Blood Transfusions, Blood Types, and Blood Disorders: Study Notes for Human Biology

Blood Transfusions

Overview of Blood Transfusions

Blood transfusions involve the administration of blood from one individual directly into the bloodstream of another. This medical procedure is essential for treating various conditions, such as severe blood loss, anemia, and certain blood disorders. Early attempts at transfusions often failed due to lack of understanding of blood compatibility, but modern transfusions are safe due to knowledge of blood types.

• Blood transfusion: Transfer of blood or blood products from a donor to a recipient.

• Compatibility: Matching blood types prevents adverse reactions.

• Historical context: Animal-to-human transfusions were unsuccessful; human-to-human transfusions have been practiced since the early 1800s.

Blood Types: Antigen and Antibody

ABO Blood Types and Immune Response

The ABO blood type system classifies blood based on the presence of specific antigens and antibodies on red blood cells. Antigens are non-self proteins that stimulate the immune system, while antibodies are proteins produced by the immune system to counteract foreign antigens.

• Antigen: A protein on the surface of red blood cells that marks cells as "self" or "invader."

• Antibody: A protein produced by the immune system that binds to foreign antigens, forming antigen-antibody complexes.

• Immune response: Antibodies bind to antigens on foreign cells, causing them to clump (agglutinate) and be destroyed.

ABO Blood System: Blood Type Classification

There are four main blood types in the ABO system, each defined by the presence or absence of A and B antigens and corresponding antibodies.

• Type A: Has A antigens and B antibodies; can receive A or O blood.

• Type B: Has B antigens and A antibodies; can receive B or O blood.

• Type AB: Has both A and B antigens, no antibodies; universal receiver.

• Type O: Has no antigens, A and B antibodies; universal donor, can only receive O blood.

Incidence of Blood Types

Blood type distribution varies among populations.

Blood Type	Red Blood Cell Antigens	Plasma Antibodies	Incidence (U.S. Caucasians)	Incidence (U.S. African Americans)	Incidence (Native Americans)
Type A	Antigen A	B	40%	27%	8%
Type B	Antigen B	A	10%	20%	1%
Type AB	Antigens A and B	Neither A nor B	5%	4%	0%
Type O	Neither A nor B	A and B	45%	49%	91%

Blood Transfusion Reactions

Mechanisms and Consequences

Antibodies against foreign antigens appear early in life and can cause transfusion reactions if incompatible blood is transfused.

• Agglutination: Clumping of red blood cells due to antibody-antigen interaction.

• Transfusion reaction: Adverse effects such as blocked blood vessels, organ damage, or kidney failure due to hemoglobin release from damaged RBCs.

Rhesus Factor (Rh)

Rh Factor and Its Clinical Significance

The Rh factor is a second surface antigen found on red blood cells.

• Rh+: Presence of Rh antigen (85% of population).

• Rh-: Absence of Rh antigen (15% of population).

• Clinical importance: Rh incompatibility can cause transfusion reactions and complications during childbirth.

Rh Factor in Blood Transfusions

Individuals who are Rh- do not have anti-Rh antibodies unless exposed to Rh+ blood.

• First exposure: Antibodies are produced, but no immediate reaction.

• Second exposure: Severe transfusion reaction due to pre-existing antibodies.

Rh Factor and Childbirth

If an Rh- mother carries an Rh+ fetus, exposure to fetal blood can cause the mother to develop antibodies against Rh antigen. In subsequent pregnancies, these antibodies can attack the fetus's red blood cells, leading to hemolytic disease of the newborn.

Hemolytic Disease at Birth

Pathophysiology and Treatment

Hemolytic disease of the newborn results from maternal antibodies attacking fetal RBCs, causing decreased RBCs and toxic hemoglobin levels.

• Treatment: Rh- mothers are given RhoGAM injections to prevent antibody formation.

• Timing: Injection at 28 weeks gestation and after childbirth if the baby is Rh+.

• Mechanism: Injected antibodies destroy fetal Rh+ RBCs in the mother before her immune system reacts.

Blood Substitutes

Types and Limitations

Blood substitutes are used when human blood is unavailable or unsuitable.

• Type 1: Modified hemoglobin in solution (from animals or genetically produced).

• Type 2: Perfluorocarbons (PFCs), colorless liquids with high O2 carrying capacity.

• Disadvantages: Disease transmission, toxicity, short lifespan, safety concerns.

Blood Disorders

Mononucleosis

Mononucleosis is a contagious viral infection caused by the Epstein-Barr virus.

• Symptoms: Fever, headache, sore throat, fatigue, swollen tonsils and lymph nodes, increased monocytes and lymphocytes.

• Transmission: Physical contact; most common in adolescence.

• Treatment: No cure; supportive care.

Blood Poisoning (Septicemia)

Blood poisoning is a bacterial infection of the blood, often arising from wounds, burns, urinary infections, or dental work.

• Symptoms: Sudden appearance of red streaks on skin near infection site, indicating inflammation of veins and lymph vessels.

• Complications: Infection can spread to systemic circulation.

Anemia

Anemia is a reduction in the blood's oxygen-carrying capacity.

• Iron-deficiency anemia: Lack of iron prevents proper hemoglobin synthesis.

• Hemorrhagic anemia: Blood loss from injuries, parasites, ulcers, or heavy menstrual flow.

• Pernicious anemia: Vitamin B12 deficiency impairs RBC production.

• Hemolytic anemia: Rupture or lysis of RBCs (e.g., sickle-cell anemia).

• Anemia due to renal failure: Reduced erythropoietin production.

Symptoms of Anemia

• Pale skin

• Headaches

• Fatigue

• Dizziness

• Difficulty breathing

• Heart palpitations

• Weird cravings

• Restless legs

• Brittle hair and nails

Leukemia

Leukemia is a cancer characterized by uncontrolled production of abnormal white blood cells in the bone marrow.

• Types: Acute (rapid onset) and chronic (slow development).

• Effects: Crowds out normal blood cell production, interferes with organ function.

Multiple Myeloma

Multiple myeloma is a cancer involving uncontrolled production of plasma cells in the bone marrow.

• Effects: Excess production of abnormal antibodies, increased vulnerability to infection, weakened bones, elevated blood calcium.

Thrombocytopenia

Thrombocytopenia is a reduction in the number of platelets, leading to increased risk of bleeding.

• Causes: Viral infection, anemia, leukemia, blood disorders, X-rays, drug reactions.

• Symptoms: Bruising, nosebleeds, bleeding in mouth, blood in urine, heavy menstrual periods.

References

• Johnson, M.D & Long, S. (2021). Human biology: Concepts and current issues (9th ed.). Pearson Education Inc.