Blood Composition and Functions

Blood

• Vital fluid tissue that circulates inside blood vessels
• Represents 8% of body weight, or 5.6 liters

Functions of blood

• Transport function: Transports oxygen, carbon dioxide, nutrients, waste products, and hormones.
• Defensive function: Contains white blood cells and antibodies.
• Hemostasis: Stops bleeding.
• Homeostasis: Maintains the internal environment (extracellular fluid) of the body for optimal cell function.

Composition of blood

• Plasma:
  • 55% of blood by volume and weight.
  • Contains water, proteins (albumin, globulins, fibrinogen, prothrombin), and other solutes like ions, nutrients, waste products, gases, and regulatory substances.
• Formed Elements:
  • 45% of blood by volume and weight.
  • Contains leukocytes, platelets, and erythrocytes.

Leukocytes

• Less than 1% of blood cell count.
• Includes neutrophils, lymphocytes, monocytes, eosinophils, and basophils.

Platelets

• Less than 1% of blood cell count.
• Involved in blood clotting.

Erythrocytes

• More than 99% of blood cell count.
• Non-nucleated circular biconcave discs containing hemoglobin, responsible for oxygen and carbon dioxide exchange.
• Average lifespan of 120 days.

Blood Plasma

• Yellow clear fluid consisting of water, proteins, and other substances.
• Plays a crucial role in maintaining blood volume and pressure, and transporting nutrients and waste products.

Plasma Proteins

• Albumin: Highest concentration, important for maintaining colloidal osmotic pressure and transporting substances.
• Globulins: Function in defense (α, β, γ globulins) and transport of certain substances.
• Fibrinogen: Essential for blood clotting and contributes to plasma viscosity.
• Prothrombin: Important for blood clotting.

Albumin/Globulin (A/G) Ratio

• The ratio of albumin to globulin concentration in the blood is between 1.2 and 1.7.
• Decreased A/G ratio can be observed in:
  • Liver disease due to decreased albumin production.
  • Kidney disease due to loss of albumin through urine.
  • Infection due to an increase in globulin concentration.

Red Blood Cells (Erythrocytes)

• Non-nucleated, circular, biconcave discs containing hemoglobin.
• Responsible for oxygen and carbon dioxide transport.
• Contain carbonic anhydrase enzyme and glucose-6-phosphate dehydrogenase (G-6-PD).

Red Blood Cell Count

• Adult males: 5-6 million per cubic mm.
• Adult females: 4-5 million per cubic mm.
• Newborns: 7 million per cubic mm.

Functions of Red Blood Cells

• Carry oxygen to tissues and remove carbon dioxide.
• Hemoglobin acts as a blood buffer.
• Red blood cells contain carbonic anhydrase, important for carbon dioxide transportation.
• The biconcave shape of red blood cells increases surface area, facilitating gas exchange.

Erythrocyte Membrane

• Keeps hemoglobin inside, preventing heart failure, increased blood viscosity, and renal failure.
• Contains agglutinogens that determine blood group.
• The plastic nature allows red blood cells to compress while passing through narrow capillaries and regain their normal shape after, preventing rupture.

Formation of Red Blood Cells (Erythropoiesis)

• Fetus: Formed in the liver and spleen.
• Last three months of fetal life and after birth: Formed in the bone marrow of all bones until adolescence.
• Age 20: Formed in the bone marrow of the upper parts of the humerus and femur and of membranous bones.
• After age 20: Formed in the bone marrow of membranous bones (skull, vertebra, sternum, and ribs).

Factors Affecting Erythropoiesis

• Oxygen Supply to Tissues: Hypoxia stimulates the release of erythropoietin hormone, primarily from the kidney, which increases red blood cell production.
• Diet:
  • Proteins: Provide essential amino acids for globin formation in hemoglobin.
  • Iron: Crucial for hemoglobin synthesis, and its absorption is influenced by factors like gastric acid, vitamin C, and the presence of substances like oxalates, phytic acids, and phosphates.
  • Vitamins:
    • Vitamin B12: Essential for red blood cell nuclear maturation, cell division, myelination of nerves, and digestive system mucosa integrity.
    • Folic Acid: Necessary for red blood cell nuclear maturation and cell division.
    • Vitamin C: Promotes tissue growth and metabolism, including bone marrow.
  • Trace Elements: Copper and cobalt act as cofactors for hemoglobin formation.
  • Hormones: Erythropoietin (specific), thyroid hormones (non-specific), and male sex hormones (androgen) promote erythropoiesis.
• Healthy Organs:
  • Bone Marrow: Site of red blood cell formation.
  • Liver: Plays a role in erythropoiesis, producing globin for hemoglobin, secreting erythropoietin, and storing iron and Vitamin B12.
  • Kidney: Secretes the majority of erythropoietin in response to hypoxia.
  • Stomach: Produces gastric HCl which is essential for iron conversion, and secretes intrinsic factor for vitamin B12 absorption.
  • Small Intestine: Site of iron and vitamin B12 absorption.

Anemia

• A condition characterized by a decrease in red blood cell count or hemoglobin content, or both.

Types and Causes of Anemia

• Normochromic Normocytic Anemia

  • Haemolytic Anemia: Caused by excessive destruction of red blood cells due to factors like incompatible blood transfusions, snake venoms, drug sensitivity, infections, antibodies, and increased red blood cell fragility.
  • Aplastic Anemia: Due to bone marrow depression, caused by radiation exposure, chemotherapy, drugs, or bone marrow destruction.
  • Haemorrhagic Anemia: Occurs due to acute blood loss.

• Microcytic Hypochromic Anemia

  • Iron Deficiency Anemia: Caused by either iron deficiency in the diet, failure of iron absorption, or chronic blood loss.

• Macrocytic (Megaloblastic) Anemia

  • Caused by deficiency of vitamin B12 or folic acid.

This quiz explores the vital aspects of blood, including its composition, functions, and the cellular elements it contains. Delve into the roles of plasma, leukocytes, and platelets in maintaining bodily functions and homeostasis. Test your understanding of how blood serves essential transport and defense mechanisms.