WEEK XII (Respiratory system) Flashcards
What are the three basic steps of respiration?
- Pulmonary ventilation/Breathing
- External (pulmonary) respiration
- Internal (tissue) respiration
What is Pulmonary ventilation/Breathing?
The inhalation and exhalation of air and involves the exchange of air between the atmosphere and the alveoli of the lungs
What is External (Pulmonary) respiration?
The exchange of gases between the alveoli of the lungs and blood in pulmonary capillaries across the respiratory membrane
[pulmonary capillary blood gains O2 and loses CO2]
What is Internal (Tissue) respiration?
The exchange of gases between blood in systemic capillaries and tissue cells
What is the importance of Cellular respiration?
- Occurs within the mitochondria
- Involves the metabolic processes of using O2 and producing CO2 while extracting energy from nutrient molecules
What is the Respiratory Quotient (RQ)?
The ratio of CO2 produced to O2 consumed during cellular respiration
RQ = CO2 PRODUCED/O2 CONSUMED
What happens in External respiration?
1) Air is moved into and out of the lungs through VENTILATION allowing for exchange of gases between the atmosphere and alveoli
2) O2 and CO2 are exchanged between the air in the alveoli and the blood in PULMONARY CAPILLARIES through DIFFUSION
3) Blood carries O2 and CO2 between the lungs and the body’s tissues
4) O2 and CO2 are exchanged between the tissue cells and the blood through diffusion across systemic capillaries
What are the Non-respiratory functions of the Respiratory system?
- Route for water loss and heat elimination (humidify + warm inspired air -> prevents drying of alveolar linings & facilitates gas exchange)
- Enhances venous return through “respiratory pump” mechanism
- Maintains normal acid-base balance by regulating amount of CO2 exhaled
- Enables speech
- Traps + removes particles -> defends against inhaled foreign matter
- Lungs act as a filter
- Lungs activate prostaglandins and activate angiotensin II
- Nose enables smell
Describe how the structure of Alveoli aid with diffusion
- Walls consist of a single layer FLATTENED TYPE I ALVEOLAR CELLS -> Short diffusion distance
- Each alveolus surrounded by a network of pulmonary capillaries -> Rich blood supply
- Alveolar air-pulmonary blood interface -> Large surface area
What is the difference between Type I and Type II Alveolar cells?
TYPE I = Flat cells that surround alveoli
TYPE II = Cover alveolar surface and secrete PULMONARY SURFACTANT which helps facilitate lung expansion
Why are defensive alveolar macrophages present within the air sacs?
To guard against foreign particles and pathogens
What is the importance of Minute pores of Kohn?
- Exist between adjacent alveoli -> allows airflow between them
- Important for ventilation in cases where a terminal conducting airway is blocked due to disease -> allows fresh air to reach affected alveolus
How are changes in lung volume achieved?
Through changes in the dimensions of the thoracic (chest) cavity rather than through muscle action within the lungs
What is Pleurisy?
An inflammation of the pleural sac which causes painful breathing
CAUSE: Friction between the inflating and deflating lungs and the inflamed pleural surfaces creates a “friction hub”
What are the three important pressure considerations in ventilation?
- ATMOSPHERIC (BAROMETRIC) PRESSURE
- INTRA-ALVEOLAR PRESSURE
- INTRAPLEURAL PRESSURE (lower than atmospheric pressure)
Why cannot air enter or leave the pleural cavity despite any pressure gradients that may exist?
Since the Pleural sac is a closed sac with no openings -> Intrapleural pressure does not equilibrate with atmospheric or intra-alveolar pressure
The lungs and thoracic wall are held in close apposition by what?
A transmural pressure gradient across the lung wall
Describe how the transmural pressure gradient stretches the lungs to fill the thoracic cavity
INTRA-ALVEOLAR PRESSURE is greater than INTRAPLEURAL PRESSURE which pushes the lungs outward and stretches them to fill the THORACIC CAVITY -> Lungs’ ELASTICITY causes them to attempt to pull inward away from the thoracic wall as they are stretched -> TRANSMURAL PRESSURE GRADIENT prevents lungs from pulling away significantly
What does a slight expansion of the pleural cavity in response to the stretching of the lung cause?
A drop in intrapleural pressure
Describe how the Pleural cavity vacuum contributes to the drop in intrapleural pressure
Pleural cavity is filled with fluid which cannot expand to fill the slightly larger volume -> Creates a vacuum in the small space not occupied by intrapleural fluid -> Vacuum contributes to the drop in intrapleural pressure below atmospheric pressure
How is the relationship between transmural pressure gradient and subatmospheric intrapleural pressure interrelated?
