Transport in Animals

• Circulatory system


  The transport system in animals
• Single circulatory system


  • Blood travels one circuit; blood flows through the heart and is pumped around the body before returning to the heart. Found in fish
• Double circulatory system


  • Blood flows through the heart twice in two circuits. Blood is pumped from the heart to the lungs before returning to the heart. It is then pumped around the body, after which it returns to the heart again. Found in mammals
• Open circulatory system


  • Transport medium pumped by the heart is not contained within vessels, but moves freely. The transport fluid comes into direct contact with the cells. Found in invertebrates, e.g. insects
• Closed circulatory system


  • Blood pumped by the heart is contained within blood vessels. The blood does not come into direct contact with the cells. Found in animals, e.g. Vertebrates
• Blood


  The transport medium in the mammalian circulatory system. It consists of plasma, red blood cells, white blood cells and platelets
• Artery


  • Carries blood away from the heart to the tissues, under high pressure. The walls contain collagen, smooth muscle and elastic fibres
• Arteriole


  • Connects the arteries and capillaries. The walls contain large amounts of smooth muscle, some elastic fibres and some collagen
• Vein


  • Carries blood towards the heart under low pressure. They have a wide lumen, a smooth inner lining and valves. The walls contain large amounts of collagen, smooth muscle and little elastic fibre
• Venule


  • Connects the capillaries and veins. The walls contain small amounts of collagen and smooth muscle
• Capillaries


  • Microscopic blood vessels that form a large network through the tissues of the body and connect the arterioles to the venules. They are the site of exchange of substances between the blood and the tissues
• Tissue fluid


  The fluid that surrounds the cells of animals. It has the same composition of plasma but does not contain red blood cells or plasma proteins
• Lymph


  Modified tissue fluid that drains into the lymphatic system. It carries less oxygen and fewer nutrients than tissue fluid, but also contains fatty acids
• Plasma


  The main component of the blood that carries red blood cells. It is a yellow liquid that contains proteins, nutrients, mineral ions, hormones, dissolved gases and waste
• Aorta


  • The artery that takes oxygenated blood away from the heart to the body
• Inferior vena cava


  • The vein that returns deoxygenated blood to the heart from the lower body
• Superior vena cava


  • The vein that returns deoxygenated blood to the heart from the head and upper body
• Atrioventricular (AV) valves


  • The valves found between the atria and ventricles. They prevent the backflow of blood from the ventricles into the atria. There are two types: bicuspid and tricuspid
• Bicuspid valves


  • The atrioventricular valves found between the left atrium and left ventricle
• Tricuspid valves


  • The atrioventricular valves found between the right atrium and right ventricle
• Pulmonary arteries


  • The arteries that carry deoxygenated blood away from the heart to the lungs
• Pulmonary veins


  • The veins that carry oxygenated blood from the lungs to the heart
• Semilunar valves


  • A pair of valves found between the ventricles and arteries. They prevent the backflow of blood from the arteries into the ventricles
• Septum


  • The wall of muscle which separates the left side of the heart from the right side of the heart, preventing oxygenated and deoxygenated blood from mixing
• Myogenic


  Describes cardiac muscle tissue that initiates its own contraction, without outside stimulation from nervous impulses
• Cardiac cycle


  Sequence of events involved in one complete contraction and relaxation of the heart. There are three stages: atrial systole, ventricular systole and diastole
• Atrioventricular node (AVN)


  • A group of cells located between the atria that slow down the wave of excitation and pass it between the ventricles, along the bundle of His
• Sinoatrial node (SAN)


  • A group of cells in the wall of the right atrium that generate electrical activity, causing the atria to contract. The SAN is often referred to as the heart's pacemaker
• Purkyne tissue


  • Specialised cardiac muscle fibres which make up the bundle of His and conduct the wave of excitation through the septum, from the AVN down to the apex of the ventricles
• Bundle of His


  • A collection of Purkyne fibres which run from the AVN down to the apex of the ventricles
• Atrial systole


  The stage of the cardiac cycle in which the atria contract, pushing blood into the ventricles. The AV valves are pushed open fully and the atria are emptied of blood
• Diastole


  The stage of the cardiac cycle in which the heart muscle relaxes. The atria and ventricles fill with blood
• Ventricular systole


  The stage of the cardiac cycle in which the ventricles contract, pushing blood into the arteries. The semi-lunar valves are pushed open fully
• Heart rate


  The number of times the heart beats in one minute
• Hydrostatic pressure


  The pressure exerted on the sides of a vessel by a fluid
• Cardiac output


  The volume of blood pumped by the heart through the circulatory system in one minute. It is calculated using the equation: cardiac output = heart rate × stroke volume
• Electrocardiogram (ECG)


  A technique used to indirectly measure the spread of electrical activity through the heart by measuring tiny changes in the skin's electrical conductivity. This produces a trace which is used to detect abnormalities in heart rhythm
• Stroke volume


  The volume of blood pumped by the left ventricle of the heart in a single contraction
• Atrial fibrillation


  An arrhythmia that involves the rapid contraction of the atria, preventing complete ventricular filling
• Ectopic heartbeat


  Additional heartbeats outside of the normal heart rhythm