In people acclimated to high altitudes, the concentration of 2,3-diphosphoglycerate (2,3-DPG) in the blood is increased, which allows these individuals to deliver a larger amount of oxygen to tissues under conditions of lower oxygen tension.

Initially given high dose O2 through mask

Electron transport

Because there are many more oxygen molecules present in a given volume when under pressure, hyperbaric oxygen dissolves in the blood in far greater amounts enabling it to be transported to the cells. Hyperbaric oxygen (HBO) also helps rid haemoglobin of the tenacious CO molecules, freeing it up for normal use once more. The actual amount of oxygen molecules at a pressure of 3ata (20msw) in a fixed volume is equal to 3 times the amount at the surface.

In cases of carbon monoxide poisoning, it normally takes over four hours for the amount of CO in the body to fall by one half, during which time the tissues are hypoxic due to replacement of O2Hb with COHb. Hyperbaric oxygen at 3ata reduces this to 20 minutes, during which time the extra oxygen dissolved in the blood alleviates hypoxia.

Prostaglandins

act in a manner similar to that of hormones, by stimulating target cells into action.

differ from hormones in that they act locally, near their site of synthesis, and they are metabolized very rapidly

the same prostaglandins act differently in different tissues

Hemostasis & Thrombosis: Hemophilia

Beth A. BouchardBIOC 212: Biochemistry of Human Disease

Spring 2005

HEMOSTASIS

1). INITIATIONVessel wall – endothelial cells and subendothelial

components

2). LOCALIZATIONPlatelets – circulating cellular elements

3). PROPAGATION/AMPLIFICATIONPlasma coagulation proteins (factors)

4). TERMINATIONPlasma coagulation protein inhibitors

5). ELIMINATIONFibrinolytic system

BLOOD COAGULATION

BLOOD COAGULATION (CONT.)

• Deficiencies in all of the factors, except factor XII, lead to a bleeding tendency in the affected individual

• Described as a ‘waterfall’ or ‘cascade’ sequence of zymogen (pro-enzyme) to enzyme conversions, with each enzyme activating the next zymogen in the seqeunce

• Activated factor enzymes are designated with an “a”, e.g. factor Xa

Common constituents of coagulation complexes

Vitamin K-dependent (VKD) zymogen

Ca2+

Appropriate membrane surface

- activated platelets (VIIIa/IXa complex, Va/Xa complex)

- subendothelial cells, typically fibroblasts (TF/VIIa complex)

Protein cofactor

Common constituents of coagulation complexes

Vitamin K-dependent (VKD) zymogen

Ca2+

Appropriate membrane surface

- activated platelets (VIIIa/IXa complex, Va/Xa complex)

- subendothelial cells, typically fibroblasts (TF/VIIa complex)

Protein cofactor

Functional Domains of the Vitamin K-dependent Zymogens

Gamma ()-carboxyglutamic acid

VITAMIN K

• Group of related, fat soluble compounds, which differ in the number of side-chain isoprenoid units

• Plant derived (vitamin K1) and synthesized by intestinal bacteria (vitamin K2)

• The reduced form of vitamin K2 (vitamin KH2) is required for the post-translational, gamma-carboxylation of several proteins involved in blood clotting

Formation of Gla residues subsequent to protein synthesis (post-translational)

Vitamin K deficiency

• Deficiency of vitamin K is rare because of its wide distribution in nature, and its production by intestinal bacteria

• Found in individuals with liver disease and fat malabsorption - it is associated with bleeding disorders

• Newborn infants (especially preemies) are also at risk- Placenta is insufficient in the transfer of maternal vitamin K- Concentration of circulating vitamin K drops immediately after birth, and it recovers upon absorption of food- Gut of the newborn is sterile

Thus, newborns are given an injection of vitamin K following birth.

Common constituents of coagulation complexes

Vitamin K-dependent (VKD) zymogen

Protein cofactor

Ca2+

Appropriate membrane surface

- activated platelets (VIIIa/IXa complex, Va/Xa complex)

- subendothelial cells, typically fibroblasts (TF/VIIa complex)

Ca2+

FXaCa2+ 30

Ca2+

FXa

FVa HC

FVa LC

Ca2+

300,000

-Thrombin

ProthrombinaseComponents

Relative Rateof Prothrombin

Activation

FXa 1Prothrombin

Ca2+

FXa

Prothrombinase

FVa HC

FVa LC

Ca2+

FXa 300FVa HC

FVa LC

Ca2+

Relevance of complex formation and its constituents

Common constituents of coagulation complexes

Vitamin K-dependent (VKD) zymogen

Protein cofactor

Ca2+

Appropriate membrane surface

- activated platelets (VIIIa/IXa complex, Va/Xa complex)

- subendothelial cells, typically fibroblasts (TF/VIIa complex)

** Express anionic phospholipids and membrane receptors for coagulation proteins.

In platelets, the expression of this membrane surface is activation-dependent.

