Chapter 14, Section 1 of 2.
Functions of Blood:
1. Transports gasses, (O2 and CO2)
2. Transport nutrients, wastes,
electrolytes, and hormones
3. Distributes heat throughout the body
4. Contains buffers
Characteristics of Blood:
Blood is a connective tissue
1. Cells are called= formed elements
• Red Blood Cells
• White Blood Cells
2. Liquid Matrix = plasma
1. Plasma, 55%
2. Buffy Coat, <1%
• Proteins and WBCs
3. Red Blood Cells, 45%
• Hematocrit = packed RBCs
Hematopoiesis is the formation of new blood cells.
• Occurs within red bone marrow
• Blood stem cells are called, hemocytoblasts ( or hematopoietic stem cells)
• Hemocytoblasts can give rise to additional blood stem cells
• Can differentiate into any of the blood cells
• The fate of hemocytoblast depends on hematopoietic growth factors
Erythropoietin (EPO = growth factor)
Erythrocytes: red blood cells (corpuscles)
Characteristics of erythrocytes
1. Biconcave cells
2. anucleated (nucleus dislodged during formation)
3. Average diameter = 7.5µm
4. 1/3 volume is hemoglobin
• Oxyhemoglobin – bright red
• Deoxyhemoglobin – dark brick red
Red Blood Cell Counts
RBC counts is the number of RBCs in a cubic
millimeter or microliter of blood
4.6 - 6.2 million cells per µL
4.2 - 5.4 million cells per µL
4.5 - 5.1 million cells per µL
Erythropoiesis: RBC production
Sites of Erythropoiesis
Adult – Erythropoiesis occurs primarily in red bone marrow, which is found
• flat bones (sternum, pelvis, ribs, skull)
• Proximal end of long bones (femur, humerus)
• Erythropoiesis occurs within the yolk sac, liver, and spleen
Example of erythropoiesi:
In red bone marrow
Erythrocytes: feedback loop
Erythopoiesis is stimulated by low blood oxygen.
• Decreased blood O2 may cause the
kidneys and the liver (to a lesser extent)
to release erythropoietin (EPO)
• EPO stimulates RBC production
• This is a negative feedback
• Within a few days many new blood
cells appear in the circulating blood
Dietary Factors of Erythropoiesis
• Iron – required for hemoglobin production
• Vitamin B12 & Folic Acid – required for DNA synthesis
(and thus, cell production)
Lifespan of Red Blood Cells
Red blood cells survive about 120 days in circulation.
• With age, RBCs become fragile and easily rupture.
• Old RBCs are removed by the liver and spleen
• Hemoglobin is liberated and recycled in new RBCs
• recycled by body
• Reused by liver in synthesis of
• Excreted as bile pigment
Jaundice: yellowish staining of skin caused by the accumulation of bile pigments.
Jaundice may indicate increased RBC destruction, destruction of liver
tissue, or blockage of the biliary tract.
Red Blood Cell Disorders
Erythrocytosis (polycythemia) is an excess number
of RBCs in the blood.
• Causes include
1. Genetic mutations
2. Poor blood oxygen levels or delivery
Polycythemia. The surplus of RBCs causes
the blood to be more viscous and it slows
its flow through the body. This increases
the likelihood of clot formation.
• Low oxygen capacity of blood, several types
1. Iron deficiency – body cannot form
2. Hemolytic – excess RBC destruction
3. Sickle cell – sickle-shaped RBCs
4. Aplastic – inability to produce RBCs
Sickle cell anemia. RBCs take on a thin sickle shape when
deoxygenated. The sickle cells sludge in capillaries, further
reducing blood flow and oxygen levels
Leukocytes (White Blood Cells)
Functions of WBCs
1. Protect against infection
2. Remove worn out cells & debris
Colony Stimulating Factors and Interleukins
are growth factors that promote the development
of white blood cells.
There are five types of white blood cells within 2 categories
• Visible lysosomes “granules” in cytoplasm
• No visible granules in cytoplasm
1. Neutrophils stain in acid-base stains
2. Constitutes 54-62% of WBCs
3. Also called polymorphonuclear leukocytes “polymorphs”
4. Contain 2-5 nuclei + fine purple granules
5. 12 hour lifespan
• Kill bacteria, protozoa, fungi, parasites
• Remove dead cells, debris, and foreign particulate
2. First to arrive at the site of infection
• Fast moving cells
1. Constitute 1-3% of all WBCs
2. Bi-lobed nucleus
3. Granules stain bright red in acid stain
1. Defend against parasitic worms (tapeworm, hookworm, fluke worm, ect)
2. mediates allergic reaction and asthma attacks
1. Constitutes <1% of WBCs
2. Deep blue granules stain in basic dye
3. Bilobed nucleus is usually obscured by the darkened granules
1. Secretes histamines
• Histamines promote inflammation
2. Secretes heparin
• Heparin is an anticoagulant “prevents clotting”
1. Constitutes 3-9% of WBC
2. Largest of all WBCs
3. Large kidney-shaped nucleus
4. May live for several weeks up to a month
1. Leave the blood to become macrophages
2. Phagocytize bacteria, dead cells and other debris
1. Constitutes 23-33% of all WBCs
2. Formed in red bone marrow and in lymphatic tissues
3. Large spherical nucleus with a thin sliver of cytoplasm
4. May live for many months to several years
5. Includes T-cells & B-cells
1. Lymphocytes provide immunity
• T-cells directly attack microorganisms and tumor cells
• B-cells produce antibodies
Functions of white blood cells
1. Leukocytes (primarily neutrophils & monocytes) are motile
• Exhibit amoeboid movement
• Neutrophils & Monocytes are the most mobile of WBCs
2. Leukocytes are capable of diapedesis.
• They can squeeze between the cells of a capillary wall and enter the tissue space
outside the blood vessel.
3. Leukocytes exhibit chemotaxis.
• They are attracted to chemicals released by damaged tissues.
4. Leukocytes contribute to the formation of pus.
• Pus is the accumulation of bacteria, damaged tissue, and dead white blood cells.
Figure 14.15 illustrates diapedesis of a WBC from
a capillary into the surrounding connective tissue.
Activation of WBCs
Figure 14.16 When bacteria invade the tissues, leukocytes migrate into the region
and destroy the microbes by phagocytosis.
White Blood Cell Counts
A typical white blood count contains 4,500-10,000 WBCs per µL (mm3)
Leukopenia is a low WBC count (below 4,500 cells/µL)
• Often associated with viral infections (influenza, chicken pox, measles, AIDS)
Leukocytosis is a high WBC count (above 10,000 cells/µL)
• Acute infection, exercise, emotional distress
DIFF (differential WBC count)
• Measures the percentages specific types of WBC
Table 14.4 illnesses associated
with various DIFF counts
1. Platelets are cell fragments released from Megakaryocytes within
red bone marrow
2. Approximately 150,000 - 450,000 platelets per µL (mm3) of blood.
3. Thrombopoietin (TPO) = growth factor that promotes formation of
4. Functions include blood coagulation and blood vessel repair
Figure 14.4. Development of platelets from hemocytoblasts.
Exposure to TPO promotes the formation of megakaryocytes,
which release thrombocytes from their plasma membrane.
Overview of Blood Cells
End of Section 1 of 2.