Upload
aphrodite-charles
View
43
Download
1
Embed Size (px)
DESCRIPTION
Blood Biochemistry. Tissue Chemistry & Biological Fluids. Biochemistry has passed from a state of descriptive to quantifiable science. As a biochemist, you should always be interested in things about metabolic sequences: - PowerPoint PPT Presentation
Citation preview
Blood Biochemistry
Tissue Chemistry & Biological Fluids
Biochemistry has passed from a state of descriptive to quantifiable science. As a biochemist, you should always be interested in things about metabolic
sequences:
The description of the enzymes & chemical changes that comprise the metabolic sequence
The rate at which material can be transformed by the sequence The amount of material utilized by the sequence among living
things The nature of the control mechanisms which adjust the amounts
of material utilized by the sequence
2
Wet weight (kg) Protein content (kg)
Skeletal muscle 30 6.6
Adipose tissue 13.2 0.92
Stomach & intestine 7.25 1.34
Liver 1.6 0.35
Brain 1.36 0.136
Kidneys 0.29 0.05
Heart 0.29 0.06
Adrenals 0.014 ?
Blood 6.4 1.02
Skin 4.9 ?
Bone 12.0 1.23
Roughly, the contributions of the different tissues to the body's metabolism are proportional to the weights of the tissue and the biological fluids
3
From the following table…
It is not the sheer mass of tissue which determines its quantitative contribution to metabolic activity
Activity of tissue is determined by its enzyme content
4
The body can be crudely divided into two components:
Circulating Tissues Biological Tissues
Blood Cartilage
Water Bone
Lymph Skin
Interstitial fluid Muscles
Cerebrospinal fluid Liver5
Vertebrates have evolved 2 principal mechanisms for supplying their cells with a continuous & adequate flow of oxygen:
A circulating system that actively delivers oxygen to the cells
Acquisition of oxygenThe oxygen carriers in vertebrates are the
proteins hemoglobin & myoglobin
6
Blood
In a normal weight, there is about 5-6 liters of blood (12%) or 85ml/kg
It circulates as a homogenous suspension of erythrocytes, leukocytes & platelets in a solution of proteins, inorganic ions, & low-molecular weight organic compounds
7
Functions of the Blood
Transport of nutrients Exchange of respiratory gases Transport of waste products Distribution of hormones & other regulatory substances Protection against microorganisms Acid-base, electrolyte & water homeostasis Heat regulation Prevention of excessive
hemorrhage by coagulation8
General Composition
By volume, 40-45% of the blood consists of erythrocytes, leukocytes & platelets
1 mm3 of blood contains: 5 x 106 RBCs; 5-103 WBCs; 5-105 platelets
Male Adults Female Adults
RBC 4.5-5.9 x 1012
cells/L
4.0-5.2 x 1012
cells/L
WBC 3.9-10.6 x 109
cells/L
3.5-10.0 x 109
cells/L
Platelets 150-400 x 109 cells/L
9
The Packed Cell Volume (PCV Hematocrit)
PCV Hematocrit = Volume of Red Cells/ Volume of whole blood x 100
Expressed as volume of erythrocyte per liter of whole
blood Normal adult males = 41-53; adult females = 36-
46 Hematocrit used to determine PCV Color of supernatant plasma gives rough idea of
bilirubin content & is often a useful clue about the nature of anemia:
White plasma ----- iron deficiency anemia Lemon yellow plasma ----- Hemolytic or
Megaloblastic anemia 10
Blood Volume & the Hematocrit
Rarely necessary to have an accurate blood volume
Hematocrit (HCT) is the volume percentage of erythrocytes in whole blood
HCT is obtained by centrifugation
The specific gravity of WBC's intermediate between plasma & RBC, thus forming "Buffy Coat"
11
Errors in the Estimation of HCT
Usually up to 5% of the apparent RBC mass is plasma
HCT differs according to blood source:
- Some particles when centrifuged tend to accumulate in the center of the tube
- HCT value is affected by movements of fluid (hydrostatic pressure)
