Lung Physiology 4

Question 1

Respiration requirement is to

Answer 1

Ensure haemoglobin is as close to full saturation with oxygen as possible

Efficient use of energy resource

Regulate PaCO2 carefully
-variations in CO2 and small variations in pH can alter physiological function quite widely

CO2 is inversely proportional to alveolar ventilation

Question 2

Breathing is automatic

Answer 2

No conscious effort for the basic rhythm
Rate and depth under additional influences
Depends on cyclical excitation and control of many muscles
-Upper airway, lower airway, diaphragm, chest wall
-Near linear activity
-Increase thoracic volume

Question 3

Input signals

Question 4

Basic breathing rhythm

-comes in summarise assessments-
Where are the major locations of the higher centre involvements in the brain?

Answer 4

In the Pons the centres are
-Pneumotaxic and Apneustic Centres
These are responsible for physical discharges

Medulla Oblongata
-Phasic discharge of action potentials
-Two main groups that set off these physicians rhythmic responses
Dorsal respiratory group (DRG)
Ventral respiratory group (VRG)

Question 5

DRG; predominantly active during inspiration
VRG; active in both inspiration and expiration

Answer 5

Each are bilateral, and project into the bulbo-spinal motor neuron pools and interconnect

Question 6

Central Pattern generator

Answer 6

Contains Neural network (interneurons)

Located within DRG/VRG

Precise functional locations not known
-Start, stop and resetting of an integrator of background ventilatory drive

Question 7

Inspiration

Answer 7

Progressive increase in inspiratory muscle activation

-Lungs fill at a constant rate until tidal volume achieved

-End of inspiration, rapid decrease in excitation of the respiratory muscles

Question 8

Expiration

Answer 8

Largely passive due to elastic recoil of thoracic wall

-First part of expiration; active slowing with some inspiratory muscle activity

-With increased demands, further muscle activity recruited

-Expiration can be become active also; with additional abdominal wall muscle activity

Question 9

Input signals

Answer 9

Central chemoreceptors

Question 10

Chemoreceptors- sensitive to CO2

Answer 10

Central (60% influence from PaCO2) and peripheral (40% influence from PaCO2)

-Stimulated by [H+] concentration and gas partial pressures in arterial blood
-This stimulates Brainstem [primary influence is PaCO2]

Carotids and aorta [sensitive to PaCO2, PaO2 and pH]

-Significant interaction

Question 11

Central chemoreceptors

Answer 11

Located in
Brainstem
Pontomedullary junction
Not within the DRG/VRG complex

Sensitive to PaCO2 of blood perfusing brain ONLY and respond to most CO2 changes
Blood brain barrier relatively impermeable to H+ and HCO3-
PaCO2 preferentially diffuses into CSF and so influences your ability to take a breath

CO2 crosses the blood brain barrier, CO2 then combines with water, which then pushes this direction along. This leads to H+ concentration increasing which then stimulates the medullary inspiratory neurones to increase ventilations (70%)

Question 12

Ventilation response to PaCO2

Answer 12

As theres an increase in alveolar CO2, theres an increase in the ventilators response

If you fix this at a standard, but lower, Oxygen level, there is a greater response for a given CO2
So the more hypoxic you are, the more likely you are to want to breathe for a given CO2.

Question 13

Peripheral chemoreceptors
Location

Answer 13

These are located in;

Carotid bodies
Bifurcation of the common carotid
(IX) cranial nerve afferents

Aortic bodies
Ascending aorta
Vagal (X) nerve afferents
These are in the ascending aorta and these are heading towards the brain

Question 14

Peripheral chemoreceptors
Role

Answer 14

Responsible for [all] ventilatory response to hypoxia (reduced PaO2)

Generally not sensitive across normal PaO2 ranges

When exposed to hypoxia, type I cells release stored neurotransmitters that stimulate the cuplike endings of the carotid sinus nerve
neurotransmitters increase the number of action potentials along the afferent nerve fibres stimulating the medullary inspiratory neurones, this increases inspiration.

The receptors also respond to an increase in the arterial [H+] increasing stimulation of the medulla inspiratory neurones increasing ventilation (30%)

Question 15

Peripheral chemoreceptors
Response to CO2

Answer 15

Linear response to PaCO2

Interactions between responses

[Poison (e.g. cyanide) and blood pressure responsive]

Question 16

Ventilatory response to PaO2

Answer 16

As the PaO2 goes down, people begin to breathe extremely rapidly particularly when their CO2 is fixed. This is so called eucapnic hypoxia.

There is a much more blunted response if you’re allowed to alter your CO2, theres a much more marked response if the CO2 is fixed

Question 17

Lung receptors

Answer 17

Stretch, J and irritant
Afferents; vagus (X)
Combination of slow and fast adapting receptors
Assist with lung volumes and responses to noxious inhaled agents

Question 18

Stretch, J and irritant

Answer 18

Stretch
Smooth muscle of conducting airways
Sense lung volume, slowly adapting

Irritant
Larger conducting airways
Rapidly adapting [cough, gasp]

J; juxtapulmonary capillary
Pulmonary and bronchial C fibres

Question 19

Airway receptors (NOT necessary to learn)

Answer 19

Nose, nasopharynx and larynx
Chemo and mechano receptors
Some appear to sense and monitor flow
-Stimulation of these receptors appears to inhibit the central controller

Pharynx
Receptors that appear to be activated by swallowing
-respiratory activity stops during swallowing protecting against the risk of aspiration of food or liquid

Question 20

Muscle proprioceptors

Answer 20

Joint, tendon and muscle spindle receptors
Intercostal muscles > > diaphragm
Important roles in perception of breathing effort

Question 21

An example; ascent

Answer 21

Ascending; PiO2 falls (FiO2 remains constant)
Decreased PAO2
Decreased PaO2
Peripheral chemoreceptors fire (e.g carotid)
Activates increased ventilation (VA)
Increased PAO2
Increased PaO2