3Air moves through the nose and nasal cavity where it is filtered (hairs) and warmed. Enters the pharynx (throat), a tube at the back of the mouth. The pharynx serves as a passageway for both air and food.
4Enters the trachea (windpipe) which is made up of fibrous and elastic tissues and smooth muscle with about twenty rings of cartilage, which help keep the trachea open.
5The trachea is lined with cilia and cells that secrete mucus The trachea is lined with cilia and cells that secrete mucus. The mucus traps tiny particles of debris, and the beating of the cilia moves the mucus up and out of the respiratory tract, keeping the lungs and air passages free.
6Air moves over or through the larynx (voice box) depending on whether you are speaking or not. Into two large passageways in the thoracic cavity called the bronchi (singular = bronchus), each leading into a lung.6. Into smaller passageways called the bronchioles.
7Both the bronchi and bronchioles are surrounded by smooth muscle that helps support them and enables the nervous system to regulate their diameter.
87. The air then enters the alveoli (alveolus) which are hollow cavities at the ends of each of the bronchioles. They are grouped in clusters (like grapes). Capillaries surround each alveolus.- about 150 million alveoli in each lung.
10Gas exchangeOxygen dissolves in the moisture on the inner surface of the alveoli and then diffuses across the one cell layer-walled capillaries into the blood.Carbon dioxide diffuses from the capillaries into the alveoli and is exhaled.*Remember diffusion
15Steps in respiration:The normally dome-shaped diaphragm contracts, flattening.The rib cage rises which expands the chest cavity.This causes the lungs to expand, increasing the volume of the lungs and causing the atmospheric pressure (the pressure exerted by the air outside the body) to become greater than the pressure inside the lungs (pulmonary pressure).Air rushes in.This air inside the lungs causes the pulmonary pressure to become greater than the air pressure.This causes the air to move out of the lungs.
16The system works because our lungs are sealed; each in a sac called a pleural membrane.
18While we can control our breathing to some extent, breathing is not entirely voluntary. The nervous system, particularly the part of the brain known as the medulla oblongata, registers the amount of carbon dioxide in our blood and, when levels of CO2 are too high, it causes nerve impulses which in turn cause the diaphragm to contract bringing air into the lungs.What is one potential problem with this system for people at high altitudes?