Respiratory SystemPart II

Respiratory Physiology

In order to supply the body with oxygen and get rid of carbon dioxide the process of respiration MUST occur.

Pulmonary ventilation: air is moved in and out of the lungs so that gas is exchanged and refreshed – breathing.

External respiration: gas exchange between pulmonary blood and alveoli must take place.

Respiratory gas transport: Oxygen and CO2 must be transported to and from the lungs and tissue cells of the body through the bloodstream

Internal respiration: at the capillaries, gas exchanges are made between the blood and tissue cells.

Mechanics of Breathing

Breathing/Pulmonary Ventilation:– Mechanical process which depends on volume

changes occurring in the thoracic cavity. – These changes can lead to pressure changes which

lead to the flow of gasses to equalize the pressure within the lungs.

– Gas always conforms to the shape of its container filling it completely. In a large volume the gas molecules are further apart and pressure will be low. If the volume is reduced the gas molecules move closer together and pressure will increase.

Inspiration – When air flows into the lungs

Diaphragm: – Inspiratory muscles– When the diaphragm contracts it flattens inferiorly and the height

of the thoracic cavity increases. External Intercostals:

– Inspiratory muscles– Contraction of the external intercostals causes the rib cage to lift

and increases the thoracic cavity. Intrapulmonary volume:

– Volume within the lungs– As the intrapulmonary volume increases the gases in the lungs

spread to fill this larger space. The decreasing pressure then causes a vacuum effect sucking air into the lungs. Air continues to move into the lungs until the intrapulmonary pressure is equal to the atmospheric pressure.

Expiration – Exhaling

Passive process that depends on the natural elasticity of the lungs vs. muscle contraction

When inspiratory muscles relax and resume their normal resting lengths the thoracic and intrapulmonary volumes decrease. When this occurs the gasses in the lungs are forced to move close together and intrapulmonary pressure increases more than atmospheric pressure and causes gasses to flow out in order to equalize the pressures.

Expiration – Exhaling

Normally expiration should be effortless but if the respiratory passages are narrowed or clogged expiration can become a forced process. In these cases the internal intercostals and abdominal muscles will be forced to contract in order to exhale the air.

Expiration – Exhaling

Intrapleural Pressure:– Pressure within the pleural space– This pressure is always negative protecting the lungs from collapsing– If the intraplueral space becomes equal to atmospheric pressure the

lungs will then collapse. Atelactasis:

– Collapse of the lungs– Usually occurs when air enters the pleural space through a chest wound

but may occur from a rupture of the visceral pleura allowing air to enter directly from the respiratory tract.

Pneumothorax:– Presence of air within the intrapleural space disrupting the fluid bond

between the pleura.– It can be reversed by inserting a tube into the chest to remove the

excess fluid and allowing the lungs to attempt to function normally again

Non-respiratory Air movements

Situations other than breathing where air moves into and out of the lungs is usually a result of reflex activity but can sometimes be voluntarily controlled. – Coughing & Sneezing: clear air passages of debris or

collected mucus– Laughing & Crying: reflect a persons emotions– Hiccups: involuntary reflex– Yawning: involuntary reflex

Respiratory volumes and capacities

Factors affecting respiratory capacity:– Persons size– Age– Sex– Physical condition

Respiratory volumes and capacities

Tidal Volume (TV):– Normal breathing– Normally approximately 500 ml. of air are moved in and out of the

lungs with each breath.

Inspiratory Reserve Volume (IRV):– The amount of air that can be taken in FORCIBLY over the tidal

volume. – Normally between 2100-3200 ml.

Expiratory Reserve volume (ERV):– The amount of air that can be forcibly EXHALED after tidal

expiration. – Approximately 1200 ml.

Respiratory volumes and capacities

Residual volume:– 1200 ml. of air that remains in the lungs and cannot be voluntarily

expelled. – Allows gas exchange to go on continuously even between

breaths and keeps the alveoli open/inflated. Vital Capacity (VC):

– Total amount of exchangeable air– The sum of TV + IRV + ERV

Dead Space Volume:– Air enters the respiratory tract and remains in the passageways

but never reaches the alveoli.– During normal breathing the dead space volume is usually about

150 ml.

Respiratory volumes and capacities

Functional Volume:– Air that actually reaches the respiratory zone.– Approximately 350 ml.

Spirometer:– Device used to measure respiratory capacities– As a person breathes the volumes of air exhaled can

be read on an indicator showing the changes in air volume inside the apparatus.

– This testing is useful for evaluating losses in the respiratory function after respiratory diseases have been diagnosed.

Respiratory Sounds

Bronchial Sounds:– Produced by air rushing through the large respiratory

passageways such as the trachea and bronchi. Vesicular Breathing:

– Sounds occurring as air fills the alveoli– Sounds are soft and resemble a muffled breeze

Abnormal sounds:– Results of diseased respiratory tissues, mucus or pus.– Rales: rasping sounds– Wheezing: whistling sounds

Laws of Diffusion

All gas exchanges are made by diffusion causing movement toward the area of a lower concentration of the diffusing substance.

