Week 4 Flashcards
Explain the Pulmonary Ventilation
Quiet Inspiration (ACTIVE PROCESS)
-Diaphragm moves down 1cm and ribs are lifted by external and internal intercostals (intercartilagenous part) and pectoralis minor
-The lungs expand with chest wall, intrapulmonary pressure drops and air is inhaled (moves from higher pressure outside to lower pressure inside)
Explain the Pulmonary Ventilation Quiet Expiration (PASSIVE PROCESS)
-Driven by elastic recoil of lung connective tissue (1/3 contribution) and surface tension in alveoli (2/3 contribution) ~ no muscle action
-In this way, intrapulmonary pressure increases and air is pushed out (moves from higher pressure inside to lower pressure outside)
Explain Pulmonary Ventilation Forced inspiration (ACTIVE PROCESS)
- sternocleidomastoid, scalenes and pectoralis minor further lift clavicle, sternum and first rib upwards and therefore increase the volume of the thoracic cavity)
- Diaphragm can move down 13 – 14 cm!!
Explain Pulmonary Ventilation Forced expiration (ACTIVE PROCESS)
-external oblique and rectus abdominis contract, increasing pressure in the abdominal cavity which pushes diaphragm up faster and harder
-internal intercostals (interosseous part) contract to depress ribs (action opposite of external intercostals)
-intrapulmonary pressure exceeds the atmospheric by up to 30mm Hg
What is Intrapleural Pressure?
The pressure in the pleural cavity
- it is always sub-atmospheric (below atmospheric pressure) and sub-pulmonary (below pressure in lungs)
- during inspiration intrapleural pressure decreases even more due to chest cavity expansion
- this pressure keeps the parietal and visceral pleura very close together (they are not physically connected)
- A pneumothorax is when intrapulmonary and intrapleural pressures are equalcollapsed lung which cannot expand with thoracic cavity expansion
What are the 3 steps in pulmonary ventilation?
What is gas flow influenced by?
apartfrompressuredifferences,gasflowisinfluenced by airway resistance
What is airway resistance mainly affected by?
thecombined diameter of all conducting airways (itisusuallyinsignificantbecauseofthelargeairway diameters in the first part of the bronchial tree)
airway resistance is increased in ….
bronchoconstriction
Equation for Relationship between flow (F), pressure (P), and resistance (R) is:
- ∆P: pressuregradientbetweenatmosphereandalveoli (2 mm Hg or less during normal quiet breathing)
- Gasflowchangesinverselywithresistance
What is surface tension?
a thin layer of watery fluid covering alveolar wall causes an inward directed force
Where does surface tension arise?
surface tension arises at all air- water interfaces because water molecules are more strongly attracted to each other (hydrogen bonding) than to molecules of air, thus resisting expansion of alveoli during inspiration
surface tension needs to be overcome during
Inspiration
What is Surfactant?
detergent-like substance
What is surfactant a mixture of?
mixture of phospholipids and lipoproteins
What is surfacant produced by?
produced by surfactant-secreting (Type 2) cells
What lowers alveolar surface tension?
Surfactant lowers alveolar surface tension and increases↑ expandability
…… is mixed with water molecules which significantly reduces the strength of attraction between water molecules thus enabling expansion of alveoli during inspiration
Surfactant
What prevents the collapse of alveoli during expiration
Surfactant
Respiratory Volumes and Capacities graph
Respiratory Volumes and Capacities table
What is Anatomical Dead Space?
volume of air in the conducting zones that never contributes to gas exchange in the alveoli (~150ml) hence only ~350ml available for alveolar ventilation (= functional volume)
• dead space also includes non functioning alveoli
What is Alveolar Ventilation Rate (AVR)?
- This is flow of gases into and out of the alveoli during a particular time
Formulae for Alveolar Ventilation Rate (AVR)?
E.g.TheAVRforapatientwithanormalrateand depth of breathing is:
What is the Composition of Air?
