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17

Blood

Human Anatomy & Physiology, Sixth Edition

Elaine N. Marieb

PowerPoint^® Lecture Slides prepared by Vince Austin, University of Kentucky

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Overview of Blood Circulation

Blood leaves the heart via arteries that branch repeatedly until they become capillaries
Oxygen (O₂) and nutrients diffuse across capillary walls and enter tissues
Carbon dioxide (CO₂) and wastes move from tissues into the blood

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Overview of Blood Circulation

Oxygen-deficient blood leaves the capillaries and flows in veins to the heart
This blood flows to the lungs where it releases CO₂ and picks up O₂
The oxygen-rich blood returns to the heart

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Composition of Blood

Blood is the body’s only fluid tissue
It is composed of liquid plasma and formed elements
Formed elements include:

Erythrocytes, or red blood cells (RBCs)
Leukocytes, or white blood cells (WBCs)
Thrombocytes, or platelets

Hematocrit – the percentage of RBCs out of the total blood volume

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Components of Whole Blood

Figure 17.1

Withdraw blood and place in tube

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Centrifuge

Plasma�(55% of whole blood)

Formed elements

Buffy coat:�leukocyctes and platelets�(<1% of whole blood)

Erythrocytes�(45% of whole blood)

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Physical Characteristics and Volume

Blood is a sticky, opaque fluid with a metallic taste
Color varies from scarlet (oxygen-rich) to dark red (oxygen-poor) and is never blue in humans
The pH of blood is 7.35–7.45
Temperature is 38^oC, slightly higher than “normal” body temperature
Average volume of blood is 5–6 L for males, and 4–5 L for females

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Blood Plasma

Blood plasma contains over 100 solutes, including:

Proteins – albumin, globulins, clotting proteins, and others
Nonprotein nitrogenous substances – lactic acid, urea, creatinine
Organic nutrients – glucose, carbohydrates, amino acids
Electrolytes – sodium, potassium, calcium, chloride, bicarbonate
Respiratory gases – oxygen and carbon dioxide

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Erythrocytes (RBCs)

Biconcave discs, anucleate, essentially no organelles
Filled with hemoglobin (Hb), a protein that functions in gas transport

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Erythrocytes (RBCs)

Figure 17.3

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Erythrocytes (RBCs)

Structural characteristics contribute to its gas transport function

Biconcave shape that has a huge surface area relative to volume
Discounting water content, erythrocytes are more than 97% hemoglobin
ATP is generated anaerobically, so the erythrocytes do not consume the oxygenthey transport

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Erythrocyte Function

Erythrocytes are dedicated to respiratory gas transport
Hemoglobin reversibly binds with oxygen and most oxygen in the blood is bound to hemoglobin
Hemoglobin is composed of the protein globin, made up of two alpha and two beta chains, each bound to a heme group
Each heme group bears an atom of iron, which can bind to one oxygenmolecule
Each hemoglobin molecule can transport four molecules of oxygen

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Structure of Hemoglobin

Figure 17.4

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Hemoglobin

Oxyhemoglobin – hemoglobin bound to oxygen

Oxygen loading takes place in the lungs

Deoxyhemoglobin – hemoglobin after oxygen diffuses into tissues (reduced Hb)
Carbaminohemoglobin – hemoglobin bound to carbon dioxide

Carbon dioxide loading takes place in the tissues

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Production of Erythrocytes

Hematopoiesis – blood cell formation
Hematopoiesis occurs in the red bone marrow of the:

Axial skeleton and girdles
Epiphyses of the humerus and femur

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Regulation and Requirements for Erythropoiesis

Circulating erythrocytes – the number remains constant and reflects a balance between RBC production and destruction

Too few red blood cells leads to tissue hypoxia
Too many red blood cells causes undesirable blood viscosity (polycythemia)

Erythropoiesis is hormonally controlled and depends on adequate supplies of iron, amino acids, and vitamin B₁₂

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Hormonal Control of Erythropoiesis

Erythropoietin (EPO) release by the kidneys is triggered by:

Hypoxia due to decreased RBCs
Decreased oxygen availability
Increased tissue demand for oxygen

Enhanced erythropoiesis increases the:

RBC count in circulating blood
Oxygen carrying ability of the blood

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Fate and Destruction of Erythrocytes

