Chapter 17
Blood
Composition of Blood

Introduction
Blood—made up of plasma and formed
elements
 Blood—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 volume
Young adult male has approximately 5 liters of
blood
 Blood volume varies according to age, body
type, sex, and method of measurement

Formed Elements of Blood

Red blood cells (erythrocytes)

Description of mature red blood cells (RBCs)


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
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
 RBCs’
of RBCs
critical role in the transport of oxygen and
carbon dioxide depends on hemoglobin
 Carbonic 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 Blood

Red 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
days
 Macrophage cells phagocytose the aged, abnormal,
or fragmented RBCs
 Hemoglobin 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 Blood
WBC 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


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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 groups
 Named according to antigens present on RBC
membranes
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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 RBCs
 Rh-negative—RBCs have no Rh antigen
present
 Anti-Rh antibodies are not normally present in
blood; anti-Rh antibodies can appear in Rhnegative 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
1905
 Identified
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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 thrombin
 Stage III—conversion of fibrinogen to fibrin and
production of fibrin clot
Blood Clotting (Coagulation)

Conditions that oppose clotting
Clot formation in intact vessels is opposed
 Several 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

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
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