The Respiratory SystemThe Respiratory System

Structure, Function, Mechanics of Structure, Function, Mechanics of Breathing (External Respiration)Breathing (External Respiration)

Questions you need to answer

• What is the function of the respiratory system?

• Describe the passage of air from the body into the blood.

• Explain the mechanics of breathing and how they change during exercise.

Air Pathways and Partial PressuresAir Pathways and Partial Pressures

• Air passes into;• Lungs• Bronchus• Bronchi• Bronchioles• Alveoli

• at alveoli air passes through the one cell thick sacs into pulmonary capillaries

• O2 passes in and CO2 out.

Mechanics of BreathingMechanics of Breathing

• Inspiration• external ribs contract - pull ribs up, sternum out• diaphragm contracts and flattens• decrease air pressure in thoracic cavity, lung

volume increases - air rushes to fill the lungs

• Expiration• passive relaxation of the respiratory muscles and

elastic recoil of lungs - air forced out of the lungs• forced expiration internal intercostal muscles and

abdominals contract to pull ribs down and pull diaphragm up

Gaseous Exchange

Internal Respiration, Breathing Control, Respiratory Volumes and

measures

Questions you need to answer

• Describe gaseous exchange at the alveoli and movement of oxygen due to partial pressure.

• Explain the effect of temperature, acidity, and carbon dioxide on oxygen dissociation.

• Explain how breathing rate and depth is controlled by the body.

• Know the definitions of breathing volumes and typical values at rest and exercise.

Partial Pressure of gases (mmHg)

Oxygen (02) Carbon Dioxide (CO2)

160 Atmosphere 0.3

105 Alveoli 40

40 Tissues 45

• O2 attracted into capillaries by partial pressure of gases and haemoglobin.

• 97% O2 carried in this way.

• Oxygen saturation of haemoglobin is affected by several factors as well as its own partial pressure

• body temperature

• partial pressure of CO2

• acidity ‘Bohr Effect’

• Only 23% CO2 carried by haemoglobin• 70% combines with water to form carbolic acid

which is buffered by hydrogen ions to form Bicarbonate.

Breathing ControlBreathing Control

• Controlled by the respiratory centre in the medulla oblongata.

• The inspiratory centre controls rhythmic cycle of in/expiration during rest.

• The expiratory centre is inactive at rest but affects breathing during exercise

• 2 methods of control• Neural• Chemical

VolumesVolumes• Tidal Volume

• air breathed in/out each breath

• Inspiratory Volume• max volume inspired

after tidal volume

• Expiratory Volume• max volume expired

after tidal volume

• Residual Volume• volume left in lungs

after max expiration (stops lungs collapsing)

MeasuresMeasures• Vital Capacity

• max air expired after inspiring as much as possible

• Total Lung Capacity• vital capacity +

residual volume

• Minute Ventilation• Tidal Volume x

frequency of breathing per minute