L2 physiology

RBC and Anemia

• Red blood cells (RBCs) are also known as erythrocytes
• RBCs are non-nucleated, biconcave discs
• The biconcave shape is created by proteins called ankyrin and spectrin
• RBC cytoplasm is mainly (34%) hemoglobin (Hb)
• Each RBC contains about 30 pg of hemoglobin, electrolytes (especially K+ and HCO3-), and enzymes (carbonic anhydrase and glucose-6-phosphate dehydrogenase (G-6-PD))
• RBC life span is 120 days, then they are destroyed and removed by the spleen
• Male RBC count ranges from 4.7 to 6.1 million/uL, while female count is from 4.2 to 5.4 million/uL
• The biconcave shape increases surface area for gas diffusion
• It allows flexibility for squeezing through capillaries
• Important in differential diagnosis of anemias
• RBCs transport hemoglobin, which carries respiratory gases
• Hemoglobin acts as a buffer for acid-base balance
• Carbonic anhydrase in RBCs catalyzes the reaction between CO2 and water to form carbonic acid (H2CO3)
• Essential for maintaining diastolic arterial blood pressure
• The thin cell membrane allows free diffusion of O2 and CO2
• Plays a role in producing blood viscosity, essential for diastolic arterial blood pressure
• Membrane glycoprotein layer contains agglutinogens that determine blood group
• Blood groups are classified as O, A, B, AB
• Blood type O is a universal donor
• Blood type AB is a universal recipient

Blood Components

• Blood is a specialized connective tissue
• Blood is a thick, homogeneous liquid
• Blood has cellular (formed elements) and liquid (plasma) components
• Plasma (55% of whole blood) contains water, plasma proteins, lipids, hormones, nutrients, waste products, and various electrolytes
• Formed elements (40-45% of whole blood) include red blood cells (erythrocytes: about 5 million/mm³), white blood cells (leukocytes: 4000-11000/mm³), and platelets (thrombocytes: 100000-400000/mm³)
• Plasma proteins (7.1%) include albumin, globulins, and fibrinogen

Plasma Proteins

• Albumin ranges from 3.5-5g/dL (average 4g/dL)
• Globulins (α, β, γ) range from 2.3-3.5g/dL (average 2.7g/dL)
• Fibrinogen is about 0.3g/dL
• All plasma proteins are synthesized in the liver, except γ-globulins, synthesized by B-lymphocytes and plasma cells
• Plasma proteins are formed from food proteins and tissue proteins (reserve type) in starvation

Blood Cells

• Platelets (thrombocytes): 100,000-400,000/mm³
• Red blood cells (erythrocytes): 4-5 millions/mm³
• White blood cells (leukocytes): 4000-11000/mm³

Blood Groups

• Two antigens (agglutinogens)-type A and type B-occur on surfaces of red blood cells
• Blood is classified into four major blood types: O, A, B, and AB
• Blood types depend on the presence or absence of A and B agglutinogens
• Blood type O is a universal donor
• Blood type AB is a universal recipient

RBC Formation

• Erythropoiesis is the process of RBC formation
• Stages of erythropoiesis include: stem cell, committed cell, developmental pathway (phases 1-3), ejection of nucleus
• Sites of erythropoiesis include yolk sac (0-2 months), liver and spleen (2-7 months), and bone marrow (5-9 months) in utero
• In adults, erythropoiesis is primarily in the red bone marrow of axial skeleton, proximal ends of femur and humerus
• Inactive bone marrow is called yellow marrow

Factors Needed for Erythropoiesis

• A healthy red bone marrow is essential
• Diet containing high biological value proteins, copper, cobalt, and vitamins (especially B12 and folate)
• Liver forms the globin part of hemoglobin, stores vitamin B12 and iron, secretes erythropoietin
• Hormonal factors, including androgens and thyroxine
• Decrease in oxygen tension (hypoxia) stimulates erythropoietin release

Fate of Anemia

• Anemia effects mostly on the circulatory system
• Increases the workload on the heart
• Accompanied by hyperdynamic circulation and functional murmurs
• Leads to tissue hypoxia and acute heart failure

Types of Anemia

• Etiological Classification: by cause
• Hemorrhagic (blood loss)
• Decreased production of RBCs (Aplastic/nutritional or deficiency anemias)
• Hemolytic (excessive breakdown) anemia
• Morphological Classification: by size and hemoglobin concentration.
• Normocytic normochromic
• Microcytic hypochromic
• Macrocytic normochromic