The Respiratory System Flashcards
(33 cards)
What is the primary function of the respiratory system and what does it include?
-to obtain oxygen for use by body’s cells + eliminate carbon dioxide that cells produce
Includes:
-conducting zone: site of air transport consisting of respiratory airways leading into and out of lungs
-respiratory zone: site of gas exchange; occurring at the respiratory membrane which consists of the cell membranes of:
-alveolar epithelial cells + -capillary endothelial cells
What does respiration involve?
-pulmonary ventilation
-external respiration
-transport of respiratory gases by the blood
-internal respiration
Functional anatomy of the conducting zone;
As conducting tubes become smaller:
*they support structures change (cartilage —> elastic fibres)
*epithelial cell type changes
*amount of circular smooth muscle increases
Functional anatomy of the respiratory zone;
Terminal bronchioles feed into respiratory bronchioles
Intrapulmonary and intrapleural pressure relationships
Pressure difference must be maintained or the lungs would collapse
What happens during inhalation?
-diaphragm contracts and moves downwards
-chest cavity expands
-pressure inside the lungs decreases and air flows into the lungs
>lungs stretch and activates stretch receptors + arterial blood pressure is lowered which activates baroreceptors
-sensory neurones relay information to the brainstem
-vagal tone is inhibited
*HR increases
What happens during exhalation?
-diaphragm relaxes and moves upwards
-chest cavity decreases
-pressure inside the lungs increases and air flows out of the lungs
>stretch receptors are no longer stimulated +arterial bp is increased= deactivating baroreceptor activity
-sensory neurones relay information to the brainstem
-vagal tone is not inhibited
*HR decreases
Mechanics of breathing
Slide 13
How is the negative intrapleural pressure established?
*inward:
-natural tendency for lungs to recoil because of elasticity= lungs will always assume smallest possible space
-surface tension of alveolar fluid= forms a film in alveoli + tries to draw alveoli to smallest possible size
*outward:
-elasticity of the chest wall= tends to pull the thorax outward and enlarge the lungs
Pulmonary ventilation
-volume changes lead to pressure changes = leads to flow of gases to equalise the pressure
Pulmonary Ventilation:
Inspiration & Expiration
-movement of the intercostal muscles and diaphragm causes changes in the volume of the thoracic cavity
* when P alv < P atm air rushes into the lungs along the pressure gradient
* when P alv > P atm the pressure gradient forces gases to flow out the lungs
Airway resistance
-small changes in the radius= large changes in the diameter of the airways
-during exercise circulating adrenaline= bronchodilation
>acts on B2 receptors via the sympathetic nervous system
-irritants can cause bronchodilation = via the parasympathetic nervous system
Asthma
-a decrease in the diameter of the airways due to;
-bronchoconstriction
-bronchial lining becomes inflamed
Symptoms;
-coughing, wheezing, breathlessness + tightening of chest
Triggers;
-exercise, allergens, airborne irritants + weather
Bronchodilators e.g. salbutamol= cause bronchodilation by replacing bronchi smooth muscle of the bronchi;
-usually in an inhaler form
-onset of action is a few mins and lasts for 3-5 hours
Alveolar surface tension
-alveolar type 2 cells= produce surfactant
*amphipilic molecule that has both hydrophilic and hydrophobic regions
*by absorbing to the air-water interface of alveoli alveoli,
• hydrophilic head groups in the water
• hydrophobic tails facing towards the air
Surfactant reduces the attractiveness of water modules for each other and decreases
the cohesiveness of the water molecules:
– Reducing the surface tension and reducing the likeness that alveoli will collapse
Infant Respiratory Distress Syndrome (IRDS)
• Occurs in premature babies born at 22-24 weeks as surfactant is produced in the last 2
months of foetal development
• Treatment:
› is positive pressure respirators to force air into the alveoli at 1 atm pressure
› Administer synthetic surfactant
What is lung compliance?
-the ability of the drugs to expand and stretch
-is the volume change that could be achieved in the lungs per unit pressure change
-due to the distensibility of the elastic tissue of the lungs
-decreases with increasing age as tissues become less elastic
What are the physical factors influencing pulmonary ventilation?
-airway resistance
-alveolar surface tension
-lung compliance
Basic properties of gases
2 gas laws providing info during
-external respiration at the lungs
-internal respiration in the tissues
=
- Dalton’s law of partial pressure= how a gas behaves when it is part of a mixture
- Henry’s law= how gases move into and out of solution
Dalton’s law
-conc of gases= partial pressure
Total pressure exerted by a mixture of gases= sum of pressures exerted independently by each gas in the mixture
-pressure contributed by a single gas is directly proportional to the % of the gas in the total gas mixture
Henrys law
• If a gas mixture is in contact with a liquid: each gas will dissolve in the liquid in proportion to its partial pressure
• Very important for the passage of gas FROM THE ALVEOLI TO THE BLOOD
• The greater the partial pressure of gas in the gas phase, the more gas will enter the liquid phase
• At equilibrium, the gas partial pressure in the two phases is equal
• If the partial pressure of one gas becomes greater in the liquid than the gas phase, some of the dissolved gas will re-enter the gaseous phase
• The direction & amount of movement of each gas is determined by its partial pressure in the two phases
Solubility and temperature
How much gas dissolves in a liquid depends on its solubility and temperature of the liquid
-solubility; the amount of gas that dissolves depends on the solubility of gas in water
› CO2 is 20 x more soluble than O2
› O2 is 2x more soluble than N2
• TEMPERATURE: the solubility of any gas decreases with increasing temperature
Atmospheric and Alveolar : Gas Partial Pressures
-alveolar gas contains more CO2 and water vapour + less O2
These differences reflect:
-gas exchange occurring in the lungs
-humidification of air from air conducting passageways
-mixing of alveolar air that occurs with each breath + gas remaining in respiratory airways
3 factors influencing external respiration
-thickness and surface area of respiratory membrane
-partial pressure gradients and gas solubilities
-ventilation-perfusion coupling
Functional anatomy of the respiratory system: respiratory membrane
-membrane is usually 0.5um thick and surface area is 100m2
*increased thickness occurs in oedema due to pneumonia or left ventricular heart failure
*decreased surface area occurs;
-during emphysema= damage to alveolar walls and enlargement of alveolar chambers
-tumours and accumulation of mucus block gas flow into alveoli
Circulation of blood through the heart
-in left ventricular heart failure= cardiac output of the left ventricle is reduced
-backup of blood in the pulmonary circulation= increased back pressure
=results in increased thickness of respiratory membrane= pulmonary oedema= resulting in pulmonary congestion:
-cough
-wheezing
-increased breathing rate- tachypnoea
