BLOOD

Blood• fluid connective tissue

• contains specialized cells-formed elements

• suspended in matrix-plasma

• containing-collagen & elastic fibers

–protein fibers are in solution-visible during clotting process

Functions• transports & distributes nutrients,

gases, hormones & waste products• regulates pH & ion composition of

interstitial fluids• restricts fluid loss at injury sites• defends against toxins & pathogens• helps to maintain body temperature

Composition• 8% of total body weight

–5-6 liters in males

–4-5L in females

• Temperature-38oC

–just above body temperature

• Viscosity 5X more viscous than water

• pH between 7.35-7.45

Composition• Whole blood = plasma +

formed elements• red blood cells (RBCs)• white blood cells (WBCs)• platelets• Centrifuged-separates into

three parts• Bottom-erythrocytes

(RBCs)• top-plasma• junction of RBC & plasma-

buffy coat– contains WBCs &

platelets

Plasma Composition• 46-63% of blood volume• 92% water• plasma proteins-made by liver• Albumin-60%

– major contributor to osmotic pressure– transports fatty acids, steroid & thyroid hormones

• Globulins-35%– from smallest to largest in molecular weights-alpha, beta &

gamma globulins– used to transport hormones, metal ions, triglycerides and

lipids – includes antibodies or immunoglobins

• defend against infections and foreign materials• Fibrinogen-4%

– blood clotting– fibrinogen is cleaved into fibrin-basic framework of clot

Erythrocytes• most numerous of formed elements• number varies with health & altitude

– Peruvians who live 18,000 feet above sea level may have as many as 8.3 x 106 RBCs/µl

• contain hemoblobin (Hb)– red pigment which transports O2 & CO2

– gives blood its color• Ratio of RBC/plasma is hematocrit

– % of whole blood occupied by cellular elements: 40-45%-women; 37-48%-men

– almost entirely due to volume of RBCs– provides estimate of packed cell volume

(PCV)– PCV increases with dehydration & with

erythropoietin-protein which stimulates RBC production

• RBCs are a major contributor to blood viscosity– as numbers increaseviscosity

increasesblood flow slowsblood thinsflows more rapidly

RBC Structure• simple-small, biconcave disc• plasma membrane-no nucleus & no organelles• bag of Hb• no nucleuscannot divide or make proteins

– can’t repair its self and has a short life span-120 days

• shape is directly related to function-most important transport of O2

– large surface area, relative to volume– 30% more surface area than spherical cells– larger surface area makes for faster gas

exchange• shape allows them to stack like dinner plates

– allows for smoother flow of blood through vessels

• Flexible– able to pass through small capillaries

• Modify shape in response to osmotic changes– Hypotonic solutionswellsforms sphere

without disrupting integrity of membrane– Hypertonic solutionshrinksforms spikey

surface• No mitochondria

– generate ATP anaerobically via glycolysis– do not need O2- makes them very efficient O2

transporters

Hemoglobin (HB) Structure• red pigment• formed by 4 globular polypeptide

chains• 2 & 2• each chain has a molecule of heme• each heme has iron (Fe) molecule• each Fe can carry one molecule of

oxygentherefore each HB molecule can carry 4 molecules of oxygen

• Fe binds with O2 oxyhemoglobin bright red

• Fe-O2 bond is weak• can separate easily without

damage to Fe or O2

• Hb from which O2 has separated is deoxyhemoglobindark red

Hemoglobin Functions• Transport gases-O2 &

CO2

– there are 280X106 Hb molecules in each RBC

– each contain 4 heme groups

– gives blood capacity to carry a billion O2 molecules

• amount of O2 bound depends on O2 content of plasma

Leukocytes-White Blood Cells• less numerous than RBCS• 1% of total blood volume• provide protection against

infections• complete cells

– typically have lobed nuclei, organelles & no Hb

• two groups based on appearance after staining

• Granulocytes– contain cytoplasmic inclusions– Basophils– Eosinophils– Neutrophils

• Agranulocytes– contain only a very few stained

granules– Lymphocytes– Monocytes

Neutrophils• 60-70% of circulating WBC population• live only about 10 hours• twice size of RBC• Nucleus-polymorphonuclear

– varied nuclear shapes– mature have 3-5 lobes connected by slender nuclear

strands• cytoplasmic granules in cytoplasm are packed with

lysosomal enzymes & bacteria killing compounds• produced in response to acute body stress

– infection, infarction, trauma, emotional distress• can double in a few hours• highly mobile

– first WBC to arrive at injury site• specialize in attacking & digesting bacteria• when binds to bacteriummetabolic rate increases

