cell development include erythroblasts and reticulocytes. Reticulocytes (immature
RBC’s) usually account for 0.8 percent of circulating red blood cells.

Circulating erythrocytes – the number remains constant and reflects a balance between RBC
production and destruction
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Too few red blood cells leads to tissue hypoxia
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Too many red blood cells causes undesirable blood viscosity
Hormonal Control of Erythropoiesis
Erythropoietin (EPO) release by the kidneys is triggered by:
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Hypoxia due to decreased RBCs
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Decreased oxygen availability
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Increased tissue demand for oxygen
Enhanced erythropoiesis increases the:
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RBC count in circulating blood
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Oxygen carrying ability of the blood increases
Erythropoiesis: Nutrient Requirements
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Erythropoiesis requires:
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Proteins, lipids, and carbohydrates
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Iron, vitamin B12, and folic acid
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The body stores iron in Hgb (65%), the liver, spleen, and bone marrow
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Intracellular iron is stored in protein-iron complexes such as ferritin and hemosiderin
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Circulating iron is loosely bound to the transport protein transferrin
Fate and Destruction of Erythrocytes
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The life span of an erythrocyte is 100–120 days
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Old erythrocytes become rigid and fragile, and their hemoglobin begins to degenerate
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Dying erythrocytes are engulfed by macrophages
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Heme and globin are separated and the iron is salvaged for reuse
Fate of Hemoglobin
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Heme is degraded to a yellow pigment called bilirubin
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The liver secretes bilirubin into the intestines as bile
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The intestines metabolize it into urobilinogen
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This degraded pigment leaves the body in feces, in a pigment called stercobilin
or as urobilinogen in urine
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Globin is metabolized into amino acids and is released into the circulation
Erythrocyte Disorders
Anemia – blood has abnormally low oxygen-carrying capacity
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It is a symptom rather than a disease itself
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Blood oxygen levels cannot support normal metabolism
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Signs/symptoms include fatigue, paleness, shortness of breath,
and chills
Anemia: Insufficient Erythrocytes
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Hemorrhagic anemia – result of acute or chronic loss of blood (e.g.Trauma & Menstruation)
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Hemolytic anemia – prematurely ruptured erythrocytes
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Aplastic anemia – destruction or inhibition of red bone marrow
Anemia: Decreased Hemoglobin Content
Iron-deficiency anemia results from:
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A secondary result of hemorrhagic anemia
Inadequate intake of iron-containing foods
Impaired iron absorption
Pernicious anemia results from:
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Deficiency of vitamin B12
Often caused by lack of intrinsic factor needed for absorption of B12
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Anemia: Abnormal Hemoglobin
Thalassemias – absent or faulty globin chain in hemoglobin
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Erythrocytes are thin, delicate, & deficient in hemoglobin
Sickle-cell anemia – results from a defective gene coding for an abnormal hemoglobin called hemoglobin S
(HbS)
Polycythemia
Polycythemia – excess RBCs that increase blood viscosity
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Blood doping in athletics
Leukocytes (WBCs)
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White blood cells are components of the immune system that defends the body against pathogens,
toxins, wastes, and abnormal or damaged cells and tissues.
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There are 6,000-9,000 white blood cells in each microliter of whole blood .
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Normal response to bacterial or viral invasion
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Move through tissue spaces
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Granular leukocytes include neutrophils, eosinophils , and basophils.
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Neutrophils are abundant, highly mobile phagocytes. Eosinophils (less common) are attracted to
foreign compounds coated with antibodies. Basophils (rare) migrate into damaged tissues and release
histamine, aiding in the inflammation response.
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Monocytes migrating into peripheral tissues become free macrophages.
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Lymphocytes, cells of the lymphatic system, include T cells and B cells. T cells migrate to peripheral
tissues and attack foreign or abnormal cells; B cells produce antibodies.
White Blood Cell Formation
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Granulocytes and monocytes are produced by stem cells in the bone marrow
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Lymphocytes are produced in bone marrow, thymus, spleen, and other lymphoid tissues.
