Transport in Animals

Introduction to Transport in Animals

  • Animals need a transport system to deliver nutrients and remove waste.
  • Small, single-celled organisms can exchange gases directly with their surroundings.
  • Larger organisms require specialised circulatory systems due to their size and complexity.

Types of Circulatory Systems

  • Open circulatory system: Found in insects; blood directly bathes organs within a cavity.
  • Closed circulatory system: Blood is confined to vessels; found in humans and most mammals.

Components of the Mammalian Circulatory System

  • Heart: The muscular organ responsible for pumping blood throughout the body.
  • Blood vessels: Includes arteries, arterioles, capillaries, venules, and veins.
  • Blood: Made up of plasma, red and white blood cells, and platelets.

The Heart

  • The heart has two upper chambers (atria) and two lower chambers (ventricles).
  • The heart contracts rhythmically, pumping blood around the body; this is known as the cardiac cycle.
  • Cardiac muscle is involuntary and never tires.

The Blood Vessels

  • Arteries carry blood away from the heart, and have thick, muscular walls to withstand high pressure.
  • Capillaries are tiny, one cell thick vessels for material exchange between blood and tissues.
  • Veins carry blood back to the heart, have thinner walls than arteries, and valves to prevent backflow.

The Blood

  • Red blood cells carry oxygen, using a molecule called haemoglobin.
  • White blood cells fight infections and form part of the immune system.
  • Platelets help blood to clot and stop bleeding.
  • Plasma, the yellow liquid in which cells and platelets are suspended, carries various dissolved substances.

Blood Flow and the Cardiac Cycle

  • Double circulatory system: In mammals, blood passes through the heart twice in one complete circuit: once for pulmonary circulation (to the lungs), and once for systemic circulation (to the rest of the body).
  • The cardiac cycle consists of diastole (relaxation and filling) and systole (contraction and emptying).

Gaseous Exchange

  • Respiration is the process by which oxygen is used to release energy from food. Carbon dioxide is produced as a waste product.
  • Gaseous exchange happens in the lungs, where these gases move between the air and the blood.

Comparing Circulatory Systems

  • The advantages of a double circulatory system over a single circulatory system include higher blood pressure, more efficient oxygen delivery, and faster circulation.