Patho Ch 21
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–Air-conducting – delivers air
•Includes the nose, mouth, trachea, bronchi, and bronchioles
–Gas exchange – swaps gases between air and blood
•Includes alveoli and capillaries
–Moves O2 into blood
–Removes CO2 from blood
•Functional structures of respiratory system.
•Function for gas exchange.
•Also inactivate vasoactive substances such as bradykinin.
•They convert angiotensin I to angiotensin II.
•Serve as reservoir for blood storage.
•Heparin-producing cells are abundant in the capillaries of the lungs where small clots may be trapped.
•Mucus, cilia, and immune cells protect the system from harmful inhaled particles
•Capillaries in the nose warms and humidifies the air to protect system from drying and damage from cold
•Mucus produced by epithelial cells form a layer in the airways.
•Entraps dust, bacteria, and foreign particles.
•Cilia are constantly in motion. They move the mucus with the entrapped particles in an “escalator fashion”.
•Move the mucus toward the oropharanx.
•From their expectorated or swallowed.
•Function is affected by O2 levels.
•Impaired by dry conditions.
•Nicotine in cigarettes paralyze cilia. All of the residue stays in the lungs. Contribute to chronic bronchitis and emphysema.
•One cigarette may paralyze for up to 2 weeks!
•Gas is exchanged with the blood
The organs and walls of the thoracic & abdominal cavities are covered with serous membranes.
Visceral membranes cover the organ.
Parietal membranes line the cavity walls.
The two membranes and the space between them allow for ease of movement.
Thoracic cavity is lined by parietal pleura
Lungs are covered by visceral pleura.
•Accessory muscles of inhalation
•Accessory muscles of exhalation
The diaphragm is the main muscle of inhalation/inspiration.
During inhalation, the diaphragm contracts and flattens (it moves downward in order to accommodate the volume of air you are taking in, allowing space for the lungs to expand).
During exhalation, the diaphragm relaxes and moves back up.
•Elasticity and recoil are vital
•Negative pressure system
•How easily lungs can be inflated depends on:
–Elastin and collagen fibers
•Surfactant – lipoprotein
–Secreted by type II alveolar cells.
–Has a detergent quality
–Reduces alveoli surface tension to prevent collapse & aid lung expansion.
–Recent research indicates four types of surfactant. Also implicated in immune function.
Pulmonary Function Tests
–Tidal volume – amount of air moved in and out with a normal breath; ~500ml
–Minute respiratory volume – amount of air moved in and out in one minute; ~ 6L
–Inspiratory reserve volume – maximum amount of air that can be inhaled over tidal volume; 2-3L
–Expiratory reserve volume -maximum amount of air that can be exhaled over tidal volume; 1-1.5L
Pulmonary Function Tests
–Vital capacity – sum of the tidal volumes and the reserves
–Residual volume – amount of air left in the lung after forced expiration; 1-1.5L
–Forced expiratory volume in one second is compared to the forced vital capacity to diagnose pulmonary disease
Total Lung Capacity
•Total lung capacity is the maximum amount of air that the lungs can hold
•everything (volume-wise) at the end of a maximal inhalation (the deepest breath one can possibly take)
•Normal TLC is approximately 6 L.
•Requires adequate ventilation and perfusion
–Ventilation/perfusion ratio (VQ ratio)
–Normal ventilation = 4L per minute
–Normal perfusion = 5L per minute
•Dependent on alveolar and capillary surface area and thickness
•Oxygen moves from alveolar air into blood
•Carbon dioxide moves from blood into alveolar air
•Blood goes to parts of the lung that do not have oxygen to give it
•Blood does not go to parts of the lung that have oxygen
Tell whether the following statement is true or false: Ventilation-perfusion
mismatch results in hypoxia
- In either case (ventilation without perfusion or perfusion without ventilation)
- oxygen is not picked up by the capillaries and delivered to the tissues. The result of decreased oxygen at the tissue
- level is termed hypoxia.
Role of pH
•Carbon dioxide is one of the body’s acids
•Lungs alter the rate and depth of breathing to regulate pH
–Increased rate of breathing expels more carbon dioxide and raises pH
–Decreased rate of breathing retains more carbon dioxide and lowers pH
•Dissolved oxygen = PaO2 or PO2
–Normal value >80 mm Hg
•Oxygen bound to hemoglobin = oxyhemoglobin
–Normal value 95% to 97% saturation
•Oxygen capacity: Amount of oxygen the blood can hold; Carried by hemoglobin
•Once to the site, hemoglobin must be able to release the gases
–Affected by a variety of things such as pH and temperature
Blood Gases—Carbon Dioxide
•Dissolved carbon dioxide = PaCO2 or PCO2
–Normal value 35–45 mm Hg
•Carbon dioxide bound to hemoglobin = carbaminohemoglobin
•Carbonic acid ↔ bicarbonate ion and H+
•When you exhale you remove CO2 from your blood and also decrease the amount of carbonic acid, raising your blood pH
Chemoreceptors Can Adjust Respiration Rate
–Measure PCO2 and pH in cerebrospinal fluid
–Increase respiration when PCO2 increases or pH decreases
–Measure PO2 in arterial blood
–Increase respiration when PO2 <60 mm Hg
•Neurally mediated reflex.
•Protects the lungs from secretions, objects, irritants, destructive substances.
•Reflex is initiated by receptors located in tracheobronchial wall.
•Transmitted through vagus nerve to medullary center.
•Requires rapid inspiration large volume of air, rapid closure of glottis, & contraction of abdominal & expiratory muscles. Rapid opening of glottis leads to explosion of air.
•Many conditions may interfere: weakened abdominal or resp muscles, prolonged inactivity, surgery, nasogastric tubes, < medullary brain function (disease or meds)
•Exhausting if frequent or prolonged, especially in children and elderly.
•Subjective sensation of difficulty in breathing.
•AKA breathlessness & shortness of breath.
•In pneumonia, asthma, emphysema, pulmonary congestion, neuromuscular d/o such as myasthenia gravis & muscular dystrophy. May occur in exercise.
•True cause is unknown.
•Often measure by level of activities of daily living.
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