The human gas exchange

• Most animals and plants consist of different types of cells organised as tissues, organs and systems.
• Gaseous exchange, the exchange of gases between the alveoli and blood in the capillaries, occurs across a short diffusion path, the walls of blood capillaries and alveoli being just one cell thick.
• The bronchi split into smaller branches and then into smaller tubes called bronchioles.
• The alveoli are lined with a thin film of moisture, allowing gases to dissolve and making the diffusion path even smaller.
• The trachea, or windpipe, is the tube that leads from the mouth towards the lungs.
• The trachea branches into two bronchi, which are the two major air tubes in the lungs, one bronchus to each lung.
• The ventilation of the lungs and the blood flow through the surrounding capillaries create steep concentration gradients for gases to diffuse.
• Rings of cartilage in the walls of the trachea help to keep it open as air is drawn in.
• Each bronchiole ends in a cluster of microscopic air sacs called alveoli.
• The human respiratory system is a body system adapted for efficient gas exchange.
• The human lungs provide an exchange surface where substances, such as gases, food substances, and wastes, are moved across membranes.
• The lungs are adapted for absorbing oxygen into the blood and transferring carbon dioxide from the blood into the lungs and then the air.
• The respiratory system allows air to pass in and out of the body and facilitates efficient gas exchange.
• The lungs are enclosed in the thorax and protected by 12 pairs of ribs.
• The ribs are moved by intercostal muscles, and there is a muscular diaphragm below the lungs.
• The lungs are sealed within two airtight pleural membranes.