overview of the respiratory system

Question 1

upper respiratory tract

Answer 1

nose
nasopharynx
pharynx
larynx

Question 2

lower respiratory tract

Answer 2

trachea
lungs
bronchii
alveoli

Question 3

primary functions of resp tract (3)

Answer 3

Exchange oxygen and carbon dioxide between blood and the atmosphere
Olfaction – smell and taste
Voice

Question 4

secondary functions of resp tract (5)

Answer 4

Warming and humidifying incoming air
Moistening of cell lining
Keeping lining clean
Keeping airways open during pressure changes
Keeping alveoli open against surface tension

Question 5

anatomy of the upper resp tract

nasal cavity?
sinuses?
larynx?

Answer 5

Nasal cavity
blood supply ensures inspired air enters lungs at body temp and fully saturated with water vapour.
Hairs -> filter harmful material

Sinuses
air cavities in the cranial bones
clarity + tone of voice
lighten weight of skull hence body can support he weight

Larynx
Speech – pitch and volume
Strength of expiration contributes to volume
Preventing material reaching LRT – during swallowing larynx closes and pulled upwards to assist process
Supplied with vagal receptors which form the sensory side of cough reflex – stimulation of larynx by ingested matter produces strong cough reflex

Question 6

Pleura

attached to?
what is it filled with?

Answer 6

Pleura
Each lung is surrounded by two membranes (pleurae)
The outer (parietal) pleura - attached to the chest wall and sensitive to pain
The inner (visceral) pleura - attached to the lung and viscera and is perfused by the pulmonary circulation

Pleural space is filled with fluid - reduces friction between layers during respiration
provides surface tension that keeps the lung surface in close apposition with the chest wall –
allows optimal inflation of the alveoli during respiration.
Also transmits pressures from the chest wall to the visceral pleural surface (and hence, the lung)

Question 7

trachea and main bronchi anatomy

where birfucates? what do the rings support?

which bronchi is longer? effect?

what does the bronchi subdivide into? numbers?

Answer 7

Trachea
Ends where it bifurcates into 2 main bronchi at the level of the sternal angle (the Angle of Louis)
Horseshoe shaped cartilaginous rings supporting the anterior and lateral walls (allow cough reflex to happen)
The posterior wall is flaccid and bulges forward during coughing.

Main bronchi
Left main bronchus – longer than right and leaves the trachea at a more abrupt angle

The right main bronchus is more directly in line with the trachea so that inhaled material tends to enter the right lung more readily than the left

Bronchi subdivide into lobar bronchi – upper mid and lower on right, upper and lower on left, then segmental bronchi and until terminal bronchioles reached

Question 8

functional area of alveoli

Answer 8

acinus

Question 9

bronchial tree

describe bronchi? bronchioles?
what is acinus?

large airways vs conducting airways?

Answer 9

Bronchi – airways with cartilage –smooth muscle spiral internal to cartilage (maintain airflow)

Bronchioles – small airways with no cartilage

Terminal bronchiole supplies the acinus (functional unit of lung)
Each acinus contains branching respiratory bronchioles communicating with alveoli

The large airways relatively rigid, and consist of muscle and cartilage. They are responsible for maintaining air-flow - but smooth muscle present can reduce diameter of airway.
The conducting bronchioles can contract greatly – allowing regulation of airflow

Question 10

alveolus

describe alveoli?
type 1 and type 2 pneumocytes?
when is small gap between capillaries and alveolar present?

Answer 10

Alveoli
0.1-0.2 microns diameter
Lined with single layer of flattened epithelial cells

Type I pneumocytes comprise 92-95% of the cells – direct contact with pulmonary capillaries for gaseous exchnage

Type II pneumocytes cover the remaining surface and secrete surfactant (reduce surface tension) also repair function

There is a small gap between the basement membrane of the capillaries and the alveolar cells which is only apparent in disease states, when it might contain fluid.

Question 11

cytology in nasal cavity

where is olfactory mucosa? cytology?
rest of nasal cavity cytology?
what counteract effect of incoming dry air?
what do goblet cells do?

Answer 11

Nasal cavity lined by skin with hairs to provide first filter
The olfactory mucosa is found only in small area in roof of nasal cavity. It contains highly pseudostratified epithelium, is ciliated, and contains olfactory cells

Rest of nasal cavity lined by respiratory mucosa –
pseudostratified columnar epithelium with cilia and goblet cells
Serous and mucous glands under epithelium - counteract effect of dry incoming air
Beneath epithelium is venous plexus – thin walled veins and venules – warm incoming air

Goblet cells – mucus secretion onto surface of epithelium – traps small particles

Question 12

cytology in lower resp

epithelium change along the tree?
what cell decreases as you go down?

Answer 12

Conducting airways

Epithelium – transition from pseudostratified in nose and trachea to simple cuboidal in terminal bronchioles

Pseudostratified epithelium function in secretion and absorption

Respiratory epithelium down to terminal bronchioles is ciliated and contains goblet cells Goblet cells decrease but cilia are found as far distally as respiratory bronchioles

Question 13

cytology in resp tract

what is mucocillary escalator?
what lines most of resp tract?

