ch17blood

CHAPTER 17BLOOD!!!

© 2013 Pearson Education, Inc.


Blood Composition

• Blood– Fluid connective tissue– Plasma – non-living fluid matrix– Formed elements – living blood "cells"

suspended in plasma• Erythrocytes (red blood cells, or RBCs) • Leukocytes (white blood cells, or WBCs) • Platelets


Blood Composition

• Spun tube of blood yields three layers– Plasma on top (~55%)– Erythrocytes on bottom (~45%)– Buffy coat (< 1%) - a whitish layer between plasma

and erythrocytes. Contains • WBCs, aka leucocytes• Platelets are cell fragments that help stop bleeding.

• Hematocrit– Percent of blood volume that is RBCs – 47% ± 5% for males; 42% ± 5% for females


Figure 17.1 The major components of whole blood.

Withdraw bloodand place in tube.

Centrifuge theblood sample.

Plasma• 55% of whole blood• Least dense componentBuffy coat• Leukocytes and platelets• <1% of whole bloodErythrocytes

• 45% of whole blood (hematocrit)• Most dense component

Formedelements

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Plasma• 55% of whole blood• Least dense componentBuffy coat• Leukocytes and platelets• <1% of whole bloodErythrocytes

• 45% of whole blood (hematocrit)• Most dense component

Formedelements

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Physical Characteristics and Volume

• Sticky, opaque fluid with metallic taste• Color varies with O2 content

– High O2 - scarlet; Low O2 - dark red• pH 7.35–7.45• ~8% of body weight• Average volume

– 5–6 L for males; 4–5 L for females


Functions of Blood• Functions include

– Distributing substances – O2, nutrients to cells; wastes to elimination sites (lungs, kidneys); hormones from glands to target sites.

– Regulating blood levels of substances• Maintaining body temperature• Maintaining normal pH via buffer systems; blood is the

reservoir for the ‘alkaline reserve’ of HCO3-

• Maintaining adequate fluid volume in the circulatory system via blood proteins.

– Protection • Preventing blood loss – damage of a blood vessel causes

platelets and plasma proteins to initiate blood clotting• Preventing infection – antibodies, complement proteins and

WBCs all help defend the body against foreign invaders, e.g., bacteria and viruses.


Blood Plasma

• 90% water• Over 100 dissolved solutes

– Nutrients, gases, hormones, wastes, proteins, inorganic ions

– Plasma proteins most abundant solutes• Remain in blood; not taken up by cells• Proteins produced mostly by liver• 60% albumin; 36% globulins; 4% fibrinogen


Table 17.1 Composition of Plasma (1 of 2)


Table 17.1 Composition of Plasma (2 of 2)


Albumin

• 60% of plasma protein• Functions

– Substance carrier– Blood buffer– Major contributor of plasma osmotic pressure


Formed Elements – WBCs, RBCs, Platelets

• Only WBCs are complete cells, i.e., with nuclei and organelles

• RBCs have no nuclei or other organelles• Platelets are cell fragments• Most formed elements survive in bloodstream

only few days• Most blood cells originate in bone marrow and

do not divide – Stem cells divide continuously in red bone

marrow to replace blood cells


Figure 17.2 Photomicrograph of a human blood smear stained with Wright's stain.Platelets Erythrocytes Monocyte

Neutrophils Lymphocyte


Erythrocytes

• Biconcave discs, anucleate, essentially no organelles

• Diameters larger than some capillaries• Filled with hemoglobin (Hb) for gas

transport• Contain plasma membrane protein

spectrin and other proteins– Spectrin provides flexibility to change shape

• Major factor contributing to blood viscosity


2.5 µm

7.5 µm

Top view

Side view (cut)

Figure 17.3 Structure of erythrocytes (red blood cells).


Erythrocytes

• Structural characteristics contribute to gas transport – Biconcave shape—huge surface area relative

to volume when compared to a spherical shape.

– >97% hemoglobin (not counting water)– No mitochondria; ATP production anaerobic;

do not consume O2 they transport• Superb example of complementarity of

structure and function


Erythrocyte Function

• RBCs dedicated to respiratory gas transport

• Hemoglobin binds reversibly with oxygen

• Normal values – Males - 13–18g/100ml; Females - 12–16

g/100ml


Hemoglobin Structure

• Globin composed of 4 polypeptide chains– Two alpha and two beta chains

• Heme pigment bonded to each globin chain– Gives blood red color

• Heme's central iron atom binds one O2

• Each Hb molecule can transport four O2

• Each RBC contains 250 million Hb molecules


Figure 17.4 Structure of hemoglobin.

