Lung Physiology Flashcards
What is the respiratory pump?
Abdominal and thoracic structures that contribute to the expansion and contraction of lungs.
What structures make up the respiratory pump?
Consist of: Bones (ribs and sternum), muscles (diaphragm and intercostals), pleura, nerves
Define transpulmonary pressure (P(tp))
difference in air pressure between inside and outside of lungs (alveolar vs intrapleural pressures)
Respiratory pump needs to move how much air per minute? What is this volume known as?
5L per min.
Aka Minute volume
Define intrapleural pressure (P(ip)) and what is another name for it
pressure in the pleural space, aka intrathoracic pressure
Define alveolar pressure (P(alv))
pressure in pulmonary alveoli
How is inspiration induced?
Neurally induced contraction of diaphragm and external intercostal muscles located btwn ribs
* Note: DIAPHRAGM in the most imp inspiratory muscle during normal quiet breathing
Which nerve is used to transmit impulses stimulating contractions to the diaphragm and where does it arise from?
Phrenic nerve
C3, 4, 5
*Note: C3, 4, 5 keeps the diaphragm alive
Describe the process of inspiration in order
- Diaphragm contracts causing its dome to move downwards -> causing thorax to enlarge and increase its volume
- Simulatenously, activation of motor neurones in intercostal nerves to external intercostal muscles causes them to contract -> resulting in upward and outward movement of ribs & further increase of thoracic volume
- As thorax expands, intrapleural pressure is lowered & transpulmonary pressure is more positive -> lung expansion since the force acting to expand to the lungs (transpulmonary pressure) is becoming greater than that of elastic recoil exerted by lungs
- lung expansion results in alveolar pressure becoming - , causing inward airflow
- At end of inspiration, chest wall no longer expanding but yet to start passive recoil since lung size no change and glottis open at this point
alveolar pressure = atmospheric pressure, since elastic recoil of lungs has been balanced by transpulmonary pressure -> no airflow
When does expiration occur
@ end of inspiration
Describe the process of expiration
- at end of inspiration, motor neurones to diaphragm & external intercostal muscles decrease their firing so these muscles can relax-> diaphragm ascends -> so thoracic volume decrease
- As they relax, lungs & chest walls start to passively collapse due to elastic recoil -> cuz muscle relaxation causes intrapleural pressure to increase-> so transpulmonary pressure decrease (become more - ) -> so transpulmonary pressure acts to expand lungs & become < elastic recoil that acts to reduce lungs. Result: Lungs passively collapse
- As lungs become smaller, air in alveoli becomes temporarily compressed -> so alveolar pressure increase (becomes more + & exceeds atmospheric pressure) Result: outward airflow
At rest expiration is active/ passive
Give explanation for your answer
passive
relies only on relaxation of external intercostal muscles & diaphragm & elastic recoil of lungs
What muscles are involved in expiration:
Diaphragm: relaxes, moves superiorly
External Intercostals: relax. ribs cage descends due to recoil of costal cartilages
Accessory muscles (if forced): Ab wall muscles (transverxe & Oblique) : increases intra abdominal pressure, pushing diaphragm upwards in thoracic cavity Internal intercostals: depresses ribs Innermost intercostals: depresses ribs
State the Henderson-Hasselbalch equation in respi
pH = 6.1 + log (HCO3/ H2 CO3)
- 1 = dissociation constant for bicarbonate buffer system
- 03*PCO2 = estimate of H2CO3
- 03 = blood CO2 solubility coefficient
What do you call the act of expiring larger volumes of air eg. during exercise
What do you call the act of expiring larger volumes of air eg. during exercise
How do the lung volume, intrapleural pressure and intrapulmonary pressure change during exhalation
Lung vol: decrease
Intrapleural P: less subatmospheric (more positive)
Intrapulmonary P: positive relative to Patm
How do the lung volume, intrapleural pressure and intrapulmonary pressure change during inhalation
Lung vol: increase
Intrapleural P: more subatmospheric / negative
Intrapulmonary P: ecomes negative relative to Patm
What happens during forced expiration?
Ribs move downwards and inwards: actively decreasing thoracic volume
Abdominal muscles contract: increase in intra abdominal pressure so relaxed diaphragm is forced further up into thorax -> further decrease of thoracic volume
Define dead space
volume of air not contributing to ventilation
*150ml anatomically + 25ml in alveoli = 175ml total
Where does gas exchange occur?
btwn alveoli and capillaries
How many alveoli per lung & how many capillaries per alveolus
300mil
1000
Terminal Bronchioles lead to respiratory bronchioles (found in centre of acinus) to alveolar ducts then Gas exchange happens between the alveoli and capillaries. What is the total combined area for gas exchange?
