Blood: Composition, Function and Donation

The Irreplaceability of Blood

• Science is able to replace many body parts, but not blood.
• Blood is essential and often required for injuries or illnesses.
• Every two seconds, someone in the U.S. requires a blood transfusion.
• The 16 million pints of blood required each year in the U.S. must come from donors.

Blood Composition and Function

• Blood has a red, sticky, salty, and metallic taste.
• Blood accounts for about 8% of body weight.
• Blood is a connective tissue comprised of living cells in a nonliving matrix, or plasma.
• Key functions of blood:
  • Transports oxygen, nutrients, waste, and hormones.
  • Regulates body temperature and pH levels.
  • Maintains fluid volume.
  • Protects against infection and blood loss.

The Blood Donation Process

• At blood drives, about a pint of blood is taken in 20 minutes after a finger prick.
• After donation, blood is tested for diseases and separated into components.

Blood Components

• Whole blood contains formed elements which are cells and fragments, water, and dissolved molecules.
• A centrifuge separates blood into:
  • Erythrocytes (red blood cells): 45% of blood volume, and they carry oxygen and carbon dioxide
  • Leukocytes (white blood cells) and Platelets: <1% of blood, leukocytes defend against toxins, platelets aid clotting
  • Plasma: 55% of blood volume, 90% water, 10% solutes (proteins, electrolytes, gases, hormones, waste)
• Electrolytes, such as calcium, sodium, potassium, phosphate, sulfate, and bicarbonate, regulate blood chemistry and osmotic pressure.
• Plasma proteins, such as albumin and globulins, maintain osmotic pressure, transport lipids, and aid in defense and clotting.

Hemostasis

• Hemostasis prevents excessive blood loss.
• The initial response is blood vessel constriction to slow blood flow.
• Platelet Plug Formation- Platelets gather at the injury site, becoming sticky when reacting with exposed collagen fibers.
• Fibrin Clot Reinforcement- Fibrin threads form a mesh to trap platelets and blood cells, closing the vessel wall.
• Clot Dissolution: The blood vessel heals and the blood clot dissolves over time.

Hemophilia

• Hemophilia is a disorder where fibrin clot formation is ineffective.
• Hemophiliacs bleed for a longer time after injury, and often require transfusions.

Blood Types

• Blood types are categorized as A, B, AB, or O, and this is based on antigens and immune system compatibility.
• Antigens are glycoprotein markers on cells that identify them.
• During an immune response, antibodies detect foreign cells and bind to antigens to tag cells for destruction.
• Agglutinogens are specialized antigens on red blood cells that activate antibodies that cause coagulation.
  • Type A has A antigens.
  • Type B has B antigens.
  • Type AB has both A and B antigens.
  • Type O has neither A nor B antigens.

Blood Type Compatibility

• AB-type blood is known as universal recipients because it is able to accept any blood type because it has both antigens and no antibodies.
• O-type blood is known as universal donors as it can mix with other blood types without causing a reaction because it lacks antigens.
• O-types can only receive O-type blood.

Rh Factor

• Rh antigens determine whether blood is Rh positive or Rh negative.
• Most of the population is Rh positive, but negative types should stick to Rh negative blood.
• The combination of A-B antigens and Rh factors results in eight different blood types.

Explore the crucial functions of blood, its key components, and the blood donation process. Blood is a connective tissue that transports oxygen, regulates body temperature and protects against infection. Learn why blood is irreplaceable and must come from donors.