The Respiratory System

Question 1

What is the primary function of the respiratory system and what does it include?

Answer 1

-to obtain oxygen for use by body’s cells + eliminate carbon dioxide that cells produce
Includes:
-conducting zone: site of air transport consisting of respiratory airways leading into and out of lungs
-respiratory zone: site of gas exchange; occurring at the respiratory membrane which consists of the cell membranes of:
-alveolar epithelial cells + -capillary endothelial cells

Question 2

What does respiration involve?

Answer 2

-pulmonary ventilation
-external respiration
-transport of respiratory gases by the blood
-internal respiration

Question 3

Functional anatomy of the conducting zone;

Answer 3

As conducting tubes become smaller:
*they support structures change (cartilage —> elastic fibres)
*epithelial cell type changes
*amount of circular smooth muscle increases

Question 4

Functional anatomy of the respiratory zone;

Answer 4

Terminal bronchioles feed into respiratory bronchioles

Question 5

Intrapulmonary and intrapleural pressure relationships

Answer 5

Pressure difference must be maintained or the lungs would collapse

Question 6

What happens during inhalation?

Answer 6

-diaphragm contracts and moves downwards
-chest cavity expands
-pressure inside the lungs decreases and air flows into the lungs
>lungs stretch and activates stretch receptors + arterial blood pressure is lowered which activates baroreceptors
-sensory neurones relay information to the brainstem
-vagal tone is inhibited
*HR increases

Question 7

What happens during exhalation?

Answer 7

-diaphragm relaxes and moves upwards
-chest cavity decreases
-pressure inside the lungs increases and air flows out of the lungs
>stretch receptors are no longer stimulated +arterial bp is increased= deactivating baroreceptor activity
-sensory neurones relay information to the brainstem
-vagal tone is not inhibited
*HR decreases

Question 8

Mechanics of breathing

Answer 8

Slide 13

Question 9

How is the negative intrapleural pressure established?

Answer 9

*inward:
-natural tendency for lungs to recoil because of elasticity= lungs will always assume smallest possible space
-surface tension of alveolar fluid= forms a film in alveoli + tries to draw alveoli to smallest possible size
*outward:
-elasticity of the chest wall= tends to pull the thorax outward and enlarge the lungs

Question 10

Pulmonary ventilation

Answer 10

-volume changes lead to pressure changes = leads to flow of gases to equalise the pressure

Question 11

Pulmonary Ventilation:
Inspiration & Expiration

Answer 11

-movement of the intercostal muscles and diaphragm causes changes in the volume of the thoracic cavity
* when P alv < P atm air rushes into the lungs along the pressure gradient
* when P alv > P atm the pressure gradient forces gases to flow out the lungs

Question 12

Airway resistance

Answer 12

-small changes in the radius= large changes in the diameter of the airways
-during exercise circulating adrenaline= bronchodilation
>acts on B2 receptors via the sympathetic nervous system
-irritants can cause bronchodilation = via the parasympathetic nervous system

Question 13

Asthma

Answer 13

-a decrease in the diameter of the airways due to;
-bronchoconstriction
-bronchial lining becomes inflamed
Symptoms;
-coughing, wheezing, breathlessness + tightening of chest
Triggers;
-exercise, allergens, airborne irritants + weather
Bronchodilators e.g. salbutamol= cause bronchodilation by replacing bronchi smooth muscle of the bronchi;
-usually in an inhaler form
-onset of action is a few mins and lasts for 3-5 hours

Question 14

Alveolar surface tension

Answer 14

-alveolar type 2 cells= produce surfactant
*amphipilic molecule that has both hydrophilic and hydrophobic regions
*by absorbing to the air-water interface of alveoli alveoli,
• hydrophilic head groups in the water
• hydrophobic tails facing towards the air
Surfactant reduces the attractiveness of water modules for each other and decreases
the cohesiveness of the water molecules:
– Reducing the surface tension and reducing the likeness that alveoli will collapse
Infant Respiratory Distress Syndrome (IRDS)
• Occurs in premature babies born at 22-24 weeks as surfactant is produced in the last 2
months of foetal development
• Treatment:
› is positive pressure respirators to force air into the alveoli at 1 atm pressure
› Administer synthetic surfactant

Question 15

What is lung compliance?

Answer 15

-the ability of the drugs to expand and stretch
-is the volume change that could be achieved in the lungs per unit pressure change
-due to the distensibility of the elastic tissue of the lungs
-decreases with increasing age as tissues become less elastic

Question 16

What are the physical factors influencing pulmonary ventilation?

