NR 507: MIDTERM REVIEW

Hematology

Hematopoiesis:

• Hematopoiesis is the process of blood cell production, which is constant throughout life to replace RBCs that age, die, are destroyed by disease, or are lost due to bleeding.
• In the fetus, hematopoiesis occurs in the liver and spleen. After birth, it takes place in the bone marrow.
• Hematopoiesis occurs in two stages:
  1. Proliferation (Mitotic Division): The process where hematopoietic stem cells (HSCs) multiply.
  2. Maturation (Differentiation): The process where HSCs differentiate into various blood cells.

Bone Marrow:

• Red Marrow: Hematopoietic and active in blood cell production.
• Yellow Marrow: Fatty and inactive.

Hematopoietic Lineages:

• Lymphoid Lineage: T cells (T-lymphocytes) and B cells (B-lymphocytes).
• Myeloid Lineage: Monocytes and Granulocytes (WBCs).
• Erythrocytes (RBCs).

Megakaryocytes (Platelets).

• All blood cells originate from HSCs.
• These cells are signaled to differentiate into specific blood cells by cytokines, chemokines, and growth factors, forming RBCs, WBCs, and platelets.

Mesenchymal Stem Cells:

• Develop into osteoclasts, fibroblasts, and adipocytes.

Erythropoietin:

• Erythropoietin is a hormone that stimulates erythrocyte production.
• It is secreted by the kidneys in response to tissue hypoxia.

Erythrocytes (Red Blood Cells):

• Erythrocytes are the most abundant cells in the body, primarily responsible for tissue oxygenation.
• Mature erythrocytes lack a nucleus and mitochondria, meaning they cannot synthesize protein, carry out oxidative reactions, or divide. They rely solely on anaerobic metabolism.
• Life Span: 100-120 days.

Stages of Erythropoiesis (7-day process):

• Hemocytoblast (Stem Cell): Binds with erythropoietin.
• Proerythroblast: Commits to becoming an RBC.
• Erythroblast: Undergoes ribosome synthesis (2 phases).
• Normoblast: Accumulates hemoglobin and ejects the nucleus.
• Reticulocyte: An immature RBC released into circulation, lacking a nucleus, ribosomes, and mitochondria.
• RBC: After maturing in the bone marrow for 1-2 days, it becomes a fully functional RBC.

Hemoglobin:

• Hemoglobin is the oxygen-carrying protein in erythrocytes.
• Hemoglobin-packed RBCs pick up oxygen in the lungs and exchange it for carbon dioxide in the tissues.
• Composition: Hemoglobin is composed of 2 pairs of polypeptide chains (globins) and 4 iron-containing complexes (hemes).
• Each hemoglobin molecule can carry up to 4 oxygen molecules.
  • Oxyhemoglobin: Hemoglobin bound to oxygen, appears red.
  • Deoxyhemoglobin: Hemoglobin after releasing oxygen to the tissues, appears blue.

Risk Factors and Causes for Developing Anemia:

• Blood loss (acute or chronic).
• Impaired erythrocyte production.
• Increased erythrocyte destruction.
• A combination of these factors.

Iron Deficiency Anemia - Microcytic-Hypochromic Anemia:

• The most common nutritional disorder.
• Occurs when iron stores are depleted, leading to reduced hemoglobin synthesis.
• Common in: Toddlers, adolescent girls, and women of childbearing age.
• Causes:
  • Dietary deficiency.
  • Impaired absorption.
  • Increased requirement.
  • Chronic blood loss.

Thalassemia - Microcytic-Hypochromic Anemia:

• An inherited autosomal recessive disorder.
• Characterized by impaired synthesis of one of the two chains of adult hemoglobin (alpha or beta).
• Common Among: Individuals of Mediterranean descent.
• Thalassemia can range from minor (asymptomatic) to major (potentially lethal, such as Cooley’s).

Sickle Cell Anemia - Normocytic-Normochromic/Hemolytic Anemia:

• An inherited autosomal recessive disorder.
• Characterized by the presence of atypical hemoglobin (Hemoglobin S).
• Cause: An amino acid change on the beta-globin chain (glutamine is replaced by valine), which distorts erythrocytes into a sickle shape, impairing their ability to carry oxygen.

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This study guide is structured to cover key concepts in hematology, providing a clear overview for exam preparation.