Circulation and Gas Exchange Animal Physiology Circulation and Gas Exchange Mr G Davidson

The Heart The function of the heart is to pump blood round the body. The blood is transported in blood vessels. The structure of the heart is ideally suited to its function. February 23, 2019 Mr G Davidson

The Heart Right atrium Left atrium Right ventricle Left ventricle Cardiac muscle February 23, 2019 Mr G Davidson

The Heart The heart consists of four chambers. It is made of cardiac muscle. The two upper chambers are called atria – the left atrium and the right atrium. February 23, 2019 Mr G Davidson

The Heart The two lower chambers are called ventricles – the left ventricle and the right ventricle. The atria both receive blood back into the heart while the ventricles both pump blood out of the heart. The heart has four valves to ensure that blood always flows in the one direction. February 23, 2019 Mr G Davidson

The heart semi-lunar valve atrio-ventricular valve February 23, 2019 Mr G Davidson

The Heart Blood enters the heart into the atria. When the atria contract, the blood moves down through the atrio-ventricular (AV) valves into the ventricles. February 23, 2019 Mr G Davidson

The Heart The valves prevent the blood flowing back up into the atria when the ventricles contract. When the ventricles contract the blood moves up through the semi-lunar (SL) valves. These valves prevent the backflow of blood into the ventricles. February 23, 2019 Mr G Davidson

The Heart All blood must pass through the heart twice in each circulation. Blood from all parts of the body enters the heart through the main veins called the vena cava. This blood enters the right atrium and carries deoxygenated blood. February 23, 2019 Mr G Davidson

The Heart It then passes through the right AV valve into the right ventricle. From here it is pumped into the pulmonary arteries through the SL valve, where it will go to the lungs. In the lungs the blood loses its carbon dioxide and gains fresh oxygen before entering the pulmonary veins. February 23, 2019 Mr G Davidson

The Heart This oxygenated blood now returns to the heart where it enters the left atrium. When the left atrium contracts it is forced through the left AV valve into the left ventricle. February 23, 2019 Mr G Davidson

The Heart The left ventricle then pumps the blood through the SL valve into the aorta, which is the main artery, which will then distribute it throughout the body. The wall of the left ventricle is very thick since it has to pump blood all round the body. The wall of the right ventricle is less thick since it pumps blood only to the lungs. February 23, 2019 Mr G Davidson

The Heart Pulmonary artery Aorta Vena cava Pulmonary vein February 23, 2019 Mr G Davidson

The Heart The heart wall is made of cardiac muscle and also requires its own blood supply. The blood vessels which do this are called the coronary arteries. February 23, 2019 Mr G Davidson

The Heart Coronary artery February 23, 2019 Mr G Davidson

The Heart These spread out over the surface of the heart and deliver fresh oxygen and glucose to all the muscle cells. Coronary veins return the blood to the vena cava. If the coronary arteries narrow or become blocked in any way, this can result in a heart attack. February 23, 2019 Mr G Davidson

Blood Vessels There are three main types of blood vessel – arteries, veins and capillaries. Arteries carry blood away from the heart. Veins carry blood back to the heart. Capillaries connect arteries to veins and this is where the exchange of essential materials takes place. February 23, 2019 Mr G Davidson

Arteries Arteries have thick muscular walls. This allows them to withstand the pressure created by the heart. Each time the heart beats, blood is forced along the arteries, and this can be felt as your pulse. February 23, 2019 Mr G Davidson

Veins Veins have thinner walls than arteries but a wider cavity. This is because the blood is now at a much lower pressure. Veins also contain valves all along their length to prevent the backflow of blood. February 23, 2019 Mr G Davidson

Capillaries Capillaries are microscopic blood vessels. Their walls are only one cell thick. This allows them to exchange essential materials between the blood and the body cells. Materials such as glucose, oxygen, carbon dioxide, etc. February 23, 2019 Mr G Davidson

Circulatory System Pulmonary vein Pulmonary artery Vena cava Aorta Hepatic artery Hepatic vein Mesenteric artery Hepatic portal vein Renal artery Renal vein February 23, 2019 Mr G Davidson

Gas Exchange Gas exchange occurs in the lungs. When we breathe in (inhale) oxygen from the air passes from the lungs into the blood and carbon dioxide passes from the blood into the lungs. We then breathe this air out (exhale) before inhaling fresh air. February 23, 2019 Mr G Davidson

Structure of the Lungs The lungs are found in the chest cavity. Air passes into the lungs from the trachea (windpipe) which splits into 2 bronchi, one to each lung. Each bronchus then splits into smaller tubes called bronchioles. These bronchioles terminate in tiny air sacs called alveoli. February 23, 2019 Mr G Davidson

Lungs Trachea Rib Bronchus Bronchiole Diaphragm February 23, 2019 Next Slide for detailed view of this area Diaphragm February 23, 2019 Mr G Davidson

Alveoli Bronchiole Blood Capillary Alveolus February 23, 2019 Mr G Davidson

Gas Exchange There are so many alveoli that they provide a huge surface area for the gases to be exchanged. The lining of each alveolus is very thin and moist. February 23, 2019 Mr G Davidson

Gas Exchange Each alveolus is surrounded by a dense network of blood capillaries. Blood arrives in the lungs from the body and is said to be deoxygenated. Oxygen diffuses through the thin lining of the alveolus into the blood capillary which is only one cell thick. This is because the concentration of oxygen in the alveolus is higher than in the blood. February 23, 2019 Mr G Davidson

Gas exchange Carbon dioxide diffuses in the opposite direction. This is because the concentration of CO2 in the blood from the body is higher than in the alveoli. The blood now leaving the lungs is said to be oxygenated. February 23, 2019 Mr G Davidson

Gas Exchange February 23, 2019 Mr G Davidson

Features which make gas exchange more efficient. Function Lining very thin Allows rapid diffusion Lining moist Allows oxygen to dissolve Large surface area Allows more oxygen to be absorbed Dense network of capillaries Allows blood to absorb oxygen February 23, 2019 Mr G Davidson