Module 4 - Respiratory System Flashcards
What is the main function of the Respiratory System?
= gas exchange between atmosphere and blood (so that cells can use oxygen and get rid of carbon dioxide)
List the 4 steps of external respiration
- Ventilation or gas exchange between the atmosphere and alveoli in the lungs
- Exchange of oxygen and carbon dioxide between air in the alveoli and the blood in the pulmonary capillaries
- Transport of oxygen and carbon dioxide by the blood between the lungs and the tissues
- Exchange of oxygen and carbon dioxide between the blood in the systemic capillaries and the tissue cells
Describe alveoli
- alveoli = respiratory air sacs
- singular = alveolus; plural = alveoli
- alveolar sac = cluster of alveoli
- covered in pulmonary capillaries
- site of gas exchange
Describe the 3 types of alveoli cells
Type 1 Alveolar Cell = squamous cells lining the alveoli
Type 11 Alveolar Cell = produce surfactant
Alveolar Macrophages = phagocytose foreign material
Describe alveoli gas exchange
- respiratory membrane = Type 1 Alveolar cell + endothelial cell + basement membrane
- gas exchange optimised by: factors affecting diffusion rate:
- large surface area
- short diffusion distance
Describe the bronchial tree
- branching of airways in the lungs:
- trachea
- bronchi
- bronchioles (<1mm diameter)
- terminal bronchioles
- respiratory bronchioles
Describe bronchial tree structural changes
- cartilage provides structural support in trachea (C-shaped rings) and bronchi (plates) -> keeps airways open
- smooth muscle in bronchioles allow small airways to dilate or constrict : bronchodilation, bronchoconstriction
Describe lungs and the thoracic cavity
- lungs: right lungs has 3 lobes; left lungs has 2 lobes
- the lungs are highly elastic
- thoracic cavity:
- thoracic wall (rib cage)
- internal and external intercostal muscles
- diaphragm
- other components: heart, major blood vessels, oesophagus
Discuss the pleural sac
- double walled closed sacs
- between lungs and thoracic wall
- filled with intrapleural fluid
- lubricates pleural surfaces
- “sticks” lungs to thoracic wall (surface tension)
Describe pressure
- units: mmHg (millimetres of mercury)
- atmospheric pressure
- pressure exerted by weight of air on objects on earths surface
- decreases with height from sea level
- sea level = 760 mmHg
List the 3 pressures influencing ventilation
- Atmospheric Pressure
- Intra-alveolar Pressure
- Intrapleural Pressure
Describe Atmospheric Pressure
= the pressure exerted by the weight of the gas in the atmosphere on objects on Earth’s surface
- 760 mmHg at sea level
Describe Intra-alveolar Pressure
= the pressure within the alveoli
- atmosphere and alveoli are linked by conducting airways -> intra-alveolar pressure quickly becomes the same as atmospheric pressure
- 760 mmHg when equilibrated with atmospheric pressure
Describe Intrapleural Pressure
= the pressure within the pleural sac
- the pressure exerted outside the lungs within the thoracic cavity
- usually less than atmospheric pressure
- 756 mmHg (also expressed as -4 mmHg)
List the 2 forces that the thoracic wall and lungs are held together by
- Surface tension of intrapleural fluid
2. Transmural pressure gradient
Describe the transmural pressure gradient
trans = across ; mural = wall
- is the pressure difference between the lungs and the pleural cavity
- pushes lungs out towards the thoracic wall
Describe gas pressure and volume
Boyle’s Law
- pressure of a gas in a container varies inversely with the volume of the gas
e.g. increasing the volume decreases the pressure
P1V1 = P2V2
Describe Inspiration
- contraction of:
- diaphragm
- external intercostal muscles
- inspiration is muscle activity working AGAINST elastic recoil
List the 4 step process of inspiration
- Diaphragm and external intercostal muscle contract
- Lung volume increases
- Slight drop in intra-alveolar pressure
- Air enters lungs
Describe Expiration
- expiration is a passive process -> no contraction of muscles
- decreased lung volume caused by:
- relaxation of muscles (diaphragm and external intercostals)
- elastic recoil of lungs
List the 4 step process of expiration
- Diaphragm and external intercostal muscles relax
- Lung volume decreases
- Slight rise in intra-alveolar pressure
- Air leaves lungs
Describe forced breathing
- normal breathing = quite breathing
- forced breathing:
- exercise or disease
- requires extra muscles
Describe Forced breathing - inspiration
- further contraction of external intercostals and diaphragm (as much as 10cm)
- contraction of accessory muscles in neck
**Inspiration is muscle activity working AGAINST elastic recoil
Describe Forced breathing - expiration
- internal intercostals draw in ribs
- abdominal muscles contract and push the diaphragm upwards
- forced expiration is not passive
**Forced expiration is muscle activity working WITH elastic recoil
List 3 physical factors that influence ventilation
- Airway Resistance
- Alveolar Surface Tension
- Lung Compliance and Elastic Recoil
Describe Airway Resistance
- airflow rate (F) depends on
- air pressure gradient (delta P): difference between atmospheric and intra-alveolar pressure
- airway resistance (R)
F = delta P/R
- airway resistance is very low in healthy individuals
- friction of air against walls of airways
- increased resistance = slower airforce
- main factor increasing resistance is reduced bronchiole radius
- bronchoconstriction
- mucous
- fluid
Describe Alveolar Surface Tension
- alveoli are lined with a layer of water
- creates surface tension
- water molecules attracted to each other, but not air
- can cause alveoli to collapse (expiration)
- resists inflation of alveoli (inspiration)
- surface tension inside an alveolus generates an inward-directed collapsing pressure
Describe Surface Tension
- Law of LaPlace: P=2T/r
- the magnitude of inward-directed pressure (P) is directly proportional to the surface tension (T) and inversely proportional to the radius (r) of the alveolus
- the collapsibility of an alveolus can be reduced by decreasing the surface tension
- for any given surface tension, small alveoli have a greater tendency to collapse
Describe Surfactant
- surfactant breaks the surface tension of water
- produced by type 11 alveolar cells
- mixture of proteins and lipids
- breaks hydrogen bonds between water molecules
- stops alveoli from collapsing
- easier to expand alveoli during inspiration
Describe Lung Compliance and Elastic Recoil
- compliance
*stretchability of the lungs during inspiration
*high compliance = easily stretched
*low compliance = hard to stretch - factors reducing compliance
*high surface tension (reduced surfactant)
*scarring of lung tissues - restrictive diseases
- elastic recoil
*ability of lungs to rebound (shrink)
*important during expiration - elastic recoil influenced by 2 factors:
i) elastic fibres
ii) surface tension
Decreased surface tension = decreased elastic recoil - emphysema
Define Inspiration Capacity (IC)
- maximum volume of air that can be inspired
- TV + IRV
Define Vital Capacity (VC)
- maximum amount of air expired after maximum inspiration
- TV + IRV + ERV
Define Functional Residual Capacity (RFC)
- volume of air in lungs after normal expiration
- ERV + RV
Define Tidal Volume (TV)
- air inspired or expired during quiet breathing
- 500 ml