BLOOD
FUNCTIONS:
1. Transports
Oxygen and CO2
Nutrients (glucose, amino acids)
Waste Products (urea)
Hormones
2. Regulates
pH through buffers and amino acids
Alkaline reserve of bicarbonate
Temperature - contains large volume of water (excellent heat absorber and coolant)
Blood volume
NaCl and albumins prevent fluid loss from blood
3. Protects against
Blood loss through clotting mechanism
Toxins and foreign microbes
WBCs phagocytose
Antibody production
BLOOD
Type of connective tissue
4½ - 5½ times more viscous than water
pH 7.35 - 7.45
0.85 - 0.90% NaCl-has salty taste
Its temperature is slightly higher (38 C or 100.4 F) than body temperature
In adult, blood volume is about 8% of total body weight
Average person has about 5 liters of blood (male - 5-6 liters; female - 4-5 liters)
When whole blood is allowed to stand or is centrifuged, it separates into two distinct fractions:
1. Formed elements - RBCs, WBCs and platelets - 45% of total volume
Buffy coat-contains WBCs and platelets-make up less than 1% of blood volume
2. Plasma - straw colored fluid - 55% of total volume
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Hematocrit - the percentage of RBCs, by volume, in whole blood after centrifugation
In men, normal range is 40 - 54%, with 47% (45%) as average
In women, normal range is between 38 - 47%, with 42% as average
Dehydration causes the blood to become more concentrated and the hematocrit rises
Athletes may have higher hematocrits
ERYTHROCYTES (RED BLOOD CELLS)
Biconcave discs without nuclei
Biconcave shape has greater surface area than cube or sphere (30% more surface area than
comparable spherical cell)
Total surface area of RBCs = 1500X surface area of body
Plasma membrane consists of protein (stromatin) and lipids (lecithin and cholesterol)
Cells are soft, flexible (may be due to protein spectrin on cytoplasmic side of membrane) and elastic
Can squeeze through passages narrower than their own diameter
RBCs live an average of 100-120 days
30 trillion RBCs in adult-most abundant cell type in body
Produced at rate of 2 million per second
4.5 to 5.5 million RBCs per cubic mm blood-the major factor contributing to blood viscosity
Adult males - average 5.4 million (+ or - 600,000) per cubic mm
Higher value in male due to his higher rate of metabolism-also testosterone enhances
erythropoietin formation by kidneys
Women - average 4.8 million (+ or - 500,000) per cubic mm
Each RBC is about 1/3 hemoglobin by volume (discounting its water content, a RBC is over 97%
hemoglobin)
RBCs evolved to trap hemoglobin and hold it in circulation - otherwise it could pass through the
wall of a capillary and be lost from circulation
200 to 300 million hemoglobin molecules in each RBC
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RBCs lack mitochondria and generate ATP anaerobically-they do not consume the oxygen they
transport
Each hemoglobin molecule can unite with 4 oxygen molecules to form oxyhemoglobin
(gives red color to blood)
Each RBC can carry about 1 billion oxygen molecules
Oxygen attaches to heme, CO2 is carried by globulin (about 23% of CO2 in blood)
In absence of oxygen, hemoglobin turns somewhat blue
Hemoglobin carries over 98% of oxygen in blood - 2% is in solution in the plasma
In adults 100 ml of blood contains an average of 15.6 g hemoglobin
Men - 14.9 (+ or -1.5 g)
Women - 13.7 (+ or -1.5 g)
At birth - 17.2 g (21.5 + or - 3 g)
Adult with a hemoglobin content less than 12 g / 100 ml is considered anemic
Adult with more than 17.5 g / 100 ml has polycythemia
ERYTHROPOIESIS
In embryo the 1st RBCs arise in the yolk sac
Liver assumes major role in RBC formation during 2nd month of intrauterine life
During 5th month the spleen is dominant producer, but this activity rapidly subsides
Erythropoiesis takes place in red bone marrow about 5th month
In certain blood diseases and following massive hemorrhage, blood formation may revert back to the
liver and spleen
At birth all bones are filled with red marrow
Red marrow of long bones is gradually replaced by fatty, yellow marrow
Becomes more fat laden in elderly - explains their difficulty in regenerating lost blood
In adult, red marrow is limited to bones of skull (diploe), clavicles, vertebrae, sternum, ribs, pelvis and
proximal ends of humerus and femur
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RBCs are formed in the red bone marrow from nucleated cells known as hemocytoblasts or stem cells
Stem cells go through several stages of development during which nucleus becomes smaller and
disappears as hemoglobin content increases
Also lose organelles (mitochondria)
Hemocytoblast -- rubriblast -- prorubricyte -- rubricyte (begins to synthesize hemoglobin) --
metarubricyte (maximum hemoglobin synthesis) -- reticulocyte
3-5 days from hemocytoblast to reticulocyte
Newly formed RBCs when they leave the bone marrow and enter the blood are called reticulocytes
Contain a netlike reticulum that represents endoplasmic reticulum
Lose nuclei by extrusion
Become erythrocytes within 1 - 2 days after release from bone marrow
Approximately 0.5 to 1.5% of RBCs in normal blood are reticulocytes
A count less than 0.5% indicates a slowdown in RBC formation
Due to nutritional or pernicious anemia or to kidney disease and too little erythropoietin
A count higher than 1.5% indicates an acceleration in RBC formation
For example, following treatment for anemia, oxygen deficiency or cancer in bone
marrow-also occurs in hemolytic anemia
For complete maturation of RBCs vitamin B12 is necessary (also folic acid which is used in synthesis of
DNA)
Intrinsic factor, secreted by parietal cells of stomach, promotes absorption of vitamin B12 in
ileum
Vitamin B12 is stored in liver, liberated as needed, and is carried in blood to bone marrow where
it functions to complete maturation of RBCs
Proteins, several vitamins, folic acid, copper, cobalt and iron are essential for RBC formation
Reticuloendothelial cells (macrophages in liver, spleen (especially) and bone marrow phagocytose RBCs
Spleen is “red blood cell graveyard”
Estimate that 1/15 of RBCs are removed from circulation each day
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Hemoglobin is broken down into heme and globin
Approximately 65% of body’s Fe supply (approx 4,000 mg) is in hemoglobin
Heme is decomposed into hemosiderin (contains Fe) and biliverdin (green)
Biliverdin is reduced to bilirubin
Bilirubin is carried by plasma to liver where it is excreted in bile into intestine where it is
metabolized to urobilinogen. Most urobilinogen leaves in feces as brown pigment, stercobilin
Because free Fe is toxic it is stored inside cells as protein-bound complexes such as ferritin and
hemosiderin
Hemosiderin (Fe) is stored in liver
Fe is combined with a transport protein, transferrin, and carried to red bone marrow
where most is used over again in RBC synthesis
Small amounts of Fe are lost each day in feces, urine and perspiration
