IPHY 3430 9-15-11

RESPIRATORY SYSTEM

Purpose:Maintain blood levels of O2 and CO2 as homeostatic variables

Fig. 13-2, p. 453

Additional parts of anatomy involved in respiration

Nervous system: Pons, MedullaPhrenic nerve and other motor nerves

Physical Principles

1. Gas flows from area of high pressure to low pressure

2. The rate of flow depends on the pressure gradient: the greater the gradient, the faster the flow and the larger the volume of air that moves

3. When gas is compressed in a smaller volume, the pressure increases.

INHALATION1. Medulla sends signal via motor nerves to diaphragm and external intercostals, causing contraction2. Those muscles cause expansion of the volume of the thoracic cavity3. The increased volume of the thoracic cavity causes the lungs to expand4. The expansion of the lungs causes a decrease in air pressure in the lungs relative to outside air5. Air flows into lungs down pressure gradient until air pressure equalized.

During inhalation/exhalation at rest:pressure differential of about 1 mm

759mmHg

760

Inhalation at rest

761

760

Exhalation at rest

EXHALATION AT REST1. Air flow in during inhalation stops when pressure equalized2. Stimulus from medulla ceases, causes muscles to relax.3. Elastic properties of the muscles and rib cage cause decrease in volume of thoracic cavity, which causes a decrease in lung volume4. Decrease in volume of lungs causes increase in air pressure in lungs relative to outside5. Air rushes out of lungs until pressure equalized.

During inhalation/exhalation at rest:pressure differential of about 1 mm

759mmHg

760

Inhalation at rest

761

760

Exhalation at rest

VARIATION IN RESPIRATORY EXCHANGE DURING EXERCISE1. In exercise, increased muscle contraction leads to greater expansion of thoracic cavity and decrease in air pressure in lungs2. Decreased air pressure in exercise leads to greater air inhalation and exhalation3. Increased number of breaths/min

During exercise, pressure differentials greater than 1 mm generated due to greater numbers of muscles contracting with greater force, resulting in larger expansion of thoracic cavity and lungs.

750

760mmHg 770

760ExhalationInhalation