Respiratory Physiology

Question 1

Functions of the Respiratory System

Answer 1

1. Provide oxygen to body tissue
2. Remove carbon dioxide
3. Help maintain pH balance
4. Sensing odors
5. Voice production
6. Defense against pathogens

Question 2

Main Function of Respiratory System

Answer 2

Pulmonary ventilation: inspiration and expiration
Gas exchange between air and blood
Transportation of gases to tissues
Gas exchange between the blood and tissues

Question 3

Systemic Respiration

Answer 3

Exchange of O2 and CO2 between atmosphere and body tissues

Question 4

Aerobic Respiration

Answer 4

Takes place in mitochondria and requires oxygen and glucose, producing carbon dioxide, water and ATP.
C6H12O6 + 6O2 → 6CO2 + 6H2O

Question 5

External Respiration

Answer 5

PalvO2 = 104 mmHg, PcapO2 = 40 mmHg
PalvCO2 = 40 mmHg, PcapCO2 = 45mmHg (small gradient, high solubility)

Question 6

Internal Respiration

Answer 6

PtissueO2 = 40 mmHg, PcapO2 = 100 mmHg

PtissueCO2 > PcapCO2

Question 7

Medullary Respiratory Centers

Answer 7

Clustered neurons in two areas of the medulla oblongata appear to be critically important in respiration:

• Dorsal respiratory group (DRG)
• Ventral respiratory group (VRG)

Question 8

Dorsal Respiratory Group

Answer 8

Integrates input from peripheral stretch and chemoreceptors and communicates this info to VRG.

Question 9

Ventral Respiratory Group

Answer 9

Rhythm generating.
When inspiratory neurons fire:
- Impulses travel along phrenic and intercostal nerves to excite diaphragm and external intercostal muscles.
- Thorax expands and air rushes in lungs.
When expiratory neurons fire:
- Output stops
- Passive expiration, inspiratory muscles relax, lungs recoil.

Question 10

Pontine Respiratory Center

Answer 10

Transmit impulses to VRG of medulla.
Modifies and fine tunes breathing rhythms generated by VRG during certain activities such as vocalization, sleep and exercise.

Question 11

Neural Influences - hypothalamic vs cortical control

Answer 11

Hypothalamic Controls: Emotions and pain send signals to respiratory centers, modifying respiratory rate and depth.
Cortical Controls: Breathing normally regulated involuntarily in brain stem, can also exert conscious control over rate and depth.

Question 12

Respiratory Pressure - Expiration

Answer 12

• Expiration: Alveoli volume decreases, Palv increases.
  Patm < Palv → Air moves out of lungs until pressures are equal again.
• End of expiration: Patm = Palv → No air movement

Question 13

Pressure Gradient that Drives Ventilation

Answer 13

Palv - Patm

Intrapulmonary pressure - Atmospheric pressure

Question 14

Respiratory Pressure - Inspiration

Answer 14

• Inspiration: Alveoli volume increases, Palv decreases. Patm > Palv → Air moves in to lungs.
• End of inspiration: because of the airflow into lungs Patm = Palv → No air movement.
  Diaphragm and external intercostal muscles contract, expansion of thoracic cavity stretches lungs: volume increases, pressure decreases.

Question 15

Atmospheric Pressure

Answer 15

760 mmHg at sea level - constant.

Question 16

Intrapleural Pressure (Pip)

Answer 16

Pressure in pleural cavity.
Decreases with inhalation
Increases with exhalation
Pip < Palv (always negative compared to Palv)
Negative Pip created by: tendency of thorax to expand outwards, tendency of lungs to recoil (elasticity). Intrapleural fluid keeps it from pulling apart.

Question 17

Transpulmonary Pressure

Answer 17

Difference between alveoli pressure and pleura pressure.
Palv - Pip
Increasing transpulmonary pressure → expansion of alveoli

Question 18

Alveolar Volume

Answer 18

Alveoli on top always inflated, on bottom no because: gravity and weight of lung increase pleural pressure (less negative) at the base of the lung and thus reducing alveolar volume.

Question 19

Dependent Region on Lungs

Answer 19

Lowest part of lung in relation to gravity (bottom lung in side-lying position). Alveoli will inflate in this region.

Question 20

Boyle’s Law

Answer 20

Pressure inversely related to its volume (under constant temperature in closed system.
Pressure ↑ → Volume ↓
Pressure ↓ → Volume ↑
Gas moves from high pressure region to low pressure region.

Question 21

Breathing

Answer 21

Process in which the respiratory pump creates ventilation.

Question 22

Respiration

Answer 22

1. Exchange of gas between the environment and tissue cells, by external respiration at alveola-capillary level and internal respiration at capillary- tissue level.
2. Regulation of the acid-base, metabolic and defense functions of the respiratory system.

Question 23

Ventilation

Answer 23

Gas movement between the outside and the alveoli.

Ventilation (L/min) = volume (L) x frequency (breaths per minute) → 0,5 L(tidal volume) x 10 (normal frequency) = 5L.

Question 24

Conducting Zone

Answer 24

No alveoli. No gas exchange. 150ml out of the 500 will stay in this area. Only 350ml will reach the alveoli.
Dead space ventilation.

Question 25

Alveolar Ventilation (VA)

Answer 25

RR x (VT - DSV) : Respiratory rate x (tidal volume - dead space ventilation). During exercise: VA must increase → increased VT Determines O2 and CO2 levels VA ↓ → PaCO2 ↑: acid-base balance disturbance, hypoxemia/hypercapnia.

