Introduction
Blood, the life-sustaining fluid, serves as a bridge, connecting various body organs and systems. Beyond its transport role, it has sophisticated components such as plasma, erythrocytes, leukocytes, and platelets that collectively maintain homeostasis, immunity, and ensure timely healing.
1. Plasma
Plasma, primarily a water-based fluid, makes up about 55% of blood's total volume.
- Composition:
- Water (90%): Acts as a solvent, enabling the transportation of nutrients, waste, and other cells.
- Salts and ions: Electrolytes like sodium, potassium, and calcium maintain pH and osmotic balance.
- Proteins: Including albumins (osmotic balance), globulins (immunity), fibrinogen (clotting), and other regulatory proteins.
- Hormones, nutrients, waste products, gases: Elements vital for cellular functions and metabolic waste removal.
- Functions:
- Transportation: Carries blood cells, nutrients, and waste products.
- Thermal Regulation: Helps in distributing body heat and regulating temperature.
- Defence: Provides antibodies that fight against infections.
2. Erythrocytes (Red Blood Cells)
Erythrocytes are the most numerous cells in the bloodstream.
- Structure:
- Biconcave shape: Maximises surface area for efficient gas exchange.
- Lack of nuclei and organelles: Allows for more room to carry haemoglobin.
- Functions:
- Oxygen Transport: Binds with oxygen in the lungs and delivers it to peripheral tissues.
- Carbon Dioxide Removal: Transports CO2, a metabolic waste, from tissues to lungs for exhalation.
- Acid-Base Balance: Through carbonic anhydrase enzyme, erythrocytes convert CO2 and water into bicarbonate ions, playing a role in pH balance.
3. Leukocytes (White Blood Cells)
Leukocytes patrol the body, safeguarding against infections, and other foreign threats.
- Types:
- Granulocytes: Include neutrophils (bacterial infections), eosinophils (parasitic infections and allergies), and basophils (allergic reactions and inflammation).
- Agranulocytes: Comprise lymphocytes (viral infections and immune responses) and monocytes (consume dead or damaged cells).
- Functions:
- Defence: Protect against pathogens by consuming them (phagocytosis) or producing antibodies.
- Immunity: Some lymphocytes have a memory, ensuring quicker response to previously encountered pathogens.
- Inflammation: Release chemicals to recruit more white blood cells to sites of infection or injury.
4. Platelets (Thrombocytes)
Platelets play a critical role in the prevention of excessive bleeding.
- Structure:
- Small cell fragments produced from megakaryocytes in the bone marrow.
- Functions:
- Clot Formation: Stick together at sites of vessel injury to form a plug.
- Wound Repair: Release growth factors that help in tissue regeneration.
- Prevent Blood Loss: By contracting after clot formation to reduce the size of the wound.
5. Blood Types
Defined by antigens on erythrocyte surfaces and antibodies in plasma, blood types are vital for transfusions.
- A Blood Type:
- Surface Antigens: A
- Plasma Antibodies: Anti-B
- B Blood Type:
- Surface Antigens: B
- Plasma Antibodies: Anti-A
- AB Blood Type:
- Surface Antigens: A and B
- Plasma Antibodies: None
- O Blood Type:
- Surface Antigens: None
- Plasma Antibodies: Anti-A and Anti-B
Receiving mismatched blood can cause agglutination and can be life-threatening.
6. Rh Factor
This antigen on red blood cells has a profound impact, especially during pregnancy.
- Presence: Individuals with this antigen are Rh+.
- Absence: Those lacking it are Rh-.
A potential conflict arises when an Rh- mother carries an Rh+ foetus. If their blood mixes, the mother's immune system can target the baby's red cells in subsequent pregnancies.
FAQ
Erythrocytes, or red blood cells, have a biconcave shape, which means they are disc-shaped with a flattened centre. This unique shape increases their surface area relative to volume, allowing for more efficient gas exchange. The biconcavity also gives erythrocytes flexibility, enabling them to pass smoothly through the narrowest capillaries without rupturing. The larger surface area facilitates the binding of oxygen molecules to haemoglobin present inside the erythrocytes, ensuring efficient oxygen delivery to the body's tissues.
Platelets, upon reaching a site of injury, adhere to the exposed collagen and other substances. As they aggregate to form a clot, they release growth factors, which play a pivotal role in wound healing. These growth factors stimulate the migration, growth, and differentiation of cells involved in tissue repair, like fibroblasts and endothelial cells. By doing so, they accelerate tissue regeneration and wound healing. Additionally, they aid in angiogenesis, the formation of new blood vessels, ensuring the newly formed tissue receives adequate nutrients and oxygen for optimal healing.
If an individual receives a transfusion with the wrong blood type, the immune system can recognise the foreign antigens on the mismatched blood cells and attack them. This response can lead to agglutination, where the red blood cells clump together, potentially causing blockages in blood vessels. Moreover, the breakdown of these foreign cells releases haemoglobin into the bloodstream, which can lead to kidney damage. Immediate symptoms of a transfusion reaction include fever, chills, and pain, and it can escalate to severe complications, even fatality, if not addressed promptly.
Plasma and serum are both components of blood, but they serve distinct functions. Plasma is the liquid component of blood, comprising water, salts, enzymes, antibodies, and other proteins. It represents about 55% of blood's total volume. Serum, on the other hand, is derived from plasma but lacks clotting factors like fibrinogen. It is the liquid left after blood has clotted. Therefore, while plasma plays a role in clotting due to the presence of fibrinogen, serum does not. The serum is often used in diagnostic tests to measure levels of certain proteins or antibodies.
Basophils are a type of granulocyte, a subset of white blood cells. They play a crucial role in the immune response, especially during allergic reactions and asthma. When activated, basophils release histamines and other chemicals that contribute to the inflammation and redness experienced during an allergic reaction. Moreover, these cells release heparin, an anticoagulant that prevents blood from clotting too quickly. Essentially, basophils help alert the immune system to the presence of pathogens and play a role in increasing blood flow to injured or infected sites.
Practice Questions
Plasma is the liquid component of blood, constituting about 55% of its total volume. It is primarily made of water, but it also contains vital dissolved substances like salts, ions, hormones, nutrients, and proteins, such as albumins, globulins, and fibrinogen. Its primary roles include acting as a transport medium for cells, nutrients, and waste, regulating body temperature, and assisting in the immune response through antibodies. Erythrocytes, or red blood cells, are biconcave-shaped cells filled with haemoglobin, a protein responsible for oxygen binding. They lack nuclei and organelles. Their main functions are to transport oxygen from the lungs to the body's tissues and carry carbon dioxide from tissues back to the lungs.
Blood types, determined by the presence of specific antigens on erythrocytes and corresponding antibodies in the plasma, are paramount for safe blood transfusions. Receiving mismatched blood can lead to agglutination, potentially causing severe complications. There are four primary blood types: A, B, AB, and O, each having specific surface antigens and plasma antibodies. The Rh factor, on the other hand, is another antigen present (Rh+) or absent (Rh-) on erythrocytes. It's especially significant during pregnancy. An Rh- mother bearing an Rh+ foetus can develop antibodies against the baby's Rh+ blood, possibly causing haemolytic disease in subsequent Rh+ pregnancies.
