Respiratory physiology W9 Flashcards
What is the main function of the respiratory system
To supply body with O2 and dispose of CO2
The respiratory system consists of two distinct processes
- Pulmonary ventilation: movement of air in and out of the lungs
- Gas exchange: exchange of O2 and CO2 between blood and alveolar air (respiration) by diffusion
The respiratory system can be anatomically divided into upper and lower. What structures are present in each divison?
Upper: nose, nasal cavity, pharynx
Lower: Larynx, trachea, bronchi, lungs
The respiratory system can be functionally divided into 2 zones, conducting and respiratory. Describe the difference
Conducting: all passageways from the nose to respiratory bronchioles - rigid. allow air to reach the site of gas exchange and warm, clean and humidfy incoming air.
Respiratory: respiratory bronchioles, alveolar ducts and aleoli. site of gas exchange
What is the function of the conducting zone?
Allows easy transfer of air to and from respiratory zone & warms, cleans and humidifies incoming air.
For efficient air exchange - maximal surface area and minimal distance between alveolar air and capillaries is needed. Solution = fractal branching tree
Trachea divides into left and right bronchi -> airways continue to divide dichotomously (24 generations) into smaller tubes until alveoli
What does airway patency refer to
Problem in respiratory system: need to keep respiratory passageways open to allow easy passage of air.
In a normal situation how is airway patency achieved
Trachea have cartilage rings (keep trachea open) = unlikely to collapse
Bronchi: cartilage plates aid to keep bronchi open
Bronchioles: kept open by air pressure in airway + support from surrounding lung tissue (radial traction)
Alveolar kept open by surfactant secreated by type 2 alveolar cells
Air movement in and out of the lungs is dependent on pressure gradients between…
- Atmospheric pressure (P atm)
- Intra-alveolar pressure (P alv)
- Intraplural pressure (P ip)
What is Boyle’s Law
Inverse relationship between volume and pressure
pressure x volume = constant (k)
P atm < or >?
Gas molecules move down pressure gradients from region of high pressure to low pressure. This pressure gradient drives pulmonary ventilation (breathing).
For air to move into and out of our lungs…
Into P alv < P atm
Out P alv > P atm
How are pressure changes achieved (in order to create pressure gradients)
By varying the volume of the thorax
Bigger volume = lower pressure
Smaller volume = higher pressure
What does inspiration involve
Increasing volume of the thorax (enlarging lungs)
How do we change (increase) the volume of the thorax during inspiration?
Inspiration is an active process
Involves contracting and relaxing muscles
What muscles are involved in quiet inspiration/breathing?
Diaphragm and external intercostals contract
= thoracic cavity and lung volume expands
= pressure decreases
What muscles are involved in active inspiration/breathing?
Diaphragm, external intercostals and accessory muscles (sternocleidomastoid and scalenes) are activated
Why does changing the volume of the thorax change the volume of the lungs
intrapleural pressure
cavity filled with fluid between visceral and parietal pleura = adhesive force
Keeps lungs vacuum sealed to thorax wall, therefore when volume of thorax increases, lungs also expand.
Expiration is primarily a passive process but can be active based on the level of respiratory activity. What muscles are involved in quiet expiration/breathing?
Diaphragm and external intercostals relax - elastic recoil
= thoracic cavity and lung volume reduced
= increase in pressure (Palv > Patm)
= air flows out
What muscles are involved in active expiration/breathing?
Diaphragm + Accessory muscles activated (internal intercostals and abdominals)
Healthy lungs are stretchy and elastic = easy expansion and recoil
What are some factors that impair lung compliance (resilence/elasticity)
Fibrosis
What does tidal volume (TV) refer to?*
Air you move in and out during quiet breathing
* 0.5L of air moves in and out per breath
* 12-18 breaths per minute in adults (respiratory rate)
What does inspiratory reserve volume (IRV) refer to?*
Air that can be inspired beyond the tidal volume ie. amount of air you can inhale after a normal tidal inhalation
* 2.1-3.2L
What does expiratory reserve volume (ERV) refer to?*
Air that can be expelled after a tidal expiration ie. air you can expel after a tidal expiration - forceful
* 1-1.2L
What does residual volume refer to?*
Air that is left in the lungs if you exhale as much air as possible. Residual air keeps airways open ie. alveoli from collapsing
What does dead space refer to?*
The volume of ventilated air that does not participate in gas exchange (does not go to respiratory zone)
What does respiratory capacities refer to
Combination of two or more selected volumes
What does vital capacity (VC) refer to?*
The sum of all volumes except residual ie. TV, ERV, IRV
total exchangeable air
* 4-5L
What does total lung capacity (TLC) refer to?*
The sum of all of the lung volumes ie. TV, ERV, IRV, RV
total amount of air a person can hold in the lungs after a forceful inhalation
* 4.2L (women) - 6L (men)
What does Inspiratory capactiy (IC) refer to?*
Sum of TV & IRV
Maximum amount of air that can be inhaled past a normal tidal expiration
What does Functinal residual capactiy (FRC) refer to?*
Sum of ERV and RV
The amount of air that remains in the lungs after a normal tidal expiration
Label lung volume trace
Physiologically where does the greatest resistance to flow occur in a normal vs in disease state - why?