Globin chains

Hemegroup

Globin chains

Hemoglobin consists of globin (two alpha and two betapolypeptide chains) and four heme groups.

Iron-containing heme pigment.


Hemoglobin (Hb)

• O2 loading in lungs– Produces oxyhemoglobin (ruby red)

• O2 unloading in tissues– Produces deoxyhemoglobin or reduced

hemoglobin (dark red) • CO2 loading in tissues

– 20% of CO2 in blood binds to Hb carbaminohemoglobin


Hematopoiesis

• Blood cell formation in red bone marrow– Composed of reticular connective tissue and

blood sinusoids • In adult, found in axial skeleton, girdles,

and proximal epiphyses of humerus and femur


Hematopoiesis

• Hematopoietic stem cells (Hemocytoblasts)– Give rise to all formed elements– Hormones and growth factors push cell

toward specific pathway of blood cell development

– Committed cells cannot change• New blood cells enter blood sinusoids


Erythropoiesis: Red Blood Cell Production

• Stages– Myeloid stem cell transformed into

proerythroblast– In 15 days proerythroblasts develop into

basophilic, then polychromatic, then orthochromatic erythroblasts, and then into reticulocytes

– Reticulocytes enter bloodstream; in 2 days mature RBC


Erythropoiesis

• As myeloid stem cell transforms1. Ribosomes synthesized2. Hemoglobin synthesized; iron accumulates3. Ejection of nucleus; formation of reticulocyte

(young RBC)• Reticulocyte ribosomes degraded; Then

become mature erythrocytes• Reticulocyte count indicates rate of RBC

formation


Figure 17.5 Erythropoiesis: formation of red blood cells.

Stem cell Committed cell Developmental pathwayPhase 1Ribosome synthesis

Phase 2Hemoglobin accumulation

Phase 3Ejection of nucleus

Hematopoietic stemcell (hemocytoblast) Proerythroblast

Basophilicerythroblast

Polychromaticerythroblast

Orthochromaticerythroblast Reticulocyte Erythrocyte

15 days from Proerythroblast to reticulocyte stage

2 days from Reticulocyte to Erythrocyte stage


Regulation of Erythropoiesis

• Too few RBCs leads to tissue hypoxia• Too many RBCs increases blood viscosity• > 2 million RBCs made per second• Balance between RBC production and

destruction depends on– Hormonal controls – Adequate supplies of iron, amino acids, and B

vitamins


Hormonal Control of Erythropoiesis

• Hormone Erythropoietin (EPO)– Direct stimulus for erythropoiesis – Always small amount in blood to maintain

basal rate• High RBC or O2 levels depress production

– Released by kidneys (some from liver) in response to hypoxia• Dialysis patients have low RBC counts



• Causes of hypoxia– Decreased RBC numbers due to hemorrhage

or increased destruction– Insufficient hemoglobin per RBC (e.g., iron

deficiency)– Reduced availability of O2 (e.g., high altitudes)



• Effects of EPO– Rapid maturation of committed marrow cells– Increased circulating reticulocyte count in 1–

2 days• Some athletes abuse artificial EPO

– Dangerous consequences• Testosterone enhances EPO production,

resulting in higher RBC counts in males


Stimulus: Hypoxia(inadequate O2

delivery) due to O2-carryingability of bloodrises.

Enhancederythropoiesisincreases RBC count. Kidney (and liver to

a smaller extent)releases erythropoietin. Erythropoietin

stimulates redbone marrow.

Figure 17.6 Erythropoietin mechanism for regulating erythropoiesis.

Homeostasis: Normal blood oxygen levels

IMBALANCE

IMBALANCE• Decreased RBC count• Decreased amount of hemoglobin• Decreased availability of O2

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delivery) due to



IMBALANCE


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delivery) due to

Kidney (and liver toa smaller extent)releases erythropoietin.



IMBALANCE


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delivery) due to

Kidney (and liver toa smaller extent)releases erythropoietin. Erythropoietin




IMBALANCE


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delivery) due to



Enhancederythropoiesisincreases RBC count.



IMBALANCE


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O2-carryingability of bloodrises.