Average daily loss is 0.9 mg in men and 1.7 mg in women (more due to menstrual losses)
About 2 million RBCs are produced each second-this rate can be increased up to 10X
The rate of production speeds up if the number of RBCs decreases or if tissue hypoxia (oxygen
deficiency) develops (at high altitude or in chronic lung diseases)
These conditions stimulate the kidneys to release an enzyme, renal erythropoietic factor, that
converts a plasma protein into the hormone erythropoietin which stimulates the bone marrow to
produce RBCs
Erythropoietin is also released from the liver but to a lesser extent
The kidneys fail to produce erythropoietin in renal dialysis patients-as a result they have have
half the RBC count of a normal person and are treated with recombinant (genetically engineered
erythropoietin
At high altitude the concentration of erythropoietin in the blood rises and the rate of RBC
formation rises sharply after 2 days to a maximum in 5 days
Fluosol - DA is a blood (hemoglobin) substitute
Slippery, white liquid with a very high capacity for 02
Used in CO poisoning, sickle-cell anemia, strokes, heart attacks and burns
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RED BLOOD CELL ABNORMALITIES
ANEMIA
Means literally “a lack of blood” - a misnomer since in most cases there is no true lack of blood
Symptoms - fatigue, intolerance to cold, and paleness
Anemia reduces the viscosity of blood and increases the work of the heart - it has to pump more blood to
do the same work
Hematocrit may be only 15% instead of 45%
Three basic causes:
1.Insufficient number of RBCs: hemorrhagic, hemolytic and aplastic anemia
2.Decreases in hemoglobin content: iron-deficiency and pernicious anemia
3.Abnormal hemoglobin: thalassemia and sickle cell anemia
HEMORRHAGIC ANEMIA
Excessive loss of RBCs through bleeding
Caused by large wounds, stomach ulcers, hemorrhoids, and heavy menstrual bleeding
HEMOLYTIC ANEMIA
Premature destruction of RBCs
Increase in number of reticulocytes
Due to inherent defects such as hemoglobin defects, abnormal RBC enzymes, or defects of RBC
membrane
Can be caused by parasites (malaria), toxins and antibodies from incompatible blood
(Ex. Erythroblastosis fetalis - Rh- mother and R+ fetus)
APLASTIC ANEMIA
Results from malfunctioning red bone marrow - results in inadequate production of RBCs
May result from destruction of bone marrow by chemical agents (benzene, arsenic) or physical factors
(X-rays and other ionizing radiation)
Bone marrow transplants are used to treat aplastic anemia
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IRON DEFICIENCY ANEMIA
Type of nutritional anemia-due to inadequate diet - lacks iron, the necessary amino acids or vitamin B12
Insufficient hemoglobin synthesis dueto lack of iron
RBCs are smaller and pale (microcytic, hypochromic) due to lack of hemoglobin
Usually follows chronic blood loss-Fe becomes depleted due to increased RBC formation
PERNICIOUS ANEMIA
When gastric muscosa (parietal cells) fails to produce intrinsic factor needed for vitamin B12 absorption
Marrow produces fewer but larger (macrocytic) RBCs
Many are immature with fragile membranes, leading to more rapid destruction
THALASSEMIA
Hereditary hemolytic anemia
Disorder in synthesis of hemoglobin produces thin and fragile RBC membranes - RBCs prematurely
removed from circulation
RBC count is generally less than 2 million/cubic mm of blood
Common in Greece and Mediterranean coastal region
SICKLE CELL ANEMIA
Occurs almost exclusively in blacks (1 in 400 U.S. blacks) and some other Mediterranean races
Abnormal type of hemoglobin which does not combine with oxygen properly-due to change in 1 of 287
amino acids in beta chain
RBCs are sickle - shaped and tend to get stuck in blood vessels
Heterozygous - 1 gene normal - not too much trouble until oxygen tension decreased
(go up in unpressurized plane, climb a mountain)
Confers resistance to malaria
Gene alters permeability of membrane
K+ leaks out of sickled cells and kills malarial parasites
Homozygous - 2 recessive genes - lethal
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Symptoms
Hand-foot syndrome in young children - swelling and pain in wrists and foot
Treatment
Fetal hemoglobin does not sickle-hydroxyurea switches fetal hemoglobin gene back on
Also use arginine butyrate (a natural fatty acid used as a flavor enhancer)
ATHLETE’S ANEMIA
When athletes exercise vigorously, blood volume can expand 15% which dilutes
Is reversed within a day or so
POLYCYTHEMIA
Condition characterized by above normal RBC count
Physiological (secondary) polycythemia - due to living at high altitudes
Occurs when less oxygen is available or erythropoietin production increases
Count may be as high as 8 million/cubic mm
Polycythemia vera-abnormally high RBC count due to malignancy of bone marrow
Counts of 10-11 million/cubic mm are not common
Hematocrit may reach 70-80% - a hematocrit above 55 is suggestive of polycythemia
Blood is very viscous
Causes rise in blood pressure
Contributes to thrombosis and hemorrhage (due to unusually large amount of blood in an organ)
LEUKOCYTES (WHITE BLOOD CELLS)
Gr. leuco, white
Account for less than 1% of blood volume
Combat inflammation and infection
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Have surface proteins or HLA (human leukocyte associated) antigens - unique for each person - used to
type tissues to prevent rejection
Most have short life span
In healthy body some live few days to several months
During infection they live only a few hours
5,000 - 9,000 per cubic mm of blood
About 1 WBC to 700 RBCs
Number may vary with time of day, exercise and other factors
Lowest in early morning and highest in afternoon
Dependent on age-count in children is somewhat higher
In newborn = 16,000/mm (greater number of lymphocytes)
Differential count indicates relative numbers of types of leukocytes
Leukopoiesis-production of WBCs due to hormones called CSFs (colony stimulating factors) produced
by macrophages and T lymphocytes
LEUKOCYTOSIS
Increase in total number of WBCs
Physiologic leukocytosis - up to 10,000 per cubic mm
Occurs under normal conditions, such as digestion, exercise, pregnancy and cold baths
Pathologic leukocytosis - more than 10,000 per cubic mm
Occurs in pneumonia, appendicitis and other acute infections
Leukemia - counts up to 500,000-1 million/cubic mm
LEUKOPENIA
WBC counts less than 5,000 per cubic mm
Mild cases are often associated with viral diseases such as measles, mumps, chickenpox or polio
Severe leukopenia is termed agranulocytosis (bone marrow stops producing WBCs)
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Is usually the result of poisoning (benzene), excessive irradiation (X-ray therapy), or
antibiotic therapy
If condition persists, the patient is in peril due to the lack of protection against bacteria
LEUKOCYTE MOVEMENT
Capable of amoeboid movement
Some can move 40 microns/min or several times their own length each minute
Neutrophils are most motile
