Blood

Blood plays a multitude of critical roles in the human body. It is a lifeline, transporting essential elements and hormones, regulating various physiological processes, and providing protection against harmful agents.

Functions of blood

• Transporting Substances

Oxygen, carbon dioxide, nutrients, waste products, and hormones are all shuttled through the bloodstream to various tissues and organs.

• Regulation of Internal Environment

Blood plays a pivotal role in maintaining the body’s internal environment. It helps regulate the pH levels, body temperature, and water content of cells. Through its efficient distribution and circulation, blood aids in balancing the body’s overall homeostasis.

• Protection

Blood offers a robust defense mechanism to protect the body from harm. It achieves this through clotting, which prevents excessive blood loss from injuries. Additionally, certain phagocytic white blood cells and specialized blood plasma proteins combat toxins and microbes, safeguarding the body from infections.

Physical Characteristics

Blood has a viscosity greater than that of water, which allows it to flow smoothly through blood vessels. The average temperature of the blood is approximately 38°C (100.4°F), contributing to maintaining body temperature within an optimal range. Moreover, blood maintains a pH level between 7.35 and 7.45, a crucial factor for physiological balance.

Blood Volume and Composition

Blood constitutes about 8% of body weight, with an average volume of 4 to 6 liters in adults. It is composed of approximately 55% blood plasma, a liquid component containing water and various solutes. The remaining 45% consists of formed elements, which include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.

Blood Plasma

Blood plasma, the liquid component of blood, primarily contains 91.5% water and 8.5% solutes. These solutes include proteins such as albumins, globulins, fibrinogen, nutrients, vitamins, hormones, respiratory gases, electrolytes, and waste products. The dynamic composition of blood plasma plays a vital role in various bodily functions.

Formation of Blood Cells

Hemopoiesis, the formation of blood cells, takes place in the red bone marrow. Two types of stem cells contribute to this process: myeloid stem cells, responsible for forming red blood cells, platelets, granulocytes, and monocytes; and lymphoid stem cells, which give rise to lymphocytes.

Red Blood Cells (Erythrocytes)

Red blood cells, or erythrocytes, are unique biconcave discs devoid of nuclei, filled with hemoglobin, a protein that carries oxygen and carbon dioxide. RBCs live for about 120 days, and their formation, erythropoiesis, occurs in adult red bone marrow. Erythropoietin, released by the kidneys in response to hypoxia, stimulates erythropoiesis. A reticulocyte count is a diagnostic test that indicates the rate of erythropoiesis.

White Blood Cells (Leukocytes)

White blood cells, or leukocytes, are nucleated cells with two principal types: granulocytes (neutrophils, eosinophils, and basophils) and agranulocytes (lymphocytes and monocytes). WBCs combat inflammation and infection, with neutrophils and macrophages performing phagocytosis. Eosinophils, basophils, B lymphocytes, and T lymphocytes play specific roles in immunity and immune response.

Platelets

Platelets are cell fragments splintered from megakaryocytes. They are instrumental in stopping blood loss from damaged blood vessels, forming platelet plugs that initiate clotting.

ABO blood group system

The ABO blood group system is determined by the presence or absence of A and B antigens on the surface of red blood cells (RBCs). Blood types are classified as A, B, AB, or O, depending on the antigens present.

Rh blood group system

The Rh blood group system depends on the presence or absence of Rh antigens on RBCs. Individuals with Rh antigens are classified as Rh+, while those without are Rh-.

Summary

Blood is a vital fluid that performs crucial functions in the body. It transports oxygen, nutrients, hormones, and waste products while regulating pH, body temperature, and water content. Blood provides protection through clotting and combatting toxins and microbes. It consists of blood plasma and formed elements, including red and white blood cells, and platelets. Red blood cells carry oxygen, while white blood cells fight infections. Blood plays a critical role in maintaining overall health.

Frequently Asked Questions on Blood

What is the primary function of blood?

Blood has multiple functions, including the transport of oxygen, nutrients, waste products, hormones, and carbon dioxide. It also helps regulate the body's pH, temperature, and water content, and provides protection through clotting and combating toxins and microbes.

What is the composition of blood?

Blood is approximately 55% blood plasma and 45% formed elements. Blood plasma contains water and various solutes like proteins, nutrients, hormones, and waste products. Formed elements include red blood cells, white blood cells, and platelets.

What are red blood cells and their function?

Red blood cells, or erythrocytes, are biconcave discs containing hemoglobin. Hemoglobin allows them to transport oxygen and carbon dioxide throughout the body. Their primary function is oxygen delivery to tissues and carbon dioxide removal.

What are white blood cells and how do they protect us?

White blood cells, or leukocytes, are nucleated cells divided into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes). They protect us by combating inflammation and infection. Neutrophils and macrophages perform phagocytosis, while lymphocytes produce antibodies and directly destroy invaders.

What are platelets and their role in blood clotting?

Platelets are cell fragments derived from megakaryocytes. They play a vital role in stopping blood loss from damaged blood vessels by forming a platelet plug. This initiates the blood clotting process, preventing excessive bleeding.

How is blood formed in the body?

Blood cells are formed through hemopoiesis, which occurs in the red bone marrow. Myeloid stem cells give rise to RBCs, platelets, granulocytes, and monocytes, while lymphoid stem cells develop into lymphocytes.

How long do red blood cells live?

Red blood cells have an average lifespan of about 120 days. After their phagocytosis by macrophages, hemoglobin is recycled, and new RBCs are constantly produced through erythropoiesis.

What is the role of blood plasma?

Blood plasma is the liquid component of blood, mainly composed of water and solutes. These solutes include proteins, nutrients, vitamins, hormones, respiratory gases, electrolytes, and waste products. It serves as a medium for transporting essential substances throughout the body.

How is blood type determined?

Blood type is determined by the presence or absence of specific antigens on the surface of red blood cells. The ABO blood group system classifies blood into different types, while the Rh system determines whether an individual is Rh+ or Rh-.