S1: Overview of the Respiratory System Flashcards
What is the upper respiratory tract?
Nose, Nasopharynx, Pharynx, Larynx
What is the lower respiratory tract?
Trachea, Lungs, Bronchi, Alveoli
What are the primary functions of the respiratory tract?
a) exchange O2 and CO2 between blood and the atmosphere
b) for olfaction (smell and taste)
c) for production of our voice
What are the secondary functions of the respiratory tract?
a) warming and humidifying incoming air
b) moistening of the cell linings
c) keeping this lining clean
d) keeping the airways open during pressure changes
e) keeping the alveoli open against surface tension.
What do hairs and blood supply do in the nasal cavity?
Hair: The number one functions of these are to warm the air and filter it respectively.
The blood supply also ensures inspired air enters the lungs fully saturated with water vapour.
Functions of sinus
They lighten the skull and also give the voice some resonance.
How does the larynx contribute to speech?
And list other functions
Controlling pitch and volume
It also prevents material reaching the lower respiratory tract, during swallowing the larynx closes and is pulled upwards to assist the process.
What forms the sensory side of the cough reflex?
Vagal receptors on the larynx
Stimulation of these receptors by ingested matter (i.e. going down the wrong way) produces a strong cough reflex.
Why is the pleural space filled with fluid?
This reduces friction between layers during breathing and provides surface tension that keeps the lung surface in close apposition with the chest wall.
Why are tracheal rings horse shoe shaped?
This allows some flexibility so the expansion of the oesophagus isn’t compromised
The posterior wall is flaccid and bulges foward during coughing
What are the subdivisions of the bronchi?
The bronchi subdivide into lobar bronchi (upper, middle and lower on right, upper and lower on the left). Then they divide into segmental bronchi until the terminal bronchioles are reached.
What level does the trachea bifurcate?
Sternal angle (angle of louis)
C4 carina
Explain the difference in the bronchi and bronchioles (smooth muscle and cartilage)
The bronchi have cartilage surrounding them, as well as smooth muscle. While the bronchioles do not have cartilage but do have smooth muscle
What allows regulation of airflow?
The large bronchi are relatively ridged, they are responsible for maintaining airflow but the smooth muscle present can reduce the diameter of the airway. The conducting bronchioles can contract greatly allowing regulation of airflow.
What are alveoli lined by?
They are lined by a single layer of flattened epithelial cells.
Explain the difference between type I and II pneuomocytes
Type I pneumocytes, which have direct contact with the pulmonary capillaries, but there is a small amount of type II pneumocytes, which secrete surfactant.
Where is the olefactory mucosa found and what is it?
The olfactory mucosa is found only in a small area in the roof the of the nasal cavity, it contains highly pseudostratified epithelium, it is ciliated and contains olfactory cells.
Where is the respiratory mucosa found and what is it?
The rest of the nasal cavity is lined by respiratory mucosa. This is a pseudostratified columnar epithelium with cilia and goblet cells. There are serous and mucous glands under the epithethelium which counteract the effect of dry air. Beneath the epithelium is a venous plexus, thin walled veins and venules to warm incoming air
What do goblet cells do?
Goblet cells are present in the nasal cavity and secrete muscus onto the surface of the epithelium to trap small particles
Explain the cytology of the lower respiratory tract
The conducting airways are lined by epithelium that transitions from pseudostratified in the nose and trachea to simple cuboidal in the terminal bronchioles.
The respiratory system down to the terminal bronchioles is ciliated and contains goblet cells. The number of goblet cells decrease as you go down, but cilia are found as far distally as the respiratory bronchioles.
Explain inspiration
Diaphragm flattens
External intercostal muscles contract
The volume of the thoracic cavity increases
Thus the lungs expand and air flows in down the pressure gradient into the lungs
What muscles are used during high levels of ventilation?
When there are high levels of ventilation, the inspiratory muscles in the neck and chest are used. For expiratory, internal intercostal muscles and abdominal muscles.
What is anatomical dead space?
There is also anatomical dead space, which is caused by not all the air reaching the alveoli but remains in the larger airways, so isn’t exchanged (20-30%), this can be increased in diseases.