Can squeeze through walls of capillaries into surrounding tissues by a process called diapedesis
It occurs normally but is greatly increased in infection and inflammation
Leukocytes hug the walls of the vessel, facilitating diapedesis - called margination
Both neutrophils and monocytes use diapedesis
Phagocytosis is facilitated by a combination of globulins in the blood called opsonins
They combine with foreign material and allow the leukocyte to adhere to the surface
WBCs differ in shape of nucleus and in character and staining qualities of cytoplasm-stain with Wright’s
stain
Most are formed in red bone marrow (granulocytes and monocytes) - others formed in lymphatic tissue
(lymphocytes)
“Never Let Monkeys Eat Bananas” is phrase to remember most abundant to least abundant WBCs
2 main types:
1. Granulocytes - cytoplasm shows granules
2. Agranulocytes (nongranular) - cytoplasm shows no granules
GRANULOCYTES
The granules are lysosomes
About twice the size of RBCs
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Formed in red marrow of bones from myeloblasts which develop from hemocytoblasts
Bone marrow stores granulocytes (but not RBCs) and usually contains 10-20 times more than are
found in blood
Life span is short-less than 24 hours in many instances – 3 granulocytes are formed for every RBC but
live much shorter duration
They are destroyed as they become old and fragile, or are killed counteracting bacterial infections
3 kinds: 1. Neutrophils 2. Eosinophils 3. Basophils
NEUTROPHILS
Also called polymorphonuclear leukocytes (“polys”) or (“segs”) [refers to segmented nucleus]
Nucleus has 2-5 (3-6) lobes and becomes more lobulated with age
Cytoplasmic granules stain “neutral” or pale blue
Most numerous WBCs - form 60-70% of total WBCs
Highly motile-exhibit diapedesis and margination
Contain defensins - amino acids that exhibit antibiotic activity against bacteria, fungi and viruses
Kill bacteria by a process called a respiratory burst, in which oxygen is metabolized to produce
germ-killing oxidizing substances such as bleach and hydrogen peroxide
Main function is to phagocytose bacteria
Release lysozyme which destroys certain bacteria
Neutrophil succumbs after ingesting 5 - 25 bacteria
High neutrophil counts (neutrophilia) often signal localized infections such as appendicitis, meningitis,
or abscesses
If need is great enough, immature forms may be released from bone marrow
Called band or stab neutrophils, because their nuclei are horseshoe-shaped
Neutropenia - marked decrease in neutrophils
Occurs in typhoid fever, undulant fever and influenza
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EOSINOPHILS
Similar in size and structure to neutrophils
Granules in cytoplasm are larger and stain with red acidic eosinophilic dye
Nucleus is usually bilobed
2-4% of WBCs
Eosinophilia - increased numbers may indicate:
Allergies
They phagocytize antigen - antibody complexes
Eosinophils deactive heparin and histamine produced by mast cells and prevent spread of
inflammation
Invasions of parasitic flatworms, tapeworms, pinworms, hookworms, flukes or roundworms such
as Trichinella spiralis, the “pork worm”
They release enzymes on surface of worm to digest it-the main enzyme is MBP (major
basic protein)
Counts may rise as high as 50% in cases of trichinosis
BASOPHILS
Rarest leukocytes - 0.5 - 1% of WBCs
Granules stain blue-purple with basic (basophilic) dyes
Nuclei are roughly S-shaped
Leave capillaries and become mast cells in tissues that secrete heparin and histamine
Their number increases during chronic inflammation
Contain large amounts of histamine, a vasodilator (½ the histamine content of blood)
Involved in allergic reactions
AGRANULOCYTES
MONOCYTES
3-8% of total WBCs
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Resemble lymphocytes except are usually larger-largest of all WBCs
Each has a bean-shaped nucleus
Function has phagocytes - clean up cellular debris following an infection
They and neutrophils are the main phagocytes
Can engulf up to 100 bacteria, worn out RBCs and malarial parasites
Unlike neutrophils they can extrude digested remains of bacteria and hence live longer
and engulf more
Formed chiefly in bone marrow
May leave blood and go into tissues
Swell and increase their diameter up to 5X
Then called tissue macrophages or histiocytes
During inflammation histiocytes divide and multiply, in many cases walling off the infected area
In a chronic inflammation such as tuberculosis the number in the blood may increase to 30 - 50% of all
WBCs
INFECTIOUS MONONUCLEOSIS
Benign disease associated with elevated WBC count with a decrease in % of polys and increase in
mononuclear cells (lymphocytes and monocytes)
Caused by Epstein-Barr virus - multiplies in lymphoid tissue
Usually occurs in children and young adults - peak incidence at 15-20 years
Called kissing disease after supposed mode of transmission
Spreads into blood where it infects and multiplies in B lymphocytes, the primary host
cells
B lymphocytes become enlarged and abnormal and resemble monocytes, the reason the
disease is called mononucleosis
Symptoms:
Fever
Enlarged and tender cervical lymph nodes
Fatigue
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Sore throat - brilliant red throat
Cough
Stiff neck
No cure - disease usually runs its course in a few weeks
LYMPHOCYTES
20 - 25% of WBCs
Several types of lymphocytes:
A. B - lymphocytes from bone marrow - 20-30% of circulating lymphocytes
B. T - lymphocytes from thymus gland - 70-80% of circulating lymphocytes
C. Others derived from lymph nodes and spleen
Have a large round nucleus
No granules in cytoplasm - thin rim of clear blue cytoplasm
Number is high in early life - 50% of total WBC count
High lymphocyte counts (lymphocytosis) are present in whooping cough and some viral infections
TYPES OF LYMPHOCYTES
In embryo lymphocytes are formed in the red bone marrow from stem cells
Half migrate to thymus and half to some other part of the body (liver or spleen)
Those preprocessed in the thymus are called T-lymphocytes or sensitized lymphocytes
Responsible for cellular immunity-attach to and destroy foreign agent
B-lymphocytes-named because in the chicken they are preprocessed in the GI tract, the bursa of
Fabricius (pouch of lymphatic tissue associated with digestive tract)
Responsible for humoral immunity (production of antibodies)
Following preprocessing both types migrate to lymphoid tissue just prior to birth or within the first few
months of life - here they remain
Only a small proportion are in blood, most are in lymphoid tissues
Lymphocytes exhibit great specificity in recognition of a particular antigen
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Basic to this specificity is that there are different clones (populations) of lymphocytes each
responsive to only 1 antigen
ANTIGENS
Usually large molecules (molecular weight = 10,000 or more) such as proteins and polysaccharides
Only small areas are immunogenic-these sites are called antigenic determinants
