Blood Clotting Pathways

Blood Coagulation

• Two pathways (extrinsic and intrinsic) lead to the common pathway, where activated Factor X forms prothrombinase, which converts prothrombin to thrombin, ultimately converting fibrinogen to fibrin and completing the clotting process
• Calcium is a necessary cofactor in both extrinsic and intrinsic phases

Extrinsic Pathway

• Begins with the release of tissue factor (Factor III) from endothelial cells or peripheral tissues
• Tissue factor combines with calcium and other clotting factors to activate Factor X

Intrinsic Pathway

• Begins with proenzymes exposed to collagen fibers at the injury site
• Proceeds with the assistance of PF-3 (factor released by aggregating platelets)
• Sequence of enzyme activation leads to Factor X

Hormones

• Amino acid derivatives: thyroid hormones (e.g., thyroxine), catecholamines (e.g., epinephrine), tryptophan (e.g., melatonin)
• Peptide hormones
• Lipid hormones
• Eicosanoids (e.g., prostaglandin)
• Steroid hormones (e.g., estrogen)

Platelet Phases of Hemostasis

• Begins with platelet attachment to sticky endothelial surfaces, basal lamina, exposed collagen fibers, and each other
• Platelets release ADP, platelet factors, platelet-derived growth factor (PDGF), and calcium ions

Nervous and Endocrine Systems

• The nervous system stimulates the adrenal medulla to release epinephrine and norepinephrine
• Anterior pituitary gland is under nervous system control and releases stimulating hormones
• Posterior pituitary gland has axons from the nervous system
• Erythropoietin (EPO) stimulates the bone marrow to produce red blood cells

Properties of Blood

• Fluid connective tissue consisting of plasma and formed elements
• Normal temperature: 38°C or 100.4°F
• pH: 7.35-7.45 (slightly alkaline)
• Viscosity: 5 times thicker than water
• Plasma composition: 90% water; blood composition: 55% plasma

White Blood Cells

• Neutrophils: granular, multilobed nucleus, phagocytic cells that engulf pathogens and debris
• Monocytes: agranular, large cells with bean-shaped nucleus, enter tissues and become macrophages (phagocytes)
• Eosinophils: granular, granules generally stain red, engulf antibody-labeled materials
• Basophils: granular, granules generally stain blue, release histamine and other chemicals promoting inflammation
• Lymphocytes: agranular, slightly larger than RBC with large round nucleus, provide defense against specific pathogens or toxins

Catecholamines

• Hormones and neurotransmitters produced by adrenals, brain, and sympathetic nervous system
• Important in stress response

Serum of Blood

• Largest component: water
• Next largest component: plasma protein
• Most plasma protein is made by the liver; some are hormones, and some are gammaglobulins made by lymphocytes (antibodies)

White Blood Cell Percentage

• Neutrophils: 60%
• Lymphocytes: 30%
• Monocytes: 8%
• Eosinophils: 3%
• Basophils: 0%