Blood Composition and RBC Functions

Study Notes

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%).

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).

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.

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.

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 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).