Chapter 17 Blood

Composition of Blood

IntroductionBlood—made up of plasma and formed

elementsBlood—complex transport medium that

performs vital pickup and delivery services for the body

Blood—keystone of body’s heat-regulating mechanism

Composition of Blood

Blood volumeYoung adult male has approximately 5 liters of

bloodBlood volume varies according to age, body

type, sex, and method of measurement

Formed Elements of BloodRed blood cells (erythrocytes)

Description of mature red blood cells (RBCs) Have no nucleus and are shaped like tiny, biconcave disks Do not contain ribosomes, mitochondria, and other organelles

typical of most body cells Primary component is hemoglobin Most numerous of the formed elements

Formed Elements of Blood

Function of RBCsRBCs’ critical role in the transport of oxygen and

carbon dioxide depends on hemoglobinCarbonic anhydrase—enzyme in RBCs that

catalyzes a reaction that joins carbon dioxide and water to form carbonic acid

Carbonic acid—dissociates and generates bicarbonate ions, which diffuse out of the RBC and serve to transport carbon dioxide in the blood plasma

Formed Elements of Blood

Red blood cells (erythrocytes) (cont.)Hemoglobin

Within each RBC are approximately 200 to 300 million molecules of hemoglobin

Hemoglobin is made up of four globin chains, each attached to a heme molecule

Hemoglobin is able to unite with four oxygen molecules to form oxyhemoglobin to allow RBCs to transport oxygen where it is needed

A male has a greater amount of hemoglobin than a female

Anemia—a decrease in number or volume of functional RBCs in a given unit of whole blood

Formed Elements of BloodRed blood cells (erythrocytes) (cont.)

Formation of red blood cells Erythropoiesis—entire process of RBC formation RBC formation begins in the red bone marrow with

hemopoietic stem cells that go through several stages of development to become erythrocytes; entire maturation process requires approximately 4 days

RBCs are created and destroyed at a rate of approximately 100 million per minute in an adult; homeostatic mechanisms operate to balance number of cells formed against number of cells destroyed

Formed Elements of Blood

Destruction of RBCs Life span of a circulating RBC averages 105 to 120

daysMacrophage cells phagocytose the aged, abnormal,

or fragmented RBCsHemoglobin is broken down and amino acids, iron,

and bilirubin are released

Formed Elements of Blood

White blood cells (leukocytes, WBCs) Granulocytes

Neutrophils —make up approximately 65% of total WBC count in a normal blood sample; highly mobile and very active phagocytic cells; capable of diapedesis; cytoplasmic granules contain lysosomes

Eosinophils —account for 2% to 5% of circulating WBCs; numerous in lining of respiratory and digestive tracts; weak phagocytes; capable of ingesting inflammatory chemicals and proteins associated with antigen-antibody reaction complexes; provide protection against infections caused by parasitic worms and allergic reactions

Basophils —account for only 0.5% to 1% of circulating WBCs; motile and capable of diapedesis; cytoplasmic granules contain histamine and heparin

Formed Elements of Blood

White blood cells (cont.) Agranulocytes (Figures 17-12 and 17-13)

Lymphocytes—smallest of the WBCs; second most numerous type of WBC; account for approximately 25% of circulating WBCs; T lymphocytes and B lymphocytes have an important role in immunity—T lymphocytes directly attack an infected or cancerous cell, and B lymphocytes produce antibodies against specific antigens

Monocytes—largest type of leukocyte; mobile and highly phagocytic cells

Formed Elements of BloodWBC numbers—a cubic millimeter of normal

blood usually contains 5,000 to 9,000 leukocytes, with different percentages for each type; WBC numbers have clinical significance because they change with certain abnormal conditions

Formation of WBCs Granular and agranular leukocytes mature from the

undifferentiated hemopoietic stem cell Neutrophils, eosinophils, basophils, and a few lymphocytes and

monocytes originate in red bone marrow; most lymphocytes and monocytes develop from hemopoietic stem cells in lymphatic tissue

Formed Elements of Blood

Platelets Structure

In circulating blood, platelets are small, pale bodies that appear as irregular spindles or oval disks

Three important properties are agglutination, adhesiveness, and aggregation

Platelet counts in adults average 250,000 per mm3 of blood; normal range is 150,000 to 400,000 per mm3

Functions of platelets Important role in hemostasis and blood coagulation Hemostasis—refers to stoppage of blood flow; however, if

injury is extensive, the blood-clotting mechanism is activated to assist

Blood Types (Blood Groups)

The ABO system Every person’s blood belongs to one of four

ABO blood groupsNamed according to antigens present on RBC

membranes Type A—antigen A on RBC Type B—antigen B on RBC Type AB—both antigen A and antigen B on RBC; known

as universal recipient Type O—neither antigen A nor antigen B on RBC; known

as universal donor

Blood Types (Blood Groups)

The Rh system Rh-positive blood—Rh antigen is present on

the RBCsRh-negative—RBCs have no Rh antigen

presentAnti-Rh antibodies are not normally present in

blood; anti-Rh antibodies can appear in Rh-negative blood if it has come in contact with Rh-positive RBCs

Blood Plasma

Plasma—liquid part of blood; clear, straw-colored fluid; made up of 90% water and 10% solutes

Solutes—6% to 8% of plasma solutes are proteins, consisting of three main compounds: Albumins—helps maintain osmotic balance of the blood Globulins—essential component of the immunity

mechanism Fibrinogen—key role in blood clotting

Plasma proteins have an essential role in maintaining normal blood circulation

Blood Plasma

Plasma—liquid part of blood; clear, straw-colored fluid; made up of 90% water and 10% solutes

Solutes—6% to 8% of plasma solutes are proteins, consisting of three main compounds: Albumins—helps maintain osmotic balance of the blood Globulins—essential component of the immunity

mechanism Fibrinogen—key role in blood clotting

Plasma proteins have an essential role in maintaining normal blood circulation

Blood Clotting (Coagulation)

Mechanism of blood clotting—goal of coagulation is to stop bleeding and prevent loss of vital body fluid in a swift and sure method; the “classic theory” is as follows:“Classic theory” of coagulation advanced in

1905Identified four components critical to coagulation:

Prothrombin Thrombin Fibrinogen Fibrin

Blood Clotting (Coagulation)

Mechanism of blood clotting (cont.)Current explanation of coagulation involves

three stages: Stage I—production of thromboplastin activator by

one or the other of the following: chemicals released from damaged tissues (extrinsic

pathway) chemicals present in the blood (intrinsic pathway)

Stage II—conversion of prothrombin to thrombinStage III—conversion of fibrinogen to fibrin and

production of fibrin clot

Blood Clotting (Coagulation)

Conditions that oppose clottingClot formation in intact vessels is opposedSeveral factors oppose clotting

Perfectly smooth surface of the normal endothelial lining of blood vessels does not allow platelets to adhere

Antithrombins—substances in the blood that oppose or inactivate thrombin; prevent thrombin from converting fibrinogen to fibrin; e.g., heparin

Blood Clotting (Coagulation)

Conditions that hasten clotting Rough spot in the endothelium Abnormally slow blood flow

Clot dissolution Fibrinolysis—physiological mechanism that

dissolves fibrin Fibrinolysin—enzyme in the blood that catalyzes the

hydrolysis of fibrin, causing it to dissolve Additional factors are presumed to aid clot

dissolution; e.g., substances that activate profibrinolysin