12
Clinical value of HCT
HCT is important in the diagnosis of anemia
Rough estimation of blood loss after hemorrhage
13
Continuation…
Whole Blood
Whole blood – formed elements = plasma
Plasma – Clotting factors = Serum
14
Physical Characteristics
Arterial blood is crimson
Venous blood is darker red
Specific gravity = 1.035-1.090 & the viscosity is 5-6 times that of water
Specific gravity of plasma = 1.015-1.035
Ph = 7.3-7.5 15
Erythrocyte Sedimentation Rate
Rate of settling of RBCs after blood is drawnIn healthy men : 1-3mm/hr; 4-7 mm/hr in
young womenLow ESR in patients with anemiaFollows Stoke's Law (settling velocity) with an
equationWhere:Vs is the particles' settling velocity (m/s) (vertically downwards if ρp > ρf, upwards if ρp < ρf), r is the Stokes radius of the particle (m), g is the standard gravity (m/s2), ρp is the density of the particles (kg/m3), ρf is the density of the fluid (kg/m3), and η is the fluid viscosity (Pa s). 16
Continuation…
ESR greatly increased during menstruation & normal pregnancy
Increased rate also found in septicemia & pulmonary tuberculosis (increased globulin & fibrinogen content of plasma; also in elevated cholesterol & phospholipid levels
Inflammation of various types that cause cell necrosis will cause rate of RBC to fall, but the viscosity remains unchanged. 17
Continuation…
In alcoholic cirrhosis there is a rise in plasma bile acids & membrane cholesterol levels may rise by 55%. This has 2 effects:
Cholesterol to phospholipid ratio is increased, reducing membrane flexibility Increased cholesterol content also raises total lipid present, expanding its
surface area Increase by 8% in the total lipid is enough to cause formation of spherocytes
(removed from the circulation as a result of alteration in size, shape and flexibility)
Elevated levels of plasma bile acids (mainly cholic & deoxycholic acids) are observed in obstructive jaundice with similar consequences for the RBC membrane
18
Plasma
Straw colored fluid with specific gravity from 1.015-1.035
Specific gravity of plasma is related to its protein content
Contains 90-92% water
19
Continuation…
Blood owes much of its physiological importance to high water content:
Maintaining blood pressure Important for heart regulation& in osmotic exchange between
body fluid & compartments
20
Plasma Composition
The solutes of the blood plasma constitute ≈ 10% of the volume
Protein ≈ 7%Inorganic salts ≈ 0.9%Other organic compounds
≈ the rest other than proteins.
21
Separation of plasma proteins
Based on the different mobility in an electric field
Electrophoresis – widely used
Isoelectric focusing
Immunoelectrophoresis –
separates proteins on the basis of electrophoretic as well as immunologic properties
22
Albumin
Alpha 1
Alpha 2 Beta
Gamma
Albumin & Globulins
Comprise most of the proteins in the blood plasma
Colloidal osmotic pressure (from the proteins of the plasma) is the force that opposes the hydrostatic pressure in the capillaries
Better terminology should be "potential osmotic pressure" or "osmotic tendency"
Albumin & Globulins
23
Proteins move in electric field by the charge they carry…
Major fractions include:
Albumin (54-58%)α1 globulins (6-7%)
α2 globulins (8-9%)
β1- globulins (13-14%)Gamma globulins (11-12%)
24
Enzymes of Plasma
Most plasma enzymes do not have metabolic roles in plasma with the exception of those involved in coagulation
Activity of certain plasma enzymes is useful as index of certain abnormal conditions:
- Serum amylase – elevated in acute pancreatitis
- Acid phosphatase – in cases of prostatic cancer
- Alkaline phosphatase – in hepatic obstruction and bone diseases
25
Assay of tissue enzymes in plasma
When organs are damaged part of their enzyme complement in released into the plasma.
