Chapter 13
The Respiratory System
Overview of the respiratory system
 The respiratory system works in coordination with the cardiovascular system to
handle gas exchange
 The respiratory system
o
delivers O2
o
expels CO2
o
maintains blood pH
The pathway of air in the body
 nose [ pharynx [ larynx [ trachea [ bronchus [ bronchioles [ alveoli
The upper respiratory tract
 nose [ pharynx [ larynx
The nose
 Opens at the nostrils/nares and leads into the nasal cavities
 Hairs and mucus in the nose filter the air
 The nasal cavity has lots of capillaries that warm and moisten the air
 Specialized cells act as odor receptors
 Tear glands drain into the nasal cavities that can lead to a “runny” nose
The pharynx
 Funnel-shaped cavity commonly called the “throat”
 3 portions based on location: nasopharynx, oropharynx, and laryngopharynx
 Tonsils provide a lymphatic defense during breathing at the junction of the oral
cavity and pharynx
The larynx
 Triangular, cartilaginous structure that passes air between the pharynx and the
trachea
 Called the voice box and houses the vocal cords
 There are 2 mucosal folds that make up the vocal cords with an opening in the
middle called the glottis
The lower respiratory tract
 larynx [ trachea [ bronchus [ bronchioles [ alveoli
The trachea
 A tube, often called the windpipe, that connects the larynx with the 1° bronchi
 Lined with cilia and mucus that help to keep the lungs clean
 Made of connective tissue, smooth muscle, and cartilaginous rings
The lungs
 The bronchi, bronchioles, and alveoli beyond the 1° bronchi make up the lungs
 The right lung has 3 lobes while the left lung has 2 lobes that divide into lobules
 Each lung is enclosed by membranes called pleura
The bronchial tree
 Starts with two main bronchi that lead from the trachea into the lungs
 The bronchi continue to branch until they are small bronchioles each about 1mm in
diameter with thinner walls
 Bronchioles eventually lead to elongated sacs called alveoli
The alveoli
 ~ 300 million in the lungs that greatly increase surface area
 Alveoli are enveloped by blood capillaries
 The alveoli and capillaries are only one layer of epithelium to allow exchange of
gases
 Alveoli are lined with surfactant that acts as a film to keep the alveoli open
Two phases of breathing/ventilation
1. Inhalation – an active process of inhalation that brings air into the lungs
2. Exhalation – usually a passive process of exhalation that expels air from the lungs
Inhalation
 The diaphragm and intercostal muscles contract
 The diaphragm flattens and the rib cage moves upward and outward
 The volume of the thoracic cavity and lungs increase
 The air pressure within the lungs decrease
 Air flows into the lungs
Exhalation
 The diaphragm and intercostal muscles relax
 The diaphragm moves upward and becomes dome-shape
 The rib cage moves downward and inward
 The volume of the thoracic cavity and lungs decrease
 The air pressure within the lungs increases
 Air flows out of the lungs
Different volumes of air during breathing
 Tidal volume – the small amount of air that usually moves in and out with each
breath
 Vital capacity – the maximum volume of air that can be moved in plus the maximum
amount that can be moved out during one huge breath
 Inspiratory and expiratory reserve volume – the increased volume of air moving in
or out of the body
 Residual volume – the air remaining in the lungs after forceful exhalation
Exchange of gases in the body
 Oxygen and carbon dioxide are exchanged
 The exchange of gases is dependent on diffusion
 Partial pressure is the amount of pressure each gas exerts (PCO or PO )
2
2
 Oxygen and carbon dioxide will diffuse from the area of higher to the area of lower
partial pressure
External respiration
 Exchange of gases between the lung alveoli and the blood capillaries
 PCO is higher in the lung capillaries than the air thus CO2 diffuses out of the plasma
2
into the lungs
 The partial pressure pattern for O2 is just the opposite so O2 diffuses from the lungs
into the red blood cells
 Carbon dioxide transport:
o
H+ + HCO3H2CO3
H2O + CO2
 Oxygen transport:
o
Hb + O2
HbO2
Internal respiration
 The exchange of gases between the blood in the capillaries outside of the lungs and
the tissue fluid
 PO is higher in the capillaries than the tissue fluid thus O2 diffuses out of the blood
2
into the tissues
 Oxyhemoglobin gives up oxygen:
o
HbO2
Hb + O2
 Most CO2 is carried as a bicarbonate ion:
o
CO2 + H2O
H2CO3
H+ + HCO3Breathing is chemically controlled
 Chemical control:
o
2 sets of chemoreceptors sense the drop in pH - one set is in the brain and
the other in the circulatory system
o
Both are sensitive to carbon dioxide levels that change blood pH
 Hemoglobin is extremely sensitive to pH and temperature variations
Lower respiratory tract disorders
 Pneumonia – infection of the lungs with thick, fluid build-up
 Tuberculosis – bacterial infection that leads to tubercles (capsules)
 Pulmonary fibrosis – lungs lose their elasticity because fibrous connective tissue
builds up in the lungs usually because of inhaled particulates
 Emphysema – chronic, incurable disorder in which alveoli are damaged
 Asthma – bronchial tree becomes irritated causing breathlessness, wheezing, and
coughing
 Lung cancer – uncontrolled cell division in the lungs that is often caused by smoking
and can lead to death
Health focus: Tobacco and health
 All forms of tobacco can cause damage
 Smoking increases a person’s chance of cancer of the lungs, mouth, larynx,
esophagus, bladder, kidney, pancreas, stomach, and cervix
o
The 5-year survival rate for people with lung cancer is only 13%
 Smoking also increases the chance of chronic bronchitis, emphysema, heart disease,
stillbirths, and harm to an unborn child
 Passive smoke can increase a nonsmokers chance of pneumonia, bronchitis, and lung
cancer