Classification of Leukocytes:
Granulocytes (Neutrophils, eosinophils, & basophils)
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Contain cytoplasmic granules that stain specifically with Wright’s stain
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Are larger and usually shorter-lived than RBCs
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Have lobed nuclei
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Are all phagocytic cells
Neutrophils (Polymorphonuclear) (60-70% of WBC’s)
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Neutrophils have two types of granules that:
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Take up both acidic and basic dyes
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Give the cytoplasm a lilac color
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Contain peroxidases, hydrolytic enzymes, and defensins (antibiotic-like proteins)
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Neutrophils are our body’s bacterial slayers
Lifespan : 1 day in blood; 1-2 days in tissue
Eosinophils (1-4% of WBC’s)
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Eosinophils account for 1–4% of WBCs
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Have red-staining, bi-lobed nuclei connected via a broad band of nuclear material
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Have red to crimson (acidophilic) large, coarse, lysosome-like granules
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Lead the body’s counterattack against parasitic worms
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Lessen the severity of allergies by phagocytizing immune complexes
Lifespan: 1 day in blood; weeks in tissue
Basophils (0.5-1% of WBC’s)
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Have U or Sshaped nuclei with two or three conspicuous constrictions
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Are functionally similar to mast cells
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Have large, purplish-black (basophilic) granules that contain histamine

Histamine – inflammatory chemical that acts as a vasodilator & attracts other WBCs
Lifespan: 1 day in blood; hours in tissue
Agranulocytes (Lymphocytes & monocytes)
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Lack visible cytoplasmic granules
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Are similar structurally, but are functionally distinct and unrelated cell types
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Have spherical (lymphocytes) or kidney-shaped (monocytes) nuclei
Lymphocytes (20-25% of WBC’s)
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Have large, dark-purple, circular nuclei with a thin rim of blue cytoplasm
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Found mostly enmeshed in lymphoid tissue (some circulate in the blood)
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There are two types of lymphocytes: T cells and B cells
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T cells function in the immune response
B cells give rise to plasma cells, which produce antibodies
Lifespan: Years
Monocytes (3-8% of WBC’s)
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They are the largest leukocytes
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They have abundant pale-blue cytoplasms
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They have purple staining, U- or kidney-shaped nuclei
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They leave the circulation, enter tissue, and differentiate into macrophages
Lifespan: Days in blood; years in tissue
Macrophages:
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Are highly mobile and actively phagocytic
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Activate lymphocytes to mount an immune response
Leukocyte Disorders: Leukemias
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Leukemia refer to cancerous conditions involving white blood cells
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Leukemias are named according to the abnormal white blood cells involved
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Immature white blood cells are found in the bloodstream in all leukemias
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Bone marrow becomes totally occupied with cancerous leukocytes
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The white blood cells produced, though numerous, are not functional
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Death is caused by internal hemorrhage and overwhelming infections
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Acute leukemia involves blast-type cells and primarily affects children
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Chronic leukemia is more prevalent in older people
Common symptoms of leukemia:
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Anemia
Fever
Weakness and fatigue
Frequent infections
Loss of appetite and/or weight
Swollen or tender lymph nodes, liver, or spleen
Easy bleeding or bruising
Tiny red spots (called petechiae) under the skin
Swollen or bleeding gums
females. Sweating, especially at night; and/or
Bone or joint pain.
Platelets
Megakaryocytes in the bone marrow release packets of cytoplasm, called platelets, into the
circulating blood. There are 150,000-500,000 platelets in each microliter of whole blood.
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Platelet granules contain serotonin, Ca2+, enzymes, ADP, and platelet-derived growth factor (PDGF)
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Platelets function in the clotting mechanism by forming a temporary plug that helps seal breaks in blood
vessels
Hemostasis (A series of reactions designed for stoppage of bleeding)
During hemostasis, three phases occur in rapid sequence
1. Vascular spasms – immediate vasoconstriction in response to injury
2. Platelet plug formation
3. Coagulation (blood clotting)
Platelet Plug Formation
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Platelets do not stick to each other or to the endothelial lining of blood vessels
Upon damage to a blood vessel, platelets:
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Stick to exposed collagen fibers and form a platelet plug
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Release serotonin and ADP, which attract still more platelets
The platelet plug is limited to the immediate area of injury by PGI
Coagulation: A set of reactions in which blood is transformed from a liquid to a gel
The coagulation phase occurs as factors released by endothelial cells (extrinsic pathway) and platelets
(intrinsic pathway) interact with clotting factors to yield thromboplastin. Thromboplastin triggers the
conversion of prothrombin to thrombin, and thrombin catalyzes the formation of fibrin from circulating
plasma fibrinogen.This results in the formation of a blood clot.

The blood clot gradually retracts (syneresis), pulling the damaged surfaces together. As repairs
proceed the clot dissolves (fibrinolysis) through the action of plasmin, the activated form of
circulating plasminogen.
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The coagulation process requires calcium ions, and Vitamin K must be available
for the synthesis of five of the clotting factors.
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Excessive or inappropriate clotting can lead to the formation of a thrombus or an embolus.
