Blood Composition, Functions, and Vessels: A Detailed Look

Posted on Apr 6, 2025 in Biology

Blood: Composition and Functions

Blood is a viscous, salty-tasting liquid that circulates within the circulatory system. The average human body contains approximately 5.5 liters of blood.

Key Features of Blood

  • Carries nutrients and oxygen to all cells.
  • Collects waste products from cell metabolism.
  • Plays a crucial role in defending the body against infection.
  • Transports hormones, which are essential for controlling bodily functions.
  • Participates in regulating body temperature by distributing heat from warmer to cooler areas.

Components of Blood

  • Plasma: The yellowish fluid component of blood, primarily composed of water, contains dissolved mineral salts, nutrients, waste products, proteins, and hormones.
  • Blood Cells: There are three main types of blood cells:
    • Red Blood Cells (Erythrocytes): The most numerous blood cells, disc-shaped, and lack a nucleus. They contain hemoglobin, an iron-rich red pigment responsible for the blood’s color. Hemoglobin carries oxygen from the lungs to all body cells.
    • White Blood Cells (Leukocytes): Fewer in number than red blood cells, leukocytes are involved in defending the body against microbes. There are several types of leukocytes:
      • Granulocytes: Possess granular cytoplasm and a multi-lobed nucleus.
      • Agranulocytes: Lack granules in the cytoplasm and are divided into:
        • Lymphocytes
        • Monocytes
    • Platelets (Thrombocytes): Cell fragments containing substances that enable blood clotting.

Blood cells are produced in the red bone marrow.

Blood Vessels

Blood vessels form a network throughout the body, facilitating blood circulation.

  • Arteries: Carry blood away from the heart. As they branch out, they become progressively thinner, eventually forming arterioles.
  • Capillaries: Microscopic blood vessels that branch from arterioles and are found throughout the body’s tissues. Their walls consist of a single layer of flat cells, facilitating the exchange of substances.
  • Veins: Capillaries merge to form venules, which then converge into larger veins that carry blood back to the heart. Veins contain valves that prevent backflow of blood.