Answer 13

Mucous membrane (mucosa) lines most of respiratory tract.

Cilia are covered with a thin layer of mucus – function to trap foreign particles, and propel them towards pharynx – hence protection against infection

Move in co-ordinated waves sweeping mucus layer towards pharynx where swallowed – mucociliary escalator

Question 14

physiology of lungs

2 main things?

Answer 14

Mechanical – ventilation
Gas exchange - perfusion
Gas transfer – distribution and diffusion

Question 15

ventilation - inhalation

what happens during higher levels of ventilation?

Answer 15

Normal/quiet breathing:
Diaphragm flattens
External intercostal muscles contract
Volume of thoracic cavity increases
Lungs expand
Air flows down pressure gradient into lungs

High levels of ventilation:
Inspiratory muscles – neck and chest
Expiratory – internal intercostal muscles, abdominal muscles

Question 16

Elastic and non-elastic resistance

what is normally active and what is passive?
what bring chest to position after expiration?
what is used when there ius abnormal resistance?
when is elsatic work increased?
when is non-elastic work increased?

Answer 16

Elastic and non-elastic resistance
Normally inspiration is active and expiration is passive

Elastic forces in lungs and chest wall – bring chest to position at the end of normal expiration. Kinetic energy brings chest to resting position
Inspiration or expiration against abnormal resistance may require use of accessory muscles
Elastic work is increased when lungs are more rigid e.g. fibrosis
Non-elastic forces – work is increased by rapid breathing and obstructive lung disease such as asthma

Question 17

lungs

muscles? effect of this?

Answer 17

Functionally - elastic bags resembling balloons.
Lack muscle which would allow them to expand or
contract themselves.

Question 18

ventilation

do children breath faster or slower?
does all air reach alveoli?
what happens is aleveolar ventilation increase or decrease?

Answer 18

Children tend to breathe faster

Not all reaches alveoli but remains in larger airways – dead space (20-30%) - can increase in disease.

If alveolar ventilation reduced in proportion to CO2 excretion, PCO2 rises (hypercapnia) and if alveolar ventilation becomes excessive, arterial PCO2 falls (hypocapnia)

Question 19

compliance

what is it?
what is distensibility of lungs?
what balances retractive forces of lung?
what effect does gravity have on lungs?

Answer 19

Compliance – a measure of ease of lung expansion

Distensibility of lungs – the elastic properties of lungs cause them to retract from chest wall
Expressed as change in lung volume

Retractive forces of lung balanced by semi-rigid structure of the thoracic cage. Gravity results in weight of lungs keeping upper parts under greater stretch. Upper parts are less compliant and less receptive to air entry during inspiration. So lower zones receive more ventilation than upper zones.

Question 20

airway resistance
where does this occur in normal individual?
in disease, where does it occur?

Answer 20

Airway resistance
Distribution of air in lungs uneven
Airway resistance to airflow in normal individual occurs in larger airways
In disease airway resistance occurs in peripheral airways

Question 21

spirometry

what is it?
total lung capacity?
tidal volume?
functional residual capacity?
residual volume?
vital capacity?

Answer 21

Spirometry is a means of measuring ventilation.

The total lung capacity is the volume of gas in the lungs after a full inspiration

The tidal volume is the amount of air which enters and leaves the lungs during normal breathing

The functional residual capacity is the volume of gas within the lungs at the end of normal expiration

After a full expiration there is still some gas remaining in the lungs – the residual volume

The vital capacity is the volume of air expelled by a maximum expiration from a position of full inspiration

Question 22

total lung capacity

Answer 22

volume of gas in the lungs after a full inspiration

Question 23

tidal volume

Answer 23

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

Question 24

functional residual capacity

Answer 24

volume of gas within the lungs at the end of normal expiration

Question 25

residual volume

Answer 25

After a full expiration there is still some gas remaining in the lungs

Question 26

vital capacity

Answer 26

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

Question 27

Lung perfusion

where does it receive blood from?
what does efficiency of gas exchange depend on?
why is distribution of ventilation and perfusion not perfect in normal lung?

Answer 27

Lungs receive blood supply from pulmonary and systemic circulation

Efficiency of gas exchange depends on alveolar distribution and blood flow in all parts of lungs

Pulmonary capillary network in alveolar walls is dense – large surface area

Low resistance

Even in normal lung, distribution of ventilation and perfusion not perfect – e.g. effects of gravity - perfusion preferentially in base of lungs

Question 28

Lung perfusion - Respiratory quotient (RQ)

what is rq?
why is PCO2 a measure of alveolar ventilation?
what happens when alveolar ventilation drops?

Answer 28

The possible values of the ventilation:perfusion ratio (VA/Q) is between ∞ (ventilation and no perfusion) and 0 (perfusion but no ventilation)

Respiratory Quotient (RQ)
At steady state: CO2 produced by body and O2 absorbed depends on metabolism
Typically 0.7 during pure fat metabolism to 1.0 during pure carbohydrate metabolism. RQ usually 0.8 (assume 1.0)

When CO2 produced at constant rate, PCO2 of alveolar air depends on amount of outside air that the CO2 is mixed with in alveoli. i.e. PCO2 is measure of alveolar ventilation
When alveolar ventilation drops, PCO2 rises

Question 29

Distribution – Oxygen transport

heamoglobin? sub units? saturation?
what happens at tissue?
what affects dissociation of O2?
what causes diffusion across alveolar membrane?
left and right shift meaning?

