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PHARM 311 Respiratory System > 3. Structure & Function of the Respiratory System > Flashcards

3. Structure & Function of the Respiratory System Flashcards

1
Q

Upper respiratory tract

A

Consists of the nose, nasal passages, paranasal sinuses, pharynx & portion of larynx above the vocal cords

NOTE: Tracheo-bronchial treee has VOLUME but no gas exchange takes place - ANATOMICAL DEAD SPACE

Tidal volume (VT_ ~500 mL

Alveolar volume: (VT – VD) ~350 mL

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2
Q

Function of the respiratory system

A
  1. Gaseous exchange (diffusion):
    - Oxygen exchange at alveolar-capillary interface
    - Carbon dioxide exchange at alveolar-capillary interface
    - Oxygen exchange at cells
    - Carbon dioxide exchange at cells
  2. Transport (conventional process):
    - Oxygen transport
    - Carbon dioxide transport

Diffusion distance overcome by coupling diffusion with transport

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3
Q

Lung volumes:

  1. Functional Residual Capacity (FRC)
  2. Tidal volume (VT)
  3. Inspiratory reserve volume
  4. Expiratory reserve volume
  5. Inspiratory capacity
  6. Vital capacity
  7. Residual volume
  8. Total lung capacity
A
  1. Functional Residual Capacity (FRC): 3L
  2. Tidal volume (VT): 0.5 L
  3. Inspiratory reserve volume: ~2 L
  4. Expiratory reserve volume: ~2 L
  5. Inspiratory capacity: ~3 L
  6. Vital capacity: ~5 L
  7. Residual volume: ~1 L
  8. Total lung capacity: ~6 L
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4
Q

Pleural membranes & Liquid layer of pleural membranes

A

Plural membranes:

  • Cover the outer surface of the lungs (visceral) & thoracic cavities (parietal)
  • Coupled together with a thin layer of liquid (~20 µm)

Liquid layer:
- Lubricant which allows the lung movement relative to chest wall

Thoracic movements are transmitted to the lungs by pressure changes in the intra-pleural space

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5
Q

Static mechanics of the lungs:

  1. Fcw
  2. FL
  3. Pip
  4. PA
A
  1. Fcw: Force exerted by chest wall
  2. FL: Force exerted by lungs
  3. Pip: Intrapleural pressure (pressure between visceral & parietal pleural membranes)
  4. PA: Atmospheric pressure

Lungs are highly elastic & tend to collapse in which reduces Pip & pulls the chest inwards

PA = PB when airways are open and no air flow

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6
Q

FRC & Compliance of lung & chest wall

A
  • FRC is determined by Compliance of the lung & chest wall
  • Compliance is inversely proportional to elastance - how easily the lung deflates

Compliance = ∆V / ∆P

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7
Q

How is compliance reduced?

A
  1. Reduced outwards mobility of the chest wall e.g. severe obesity, constrictive bandages
  2. Reduced lung volumes e.g. pulmonary oedema
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8
Q

Relaxation Pressure-Volume Relationship

A

When flow is zero: Ptotal = Pelastic = V / C

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9
Q

Ventilation - Definition & how it occurs

A

Movement of air into & out of the lungs

Occurs via bulk flow down the pressure gradient (convection):
Convection is the bulk movement of a fluid (gas/liquid) driven by a pressure gradient

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10
Q

Respiratory muscles: Inspiratory & Expiratory

A

Respiratory muscles (intercostals & others) are utilised to change thoracic volume & create pressure gradients

Inspiratory muscles:

  • Diaphragm
  • External intercostals
  • +/- Accessory muscles (strenuous exercise)

Expiratory muscles:

  • Abdominal wall muscles
  • Internal intercostals
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11
Q

Ventilator settings/requirements

A
  • VT required (10 - 15 mL/kg)
  • Respiratory rate
  • Set concentration of oxygen inspired to maintain normal PaO2 (80 - 100 mmHg)
    Peak inspiratory pressure (5 - 10 cm H2O)
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12
Q

Minute ventilation:

A

Volume of air shifted in & out of the lungs per minute

At rest: VT x fR = 0.5 L x 12 min-1 = 6 L min-1

Exercise: VT x fR = 3 L x 40 min-1 = 120 L min-1

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13
Q

Alveolar ventilation

A

VT: ~ 500 mL
VD: ~ 150 mL
Pulmonary blood volume: ~ 70 mL
Pulmonary blood flow: ~5000 mL/min

V̇A = fR x (VT – VD)
V̇A = 15 x (500 – 150) = ~5250 mL min-1
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14
Q

Factors affecting ventilation

A

A pressure gradient is required to change lung volume & generate air flow V̇

3 other factors that affect the flow rate & ease of ventilation:

  • Surface tension of alveolar fluid
  • Compliance of the lungs
  • Airway resistance

Ptotal = Pelastic + Presistive
Ptotal = V/C + V̇R
where C is compliance & R is resistance

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15
Q

Effect of surface tension: Saline vs Air filled lungs

A

Saline-filled lungs:
- Lungs inflated with saline have much larger compliance

Air-filled lungs:

  • Effects of elasticity & surface tension are seen
  • Larger pressure is required during inflation (hysteresis)
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16
Q

Alveoli - features of cells present

A

Type I cells: Gaseous exchange
Type II cells: Secrete surfactant
Many elastic fibres & capillaries
Large volume of blood in pulmonary circulation (entire RV output)

17
Q

Pulmonary resistance

A

Ptotal = Pelastic + Presistive = V/C + V̇R

Composed of:

  • Frictional resistance of lung & chest wall tissue (~20%)
  • Airway resistance (~80%)

Movement of fluid (air) through a rigid, smooth bore tube is governed by Poiseuille’s Law

18
Q

Airway flow: Laminar vs Turbulant

A

Laminar flow has orderly layers & low resistance

Turbulent flow has disorganised layers & high resistance

19
Q

Airway resistance

A

Total airflow resistance: All the resistances of the nose & mouth (substantial portion of the total) + 23 generation of the tracheobronchial tree

Airway resistance is from the friction between gas molecules & between gas molecules & the airway walls

Airway resistance is important & makes the sliding of lung tissue over each other (viscous tissue resistance) a minor issue

20
Q

Poiseuille’s Law

A 
V̇ = (∆P πr^4) / 8nl
r = radius of cylinder
l = length of cylinder
n = viscosity

The rate of flow is due to the difference in pressure between the 2 ends i.e. Flow is proportional to ∆P

Turbulent flow requires a higher driving pressure

21
Q

Airways - Bronchioles

A

Bronchioles are small passages surrounded by bands of muscles

They divide into smaller & smaller units until they reach the alveoli

22
Q

Distribution of airway resistance

A

Airway resistance is proportional to the length of the air way i.e. doubling length doubles airway resistance

Halving the radius increases the resistance 16-fold

R = (8nl) / πr^4

23
Q

Features of airway resistance

A
  • Most of the resistance is observed in the intermediate sized airways
  • Total cross sectional area increases towards periphery where total airflow is constant
  • Flow is more laminar in small airways
24
Q

Flow volume curves

A

Flow is:

  • Effort dependent at high lung volume
  • Effort independent at low lung volumes
25
Q

Work of breathing

A

Work of inspiration consists of:

  • Compliance work/Elastic work: Work required to expand lungs against elastic forces
  • Tissue resistance work: Work required to overcome the viscosity of the lungs & chest wall structures
  • Airway resistance work: Work required to move air through the airway into the lungs

Work is proportional to ∆P x ∆V

26
Q

Breathing rates that can affect the work of breathing

A

Rapid shallow breathing: Decrease elastic work but increase frictional (viscous) work

Slow deep breathing: Decrease frictional work but increase elastic work

Ventilation can increase to levels of ~ 50L/min

27
Q

Control of breathing

A
  1. Central control:
    - Pons, medulla & other parts of the brain
    - Controls frequency & duration
  2. Sensors:
    - Chemoreceptor, lungs & other receptors
  3. Effectors:
    - Respiratory muscles

All work in sync

Refer to diagram on lecture slides

PHARM 311 Respiratory System (10 decks)

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