Composition of air: 78.6% nitrogen, 20.9% oxygen, 0.04% carbon dioxide, 0.5% water vapour (depending on temperature and humidity), and minor gases argon, neon, helium, ozone and methane
What is the composition of Partial Pressure?
• Dalton’s Law – the total atmospheric pressure is the sum of the contributions of the individual gases
– partial pressure – separate contribution of each gas in a mixture
– at sea level air pressure is 760 mmHg so partial pressures are:
• PN2=78.6%x760mmHg=597mmHg
• PO2=20.9%x760mmHg=159mmHg • PH2O=0.5%x760mmHg=3.7mmHg
• PCO2=0.04%x760mmHg=0.3mmHg • PN2+PO2+PH2O+PCO2=760mmHg
Composition of inspired air and alveolar air is different because of three influences:
– air is humidified by contact with mucous membranes (alveolar PH2O is more than 10 times higher than inhaled air)
– freshly inhaled air mixes with residual air left from the previous respiratory cycle
– alveolar air exchanges O2 and CO2 with the blood
The main difference between inspired air and alveolar air
PO2 of alveolar air is about 65%
that of inspired air (meaning less oxygen in the air in our lungs than the atmospheric air),
while PCO2 is more than 130 times higher (meaning more carbon dioxide in the air in our lungs compared to atmospheric air)
What is Henry’s law?
When a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure
Dissolving of gases in fluid: At equilibrium,…..
At equilibrium, the partial pressures in the two phases (alveolar air and blood) will be equal
The amount of gas that will dissolve in a liquid also depends upon its ……
The amount of gas that will dissolve in a liquid also depends upon its solubility
– CO2 is 20 times more soluble in water than O2
– very little nitrogen dissolves in water
External Respiration: Gas Exchange Process.
What is partial pressure gradient for O2?
Partial pressure gradient for O2 in the alveoli is steep
– bloodPO2=40mmHg
– alveolar PO2 = 104 mm Hg
External Respiration: Gas Exchange Process. Oxygen partial pressures in
alveolar air and blood will
equalise in …..
Oxygen partial pressures in
alveolar air and blood will
equalise in ~0.25 seconds
(about 1/3 the time a red
blood cell is in a pulmonary capillary)
External Respiration: Gas Exchange Process. Partial pressure gradient for CO2 in the lungs is….
Partial pressure gradient for CO2 in the lungs is less
steep:
– blood PCO2 = 45 mm Hg
– alveolar PCO2 = 40 mm Hg
• But CO2 diffuses much faster than oxygen so CO2 moves in
equal amounts with oxygen
External Respiration: O2 diagram
Does o2 dissolve in water easily, explain?
O2 does not easily dissolve in water - only 1.5% of O2 is transported physically dissolved in blood
What is oxyhaemoglobin?
98.5% of O2 in blood is chemically combined with iron in haemoglobin (Hb) in form of oxyhaemoglobin
Blood contains …
Bloodcontains20mLoxygenper100mL
How much Oxygen in arterial blood?
Normally in arterial blood almost all haemoglobin is saturated with oxygen (98% saturation)
What does an increase in PO2 produce?
Further increases in PO2 (e.g. breathing deeply, breathing air with greater oxygen concentration) produce minimal increases in O2 binding and dissolving in blood
What is Anaemia?
Anaemia (reduced concentration of haemoglobin)
reduces ability of blood to carry O2)
What type of o2 is allowed to diffuse into tissue?
Only the dissolved O2 can diffuse into tissues (O2 needs to be separated from haemoglobin before it can diffuse into tissues)
How much o2 is unloaded during one systemic circulation?
Only 20-25% of bound O2 is unloaded during one systemic circulation (i.e. 4-5 mL of that 20 mL oxygen per 100 mL). Thus venous blood contains a bit of oxygen
What happens when o2 levels in tissues drop?
If O2 levels in tissues drop (e.g. during increased metabolic activity as in exercise) more oxygen dissociates from haemoglobin and is used by cells
• With moderate increase in oxygen consumption respiratory rate or cardiac output need not increase