Respiratory System Flashcards
What is the function of the respiratory system?
Exchange of O2 and CO2 between external environment and body’s circulatory system
What is ventilation?
The process by which air enters and exits the lungs
Inspiration: Air moves into the lungs
Expiration: Air moves out of lungs
What is the upper respiratory tract and what’s the function?
A system of organs and structures that functions to warm, moisten and clean air as it conducts from outside, down to the lower respiratory tract
What structures make up the upper respiratory tract, and does food or air (or both) pass through them?
Nasal Cavity (air only)
Oral Cavity (air and food)
Pharynx:
- Nasopharynx (air only)
- Oropharynx (air and food)
- Laryngopharynx (air and food)
What is the function of the lower respiratory tract?
Conducts air from the upper respiratory tract, down to the gas exchange surface
What structures make up the lower respiratory tract?
Larynx: epiglottis closes over trachea to prevent food entering airway
Trachea: rigid tube that maintains an open pathway for air
Bronchi: primary (1 each lung) and secondary (2 in the left, 3 in the right)
Bronchioles
Alveolar ducts
Alveoli: gas exchange surface
What happens in asthma?
Swelling, and bronchoconstriction can restrict or prevent airflow. lumen gets smaller which narrows the airway which means air can’t get through
What’s the alveoli?
Lined with really thin cells (simple, squamous epithelium). In clusters surrounded by pulmonary capillaries. The place where gas exchange occurs
What is surfactant?
Secreted by the alveoli cells to reduce the surface tension and keep alveoli open.
How do we generate airflow?
Diaphragm: our main respiratory muscle
Intercostal muscles: Internal and external
Accessory Muscles: used for forced breathing.
The diaphragm and external intercostal muscles are used at rest.
What is Boyle’s Law?
The pressure-volume relationship.
They are inversely related (when one increases, the other decreases)
What is inspiration and how is volume increased?
An active process and occurs when pressure in the lungs (Palv) is lower than the atmosphere (Patm) - air moves in.
Volume increases by contraction of external intercostal muscles elevating the ribs and contraction of the diaphragm flattens the floor of thoracic cavity.
What is expiration and how is volume decreased?
A passive process and occurs when pressure in the lungs is higher than the atmosphere - air moves out.
Volume decreases when diaphragm and intercostal muscles relax. Lungs have elastic elements causing elastic recoil inwards.
Mechanics of Breathing
The chest wall tends to recoil outwards and the lungs tend to recoil inwards.
This develops a negative pressure within the pleural space/cavity relative to the atmospheric pressure called the intrapleural pressure (always negative)
i.e when the chest wall expands outwards, the lungs expand with it
What is Tidal Volume (Vt)?
Volume of air that moves in and out with each breath. (normal quiet breathing)
What is Inspiratory Reserve Volume (IRV)?
The maximum volume of air that can be inspired beyond a normal tidal inspiration (forced inspiration)
What is Expiratory Reserve Volume (ERV)?
The maximum volume of air that can be exhaled after a normal tidal expiration (forced expiration)
Residual Volume (RV)
The amount of air remaining in the lungs after maximal forced expiration.
What is the vital capacity (VC)?
The maximum volume of air that can be expired after maximal inspiration (ERV + Vt + IRV)
What is total lung capacity (TLC)?
The maximum volume of air in the lungs after a maximal inspiration (VC + RV)
What is inspiratory capacity (IC)?
The maximum volume of air that can be inspired after a normal tidal expiration (Vt + IRV)
What is functional residual capacity (FRC)?
The amount of air in the lungs after a normal tidal expiration (RV + ERV)
How to calculate minute ventilation (Ve)?
Minute ventilation (Ve) = tidal volume (Vt) x breathing frequency (f)
What is dead space (Vd)?
The inhaled air that never gets to the alveoli so cannot gas exchange
What is alveolar ventilation (Va) and how to calculate it?