Normally: In medium sized bronchi near the trachea
In disease states: in smaller sized bronchioles because they can be easily blocked (by mucus, swelling and oedema), have more smooth muscle (readily constricts) and are less rigid (more easy to compress)
Obstructive airway diseases are associated with obstruction (narrowing) of the airways = problems with expiration…airways easily collapse
What are some diseases under this classification and how do we detect these?
Asthma, chronic bronchitis, emphysema
associated with decrease in peak expiratory flow rate and forced expiratory volume
Restrictive airway diseases are associated with lack of expansion of airways = problems with inspiration…can’t expand lungs Give an Example of physiological issue to cause this
Fibrosis
Goblet cells secreate mucus, what is the role of mucus in the airways?
Moistens entire surface of all respiratory passages
First line of defense: physical barrier to protect the lung with properties that help trap/disarm potentially infectious bacteria, fungi, virus
How is mucus cleared from respiratory passages
Mucociliary clearance by Cilia
* continuous beat/powerstroke towards pharynx -> mucus is swallowed or coughed out
* Prevents respiratory infection ex. pneumonia
Note: alveolar macrophages clear particles from alveoli
Diffusion refers to the random molecular movement driven by concentration gradients. Rate of diffusion is critical for respiratory function. What does partial pressure refer to?
Partial pressure of a gas reflects its concentration - directly related to its relative proportion in a mixture
What does Dalton’s Law explain
Total pressure exerted by a mix of gases represents the sum of pressures exerted by the individual gases.
i.e. Sum of partial pressures = total pressure of mix
Ex. Atmospheric air is a mixture of gases. Total atmospheric pressure = 760mmHg therefore the sum of the seperate pressures of the components of air (partial pressures) have to equal 760mmHg.
What happens to atmospheric pressure as altitude increases
Atmospheric pressure decreases
Proportions of gases stay the same but partial pressures change = change in atmospheric pressures
Gases dissolved in water or body fluid also exert pressure. Partial pressures of gases in solutions is determined by…
Pressure of gas in solutions determined by its concentration and by the solubility coefficient of the gas
The partial pressure of a gas in a solvent is inversley proportional to its solubility in this solvent. What solubility coefficent will be present for gases that easily dissolve and dont increase pressure vs gases that do not easily dissolve and increase pressure.
Solubility coefficient = high with gases that easily dissolve (doesn’t increase pressure ie. low pressure)
Solubility coefficient = low with gases that don’t easily dissolve (high pressure)
Net diffusion is determined by differences in partial pressures ie. which way gas will go.
Rate of diffusion is determined by alveolar and blood partial pressure ie. how fast diffusion occurs.
What is the PP’s of CO2 and O2 in the blood and alveoli and how does this determine net diffusion.
CO2
* Partial pressure is greater in dissolved blood state than alveoli gas state
= CO2 moves down gradient and into alveoli (for removal)
O2
* Partial pressure is greater in the alveoli gas state than dissolved blood state
= net diffusion into the blood
Only one-seventh of total alveolar air is replaced with each breath (due to FRC). Therefore multiple breaths are required to exchange most of the alveolar air. Why is this a good thing?
This slow replacement of the alveolar air is advantageous as its prevents sudden changes in gas concentrations in the blood. ie. presents excessive increases and decreases in tissue oxygenation, carbon dioxide concentrations and pH levels.
and makes respiratory control mechanisms more stable
Where does gas exchange occur
Respiratory membranes: the membranes of all terminal portions of the lungs
note: Alveolar walls are extremely thin (0.6um) and in close proximity, allowing easy diffusion to and from capillaries.