In a healthy persons, levels of intracellular enzymes are very low & a result of cellular turnover
Tissues contain 103-104 times higher content of soluble enzymes within their cells
Intracellular enzymes released into the plasma are inactivated & removed within days
Amount of enzyme released depends on the concentration of that enzyme & extent of tissue damage
Knowledge of cellular location of enzyme provides good clinical information
In practice, enzyme assays are most useful in detecting damage to the liver, muscles and blood cells 26
Enzyme Organ Distribution Comments
GOT Widespread but little in red cells Analysis of these enzyme started clinical enzymology
CPK Widespread but skeletal muscle is richest source
Monitoring skeletal & heart muscle disorder
Γ-GT Mainly liver Marker for hepatocellular diseases
LDH Widespread but has distinctive isoenzyme distribution
Monitor heart & liver disease
Acid phosphatase Specific activity in prostate gland Monitor prostatic cancer
Alkaline phosphatase
Widespread in tissues Diagnosis of bone disease
Some enzymes commonly assayed as part of clinical diagnosis
27
Continuation…
CPK (Creatinine phosphokinase) & LDH1 (Isoenzyme of LDH) indicate amounts of myocardial infarct. If no further damage occurs, levels return to normal.
Congested liver can be due to inefficient pumping of the right side of the heart.
Most patients with metastatic prostatic carcinoma have elevated plasma phosphatase levels. RIA is used for the detection of this enzyme.
Enzyme assays may also reveal other organ involvement…
28
Erythrocytes
Circulating erythrocytes are derived from erythropoietic cells (or erythron), the precursors of erythrocytes. RBCs arise from mesenchymal cells present in bone marrow
Major functions
Transport of oxygen from the lungs to the tissues Controls blood pH (CO2) is converted to
bicarbonate by carbonic anhydrase = major buffering
system) RBCs lack nucleus & other organelles;
utilizes anaerobic metabolism
29
30
Structure & Composition
RBC s have a biconcave disc shape (6-9 µm in diameter; 1 µm thick; 2-2.25 µm at the periphery)
Most of the solid matter is hemoglobin ( the conjugated protein responsible for the red color of the blood)
Behaves like an osmometer
31
The Erythrocyte Membrane
Composed largely of protein (49%) & lipid (43%) with a small amount of carbohydrate (8%)
Has a cytoskeleton which controls the shape of the membrane & limits the lateral mobility of some intrinsic proteins
Some of the protein is glycoprotein covalently linked to CHO (Sialic acid)
32
Membrane Changes in Diseases
Mature RBCs synthesize very little lipids but:
SphingomyelinPhosphatidylcholine in the outer half of the bilayer those in plasma lipoproteins
Cholesterol exhanges freely with serum cholesterol
The important factor that affects this exchange is the activity of the plasma enzyme Lecithin-Choelsterol Acyl Transferase (LCAT) – responsible for the formation of majority of esterified cholesterol and is inhibited by bile acids 33
Erythropoiesis
During gestation, erythrocytes are formed in various tissues occurring successively in:
Yolk sac – main site for the 1st weeks of gestation
Liver & Spleen - from 6 weeks to 6-7 months & can continue to produce until about 2 weeks after birth
Lymph Nodes
34
Continuation…
From 6-7 months of fetal life onwards… the bone marrow is the only source of new blood cells
35
Continuation…
Erythroid cells in the bone marrow are called normoblast (a large cell with dark blue cytoplasm, a central nucleus with nucleoli & slightly clumped chromatin
Reticulocytes A reticulocyte stage results when the nucleus is
finally extruded from the late normoblast. In this stage it still contains some ribosomal RNA and can still synthesize Hb
Reticulocytes spends 1-2 days each in the circulation & bone marrow before it matures mainly in the spleen when RNA is completely lost
A single pronormoblast usually gives rise to 16 mature red cells
36
Substances needed for erythropoiesis
The bone marrow requires many precursors to synthesize new cells: Metals: Iron, manganese, cobalt
Vitamins: B12, folate, ascorbic acid
Amino acids
Hormones
37
Hemolysis
Maybe produced by substances that dissolve or change the state of membrane lipids (ether, chloroform, bile salts & soaps) .