The rate at which air reaches the alveoli for gas exchange (Va = f x (Vt-Vd))
What is hyperventilation and hypoventilation?
Hyperventilation is increased alveolar ventilation (fast deep breathing)
Hypoventilation is decreased alveolar ventilation (slow shallow breathing)
What is Dalton’s Law?
Each individual gas exerts its own individual pressure or partial pressure (Po2, Pco2)
In a mixture of gases, the total pressure exerted is simply the sum of the partial pressures.
Atmospheric air consists of:
Nitrogen - 78%
Oxygen - 21%
Carbon Dioxide - 0.04%
Partial Pressure of Gases in the Alveoli?
Alveolar Po2 is lower than that of atmospheric O2
Alveolar Pco2 is much higher than that in atmospheric air
What is Fick’s Law of Diffusion?
F = D x A x (P1 - P2) / T
F: flux (amount flowing)
D: diffusion constant
A: surface area
P: pressure gradient
T: thickness
What is pulmonary fibrosis?
Involves thickening and scarring of the alveolar membranes. Can arise from chronic inflammation, drugs, industrial chemicals.
What are the factors affecting diffusion and whats the most important?
- surface area
- thickness
- solubility of the gas (diffusion constant)
- pressure gradient (most important factor)
Gas exchange direction and speed?
O2= alveoli –> blood
CO2 = blood -> alveoli
Although O2 has a larger gradient, CO2 diffuses across the gas exchange barrier 20x faster because its more soluble
What are the forms of oxygen transport?
- Combined with haemoglobin (Hb)(majority)
- Dissolved in plasma
Describe oxygen transport via binding to haemoglobin (Hb).
1 Hb molecule can carry 4 molecules of O2. O2 binds to haem group which contains iron ions. Without the haem group you can’t form the haemoglobin molecule - less haem groups, less oxygen carry capacity
What are the forms of carbon dioxide transport?
- Dissolved in Plasma
- Combined with haemoglobin
- As bicarbonate - HCO3 (majority)
Describe carbon dioxide transport via bicarbonate ions
Conversion from CO2 –> HCO3 happens in the red blood cells with the assistance of an enzyme. HCO3 produced can then move out into the plasma.
What is the co-operative effect?
Each molecule of O2 that binds to Hb facilitates another molecule of O2 binding.
There will always be one oxygen bound to the haem group, otherwise it’ll be really hard for the next one to bind.
What is oxygenation?
The binding of O2 to Hb. The complex is called OxyHb (HbO2).
What is Hb-O2 saturation?
The saturation percentage of Hb describes whether the sites on Hb are fully or partially occupied by O2
What is the Hb-O2 saturation percentage of arterial blood?
98%
What is the Hb-O2 saturation percentage of venous blood?
75%
What is the Hb-O2 dissociation curve?
The amount of O2 bound to Hb is determined by the Po2 in the blood. Its a sigmoidal curve due to the co-operative effect.
What is the Bohr effect?
Describes haemoglobin’s affinity for oxygen. It refers to either a left or right shift in the OxyHb dissociation curve which is caused by either a decrease/increase in CO2/H+ions (pH) and temperature
What does a left shift in the Bohr effect mean?
Left shift occurs in the lungs and facilitates more loading of oxygen (increased loading).
Caused by lower levels of CO2/H+ and low temperature
What does a right shift in the Bohr effect mean?
Right shift occurs in the tissues and facilitates more release of oxygen (increased unloading).
Caused by higher levels of CO2/H+ and high temperature
What is Alkalosis and how is it compensated?
Increased pH (above normal range) due to decreased concentration of H+ ions.
Compensated for by hypo-ventilating to increase CO2. Therefore increasing H+ ion concentration in the blood.
What is acidosis and how is it compensated?
Decreased pH (below normal range) due to increased concentration of H+ ions.
Compensated for by hyperventilating to decrease CO2. Therefore decreasing H+ ion concentration in the blood.
