Respiratory system Flashcards
What are the 5 components of the respiratory system?
- Airways
- Lungs
- Pulmonary circulation
- Thoracic cage
- Respiratory muscles
What is Boyle’s Law?
P1V1=P2V2
‘The pressure of a given quantity of gas varies inversely with its volume at constant temperature’.
What does the diaphragm do during inhalation?
It contracts and draws lungs downwards to increase lung volume
What is vital capacity of the lungs?
Vital capacity = The sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume
What is Total Lung Capacity?
Total Lung Capacity = The sum of vital capacity and residual volume
What is residual volume?
Residual Volume = The volume of air left in the lungs after the expiratory reserve volume is exhaled, this cannot be measured by spirometry.
What are the 3 parts of the respiratory process?
- Ventilation of lungs with air
- Gas exchange between air and blood (pulmonary circulation)
- Perfusion of lungs with blood
All vital for efficient uptake of O2 and elimination of CO2
What is ventilation?
The exchange of air between the atmosphere and the alveoli
Describe the structure of the airways
- Air enters trachea through nose and mouth
- Trachea divides in the left and right bronchus
- They divide sequentially into small bronchi and bronchioles
- Bronchioles end in alveoli which is the major site of gas exchanges
Describe the alveoli
Tiny hollow sacs
Alveolar walls contain capillaries
Large surface area of alveoli in contact with the capillaries means gas exchange of CO2 and O2 by diffusion is rapid
Describe the process of inspiration and expiration
Inspiration
- Inspiratory muscles contract, diaphragm moves down and flattens and external intercostal muscles lift ribs cage and pull up sternum
- Thoracic cavity volume increases
- Intrapulmonary volume increases as lungs are stretched
- Intrapulmonary volume decreases
- Air flows into lungs down pressure gradient until intrapulmonary pressure is 0
Expiration
- Inspiratory muscles relax, diaphragm rises, the rib cages descends
- Lungs recoil
- Thoracic cavity volume and intrapulmonary volume decreases. The volume decrease compresses the alveoli and intrapulmonary pressure increases.
- Air flows out of lungs down pressure gradient until the intrapulmonary pressure is 0
Describe the process of forced expiration
- An active process produced by contraction of abdominal wall muscles.
- The contraction causes an increase in intra-abdominal pressure which forces abdominal organs against the diaphragm and depress the ribcage. Internal intercostal muscles help depress rib cage and decrease thoracic volume.
What influences uptake of O2 and CO2
- Partial pressure gradient and gas solubilities
- Matching of alveolar ventilation and pulmonary blood perfusion
- Structural characteristics of the respiratory membrane
What is the partial pressure of O2 in the alveoli
Around 104mmHg
What is the PO2 in the pulmonary arteries?
40mm Hg
What happens when the PO2 in alveoli is low?
The terminal arterioles constrict and blood is redirected to an area with high PO2 so it can be easily diffused
What happens when the PO2 is low and the PCO2 is high in the alveoli?
Pulmonary arterioles constrict and there is reduced alveolar ventilation, reduced perfusion
What happens when there is a high PO2 and low PCO2 in the alveoli?
And what causes this?
Pulmonary arteries serving these alveoli dilate and there is enhanced alveolar ventilation and enhanced perfusion
This is caused by enhanced alveolar ventilation and inadequate perfusion.
Why is PO2 in tissues always lower than in the systemic arterial blood?
Because tissue cells are continuously using O2 for metabolic activities while producing CO2.
It allows O2 to move rapidly from the blood to the tissues.
Describe haemaglobin and its relationship with oxygen
Haemoglobin has four polypeptide chains each bound to an iron containing heme group which can bind with oxygen.
When Hb is saturated with O2 it become Oxyhaemoglobin HbO2.
After the first O2 has bound the the iron in the Hb, Hb changes shape to make it easier for the next O2 molecule to bind.
Affinity for oxygen changes with saturation level.
What effects the rate Hb binds to O2?
PO2 Temperature Blood pH PCO2 Blood concentration of BPG (organic chemical)
What 3 ways can CO2 leave tissues in the blood?
- Dissolved in plasma (7-10%)
- Chemically bound to hameoglobin by being carried in RBC as carbaminohaemoglobin (20%)
- As a bicarbonate ion, HCO3-) in plasma (70%)
Describe the formation of carbaminohaemoglobin.
And its loading and unloading process.
CO2 rapidly binds to HB without a catalyst.
It binds to the amino acid of globin.
The loading and unloading are influenced by the PCO2 and degree of Hb oxygenation.
CO2 rapidly dissociate from haemoglobin in the lungs due to the PCO2 in alveoli being lower than in the blood. This means it can easily diffuse out of the blood, down its pressure gradient into the alveoli and be breathed out of the body.
In CO2 loading, the PCO2 is higher in tissues than the blood so it diffuses in down pressure gradient to be removed from the tissues.
Describe the process of CO2 being removed from tissues as a bicarbonate ion?
What is that ion?
The ion is HCO3-
CO2 enters the red blood cells and combines with H20 to form H2CO3, carbonic acid, catalysed by carbonic anhydrase
Carbonic acids is very unstable so dissociated in to H+ and HCO3-.
The HCO3- the moves into the blood plasma with a CL- ion during the chloride shift.
This process can occur in the plasma but is much faster if it happens in the RBC.