Enhancederythropoiesisincreases RBC count.


delivery) due to





IMBALANCE


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Dietary Requirements for Erythropoiesis

• Nutrients—amino acids, lipids, and carbohydrates

• Iron– Available from diet– 65% in Hb; rest in liver, spleen, and bone marrow– Free iron ions toxic

• Stored in cells as ferritin and hemosiderin• Transported in blood bound to protein transferrin

• Vitamin B12 and folic acid necessary for DNA synthesis for rapidly dividing cells (developing RBCs)


Fate and Destruction of Erythrocytes

• Life span: 100–120 days– No protein synthesis, growth, division

• Old RBCs become fragile; Hb begins to degenerate

• Get trapped in smaller circulatory channels especially in spleen

• Macrophages engulf dying RBCs in spleen


Fate and Destruction of Erythrocytes

• Heme and globin are separated– Iron salvaged for reuse– Heme degraded to yellow pigment bilirubin– Liver secretes bilirubin (in bile) into intestines

• Degraded to pigment urobilinogen• Pigment leaves body in feces as stercobilin

– Globin metabolized into amino acids• Released into circulation


Raw materials aremade available in bloodfor erythrocyte synthesis.

Aged and damagedred blood cells are engulfedby macrophages of spleen,liver, and bone marrow; thehemoglobin is broken down.

New erythrocytesenter bloodstream;function about 120days.

Erythropoietin and necessaryraw materials in blood promoteerythropoiesis in red bone marrow.

Erythropoietin levels rise in blood.

Low O2 levels in blood stimulatekidneys to produce erythropoietin.

Figure 17.7 Life cycle of red blood cells.

Hemoglobin

Heme Globin

Bilirubin ispicked upby the liver.

Iron is storedas ferritin orhemosiderin.

Aminoacids

Iron is bound to transferrinand released to bloodfrom liver as neededfor erythropoiesis.

Bilirubin is secreted intointestine in bile whereit is metabolized tostercobilin by bacteria.

Circulation

Food nutrients(amino acids, Fe,B12, and folic acid)are absorbed fromintestine and enterblood.

Stercobilinis excretedin feces.

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Low O2 levels in blood stimulatekidneys to produce erythropoietin.1

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5Figure 17.7 Life cycle of red blood cells.

Hemoglobin

Heme Globin



Aminoacids


Circulation

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Hemoglobin

Heme Globin



Aminoacids



Circulation



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Figure 17.7 Life cycle of red blood cells. Slide 8







Hemoglobin

Heme Globin



Aminoacids



Circulation



1

2

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Erythrocyte Disorders

• Anemia– Blood has abnormally low O2-carrying

capacity– Sign rather than disease itself– Blood O2 levels cannot support normal

metabolism– Accompanied by fatigue, pallor, shortness of

breath, and chills


Causes of Anemia

• Three groups– Blood loss– Low RBC production– High RBC destruction


Causes of Anemia: Blood Loss

• Hemorrhagic anemia– Blood loss rapid (e.g., stab wound)– Treated by blood replacement

• Chronic hemorrhagic anemia– Slight but persistent blood loss

• Hemorrhoids, bleeding ulcer– Primary problem treated


Causes of Anemia: Low RBC Production

• Iron-deficiency anemia– Caused by hemorrhagic anemia, low iron

intake, or impaired absorption– Microcytic, hypochromic RBCs– Iron supplements to treat



• Pernicious anemia– Autoimmune disease - destroys stomach

mucosa– Lack of intrinsic factor needed to absorb B12

• Deficiency of vitamin B12

– RBCs cannot divide macrocytes– Treated with B12 injections or nasal gel– Also caused by low dietary B12 (vegetarians)



• Renal anemia– Lack of EPO– Often accompanies renal disease– Treated with synthetic EPO



• Aplastic anemia– Destruction or inhibition of red marrow by

drugs, chemicals, radiation, viruses– Usually cause unknown– All cell lines affected

• Anemia; clotting and immunity defects– Treated short-term with transfusions; long-

term with transplanted stem cells


Causes of Anemia: High RBC Destruction

• Hemolytic anemias– Premature RBC lysis– Caused by

• Hb abnormalities• Incompatible transfusions• Infections



• Usually genetic basis for abnormal Hb• Globin abnormal

– Fragile RBCs lyse prematurely



• Thalassemias– Typically Mediterranean ancestry– One globin chain absent or faulty– RBCs thin, delicate, deficient in Hb– Many subtypes

• Severity from mild to severe



• Sickle-cell anemia– Hemoglobin S

• One amino acid wrong in a globin beta chain– RBCs crescent shaped when unload O2 or

blood O2 low– RBCs rupture easily and block small vessels

• Poor O2 delivery; pain


Sickle-cell Anemia

• Black people of African malarial belt and descendants

• Malaria– Kills 1 million each year

• Sickle-cell gene– Two copies Sickle-cell anemia– One copy Sickle-cell trait; milder disease;

better chance to survive malaria


Sickle-cell Anemia: Treatments

• Acute crisis treated with transfusions; inhaled nitric oxide increases diameter of blood vessels.

