The Mechanics

of Breathing

Breathing

Recall: Breathing is the mechanism by which

mammals bring air in and out of their lungs.

This process is possible due to changes in volume

and pressure.

These changes are a result of contractions and

relaxations of muscles such as the diaphragm.

The two other sets of muscles involved are the

external intercostal muscles and the internal

intercostal muscles.

Inhalation Contraction of the

diaphragm flattens it

downward, increasing the

volume in the chest cavity

Contraction of the external

intercostal muscles pulls up

on the rib cage, increasing

volume in the chest cavity.

Increased volume produces

a decrease in air pressure,

which is lower than external

atmospheric pressure.

Lungs expand and air enters

the lungs (movement from

high pressure to low pressure)

Exhalation Relaxation of the diaphragm

domes it upward, decreasing the volume in the chest cavity

Relaxation of the external intercostal muscles relaxes the rib cage down, decreasing volume in the chest cavity.

For active expiration, internal intercostal muscles can be contracted to further decrease volume of the chest cavity.

Decreased volume produces an increase in air pressure, which is higher than external atmospheric pressure.

Lungs shrink and air exits the lungs (movement from high pressure to low pressure)

Gas Exchange

Gas exchange occurs across the cell membranes of

the alveoli and the adjacent capillaries, each of

which are only one cell thick.

Gases diffuse across the membrane according to

concentration gradients.

Lung Capacity

Tidal volume

Volume of air inhaled and exhaled in a normal

breathing movement

Inspiratory reserve volume

Additional volume of air that can be taken in, beyond

a regular or tidal inhalation

Expiratory reserve volume

Additional volume that can be forced out of the lungs,

beyond a regular or tidal exhalation

Lung Capacity

Vital capacity

Total volume of gas that can be moved in or out of

the lungs. It is the sum of tidal, inspiratory reserve, and

expiratory reserve volumes.

Residual volume

Amount of gas that remains in the lungs and the

passageways of the respiratory system even after a full

exhalation.

Respiratory efficiency

Rate at which oxygen can be transferred into the

blood stream for transport.

Lung Capacity

Control and

Regulation

High Altitude Breathing

At high elevations, air pressure is lower. Although oxygen and other gases are present in the same proportions, there is less air in total.

At higher altitudes, the body cannot get enough oxygen, which results in altitude sickness.

To adjust to the higher altitude, the body has several responses:

Increased breathing rate

Temporary increase in red blood cell production

These temporary adjustments can be used for training by athletes.

More permanent changes are also possible through evolution of populations that live at high altitudes.

Control of Breathing

When working out, muscle cells use more oxygen and produce more carbon dioxide through cellular respiration.

Increased need for oxygen results in a increased breathing rate.

This is accomplished when the body detects a high concentration of carbon dioxide in the body.

When carbon dioxide concentrations are high in the blood, the medulla oblongata of the brain will detect this and send out nerve impulses to initiate faster movement of the muscles controlling volume in the chest cavity.

Respiratory Impairment: Drowning Our respiratory system is able to adapt to small

changes in the environment. However, there are

some changes to which it cannot adapt.

When an individual is submerged in water, the main

reason for death can vary.

A laryngospasm, which is a reflex closing of the larynx,

can cause death through asphyxiation

Fresh water entering the lungs

washes away the film which

coats the alveoli which causes

them to collapse

Salt water causes fluid to

leave the capillaries and

blocks oxygen from reaching

the alveoli

Carbon Monoxide Poisoning Carbon monoxide is a invisible, odourless, tasteless

gas. It can be released during combustion.

Carbon monoxide is dangerous because it can

bind to red blood cells better than oxygen.

This prevents oxygen binding which prevents

oxygen from being transported to body cells.

This suffocation effect can happen even at low

concentrations.

Early symptoms include

headaches, weakness, dizziness,

nausea. This could lead to

coma and death.

Smoking Cigarette smoke can slow the action of cilia in the

trachea or destroy them. This removes a mechanism

of protection.

Cigarette smoke also contain carbon monoxide

causing mild carbon monoxide poisoning.

Some chemicals also cause cancer.

Particles in the smoke can block passageways of

the respiratory system and prevent gas exchange.

Lungs can lose elasticity and become brittle.

Air Pollution

Common airborne pollutants include carbon

monoxide, nitrogen oxides, chlorine, and methane,

as well as small particles of dust and other

compounds.

In urban areas, a combination of pollutants

produces smog. Chemicals in smog have effects

similar to cigarette smoke.

This could causes irritation and

respiratory problems such as

asthma and loss of

lung elasticity.