Answer 16

-airway resistance
-alveolar surface tension
-lung compliance

Question 17

Basic properties of gases

Answer 17

2 gas laws providing info during
-external respiration at the lungs
-internal respiration in the tissues
=
- Dalton’s law of partial pressure= how a gas behaves when it is part of a mixture
- Henry’s law= how gases move into and out of solution

Question 18

Dalton’s law

Answer 18

-conc of gases= partial pressure
Total pressure exerted by a mixture of gases= sum of pressures exerted independently by each gas in the mixture
-pressure contributed by a single gas is directly proportional to the % of the gas in the total gas mixture

Question 19

Henrys law

Answer 19

• If a gas mixture is in contact with a liquid: each gas will dissolve in the liquid in proportion to its partial pressure
• Very important for the passage of gas FROM THE ALVEOLI TO THE BLOOD
• The greater the partial pressure of gas in the gas phase, the more gas will enter the liquid phase
• At equilibrium, the gas partial pressure in the two phases is equal
• If the partial pressure of one gas becomes greater in the liquid than the gas phase, some of the dissolved gas will re-enter the gaseous phase
• The direction & amount of movement of each gas is determined by its partial pressure in the two phases

Question 20

Solubility and temperature

Answer 20

How much gas dissolves in a liquid depends on its solubility and temperature of the liquid
-solubility; the amount of gas that dissolves depends on the solubility of gas in water
› CO2 is 20 x more soluble than O2
› O2 is 2x more soluble than N2
• TEMPERATURE: the solubility of any gas decreases with increasing temperature

Question 21

Atmospheric and Alveolar : Gas Partial Pressures

Answer 21

-alveolar gas contains more CO2 and water vapour + less O2
These differences reflect:
-gas exchange occurring in the lungs
-humidification of air from air conducting passageways
-mixing of alveolar air that occurs with each breath + gas remaining in respiratory airways

Question 22

3 factors influencing external respiration

Answer 22

-thickness and surface area of respiratory membrane
-partial pressure gradients and gas solubilities
-ventilation-perfusion coupling

Question 23

Functional anatomy of the respiratory system: respiratory membrane

Answer 23

-membrane is usually 0.5um thick and surface area is 100m2
*increased thickness occurs in oedema due to pneumonia or left ventricular heart failure
*decreased surface area occurs;
-during emphysema= damage to alveolar walls and enlargement of alveolar chambers
-tumours and accumulation of mucus block gas flow into alveoli

Question 24

Circulation of blood through the heart

Answer 24

-in left ventricular heart failure= cardiac output of the left ventricle is reduced
-backup of blood in the pulmonary circulation= increased back pressure
=results in increased thickness of respiratory membrane= pulmonary oedema= resulting in pulmonary congestion:
-cough
-wheezing
-increased breathing rate- tachypnoea

Question 25

Emphysema

Answer 25

Obstructive disease= lungs unable to move air in and out efficiently
Main cause= long-term exposure to airborne irritants including;
-tobacco smoke
-marijuana smoke
-air pollution
-chemical fumes and dust

Question 26

Oxygenation of blood in the pulmonary capillaries at rest

Answer 26

-equilibrium occurs in 0.25 seconds = one third the time spent in the pulmonary capillary
-blood can travel through the pulmonary capillaries 3x faster and still reach equilibrium

Question 27

Ventilation-perfusion coupling

Answer 27

Poor ventilated alveolus=
-excessive perfusion
-arterioles constrict
-reduced blood supply

Well-ventilated alveolus=
-inadequate perfusion
-arterioles dilate
-enhanced perfusion

Question 28

Oxygen binding to haemoglobin

Answer 28

-4 polypeptide chains= each bound to an iron containing haem group
-each molecule of hb can bind 4 molecules of O2
-binding of O2 to Hb is CO- operative as the affinity of Hb for O2 changes with the O2 saturation

Question 29

Oxygen-haemoglobin dissociation curves

Answer 29

Slide 21, 22, 23 + 24

Question 30

The relationship between the Haldane and Bohr effect at the tissues

Answer 30

• Haldane effect
› The lower the PO2 and the lower the Hb saturation with O2, the more CO2 can be carried in the blood
› Reduced Hb forms carbaminohaemoglobin and buffers H+ ions
• Bohr effect
› As CO2 enters the systemic blood, it caused more O2 to dissociate from Hb due to an increase in H+ ions (Bohr effect)
› This allows more CO2 to combine with Hb and HCO-3 to be formed (Haldane effect)
• Result
› The result is to facilitate O2 transport into the tissues and CO2 transport into
the blood

Question 31

Locations of respiratory centres and their postulated connections

Answer 31

-PRC regulates the LENGTH OF EACH BREATH and SWITCHES between inspiration and expiration
-The neurons of the VRG are NOT ACTIVE WHEN BREATHING AT REST. The VRG controls VOLUNTARY FORCED EXPIRATION and acts to INCREASE THE FORCE OF INSPIRATION
The DRG represents the INSPIRATORY CENTRE and
initiates inspiration. It sets and maintains THE RATE OF RESPIRATION. It acts as the PACEMAKER OF RESPIRATORY MOVEMENTS

Question 32

Chemical influences on respiratory centres

Answer 32

Slide 31

Question 33

Summary

Answer 33

Slide 32