Components of blood

Cardiovascular System

A pump (the heart)

A conducting system (blood vessels)

A fluid medium (blood)

  • Is specialized fluid of connective tissue
  • Contains cells suspended in a fluid matrix

Physical Characteristics of Blood

Three General Characteristics of Blood

1.38°C (100.4°F) is normal temperature

2.High viscosity

3.Slightly alkaline pH (7.35–7.45)

Blood volume (liters) = 7 percent of body weight (kilograms)

  • Adult male: 5–6 liters
  • Adult female: 4–5 liters

Important Functions of Blood

Transportation of dissolved substances

  • Oxygen and carbon dioxide
  • Nutrients
  • Hormones
  • Immune system components
  • Waste products


  • Restriction of fluid losses at injury sites
  • Defense against toxins and pathogens


  • Stabilization of body temperature
  • Regulation of pH and ions

Hemopoiesis - Blood formation

Process of producing formed elements

Myeloid and lymphoid stem cells form from pluripotent stem cell

  • cells with capacity to develop into several types of cells


Process of separating whole blood into plasma and formed elements for clinical analysis

Breakdown of Whole Blood

Whole Blood

Plasma: A fluid consisting of:

  • Water
  • Dissolved plasma proteins
  • Other solutes

Formed elements

  • RBC = red blood cell or erythrocytes (Transport oxygen)
  • WBC = white blood cells or leukocytes (Part of the immune system)
  • Platelets = Cell fragments involved in clotting
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Makes up 50–60 percent of blood volume

More than 90 percent of plasma is water

Extracellular fluids

Interstitial fluid (IF) and plasma

Plasma and IF exchange materials across capillary walls

  • Water
  • Ions
  • Small solutes

Intracellular vs extracellular

The fluids of the body may be classified into two main divisions: the fluid within cells (intracellular fluid) and the fluid outside the cell (extracellular fluid). The extracellular fluid can be further divided into interstitial fluid, plasma, lymph, cerebrospinal fluid, and milk (in mammals).

Plasma proteins

More than 90 percent made in liver

  • Antibodies made by plasma cells

  • Peptide hormones made by endocrine organs

Albumins (60 percent)

  • •Transport substances such as fatty acids, thyroid hormones, and steroid hormones

Globulins (35 percent)

  • Antibodies, also called immunoglobulins
  • Transport globulins (small molecules): hormone-binding proteins, metalloproteins, apolipoproteins (lipoproteins), and steroid-binding proteins
  • Help to transport ions, hormones and lipids

Fibrinogen (4 percent)

  • Molecules that form clots and produce long, insoluble strands of fibrin for clotting

•Other Plasma Proteins

•1 percent of plasma

•Changing quantities of specialized plasma proteins

•Peptide hormones normally present in circulating blood


•prolactin (PRL)

•glycoproteins thyroid-stimulating hormone (TSH)

•follicle-stimulating hormone (FSH)

•luteinizing hormone (LH)

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Formed Elements

Red blood cells (RBCs; 99%)

White blood cells (WBCs; less than 1%)






Platelets – cell fragments

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Liquid part of a blood sample

•In which dissolved fibrinogen converts to solid fibrin

Red Blood Cells

•Red blood cells (RBCs)

•Make up 99.9 percent of blood’s formed elements


•The red pigment that gives whole blood its color

•Binds and transports oxygen and carbon dioxide

•Abundance of RBCs

Red blood cell count – the number of RBCs in 1 microliter of whole blood

•Male: 4.5–6.3 million

•Female: 4.2–5.5 million

•Three Important Effects of RBC Shape on Function

1.High surface-to-volume ratio

•Quickly absorbs and releases oxygen

2.Discs form stacks called rouleaux

•Smooth the flow through narrow blood vessels

3.Discs bend and flex entering small capillaries

•A 7.8-µm RBC passes through 4-µm capillary

Produced and enter circulation at same rate destroyed (about 2 million per second)

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Red Blood Cell (con't)

•Life Span of RBCs

•Lack nuclei, mitochondria, and ribosomes

•No cell repair

•Anaerobic metabolism

•Live about 120 days


Hemoglobin (Hb)

•Protein molecule that transports respiratory gases

•Normal hemoglobin (adult male)

•14–18 g/dL whole blood

•Normal hemoglobin (adult female)

•12–16 g/dL whole blood

Hemoglobin Structure

•Complex quaternary structure

•Four globular protein subunits

•Each with one molecule of heme

•Each heme contains one iron ion

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Hemoglobin function

•Carries oxygen

•With low oxygen (peripheral capillaries):

•Hemoglobin releases oxygen

•Binds carbon dioxide and carries it to lungs

•Forms carbaminohemoglobin

Fetal Hemoglobin

•Strong form of hemoglobin found in embryos

•Takes oxygen from mother’s hemoglobin

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Process of RBC formation

Begins in the red bone marrow

Proerythroblast ejects its nucleus, becomes a reticulocyte, and enters the bloodstream

Within 1 to 2 days become mature erythrocyte

Typically, rate equals blood cell destruction to maintain oxygen-carrying capacity of blood

Hypoxia (cellular oxygen deficiency) stimulates release of erythropoietin by the kidneys, that speeds the development of reticulocytes