The life span of an erythrocyte is 100–120 days
Old erythrocytes become rigid and fragile, and their hemoglobin begins to degenerate
Dying erythrocytes are engulfed by macrophages
Heme and globin are separated and the iron is salvaged for reuse

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Fate and Destruction of Erythrocytes

Heme is degraded to a yellow pigment called bilirubin
The liver secretes bilirubin into the intestines as bile
Globin is metabolized into amino acids and is released into the circulation

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Erythrocyte Disorders

Anemia – blood has abnormally low oxygen-carrying capacity

It is a symptom rather than a disease itself
Blood oxygen levels cannot support normal metabolism
Signs/symptoms include fatigue, paleness, shortness of breath, and chills

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Anemia: Insufficient Erythrocytes

Hemorrhagic anemia – result of acute or chronic loss of blood
Hemolytic anemia – prematurely ruptured erythrocytes
Aplastic anemia – destruction or inhibition of red bone marrow

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Anemia: Decreased Hemoglobin Content

Iron-deficiency anemia results from:

A secondary result of hemorrhagic anemia
Inadequate intake of iron-containing foods
Impaired iron absorption

Pernicious anemia results from:

Deficiency of vitamin B₁₂
Lack of intrinsic factor needed for absorption of B₁₂

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Anemia: Abnormal Hemoglobin

Thalassemias – absent or faulty globin chain in hemoglobin

Erythrocytes are thin, delicate, and deficient in hemoglobin

Sickle-cell anemia – results from a defective gene coding for an abnormal hemoglobin called hemoglobin S (HbS)

HbS has a single amino acid substitution in the beta chain
This defect causes RBCs to become sickle-shaped in low oxygen situations

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Anemia: Abnormal Hemoglobin

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Polycythemia

Polycythemia – excess RBCs that increase blood viscosity

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Leukocytes (WBCs)

Leukocytes, the only blood components that are complete cells:

Are less numerous than RBCs
Make up 1% of the total blood volume

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Granulocytes

Granulocytes – neutrophils, eosinophils, and basophils

Contain cytoplasmic granules that stain specifically (acidic, basic, or both) with Wright’s stain
Are larger than RBCs
Have lobed nuclei
Are all phagocytic cells
Live only about 12 hours

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Neutrophils

Neutrophils (60-70% of a blood sample)

have two types of granules that:

Take up both acidic and basic dyes
Give the cytoplasm a lilac color
Contain peroxidases, hydrolytic enzymes, and defensins (antibiotic-like proteins)

Neutrophils are our body’s bacteria slayers (phagocytes)

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Eosinophils

Eosinophils account for 1–4% of WBCs

Take up acidic dyes (acidophilic)
Have red-staining nuclei and granules
Lead the body’s counterattack against parasitic worms

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Basophils

Account for 0.5% of WBCs and:

Take up alkaline/basic dyes
Have large, purplish-black (basophilic) granules that contain histamine

Histamine – inflammatory chemical that acts as a vasodilator and attracts other WBCs (antihistamines counter this effect)

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Agranulocytes

Agranulocytes – lymphocytes and monocytes:

Lack visible cytoplasmic granules
Live from weeks to years

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Lymphocytes

Account for 25% or more of WBCs and:

Have large, dark-purple, circular nuclei with a thin rim of blue cytoplasm
Are found mostly enmeshed in lymphoid tissue (some circulate in the blood)

There are two types of lymphocytes: T cells and B cells

T cells function in the immune response
B cells give rise to plasma cells, which produce antibodies

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Monocytes

Monocytes account for 4–8% of leukocytes

They are the largest leukocytes
They have purple-staining, U- or kidney-shaped nuclei
They leave the circulation, enter tissue, and differentiate into macrophages

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Monocytes

Macrophages:

Are highly mobile and actively phagocytic
Activate lymphocytes to mount an immune response

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Leukocytes (WBCs)

eosinophil

basophil

neutrophil

lymphocyte

monocyte

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Leukocytes Disorders: Leukemias

Leukemia refers to cancerous conditions involving white blood cells
Immature white blood cells are found in the bloodstream in all leukemias
Bone marrow becomes totally occupied with cancerous leukocytes
The white blood cells produced, though numerous, are not functional

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Platelets

Platelets are fragments of megakaryocytes with a blue-staining outer region and a purple granular center
Platelets function in the clotting mechanism by forming a temporary plug that helps seal breaks in blood vessels

