Organisation-The cardiovascular respiratory system

• Adaptations for gas exchange in the lungs:

  • Large surface area to allow faster diffusion of gases across the surface
  • Thin walls to ensure diffusion distances remain short
  • Good ventilation with air to maintain diffusion gradients
  • Good blood supply (dense capillary network) to maintain a high concentration gradient for faster diffusion
• Structures and functions of the lungs:

  • Each lung contains around 250 - 300 million alveoli
  • Total surface area of each lung is around 70m^2
• Ventilation of the lungs:

  • Air passes through the trachea, bronchus (bronchi), bronchiole, and alveoli for gas exchange
  • The diaphragm controls ventilation in the lungs
  • During inhalation, the external intercostal muscles contract to increase the volume of the chest cavity, drawing air in
  • During exhalation, the external intercostal muscles relax to decrease the volume of the chest cavity, forcing air out
  • Internal intercostal muscles work during forced exhalation to decrease thorax volume more, allowing for more forceful air expulsion
• Air enters the lungs through the mouth and nose
• Air passes into the trachea, which is a big central tube
• The trachea splits into two tubes called bronchi, which go to the left and right lungs
• Each bronchus splits into lots of smaller tubes called bronchioles, which move through the lungs
• Each bronchiole ends in lots of small air sacs called alveoli
• Alveoli are specialised for gas exchange
• The diaphragm is a flat sheet of muscle that separates the abdomen from the thorax
• Ribs form a cage around the lungs and expand and relax to aid ventilation
• Intercostal Muscles (Internal and External) are muscles that lie between the ribs
• The human heart is part of a double circulatory system
• The circulatory system consists of blood vessels, a pump (the heart), and valves that maintain a one-way flow of blood around the body
• The heart has four chambers separated into two halves
• The right side of the heart pumps blood to the lungs for gas exchange (pulmonary circuit)
• The left side of the heart pumps blood under high pressure to the body (systemic circulation)
• The benefits of a double circulatory system include reducing the speed of blood flow through small capillaries in the lungs and supplying cells with oxygenated blood more quickly
• The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs
• The left side of the heart receives oxygenated blood from the lungs and pumps it to the body
• Blood is pumped towards the heart in veins and away from the heart in arteries
• The chambers at the top of the heart are the atria, and the chambers at the bottom are the ventricles
• The heart is made of a special type of cardiac muscle tissue that does not fatigue like skeletal muscle
• Pathway of blood through the heart
• Deoxygenated blood enters the heart via the vena cava into the right atrium
• Blood flows down through atrioventricular valves into the right ventricle
• Oxygenated blood returns to the heart via the pulmonary vein into the left atrium
• Blood flows down through atrioventricular valves into the left ventricle
• When the ventricles contract, blood travels up through the aorta to the rest of the body
• Adaptations of the heart
• The walls of the ventricles are thicker than those of the atria to pump blood out of the heart at higher pressure
• The left ventricle wall is thicker than the right ventricle to pump blood at high pressure around the entire body
• The heart has two sets of valves to prevent backflow of blood: atrioventricular valves and semilunar valves
• The septum separates the two sides of the heart to prevent the mixing of deoxygenated and oxygenated blood
• The heart has coronary arteries that supply oxygenated blood to the heart tissue
• Heart Rate
• The natural resting heart rate is controlled by a group of cells located in the right atrium called the pacemaker
• The pacemaker coordinates the contraction of the heart muscle and regulates the heart rate
• Faster heart contractions deliver oxygenated blood more quickly around the body
• Artificial pacemakers are used to correct irregularities in the heart rate