What is hypercapnia?
Alveolar ventilation decreases
Partial pressure of CO2 increases
What is hypocapnia?
Increase in alveolar ventilation
Decrease in partial pressure of CO2
What is compliance?
Measure of the ease of lung expansion
What is distensibility?
The fact the elastic properties of the lungs cause them to retract from the chest wall - expressed as change in lung volume
Why do the lower zones of the lung receive more ventilation than upper zones?
Retractive forces of the lung are balanced by the semi-rigid structure of the thoracic cage, gravity results in the weight of lungs keeping the upper parts under greater stretch. The upper parts are hence less compliant (harder to expand) and less receptive to air during inspiration.
Is inspiration passive
yes
What is spirometry?
Measuring ventilation
What does ventilation of the alveoli depend on?
Tidal volume
Airway resistance
Compliance
Total lung capacity
The volume of gas in lungs after full inspiration
Tidal volume
Amount of air which enters and leaves the lungs during normal breathing
Inspiratory capcity
Max volume of air that can be inhaled at the end of normal expiration
sum of tidal volume and inspiratory reserve volume
Inspiratory reserve volume
Volume of additional air that be forcibly drawn in at the end of normal tidal volume
Functional residual capacity
Volume of gas within the lungs at the end of normal expiration, after full expiration there is still some gas remaining in the lungs, this is the residual volume
Vital capacity
Volume of air expelled by a maximum expiration from a position of full inspiration
What is the respiratory quotient?
Relationship between amount of CO2 produced and oxygen absorbed
Possible values are infinite- 0
Decreased alveolar ventilation means an increase in pCO2.
What affects gaseous diffusion across alveolar membrane ?
pressure gradient
What is dissociation of O2 affected by?
PH and temp
Role of mechanoreceptors in walls of bronchi and bronchioles
Their main function is to prevent over inflation of the lungs. Inflation activates these receptors which inhibit the neurones in the respiratory centre via the vagus nerve. Once expiration starts activation of the stretch receptors ceases allowing the inspiratory neurones to become active again
2 types of chemoreceptors and explain
1) Central chemoreceptors
Mainly respond to hypercapnia (increased pp of CO2). This is due to changes in H+ in CSF. WHen pCO2 increase, CO2 diffuses into CSF and liberates H+.
They will stimulate increased ventilatory rate and increased depth of ventilation.
Reduced by e,g, sleep, age, increase athletic trainng
- Perpheral chemocepors
Respond mainly to hypoxia (lack of O2) and also stimulate an increased ventilator rate and increased depth of breathing
Where are central chemoceptors found?
Ventrolateral surface on either side of the medulla
Where are peripheral chemoreceptors found?
Carotid bodies at the origin of the internal carotid artery and in ascending aortic wall
Explain neural control of breathing
The upper motor neurones (UMN’s) “drive” the lower motor neurones (LMN’s).
The UMN’s originate in the medulla and forebrain. Activity in the UMN’s controls the frequency and duration of LMN discharge to muscles of breathing. Impulses reach the spinal motor neurones via the reticulospinal tract.
LMN’s cell bodies are in the anterior horn of the spinal cord at C3-C5 (phrenic nerve to diaphragm) and T1-12 (external and internal intercostal muscles). The impulses mediating conscious change travel via the corticospinal tract.
Explain neural control of ventilation during normal breathing and high levels
Normal/quiet breathing = Inspiratory UMN’s fire strongly enough to only excite a few inspiratory LMN’s. The expiratory UMN’s are active but not sufficiently to make the LMN’s fire.
High levels of ventilation: UMN activity increases, LMN’s start to fire first in inspiratory intercostal nerves and then in nerves to the abdominal muscles. The increasing respiratory drive recruits more muscles of breathing makes them contract harder.
What is cholinergic innervation of airways?
Vagus nerve
Release of Ach causes contraction in airway smooth muscle (M3) receptors which constricts bronchi and mucus seretion
Is there adrenergic innervation to lungs)
NO
There are beta 2 adrenoreceptors in the human lung, primarily in the airways smooth muscle of intermediate and small diameter bronchi. This allows airways tone to be regulated by circulating adrenaline.