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Hemostasis

A series of reactions designed for stoppage of bleeding
During hemostasis, three phases occur in rapid sequence

Vascular spasms – immediate vasoconstriction in response to injury
Platelet plug formation
Coagulation (blood clotting)

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Platelet Plug Formation

Platelets do not stick to each other or to the endothelial lining of blood vessels
Upon damage to blood vessel endothelium (which exposes collagen) platelets:

Stick to exposed collagen fibers and form a platelet plug

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Coagulation

A set of reactions in which blood is transformed from a liquid to a gel
The final three steps of this series of reactions are:

Prothrombin activator is formed
Prothrombin is converted into thrombin
Thrombin catalyzes the reaction converting soluble fibrinogen into an insoluble fibrin mesh

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Detailed Events of Coagulation

Figure 17.13b

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Coagulation

Figure 17.13a

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Coagulation

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Hemostasis Disorders:�Thromboembolytic Conditions

Thrombus – a clot that develops and persists in an unbroken blood vessel

Thrombi can block circulation, resulting in tissue death
Coronary thrombosis – thrombus in blood vessel of the heart

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Hemostasis Disorders:�Thromboembolytic Conditions

Embolus – a thrombus freely floating in the blood stream

Pulmonary emboli can impair the ability of the body to obtain oxygen
Cerebral emboli can cause strokes

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Prevention of Undesirable Clots

Substances used to prevent undesirable clots include:

Aspirin, Heparin, Warfarin

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Hemostasis Disorders: Bleeding Disorders

Thrombocytopenia – condition where the number of circulating platelets is deficient

Patients show petechiae (small purple blotches on the skin) due to spontaneous, widespread hemorrhage (bruises)
Treated with whole blood transfusions

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Hemostasis Disorders: Bleeding Disorders

Liver disease can result in severe bleeding disorders
Causes can range from vitamin K deficiency to hepatitis and cirrhosis
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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Hemostasis Disorders: Bleeding Disorders

Hemophilias – hereditary bleeding disorders caused by lack of clotting factors

Symptoms include prolonged bleeding and painful and disabled joints
Treatment is with blood transfusions and the injection of missing factors

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Human Blood Groups

RBC membranes have antigens on their external surfaces
These antigens are:

Unique to the individual
Recognized as foreign if transfused into another individual
Promoters of agglutination and are referred to as agglutinogens

Presence or absence of these antigens is used to classify blood groups

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ABO Blood Groups

The ABO blood groups consists of:

Two antigens (A and B) on the surface of the RBCs
Two antibodies in the plasma (anti-A and anti-B)

Antigens and their corresponding antibodies cannot be mixed without serious hemolytic reactions

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ABO Blood Groups

Table 17.4

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Rh Blood Groups

Presence of the Rh agglutinogens on RBCs is indicated as Rh⁺
If an Rh^– individual receives Rh⁺ blood, anti-Rh antibodies form
A second exposure to Rh⁺ blood will result in a typical transfusion reaction

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Hemolytic Disease of the Newborn

Hemolytic disease of the newborn – Rh⁺ antibodies of a sensitized Rh^– mother cross the placenta and attack and destroy the RBCs of an Rh⁺ baby
Rh^– mother becomes 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
Treatment of hemolytic disease of the newborn involves pre-birth transfusions and exchange transfusions after birth

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Transfusion Reactions

Transfusion reactions occur when mismatched blood is infused
Donor’s cells are attacked by the recipient’s plasma agglutinins causing:

Diminished oxygen-carrying capacity
Clumped cells that impede blood flow
Ruptured RBCs that release free hemoglobin into the bloodstream

Circulating hemoglobin precipitates in the kidneys and causes renal failure

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Blood Typing

When serum containing anti-A or anti-B agglutinins is added to blood, agglutination will occur between the agglutinin and the corresponding agglutinogens
Positive reactions indicate agglutination

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Blood Typing

Blood type being tested	RBC agglutinogens	Serum Reaction
		Anti-A	Anti-B
AB	A and B	+	+
B	B	–	+
A	A	+	–
O	None	–	–

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Developmental Aspects

Before birth, blood cell formation takes place in the fetal yolk sac, liver, and spleen
By the seventh month, red bone marrow is the primary hematopoietic area

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