Ca2+FVIIaTF

Extrinsic TenaseCa2+

Prothrombinase

Ca2+

FXa

FVa HC

FVa LC

Ca2+

Ca2+FIXaFVIIIaCa2+

Intrinsic Tenase

FXa

FIXa

IIa

ThrombinCleaves Fibrinogen

Activates Platelets

Activates procofactors (FV and FVIII)

Activates zymogens (FVII, FXI and FXIII)

Intrinsic Pathway of Blood Coagulation

• No factors extrinsic to the blood are involved

• Clinical test to assess the functionality of this pathway is the activated partial thromboplastin time (aPTT)– Kaolin and cephalin are added to the test plasma sample– The normal range is ~30 – 50 seconds (varies slightly

depending on the laboratory)– Prolongations in the aPTT are observed in deficiencies of

factors XI, IX, VIII, X, and V, prothrombin, or fibrinogen.– Used to test for common congenital hemophilias

(deficiencies in IX, VIII, or XI) and to monitor heparin treatment

Extrinsic Pathway of Blood Coagulation

• Extrinsic refers to tissue factor, which is expressed on subendothelial cells

• Clinical test to assess the functionality of this pathway is the prothrombin time (PT)– Lipidated tissue factor is added to test plasma sample– The normal range is ~10-15 seconds (varies slightly

depending on the laboratory)– Prolongations in the PT are observed in deficiencies of

factors VII, X, V, prothrombin, or fibrinogen.– Used to test for the rare congenital deficiencies in these

factors: More often it is used to diagnose acquired bleeding disorders resulting from vitamin K deficiency, oral anticoagulants (e.g. warfarin), and liver disease

Thrombin Time (TT)

In this test, thrombin is added to plasma

– The normal range is ~10-15 seconds (varies slightly depending on the laboratory)

– Prolongations in the TT are observed in congenital fibrinogen deficiency or acquired fibrinogen deficiency resulting from consumption of fibrinogen in DIC (disseminated intravascular coagulation), or may occur following treatment with fibrinolytic drugs

Hemophilias A and B

• Hemophilias A and B are cause by deficiencies in factors VIII or IX, respectively

• Affect ~1 in 10,000 males

• Inherited as a recessive X-linked trait (Mom would be an unaffected carrier)

• Treated by administration of factor VIII or factor IX concentrates

• Recombinant factor VIII or XI• Gene therapy trials

HEMOSTASIS (CONT.)

1). INITIATIONVessel wall – endothelial cells and subendothelial

components

2). LOCALIZATIONPlatelets – circulating cellular elements

3). PROPAGATION/AMPLIFICATIONPlasma coagulation proteins (factors)

4). TERMINATIONPlasma coagulation protein inhibitors

5). ELIMINATIONFibrinolytic system

INHIBITORS

INHIBITORS (cont.)

FIBRINOLYSIS

FIBRINOLYSIS (CONT.)

Hemorrhage

Bleeding disorders can span the spectrum from weeping blood vessels to full-fledged internal and external hemorrhage

Genetic defects:platelet abnormalitiesblood vessel wall abnormalitiesclotting factor deficiencies (hemophilias)excess clot breakdown (fibrinolysis)

Acquired defects:liver disease (site of clotting factor synthesis)vitamin K deficiencyautoimmune disease (platelet destruction)trauma

Hemorrhage

Bleeding disorders can span the spectrum from weeping blood vessels to full-fledged internal and external hemorrhage

Treated by factor replacement

Thrombosis

Thrombosis can be manifested as a transient, short-term or episodic event in individuals with chronic or recurring clotting. It is the major cause of both stroke and heart attacks.

Genetic defects:clotting factor INHIBITOR deficienciesdecreased fibrinolysis

Acquired defects:atherosclerosis

Antithrombotic Attributes of Vascular Endothelium

Pharmacologic Approaches to Prevent Thrombosis

Antiplatelet agents - block activation, aggregation or intraplatelet agonist synthesis

Effective anticoagulant therapy includes both antiplatelet and antithrombin agents

Blood “thinners” - coumadin (warfarin): inhibition of “gla” formation in the liver

Coumadin blocks reformation of reduced vitamin K, which essentially stops the post-translational modification of the glutamic acid residues at the amino-termini of the VKDP’s, since vitamin K is oxidized during the reaction.

Blood “thinners” - heparin: potent cofactor for ATIII-catalyzedinhibition of procoagulant serine proteases

Snakes

Leeches

Blood-sucking Insects