Most antigens have many antigenic determinants-the number is the valence
Proteins have hundreds of antigenic determinants
Plastics have few and hence are used for implants since they are not likely to be rejected
Hapten – incomplete antigen - smaller molecule than can trigger an immune response by combining
with larger molecule
Link up with body’s own proteins to produce a foreign combination that provokes an allergic
reaction
Substances that serve as haptens occur in:
Drugs (penicillin)
Household and industrial chemicals
Dust particles
Animal skin (dander)
Poison ivy
ANTIBODY PRODUCTION
When an antigen enters, the B-lymphocyte clone specific to it increases in size and is transformed to
mature plasma cells that secrete antibody
Estimate that plasma cell clones can make over 100 billion different types of antibodies but
people only encounter several thousand in a lifetime
Plasma cell manufactures 2,000 antibodies per second but only lives 4-5 days
Antibodies are secreted into the lymph and from there enter the circulation
B cells are responsible for humoral immunity (antibody production)
Are stimulated by bacteria primarily (streptococci, pneumococci, some influenza bacilli,
meningococci) and against viral reinfections
Antibodies bind to bacteria and their toxins and to free viruses
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Some B - lymphocytes do not mature into plasma cells
Instead divide, increasing the number of B-lymphocytes with memory of that specific antigen
Thus, on 2nd exposure to antigen there is much more rapid and efficient production of that
antibody
Reason for giving “booster shots” in immunization
Primary immune response-when body first exposed to antigen
Lag period of 3-6 days for B cells to proliferate
Plasma antibody levels peak in about 10 days and then decline
Secondary immune response-when reexposed to same antigen
Peak levels of antibodies are reached in about 2 days and levels remain high for weeks or months
Antibodies belong to a family of proteins in the blood called gamma globulins (immune globulins -Ig)
Antibody is a “Y-shaped” molecule made up of 4 polypeptide chains-2 long heavy chains and 2
short light chains
Each molecule has a variable region and a constant region
5 types - designated by letters G, A, M, D, and E – each type has same constant region
Antibodies may be found either free in plasma or bound to surface of lymphocytes
IgG, IgA and IgM provide bulk of specific antibodies against infection
IgG makes up 70% (80%) of circulating antibodies - occur in plasma and tissue fluids (most
abundant antibody in plasma)
Particularly effective against bacteria, viruses and certain toxins
Enhance phagocytosis, neutralize toxins and protect fetus and newborn (only class that
crosses placenta-provides passive immunity to fetus)
IgA antibodies are produced by lymphoid tissue in GI tract and act locally
13% of antibodies
During stress, IgA levels decrease – can lower resistance to infection
Help control bacterial and viral infections– provide localized protection on mucosal
surfaces
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Found in exocrine secretions (called secretory IgA) - milk, tears, gastric juice, intestinal
juice, bile and urine
Do not pass across placenta
Pass from mother to infant in milk and offer some protection against digestive and
respiratory disorders
IgM - 6% of antibodies
Largest antibodies-pentamer (5 Y-shaped monomers stuck together)
Consist of anti -A and anti-B antibodies in blood
First class released to blood by plasma cells
Are especially effective against microbes by causing agglutination and lysis
IgE occurs in various exocrine secretions along with IgA
Responsible for the physiological manifestations of allergic reactions
Hay fever, asthma, hives, reactions to bee stings and drugs
Antibodies adhere to mast cells which rupture and release histamine
Histamine causes vasodilation and increased capillary permeability
Loss of fluid may lead to death due to circulatory shock (anaphylaxis)
IgD antibodies - function not known - significance thought to be minor
Found on surface of most B lymphocytes, especially those of infants
May stimulate antibody-producing cells to manufacture antibodies
ACTIONS OF ANTIBODIES
General Action Effect Description
1. Direct attack
Agglutination Causes antigens to clump together (esp. IgM
in mismatched blood)
Precipitation Causes antigens to form insoluble
substances
Neutralization Causes antigens to lose toxic properties
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(block specific sites on viruses or bacterial
toxins so they cannot bind to tissue cells)
Lysis Causes cell membranes to rupture
2. Activation of complement
Antigen - antibody complexes activate complement proteins (inactive enzymes) in plasma
Chemotaxis Attracts macrophages and neutrophils into region
Opsonization Alter cell membranes so cells are more susceptible to being
phagocytized
Opsonins - globulins in blood - combine with antigen and allow
leukocyte to adhere and phagocytize
Inflammation Promote local tissue changes that help to prevent the spread of
antigens
COMPLEMENT SYSTEM
A group of plasma proteins (enzymes) - powerful aid to inflammatory response
Complement proteins enhance vasodilation, capillary permeability and phagocytosis
Facilitate neutrophil movement by acting as chemotactic agents
T-LYMPHOCYTE RESPONSE
Macrophages engulf foreign particles and present parts of their surface antigens to T cells
Upon exposure to a specific antigen, a clone of T-lymphocytes is sensitized to release chemicals
injurious to the antigen
Cytotoxic T cells roam body, in and out of blood and lymph-are stimulated by viruses, fungi and
parasites (worms), parasite-infected cells, cancer cells and grafts
Some of the clone of T’s reproduce to serve as a “memory bank”
On 2nd exposure they greatly speed up the immune response
T cells travel to the invasion site to release their chemicals locally
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T’s secrete:
1. Lymphokines (proteins) that attract and activate macrophages
2. Lymphotoxins - lethal to target cells
3. Growth - inhibiting factors - prevent target cell growth
4. Interferon - prevents viral proliferation
T cells can act directly as killers, as in rejection of transplants and the destruction
of maglignant cells - called cell - mediated immunity
Maintain immune surveillance
Estimate that 1 body cell becomes cancerous per day but is killed by T cells
Since T cell function declines with age - may help explain why some types of
cancer appear more commonly in elderly
Only grafts from a genetically closely related individual will be tolerated by the recipient
It is possible to “type” individuals on the basis of antigens located on the leukocyte
Called HLA (human leukocyte antigen typing)
Hence can match recipient with suitable donor
Surgeons give antilymphocyte serum (ALS) to transplant patients to decrease
lymphocytes and antibodies