• Preventing sickling– Hydroxyurea induces fetal hemoglobin (which does

not sickle) formation – Blocking RBC ion channels– Stem cell transplants– Gene therapy


Figure 17.8 Sickle-cell anemia.

Val His Leu Thr Pro Glu Glu …

1 2 3 4 5 6 7 146

Normal erythrocyte has normalhemoglobin amino acid sequence in the beta chain.

Val His Leu Thr Pro Val Glu …

1 2 3 4 5 6 7 146

Sickled erythrocyte results from asingle amino acid change in thebeta chain of hemoglobin.


Erythrocyte Disorders• Polycythemia vera

– This is a bone marrow cancer that produces excess RBCs– Severely increased blood viscosity; sluggish flow

• RBC count extremely high - 8-11 million cells per microliter, μL (normal levels: female = 4.2-5.4 million cells/μL, male = 4.7-6.1 million cells/μL).

• Circulation is impaired; have to dilute the blood by removing some and replacing with saline fluid.

• Secondary polycythemia– Less O2 available (at high altitude) or EPO production increases

higher RBC count. E.g., people who at high altitudes– Blood doping in athletes – blood is withdrawn to stimulate EPO

production, and blood is reinjected. Results in high RBCs


Leukocytes• Make up <1% of total blood volume

– 4,800 – 10,800 WBCs per μl blood• Function in defense against disease

– Cells flatten and ‘slip out’ between the endothelial cells of the capillaries via diapedesis

– Move through tissue spaces by• ameboid motion – form flowing cytoplasmic extensions• positive chemotaxis – follow a chemical trail to site of

infection.• Leukocytosis: WBC count over 11,000 per μL

– The body speeds up production of WBCs and can double the number in a few hours.

– This is a normal response to infection


Leukocytes: Two Major Categories

1. Granulocytes – Have visible cytoplasmic granules– Neutrophils, eosinophils, basophils

2. Agranulocytes – No visible cytoplasmic granules– Lymphocytes, monocytes

3. Mnemonic to help remember order of decreasing abundance in blood: – Never let monkeys eat bananas


Figure 17.9 Types and relative percentages of leukocytes in normal blood.

Formedelements

(All total 4800–10,800/ µl)

GranulocytesNeutrophils (50–70%)

Eosinophils (2–4%)

Basophils (0.5–1%)

AgranulocytesLymphocytes (25–45%)

Monocytes (3–8%)

Platelets

Leukocytes

Erythrocytes

(not drawnto scale)

DifferentialWBC count


Granulocytes

• Granulocytes – Neutrophils, Eosinophils, Basophils– Larger and shorter-lived than RBCs– Lobed nuclei– Cytoplasmic granules stain specifically with

Wright's stain– All phagocytic to some degree


Neutrophils

• Most numerous WBCs• Called neutrophils, ‘neutral-loving’, because the granules

can be stained with both acidic (red) and alkaline (blue) dyes.

• Also called Polymorphonuclear leukocytes (PMNs or polys) – nuclei have multiple ‘many’ lobes, 3-6 lobes.

• Granules stain lilac; contain hydrolytic enzymes (lysosomes), or anti-microbial defensins

• twice the size of RBCs• Very phagocytic—"bacteria slayers”

– Use oxygen to form hydrogen peroxide and bleach to kill bacteria and certain fungi.


Eosinophils

• Red-staining granules• Bi-lobed nucleus – looks like an old-fashioned

telephone receiver, or a pair of spectacles• Granules are lysosome-like

– Release enzymes to digest parasitic worms, such as flatworms and roundworms

• Role in allergies and asthma• Play a role in modulating immune response


Basophils

• Rarest WBCs• Nucleus deep purple with 1-2 constrictions• Large, purplish-black (basophilic) granules

contain histamine– Histamine: inflammatory chemical that acts as

vasodilator to attract WBCs to inflamed sites• Are functionally similar to mast cells


Figure 17.10a Leukocytes.Granulocytes

Neutrophil: Multilobed nucleus, pale red and blue cytoplasmic granules


Figure 17.10b Leukocytes.Granulocytes

Eosinophil: Bilobed nucleus, red cytoplasmic granules


Figure 17.10c Leukocytes.

