Blood Clotting: monster cascade of reactions (Humans)

by David Turell , Wednesday, August 30, 2023, 20:08 (450 days ago) @ David Turell

Irreducibly complex and under tight controls:

https://evolutionnews.org/2023/08/the-incredible-design-of-vertebrate-blood-clotting/

"Thus, the formation of this platelet plug (and the injury itself) initiates the coagulation cascade.

***

"Vertebrate blood coagulation is best understood by focusing first on the ultimate objective of the cascade, which is the formation of a fibrin gel that reinforces the initial platelet plug, thereby strengthening the clot. The clot itself is made of fibers composed of the protein fibrin, which circulates in an inactive form (fibrinogen) in the blood plasma.

***

'The cleavage of fibrinopeptides exposes new binding sites on the fibrin molecule, allowing the individual fibrin molecules to polymerize into a clot.8 The fibrin molecules further aggregate and form a mesh-like network, which is stabilized by the enzyme factor XIIIa.9 Factor XIIIa catalyzes the crosslinking of fibrin molecules through the formation of covalent bonds between specific amino acid residues, creating a stable fibrin clot. The resulting fibrin clot, together with the platelets, provides a physical barrier at the site of injury, preventing further blood loss. It also serves as a scaffold for other components of the clotting process, which aggregate on the fibrin network to form a stable blood clot.

"If the pathway consisted only of fibrinogen and thrombin, thrombin would constantly cleave fibrinogen, and the consequence would be uncontrolled and excessive clotting throughout the bloodstream. To avoid this, it is essential that the process be carefully regulated. Blood clotting involves the use of proenzymes, which are enzymes that are retained in an inactive state and need to be converted into active enzymes through specific cleavage by proteases such as thrombin.

***

"Once activated, factor Va plays a critical role in the amplification of the coagulation process by enhancing the activity of factor X and promoting the production of more thrombin. This makes the coagulation cascade autocatalytic, since the activation of clotting factors leads to the activation of more of the same proteins.

***

"To prevent excess clotting and ensure that the clotting cascade remains localized to the site of injury, there are several regulatory mechanisms.16 Antithrombin III (ATIII) is a natural anticoagulant that inhibits the activity of thrombin and several other coagulation factors, including factor Xa and factor IXa. It achieves its anticoagulant effects through a mechanism called “serpin” inhibition.17 Serpins (serine protease inhibitors) are a class of proteins that regulate the activity of proteases, including those involved in blood clotting. ATIII binds to Thrombin’s active site, effectively blocking its ability to cleave fibrinogen into fibrin. By inhibiting thrombin, antithrombin III indirectly helps regulate the activation of factor V and thereby prevents excessive clotting.

***

"To prevent excess clotting and ensure that the clotting cascade remains localized to the site of injury, there are several regulatory mechanisms.16 Antithrombin III (ATIII) is a natural anticoagulant that inhibits the activity of thrombin and several other coagulation factors, including factor Xa and factor IXa. It achieves its anticoagulant effects through a mechanism called “serpin” inhibition.17 Serpins (serine protease inhibitors) are a class of proteins that regulate the activity of proteases, including those involved in blood clotting. ATIII binds to Thrombin’s active site, effectively blocking its ability to cleave fibrinogen into fibrin. By inhibiting thrombin, antithrombin III indirectly helps regulate the activation of factor V and thereby prevents excessive clotting.

***

"After the clot is formed, it undergoes retraction, which involves the contraction of fibrin by platelets within the clot, resulting in the clot becoming denser.21 This process helps to reduce the size of the clot and brings the edges of the wound closer together. Eventually, as the wound heals, the clot needs to be dissolved to restore normal blood flow. Plasmin, a proteolytic enzyme, breaks down the fibrin meshwork into soluble fragments, leading to the dissolution of the clot.22 Plasmin is generated from plasminogen by tissue plasminogen activator (t-PA) or urokinase-type plasminogen activator (u-Pa), among other molecules.

***

"Several of the proteins discussed here depend upon vitamin K for their synthesis — these are prothrombin, factors VII, IX, and X, as well as proteins C and S (i.e., the anticoagulant proteins that serve to inhibit excessive clot formation). Vitamin K is essential for the post-translational modification of these clotting factors. Without adequate vitamin K, these proteins cannot undergo the necessary chemical changes, which would impair their ability to function properly in the coagulation process."

comment: this enormous process contains more than 25-6 steps. (see diagram) I've boiled down an enormous article which discusses every intricacy in detail. Earlier forms before vertebrates on land had simpler systems from which this developed, but the jump to this sophistication was enormous, irreducibly complex and not explained by Darwinism. Designer always fits.