T cells can activate or suppress B cells
T helper cells - necessary for B cells to transform into plasma cells
Also stimulate proliferation of other T cells
Release lymphokines that mobilize immune cells, macrophages and neutrophils
AIDS attacks T helper or T4 cells
T suppressor cells - inhibit B cell activity after response to antigen has begun
Supress activity of both B and T cells
Important in preventing autoimmune reactions
LEUKEMIA
Means “white blood”
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WBC count soars to as high as 500,000-1 million/cubic mm
Form of cancer and usually proves fatal
The human T-cell leukemia - lymphoma virus -1 (HTLV-1) is strongly associated with leukemia
2 major types:
1. Myeloid - abnormal production of granulocytes by red bone marrow
2. Lymphoid - increased formation of lymphocytes in lymph nodes
Acute lymphoid leukemia is the most common cancerous condition in children
Greatest success in treating this form of leukemia
The type of leukocyte involved differentiates the varieties
Granulocytic, lymphocytic and monocytic
Leukemias are classified as acute or chronic
Acute - appears suddenly, progresses rapidly - death occurs in a few months – usually affect
children
Chronic - begins more slowly - without treatment may live 3 years –seen more in elderly
WBCs are formed so rapidly in bone that immature RBCs and platelets are starved out
Leads to severe anemia and bleeding problems
One common cause of death is internal hemorrhaging, especially cerebral
WBCs plug blood vessels in brain, heart, lungs and kidney
Leukemic cells from bone marrow may invade other areas of bone weakening its structure
and stimulating pain receptors
Leukemia cells are usually abnormal and often have little phagocytic ability
Most frequent cause death is uncontrolled infection due to lack of normal mature WBCs
Causes - radiation, benzene and other chemicals
Partial or complete remissions may be induced, some lasting as long as 15 years
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PLATELETS (THROMBOCYTES)
Thrombo clot; cyte - cell
Are fragments of cytoplasm of megakaryocytes formed in red bone marrow
Hemocytoblasts - megakaryoblasts - megakaryocytes - platelets
250,000 - 400,000 per cubic mm of blood (Average = 300,000)
Average life span of 5-9 days
Cytoplasm contains:
Alpha granules-contain clotting factors and platelet-derived growth factor (PDGF) which
stimulates endothelial cells, smooth muscle cells and fibroblasts to proliferate to repair damaged
blood vessel walls
Dense granules contain ADP, ATP and serotonin
Enzyme systems that produce prostaglandins
Fibrin-stabilizing factor which helps strengthen a blood clot
Initiate hemostasis - stop bleeding
3 mechanisms to prevent blood loss:
1. Vascular spasm - when blood vessel is damaged, smooth muscle contracts for up
to 30 minutes
2. Platelet plug formation
3. Clotting or coagulation
Contact with collagen fibers of vascular wall changes the form of platelets - they enlarge and become
irregular
Processes protrude from their surface and they become sticky
Stick to collagen fibers
Once attached, thromboxane A2 (a prostaglandin derivative) is generated from lipids in platelet
membranes-causes release of serotonin and ADP
Aspirin inhibits formation of thromboxane
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ADP acts on nearby platelets to make them sticky
This produces a soft platelet plug which becomes tight when reinforced by fibrin threads
The plug is limited to the immediate area by the prostaglandin PGI2 or prostacyclin-an
inhibitor of platelet aggregation produced by endothelial cells
This mechanism takes care of minute capillary ruptures that occur hundreds of times each day
Platelets release serotonin (vasoconstrictor) and a platelet factor which initiates reactions that lead to
clot formation
Platelets then cause the clot to shrink, squeezing out serum – they contain contractile actomyosin
Thrombocytopenia - a deficiency of platelets (less than 50,000-100,000/cubic mm)
Causes excessive bleeding
PLASMA
55% of total blood volume
Amber (straw) color
Serum is fluid remaining after formation of blood clot (plasma minus clotting factors)
Consists of 90% water and 10% solutes (100 different dissolved solutes-most are proteins)
pH = 7.4
BLOOD PROTEINS
Hemoglobin of RBCs represents about 2/3 of the blood proteins
Plasma proteins represent about 1/3
PLASMA PROTEINS
Normal concentration of plasma proteins is 6-8 g per 100 ml of plasma
Plasma proteins contribute to the solution and transport of lipids, fat-soluble vitamins, bile salts and
hormones in the blood and help regulate acid - base balance
3 major types of proteins in plasma:
1. Serum albumin – 55-60% of total plasma proteins - largely responsible for blood viscosity
Smallest plasma proteins
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Albumin is especially important in maintaining blood volume
Responsible for osmotic (“pull”) pressure of the plasma
Essential for holding and pulling water from the tissue fluid into blood vessels
A decrease in plasma proteins can result in edema (accumulation of fluid in tissues)
If serum albumin leaks from capillaries as a result of injury (severe burn), water
cannot be retained and blood volume and pressure drop-shock may result
Treat with intravenous injection of serum albumin
2. Serum globulin –36-38% of total plasma proteins-include:
Opsonins-facilitate phagocytosis by WBCs
Alpha globulins-antithrombin
Beta globulins-clotting factors
Alpha and beta globulins also transport lipids and other substances in blood
Gamma globulins-antibodies
Prothrombin
3. Fibrinogen – 4-7% of total plasma proteins - largest plasma protein molecule
Practically all the serum albumin and fibrinogen are formed in liver
Globulins are formed by the liver (Ex. Alpha and beta globulins) and the lymphatic system (Ex. Gamma
globulins are synthesized by plasma cells)
NUTRIENTS IN PLASMA
End products of digestion - amino acids, glucose and neutral fats
Glucose concentration is 80 - 120 mg per 100 ml of blood
Fats occur in plasma in form of small particles called chylomicrons
Cholesterol in plasma
In adult concentration should not exceed 250 mg per 100 ml
Desirable level is less than 200 mg/100 ml (Average U.S. value=205 mg/100 ml)
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Borderline high-risk=200-239 mg/100 ml
High risk=more than 240 mg/100 ml
Familial hyperlipidemia - concentration may reach 1000 mg/100 ml - high
incidence of atherosclerosis and heart disease
Cholesterol is found in all tissues and body fluids - 2 sources:
1. Absorption in intestinal tract from saturated fats - exogenous cholesterol
2. Formation in cells (especially liver cells) - endogenous cholesterol
Used by liver to form cholic acid which helps form bile salts
adrenal gland to form cortical hormones
ovaries to form progesterone and estrogen
testes to form testosterone
Large amounts in skin to prevent water evaporation, etc.
