Amphipathic Molecules: Components of Blood

Erythrocytes - Metabolism

RBCs use glucose as its only (absolute) energy source - glucose is preferred energy source for brain neurons

Plasma

in vivo- extracellular fluid in the blood - in vitro - extracellular fluid portion of the blood when an appropriate anticoagulant is added and then is centrifuged, the overlying fluid is plasma (no consumption of fibrinogen)

Folic Acid

present in green vegetables, some fruits and liver Deficiency -> anemia, neural tube defects in fetus

Hypoxia as a regulator for RBC production

when there is low oxygen, it stimulates a release of erythropoietin from the kidneys (takes hours) which then stimulates bone marrow to produce RBCs (takes days)

Use of glucose in RBCs

- 90-95% of glucose - for generating ATP through glycolysis - 5-10% of glucose - for the hexose monophosphate pathway (HM) or pentose phosphate pathway) to produce NADPH (prevent hemolysis) - NADPH can reduce oxidative stress (O2-, free radicals)

Principle of Amphipathic Molecules

- Contain both polar (hydrophilic) head group and nonpolar (hydrophobic) tail group in their structures - Ex: Membrane phospholipids, pulmonary surfactants, bile acids, transport proteins in blood for lipids

Platelets

- Formed in bone marrow from megakaryocytes - Do not have nuclei - cannot reproduce - contain actin, myosin and thrombosthenin (contractile proteins) which cause contraction when activated - Contain mitochondria - form ATP for energy and ADP for vasoconstriction and synthesize prostaglandins that cause vascular reactions

Cell membrane of Platelets

- coat of glycoproteins - repulse adherence to normal endothelium and yet causes adherence to injured area of vessel wall (endothelial cell and collagen) - rich in phospholipids - coagulation

Major Components of Plasma

- water - 93% - proteins - 7% - albumin, globulins, fibrinogen - Small M.W. material - ~0.1% - nutrients, catabolic products, electrolytes, hormones - Lipids are included in the proteins section because they are transported through the blood on lipoproteins

Sites of RBC production

- embryonic stage - yolk sac, liver, lymphoid tissue - after birth - bone marrow - most essential regulator of production - hypoxia

Characteristics of Erythrocytes

- mature mammalian RBCs are non-nucleated and lack most organelle including mitochondria - Metabolically active because they have to transport oxygen and CO2 throughout the body constantly and they can only do this through glycolysis which produces 2 ATP - Biconcave in shape because they need to maximize contact area in order to load and unload oxygen and CO2

Maturation of RBC

- requires vitamin B12 and folic acid

Hydrophilic and Hydrophobic Substances

- water is a polar solvent and tends to interact better with polar (hydrophilic) molecules - Amino acids, proteins, carbohydrates, and nucleotides are highly polar - water soluble - The bulk of any lipid molecule is non polar (symmetrical) - water insoluble (hydrophobic), yet soluble in non polar solvents such as benzene

Vit B12

-extrinsic factor, needs intrinsic factor form GI tract for absorption Malabsorption of B12 -> pernicious anemia

Major Components of Blood

Cellular fraction - erythrocytes, leukocytes, thrombocytes Noncellular fraction of the blood - plasma, serum Major components of plasma - water, proteins, other

Cellular fraction of the blood

Cellular fraction is 40-45% of blood volume (hematocrit) - erythrocytes - most of cell mass - Leukocytes - body defense, granulocytes (neutrophils, eosinophils, basophils), granulocytes (lymphocytes, monocytes) - Thrombocytes - fragments of megakaryocytes

Serum

overlying extracellular fluid in blood after clot formation - blood removed from the vascular system will clot (fibrinogen is consumed by converting into insoluble fibrin) - the fluid portion after blood clot formation is serum - serum = plama - clotting factors