Granulocytes

Basophil: Bilobed nucleus, purplish-black cytoplasmic granules


Agranulocytes

• Agranulocytes– Lack visible cytoplasmic granules– Have spherical or kidney-shaped nuclei


Lymphocytes

• Second most numerous WBC• Large, dark-purple, circular nuclei with thin

rim of blue cytoplasm• Mostly in lymphoid tissue (e.g., lymph

nodes, spleen); few circulate in blood• Crucial to immunity


Lymphocytes

• Two types – T lymphocytes (T cells) act against virus-

infected cells and tumor cells– B lymphocytes (B cells) give rise to plasma

cells, which produce antibodies


Monocytes

• Largest leukocytes• Abundant pale-blue cytoplasm• Dark purple-staining, U- or kidney-shaped

nuclei


Monocytes

• Leave circulation, enter tissues, and differentiate into macrophages– Actively phagocytic cells; crucial against

viruses, intracellular bacterial parasites, and chronic infections

• Activate lymphocytes to mount an immune response


Agranulocytes

Lymphocyte (small):Large sphericalnucleus, thin rim ofpale blue cytoplasm

Figure 17.10d Leukocytes.


Agranulocytes

Monocyte: Kidney-shaped nucleus, abundant pale blue cytoplasm

Figure 17.10e Leukocytes.


Leukopoiesis

• Production of WBCs– Stimulated by 2 types of chemical

messengers from red bone marrow and mature WBCs• Interleukins (e.g., IL-3, IL-5)• Colony-stimulating factors (CSFs) named for WBC

type they stimulate (e.g., granulocyte-CSF stimulates granulocytes)

• All leukocytes originate from hemocytoblasts


Leukopoiesis

• Lymphoid stem cells lymphocytes• Myeloid stem cells all others• Progression of all granulocytes

– Myeloblast promyelocyte myelocyte band mature cell

• Granulocytes stored in bone marrow• 3 times more WBCs produced than RBCs

– Shorter life span; die fighting microbes


Leukopoiesis

• Progression of agranulocytes differs• Monocytes – live several months

– Share common precursor with neutrophils– Monoblast promonocyte monocyte

• Lymphocytes – live few hours to decades– Lymphoid stem cell T lymphocyte

precursors (travel to thymus) and B lymphocyte precursors


Figure 17.11 Leukocyte formation.Stem cells

Committedcells

Developmentalpathway

Hematopoietic stem cell(hemocytoblast)

Myeloid stem cell Lymphoid stem cell

Myeloblast Myeloblast Myeloblast Monoblast B lymphocyteprecursor

T lymphocyteprecursor

Promyelocyte Promyelocyte Promyelocyte Promonocyte

Eosinophilicmyelocyte

Basophilicmyelocyte

Neutrophilicmyelocyte

Eosinophilicband cells

Basophilicband cells

Neutrophilicband cells

Granularleukocytes

Agranularleukocytes

Eosinophils Basophils Neutrophils Monocytes B lymphocytes T lymphocytes

Macrophages (tissues) Plasma cells Effector T cells

Some become Some become

(a) (b) (c) (d) (e) (f)

Some become


Leukocyte disorders

• Leukopenia– Abnormally low WBC count—drug induced

• Leukemias – all fatal if untreated– Cancer overproduction of abnormal WBCs– Named according to abnormal WBC clone involved– Myeloid leukemia involves myeloblast descendants– Lymphocytic leukemia involves lymphocytes

• Acute leukemia derives from stem cells; primarily affects children

• Chronic leukemia more prevalent in older people


Leukemia

• Cancerous leukocytes fill red bone marrow– Other lines crowded out anemia; bleeding

• Immature nonfunctional WBCs in bloodstream

• Death from internal hemorrhage; overwhelming infections

• Treatments– Irradiation, antileukemic drugs; stem cell

transplants


Infectious Mononucleosis

• Highly contagious viral disease– Epstein-Barr virus

• High numbers atypical agranulocytes• Symptoms

– Tired, achy, chronic sore throat, low fever• Runs course with rest


Platelets

• Cytoplasmic fragments of megakaryocytes

• Blue-staining outer region; purple granules• Granules contain serotonin, Ca2+,

enzymes, ADP, and platelet-derived growth factor (PDGF)– Act in clotting process

• Normal = 150,000 – 400,000 platelets /ml of blood


Platelets

• Form temporary platelet plug that helps seal breaks in blood vessels

• Circulating platelets kept inactive and mobile by nitric oxide (NO) and prostacyclin from endothelial cells lining blood vessels

• Age quickly; degenerate in about 10 days• Formation regulated by thrombopoietin• Derive from megakaryoblast

– Mitosis but no cytokinesis megakaryocyte - large cell with multilobed nucleus


Figure 17.12 Formation of platelets.

