Respiratory system Function – to bring about the exchange of oxygen and carbon dioxide between the blood, the air, and tissues

Figure 37-14 The Respiratory System Section 37-3 Pharynx Nose Larynx Trachea Mouth Lung Bronchiole Epiglottis Bronchus Alveoli Bronchioles Diaphragm Capillaries Edge of pleural membrane

Parts of respiratory system Nose/nasal cavity – entrance to respiratory system, filters air with hair and mucus, removes dust and other particles. Warms and humidifies air. Mouth/oral cavity – entrance to respiratory system, less filtering and humidifying. Best to take in air through nose. Pharynx – back of mouth/throat. Passage for air and food.

Parts of respiratory system Trachea – Windpipe, passage to lungs, air travels down trachea to bronchi. Walls made of C-shaped cartilage to keep it from collapsing and to keep it flexible. Mucus is swept out of trachea by cilia then sent to esophagus. This removes particles from the trachea. Smoking paralyzes the cilia and particles get stuck causing smoker’s cough.

Parts of respiratory system Larynx – Voice box on top of trachea. Contains two vocal cords (elastic folds of tissue). Air rushes past, muscles cause the vocal cords to contract producing sound. Short vocal cords = high pitched sound. Long vocal cords = low pitched sound. Also called Adam’s apple in men.

Parts of respiratory system The trachea divides into two bronchi (bronchus = singular). These branch into even smaller passages called bronchioles. The bronchi and bronchioles have smooth muscle in their walls. The bronchioles end in alveoli (alveolus = singular). These are hollow air sacs with thin flexible membranes, which separate gas (air) from liquid (blood). Gas exchange occurs across the membranes of the alveoli.

Figure 37-15 Gas Exchange in the Lungs Section 37-3 Alveoli Bronchiole Capillary

How we breathe Inhalation (O2 removed from air, CO2 and H2O added to air). The diaphragm moves down (contracts), chest volume increases, pressure decreases, air moves in to lungs. Exhalation. The diaphragm moves up (relaxes), chest volume decreases, air pressure increases (squeezes lungs), air pushed out of lungs.

Figure 37-16 The Mechanics of Breathing Section 37-3 Air exhaled Air inhaled Rib cage descends Rib cage rises Diaphragm Diaphragm Inhalation Exhalation

During vigorous breathing, other accessory muscles are involved During vigorous breathing, other accessory muscles are involved. Lungs can only work if space around them is sealed. A hole in the chest can destroy the pressure system. Breathing is involuntary. Sensory neurons in the medulla oblongata control motor neurons to the diaphragm. Sensory neurons check gas levels in the blood. One in carotid artery in the neck, the other located near the aorta. The neurons are sensitive to pH levels. When blood becomes acidic due to build up of CO2 (CO2 becomes carbonic acid with releases H+), the medulla oblongata sends a message to breathe.