Plasma cholesterol is complexed with lipoproteins
The risk of heart attack may be due to form which cholesterol is being transported rather
than total level
LDL (low density lipoprotein) transports cholesterol from liver to body cells
Excess LDL - cholesterol deposited in artery walls – atherosclerosis
Desirable level – less than 130 mg/100 ml
Borderline high-risk – 130-159 mg/100 ml
High risk – more than 160 mg/100 ml
HDL (high density lipoprotein) removes cholesterol from artery walls and
prevents its deposition
Desirable level – 60 mg or more/100 ml
Risk factor – below 35 mg/100 ml
Recommended ratio of total cholesterol/HDL - Less than 4 – males, less than 3.5 -
females
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ELECTROLYTES
Help maintain osmotic pressure, normal pH, and physiological balance between tissue and blood
Most abundant is NaCl
Variations in K+ may prove fatal - toxic to heart muscle
NITROGEN
A major constituent of plasma proteins
Other compounds also contain N- called nonprotein nitrogen (NPN)
Urea, uric acid, creatinine, creatine, ammonia salts, amino acids
NPN amounts to 2% of the total nitrogen in the blood
Urea is the major component
The NPN level of plasma is a good determinant of protein balance
NPN is elevated:
In various kidney abnormalities when excretion is decreased (uremia)
When there is excessive protein catabolism - in infections, hyperthyroidism, and
inadequate protein ingestion
GASES
Oxygen, nitrogen and carbon dioxide are dissolved in plasma
COAGULATION (BLOOD CLOTTING)
2 basic pathways:
1. Extrinsic pathway - initiated by substances released by damaged blood vessels or
surrounding tissues outside the blood
2. Intrinsic pathway - begins in the blood – involved in clotting blood outside of body
In the body both pathways are usually triggered by the same vessel-damaging events
A pivotal molecule in both mechanisms is a phospholipid PF3 on the surfaces of aggregated platelets
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Each pathway requires Ca++ and steps which cascade toward factor X-from this point on they are the
same
In both pathways a series of plasma proteins, especially beta-globulins, play major roles
Called blood clotting factors (most are inactive forms of proteolytic enzymes)
Most are in plasma, a few are released by platelets and one is released by damaged tissue
Most are designated by Roman numerals (I-XIII) – numbered according to the order of discovery
An important difference between the pathways is their speed of action
Extrinsic pathway is very quick-clotting can occur in as little as 15 seconds
Intrinsic pathway - is more complex than extrinsic pathway
Usually requires 2-6 minutes to cause clotting
3 basic stages in clotting:
1. Formation of prothrombin activator
2. Conversion of prothrombin into thrombin
3. Conversion of fibrinogen into fibrin
Extrinsic clotting
Named because formation of prothrombin activator is initiated by substances released by
damaged blood vessels or tissues outside the blood
The initiating substance is tissue thromboplastin or tissue factor (TF)
Thromboplastin, factor VII and Ca++ activate factor X
Factor X reacts with factor V and Ca++ to form prothrombin activator
Prothrombin activator and Ca++ convert prothrombin (Factor II) into thrombin
Prothrombin activator + Ca++
Prothrombin------------------------------------------------------------------thrombin (factor XIII)
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Thrombin + Ca++
Fibrinogen (factor I)---------------------------------------------------------fibrin
Fibrinogen - protein produced by liver - high molecular weight (largest plasma protein)
Thrombin - enzyme that converts soluble fibrinogen to insoluble fibrin threads
Threads of fibrin form a mesh that traps RBCs and plasma
The clot then undergoes contraction and pulls edges of damaged vessel together
Serum (defibrinated plasma) is squeezed out - most in 30-60 minutes
Intrinsic clotting - blood clots when drawn from circulation and left to stand
Can be triggered by contact with glass which activates clotting factor XII (Hageman or glass
factor)-named after an engineer, Hageman, who had a deficiency of this factor and died of a
pulmonary embolism
Pathway named because formation of prothrombin activator is initiated by a substance within the
blood (a tissue factor found on endothelial cells and monocytes)
Intravascular clotting sometimes results from factors that activate the intrinsic pathway
Ex. antigen - antibody reactions or septicemia due to bacterial toxins
Deficiencies in the intrinsic pathway are associated with a number of hereditary bleeding
diseases - especially Factor VIII in hemophilia A
Intrinsic pathway is initiated when blood comes in contact with collagen in damaged blood vessels
This causes activation of Factor XII (Hageman) and damage to platelets, resulting in release of
phospholipids by platelets
Factor XII activates Factor XI which activates Factor IX (Christmas factor)
Factor IX acts together with factor VIII, Ca++ and platelet phospholipids to activate Factor X (Stuart)
Factor X reacts with platelet phospholipids, factor V and Ca++ to form prothrombin activator
Prothrombin activator converts prothrombin into thrombin
Thrombin causes more platelets to adhere to each other, resulting in release of more platelet
phospholipids (positive feedback cycle)
Prothrombin is inactive precursor of thrombin
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Protein formed in the liver and is in the plasma in excess amounts
Blood clots normally, even when the amount. of prothrombin is reduced by 50% or more
Synthesis of prothrombin by the liver requires vitamin K
Some foods (especially green leafy vegetables) contain vitamin K, but it is also
synthesized in large intestine by certain bacteria
Antibiotics which wipe out the intestinal flora may lead to vitamin K deficiency
Vitamin K is required for synthesis of factors VII, IX, and X as well as prothrombin
Newborn may have a deficiency and be prone to hemorrhage since vitamin K is not
readily passed from mother to fetus
Hence the need for giving it to the newborn and mothers before delivery
Vitamin K is fat soluble - inadequate fat absorption due to lack of bile salts will limit it
Ex. If bile ducts become obstructed, a vitamin K deficiency develops
Blood with a deficiency of vitamin K shows lowered prothrombin and delayed
