Main Difference – Platelets vs Plasma
Blood is a red color liquid that serves as the main circulating fluid of vertebrates. Blood is composed of blood cells and plasma. The three types of blood cells are red blood cell, white blood cells, and platelets. Plasma is a straw-colored liquid. On that account, both platelets and plasma are components of blood. The main difference between platelets and plasma is that platelets are a type of blood cells whereas plasma is the liquid that holds platelets. Platelets are small, colorless fragments, which are critical in blood clotting. Plasma suspends blood cells and other important substances.
Key Areas Covered
1. What are Platelets
– Definition, Structure, Function
2. What is Plasma
– Definition, Composition, Function
3. What are the Similarities Between Platelets and Plasma
– Outline of Common Features
4. What is the Difference Between Platelets and Plasma
– Comparison of Key Differences
Key Terms: Blood, Circulation, Clotting, Fresh-Frozen Plasma (FFP), Frozen Plasma (FP), Plasma, Plasma, , Platelets
What are Platelets
Platelets refer to small, colorless, disk-shaped cell fragments found in large numbers in blood, involving in blood clotting. Platelets are also called thrombocytes. They lack nuclei. The diameter of a platelet is equal to 20% of the diameter of a red blood cell. About 150,000 to 350,000 platelets can be identified per microliter of blood. The main function of platelets is to prevent bleeding.
Platelet Production
The bone marrow is the site of production of platelets. Megakaryocytes in bone marrow develop into giant cells followed by fragmentation. Over 1,000 platelets are produced per megakaryocyte. Thrombopoietin is the hormone that controls the development of megakaryocytes. The development of platelets is shown in figure 1.
Figure 1: Platelet Production
Structure of Platelets
Platelets are not true cells but, circulating cellular fragments. The proteins on the surface of platelets allow them to stick to the walls of the blood vessels as well as with each other. Their granules contain other proteins involved in the formation of a firm plug, sealing the blood vessel break. Inactive platelets are disk-shaped. Once stimulated, platelets become round with extended filaments. These platelets are active. Both inactive and active platelets are shown in figure 2.
Figure 2: Platelets
Function of Platelets
As platelets are the smallest and the lightest blood cells in the blood, they are pushed away from the central blood flow inside the blood vessels. Thus, they roll along the surface of the blood vessels along the endothelial cell layer. Typically, neither blood cells stick to the endothelial layer. However, when the endothelial layer is broken, the fibers that form blood vessels are exposed to the blood flow. Thus, platelets attract the fibers, becoming active. The clumping of platelets on the fibers forms the initial seal that prevents the leakage of red blood cells from the blood vessel. The blood clotting is shown in figure 3.
Figure 3: Blood Clotting
Disorders
Asprin can prevent blood clotting by platelets. Too many platelets increase the risk of blood clots. Low platelet counts in the blood are called thrombocytopenias.
What is Plasma
Plasma is a straw-colored, liquid component of blood where blood cells are suspended. It forms the liquid component of both lymph and milk. 55% of the total blood is composed of plasma. Since plasma is inside the blood vessels, it is called the intravascular fluid part of the extracellular fluid (ECF). Plasma is mainly composed of water (93% by volume). It also contains dissolved proteins such as fibrinogens, globulins and albumins, glucose, clotting factors, mineral ions such as Na+, Ca2+, Mg2+, HCO3–, Cl–, etc., hormones, and carbon dioxide. Plasma serves as the main medium for the transportation of excretory products. It maintains the osmotic balance. It also maintains a satisfactory blood pressure and volume, balances the body pH, and serves as a medium for exchanging minerals like sodium and potassium.
Figure 4: Fresh, Frozen Plasma
Plasma can be separated from its cellular portion by centrifugation. Four units of plasma are diluted with one part of the anticoagulant, citrate phosphate dextrose (CPD) up to a total volume of 300 mL. When the plasma sample is frozen within 8 hours of collection, it is called fresh-frozen plasma (FFP). When it is frozen longer than 8 hours but less than 24 hours, the plasma sample is called frozen plasma (FP). After preservation by adding anticoagulants, frozen plasma can be stored up to one year at -18 ºC. Plasma transfusion is done for trauma patients, patients with severe liver diseases, and in multiple clotting factor deficiencies. Plasma derivatives like special plasma proteins can be obtained by fractionation. Viruses that cause HIV, hepatitis B and C, are destroyed by treating with heat or solvent detergents.
Similarities Between Platelets and Plasma
- Both platelets and plasma are two components of blood in vertebrates.
- Both platelets and plasma have a critical function in the body.
- Both platelets and plasma can be donated.
Difference Between Platelets and Plasma
Definition
Platelets: Platelets are small, colorless, disk-shaped cell fragments found in large numbers in the blood.
Plasma: Plasma is a straw-colored, liquid component of blood where blood cells are suspended.
Significance
Platelets: Platelets are a type of blood cells.
Plasma: Plasma is the liquid that holds blood cells.
Proportion
Platelets: Platelets and leukocytes account for less than 1% of whole blood.
Plasma: Plasma accounts for 55% of the whole blood.
Function
Platelets: Platelets are involved in blood clotting.
Plasma: Plasma suspends blood cells and other important substances.
Conclusion
Platelets and plasma are two components of blood. Platelets are a type of blood cells, involved in blood clotting. Plasma is the straw-colored liquid in which the blood cells and other substances are suspended in. The main difference between platelets and plasma is the role of each component in the blood.
Reference:
1. Charity Karpac “Platelets.” Platelets on the Web, Available here.
2. Hoffman, Matthew. “Picture of Blood.” WebMD, WebMD, Available here.
Image Courtesy:
1. “1908 Platelet Development” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “Blausen 0740 Platelets” By Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work (CC BY 3.0) via Commons Wikimedia
3. “1909 Blood Clotting” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
4. “FreshFrozenPlasma” By DiverDave – Own work (CC BY-SA 3.0) via Commons Wikimedia
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