Ch. 17 - Blood & Blood Vessels (17.8 Only Pg 590-591)

Platelets are small, colorless cell fragments that play a crucial role in blood clotting. They adhere to collagen beneath the endothelium, which is the inner lining of blood vessels. This adhesion helps in forming a plug at the site of injury to prevent excessive bleeding. Therefore, the description "adhere to collagen beneath endothelium" best matches the term platelets.

Platelets play a crucial role in the clotting process, but they do not dissolve formed clots. Instead, platelets are responsible for forming temporary clumps in injured areas, contracting after clot formation to reinforce the clot, and releasing chemicals that stimulate clotting. Additionally, platelets initiate the clotting process by adhering to the damaged blood vessel walls and forming a platelet plug. However, once a clot is formed, other components of the blood, such as fibrinolytic enzymes, are responsible for dissolving the clot.

Coagulation is the correct answer because it involves a cascade of reactions that ultimately lead to the conversion of fibrinogen, a soluble protein, into fibrin, an insoluble protein. This process is essential for the formation of blood clots, which help to prevent excessive bleeding.

Rat poisons that block the liver's use of vitamin K prevent blood clotting, leading to excessive bleeding or hemorrhage. Without the ability to form clots, even small injuries can result in significant blood loss, eventually causing death. This is why consuming such poison would lead to hemorrhage rather than anemia, acidosis, thrombocytopenia, or starvation.

Fibrinolysis is the process of breaking down fibrin, a protein involved in blood clot formation. It occurs when an enzyme called plasmin breaks down the fibrin meshwork, leading to the dissolution of blood clots. Therefore, the correct answer is "dissolves clots."

Platelets are small, disc-shaped cells in the blood that help with clotting and preventing excessive bleeding. They are stored as a reserve in case of hemorrhage, which is a severe bleeding event. The spleen is an organ in the body that filters the blood and removes old or damaged blood cells, including platelets. Additionally, platelets can also be stored in other vascular organs, such as the liver or bone marrow. Therefore, the correct answer is that platelets are stored as a reserve in the spleen and other vascular organs.

The extrinsic pathway of coagulation is initiated by the release of tissue factor (Factor III) by damaged endothelium. Tissue factor is a protein that is normally found in the subendothelial cells beneath the endothelium. When there is damage to the endothelium, tissue factor is exposed to the blood. This exposure triggers a cascade of reactions that ultimately leads to the formation of a blood clot. Tissue factor binds to and activates Factor VII, which then activates Factor X, leading to the conversion of prothrombin to thrombin. Thrombin is a key enzyme in the coagulation process that converts fibrinogen to fibrin, forming a stable blood clot.

Tissue factor, also known as Factor III, is a factor in the extrinsic pathway. The extrinsic pathway is one of the two pathways involved in blood coagulation. It is initiated by the release of tissue factor from damaged blood vessels, which then activates a cascade of reactions leading to the formation of a blood clot. The intrinsic pathway, on the other hand, is initiated by factors present within the blood itself. Therefore, the correct answer is extrinsic.

Platelet factor (PF-3) is a factor in the intrinsic pathway. The intrinsic pathway is one of the two pathways involved in the coagulation cascade. It is initiated by factors within the blood, such as collagen and platelet factor (PF-3). This pathway leads to the formation of a clot by activating various clotting factors. Platelet factor (PF-3) plays a crucial role in this process by promoting platelet aggregation and the activation of clotting factors. Therefore, the correct answer is intrinsic.

The removal of calcium ions from a blood sample would affect coagulation by causing the coagulation pathway to lack a required cofactor at many steps. This cofactor is necessary for the proper functioning of the coagulation pathway, which is responsible for the formation of blood clots. Without the cofactor, coagulation would be prevented, leading to difficulties in blood clotting and potentially causing excessive bleeding. The statement also clarifies that magnesium cannot substitute for calcium in this process, indicating that the absence of calcium would have a significant and negative impact on coagulation.

Plasmin is the correct answer because it is an enzyme that specifically targets and breaks down fibrin, the protein that forms blood clots. Plasmin acts as a fibrinolytic enzyme, dissolving the clot and restoring blood flow. Thrombin, on the other hand, is involved in the formation of clots, not their dissolution. Heparin is an anticoagulant that prevents clot formation but does not directly dissolve clots. Fibrinase and phosphokinase are not enzymes involved in clot digestion.

Thrombin is the enzyme that catalyzes the conversion of fibrinogen to fibrin. Fibrinogen is a soluble protein found in blood plasma, and when it is converted to fibrin, it forms a mesh-like network that helps in blood clotting. Thrombin plays a crucial role in this process by cleaving specific bonds in fibrinogen and activating it to form fibrin. This conversion is essential for the formation of stable blood clots and the prevention of excessive bleeding.

A substance that activates plasminogen can enhance the process of clot dissolution, which means it can break down existing blood clots more quickly. This can be beneficial in situations where there is a need to prevent or treat conditions caused by blood clot formation, such as deep vein thrombosis or pulmonary embolism. By promoting faster clot dissolution, the substance can help restore normal blood flow and prevent further complications.

The common pathway of coagulation begins with the conversion of Factor X to prothrombinase. Prothrombinase is an enzyme that converts prothrombin to thrombin. Thrombin then converts fibrinogen to fibrin, which forms a mesh-like network to create a blood clot. This conversion of Factor X to prothrombinase is a crucial step in the coagulation cascade, as it initiates the formation of thrombin and ultimately leads to the formation of a stable blood clot.

The correct answer is the activation of proenzymes exposed to collagen. The intrinsic pathway of coagulation is initiated by the exposure of collagen in damaged tissue. This exposure causes the activation of proenzymes, which leads to a cascade of reactions ultimately resulting in the formation of a blood clot. Platelet sticking to damaged tissue, release of tissue factor, release of heparin, and conversion of prothrombin to thrombin are not directly related to the activation of the intrinsic pathway.