Certain biological toxins (venomous snakes & hemolytic bacteria)
Physical forces (UV rays, freezing, thawing)
Aging – this is why whole citrated blood cannot be used after 5-7 days
38
Red Cell Metabolism
The components required for these include:
1. ATP – maintenance of membrane function
2. 2,3 –diphosphoglycerate (2,3 – DPG) to modulate O2 affinity
3. NADPH – to prevent hemoglobin denaturation
4. NADH – to maintain the heme in the Fe(II) state
39
Continuation…
The predominant metabolic fuel is glucose where they serve as gluconeogenic precursors
The 2 ATP molecules are utilized in the ion pump in the cell membrane
Failure to produce enough ATP results in an ability to maintain ionic balance leading to accumulation of Ca2+ and shape change
40
41
Continuation…
2,3 DPG is a metabolite unique to the RBC. At a concentration of 4-5mM, it is almost equimolar to Hb
20-25% of 1, 3 DPG pass to 2, 3 DPG by mutase, therefore ATP yield decreases from glucose
2,3 DPG depends on the relative rates of the mutase& phosphatase reactions
42
Glutathione
Can be used for the removal of H202. This reaction protects the membrane from
oxidative damage. A deficiency of any enzyme of the glycolytic,
phosphogluconate or GSH-GSSG pathway may seriously compromise the energy dependent maintenance of membrane integrity.
43
Hereditary Hemolytic Anemias
Have been associated with deficiencies of the following enzymes:
Enolase enzyme – deficiency leads to decreased ATP required to maintain the biconcave shape of RBC
Glucose-6-P-Dehydrogenase – deficiency may result in increased hemolysis & severe hemolytic anemia
Pyruvate Kinase - deficiency may lead to bizarre model which is extremely fragile and readily hemolyzed
Other enzymes such as hexokinase,glucose –phosphoisomerase, phosphofructokinase, triose phosphate isomerase, 2-3 diphosphoglycerate dismutase
44
Erythrocyte Destruction Senescent erythrocytes are
engulfed primarily in the reticuloendothelial cells of the spleen
Free hemoglobin is released and binds to plasma proteins (e.g. haptoglobin)
Complex is transported to liver where Hb portion is split
Heme portion is transported to plasma & converted to bilirubin; excreted in the bile
Iron is released & stored in the
liver for reuse45
Hemoglobin
1 liter of blood usually contains 150g of hemoglobin; each gram can combine with 1.34ml of oxygen
46
Continuation…
1 liter of blood can carry 200ml of oxygen, 87 times higher than plasma alone.
Each RBC contains ≈ 640 million Hb molecules
47
Hemoglobin Structure
The 4 chains are held together by non-covalent bonds
There are 4 binding sites for oxygen
The Hb molecule is nearly spherical; packed together in a tetrahedrical way
48
Continuation…
The amino acid sequence of hemoglobin is known for 20 species. However there are 9 positions in the sequence that contain the same amino acid in nearly or all species studied. These conserved positions are especially important for the function of hemoglobin:
1. Some of them are involved in oxygen binding sites
2. Stabilizing the molecule via forming H-bond between the helix
3. Some (e.g. GLY) for easy contact between the chains
4. Some (e.g. PRO) to terminate the elix
5. The non-polar residues (Alanine, Isoleucine) are important because reversible oxygenation of heme group depends on its location where it is protected from water.
49
Continuation…
Normal hemoglobin is of several types containing 4 sub-units made up of various combinations of 4-5 different related peptide chains
Hemoglobin Structure Stage of Life % in Adult % in Newborn
Gower I ζ2ε2 0-5 weeks embryo None Up to 40
Gower II α2ε2 4-13 weeks embryo
None Up to 35
Portland ζ2γ2 4-13 weeks embryo
None Up to 35
Fetal (F) α2γ2 Newborn & adult < 1.0 80
A1 α2β2 Newborn & adult 97 20
A2 α2δ2 Newborn & adult 2.5 < 0.5 50
Biosynthesis of Hemoglobin
It has been estimated that there are 30 trillion erythrocytes in the circulating blood & ≈ 3 million/sec are destroyed
Globin moiety is formed from amino acids from the body pool in amounts of about 8g/day in the normal adult
14% of the amino acids from an average daily protein intake are used for globin formation
51
52
Availability of Fe++
Total body content of iron is about 2-6g & is not excreted in this form
Found in porphyrin ring of the heme complexThe first type of compounds (Hb, myoglobin,
cytochromes,catalase) are associated with the physiology
The second type is concerned with absorption, transport & storage of iron
53
Iron Absorption No iron absorption takes place in
the stomach Stomach acid is essential for iron
reduction Duodenum contains "apoferritin"
(converts Fe ++ to Fe+++) Ferritin may then act as an iron
store or transported to the serosal side where it is released in the ferrous form
In the blood, iron is bound by specific α-1 Globulin (transferrin)
54Iron is stored in the liver & bone marrow in 2 forms: Ferritin & Hemosiderin (agglomeration of ferritin molecules)
Transport of Oxygen
If arterial blood is analyzed for its oxygen content, it is found to contain 18-20% volume
Hb is an allosteric protein: the binding of additional O2 Hb enters the binding of additional O2 to the same Hb molecule
55
Continuation…
The sigmoidal property of the curve is believed to be due to heme-heme interactions
Heme-heme interaction means binding at one heme facilitates the binding of oxygen at the other hemes on the same tetramer & vice versa
56
Cooperative Property
When environmental oxygen levels are high, partially saturated hemoglobin molecules exhibit enhanced affinity for binding additional oxygen molecules, a specialized behavior referred to as cooperativity.