clotting time
Patients with obstructive jaundice are given vitamin K as a preoperative safeguard
FACTORS THAT OPPOSE CLOTTING
Endothelium lining blood vessels carries a negative charge that repels platelets and various clotting
factors - prevents clotting
Clotting occurs all the time throughout the body
To prevent clotting, antithrombin (Factor III) (alpha globulin) is present in plasma and
inactivates thrombin and factor X
Other anticoagulants in blood:
Alpha-2 –macroglobulin inactivates thrombin and plasmin
Alpha-1- antitrypsin inhibits factor XI
Protein C inactivates factors V and VIII and stimulates plasminogen activators
HEPARIN
1st prepared from liver (hence its name)
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Secreted by basophils and mast cells in connective tissue around capillaries
Heparin secreting cells are especially abundant in the liver and lungs where capillaries are likely
to trap small clots in the slow-moving venous blood
Heparin enhances the activity of antithrombin III-it combines with antithrombin III (alpha
globulin in plasma) to increase its effectiveness in removing thrombin
Heparin’s normal concentration in the blood is too low to have much effect in keeping blood
fluid
Injections of heparin are used to prevent clots from forming Ex. In open heart surgery and
during hemodialysis
It is extracted from bovine lung tissue and from bovine and porcine intestinal mucosa
Blood removed from body will clot unless steps are taken
If it is carefully drawn into a syringe coated with paraffin or silicon (it clots in contact with glass)
clotting may not occur
Probably due to minimal platelet destruction and inadequate thromboplastin formation to
initiate clotting
Another mechanical way to prevent clotting is vigorous stirring with a glass rod - fibrin adheres
to the rod and can be removed
Oxalates and citrates act as anticoagulants by precipitating Ca++
In absence of Ca++, blood does not clot
Oxalate is toxic to body, whereas small quantities of citrate can be injected intravenously
Citrate is removed from blood within a few minutes by liver
Hence citrate is the anticoagulant used in transfusion blood
CPD (citrate phosphate dextrose), ACD (acid citrate dextrose), and EDTA (ethylenediamine
tetracetic acid) react with Ca++
Used by labs and blood banks to prevent blood samples from clotting
Coumarin or dicoumarin (dicoumarol) impair liver’s utilization of vitamin K and slow its
synthesis of prothrombin
Warfarin (Coumadin) is slower acting than heparin and is used primarily as a
preventative.
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In 1920s farmers in Midwest noticed cattle developed blood blisters and bled to death
because they ate spoiled sweet clover containing coumarin
Aspirin- inhibits thromboxane A2 formation and thus prevents platelet aggregation and plug formation
FACTORS THAT HASTEN CLOTTING
Thrombus - abnormal clot that forms inside a blood vessel. Condition called thrombosis
Embolus - a thrombus that becomes dislodged from its place of formation. Condition called
embolism
Danger that it may lodge in lung or brain
Conditions that favor thrombus formation
1. Foreign substances (even air) introduced into blood
2. Rough spot or injury to blood vessel lining
Atherosclerosis increases thrombosis because of cholesterol - lipid plaques on
endothelium
Ligature or bruising incidental to operations
Products of bacteria and other toxic substances may injure lining of blood vessel
Phlebitis - inflammation of the lining of a vein
3. Abnormally slow blood flow
Major reason why physicians insist patients move or be moved
Sluggish flow may allow thromboplastin to accumulate in a concentration adequate for
clotting
CLOT DISSOLUTION
Dissolution of a clot depends upon the enzymatic digestion of fibrin. Process called fibrinolysis.
Begins within 2 days and continues slowly over several days until clot dissolves
Plasma contains profibrinolysin (plasminogen), an inactive form of fibrinolysin (plasmin), a proteolytic
enzyme, that dissolves fibrin
Removes clots that occur constantly
Fibrinolytic activity is increased during exercise. Used to prevent cardiovascular problems
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A recently developed drug used to dissolve blood clots is t-PA (tissue plasminogen activator)-brand
name Activase
A genetically engineered artificial version of an enzyme normally found in very small amounts
in the body
Presence of a clot causes endothelial cells of blood vessel to secrete t-PA
t-PA initiates a process that converts plasminogen into plasmin
Other enzymes used to dissolve clots are streptokinase and urokinase but they are less desirable than
t-PA because:
1. They must be introduced directly into clot via catheterization, whereas t-PA can be
administered intravenously
2. t-PA acts only on blood clots, whereas the other enzymes act throughout the
bloodstream and may cause excess bleeding
3. t-PA is a naturally occurring protein not likely to cause antibody production or an
allergic reaction
BLEEDING TIME
Time required for cessation of bleeding from a small skin puncture on finger tip or ear lobe
Unlike clotting time, which invloves only the breakdown of platelets, bleeding time involves
vasoconstriction and all stages of clot formation
In 1 technique, a blood pressure cuff is placed around the arm and inflated to 40 mm Hg to produce a
constant blood pressure in capillaries and forearm is punctured
Normal bleeding time is 4-8 (2-8) minutes
CLOTTING TIME
Collect blood in glass tube
Clotting is initiated when platelets break up on contact with glass
Clotting time is usually 5 to 10 minutes
Prolonged clotting time may be due to a deficiency of a clotting factor (usually VIII or IX) [hemophilia]
or the presence of anticoagulants
PROTHROMBIN TIME
Test used to determine amount of prothrombin in blood
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Time for clotting depends on amount of prothrombin
Normal prothrombin time is 11-15 seconds
Used to evaluate a bleeding disorder, to monitor anticoagulant therapy, and to evaluate liver disorders
HEMOPHILIA
“Loving Blood”
Hereditary blood disease characterized by greatly prolonged coagulation time
Recessive gene located on X chromosome (sex-linked)
Carried by heterozygous females
Occurs almost exclusively in males
Deficiency of a factor in the plasma necessary for coagulation