Stem cell Developmental pathway

Hematopoietic stemcell (hemocytoblast)

Megakaryoblast(stage I megakaryocyte)

Megakaryocyte(stage II/III)

Megakaryocyte(stage IV)

Platelets


Table 17.2 Summary of Formed Elements of the Blood (1 of 2)


Table 17.2 Summary of Formed Elements of the Blood (2 of 2)

Blood cell videos

• http://www.youtube.com/watch?v=ZOH9kZcvrK4

• http://www.youtube.com/watch?v=xpsGsfuffEM

• http://www.youtube.com/watch?v=tDTLC2swhlQ


http://www.youtube.com/watch?v=ZOH9kZcvrK4



http://www.youtube.com/watch?v=xpsGsfuffEM

http://www.youtube.com/watch?v=xpsGsfuffEM

http://www.youtube.com/watch?v=tDTLC2swhlQ

http://www.youtube.com/watch?v=tDTLC2swhlQ


Hemostasis

• Fast series of reactions for stoppage of bleeding

• Requires clotting factors, and substances released by platelets and injured tissues

• Three steps1. Vascular spasm 2. Platelet plug formation3. Coagulation (blood clotting)


Hemostasis: Vascular Spasm

• Vasoconstriction of damaged blood vessel• Triggers

– Direct injury to vascular smooth muscle, i.e., blood vessels

– Chemicals released by endothelial cells and platelets

– Pain reflexes• Most effective in smaller blood vessels


Hemostasis: Platelet Plug Formation

• Positive feedback cycle• Damaged endothelium exposes collagen

fibers– Platelets stick to collagen fibers via plasma

protein von Willebrand factor– Swell, become spiked and sticky, and release

chemical messengers• ADP causes more platelets to stick and release

their contents • Serotonin and thromboxane A2 enhance vascular

spasm and platelet aggregation


Hemostasis: Coagulation

• Reinforces platelet plug with fibrin threads• Blood transformed from liquid to gel• Series of reactions using clotting factors

(procoagulants)– # I – XIII; most plasma proteins– Vitamin K needed to synthesize 4 of them


Figure 17.13 Events of hemostasis. Slide 1

Step 1 Vascular spasm• Smooth muscle contracts, causing vasoconstriction.

Step 2 Platelet plugformation• Injury to lining of vessel exposes collagen fibers; platelets adhere.

• Platelets release chemicals that make nearby platelets sticky; platelet plug forms.

Step 3 Coagulation• Fibrin forms a mesh that traps red blood cells and platelets, forming the clot.

Collagenfibers

Platelets

Fibrin





Collagenfibers






Collagenfibers

Platelets






Step 3 Coagulation• Fibrin forms a mesh that traps red blood cells and platelets, forming the clot.

Collagenfibers

Platelets

Fibrin


Coagulation: Overview

• Three phases of coagulation– Prothrombin activator formed in both

intrinsic and extrinsic pathways– Prothrombin converted to enzyme thrombin– Thrombin catalyzes fibrinogen fibrin


Coagulation Phase 1: Two Pathways to Prothrombin Activator• Initiated by either intrinsic or extrinsic

pathway (usually both)– Triggered by tissue-damaging events– Involves a series of procoagulants– Each pathway cascades toward factor X

• Factor X complexes with Ca2+, PF3, and factor V to form prothrombin activator


Coagulation Phase 1: Two Pathways to Prothrombin Activator• Intrinsic pathway

– Triggered by negatively charged surfaces (activated platelets, collagen, glass)

– Uses factors present within blood (intrinsic)• Extrinsic pathway

– Triggered by exposure to tissue factor (TF) or factor III (an extrinsic factor)

– Bypasses several steps of intrinsic pathway, so faster


Coagulation Phase 2: Pathway to Thrombin

• Prothrombin activator catalyzes transformation of prothrombin to active enzyme thrombin

• Once prothrombin activator formed, clot forms in 10–15 seconds


Coagulation Phase 3: Common Pathway to the Fibrin Mesh• Thrombin converts soluble fibrinogen to

fibrin• Fibrin strands form structural basis of clot• Fibrin causes plasma to become a gel-like

trap for formed elements • Thrombin (with Ca2+) activates factor XIII

which:– Cross-links fibrin– Strengthens and stabilizes clot


Figure 17.14 The intrinsic and extrinsic pathways of blood clotting (coagulation). (1 of 2)

Intrinsic pathway Extrinsic pathwayVessel endotheliumruptures, exposingunderlying tissues(e.g., collagen)

Tissue cell traumaexposes blood to

Platelets cling and theirsurfaces provide sites formobilization of factors

Tissue factor (TF)

XII

XIIa

Ca2+

VIIXIXIa

IX Ca2+

VIIa

IXa

VIII

VIIIa

IXa/VIIIa complex TF/VIIa complex

X

Xa

Ca2+

PF3 Va V

Prothrombinactivator

PF3released byaggregated

platelets

Phase 1


Figure 17.14 The intrinsic and extrinsic pathways of blood clotting (coagulation). (2 of 2)

Phase 2 Prothrombin (II)

Thrombin (IIa)

Phase 3 Fibrinogen (I)

(soluble) Fibrin(insolublepolymer)

Cross-linkedfibrin mesh

XIIIa

XIII

Ca2+


Figure 17.15 Scanning electron micrograph of erythrocytes trapped in a fibrin mesh.