Hb has the capacity to bind between 1 and 4 O2 molecules, ranging from fully "desaturated" Hb (deoxyHb) to fully "saturated" Hb (oxyHb).
As part of this process, Hb also serves to replenish the "oxygen stores" maintained by myoglobin (Mb), the O2-binding protein in muscle which releases its oxygen in response to high levels of muscle activity.
57
2, 3 Bispospoglycerate (2,3 –DPG)
Is very important for long-term regulation of Hb affinity to O2
2,3 BPG shunt is a pathway derived from glycolysis. Competition with oxygen for binding site on ß-subunits Hypoxia stimulates 2,3 BPG synthesis, i.e. improve O2
release 2,3 DPG binds electrostatically to β- subunits through Lys
82, His 143 & N-term. The juxtaposition of these groups is favorable for 2,3-DPG binding only in the T-state.
DPG stabilizes the deoxyHb by cross-linking the β chains. In other words, DPG shifts the equilibrium to tense form.
58
Clinical Significance of DPG
It has been approved that DPG levels decrease from 4.5mM to 5.0mM Ill patients may take longer time to regain DPG when blood is
transfused Inosine can be converted to DPG inside RBC. Inosine can now be used
to preserve integrity of stored blood In hypoxia (e.g. emphysema), airflow in the bronchioles is blocked so
the pressure increases as DPG increases. DPG levels lead to 27% increase in the amount of oxygen due to pressure changes. (Also in high altitude adaptations)
Fetal Hb has high affinity to transfer oxygen from maternal to fetal circulation. HbF binds DPG less strongly than does HbA & consequently has higher oxygen affinity.
59
Life span of RBCs RBCs have a limited life span of 120
days The "Red Cell Theory of
Aging" is based on observed Ca2+ that occurs in old erythrocytes
Ca2+ rises to 0.5mM, enough to activate transglutaminase present in cell membrane
Transglutaminase form cross-links by creating iso-peptide bonds
Red cells with cross-linked membrane proteins are less flexible & are removed in the circulation by the spleen
60
RBC Destruction Hemoglobin from senescent
erythrocytes (phagocytosed in the reticuloendothelial cells of the spleen) are transported to the liver bound to the plasma protein haptoglobin
The globin portion is reused as amino acids & the heme moiety is converted to several steps to the bile pigments
Bilirubin, Urobilin & Stercobilin are colored (BILE PIGMENTS)
61
Continuation…
The pigments (biliverdin & bilirubin) are extracted in bile
The iron of heme is removed & the process, bound to plasma transferrin & either recycled as new hemoglobin or stored in the liver as ferritin
In the liver, bilirubin, either from Hb or from other hemoporteins is transported bound or loosely associated with plasma albumin
In the small intestine… Conjugates with glucoronic acid to form
bilirubin diglucoronide which is water soluble & is readily excreted by means of the bile into the intestine
Hydrolysis in the intestine by a β-glucoronidase into bilirubin & glucoronic acid
Reduction of bilirubin by bacterial floral action to colorless D or L- Urobilinogen
62
Urobilinogen
First part is reabsorbed & excreted in the urine as oxidized orange-yellow pigment L-Urobilin
Second part is reduced in the intestine to L-Stercobilinogen & excreted as an oxidized pigment L-Stercobilin in the feces (Faecal urobilinogen)