40-100m^2
Name the 7 layers O2 and CO2 needs to diffuse through to go from alveoli to capillaries and vice versa
- alveolar epithelium
- tissue interstitium
- capillary endothelium
- plasma layer
- rbc membrane
- rbc cytoplasm
- haemoglobin binding
Describe what is Ventilation/ Perfusion Mismatch
Ventilation-perfusion inequality
When the alveolar airflow (ventilation) and capillary blood flow (perfusion) to each alveolus is not in correct proportion.
What is the main effect of ventilation/ perfusion mismatch
partial pressure of O2 (pO2) is decreased in systemic-arterial blood
What are the two extreme causes of Ventilation/ perfusion mismatch
- May be ventilated alveoli but no blood supply at all (aka dead space/ wasted ventilation) eg. due to blood clot
- Adequate blood flow through areas of lung but no ventilation (aka shunt) eg. due to collapsed alveoli
Name 2 body responses of ventilation/ perfusion mismatch
- hypoxic pulmonary constriction
- most imp one
- decrease in ventilation within a grp of alveoli
eg. as a result of mucus plug blocking small airways -> decrease in alveolar pO2 & in the area around it, including lood vessels
- this decrease of pO2 in alveoli & nearby blood vessels leads to vasoconstriction -> divert blood away from poorly ventilated area
- unique to pulmonary arterial vessels (cuz in systemic, opp would occur) -> ensures blood flow is directed away from diseased areas of lungs - local bronchoconstriction
- if there is decrease in blood flow within lung region cuz of eg. small clot in pulmonary arteriole
- local decrease in blood flow means less systemic CO2 in area so local decrease in partial pressure of CO2
- results in bronchoconstriction which diverts airflow away to areas of lung w/ better perfusion
Name the symbols: PaCO2 PACO2 PaO2 PAO2 PIO2 V̇A V̇CO2
PaCO2: arterial CO2 PACO2: alveolar CO2 PaO2: arterial O2 PAO2: alveolar O2 PIO2: pressure of inspired O2 V̇A: (timed volume) of alveolar ventilation V̇CO2: (timed volume) of CO2 production
Fill in each of the ?
Each haemoglobin molecule is made up of ? subunits bound tgt.
Each subunit consists of a molecular group known as ? and a polypeptide attached to it.
4 polypeptides of a haemoglobin molecule are collectively called ? .
Each of the 4 hemmed groups in a haemoglobin molecule contain one atom of ? to which molecular O2 binds
This a single haemoglobin molecule can bind up to ? O2 molecules
4 heme globin Fe2+ 4
CO2 is carried in 3 ways in blood:
- bound to haemoglobin
- approx 23%
- CO2 + Hb ⇌ HbCO2 - plasma dissolved CO2
- approx 10% - As HCO3- (bicarbonate)
- approx 60-65%
- CO2 + H2O ⇌(w/ carbonic anhydrase) H2CO3 (aka carbonic acid) ⇌ HCO3- (aka bicarbonate) + H+
What is the normal arterial pH
7.4 (7.35-7.45)
When the O2 dissociation curve shifts to the right, what does it mean for O2 affinity? What are the factors that could have caused it and did they increase/ decrease?
O2 affinity decrease when curve shifts to right
Factors: CO2 increase pH decrease temp increase DPG increase
When the O2 dissociation curve shifts to the left, what does it mean for O2 affinity? What are the factors that could have caused it and did they increase/ decrease?
O2 affinity increase when curve shifts to left
Factors: CO2 decrease pH increase temp decrease DPG decrease
What does the plateau on the O2 dissociation curve mean? Explain why
Signifies that high pO2 does not cause large change in O2 saturation percentage
Cuz of positive cooperation where the binding of one O2 molecule leads to higher affinity for the binding of the following O2 molecules
How does CO affect the O2 dissociation curve? Explain why
shifts to left
CO 200 times higher affinity for for haemoglobin than O2. So amt of O2 bound to haemoglobin decrease because CO is competing for binding sites. This means haemoglobin less affinity for O2 so there is less unloading of O2 from haemoglobin in tissues
What leads to respiratory acidosis?
Caused by pCO2 increase
eg. When a person hypoventilates, this means there is inadequate ventilation of alveoli so CO2 cannot be expired properly. pCO2 increases so more carbonic acid is produced, leading to a decrease in blood pH
What leads to respiratory alkalosis?
caused by decrease of pCO2
eg. when a person hyperventilates, pCO2 decreases. This is due to increase in alveolar respiration, leading to a fall in H+ conc and decrease in blood pH