H2O2 -hydrogen peroxide & O2- superoxide anions are produced which kill bacteria

• neutrophil + bacterium will fuse with a lysosome which contains digestive enzymes & defensins

• defensins kill bacteria & lysozymes digest them• makes prostaglandins & leukotrienes during this process

– restricts spread of infection & attracts other phagocytotic cells

• cell kills its self in the process• Neutrophils + other waste = pus

Eosinophils• 2-4% of WBCs• bilobed nuclei• contain deep red

granules • population increases

sharply during parasitic infections & allergic responses

• release histaminases which combat the effects of histamine

Basophils• smallest part of WBC population-

0.5-1%• large, deep purple granules in

cytoplasm– hides nucleus

• increase in number during infections

• leave blood & develop into mast cells

• granules contain histamine, serotonin & heparin

• histamine increases blood flow to area which dilates blood vessels

• heparin prevents blood clotting

Monocytes• largest agranulocytes• 3-8% of WBC population• nucleus is large

– clearly visible– ovoid or kidney shaped

• cytoplasm contains sparse, fine granules

• arrive in large numbers at the site of an infection

• enlarge & differentiate into wandering macrophages

Lymphocytes• second most numerous circulating leukocyte-

25-33% • Nucleus-large, round or slightly dimpled on one

side• continually migrates from blood stream through

peripheral tissues & back to blood stream• life span varies from several days to years• B cells or B lymphocytes

– bone marrow derived– make antibodies which attack foreign

antigens• T lymphocytes or T cells

– thymus dependent cells– provide cell mediated immunity– attack foreign cells

• Natural Killer Cells– immune surveillance cells– detect &destroy abnormal tissue cells– may help prevent cancer

Differential Cell Count• determines number of each type of WBC in a

sample • gives valuable information• pathogens, infections, inflammation & allergic

reactions change WBC numbers• count of different types can help to diagnose

disease and illness• Leukopenia

– inadequate number

• Leuocytosis– Excessive number

Blood Cell Formation• all formed elements arise from

a single cell type: pluripotent stem cell

• Hemocytoblast• hematopoietic stem cell or

hemocytoblast• rare-one in 10,000 bone

marrow cells• cell differentiates along

maturation path which leads to different kinds of blood cells

• each type produced in different numbers in response to needs & regulatory factors-cytokines or hormones

Hemopoietic Tissues• Tissues producing blood cells• first-yolk sac

– makes stem cells that migrate into embryo populate bone marrow, liver, spleen & thymus stem cells multiply & give rise to blood cells throughout fetal development

• Liver– primary site of RBC production

during 2-5th month neonatally is liver & spleen

– stops making blood cells at time of birth

• Spleen– stops soon after but continues

to make white blood cells throughout life

• red bone marrow produces all formed elements from infancy onward

Erythropoiesis• inadequate oxygen (hypoxia)kidney EPO (erythopoietin)

stimulates production of RBCs• Hemoblasts myeloid stem cellsproethryoblastearly erythroblasts• early erhtyhroblasts multiply & make hemoglobinlate erythroblast

normoblast• once normoblast accoulates 34% Hborganelles are ejected, nucleus

degeneratescell collapses inwardreticulocyte• still has ribosomes & rough ER; leaves bone marrow• matures in two daysmature erythrocyte

RBC LifeCycle• RBC is terminally differentiated• cannot synthesize proteins, enzymes or renew

membranes• life span-about 120 days• engulfed & destroyed by phagocytotic cells in

liver, spleen and bone marrow• process is hemolysis• once hemolyzed-parts are broken down• globular proteins are disassembled into amino

acids • Heme splits from globin of HB molecule• Iron is stripped from hemebiliverdin (green,

organic compound)bilirubin (orange/yellow pigment)released into blood binds albumin transported to liver for excretion in bile

– If circulating levels cannot be handled by liverhyperbilirubinemia-condition which turns peripheral tissues yellowjaundice

• Fe salvaged for reuse• toxic to body-must be stored &

transported bound to a protein• Tranferrin used for iron transport• hemosiderin for iron storage• in bone marrow Fe is taken into the

mitochondria of developing RBCs and is used to make heme

WBC Production-Leukopoiesis• begins with same pluripotent stem used in erythropoiesis-

hemocytoblast• differentiate into distinct types of CFUs-colony forming units• CFUs go on to produce 3 cell lines committed to a certain outcome• Myleoblasts• Monoblasts• Lymphoblasts