Urinary urobilin is increased if… Hemolysis is excessive when large amounts of bilirubin enter the
bowel & are converted to stercobilinogen There is liver damage (impairs re-excretion of normal amounts of
urobilinogen into the bile)
63
Erythrocyte Abnormalities
A large number of human diseases are associated with abnormal function of the erythrocytes including
Altered rates of erythrocyte production & destruction
Defects in iron or heme metabolismCombination of these conditions
These diseases are called ANEMIAs…64
Nutritional Deficiency Anemia
Hematopoietic precursor cells are particularly sensitive to any insult that impairs DNA synthesis. This leads to appearance of characteristic megaloblasts - corresponds to normoblasts (characterized by increased ratio of RNA to DNA). The cause can be deficiencies in metal traces, folic acid & vitamin B12
Larger amount of hemoglobin than other proteins, & constant daily losses of Hb must be replaced by resynthesis
65
Continuation…
Iron-deficiency – lack of dietary iron or excess blood loss (e.g menstruation)
Folic acid deficiency – its deficiency leads to megaloblastic anemia as it is a co-factor for a variety of reactions to 1-carbon metabolism (synthesis of purines & thymines)
Vitamin B12 deficiency – deficiency leads to pernicious anemia. Based on malabsorption of Vitamin B12 due to failure of the gastric mucosa to secrete adequate intrinsic factors
66
Hemolytic anemias
Anemias associated with increased destruction of erythrocytes, characterized by shortened life span of cells
Isoimmune hemolytic disease – in newborns; caused by transplacental transfer of maternal blood-group Abs capable of reacting with fetal erythrocytes
Hereditary spherocytosis - associated with the presence of spherical erythrocytes that are more fragile to hypotonic solutions; nature of defect unknown
67
Continuation…
Paroxysmal nocturnal hemoglobinuria – erythrocytes are abnormally sensitive to lysis by complement
Sickle Cell anemia – abnormal Hb, HbS aggregates on deoxygenation & the aggregates deform the shape of the cell, rendering susceptible to lysis
Thalassemias – caused by defective synthesis of α & β globin chains
68
Sickle Cell Anemia
1. Characterized by the sickle-cell or crescent shape of the erythrocytes when the oxy HBs is converted to deoxy HbS at low PO2.
2. At intracellular concentrations, molecules of deoxy HbS aggregate to form filaments on tubules of indeterminately high molecular weight
3. The sickle-cell causes severe anemia since they have increased mechanical fragility
4. Sickle cells also impede blood flow through capillaries
5. It is genetically transmitted
6. Vigorous physical activity at high altitude, air travel in unpressurized plane, & anesthesia can be potentially hazardous to a person with this disease
69
Characterization of HbS
HbS has between 2 & 4 more net + charges per molecule than net HbA
Non-polar residue on the outside of HbS (due to Val) causing low solubility
Sticky patch on the outside of its β chains & are present on both deoxy HbS & oxy HbS but not on HbA
70
A S
pI of Oxy Hb 6.87 7.09 = 0.22
pI of deoxy Hb 6.88 6.91 = 0.23
Thalassemias
Normally the rates of synthesis of the α & β chains of Hb must be virtually identical.
