Transport in animals 3.1.2

• Circulatory systems

  Can be open (e.g. in insects) or closed (e.g. in fish and mammals where the blood is confined to blood vessels only)
• Closed circulatory systems

  • Can be single (heart with two chambers, blood passes through once per circuit) or double (heart with four chambers, blood passes through twice per circuit)
• Arteries

  Adapted to carry blood away from the heart, thick walled to withstand high blood pressure, contain elastic tissue and smooth muscle to vary blood flow, lined with smooth endothelium to reduce friction
• Arterioles

  Branch off arteries, have thinner and less muscular walls, feed blood into capillaries
• Capillaries

  Smallest blood vessels, site of metabolic exchange, only one cell thick for fast exchange of substances
• Venules

  Larger than capillaries but smaller than veins
• Veins

  Carry blood from the body to the heart, contain a wide lumen to maximise volume, thin walled as blood is under low pressure, contain valves to prevent backflow
• Tissue fluid

  Liquid containing dissolved oxygen and nutrients, enables exchange of substances between blood and cells
• Formation of tissue fluid


  1. Hydrostatic pressure forces blood fluid out of capillaries

  2. Only small substances can escape through capillary wall

  3. Osmotic pressure pushes some fluid back into capillaries

  4. Remaining fluid carried by lymphatic system
• Lymphatic system


  Contains lymph fluid similar to tissue fluid but with less oxygen and nutrients, filters out bacteria and foreign material with help of lymphocytes
• Myogenic heart


  Can initiate its own contraction, sinoatrial node is the pacemaker
• Cardiac cycle


  1. Atrial systole (atria contract, blood flows into ventricles)

  2. Ventricular systole (ventricles contract, blood leaves heart)

  3. Cardiac diastole (atria and ventricles relax, blood drawn in)
• Haemoglobin


  Water soluble globular protein with two alpha and two beta polypeptide chains, each containing a haem group that can bind oxygen
• Partial pressure of oxygen

  Affects the affinity of haemoglobin for oxygen (higher pressure = higher affinity)
• Oxygen saturation of haemoglobin

  Affects its affinity for oxygen (higher saturation = higher affinity)
• Fetal haemoglobin


  Has higher affinity for oxygen than adult haemoglobin to absorb oxygen at lower partial pressures
• Partial pressure of carbon dioxide


  Decreases the affinity of haemoglobin for oxygen (Bohr effect)
• The circulatory system is responsible for the transportation of oxygen, nutrients, hormones, waste products, and other substances throughout the body.
• Blood vessels include arteries (carry blood away from heart), veins (return blood to heart), and capillaries (smallest blood vessels that connect arterioles and venules).
• Arteries have thick walls with elastic tissue to resist high pressure during contraction of the heart.
• Blood carries out these functions by flowing through arteries, capillaries, veins, and the heart.
• It consists of the heart, blood vessels, and blood.
• Capillary beds are networks of tiny blood vessels where exchange between tissues and blood occurs through diffusion.
• Arteries carry blood away from the heart under high pressure.
• Arterial blood carries oxygenated blood away from the lungs or heart, while venous blood returns deoxygenated blood back to the lungs or heart.
• Veins have valves to prevent backward flow of blood.
• Veins have thinner walls compared to arteries due to low pressure during relaxation of the heart.
• Capillary beds are networks of tiny blood vessels where exchange between cells occurs.
• Capillaries are small and thin-walled vessels where exchange between tissues and blood occurs through diffusion.
• Oxygen diffuses into cells and carbon dioxide diffuses out of cells.
• Veins return blood to the heart at low pressure.
• Heart rate refers to the number of times the heart beats per minute.
• Veins carry deoxygenated blood back to the heart.
• Plasma transports water-soluble materials such as glucose, amino acids, urea, salts, and hormones.
• The circulatory system is responsible for delivering nutrients, hormones, gases, and waste products throughout the body.
• The circulatory system is responsible for delivering oxygen, nutrients, hormones, and other substances throughout the body while removing waste products such as carbon dioxide.
• Heart pumps blood around the body.
• The circulatory system also helps regulate body temperature, maintain pH balance, and defend against pathogens.
• Blood transports these substances by dissolving them into its fluid component (plasma) or binding them to red blood cells.
• The circulatory system is responsible for delivering nutrients, hormones, and waste products throughout the body.