Blood Composition and RBC Functions

Blood Composition and Functions

• Blood is composed of 55% plasma and 45% formed elements.
• Plasma is 90% water, 0.9% inorganic salts (NaCl, HCO3), and 7.1 gm% plasma proteins (albumin, globulin, fibrinogen, prothrombin), plus organic substances and waste products, hormones, enzymes, and vitamins (2%).
• Formed elements include red blood cells (45%), white blood cells (<1%), and platelets (<1%).

Red Blood Cells (RBCs)

• Structure: Flat, biconcave disc, non-nucleated, made of a protein framework, contains hemoglobin, diameter 7.2μm, thickness 2.2μm, and volume 90 femtoliters (FL).
• Function: Carry hemoglobin, transport oxygen and carbon dioxide, and regulate pH. Metabolically active cells use glucose for energy.
• Count: Males 4.8-5.8 million cells/mm3, Females 4.2-5.2 million cells/mm3.
• Life span: 120 days (4 months).

Erythropoiesis (RBC Formation)

• Stages: Stem cell → Proerthroblast → Early, Intermediate, Late Normoblast → Reticulocytes → Erythrocytes.
• Rapid RBC production increases reticulocytes in circulation.
• Site of formation:
  • Fetus: Liver and spleen
  • Baby: Bone marrow of all bones
  • Adult: Bone marrow of flat bones (skull, iliac bones, sternum, ribs, scapula).
• Extramedullary erythropoiesis: Return of liver and spleen to form blood cells when needed.

Factors Affecting Erythropoiesis

• Control of erythropoiesis: Erythropoietin
• Substances essential to erythropoiesis:
  • Proteins and amino acids: Important for globin synthesis
  • Iron: Essential for hemoglobin synthesis
  • Folic acid and Vitamin B12: Needed for DNA synthesis
  • Trace elements (copper, cobalt): Cofactors for hemoglobin formation
  • Hormones (androgens, thyroxine, glucocorticoids): Stimulate erythropoiesis, Estrogen inhibits it
  • Healthy bone marrow and liver: Essential for processes

Plasma Proteins

• Types: Albumin (4.8 g/100 ml), globulin (2.3 g/100 ml), fibrinogen (0.3 g/100 ml) (Total: 7.4 g/100 ml)
• Structures: Specific molecular weights and functions.
• Synthesized in the liver.
• Functions: Transportation, maintenance of fluid balance, osmotic pressure, viscosity, clotting, defense mechanisms (antibodies), and acting as a holding place for certain hormones.

Iron Absorption

• Amount absorbed: 15-20 mg/day
• Iron losses: 0.6-1.0 mg/day in males; varies in females, potentially up to 2 mg/day for menstruating females
• Iron is more readily absorbed in the ferrous state (Fe++).
• Factors that help iron absorption: Vitamin C
• Factors that decrease iron absorption: Phytic acid, oxalates, phosphates which cause insoluble iron salts
• Apoferritin: Protein in mucosal cells that binds to iron.
• Ferritin: Complex of apoferritin and Fe++
• Storage iron: Iron in ferritin is an iron storage form
• Transferrin: Plasma protein that transports iron
• Sources: Diet, heme iron, non-heme iron

Folic Acid and Vitamin B12

• Folic acid functions: Synthesis of pyrimidines and thymine, essential for DNA and cell division, erythrocyte division, important for RNA to DNA transformation
• Vitamin B12 functions: Required for folic acid action, required for myelin formation, dependent on dietary intake (animal products), needs intrinsic factor for absorption. Vitamin deficiencies can lead to neurological issues and megaloblastic anemia (a type of blood disorder).

Additional Notes on blood

• 3500ml Plasma in 70kg man, 5% of body weight
• pH:7.4
• Osmotic pressure: 290 mOsmol
• Plasma protein osmolarity=5000 mmHg

Test your knowledge on blood composition, functions, and the formation of red blood cells (RBCs). This quiz covers key elements such as the components of blood, the structure and function of RBCs, and the process of erythropoiesis. Dive in to see how well you understand these vital topics in human biology.