α-Thalassemia
In α-Thalassemia, there is deficiency in α chains & hence β chains precipitate; β- thalassemia is the reverse
Results from deletion of the α-globulin gene (Homozygotes with α-Thalassemia exhibit a syndrome known as hydrops fetalis)
71
Continuation…
β- thalassemia β- thalassemia are heterogenous β- globin gene is deleted β- globin gene remains intact & β- globin
mRNA is synthesized but not translated In many β- thalassemia, the β- globin gene is
present but very little β- globin mRNA is produced
72
Blood Groups Isoagglutinins (blood group substances) are found on the erythrocyte
surfaces & are responsible for the major immunological reactions of erythrocytes (Blood Types)
Surface of RBCs carry antigens (agglutinogens), the plasma carry agglutinins
73
Continuation…
ABO system is more complicated than the outline given. The ABO groups actually have 6 groups:
A1 A2 B AB A2B O
The following rules must be observed in blood transfusion:
• If the recipient's ABO group is known, give blood of the same group if possible
• Give Blood group O if the ABO group is unknown
• If the recipient's blood group is AB, neither antibodies are found are found in plasma so any red cells can be given
74
Rhesus Groups The term Rhesus (Rh) blood group system refers to the 5 main Rhesus
antigens (C, c, D, E and e) as well as the many other less frequent Rhesus antigens. The terms Rhesus factor and Rh factor are equivalent and refer to the Rh D antigen only. Rh + gene is the dominant gene; Rh – is the recessive gene
Genotype Symbol Rh(D) status
cde/cde rr -
CDe/cde R1r +
CDe/CDe R1R1 +
cDE/cde R2r +
CDe/cDE R1R2 +
cDE/cDE R2R2 +75
Blood Coagulation Injury to a blood vessel initiates a
series of reaction involving 3 separate processes:
1. The damage end contracts
2. Platelets begin to adhere to the injured endothelium & form a plug
3. Blood clot formation
76
Clotting
When the vessel is punctured or cut, the endothelium brings blood into contact with sub-endothelial collagen
Platelets at the site of injury are influenced to stick
As the platelets aggregate they release vasoactive amines (serotonin & epinephrine) & prostaglandin metabolites (thromboxane A2) which stimulate vasoconstriction
The plug is called thrombus & it is a major chemical defense against blood loss
The actual blood clotting processes that lead to a proper clot are set into motion by 2 mechanisms: intrinsic & extrinsic pathways: 77
Must be initiated rapidly when the vascular system is damaged but must occur when the circulatory system is intact
The Coagulation Cascade
78
The Intrinsic (Intravascular system)
So termed because all factors involved are present in the vascular system The 3 factors involved lead to the activation of factor X & in turn to the
conversion of prothrombin to thrombin
A. The Hageman factor binds to collagen or to vasoactive peptide such as Kallikrein, resulting to a proteolytically active form XIIa
B. XIIa activates XI by hydrolyzing an internal peptide bond
C. In the presence of Ca2+, IX is activated to IXa. This activation is vitamin K dependent.
D. In the final step factor X is converted to Xa by IXa in the presence of VIII (hemophilia A factor), platelet phospholipids and Ca2+ ions
79
The Extrinsic (Extravascular system)
The factors involved are supplements of the intrinsic to ensure more rapid coagulation
Factor VII is converted to active form VIIa by factor III in the presence of Ca 2+
80
Conversion of factor II (Prothrombin) to factor IIa (Thrombin)
The rest of the reactions are common in both patrhways
Factor Va, platelets, phospholipids & Ca 2+ to promote the reaction
81
Conversion of Factor I (Fibrinogen) to factor Ia (Fibrin) By thrombin, ARG-GLY in α-A & β-B chains of fibrinogen is
released in a form of fibrinopeptide A & B from NH2 terminal ends of the chains.
The gamma chain is not affected Factor VIIIa (the fibrin-stabilizing factors FSF is present in
human platelets & in plasma Factor VIIIa (fibrinoligase) is a trans glutaminase that catalyzes
the formation of cross-linked peptide bonds
82
Continuation…
Once the clotting cascade is initiated, mechanisms must operate to prevent clotting from spreading throughout the intravascular system.
Plasmin & fibrinolysin prevent such spread & dissolve any clots that do form.
Plasmin is derived from inactive plasminogen in a reaction that requires blood & tissue factors including factor XIIa & Kallikrein
83
ANTICOAGULANTS
In vitro… A number of substances prevent coagulation [oxalate,
fluoride, citrate, EDTA – they precipitate Ca 2+ and bind to it]
Bile salts are inhibitors of thromboplastin Dicumarol – is an antagonist of vitamin K by impairing
its biosynthesis Heparin – is a complex polysaccharide β- diglucoronic
acid & α-D-glucosamine
84