Lungs and breathing Flashcards
How is the lung innervated?
Sympathetic - from T4-6 ganglia of the sympathetic trunk
Parasympathetic - from vagus
What results from sympathetic input to the lungs?
Bronchodilation
What results from parasympathetic input to the lungs?
Bronchoconstriction
What is intrapleural pressure (Pip)?
Pressure of intrapleural fluid
What is alveolar pressure (Palv)?
Gas pressure in the alveoli
What is atmospheric pressure (Patm)?
Pressure of air surrounding the body
Flow =
(Palv-Patm) / R
When F= negative…
Palv < Patm
Inspiration takes place (air flows in)
When F= positive…
Palv > Patm
Expiration takes place (air flows out)
What does F equal when there’s no airflow?
F= 0 and Palv = Patm
What is Boyle’s law?
P1V1 = P2V2 (@ constant temperautre)
What is Pip at rest?
A balance between the tendency of lungs to collapse and the tendency of the chest wall to expand
What keeps the lungs paritally expanded between breaths?
A negative Pip (-4mmHg)
How is a negative Pip caused?
Tiny enlargement of the IP space caused when pleural layer move slightly away from each other (due to tendencies of lung to collapse and chest all to expand)
What is pneumothorax?
The entry of atm air into the IP space through a wound
Lung collapses
Describe the process of INSPIRATION
- Contraction of diaphragm and ext. intercostals
- Diaphragm flattens and ribs move upwards + outwards
- Thoracic volume increases, thorax expands
- Pip becomes more subatmospheric
- Transpulmonary pressure increases > elastic recoil of lungs
- Lungs expand
- Palv < Patm
- Air flows IN
Describe the process of EXPIRATION
- Diaphragm and external intercostals relax
- Thoracic volume decreases, chest wall recoils inwards
- Pip increases and becomes less subatmospheric
- Transpulmonary pressure decreases < elastic recoil of lungs
- Lungs passively recoil
- Palv > Patm
- Air flows OUT
How does forced expiration take place?
- Internal intercostal muscles contract, decreasing thoracic volume
- Abdominal muscles contract, further decreasing thoracic volume
What is dead space?
Volume of air not contributing to ventilation (anatomical and alveolar DS)
How much air is in the physiological dead space?
175mls (anatomical DS = 150mls, alveolar DS = 25mls)
What are the 7 layers gases must diffuse through in the air-blood barrier?
- Fluid lining alveolus
- Alveolar epithelium (/type 1 pneumocytes)
- Basement membrane of alveolar cells
- Interstitial space between epithelial and endothelial cells
- Basement membrane of capillary endothelium
- Capillary endothelial cells
- RBC
What is ventilation-perfusion mismatch?
Condition where areas of the lung receive oxygen but no blood flow (dead space/wasted ventilation) OR they receive blood but no oxygen
What is hypoxic pulmonary constriction?
Decrease in local alveolar ventilation –> decrease in alveolar and arterial pO2 –> VASOCONSTRICTION, diverting blood away from poorly ventilated area
What is local bronchoconstriction?
Decrease in local blood flow –> reduced local pCO2 –> BRONCHOCONSTRICTION, diverting airflow away from poorly perfused areas
What is PaCO2?
Arterial CO2
What is PACO2?
Alveolar CO2
What is PaO2?
Arterial O2
What is PAO2?
Alveolar O2
What is PIO2?
Pressure of inspired O2
What is V.A?
Alveolar ventilation
What is V.CO2?
CO2 production
In what two forms can Hb exist?
Oxyhaemoglobin (HbO2)
Deoxyhaemoglobin (Hb)
How does oxygen bind to Hb?
The binding of one molecule of O2 causes a shape change that increases Hb’s affinity by exposing remaining oxygen-binding sites
At what partial pressure is Hb said to be 90% saturated?
60mmHg
What contributes to the pO2 of the blood?
Only dissolved oxygen (oxygen bond to Hb doesn’t)
What factors cause Hb to have a lower affinity for O2?
- Increased DPG
- Increased temperature
- Decreased pH (acidic)
What factors cause Hb to have a lower affinity for O2?
- Decreased DPG
- Decreased temperature
- Increased pH (alkaline)
What is the effect of CO (carbon monoxide) on oxygen binding to Hb? (3)
- CO has 200x greater affinity for oxygen binding sites on HB
- CO competes w/ O2
- Reduces Hb’s affinity for O2
PaCO2 =
k V.CO2 / V.A
partial pressure of arterial CO2 is inversely related to alveolar ventilation
What are the 3 ways CO2 is carried in the blood?
- Bound to Hb - carbaminohaemoglobin (HbCO2)
- Plasma dissolved CO2
- As HCO3-
What constitutes total-blood carbon dioxide?
Dissolved CO2
HCO3-
CO2 in HbCO2
Why is venous blood (pH 7.36) only slightly more acidic than arterial blood (pH 7.4)?
Deoxyhaemoglobin buffers H+ so only a small amount of H+ generated remains free in the blood
What are the 3 main pH buffering systems of the body??
- Intracellular/ extracellular buffers
- Lunds eliminating CO2
- Renal HCO3- reabsorption and H+ excretion
What can hypoventilation lead to?
Respiratory acidosis (decreased pH and HCO3-)
What can hyperventilation lead to?
Respiratory alkalosis (increased pH and HCO3-)
pH = (Henderson-Hasselbalch equation)
6.1 + log10([HCO3-] / [0.03*PCO2])
What is Dalton’s law?
Pressure exerted by each gas in a mixture of gases is independent of the pressure exerted by the other gases
What is the total pressure of a mixture of gases?
The sum of the individual partial pressures exerted by the gases
The partial pressure of a gas is directly proportional to what?
Its concentration
PAO2= (alveolar gas equation)
PiO2 - PaCO2 / R
R is the respiratory quotient
What is the law of Laplace? Pressure=
P = 2T / r
What is lung compliance?
The change in lung volume caused by a given change in transpulmonary pressure.
(Greater lung compliance, the more readily the lungs expand)
What determines lung compliance?
- Stretchability of lung tissue
2. Surface tension of air-water interface of alveoli
What is surfactant?
Detergent-like substance that reduces surface tension thus increasing lung compliance so lungs expand more easily
How is fetal circulation different from adults?
3 ducts (foramen ovale, ductus arteriosus and ductus venusom)
2 umbilical arteries
1 umbilical vein
What stimulates surfactant secretion?
Deep breaths, which stretch type 2 pneumocytes to secrete surfactant
What does O2 do in systemic arteries?
Vasoconstrictor (as O2 needs to go to hypoxic tissues)
What does O2 do in pulmonary arteries?
Vasodilator
What does hypoxia/ acidosis/ CO2 do in systemic arteries?
Vasodilator
What does hypoxia/ acidosis do in pulmonary arteries?
Vasoconstrictor
What neurotransmitter is involved in parasympathetic regulation of airways?
ACh
What receptor is involved in parasympathetic regulation of airways?
M3 (muscarinic)
Does parasympathetic regulation have a direct/ indirect effect on airways?
Direct
What neurotransmitter is involved in sympathetic regulation of airways?
Noradrenaline
What receptor is involved in sympathetic regulation of airways?
B2 (beta-adrenergic)
Does sympathetic regulation have a direct/ indirect effect on airways?
Indirect
