The Respiratory System Ventilation to Gas Exchange

The Respiratory System

Ventilation to Gas Exchange


Respiration takes place in 5 steps:1.) Pulmonary ventilation, breathing

2.) External respiration, air into and outof the lungs

3.) Transport of respiratory gases, blood stream

4.) Internal respiration, gas exchange in capillary

5.) Cellular respiration, use of O2 by cells


The organs of the respiratory system are divided into the upper and lower respiratory organs.

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The organs of the upper respiratory tract are lined with mucous membranes.

The mucous functions as a debris trap.

The mucous membrane also serves to warm up the air on its way into the lungs.

Upper Respiratory Organs

The nose is an external appendage on the face which is made up of bone and cartilage.

The nose is lined with small hairs that are responsible for trapping large particles.

The nose connects to the lungs and is the primary entry point for air.


The nasal cavity is the vault like opening behind the nose.

The nasal cavity is responsible for warming air before entry into the lungs.

The olfactory senses are based in the nasal cavity.

It is also a resonating chamber for speech.


The nasal conchae divides the nasal cavity into a system of groove like passageways.

Air is filtered down through these grooves.

These grooves help warm the air more efficiently and filter out more particles.


The paranasal sinuses are a series of chambers in the skull which reduce the weight.

These sinuses are responsible for draining fluids out of the nasal cavity.

These also act as resonating chambers for speech.


The pharynx is a tube of cartilage which is the passage way for air into the lungs.

The epiglottis is a trap door which stops food from entering the lungs.


The larynx is the tube of cartilage that attaches to the lungs.

Within the larynx there are two pairs of vocal folds, there is a set of false vocal chords over top of the true vocal chords.

These vocal chords expand and contract as well as vibrate to produce sounds (your voice).


Larynx (cont.)

The slit between the vocal chords is the glottis which is where sound originates from.

The first ring of hyaline cartilage which attaches to the trachea is made up of cricoid cartilage which is the sight of a tracheotomy.

Lower Respiratory Organs

The trachea is the portion of the respiratory tract that splits off at the same point as the esophagus.

The trachea is made up of 16-20 incomplete C rings which are completed by smooth muscle and elastic CT.

The trachea divides at the carina in the left and right bronchus.


The bronchial tree Is the “tubing” which branches down into each of the lungs.

The primary bronchus is the first branching that occurs to each lung.

The secondary bronchus is branching which leads to each lobe of the lungs.


Bronchial tree (cont.)

The tertiary bronchi branch off into the bronchials which branch off into terminal bronchioles.

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As this branching occurs the cartilage decreases and the smooth muscle increases to allow for more expansion.

The expansion and contraction of these bronchi is an important tool to doctors.



Bronchodilators are much like epinephrine and are used to treat asthma.

Bronchoconstrictors are histamines that are used to help treat air borne allergies.


The lungs are the organs where the bronchial tree is located.

The lungs are covered by pleural (serous) membranes.

These membranes act as a lubricant for the lungs as they expand and contract.


Lungs (cont.)

There is a right and a left lung and each is divided into lobes.

The right lung has three lobes.

The left lung has two lobes.


Lungs (cont.)

Each of the lobes of the lungs is divided up into lobules is wrapped in elastic CT which allow for stretching when they become filled with air.

Each lobule contains a terminal bronchiole.


Lungs (cont.)

Each terminal bronchiole is subdivided into branches called respiratory bronchioles, which are subdivided into alveoli.

These alveoli meet up with capillaries and allow for gas exchange.


Lungs (cont.)

There are two types of cells in the walls of alveoli:

1.) Type I alveolar cells make up the majority of the structure.

2.) Type II alveolar cells are responsible for creating surfactant, which is a substance that stops your lungs from collapsing.

Physiology of Pulmonary Ventilation Atmospheric pressure is required for

inhalation and the pressure inside is equal to the pressure outside.

The diaphragm is curved upward when at rest.

Upon contraction the center of the diaphragm pushes down expanding the volume of the chest cavity.

Physiology of Pulmonary VentilationThis expansion of the chest cavity

causes the pressure within to decrease.

Air rushes into the cavity to equalize the pressure.

P1V1=P2V2

Physiology of Pulmonary VentilationContraction of the intercostal muscles

(muscles between the ribs) also help in expansion and contraction of the chest cavity.

The elastic recoil of the tissue in the chest cavity and lungs allow for exhaling of gases.

Physiology of Pulmonary VentilationThe process of exhaling causes

extreme pressure to push on the walls of the small alveoli.

Surfactant helps to break the surface tension of the air as it is being pushed out of the lungs.

Physiology of Pulmonary VentilationIn times of extreme contraction and

stress the surfactant isn’t enough to stop a complete contraction of the alveoli, this is called a collapsed lung.

Respiratory Distress Syndrome (RDS) occurs in newborns. It is a collapsed lung due to a lack of surfactant in the alveoli.