Answer 29

Haemoglobin contains 4 haem units
Hb almost saturates with O2 as blood passes through alveolar capillaries
Once in tissue, O2 released and PO2 decreases
Dissociation of O2 affected by pH and temperature
Diffusion across alveolar membrane due to pressure gradient
Left shift: higher O2 affinity
Right shift: lower O2 affinity

Question 30

Distribution – Carbon Dioxide transport

where is co2 carried to?
what is the cause of diffusion?
solubility?

Answer 30

CO2 carried from tissues to lungs

Diffusion from cell to blood across the alveolar membrane due to pressure gradient

24x more soluble than O2 – no carrier

Question 31

Sensory control of ventilation
Mechanoreceptors

where are they found?
main function?
what activates the receptors? effect?
when does this stop? important when?

Answer 31

Mechanoreceptors – found in walls of bronchi and bronchioles.

Main function is to prevent over inflation of lungs.

Inflation activates the receptors which inhibit the neurones in the respiratory centre via vagus nerve.

Once expiration starts, activation of the stretch receptors ceases allowing inspiratory neurones to become active again. This is important in infants but in adults it is only functional during exercise when the tidal volume is larger than normal.

Question 32

Sensory control of ventilation
Chemo- receptors

what do chemo receptors respond to?
how do they detect it?
what does this stimulate?
when is this response decreased?

where are the two types of chemo recepotrs found?
what do they both respond to?

Answer 32

Chemoreceptors respond to O2, CO2 and H+
Central chemoreceptors –Lie on ventrolateral surface on either side of medulla.

They respond mainly to hypercapnia but not directly due to gas pressure but to changes in levels of H+ in the CSF.

When PCO2 in blood increases, CO2 diffuses into the CSF and liberates H+
They stimulate an increased ventilatory rate and increased depth of ventilation
The response is reduced by factors including sleep, increasing age, narcotic analgesics, alcohol, athletic training and anaesthetics

Peripheral chemoreceptors are found in the carotid bodies at the origin of the internal carotid artery and in the ascending aortic wall.
They respond mainly to hypoxia.
They also stimulate and increased ventilatory rate and increased depth of breathing

Question 33

control of breathing

what is the prime effector of ventilatory control?
when can another factor become a more potent effector?
what can reduce sensitivity of resp centre?
name a non-resp cause that can do this
drugs that can stimulate and depress resp centre?

Answer 33

Under normal circumstances, the prime effector of ventilatory control is alteration in arterial pCO2.

However, in circumstances of hypoxia (PO2 <8 Kpa), the PO2 is the most potent stimulus to ventilation.

Raised PCO2 is accompanied by increasing acidity of blood and CSF and stimulates both peripheral and central chemoreceptors

Chronic CO2 retention reduces sensitivity of the respiratory centre.

H+ also increased by non-respiratory causes such as diabetic ketoacidosis

Drugs – aspirin can stimulate respiratory control centres directly. Other drugs e.g. sedatives may depress it

Question 34

Neural control of breathing

UMN effect on LMN
what are UMN
what does activity in UMNS do?
how do impulses reach spinal motor neurones?
LMNs - cell bodies where?
impulses that have a conscious change travel via?

Answer 34

The distribution and organisation of the respiratory centre highly complex

Upper motor neurones (UMNs) “drive” lower motor neurones

The UMNs originate in the medulla and forebrain

Activity in UMNs controls frequency and duration of LMN discharge to muscles of breathing

Impulses reach spinal motor neurones via reticulospinal tract. Lower motor neurones (LMNs) – cell bodies in anterior horn of spinal cord at C3-C5 (phrenic nerve to diaphragm) and T1-T12 (external and internal intercostal nerves/muscles)

Impulses mediating conscious change travel via corticospinal tract

Question 35

ventilation and UMN/LMN

effect of UMN and LMN during quiet/normal breathing?
change during higher levels of ventilation?

Answer 35

Quiet/normal breathing:
Inspiratory UMNs fire strongly enough only to excite a few inspiratory LMNs
The expiratory UMNs are also active but not sufficiently to

High levels of ventilation:
UMN activity increases
LMNs start to fire
Inspiratory intercostal muscles then abdominal muscles
make the LMNs fire.

Question 36

Airway pharmacology

cholinergic innervation effect?

noradrenergic innervation effect?

Answer 36

Airways contain afferent (sensory) and efferent (motor) nerves

Cholinergic innervation
Stimulation of the vagus nerve causes the release of Ach – leads to contraction of airway smooth muscle which constricts bronchi and mucus secretion

Noradrenergic innervation
Human airways have little or no noradrenergic innervation but there are b2 adrenoceptors in human lung, primarily in airway smooth muscle of intermediate and small diameter bronchi. Allow airway tone to be regulated by circulating adrenaline.