Physiology Quiz: Blood Composition and Thermoregulation

Body Temperature Regulation

• Water has high heat capacity, thermal conductivity, and heat of vaporization, which helps regulate body temperature
• Typical heat generation is 3000 kcal/day

Blood Composition

• Blood is a suspension of cells in plasma (carrier fluid)
• Cells make up 45% of blood, while plasma makes up 55%
• Red blood cells (erythrocytes) are 5x10^6/mL
• White blood cells (leukocytes) are 7x10^3/mL
• Platelets (thrombocytes) are 3x10^5/mL

Blood Plasma

• Plasma is a straw-colored clear liquid that contains 90% water
• 7% of plasma is made up of plasma proteins, which are created in the liver and confined to the bloodstream
• Plasma proteins include:
  • Albumin, which maintains blood osmotic pressure
  • Immunoglobulins, which are antibodies that bind to foreign substances called antigens
  • Fibrinogen, which is involved in blood clotting
• Other substances in plasma include nutrients, electrolytes, gases, hormones, and waste products

Functions of Plasma Proteins

• Coagulation of blood
• Defense mechanism
• Transport mechanism
• Maintenance of osmotic pressure
• Acid-base balance
• Providing viscosity to blood
• Providing suspension stability of RBC

Formed Elements of Blood

• Red blood cells (RBC)
• White blood cells (WBC)
  • Granular leukocytes: neutrophils (60-70%), eosinophils (1-4%), and basophils (1%)
  • Agranular leukocytes: lymphocytes (20-40%) and monocytes (3-10%)
• Platelets (special cell fragments)

Functions of RBC

• Transport oxygen from lungs to tissues
• Transport carbon dioxide from tissues to lungs
• Hemoglobin acts as a buffer and regulates hydrogen ion concentration (acid-base balance)
• Carry blood group antigens and Rh factor

Functions of Neutrophils

• First line of defense against invading microorganisms
• Powerful and effective killer machine with enzymes like protease, elastase, metalloproteinase, and NADPH oxidase
• Secrete Platelet Aggregation Factor (PAF) to accelerate platelet aggregation during injury

Functions of Eosinophils

• Secrete lethal substances to destroy foreign proteins and parasites
• Secrete eosinophil peroxidase, major basic protein, eosinophil cationic protein, and eosinophils derived neurotoxin

Functions of Basophils

• Release histamine, heparin, hyaluronic acid, and proteases from basophil granules
• Histamine causes acute hypersensitivity reactions and vascular changes
• Heparin prevents intravascular blood clotting
• Hyaluronic acid is necessary for deposition of ground substances in basement membrane
• Basophils have IgE receptors, which are involved in hypersensitivity reactions

Functions of Platelets

• Blood clotting
• Clot retraction
• Defense mechanism