Anticoagulant drugs include heparin and coumadin; in some cases clots may be dissolved by activating
plasminogen with streptokinase, urokinase, or tissue plasminogen activator.
Hemostasis Disorders: Thromboembolytic Disorders
Thrombus – a clot that develops and persist in an unbroken blood vessel
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Thrombi can block circulation, resulting in tissue death
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Coronary thrombosis – thrombus in blood vessel of the heart
Embolus – a thrombus freely floating in the blood stream
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Pulmonary emboli can impair the ability of the body to obtain oxygen
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Cerebral emboli can cause strokes
Prevention of Undesirable Clots
Substances used to prevent undesirable clots include:
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Aspirin
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Heparin
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Warfarinin (Coumadin)
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Flavonoids – substances found in tea, red wine, and grape juice that have natural anticoagulant activity
Hemostasis Disorders: Bleeding Disorders
Thrombocytopenia – condition where the number of circulating platelets is deficient
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Patients show petechiae (small purple blotches on the skin) due to spontaneous, widespread
hemorrhage
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Caused by suppression or destruction of bone marrow (e.g., malignancy, radiation)
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Platelet counts less than 50,000/mm3 is diagnostic for this condition
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Treated with whole blood transfusions
Inability to synthesize procoagulants by the liver results in severe bleeding disorders
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Causes can range from vitamin K deficiency to hepatitis and cirrhosis
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Inability to absorb fat can lead to vitamin K deficiencies as it is a fat-
soluble substance and is absorbed along with fat
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Liver disease can also prevent the liver from producing bile, which is
required for fat and vitamin K absorption
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Hemophilias – hereditary bleeding disorders caused by lack of clotting
factors
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Hemophilia A – most common type (83% of all cases) due to a
deficiency of factor VIII
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Hemophilia B – results from a deficiency of factor IX
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Hemophilia C – mild type, caused by a deficiency of factor XI
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Symptoms include prolonged bleeding and painful and disabled joints
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Treatment is with blood transfusions and the injection of missing
factors
Blood Transfusions
Transfusions are necessary:
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When substantial blood loss occurs
Whole blood transfusions are used:
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When blood loss is substantial
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In treating thrombocytopenia
Packed red cells (cells with plasma removed) are used to treat anemia
Human Blood Groups
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RBC membranes have glycoprotein antigens on their external surfaces
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These antigens are:
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Unique to the individual
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Recognized as foreign if transfused into another individual
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Promoters of agglutination and are referred to as agglutinogens
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Presence/absence of these antigens are used to classify blood groups
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The antigens of the ABO and Rh blood groups cause vigorous transfusion reactions when they are
improperly transfused
ABO Blood Groups
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The ABO blood groups consists of:
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Two antigens (A and B) on the surface of the RBCs
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Two antibodies in the plasma (anti-A and anti-B)
The following list, from The American National Red Cross, shows the percentage of people in the United
States with a particular blood type..
O Positive - 38.4%
A Positive - 32.3%
B Positive - 9.4%
O Negative - 7.7%
A Negative - 6.5%
AB Positive - 3.2%
B Negative - 1.7%
AB Negative - 0.7%
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Cross-matching involves exposing donor RBCs to the recipient's plasma to detect other possible cross
reactions.
Rh Blood Groups
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Presence of the Rh agglutinogens on RBCs is indicated as Rh+
•
Anti-Rh antibodies are not spontaneously formed in Rh– individuals
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However, if an Rh– individual receives Rh+ blood, anti-Rh antibodies form
•
A second expose to Rh+ blood will result in a typical transfusion reaction
Hemolytic Disease of the Newborn (Erythroblastosis fetalis)
Rh+ antibodies of a sensitized Rh– mother cross the placenta and attack and destroy the RBCs of an Rh +
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baby
Rh– mother become sensitized when Rh+ blood (from a previous pregnancy of an Rh+ baby or a Rh+
•
transfusion) causes her body to synthesis Rh+ antibodies
The drug RhoGAM can prevent the Rh– mother from becoming sensitized
•
Transfusion Reactions
•
Transfusion reactions occur when mismatched blood is infused
•
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Donor’s cells are attacked by the recipient’s plasma agglutinins causing:
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Diminished oxygen-carrying capacity
•
Clumped cells that impede blood flow
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Ruptured RBCs that release free hemoglobin into the bloodstream
Circulating hemoglobin precipitates in the kidneys and causes renal failure
Blood Typing
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When serum containing anti-A or anti-B agglutinins is added to blood, agglutination will occur between the
agglutinin and the corresponding agglutinogens
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Positive reactions indicate agglutination