Blood Composition Overview

Blood Overview

• Blood is a fluid connective tissue with a complex composition
• Blood comprises plasma (55%) and formed elements (45%)
  • Plasma is mostly water (over 90%) with proteins like albumin, globulins, and fibrinogen, along with electrolytes, nutrients, hormones, gases, and waste products.
  • Formed elements include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

Blood Composition

• Plasma: the liquid portion of blood.
  • 55% of total blood volume
  • Mostly comprised of water
  • Contains dissolved proteins, electrolytes, nutrients, hormones, gases, and waste products.
• Formed elements: the cellular components of blood.
  • 45% of total blood volume is formed elements.
  • 99% of formed elements are red blood cells
  • <1% of formed elements are white blood cells and platelets.
• Haematocrit: the percentage of blood volume occupied by red blood cells.
  • Normal values: males ~47% ± 5%; females ~42% ± 5%.

Physical Characteristics of Blood

• Viscosity (thickness): thicker than water, flows more slowly than water.
• Temperature: 38°C
• pH: around 7.4 (range 7.35-7.45)
• Volume: approximately 5-6 liters in males and 4-5 liters in females
• 8% of total body weight.

Blood Functions

• Transportation: carries oxygen, carbon dioxide, metabolic wastes, nutrients, heat, hormones, and medications.
• Regulation: regulates pH (through buffers), body temperature, and the composition of intracellular fluid.
• Protection: protects against disease (immunity) and inflammation (through components like white blood cells and platelets).

Blood Cells

• Red blood cells (erythrocytes):
  • Contain haemoglobin which gives blood its red color.
  • Biconcave disc shape increases surface area for oxygen absorption and transportation
  • No nucleus or organelles, thus don't divide.
  • Lifespan of 120 days
  • Responsible for transportation of oxygen and CO2
• White blood cells (leukocytes):
  • Granulocytes (eosinophils, basophils, neutrophils) have granules in cytoplasm & are involved in immunity and inflammation.
  • Agranulocytes (lymphocytes, monocytes) lack granules & play important roles in immune responses.
• Platelets (thrombocytes)
  • Help in blood clotting
  • Cell fragments, not complete cells.

Blood Groups

• ABO blood group system: based on the presence or absence of A and/or B antigens on red blood cells and corresponding antibodies in the plasma.
  • Blood types: A, B, AB, and O.
• Rh factor: another blood group system. Presence or absence of Rh antigen.
  • Rh-positive or Rh-negative.

Haematopoiesis

• Process of blood cell production.
• Occurs in bone marrow, liver, and spleen.
• Stem cells called pluripotent hematopoietic stem cells are the origin of all blood cells.

Blood Clotting (Haemostasis)

• Three stages: 1) Vascular spasm, 2) Platelet plug formation, 3) Blood clotting (coagulation)
• Clotting factors, calcium, and substances released by platelets are needed in cascade reactions.

Blood Clotting Continued

• Extrinsic pathway: activated by trauma to tissues outside blood vessels.
• Intrinsic pathway: activated by trauma to the inside lining of blood vessels.

Haemolytic Disease of the Newborn (HDN)

• Incompatibility of Rh factors between a pregnant woman and her fetus.
• Antibodies produced against Rh+ blood, leading to destruction of the baby's red blood cells.
• Management involves preventing an initial sensitization of the mother and managing or treating the effects on the fetus if sensitization has occurred.