Blood

Functions of Blood:1. Transports gasses, (O2 and CO2)2. Transport nutrients, wastes,

electrolytes, and hormones3. Distributes heat throughout the

body4. Contains buffers5. Immunity

Chapter 14, Section 1 of 2.

ivyanatomy.com

Centrifuged Blood:1. Plasma, 55%

2. Buffy Coat, <1%• Proteins and WBCs

3. Red Blood Cells, 45%• Hematocrit = packed

RBCs

Characteristics of Blood: Blood is a connective tissue

1. Cells are called= formed elements• Red Blood Cells• White Blood Cells• Platelets

2. Liquid Matrix = plasma

Introduction

HematopoiesisHematopoiesis 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

Hemocytoblast erythroblast reticulocyte erythrocyte (RBC)

Example:

Erythropoietin (EPO = growth factor)

Erythrocytes: red blood cells (corpuscles)

Characteristics of erythrocytes1. Biconcave cells2. anucleated (nucleus dislodged during

formation)3. Average diameter = 7.5µm4. 1/3 volume is hemoglobin

• Oxyhemoglobin – bright red• Deoxyhemoglobin – dark brick red

Red Blood Cell CountsRBC counts is the number of RBCs in a cubic millimeter or microliter of blood

1. Male 4.6 - 6.2 million cells per µL2. Female 4.2 - 5.4 million cells per µL3. Child 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 within

• flat bones (sternum, pelvis, ribs, skull)• Proximal end of long bones (femur, humerus)

Child• Erythropoiesis occurs within the yolk sac, liver, and spleen

Example of erythropoiesi:

In red bone marrow

circulation

Erythropoietin (EPO)

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 mechanism

• Within a few days many new blood cells appear in the circulating blood

• Iron – required for hemoglobin production

• Vitamin B12 & Folic Acid – required for DNA synthesis (and thus, cell production)

Dietary Factors of Erythropoiesis

Erythrocytes: feedback loop

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

Hemoglobin breakdownHemoglobin

Heme Globin

Biliverdin Iron (Fe2+)• Reused by liver in synthesis

of new hemoglobinBilirubin• Excreted as bile

pigment

Amino acids • recycled by body

+

+

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 DisordersErythrocytosis (polycythemia) is an excess number of RBCs in the blood.

• Causes include1. Genetic mutations2. Poor blood oxygen levels or

delivery3. tumor

Anemia• Low oxygen capacity of blood, several types

1. Iron deficiency – body cannot form hemoglobin

2. Hemolytic – excess RBC destruction3. 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

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.

Leukocytes (White Blood Cells)Functions of WBCs1. Protect against infection2. Remove worn out cells & debris3. immunity

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

Granulocytes • Visible lysosomes “granules” in cytoplasm

1. Neutrophil2. Eosinophil3. Basophil

Agranulocytes• No visible granules in cytoplasm

1. Monocyte2. Lymphocyte

Neutrophils

Functions1. Phagocytosis

• Kill bacteria, protozoa, fungi, parasites• Remove dead cells, debris, and foreign particulate

2. First to arrive at the site of infection• Fast moving cells

Overview:1. Neutrophils stain in acid-base stains 2. Constitutes 54-62% of WBCs3. Also called polymorphonuclear leukocytes “polymorphs”4. Contain 2-5 nuclei + fine purple granules5. 12 hour lifespan

neutrophil, 1000x

EosinophilsOverview:

1. Constitute 1-3% of all WBCs2. Bi-lobed nucleus3. Granules stain bright red in acid stain

Functions1. Defend against parasitic worms (tapeworm, hookworm, fluke worm,

ect)2. mediates allergic reaction and asthma attacks

eosinophil, 1000x

BasophilsOverview:

1. Constitutes <1% of WBCs2. Deep blue granules stain in basic dye3. Bilobed nucleus is usually obscured by the darkened granules

Functions1. Secretes histamines

• Histamines promote inflammation2. Secretes heparin

• Heparin is an anticoagulant “prevents clotting”

basophil, 1000x

MonocytesOverview:

1. Constitutes 3-9% of WBC2. Largest of all WBCs3. Large kidney-shaped nucleus4. May live for several weeks up to a month

Functions1. Leave the blood to become macrophages2. Phagocytize bacteria, dead cells and other debris

monocyte, 1000x

platelet

Overview:1. Constitutes 23-33% of all WBCs2. Formed in red bone marrow and in lymphatic tissues3. Large spherical nucleus with a thin sliver of cytoplasm4. May live for many months to several years5. Includes T-cells & B-cells

Lymphocytes

Functions1. Lymphocytes provide immunity

• T-cells directly attack microorganisms and tumor cells• B-cells produce antibodies

lymphocyte, 1000x

Functions of white blood cells1. 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.

Figure 14.16 When bacteria invade the tissues, leukocytes migrate into the region and destroy the microbes by phagocytosis.

Activation of WBCs

White Blood Cell CountsA 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

Thrombocytes (platelets)

Overview1. 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 platelets.

4. Functions include blood coagulation and blood vessel repair

TPO

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.