Leukopoiesis

Platelets-Thrombocytes • not cells in strictest sense

– Fragments• continuously replaced• always present-not active unless damage

has occurred• Thrombocytosis

– too many• Throbocytopenia

– Too few• if numbers drop below 50 X 103/ul there

is danger of uncontrolled bleeding • Functions

– contain chemicals for clotting– form temporary platelet plug needed in

clotting– secrete growth factors– secrete chemical to attract neutrophils

and monocytes to site of inflammation

Thrombocytopoiesis• occurs in bone marrow• thrombopoieten-secreted by liverstimulate growth & maturation of

hemocytoblastsrepeated mitosis (up to 7X) without nuclear or cytoplasmic divisionvery large polypoloid cell-megakaryocyte

• presses against sinusoid wallruptureplatelet fragments• life span-about 5 – 9 days

Hemostasis• cut or damaged blood vessels bleed• outflow must be stopped before shock & death occur• accomplished by solidification of blood or coagulation• also called clotting or hemostasis• clotting is• fast• localized• carefully controlled• three phases

– vascular spasm– platelet plug formation– coagulation phase

Vascular Spasm Phase• blood vessels vasoconstrict

–diameter decreases at injury site• immediate & most effective in

small vessels• contraction exposes underlying

basement membrane to bloodstream

Platelet Plug Formation• endothelial cell membranes become sticky• sticky membranes allow platelets to adhere to injury

site• forms temporary plug within 1 minute of injury• as platelets keep arriving continue sticking to each

otherplatelet aggregationplatelet plug• plug seals break in vessel• as arrive become activatedchange shape• become more spherical & develop cytoplasmic

processes that extend toward other platelets• Release

– ADP-adenosine diphosphate• aggregating agent

– Serotonin• enhances vascular spasms

– Enzymes that help make Thromboxane A2• recruits & activates more platelets &

stimulates vascular spasms– PDGF

• platelet derived growth factor• promotes vessel repair

– Calcium• required for platelet aggregation

Coagulation Phase• occurs in asequence of steps• requires 13 clotting factors called

procoagulants• designated by Roman numerals

– many circulate as proenzymes- inactive precursors

• converted to active forms during clotting process

• activated by proteolytic cleavage & active proteases

• all but 3 are made & released by the liver (III, IV, VIII)

• all but 2 (III & VIII) are always present in blood

• activated platelets release 5 during platelet phase (III, IV, V, VIII & XIII)

Coagulation Cascade• activation of one

proenzymeactivates another proenzyme

• chain reaction or reaction cascade

• 2 reaction pathways to coagulation:

• extrinsic• Intrinsic• Both lead to the formation of

prothrombinase• at this point the two unite-

common pathway

Extrinsic Pathway• shorter & faster-fewer

steps• TF-tissue factor or

thromboplastin or clotting factor III is released by damaged blood vessels

• leaks into blood (extrinsic to it)

• TF binds Ca++ & Factor VII forming an enzyme complex

• complex cleaves Factor X (prothrombinase) active factor X

• first step in common pathway of coagulation

Intrinsic Pathway• more complex & slower• activators are in blood or

in direct contact with it (intrinsic to it)

• contact with collagen fibers or even glass of a collecting vialactivates Factor XII

• Begins a series of reactions

• activated factors VIII & IX combine to form enzyme complex which activates Factor X

Common Coagulation Pathway• the two paths unite at a

common pathwaythrombin synthesis

• begins when activated Factor X or prothombinase converts prothombin or Factor IIthrombin

• Thrombin cleaves fibrinogen or Factor I (soluble)insoluble fibrin

The Clot• fibrin glues platelets

together forming intertwined web– structural basis of a clot

• thrombin & Ca++ activate Factor XIII-fibrin stabilizing factor

• cross linking enzyme• forms covalent bonds

between fibrin molecules converting them into insoluble meshwork

• stabilizes clot

Clot Retraction• further stabilizes clot• occurs minutes after

initial clot formation• platelets contain

contractile proteins-actin & myosin

• these contract pull fibrin strands together

• squeezing out serum compacts clot

• functions to:• pull torn edges of broken

vessel together• reduce size of damaged

area

Rebuilding • begins with clot formation

• PDGFstimulates smooth muscle cells & fibroblast division to rebuild vessel wall– angiogenesis

• Thrombin, factors VII & X promote healing by stimulating growth of new blood vessels at site of damage