Clot Retraction

• Stabilizes clot• Actin and myosin in platelets contract

within 30–60 minutes• Contraction pulls on fibrin strands,

squeezing serum from clot• Draws ruptured blood vessel edges

together


Vessel Repair

• Vessel is healing as clot retraction occurs• Platelet-derived growth factor (PDGF)

stimulates division of smooth muscle cells and fibroblasts to rebuild blood vessel wall

• Vascular endothelial growth factor (VEGF) stimulates endothelial cells to multiply and restore endothelial lining


Fibrinolysis

• Removes unneeded clots after healing• Begins within two days; continues for

several• Plasminogen in clot is converted to

plasmin by tissue plasminogen activator (tPA), factor XII and thrombin

• Plasmin is a fibrin-digesting enzyme


Factors Limiting Clot Growth or Formation

• Two mechanisms limit clot size– Swift removal and dilution of clotting factors – Inhibition of activated clotting factors

• Thrombin bound onto fibrin threads• Antithrombin III inactivates unbound

thrombin• Heparin in basophil and mast cells inhibits

thrombin by enhancing antithrombin III


Factors Preventing Undesirable Clotting

• Platelet adhesion is prevented by– Smooth endothelium of blood vessels

prevents platelets from clinging– Antithrombic substances nitric oxide and

prostacyclin secreted by endothelial cells– Vitamin E quinone acts as potent

anticoagulant

Hemostasis Video:– http://

www.youtube.com/watch?v=HFNWGCx_Eu4

http://www.youtube.com/watch?v=HFNWGCx_Eu4

http://www.youtube.com/watch?v=HFNWGCx_Eu4


Disorders of Hemostasis

• Thromboembolic disorders: undesirable clot formation

• Bleeding disorders: abnormalities that prevent normal clot formation

• Disseminated intravascular coagulation (DIC)– Involves both types of disorders


Thromboembolic Conditions

• Thrombus: clot that develops and persists in unbroken blood vessel– May block circulation leading to tissue death

• Embolus: thrombus freely floating in bloodstream

• Embolism: embolus obstructing a vessel– E.g., pulmonary and cerebral emboli

• Risk factors – atherosclerosis, inflammation, slowly flowing blood or blood stasis from immobility


Anticoagulant Drugs

• Aspirin– Antiprostaglandin that inhibits thromboxane A2

• Heparin– Anticoagulant used clinically for pre- and

postoperative cardiac care• Warfarin (Coumadin)

– Used for those prone to atrial fibrillation– Interferes with action of vitamin K

• Dabigatran directly inhibits thrombin


Bleeding Disorders

• Thrombocytopenia: deficient number of circulating platelets– Petechiae appear due to spontaneous,

widespread hemorrhage – Due to suppression or destruction of red bone

marrow (e.g., malignancy, radiation, drugs)– Platelet count <50,000/μl is diagnostic – Treated with transfusion of concentrated

platelets


Bleeding Disorders

• Impaired liver function– Inability to synthesize procoagulants – Causes include vitamin K deficiency, hepatitis,

and cirrhosis– Impaired fat absorption and liver disease can

also prevent liver from producing bile, impairing fat and vitamin K absorption


Bleeding Disorders

• Hemophilia includes several similar hereditary bleeding disorders – Hemophilia A: most common type (77% of all cases);

factor VIII deficiency– Hemophilia B: factor IX deficiency – Hemophilia C: mild type; factor XI deficiency

• Symptoms include prolonged bleeding, especially into joint cavities

• Treated with plasma transfusions and injection of missing factors– Increased hepatitis and HIV risk


Disseminated Intravascular Coagulation (DIC)• Clotting causes bleeding

– Widespread clotting blocks intact blood vessels

– Severe bleeding occurs because residual blood unable to clot

• Occurs as pregnancy complication; in septicemia, or incompatible blood transfusions


Transfusions

• Whole-blood transfusions used when blood loss rapid and substantial

• Packed red cells (plasma and WBCs removed) transfused to restore oxygen-carrying capacity

• Transfusion of incompatible blood can be fatal


Human Blood Groups

• RBC membranes bear 30 types of glycoprotein antigens – Anything perceived as foreign; generates an immune

response– Promoters of agglutination; called agglutinogens

• Mismatched transfused blood perceived as foreign– May be agglutinated and destroyed; can be fatal

