Transport System in Humans

  • Blood Composition

    • Blood is a vital fluid in the human body, composed of several key components:

    • Red Blood Cells (RBCs): Responsible for transporting oxygen from the lungs to the body and returning carbon dioxide from the body back to the lungs.

    • White Blood Cells (WBCs): Part of the immune system, tasked with fighting infections and other diseases.

    • Platelets: Cell fragments that play a crucial role in blood clotting, preventing excessive bleeding when injuries occur.

    • Plasma: Around 55% of blood volume, appears as a light straw-colored liquid. It carries nutrients, hormones, and proteins.

      Plasma: The liquid portion of blood, making up about 55% of its volume, which contains water, electrolytes, proteins, hormones, and waste products.

      When blood is subjected to centrifugation, it separates into two distinct

      • Blood Cells: Comprising about 45% of blood volume, this fraction includes RBCs, WBCs, and platelets, playing pivotal roles in oxygen transport, immune response, and clotting mechanisms.

        layers:

  • Role of Blood Components

    • Centrifugation of Blood

    • Plasma Functions:

    • The plasma serves multiple essential functions, primarily focused on transport:

      • Carries carbon dioxide back to the lungs for exhalation.

      • Transports digested nutrients from the gastrointestinal tract to cells throughout the body.

      • Distributes urea, a waste product from protein metabolism, to the kidneys for excretion.

      • Carries hormones from endocrine glands to target organs and tissues.

      • Helps regulate body temperature by distributing heat throughout the body.

    • Red Blood Cells (Erythrocytes):

    • Their primary function is oxygen transport via haemoglobin, which binds oxygen in the lungs and releases it in tissues.

    • Key adaptations enhance their function:

      • Biconcave Shape: This increases the surface area-to-volume ratio, facilitating gas exchange.

      • Absence of Nucleus: Provides more internal space for haemoglobin, maximizing oxygen-carrying capacity.

      • Count: Approximately 5,000,000 RBCs per cubic millimeter of blood, indicating a highly efficient transport system.

  • White Blood Cells

    • Functions include:

    • Phagocytes: Comprising about 70% of WBCs, these cells engulf and digest pathogens through phagocytosis, using digestive enzymes to neutralize threats.

    • Lymphocytes: Accounting for roughly 25% of WBCs; they are vital in producing antibodies that target specific pathogens and antigens.

      • Antibodies function to neutralize toxins, cause bacteria to lyse, or clump pathogens together for easier detection by phagocytes.

      • Certain lymphocytes develop into memory cells, which confer accelerated responses to previously encountered pathogens.

    • Vaccination:

    • A strategy that mimics a natural infection, stimulating immune responses and resulting in the formation of memory cells, enabling faster antibody production upon subsequent exposures to the pathogen.

  • Platelets

    • Function primarily in hemostasis (the process of blood clotting).

    • They aggregate at sites of vascular injury, adhering to the damaged vessel wall and each other, producing fibrin from fibrinogen to form a stable clot.

    • This process is crucial for preventing excessive blood loss and aiding in wound healing.

  • Heart Structure

    • The heart is a muscular organ comprised of four chambers:

    • Right Atrium: Receives deoxygenated blood from the body.

    • Right Ventricle: Pumps deoxygenated blood to the lungs for oxygenation.

    • Left Atrium: Receives oxygenated blood from the lungs.

    • Left Ventricle: Responsible for pumping oxygenated blood out to the entire body.

    • Valves ensure unidirectional blood flow:

      • Tricuspid Valve: Located on the right side, prevents backflow into the atrium when the ventricle contracts.

      • Bicuspid (Mitral) Valve: On the left side, prevents backflow from the ventricle to the atrium.

      • Semi-lunar Valves: Located at the ventricles, prevent backflow into the heart after blood is pumped into arteries.

    • The cardiac cycle is a series of events that consist of:

    • Blood entering the atria, which contract to push blood into the ventricles.

    • Ventricular contraction closing the atrial valves and forcing blood into the arteries.

    • A relaxation phase allowing the heart chambers to refill with blood.

  • Factors Affecting Heart Rate

    • Exercise:

    • Increases the demand for oxygen and the removal of carbon dioxide, resulting in elevated heart rates to meet metabolic needs.

    • Sensors located in arteries send feedback to the brain, which adjusts heart rate to maintain homeostasis.

    • Adrenaline:

    • The hormone adrenaline, released during stress or physical excitement, accelerates heart rate by signalling the heart to pump more forcefully, thus delivering more oxygen and glucose to muscles.

  • Coronary Heart Disease

    • A condition characterized by the narrowing of coronary arteries due to atherosclerosis, which can result in heart attacks from insufficient blood flow to the heart muscle.

    • Risk factors include:

    • Smoking: Contributes to artery damage and plaque formation.

    • High Cholesterol Diet: Increases plaque buildup in the arteries.

    • High Blood Pressure: Exerts extra force on artery walls, damaging them.

    • Family History: Gene predisposition can increase individual risk.

    • Lack of Exercise: Sedentary lifestyle contributes to obesity and cardiovascular strain.

  • Blood Vessel Types

    • Arteries:;

    • Transport oxygenated blood away from the heart at high pressure, characterized by thick, elastic walls to withstand the pressure.

    • Veins:

    • Carry deoxygenated blood back to the heart; thinner walls and valves prevent backflow, adapting to lower pressure conditions.

    • Capillaries:

    • Microscopic vessels facilitating the exchange of materials between blood and tissues; walls are only one cell thick for optimal diffusion.

    • Collectively, blood vessels form an extensive network in the body, totaling approximately 100,000 miles in length, significantly impacting overall circulation and health.