Blood Clotting Pathways

Study Notes

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%

Description

This quiz covers the extrinsic and intrinsic pathways of blood clotting, including the common pathway and the role of various clotting factors. Learn how tissue factor, calcium, and proenzymes work together to form a blood clot.