• Presence or absence of each antigen is used to classify blood cells into different groups


Blood Groups

• Antigens of ABO and Rh blood groups cause vigorous transfusion reactions

• Other blood groups (MNS, Duffy, Kell, and Lewis) usually weak agglutinogens


ABO Blood Groups

• Types A, B, AB, and O• Based on presence or absence of two

agglutinogens (A and B) on surface of RBCs

• Blood may contain preformed anti-A or anti-B antibodies (agglutinins)– Act against transfused RBCs with ABO

antigens not present on recipient's RBCs• Anti-A or anti-B form in blood at about

2 months of age; adult levels by 8-10


Table 17.4 ABO Blood Groups


Rh Blood Groups

• 52 named Rh agglutinogens (Rh factors)• C, D, and E are most common• Rh+ indicates presence of D antigen

– 85% Americans Rh+


Rh Blood Groups

• Anti-Rh antibodies not spontaneously formed in Rh– individuals– Anti-Rh antibodies form if Rh– individual

receives Rh+ blood, or Rh– mom carrying Rh+ fetus

• Second exposure to Rh+ blood will result in typical transfusion reaction


Homeostatic Imbalance: Hemolytic Disease of the Newborn• Also called erythroblastosis fetalis

– Only occurs in Rh– mom with Rh+ fetus• Rh– mom exposed to Rh+ blood of fetus

during delivery of first baby – baby healthy – Mother synthesizes anti-Rh antibodies

• Second pregnancy– Mom's anti-Rh antibodies cross placenta and

destroy RBCs of Rh+ baby


Homeostatic Imbalance: Hemolytic Disease of the Newborn• Baby treated with prebirth transfusions

and exchange transfusions after birth• RhoGAM serum containing anti-Rh can

prevent Rh– mother from becoming sensitized


Transfusion Reactions

• Occur if mismatched blood infused• Donor's cells

– Attacked by recipient's plasma agglutinins– Agglutinate and clog small vessels– Rupture and release hemoglobin into

bloodstream • Result in

– Diminished oxygen-carrying capacity– Diminished blood flow beyond blocked

vessels– Hemoglobin in kidney tubules renal failure


Transfusion Reactions

• Symptoms– Fever, chills, low blood pressure, rapid

heartbeat, nausea, vomiting• Treatment

– Preventing kidney damage• Fluids and diuretics to wash out hemoglobin


Transfusions

• Type O universal donor– No A or B antigens

• Type AB universal recipient– No anti-A or anti-B antibodies

• Misleading - other agglutinogens cause transfusion reactions

• Autologous transfusions– Patient predonates


Before Transfusion

• Blood typing– Mixing RBCs with antibodies against its

agglutinogen(s) causes clumping of RBCs– Done for ABO and for Rh factor

• Cross matching– Mix recipient's serum with donor RBCs– Mix recipient's RBCs with donor serum


Figure 17.16 Blood typing of ABO blood types.

Blood being tested SerumAnti-A Anti-B

Type AB (containsagglutinogens A and B;agglutinates with bothsera)

Type A (containsagglutinogen A;agglutinates with anti-A)

Type B (containsagglutinogen B;agglutinates with anti-B)

Type O (contains noagglutinogens; does notagglutinate with eitherserum)

RBCs


Restoring Blood Volume

• Death from shock may result from low blood volume

• Volume must be replaced immediately with– Normal saline or multiple-electrolyte solution

(Ringer's solution) that mimics plasma electrolyte composition

– Plasma expanders (e.g., purified human serum albumin, hetastarch, and dextran) • Mimic osmotic properties of albumin• More expensive and may cause significant

complications


Diagnostic Blood Tests

• Hematocrit – test for anemia• Blood glucose tests – diabetes• Microscopic examination reveals

variations in size and shape of RBCs, indications of anemias


Diagnostic Blood Tests

• Differential WBC count• Prothrombin time and platelet counts

assess hemostasis• SMAC, a blood chemistry profile – liver

and kidney disorders• Complete blood count (CBC) – checks

formed elements, hematocrit, hemoglobin


Developmental Aspects

• Fetal blood cells form in fetal yolk sac, liver, and spleen

• Red bone marrow is primary hematopoietic area by seventh month

• Blood cells develop from mesenchymal cells called blood islands

• The fetus forms Hemoglobin F, which has higher affinity for O2 than hemoglobin A formed after birth


Developmental Aspects

• Blood diseases of aging– Chronic leukemias, anemias, clotting

disorders– Usually precipitated by disorders of heart,

blood vessels, or immune system

ch17blood

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