1. Section A: Applied Anatomy and Physiology
11. Structure and function of the respiratory system

2. Syllabus
Structure of the nasal passages, trachea, bronchii, bronchioles, and alveoli
Lobes of the lung and pleural membrane
Mechanics of breathing at rest and during exercise
Respiratory muscles, to include: diaphragm, external intercostals, sternocleidomastoid, pectoralis minor, internal intercostals, and abdominal muscles
Control of ventilation
Definitions, values and measurement of respiratory volumes at rest and during exercise
Effect of exercise on respiratory volumes and pulmonary ventilation
Gaseous exchange, partial pressures and tissue respiration
The effect of altitude on the respiratory system

3. External Respiration
Involves the movement of gases into and out of the lungs.
The exchange of gases between the lungs and blood is known as pulmonary diffusion.

4. Nasal Passages
Nasal cavity is divided by a cartilaginous septum that forms the passages.
Interior structures aid the process by:
Mucous membranes and blood capillaries moisten and warm the inspired air
Ciliated epithelium filters and traps dust particles
Small bones (chonchae) increase the surface area to improve efficiency

5. Oral Pharynx and Larynx
Air entering the larynx passes over the vocal chords and into the trachea
Swallowing – the larynx is drawn upwards and forwards against the base of the epiglottis (preventing entry of food)

7. Trachea Approx. 10cm in length and lies in front of the oesophagus.
Composed of 18 ‘rings’ of cartilage, which are also lined by a mucous membrane and ciliated cells.
Extends from larynx and directs air into the right and left primary bronchi.

11. Bronchi and Bronchioles
Trachea divides into right and left bronchi, which further subdivide into lobar bronchi
Three feeding the lobes of the right lung
Two feeding the lobes of the left lung
Further subdivision of these form bronchioles
Bronchioles enable the air to pass into the alveoli via the alveolar ducts

12. Alveoli
Responsible for the exchange of gases between the lungs and the blood
The alveolar wall are extremely thin, are lined by a film of water
Essential for dissolving oxygen from inspired air
Alveoli walls also contain elastic fibres further increasing surface area
Surrounding each alveolus is an extensive capillary network

15. Mechanics of Breathing

18. Breathing
Lungs are surrounded by pleural sacs containing pleural fluid, which reduces friction
Sacs are attached to both the lungs and the thoracic cage, which enables the lungs to inflate and deflate as the chest expands and flattens

20. Inspiration Active Occurs as a result of contraction of;
External intercostals
Diaphragm
As the chest expands through these muscular contractions, the surface tension created by the film of pleural fluid causes the lungs to be pulled outwards

21. Inspiration During Exercise
Additional muscles;
Sternocleidomastoid
Scalenes
Pectoralis major

22. Expiration Generally a passive process
During exercise, the process becomes more active;
The internal intercostals
Abdominals
Latissimus dorsi

25. Respiratory Regulation
Controlled by nervous system
Basic rhythm is governed and co-ordinated by the respiratory centre (medulla)
Inspiration generally lasts up to 2 seconds after which impulses cease and expiration occurs by elastic recoil of lungs

26. Factors Controlling Rate of Breathing
Chemoreceptors
CO2 levels
Proprioceptors and Mechanoreceptors
Stretch receptors
Hering-Breur reflex (prevents overinflation)
Thermoreceptors
Temperature of blood
Baroreceptors
State of lung inflation

27. Neural Control
The respiratory centre in the medulla of the brain controls breathing.
It is made up of two main areas:
The inspiratory centre is responsible for the rhythmic cycle of inspiration and expiration
The expiratory centre is inactive during quiet ventilation. When the rate and depth of breathing increases (detected by stretch receptors in the lungs) the expiratory centre inhibits the inspiratory centre and stimulates expiratory muscles.

29. Cont.
In most circumstances the neural control of breathing is involuntary
The resp centre sends out impulses via the phrenic and intercostal nerves to the respiratory muscles
The muscles are stimulated for a short period, causing insipration
Then when the stimulus stops, expiration occurs

30. Other factors influencing the neural control of breathing include:
A large drop in oxygen tension.
This is monitored by chemoreceptors in the aorta and carotid arteries and results in an increase in the rate and depth of breathing.
A rise in blood pressure, monitored by baroreceptors in the aorta and carotid arteries, resulting in a decrease in ventilation rate
Proprioceptors in the muscles responding to movement stimulate the respiratory centre, increasing the rate and depth of breathing
The respiratory centre can also be affected by higher centres in the brain, e.g. emotional influences

31. Chemical Control
The respiratory centre responds mainly to changes in the chemistry and temperature of the blood
The most significant factor is a lowering in pH
This occurs when there is an increase in the amount of CO2 being produced by the cells
The increase is detected by the respiratory centre (in the brain)
It results in an increase in the rate and depth of breathing
A rise in body temperature will cause an increase in the rate but not the depth of breathing

32. Reminder Pulmonary diffusion – gaseous exchange at the lungs
Its functions
Replenish oxygen
Remove carbon dioxide

33. Partial Pressure of Gases
Central to understanding of gaseous exchange is the concept of partial pressure
“the individual pressure that the gas exerts when it occurs in a mixture of gases”
The pressure is proportional to its concentration
Partial pressures added together = total pressure of gas

34. Composition of Air Nitrogen = 79% Oxygen = 20.9%
Carbon dioxide = 0.03%
The percentages are obviously the relative concentrations!