Hemophilia A (classic hemophilia) - most common type (83% of cases) – sex-linked and
primarily in males
Lack factor VIII, antihemophilic factor (AHF)
Hemophilia B - lack factor IX (Christmas factor)– sex-linked and primarily in males
Named in 1952 after Christmas family who had deficiency of this factor
Hemophilia C - lack factor XI - mild form affecting both males and females
Symptoms:
Hemorrhage after minor injuries
Bleeding into joints and body cavities (cause pain and disability)
No cure but can be controlled by transfusions of plasma
BLOOD TYPES
Type of antigens present on RBC membranes
Not discovered until 1901 by Landsteiner
At least 14 human blood group systems
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ABO is most important, Rh is 2nd in importance
M and N antigens are inherited the same way A and B are, but both genes are dominant and there is no
recessive gene - thus the only possible types are M, N and MN
Of little medical importance because few people produce anti-M or anti-N antibodies even after
repeated exposures to the antigens
System is of interest to geneticists and anthropologists
Landsteiner in 1927 discovered the M and N factors and in 1940, at age 72, discovered the
Rh factors
6 MAJOR BLOOD TYPES
PLASMA
BLOOD TYPE GENOTYPE RBC ANTIGEN ANTIBODIES FREQ. (%)
O ii None Anti A & B 45
A1 A1 Anti B 31
A2 A2 Anti B 10
B B Anti A 10
A1B A1B None 2.9
A2B A2B None 1.1
Plasma never contains antibodies against the antigens present on its own RBCs, but it does contain
antibodies to other antigens
Rare instance of preformation of antibodies without prior exposure
In the embryo antigens are found on the RBCs about the 6th week
At birth the concentration is about 1/5 the adult level
Normal concentrations are reached during adolescence
Antibodies (IgM) are gamma globulins in plasma - 6% of all plasma antibodies
Not present at birth
Are formed in 1st 2 weeks of life
Reach the highest concentration at 10 years of age
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TRANSFUSION DANGER
Antibodies of recipient must be compatible with donor’s RBCs
When blood is given to a patient, it is greatly diluted by the volume of the patient’s blood, so
the injected plasma antibodies become too dilute to agglutinate the host RBCs
Type O is universal donor
Since the cells of O blood have no antigens and are not agglutinated by any plasma
Type AB is universal recipient
Plasma lacks antibodies and hence will not agglutinate the cells of any donor
BLOOD TYPING
A small amount of blood is diluted with saline solution and then a drop is added to 2 test sera, one
containing anti-A antibodies and the other containing anti-B antibodies
SERUM (FROM TYPE) A SERUM (FROM TYPE) B
TYPE ANTI-B ANTIBODIES ANTI-A ANTIBODIES
O No agglutination No agglutination
A No agglutination Agglutination
B Agglutination No agglutination
AB Agglutination Agglutination
CROSS MATCHING
Carried out before transfusion whenever possible
Because the reaction of the donor cells is of vital importance, a suspension of these cells is mixed with
the recipient’s serum
No agglutination should occur
To be certain, the reverse procedure is also done
Mixing cells from the recipient with serum from the donor
CLINICAL APPLICATION
Blood typing is used to disprove paternity, link suspects to crimes and in anthropology to establish a
relationship among races
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In about 80 % of the population (called secretors), soluble antigens of the ABO type appear in saliva and
other bodily fluids
In criminal investigations it is possible to type saliva on a cigarette or semen in cases of rape
Rh SYSTEM
Consists of over 40 antigens found on RBCs
Named after the Rhesus monkey in which it was 1st identified
Major Rh types include Rho, Rh’, and Rh” factors
Most are weak and seldom elicit antibody production
Rho factor is strongest = antigen D
If antigen is present on RBC membrane, the person is Rh+
85% of American Caucasians and 88% of American blacks
98% of Japanese and Chinese
One major difference between ABO and Rh blood systems is that there are no Rh antibodies unless there
was previous contact with Rh antigens
Anti - Rh antibodies appear in the blood of an Rh- person provided Rh+ RBCs entered his circulation
(Ex. transfusion)
Generally there are no ill effects due to the 1st transfusion of Rh+ blood into an Rh- person
because it takes time to form antibodies
But if another Rh+ transfusion is given, serious agglutination may occur
If an Rh- woman carried an Rh+ fetus
Some of its blood may enter her circulation causing her plasma to develop anti-D antibodies –
the greatest blood transfer occurs at delivery
These may diffuse across placenta and agglutinate blood of the fetus in future pregnancies
As a result fetus may die or be born with a severe blood disease called erythroblastosis fetalis -
named because of relese of many immature RBCs called erythroblasts
Estimate in U.S. that 1 child in 10 is an Rh+ child of an Rh- mother, but only 1 in 500 is likely to
develop erythroblastosis fetalis (a form of hemolytic anemia due to massive destruction of
baby’s RBCs)
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Also characterized by:
Enlargement of liver and spleen
Generalized edema
High concentration of bilirubin (RBC breakdown product) leading to jaundice and
damage to brain cells (kernicterus)
90% of cases caused by the production of anti-Rh antibodies in the mother’s blood
10% of cases due to ABO incompatibilities - other blood groups such as Kell,
Kidd and Duffy groups are frequently implicated
RhoGAM [Rho (D) Immune Globulin]
New treatment in 1970’s
Commercial preparation designed to suppress maternal antibody production
Prepared from plasma of a person with a high concentration of Rh antibodies
Flooding the mother’s system with antibodies relieves her own immune system of the stimulus to
manufacture antibodies on its own
The injected antibodies disappear after a while - hence the need for retreatment after each
pregnancy
Administer intramuscularly
Need not be admininistered during pregnancy, protection is accomplished if given within 72 hours after
delivery
Must be given following each pregnancy
Since Rh antigens are developed about 6th week in fetal life, RhoGAM should also be given to Rh-
mothers after miscarriages or abortions
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