Respiratory System

Lungs Lungs are lateral to the heart Each is located in its own enclosed pleural cavity within the thoracic cavity Each lung is covered by a pleural membrane A pleural space lubricated with fluid also surrounds each lung

Pathway of Air to the Lungs Pharynx - throat (extends to larynx) Larynx - houses vocal chords - leads to trachea Trachea - air passes through this tube on way to the lungs (windpipe) Bronchi - branches of trachea going to each lung Bronchioles - smaller branches of the bronchi Alveoli - air sacs surrounded by capillaries where oxygen is exchanged for CO 2 - (blood returns to heart from here)

Pathway of Air Into the Lungs Can be divided into 2 zones: Conducting Zone Respiratory Zone

Conducting Zone Nose, nasal cavity, pharynx, larynx, trachea, bronchi Function: warm, filter and moisten inspired air Mucous traps airborne pathogens and cilia propel matter into the pharynx to be swallowed

Respiratory Zone Bronchioles, alveoli Function: gas exchange (CO 2 enters alveoli from blood and O 2 passes into blood from the alveoli) Capillaries surround each alveolus for efficient gas exchange * In emphysema, the alveoli are damaged, reducing ability for gas exchange

Mechanics of Breathing Diaphragm - muscle at the base of the lungs that regulates pressure within the pleural cavities by moving up and down

Inspiration & Expiration (see Figure 22.13) Inspiration (breathing in) Diaphragm contracts and moves down Intercostal muscles contract and expand ribcage Volume of thoracic cavity is increased as intrapulmonary (inside alveoli) pressure decreases Air moves into lungs because atmospheric pressure is greater than intrapulmonary pressure Expiration (breathing out) Diaphragm relaxes and moves upwards Intercostal muscles relax and ribcage collapses Volume of thoracic cavity decreases as intrapulmonary pressure increases Air is forced out of lungs because atmospheric pressure is less than intrapulmonary pressure

Diaphragm movements

Regulation of Breathing The medulla and pons contain respiratory centers that control breathing (figure 22.24) The depth and rate of breathing are controlled by CO 2, O 2 and pH (H + ) concentrations in the blood CO 2 levels are the strongest stimulus for breathing Chemoreceptors in aorta and carotid arteries monitor blood and send signals to respiratory centers in pons and medulla