35. Calculating Partial Pressure

38. Effect of Altitude

39. Effect of Altitude
With altitude there is a decrease in atmospheric pressure BUT the percentages of gases within the air remain identical to those found at sea level
It is the partial pressure of the gases that changes in direct proportion to an increase in altitude

40. Effect of Altitude cont.
E.G. – at rest the pO2 of arterial blood is approx 100mmHg, while in the resting muscles and tissues it is 40mmHg.
The difference between the two indicates the pressure gradient.
The pO2 of arterial blood at an altitude of 8000ft drops to 60mmHg, while that in the muscles remains at 40mmHg!

41. Altitude Training The principle:
With an increase in altitude, the partial pressure of oxygen in the atmosphere decreases by about a half, causing the body to adapt by INCREASING RED BLOOD CELL MASS AND HAEMOGLOBIN LEVELS to cope with a lower pO2

42. Altitude Training
It is widely used by endurance athletes to enhance their oxygen-carrying capacity
Recent evidence:
Living at altitude and training at sea level produces the greatest endurance performance
Can increase the oxygen-carrying capacity of the blood by up to 150%

43. Altitude Training Disadvantages: Expensive Can cause altitude sickness
Due to lack of oxygen , training at higher intensities is difficult
Any benefits are soon lost on return to sea level

44. Oxyhaemoglobin Dissociation Curve

45. Transport of Oxygen
Each molecule of haemoglobin can combine with 4 molecules of oxygen
The amount of oxygen that can combine with haemoglobin is determined by the partial pressure of oxygen
High pO2 = complete saturation
Low pO2 = saturation decreases

46. Transport of Oxygen and Dissociation
Hb is totally saturated at the lungs (alveoli)
As the pO2 is reduced, Hb saturation decreases accordingly.
This is largely due to the increased acidity of the blood (decrease in blood pH), caused by an increase in CO2 or LA and the increase in body temperature, which causes a shift to the right in the haemoglobin saturation curve.

47. The Release of Oxygen from Haemoglobin
At rest
The pO2 in the alveoli is approx 100mmHg
100% saturation
In resting muscle and tissue the pO2 is 40mmHg
75% saturation
Means that 25% of the oxygen picked up at the lungs is released into the muscle to help in energy production

48. The Release of Oxygen from Haemoglobin
During exercise
The pO2 in the alveoli remains at approx 100mmHg
100% saturation
In working muscles the pO2 can be greatly reduced, up to 15mmHg
25% saturation
Means that 75% of the oxygen picked up at the lungs is released into the muscle to help meet the extra energy demands

49. The Bohr Shift
Increased oxygen released to tissues!

50. Gas Exchange at Muscles and Tissues
High pO2 in arterial blood and relatively low pO2 in muscles causes a pressure gradient
High pCO2 in tissues and low pCO2 in arterial blood causes a movement of CO2 in opposite direction
Production of CO2 stimulates the dissociation of oxygen from haemoglobin
Myoglobin has a much higher affinity for oxygen than haemoglobin

51. a-VO2 difference
The arterial-venous oxygen difference is the difference in oxygen content of the blood in the arteries and the veins.
It is a measure of the amount of oxygen consumed by the muscles

52. Lung Volumes LUNG VOLUME DEFINITION TYPICAL REST VALUE
CHANGE DURING EXERCISE
Tidal volume (TV)
Volume inspired or expired per breath
500ml
Increase
Inspiratory reserve volume
Maximal volume inspired following end of resting inspiration
3100ml
Decrease
Expiratory reserve volume
Maximal volume expired following end of resting expiration
1200ml
Residual volume (RV)
Volume of air remaining in the lungs at the end of maximal expiration
Remains the same

53. Lung Capacities LUNG CAPACITIES DEFINITION TYPICAL REST VALUE
CHANGES DURING EXERCISE
Inspiratory capacity (TV + IRV)
Maximum volume of air inspired from resting expiratory levels
3600ml
Increase
Vital capacity (TV + IRV + ERV)
The maximum volume forcibly expired following maximal inspiration
5000ml
Slight decrease
Total lung capacity (VC + RV)
The volume of air that is in the lungs following maximal inspiration
6000ml
Minute ventilation (TV * f)
The volume of air inspired or expired per minute
7500ml
Dramatic increase

55. Minute Ventilation TIDAL VOLUME (TV) * FREQUENCY (BREATHS/MIN)
REST
500ml * 15
= 7.5L / min
MAXIMAL WORK
4,000ml * 50
= 200L / min

56. Adaptive Responses of Respiratory System to Training
SMALL INCREASES IN LUNG VOLUMES
Result from increased strength in respiratory muscles
IMPROVED TRANSPORT OF RESPIRATORY GASES
Increased amount of RBC’s (haemoglobin)
Increased blood plasma reduces viscosity
ENHANCED GASEOUS EXCHANGE AT THE ALVEOLI AND TISSUES
Increased capillary density
GREATER UPTAKE OF OXYGEN BY THE MUSCLES
Increased myoglobin and mitochondrial density
Increase in a-VO2 difference