Describe the 6 layers of the respiratory membrane
- Fluid lining the alveoli with surfactant reduces surface tension - without = collapse
- Alveolar epithelium composed of thing epithelial cells
- Epithelium basement membrane
- Thin interstitial space between alveolar epithelium and capillary membrane
- Capillary basement membrane - fuses with alveolar epithelial basement membrane in many places
- Capillary endothelium
Rate of diffusion depends on… (3)
- Thickness of respiratory membrane
- Surface area of membrane
- Gas Pressure difference between 2 sides of membrane
How is O2 transported in blood?
O2 not very soluble in blood (low solubility coefficient)
Calculating how much O2 is dissolved in blood = 1.5% not enough
Therefore need Haemoglobin to increase O2 levels in the blood (98.5%)
How many O2 molecules are carried by 1 haemoglobin and How?
4 - rapid and reversible combination/rapid loading and unloading
Liver produces apoferritin, combined with iron = ferritin. O2 attaches to Haem via ferritin.
When is unloading of O2 in tissues enhanced?
Enhanced by heat, high Co2, acidity ie. during exercise
Shift to right on dissociation curve= lower saturation at lower partial pressure of O2
Know how to interpret O2 haemoglobin dissociation curve*
- What are the axis?
Y axis = percent of saturation of haemoglobin (O2 to haemoglobin)
X axis = partial pressure of O2
transported in 3 forms
How is CO2 transported in blood
- 10% dissolved in blood (high solubility coefficient)
-
25% bound to Haem in RBC’s
loading and unloading of CO2 influenced by degree of saturation of O2 to Haem ex. low O2 saturation favours association of CO2 -
65% transported as bicarbonate (HCO3-) in blood
Facilitated by carbonic anhydrase (RBC enzyme)
Write chemical conversion of CO2 to bicarbonate
In Alveolar blood we want to reverse the conversion of CO2 to carbonate in order to breathe out CO2. How does this occur?*
Binding of O2 to Haem causes the release of H+ which binds to bicarbonate, shifts reaction to left = CO2 + H2O
How do we control the rate of breathing and therefore respiration?
The respiratory centres
* Nervous system adjusts rate of alveolar ventilation to keep partial pressures of CO2 and O2 in blood constant.
* Skeletal muscles involved in ventilation (by neural input)
What do the respiratory centres refer to
Groups of neurons in the medulla and pons (of the brainstem) that regulate respiration
What are the three major collections of neurons in the respiratory centres
- dorsal respiratory group in dorsal portion of medulla -> causes inspiration
- ventral respiratory group in ventrolateral part of medulla -> mainly causes expiration but also involved in inspiration
- pneumotaxic centre in dorsal superior portion of pons -> controls rate and depth of breathing
Groups communicate with one another in a concerted effort as the pace makers of respiration
Describe the role of the dorsal respiratory group
Inspiratory centre
Emits repetitive bursts of inspiratory neuronal action potentials
Describe the role of the ventral respiratory group
- Contains both inspiratory and expiratory neurons
- Almost completely inactive during quiet breathing -> active during exercise/heavy breathing = recruits external intercostals and accessory muscles = increased depth of breathing
- Also drives active expiration by stimulating the internal intercostals and abdominal muscles
Describe the role of the pneumotaxic centre respiratory group
Influence and modify activity of the medullary neurons (other respiratory centres)
* smooth transition from inspiration to expiration
* Primarily ‘switch off’ the inspiratory ramp -> controls duration of lung filling ie. says enough inhaling!
Describe the mechanism of the inspiratory ramp signal controlled by the pneumotaxic centre
How do we control ventilation ie. where do signals come from to respiratory centres
chemoreceptors sense chemical changes in CO2 (most closely controlled!), H+, O2
A change of 5mmHg in CO2 doubles ventilation rate ie. Small changes = big reaction
Where are chemoreceptors found and what do they primarily repond to?
Peripheral - within the main arteries of the neck ie. carotid body and aortic body
* Respond primarily to O2 - larger change needed to change ventilation rate
Central - located in medulla
* Respond to CO2 - only small change needed to change ventilation rate (or H+ ions)
What is the main goal of respiration
To maintain proper concentrations of O2 and CO2 and H+ ions in the tissues
What happens when there is…
1. excess CO2 (hypercapnia) or excess H+ in the blood
2. low CO2 (hypocapnia) levels
- is due to hypoventilation- Central chemoreceptors are stimulated when O2 is low and CO2 is high.
Increased rate and depth of breathing to get rid of it - Hypocapnia- due to hyperventilation.
Is breathing voluntary?
Partly…
* Some conscious control of rate and depth of breathing (by motor cortex)
* Medullary respiratory centres initiate breathing when critical (overruns)
