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.