Fibrinolysis• hemostasis is not complete until clot has been dissolved • plasminogen is incorporated into clot as it forms• nearby cells release TPA-tissue pasminogen activator • binds to fibren and activates plasimnogen converting it

to plasmin • plasmin digests fibrindissolving clot

Control of Clotting• clotting must be carefully

regulated• inappropriate formation-

life-threatening– too much-thrombus

• clotting-restricted by several mechanisms

• 1. Platelets do not adhere to normal endothelium – intact endothelial cells

convert membrane lipids into prostacyclin

• blocks platelet adhesion & aggregation

• limits platelet plug to area of damage

Control of Clotting• Plasma contains

anticoagulants– Antithrombin III

inactivates thrombin– Heparin accelerates

activation of antithrombin III enhances inhibition of thrombin synthesis

Control of Clotting• 3. Endothelial cells

release thrombomodulin-binds to thrombin converts it into enzyme that activates protein c

• Protein Cinactivates clotting factors & stimulates plasmin formation

Thromboembolytic Disorders

• Undesirable clottingthrombus– blood clots in unbroken

vessels• gets into coronary

circulationheart attack• thrombus that breaks away

& floats freeembolus• Cerebral embolusstroke• Pulmonary emboluslung• Conditions that roughen

endothelium encourage clot formation-– Arteriosclerosis

Bleeding Disorders• Thrombocytopenia

– deficient platelet number– can result in spontaneous bleeding from small vessels

• Impaired liver function– liver makes procoagulants & when unable to do so result is severe bleeding

• Deficiency of Vitamin K– may be a cause of liver dysfunction– cofactor needed for synthesis of factors II, VII, IX, X & proteins C & S– blocking action of vitamin K helps prevent inappropriate clotting

• Warfarin-vitamin K antagonist

• Deficiency of clotting factors– not enough produced or mutant version fails to perform properly– von Willebrand disease-most common– Hemophilia A-classic-factor VIII deficiency– antihemophilic factor-hemophilia B– factor XI deficiency-hemophilia C-– actor XI deficiency-in both sexes

• Lowered Calcium – affects nearly all clotting pathways– any lowering of Ca impairs blood clotting

Hemophilia Inheritance

ABO Blood Types• blood type-determined by

presence or absence of antigens-A and B

• Presence of A-blood type A• Presence of B-blood type B• Presense of both-blood type

AB• Absence of both-blood type

O

ABO Blood Types• antibodies begin to appear in

plasma 2 to 8 months after birth

• person produces antibodies against antigens that are not present on his or her RBCs

• Blood type A-makes antibody B• Blood type B-makes antibody A• Blood type O-makes antibodies

A & B • Blood type AB-does not make

antibodies

Blood Type• Antigens are often referred to as agglutinogens• Antibodies-immunoglobulins are made by immune

system in response to foreign material-agglutinins• antibody adheres to foreign material & eliminates it• presence of antigens on cells is a way for immune

system to decide whether substance is foreign or not• immune system ignores surface antigens on your RBCs• when blood-type antigen senses foreign antigen has

entered system alerts immune system to create antibodies to that antigen– antibodies attach themselves to foreign antigens

destroy them• when attack foreign cellsclump together-agglutinate-

termed agglutination

Agglutination• Antibodies react against A or B antigen except those of one’s own RBCs• person with antigen A produces anti-B antibodiesattack type B antigens• person with antigen B produces anti-A antibodiesattack type A antigens• person with neither A or B antigens produces both anti-A & anti-B antibodies• person with both antigens A & B will produce no antibodies• When antibody meets specific surface antigenRBCs agglutinate & may

hemolyze– Cross reaction or transfusion reaction– can be dangerous to receive wrong blood type during a transfusion

• Compatibility can be verified with blood typing– mix small sample of blood with anti-A or anti-B antibodies-called

antiserum– presence or absence of clumping is determined for each type of

antiserum– clumping only with anti-A serum blood type A– clumping only with anti-B serumblood type B– clumping with both antigensblood type AB– Absence of clumping with either antigenblood type O

Universal Donor & Recipient

• Type O-universal donor

–no surface antigensrecipient’s blood can have antibodies but there will be no clumping

• Type AB-universal receiver

–holds no antibodies to react with antigens

Antigen D-Rh Factor• rhesus antigen• in Rh negative individuals D antigen is missing• 84% of humans are Rh positive• Blood Type A+ carries A & Rh antigens• shouldn't mix A+ with A- blood• blood must also be typed for Rh factor• Anti-D antibodies are not normally found in blood as anti a and b

antibodies are• form only in Rh negative individuals who are exposed to Rh positive

blood• Rh negative person receives Rh positive transfusionrecipient

produces anti-d antibodies• Anti-d does not appear instantaneously• presents little danger• if person gets another Rh positive transfusion, his or her anti-D could

agglutinate donor’s RBCs