External Respiration

As dark red blood flows through the pulmonary circuit it is then transformed to a lighter scarlet color as it is returned to the heart.

This color change is due to the oxygen pickup by hemoglobin in the lungs

Carbon dioxide is then removed from the blood equally as fast as the O2 pickup

Body cells continually remove oxygen from the blood but the alveoli continually hold more oxygen in their sacs.

How External Respiration occurs

Oxygen moves from the air of the alveoli into the respiratory membrane

From the respiratory membrane oxygen poor blood is then transported to the blood of the pulmonary capillaries

As tissue removes oxygen from the blood during systemic circulation carbon dioxide is released into the blood.

Because the concentration of CO2 is higher in the pulmonary capillaries than in the alveolar air it leaves the blood to pass into the alveoli and is flushed out of the lungs during expiration.

Therefore blood that is draining from the lungs into the pulmonary veins is oxygen rich and carbon dioxide poor and ready for systemic circulation!

Gas Transport in the Blood

Oxygen is transported in the blood in two ways:– Oxyhemoglobin (HbO2): oxygen attaches to

hemoglobin molecules inside the red blood cells and produces HbO2

– Dissolved in the plasma: very small amounts of oxygen are carried this way.

Carbon dioxide transport

CO2 is transported by a Bicarbonate Ion (HC03) inside the plasma and bound to hemoglobin.

It binds at different sites from oxygen so that it does not interfere with the oxygen transport.

Before CO2 can diffuse out of the blood into the alveoli it must be released from the bicarbonate form

For this to occur bicarbonate ions must combine with hydrogen ions to form carbonic acid (H2CO3)

The carbonic acid quickly splits for form water and carbon dioxide

The CO2 then diffuses from the blood and enters the alveoli

Internal Respiration

The exchange of gases that takes place between the blood and the tissue cells.

Opposite of what occurs in the lungs. It is the process of unloading oxygen and

loading CO2 into the blood.

How Internal Respiration Occurs

CO2 diffuses out of the tissue cells and enters the blood.

When it enters blood it combines with water to form carbonic acid

From here it releases bicarbonate ions and diffuses out into the plasma where it is then transported.

How Internal Respiration Occurs

At the same time oxygen is released from the hemoglobin and the oxygen diffuses out of the blood to enter tissue cells it causes the exchanges in venous blood to be much more oxygen poor and carbon dioxide rich than the blood leaving the lungs.

Most of this conversion occurs inside the red blood cells

RBC’s also contain carbonic anyhydrase – a special enzyme which speeds up the reaction time!

Impaired Oxygen Transport

Hypoxia:– Inadequate oxygen delivery to the body tissues– Skin becomes cyanotic (blue) – Can be the result of anemia, pulmonary disease, impaired or

blocked circulation Carbon Monoxide Poisoning:

– Unique type of hypoxia– Because carbon dioxide binds to hemoglobin at the same sites

as oxygen it can crowd out or displace the oxygen.– It is the leading cause of death from fire and does not produce

typical signs and symptoms of hypoxia– Victims become confused, have throbbing headache and skin

can become red in color– They must be given 100% oxygen to breathe until CO2 is cleared

from the body.

Control of Respiration

Neural Regulation:– Phrenic and Intercostal nerves control the diaphragm and

intercostal muscles used during breathing.– Self-Exciting Inspiratory center: located in the medulla and pons.

Sets the basic rhythm for breathing. Impulses going between the two centers of the brain maintain a rate of 12-15 respirations per minute (rpm)

– Eupnea: normal respiratory rate & response– Stretch receptors: located in the bronchioles and alveoli.

Respond to extreme over inflation. Impulses are then sent from the stretch receptors to the medulla through vegus nerves where they will end inspiration and begin expiration.

Factors influencing respiratory rate and depth

Physical factors:– Talking– Coughing– Exercise– Increased body temperature– Increased rate and depth of breathing

Factors influencing respiratory rate and depth

Volition:– Voluntary controls of breathing is limited– Respiratory centers ignore messages from the cortex

when oxygen supply is getting low or blood Ph is falling

Emotional factors:– Scared– Gasping at touching something cold, clammy or hot– Reflexes initiated by emotional stimuli from the

hypothalamus.

Factors influencing respiratory rate and depth

Chemical Factors:– Level of O2 and CO2 in the blood– Increased CO2 and decreased blood pH = increase in rate and

depth of breathing– Decrease in O2 only become important stimuli when they are

critically low– Hyperventilation: Extremely slow or shallow breathing brought on

by anxiety dramatically decreases the amount of carbonic acid in the blood – leads to periods of …

– Apnea: cessation of breathing until CO2 builds up in the blood. If breathing is stopped for a significant amount of time …

– Cyanosis may occur. Cyanosis: insufficient oxygen in the blood