S1: Overview of the Respiratory System

Question 1

What is the upper respiratory tract?

Answer 1

Nose, Nasopharynx, Pharynx, Larynx

Question 2

What is the lower respiratory tract?

Answer 2

Trachea, Lungs, Bronchi, Alveoli

Question 3

What are the primary functions of the respiratory tract?

Answer 3

a) exchange O2 and CO2 between blood and the atmosphere
b) for olfaction (smell and taste)
c) for production of our voice

Question 4

What are the secondary functions of the respiratory tract?

Answer 4

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.

Question 5

What do hairs and blood supply do in the nasal cavity?

Answer 5

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.

Question 6

Functions of sinus

Answer 6

They lighten the skull and also give the voice some resonance.

Question 7

How does the larynx contribute to speech?

And list other functions

Answer 7

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.

Question 8

What forms the sensory side of the cough reflex?

Answer 8

Vagal receptors on the larynx

Stimulation of these receptors by ingested matter (i.e. going down the wrong way) produces a strong cough reflex.

Question 9

Why is the pleural space filled with fluid?

Answer 9

This reduces friction between layers during breathing and provides surface tension that keeps the lung surface in close apposition with the chest wall.

Question 10

Why are tracheal rings horse shoe shaped?

Answer 10

This allows some flexibility so the expansion of the oesophagus isn’t compromised

The posterior wall is flaccid and bulges foward during coughing

Question 11

What are the subdivisions of the bronchi?

Answer 11

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.

Question 12

What level does the trachea bifurcate?

Answer 12

Sternal angle (angle of louis)

C4 carina

Question 13

Explain the difference in the bronchi and bronchioles (smooth muscle and cartilage)

Answer 13

The bronchi have cartilage surrounding them, as well as smooth muscle. While the bronchioles do not have cartilage but do have smooth muscle

Question 14

What allows regulation of airflow?

Answer 14

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.

Question 15

What are alveoli lined by?

Answer 15

They are lined by a single layer of flattened epithelial cells.

Question 16

Explain the difference between type I and II pneuomocytes

Answer 16

Type I pneumocytes, which have direct contact with the pulmonary capillaries, but there is a small amount of type II pneumocytes, which secrete surfactant.

Question 17

Where is the olefactory mucosa found and what is it?

Answer 17

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.

Question 18

Where is the respiratory mucosa found and what is it?

Answer 18

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

Question 19

What do goblet cells do?

Answer 19

Goblet cells are present in the nasal cavity and secrete muscus onto the surface of the epithelium to trap small particles

Question 20

Explain the cytology of the lower respiratory tract

Answer 20

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.

Question 21

Explain inspiration

Answer 21

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

Question 22

What muscles are used during high levels of ventilation?

Answer 22

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.

Question 23

What is anatomical dead space?

Answer 23

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.

Question 24

What is hypercapnia?

Answer 24

Alveolar ventilation decreases

Partial pressure of CO2 increases

Question 25

What is hypocapnia?

Answer 25

Increase in alveolar ventilation

Decrease in partial pressure of CO2

Question 26

What is compliance?

Answer 26

Measure of the ease of lung expansion

Question 27

What is distensibility?

Answer 27

The fact the elastic properties of the lungs cause them to retract from the chest wall - expressed as change in lung volume

Question 28

Why do the lower zones of the lung receive more ventilation than upper zones?

Answer 28

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.

Question 29

Is inspiration passive

Answer 29

yes

Question 30

What is spirometry?

Answer 30

Measuring ventilation

Question 31

What does ventilation of the alveoli depend on?

Answer 31

Tidal volume
Airway resistance
Compliance

Question 32

Total lung capacity

Answer 32

The volume of gas in lungs after full inspiration

Question 33

Tidal volume

Answer 33

Amount of air which enters and leaves the lungs during normal breathing

Question 34

Inspiratory capcity

Answer 34

Max volume of air that can be inhaled at the end of normal expiration

sum of tidal volume and inspiratory reserve volume

Question 35

Inspiratory reserve volume

Answer 35

Volume of additional air that be forcibly drawn in at the end of normal tidal volume

Question 36

Functional residual capacity

Answer 36

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

Question 37

Vital capacity

Answer 37

Volume of air expelled by a maximum expiration from a position of full inspiration

Question 38

What is the respiratory quotient?

Answer 38

Relationship between amount of CO2 produced and oxygen absorbed

Possible values are infinite- 0

Decreased alveolar ventilation means an increase in pCO2.

Question 39

What affects gaseous diffusion across alveolar membrane ?

Answer 39

pressure gradient

Question 40

What is dissociation of O2 affected by?

Answer 40

PH and temp

Question 41

Role of mechanoreceptors in walls of bronchi and bronchioles

Answer 41

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

Question 42

2 types of chemoreceptors and explain

Answer 42

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

2. Perpheral chemocepors

Respond mainly to hypoxia (lack of O2) and also stimulate an increased ventilator rate and increased depth of breathing

Question 43

Where are central chemoceptors found?

Answer 43

Ventrolateral surface on either side of the medulla

Question 44

Where are peripheral chemoreceptors found?

Answer 44

Carotid bodies at the origin of the internal carotid artery and in ascending aortic wall

Question 45

Explain neural control of breathing

Answer 45

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.

Question 46

Explain neural control of ventilation during normal breathing and high levels

Answer 46

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.

Question 47

What is cholinergic innervation of airways?

Answer 47

Vagus nerve

Release of Ach causes contraction in airway smooth muscle (M3) receptors which constricts bronchi and mucus seretion

Question 48

Is there adrenergic innervation to lungs)

Answer 48

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.