Lungs are stretched due to the TRANSMURAL PRESSURE GRADIENT which exists because the INTRAPLEURAL PRESSURE is less than atmospheric pressure -> SUBATMOSPHERIC INTRAPLEURAL PRESSURE is a result of the stretched lungs attempting to pull away from the larger thoracic wall -> Causes a slight expansion of the pleural cavity and a drop in intrapleural pressure
What happens in a Pneumothorax?
Air enters the pleural cavity -> Intrapleural and intra-alveolar pressures equilibrate with atmospheric pressure -> Transmural pressure gradient across lung wall no longer exists -> Without Transmural pressure gradient to stretch the lung, lung collapses due to unstretched size
Describe what happens in Inspiration
1) Respiratory muscles CONTRACT (including diaphragm and external intercostal muscles)
2) Contraction of diaphragm causes it to flatten + external intercostal muscles elevate the ribs -> expand thoracic cavity
3) Thoracic cavity expands -> intrapleural volume increases -> decrease in intrapleural pressure -> creates a TRANSMURAL PRESSURE GRADIENT across the lung wall
4) Transmural pressure gradient causes the lungs to stretch and expand -> volume of alveoli increases -> decrease in intra-alveolar pressure
5) Decreased intra-alveolar pressure allows air to flow into the lungs down the pressure gradient
Describe what happens in Expiration
1) Respiratory muscles RELAX (including diaphragm and external intercostal muscles)
2) Relaxation of diaphragm causes it to return to dome-shape + external intercostal muscles descends the ribs -> reduce volume of thoracic cavity
3) Decrease in thoracic cavity reduces intrapleural volume -> increase in intrapleural pressure -> compresses lungs -> creates a TRANSMURAL PRESSURE GRADIENT that favours air movement out of lungs
4) Compressed lungs reduce the volume of alveoli -> increase in intra-alveolar pressure
5) Increased intra-alveolar pressure allows air to flow out of lungs down the pressure gradient
Contraction of the diaphragm is stimulated by which nerve?
Phrenic nerve
What are the properties of External intercostal muscles?
- Lie on top of the internal intercostal muscles and run DOWNWARD and FORWARD between adjacent ribs
- Contraction elevated ribs + sternum upward and outward -> enlarges thoracic cavity
What is the difference between External and Internal intercostal muscles?
EXTERNAL INTERCOSTAL MUSCLES:
- lie on top of the internal intercostal muscles and run DOWNWARD and FORWARD between adjacent ribs
- contraction elevated ribs + sternum upward and outward -> enlarges thoracic cavity
Which nerves activate the External and Internal Intercostal muscles during inspiration?
Intercostal nerves
What does the decrease in intrapleural pressure during inspiration contribute to?
- Expansion of the thoracic cavity
- Helps maintain the transmural pressure gradient necessary for lung expansion
How can deeper inspirations be achieved?
- Increased contraction of the diaphragm and external intercostal muscles
- Involvement of accessory inspiratory muscles
How can increased contraction of the diaphragm and external intercostal muscles cause deeper inspirations?
- Thoracic cavity is greater expanded
- Larger increase in thoracic cavity volume -> allows lungs to expand even more
- More significant decrease in intra-alveolar pressure
How can Involvement of accessory inspiratory muscles cause deeper inspirations?
- Raises sternum and elevated the first two ribs -> increases thoracic volume
- Lungs expand even more
- More significant decrease in intra-alveolar pressure
What happens during expiration?
The expiration of inspiratory muscles leads to a return of the thoracic cavity and lungs to their pre-inspiratory size
What causes Expiration?
- Diaphragm relaxation
- Recoil and increased intra-alveolar pressure
Describe how diaphragm relaxation causes expiration
When the diaphragm relaxes, it assumes the original dome-shaped position -> Elevated rib cage falls due to gravity when the external intercostal muscles relax -> Without forces expanding the chest wall and lungs, recoil to their pre-inspiratory size due to elastic properties
Describe how Recoil and increased intra-alveolar pressure causes expiration
Lungs recoil and become smaller in volume -> Intra-alveolar pressure increases -> Great number of air molecules are now compressed into a smaller volume -> Air flows out of lungs down this pressure gradient until intra-alveolar pressure becomes equal to atmospheric pressure
What is COPD?
Chronic obstructive pulmonary disease, or COPD, refers to a group of diseases that cause airflow blockage and breathing-related problems
Which diseases contribute to COPD?
Emphysema & Chronic Bronchitis
