Plasma Composition and Function

Plasma

• Plasma is the liquid component of blood that can be isolated by centrifuging whole blood at high speeds
• The formula Plasma + (RBC+WBC+Plt) = Blood represents the composition of blood
• Denser cells and platelets move to the bottom during centrifugation, separating into red and white layers
• Plasma remains on top, appearing as a yellow layer

Composition of Plasma

• Plasma is about 92% water, with the remaining 8% consisting of ions, proteins, nutrients, wastes, and dissolved gases
• Includes proteins, enzymes, nutrients, wastes, hormones, gases, electrolytes and water
• Plasma ions, proteins, and molecules help maintain blood pH and osmotic balance
• Hormones in plasma act as long-distance signals
• Antibodies recognize and neutralize pathogens

Plasma Proteins

• Proteins are the most abundant substance in plasma by weight
• Proteins play various roles, including clotting, defense, and transport
• Proteins supply amino acids for cell nutrition; macrophages break down plasma proteins to release amino acids, which other cells use to synthesize new products
• They also act as carriers for other molecules; transporting small molecules to tissues for utilization
• Proteins help maintain a stable blood pH by acting as weak bases to bind excess H+ ions
• Plasma proteins interact to cause blood to coagulate as part of the body's response to blood vessel injury
• This helps protect against blood loss and foreign microorganisms and viruses

Categories of Plasma Proteins

• There are three main categories of plasma proteins, each with specific functions
• Albumins are the smallest and most abundant plasma proteins
• Albumins aid in fluid gain in the interstitial space during fluid loss from the blood
• Albumin helps dissolve substances in the plasma and transports substances like drugs, hormones, and fatty acids
• Globulins are subdivided into alpha, beta, and gamma globulins based on molecular weight

Types Of Globulins

• High-density lipoproteins (HDL) function in lipid transport and energy metabolism
• HDLs prevent cholesterol from invading and settling in the walls of arteries
• Low-density lipoproteins (LDL) transport cholesterol and fats but also favor deposition in arterial walls
• Fibrinogen is a soluble precursor of fibrin and plays a role in blood coagulation

Plasma Protein Breakdown

• Plasma contains 8% plasma volume and contributes to osmotic pressure and water balance
• Albumin makes up 60% of plasma proteins that produced by the liver, contributing to osmotic pressure
• Globulins make up 36% of plasma proteins
• Alpha, beta globulins transport proteins that bind to lipids, metal ions, and fat-soluble vitamins; produced by the liver
• Gamma globulins are antibodies released during the immune response
• Fibrinogen makes up 4% of plasma proteins produced by the liver to form fibrin threads of blood clot

Other Plasma Components

• Amino acids formed during the breakdown of tissue or digested food proteins
• Nitrogenous wastes are toxic end products of bodily substances that are cleared by the kidneys
• Nutrients, including glucose, amino acids, fats, cholesterol, phospholipids, vitamins, and minerals absorbed by the digestive tract, are transported by plasma
• Oxygen and carbon dioxide gases are transported; with a substantial amount of dissolved nitrogen
• Electrolytes, mainly sodium ions, help maintain body osmolarity

Plasma Donations

• Plasma donations are needed when people lose blood due to traumatic events or surgery
• Plasma can be donated through donating whole blood or plasmapheresis
• Plasmapheresis involves drawing blood, separating plasma using a centrifuge, and returning other components
• Donated plasma is usually frozen until needed

Plasma Donation Requirements

• Donors must be between 18 to 69 years old
• Donors must weigh at least 110 pounds
• Donors cannot have donated plasma in the last 28 days

Plasma Hemostasis

• Damage in blood vessels responds to injury by constricting causing Vasoconstriction
• Vascular spasm is triggered by direct injury to vascular smooth muscle, chemicals released by endothelial cells and platelets, plus local pain receptors
• Spasm mechanism becomes more efficient with the damaged tissues and is most effective in smaller blood vessels
• Vascular spasm reduces blood loss for 20–30 minutes, allowing time for platelet plug formation and blood clotting

Platelet Plug Formation

• Platelets sticks together, forming a plug that temporarily seals the break in the vessel wall and lead to blood clot formation
• Endothelial cells release nitric oxide and a prostaglandin also known as prostacyclin (or PGI2).
• Nitric oxide and prostacyclin prevent platelet aggregation in undamaged tissue and restrict aggregation to the site of injury
• Plasma protein also known as von Willebrand factor stabilizes bound platelets by forming a bridge between collagen and platelets
• Platelets swell, form spiked processes, become stickier, and release chemical messengers
• Adenosine diphosphate (ADP) causes more platelets to stick to the area and release their contents
• Serotonin and thromboxane A2 enhance vascular spasm and platelet aggregation in a positive feedback cycle
• A platelet plug is built up in a minute, reducing blood loss and sealing small rips in blood vessels
• Platelet plugs are loosely knit, and need additional reinforcement for larger breaks

Coagulation

• Coagulation helps reinforce the platelet plug with fibrin threads that act as a glue for the aggregated platelets
• Blood is transformed from a liquid to a gel in a multistep process that involves clotting factors, or procoagulants
• Most clotting factors are plasma proteins synthesized by the liver
• Although vitamin K is not directly involved in coagulation, this fat-soluble vitaminis required for the synthesis of four of the clotting factors

Phases of Coagulation

• Three phases occur during coagulation
• Phase 1 involves two pathways to prothrombin activator
• Phase 2 is the common pathway to thrombin; prothrombin activator converts prothrombin into thrombin
• Phase 3 is the common pathway to the fibrin mesh; Thrombin catalyzes the joining of fibrinogen molecules in plasmas to create a fibrin mesh which traps blood cells
• Phase 1 initiates intrinsic and extrinsic pathways
• Both pathways are triggered by the same tissue-damaging events in the body
• Clotting only occurs in the intrinsic pathway in blood outside the body like in a test tube
• Intermediates of the pathways need to be used in the presence of PF3
• Factors activate only in the presence of PF3 and cascade to Factor X common intermediate
• Factor X complexes with calcium ions, PF3, and factor V to form prothrombin activator

Features of Intrinsic and Extrinsic Pathways

• Intrinsic pathway is triggered by negatively charged surfaces such as activated platelets, collagen, or glass, and is slower due to having the factors within the blood
• The extrinsic pathway is triggered by exposing blood to the TF or factor III from damaged endothelium
• Is faster because it Bypasses steps and accelerates clot formation in 15 seconds
• With calcium ions, thrombin activates factor XIII (fibrin stabilizing factor) which binds fibrin strands tightly together to strengthen clot
• Anticoagulants inhibit clotting and maintain a balance with clotting factors under normal conditions
• With a ruptured vessel, vessel ruptures it increases procoagulant activity and a clot forms within 3 to 6 minutes due to vessel damage
• Fibrinogen and Ca2+ are important exceptions to the activation generalization
• Activation that turns clotting factors into enzymes will form a clot