Question 26

Dead Space Ventilation

Answer 26

Wasted ventilation in conducting zone. Anatomic dead space: conducting part of respiratory tract. 150 ml of VT. Physiological dead space: anatomic + alveolar dead space (alveoli not taking part in gas exchange).

Question 27

Collateral Ventilation

Answer 27

Network connection between alveoli. If alveoli is not ventilating, the collateral channel will open. - Interalveolar pores of Kohn - Interbronchial channels - Bronchiole-alveolar channels

Question 28

Hyperventilation

Answer 28

incresing of the exhaled volume (VE) that eliminates carbon dioxide leading to hypocapnea. Related to ventilation not respiratory frequency.

Question 29

Hypoventilation

Answer 29

Reduce alveolar ventilation due to reduced tidal volume (VT) followed by hypercapnea. Short breaths. Related to ventilation, not to respiratory frequency.

Question 30

Tachypnoea

Answer 30

increased RR > 20 breaths/min. | Cannot breath slowly.

Question 31

Bradypnoea

Answer 31

decreased RR < 10 breaths/min.

Question 32

Apnea

Answer 32

Cessation of breathing (more than 30 sec)

Question 33

Laminar Flow

Answer 33

Facilitated by slow smooth breath. In order to overcome peripheral resistance to reach alveoli with least amount of energy. Fast breath encourages unhelpful turbulence.

Question 34

What are the physical factors influencing pulmonary ventilation?

Answer 34

* Airway resistance * Lung compliance * Alveolar surface tension (pulmonary surfactant)

Question 35

Airway Resistance - Poiseuille's law

Answer 35

``` Resistance (R) through an airway depends on: • Viscosity (ƞ) of gas • Length of tube (l) • Radius of tube (r) ↑ diameter → ↑ resistance ↑ length of tube → ↑ resistance ↑ viscosity of gas → ↑ resistance ```

Question 36

Consequences of Increased Airway Resistance

Answer 36

↓ airway caliber ↓ airflow ↑ work of breathing Breathlessness

Question 37

Work of Breathing (WOB)

Answer 37

Work done during inspiration to overcome resistive and elastic forces of airways, lungs and chest wall. Elastic resistance: 80% of WOB (deep breathing) Airflow resistance: 20% of WOB (rapid breathing)

Question 38

Compliance

Answer 38

Willingness of elastic structure to distend (change its state). Lung is least compliant at either extreme of lung volume. - Difficult to inflate closed alveoli - Difficult to hyperinflate those that are fully inflated.

Question 39

Pulmonary Surfactant

Answer 39

surface-active lipoprotein complex formed by Type II pneumocytes. Reduces the surface tension inside alveoli. Cannot ventilate without it! Alveoli will collapse.

Question 40

Lung Volumes - VT, ERV, IRV, RV

Answer 40

- Tidal Volume (VT): movement of air during quite breathing, 0.5 L. - Expiratory reserve volume (ERV): Extra air pushed out of lungs beyond VT after full exhalation. 1.7 L. - Inspiratory reserve volume (IRV): extra air drawn in beyond VT after full inhalation. 3 L. - Residual volume (RV): air remaining in lungs after full exhalation. 1.3 L.

Question 41

Total Lung Capacity

Answer 41

Sum of lung volumes. Total air in lungs after full inhilation. VT+ERV+RV+IRV

Question 42

Fick's Law of Diffusion

Answer 42

``` Diffusion (gas exchange): • Concentration / pressure gradient • Gas solubility • Transit time red blood cells (RBC) • Surface area of alveolar membrane • Thickness of alveolar membrane • Ventilation/perfusion coupling ```

Question 43

Thickness of Alveocapillary Membrane

Answer 43

0.5 - 1 u(mju)m - very efficient | Thicker membrane → impaired diffusion → ↓O2

Question 44

Essential Components for Gas Exchange

Answer 44

• V̇ : air which reaches lungs (alveolar ventilation) • Q̇ : blood which reaches lungs (alveolar perfusion) V̇ / Q̇ : matching between (alveolar) ventilation and perfusion

Question 45

Zones of Gas Exchange

Answer 45

1. Alveoli (full volume) squeezes capillary. Pressure of alveoli is bigger than pressure of artery and vein. PA > Pa > Pv - No gas exchange. Top part of lung. 2. Depends on cardiac cycle. Psystolic > PA > Pdiastolic. Gas exchange possible during systole. 50% efficient. Middle part of lung 3. Artery and vein pressure more than alveoli. Pa > Pv > PA. Gas exchange. 100% efficient. Bottom part, dependent zone.

Question 46

Shunt vs. Dead Space

Answer 46

No gas exchange in either. Dead space: Alveoli ventilating without perfusion (gas exchange). Shunt: Fraction of blood not getting oxygen (no gas exchange).

Question 47

Pathological Mismatch - Ventilation/Perfusion

Answer 47

V/Q should be equal to 1. Pathological mismatch is due to a high or low ratio • High ratio : alveoli ventilated but perfusion impaired - V/Q = 5/0 = infinite. • Low ratio : lung perfused but not adequately ventilated - V/Q = 0/5 = 0.

Question 48

V/Q Regulation

Answer 48

V: regulated by diameter airways Q: regulated by diameter blood vessels