The lungs are a pair of structures made up of branched tubules called bronchioles which end in tiny air sacs called alveoli
The trachea is a flexible tube that leads to the buccal(mouth) and nasal cavities through which air can flow to and from the external environment.It is supported by C-rings or incomplete rings of cartilage. The walls are made up smooth muscle lined with ciliated epithelial cells and goblet cells. Goblet cells secrete mucus which traps bacteria and dust particles.The trachea branches into two bronchi.They are lined with ciliated epithelia and goblet cells and produce mucus to trap dust particles. The mucus is then wafted up to the throat by cilia and then swallowed.The acid in the stomach then kills the bacteria.Larger bronchi are supported by incomplete rings of cartilage. The amount of cartilage is reduced as the bronchi get smaller.Each bronchus divides into many bronchioles. These are not supported by cartilage. The walls are made of smooth muscle lined with epithelial cells. They constrict to control the flow of air into the alveoli.The alveoli are tiny air sacs 100-300 μm in diameter made up of a single epithelial layer. There are collagen and elastic fibres between the alveoli. The elastic fibres allow the alveoli to stretch when breathing in and recoil to expel the air.
The trachea is a flexible tube that leads to the buccal(mouth) and nasal cavities through which air can flow to and from the external environment.It is supported by C-rings or incomplete rings of cartilage. The walls are made up smooth muscle lined with ciliated epithelial cells and goblet cells. Goblet cells secrete mucus which traps bacteria and dust particles.The trachea branches into two bronchi.They are lined with ciliated epithelia and goblet cells and produce mucus to trap dust particles. The mucus is then wafted up to the throat by cilia and then swallowed.The acid in the stomach then kills the bacteria.Larger bronchi are supported by incomplete rings of cartilage. The amount of cartilage is reduced as the bronchi get smaller.Each bronchus divides into many bronchioles. These are not supported by cartilage. The walls are made of smooth muscle lined with epithelial cells. They constrict to control the flow of air into the alveoli.The alveoli are tiny air sacs 100-300 μm in diameter made up of a single epithelial layer. There are collagen and elastic fibres between the alveoli. The elastic fibres allow the alveoli to stretch when breathing in and recoil to expel the air.