The gaseous exchange system links the circulatory system with the atmosphere. It is adapted to:
Lungs and System of Airways
The lungs are the site of gaseous exchange between air and blood and they present a huge surface area to the air that flows in and out. The lungs are ventilated with air which passes through a branching system of airways. Leading from the throat to the lungs is the trachea. At the base of the trachea are two bronchi, which subdivide and branch exclusively forming a bronchial tree in each lung. Cartilage in the trachea and bronchi keeps these airways open and air resistance low, and prevents from collapsing or bursting as the air pressure changes during breathing.
Warming and Cleaning the Air
As air flows through the nose and the trachea it is warmed to body temperature and moistened by evaporation from the lining, so protecting the delicate surfaces inside the lugs from desiccation (drying out). Protection is also needed against the suspended matter carried in the air, which may include dust, pollen, bacteria, fungal spores, sand, and viruses. The larger particle are caught by nose hair and mucus lining. In the trachea and bronchi, the mucus is produced by the goblet of the ciliated epithelium. The upper part of each goblet cell is swollen mucin droplets which have been secreted by the cell. Mucus is a slimy solution of mucin, which is composed of glycoproteins with many carbohydrate chains. The particles that are not caught by mucus and nose hairs are scavenged by macrophages (white blood cells that patrol surfaces of the airways.
- Clean and warm the air that enters during breathing;
- Maximize the surface area for diffusion of oxygen and carbon dioxide between the blood and atmosphere;
- Minimize the distance for this diffusion;
- Maintain adequate gradients for this diffusion.
Lungs and System of Airways
The lungs are the site of gaseous exchange between air and blood and they present a huge surface area to the air that flows in and out. The lungs are ventilated with air which passes through a branching system of airways. Leading from the throat to the lungs is the trachea. At the base of the trachea are two bronchi, which subdivide and branch exclusively forming a bronchial tree in each lung. Cartilage in the trachea and bronchi keeps these airways open and air resistance low, and prevents from collapsing or bursting as the air pressure changes during breathing.
Warming and Cleaning the Air
As air flows through the nose and the trachea it is warmed to body temperature and moistened by evaporation from the lining, so protecting the delicate surfaces inside the lugs from desiccation (drying out). Protection is also needed against the suspended matter carried in the air, which may include dust, pollen, bacteria, fungal spores, sand, and viruses. The larger particle are caught by nose hair and mucus lining. In the trachea and bronchi, the mucus is produced by the goblet of the ciliated epithelium. The upper part of each goblet cell is swollen mucin droplets which have been secreted by the cell. Mucus is a slimy solution of mucin, which is composed of glycoproteins with many carbohydrate chains. The particles that are not caught by mucus and nose hairs are scavenged by macrophages (white blood cells that patrol surfaces of the airways.
Alveoli
At the end of the pathway between the atmosphere and the bloodstream are the alveoli (shown in the picture to the left). These have a very thin epithelial lining and are surrounded by many blood capillaries carrying deoxygenated blood. The short distance between air and blood mean that oxygen and carbon dioxide can be exchanged by diffusion. Any of the many tiny air sacs in the lungs where the exchange of oxygen and carbon dioxide takes place are also known as alveoli. Alveolar walls contain elastic fibres which stretch during breathing and recoil during expiration to help force air out.
Breathing Rate and Heart Rate
Breathing Rate and Depth
Breathing refreshes the air in the alveoli so that the concentrations of oxygen and carbon dioxide within them remain constant whatever our level of activity. It is impossible to empty the lungs completely and, even when the chest is compressed during forced exhalation, there is still air remaining in the alveoli and in the airways. This is the volume is the residual volume. As exercise becomes harder the depth of breathing increases. The effect of exercise on breathing is measured by calculating the ventilation rate. This is the total volume of air moved into the lungs in one minute.
Pulse Rate
When the ventricles of the heart contract, a surge of blood flows into the aorta and the pulmonary arteries under pressure. The volume of blood pumped out from each ventricle during each contraction is the stroke volume. The total volume pumped out per minute is the cardiac output. The stretch and subsequent recoil of the aorta and the arteries travels as a wave along all the arteries. This is the pulse rate is identical to the heart rate. It is usually measured at the wrist where the radial artery passes over a bone, or at the carotid artery in the neck and is counted for 30 seconds with the person sitting still.
Blood Pressure
During systole in the cardiac cycle both ventricles contract. Contraction of the left ventricle forces oxygenated blood out of the heart to supply the body. The maximum arterial pressure during this active stroke is the stroke pressure and this is the pressure at which blood leaves the heart through the aorta. The minimum pressure in the arteries is the diastolic pressure. The value of the diastolic pressure reflects the resistance of the small arteries and capillaries to blod flow and therefore the load against which the heart must work. Blood pressures are determined using a sphygmomanometer. It is conventional to give the values in millimeters of mercury even if the equipment is digital and computerized. Blood pressure is the measure of how hard the heart is working to pump blood around the body.
Hypertension
If systolic and diastolic blood pressures are high at rest, this indicates that the heart is working too hard at pumping blood, this condition is known as hypertension. In 90% of cases the exact cause of hypertension is unknown, but the condition is known to be closely linked to:
Breathing refreshes the air in the alveoli so that the concentrations of oxygen and carbon dioxide within them remain constant whatever our level of activity. It is impossible to empty the lungs completely and, even when the chest is compressed during forced exhalation, there is still air remaining in the alveoli and in the airways. This is the volume is the residual volume. As exercise becomes harder the depth of breathing increases. The effect of exercise on breathing is measured by calculating the ventilation rate. This is the total volume of air moved into the lungs in one minute.
Pulse Rate
When the ventricles of the heart contract, a surge of blood flows into the aorta and the pulmonary arteries under pressure. The volume of blood pumped out from each ventricle during each contraction is the stroke volume. The total volume pumped out per minute is the cardiac output. The stretch and subsequent recoil of the aorta and the arteries travels as a wave along all the arteries. This is the pulse rate is identical to the heart rate. It is usually measured at the wrist where the radial artery passes over a bone, or at the carotid artery in the neck and is counted for 30 seconds with the person sitting still.
Blood Pressure
During systole in the cardiac cycle both ventricles contract. Contraction of the left ventricle forces oxygenated blood out of the heart to supply the body. The maximum arterial pressure during this active stroke is the stroke pressure and this is the pressure at which blood leaves the heart through the aorta. The minimum pressure in the arteries is the diastolic pressure. The value of the diastolic pressure reflects the resistance of the small arteries and capillaries to blod flow and therefore the load against which the heart must work. Blood pressures are determined using a sphygmomanometer. It is conventional to give the values in millimeters of mercury even if the equipment is digital and computerized. Blood pressure is the measure of how hard the heart is working to pump blood around the body.
Hypertension
If systolic and diastolic blood pressures are high at rest, this indicates that the heart is working too hard at pumping blood, this condition is known as hypertension. In 90% of cases the exact cause of hypertension is unknown, but the condition is known to be closely linked to:
- Excessive alcohol intake
- Smoking
- Obesity
- Too much salt in the diet
- Genetic factors