Physiology of Pulmonary Ventilation The air volume of your lungs is measured by

a spirometer.

The tidal volume of a persons lungs is the amount of air that enters and exits the lungs while inhaling and exhaling respectively.

The average person has a tidal volume of 500ml.

Physiology of Pulmonary VentilationInspiratory Reserve Volume (IRV) is

the amount air that can be forcibly inhaled after the tidal volume, basically a deep breath.

In the average person this is approximately 3000ml.

Physiology of Pulmonary VentilationExpiratory Reserve Volume (ERV) is

the amount of air that can be forcibly exhaled after the normal tidal volume, pushing air out after you exhale.

This is about 1100ml for the average person.

Physiology of Pulmonary VentilationVital Capacity (VC) is the maximum

amount of air that can be exhaled after a maximum inhalation.

VC = TV + IRV + TV + ERV

An Average persons vital capacity is about 5100ml.

Physiology of Pulmonary VentilationThe lungs are NEVER without some air,

unless they are collapsed.

The residual volume (rv) is the amount of air that always remains in the lungs no matter how much you try and exhale.

The average residual volume is 1200ml.

Physiology of Pulmonary Ventilation There are modified respiratory movements

which occur in addition to normal breathing as a result of reflexes.

A cough sends a blast of air which clears the upper respiratory system of blockages.

A sneeze forcefully expels air through the nose in response to dust in the mouth or nose.

Physiology of Pulmonary VentilationA laugh is a deep breath released in a

series of short convulsive expirations.

A hiccup is a spasm of the diaphragm.

A yawn is a deep inspiration through an open mouth, which ventilates the alveoli.

Control of Breathing

It is controlled in the respiratory center of the brain, which is located in the pons and medulla of the brain stem.

Its location in the brain stem shows that it is a primitive neurological command that is why you can breathe with out even thinking about it.


Breathing speed is regulated by chemo- receptors located in major arteries.

These chemo-receptors measure levels of oxygen and carbon dioxide.

If the levels of O2 are too low or the levels of CO2 are too high a signal is sent to the brain stem to increase the breathing rate.


There are required levels of oxygen and carbon dioxide in the blood which keep homeostatic levels.

If a person begins to hyperventilate (quick shallow breathing) oxygen levels will increase and can cause problems in the gas levels in the blood.

Breathing into a paper bag rich in carbon dioxide is a way to equalize gas levels.


There are a few factors which influence the control of breathing:1.) Stretchiness of the tissue (decreases with age)

2.) Low blood oxygen (decreases when cells are working strenuously)

3.) High blood CO2 (rises when cells are working strenuously)

4.) Low Blood pH (normal is 7.4)

External Respiration

The definition of external respiration is the exchange of oxygen and carbon dioxide between the alveoli and lung capillaries.

Dalton’s Law states that the pressure of a gas determines the rate at which it will diffuse from a region.


Air is a mixture of 74% nitrogen, 21% oxygen and 0.04% carbon dioxide.

In a mixture of gases the amount of pressure each gas creates is called its partial pressure.

A gases partial pressure is directly related to the concentration of that gas in a mixture.


Diffusion of gases across a membrane proceeds from where a gas is in high partial pressure to low partial pressure.

This idea is why oxygen diffuses into the capillaries and out the alveoli and the opposite is true for carbon dioxide.


ALVEOLI CAPILLARY

PCO2 = 40mmHg PCO2 = 45mmHg

PO2 = 104mmHg PO2 = 40mmHg


The rate of diffusion also depends on other factors like:

Surface area available for gas exchange

Diffusion distance

Breathing rate and depth

Internal Respiration

The definition of internal respiration is the exchange of oxygen and carbon dioxide between capillaries and body tissues.

All of the same partial pressure rules hold true here as well.

The tissues have oxygen at a lower pressure and carbon dioxide at a higher pressure.

Transport of Gases in the Blood

Oxygen binds to hemoglobin in the blood to form the compound oxyhemoglobin.

The rate at which oxygen is released from this compound is depends on: Blood temp. Blood pH CO2 levels


Carbon Monoxide is much better at binding to hemoglobin then oxygen is.

This is why carbon monoxide is so dangerous, if all of the hemoglobin is bound to the useless carbon monoxide then hypoxia of essential tissues results.


Carbon Dioxide is usually transported as carbaminohemoglobin and bicarbonate ions, very rarely is it transported as carbon dioxide.

When carbon dioxide is transported as CO2 it usually reacts with the water in the blood to form carbonic acid which could lower the pH of the blood…dangerous!!!

Life Span Changes

Exposure to pollutants such as SMOKE increases the risk of respiratory illnesses.

Loss of cilia and thickening of the mucous can cause increased illness as one ages.

Vital capacity decreases with age…you get out of breath easier as you age.

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The Respiratory System Ventilation to Gas Exchange