Human Blood Characteristics and Composition

Blood Characteristics

• Blood is a sticky, opaque fluid that is heavier and thicker than water.
• Oxygen-rich blood is scarlet red, while oxygen-poor blood is duller red or purple.
• Blood has a metallic, salty taste.
• The pH of blood is slightly alkaline, ranging from 7.35 to 7.45.
• Blood temperature is slightly higher than body temperature, around 38°C or 100.4°F.

Blood Volume

• A healthy adult has approximately 5-6 liters, or about 6 quarts, of blood.
• Blood accounts for approximately 8% of body weight.

Plasma Composition

• Plasma is primarily made up of water (90%).
• It is a straw-colored fluid containing many dissolved substances, including nutrients, salts (electrolytes), respiratory gases, hormones, plasma proteins, and waste products.

Plasma Proteins

• Plasma proteins are the most abundant solutes in plasma, primarily produced by the liver.
• Albumin is an essential blood buffer and contributes to osmotic pressure.
• Clotting proteins help to stop blood loss when a blood vessel is injured.
• Antibodies protect the body from pathogens.

Blood Composition Variability

• The composition of blood fluctuates as cells exchange substances with the blood.
• The liver produces more proteins when levels decline.
• The respiratory and urinary systems regulate blood pH to normal levels when it becomes too acidic or alkaline.
• Plasma distributes body heat.

Formed Elements

• Blood contains:
  • Erythrocytes (RBCs)
  • Leukocytes (WBCs)
  • Platelets

Erythrocytes (Red Blood Cells)

• Their main function is to carry oxygen.
• They lack a nucleus, contain few organelles, and have no mitochondria.
• Erythrocytes are essentially bags of hemoglobin (Hb).
• They are shaped like biconcave discs.
• Normal blood contains around 5 million RBCs per cubic millimeter (mm3) of blood.

Hemoglobin

• Hemoglobin is an iron-bearing protein that binds oxygen.
• Each hemoglobin molecule can bind to 4 oxygen molecules.
• An individual erythrocyte has 250 million hemoglobin molecules.
• Normal blood contains 12-18 g of hemoglobin per 100 milliliters (ml) of blood.

Anemia

• A decrease in the blood's oxygen-carrying capacity due to:
  • Lower than usual RBC count
  • Abnormal or deficient hemoglobin content in RBCs
• Sickle cell anemia (SCA) is caused by abnormally shaped hemoglobin.

Granulocytes

• Neutrophils:

  • The most common type of WBC.
  • Have a multilobed nucleus.
  • Cytoplasm stains pink and contains fine granules.
  • They are phagocytes that function at active sites of infection.
  • Numbers increase during infection.
  • There are 3,000-7,000 neutrophils per mm3 of blood (40-70 percent of WBCs).

• Eosinophils:

  • Have a nucleus that stains blue-red.
  • Have brick-red cytoplasmic granules.
  • Function to kill parasitic worms and participate in allergy attacks.
  • There are 100-400 eosinophils per mm3 of blood (1-4 percent of WBCs).

• Basophils:

  • The rarest of the WBCs.
  • Possess large histamine-containing granules that stain dark blue.
  • Contain heparin (an anticoagulant).
  • There are 20-50 basophils per mm3 of blood (0-1 percent of WBCs).

Agranulocytes

• Lymphocytes:

  • Have a large, dark purple nucleus.
  • Slightly larger than RBCs.
  • Reside in lymphatic tissues.
  • Play a crucial role in immune responses.
  • There are 1,500-3,000 lymphocytes per mm3 of blood (20-45 percent of WBCs).

• Monocytes:

  • The largest of the white blood cells.
  • Have a unique U- or kidney-shaped nucleus.
  • Function as macrophages when they migrate into tissues.
  • Important in fighting chronic infections.
  • There are 100-700 monocytes per mm3 of blood (4-8 percent of WBCs).

Platelets

• Fragments of megakaryocytes (multinucleate cells).
• Essential for the clotting process.
• Normal platelet count is 300,000 platelets per mm3 of blood.

Regulation of Red Blood Cell Production

• Normal blood oxygen levels are maintained by a feedback mechanism that regulates the rate of RBC production.
• When oxygen-carrying ability decreases (due to low RBC count, decreased hemoglobin, or reduced oxygen availability), the kidneys (and liver to a lesser extent) release erythropoietin.
• Erythropoietin stimulates red bone marrow to produce more RBCs, thereby increasing the blood's oxygen-carrying capacity.

This quiz explores the various characteristics and composition of human blood, including its appearance, volume, and the components of plasma. It covers essential details such as blood pH, temperature, and the role of plasma proteins in the body.