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Blood Groups and Types

  • Based on genetically determined cell surface protein antigens called agglutinogens
  • Plasma typically contains antibodies called agglutinins, which react with antigens not on RBC surface
  • Blood groups based on presence or absence of antigen, including ABO and Rh groups, but also several others
  • With each group, two or more different blood types
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ABO Blood Group

Blood Types
  • Type A blood – antigen A; anti-B antibodies
  • Type B blood –antigen B; anti-A antibodies
  • Type AB blood – both antigen A and antigen B; no antibodies
  • Type O blood – neither antigen; both anti-A and anti-B antibodies

Blood Transfusions

Incompatible when the recipient’s antibodies (agglutinins in plasma) bind to antigens on the donated blood’s RBCs, which causes agglutination (clumping) and hemolysis (RBC rupture)

Universal recipients – Type AB: in theory can receive blood from donors of all 4 blood types because they have no antibodies to attack the donated RBCs

Universal donor – Type O: in theory can donate blood to all 4 blood types because no antigens on RBCs to trigger transfusion reaction

To avoid mismatches, recipient’s blood is typed, then cross-matched to potential donor

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Rh Factor

  • Based on the presence (+) or absence (-) of the Rh antigen, first discovered in the Rhesus monkey

Blood Types

  • Type Rh+ blood - has antigen
  • Type Rh- blood – no antigen;

An Rh- person will only produce anti-Rh antibodies in plasma if exposed to Rh+ antigen, such as during incompatible blood transfusion, sharing hypodermic needles, or when a pregnant Rh- woman is carrying an Rh+ fetus (hemolytic disease of the newborn)!

Leukocytes (WBCs)

Have a nucleus

  • Lack hemoglobin
  • Classified based on presence or absence of visible cytoplasmic granules (vesicles)

Granulocytes – differential staining visible in light microscope

  • Neutrophil (also called polymorphonuclear leukocytes PMNs)
  • Eosinophil
  • Basophil

Agranulocytes – granules present, but small and don’t stain, so not visible under light microscope

  • Lymphocyte
  • Monocyte
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Leukocyte (WBC) Function

Emigrate from bloodstream
  • Adhesion molecules slow down select WBC with receptors to assist movement through capillary wall
  • Except for lymphocytes, once leave blood vessel do not return to blood vessel


  • Pathogens and inflamed tissue release chemicals that attract phagocytic cells
  • Neutrophils respond most rapidly to infection site, and monocytes arrive later but in large numbers

The Lifecycle of a Leukocyte

Most live only a few days

  • During infection, some live only a few hours
  • Some lymphocytes (B and T cells) can live for several months or years

Differential white blood cell count

  • Measures number of each type of WBC in a sample of 100 WBCs
  • Because each type of WBC plays a different role in immune response, determining percentage of each type in the blood at a particular time can assist in diagnosing the condition

Platelets (Thrombocytes)

  • Disc shaped cell fragments that lack a nucleus
  • Develop from megakayoblasts under influence of hormone thrombopoietin
  • Stop blood loss in damaged vessels
  • Form a platelet plug in the vessel wall
  • Release chemicals that promote blood clotting
  • Life span of 5 to 9 days - removed by fixed macrophages in spleen and liver


Sequence of responses to stop blood loss from a damaged blood vessel

Quick, localized to region of damage, and carefully controlled by positive feedback

1. Vascular spasm

Smooth muscle in wall of damaged vessel contracts immediately to reduce blood loss

2. Platelet plug formation

3. Blood Clotting

  • Clot is a thickened gel of blood with a network of insoluble protein fibers that trap formed elements
  • Cascade of reactions involving calcium ions and clotting factors that activate one another
  • Prothrombinase enzyme is formed by one of two pathways (extrinsic or intrinsic)
  • Prothrombinase converts prothrombin into thrombin
  • Thrombin enzyme converts soluble fibrinogen into insoluble fibrin
  • Fibrin forms the threads of the clot
  • Clot retraction pulls blood vessel edges together
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Extrinsic vs Intrinsic

Extrinsic pathway

  • Occurs rapidly, within seconds if trauma is severe
  • Tissue factor leaked into blood from outside blood vessels

Intrinsic pathway

  • More complex and slower, usually requiring several minutes
  • Activators in direct contact with blood without outside tissue damage or contained within the blood

Common pathway

  • Same steps to clot formation once prothrombinase is formed by either pathway
  • Thrombin has positive feedback effects

Controlling clotting

Because of positive feedback cycles, a clot has a tendency to enlarge and potentially block blood flow through undamaged vessels

  • Fibrinolysis - Dissolve small, inappropriate clots
  • Activate enzyme plasmin to digest fibrin threads and inactivate fibrinogen and prothrombin
  • Anticoagulants-Substances that suppress or prevent clotting present in blood, including heparin from basophils block the action of clotting factors

Blood Clots

Initiation of clots within blood vessels

Atherosclerosis – accumulation of fatty substances on arterial walls

Trauma or infection roughening endothelial lining of blood vessel

Thrombosis - clotting in unbroken blood vessel to form a thrombus

Embolus- a thrombus that dislodges and carried in blood; can block blood flow to organ in smaller diameter vessel further in circulation (stroke, kidney failure, heart attack, pulmonary embolism)