The Respiratory System

The Function of Respiration

The respiratory system is the group of organs that ensure that oxygen is brought in and carbon dioxide is removed from each cell in the body.

Four stages of Respiration

•       Breathing (inspiration and expiration)

•       External respiration (exchange of gases between lungs and blood)

•       Internal respiration (exchange of gases between blood and cells)

•        Cellular respiration (energy-releasing reactions in cells)

 

Stages of Respiration

Breathing is the process by which air enters and leaves the lungs. 

  • External respiration is the exchange of oxygen and carbon dioxide between the inside of the lungs and the blood.

  • Internal respiration is the exchange of oxygen and carbon dioxide between the blood and the body’s tissue cells.

Respiratory Surfaces

There are two requirements for respiratory surfaces.

They must be large enough for gas exchange to occur quickly enough to meet the body’s needs.

They must be moist so gases can dissolve; some are aquatic, some are subterranean.

However, ventilation, the process of drawing or pumping an oxygen-containing medium over the respiratory surface, is common for all.

 

Types of Respiratory Surfaces


Outer Skin:

•       Entire outer skin is used

•       Diffusion from skin into thin walled capillaries transports O2 and CO2 in and out of cells from blood

•       Organism must live in moist environments  and have a high surface to body volume ratio.

•       Ex: Worms and some amphibians

 Gills:

•       Gills are extensions of folds in the body surface that increase surface area available for gas exchange

•       Oxygen from water diffuses across gill surfaces into capillaries, and CO2 diffuses out

•       All gill breathers live in aquatic environments, ensures respiratory surface is moist.

Ex: Fish

Counter Current Flow

Fish also employ a counter-current exchange system where O2 and CO2 flows down diffusion gradients (high to low), since water and blood flow in opposite directions.



 Tracheal Respiration

•       internal system of branching respiratory tracheae (tubes)

•       tracheae connect cells directly to environment for gas exchange (blood not required)  via spiracles (even smaller tubes)

•       Oxygen enters through spiracles and diffuses into tracheae, CO2 moves in opposite direaction.

•       Rhythmic contractions of abdomen help this to occur.

Ex: insects

 Lungs

•       Large animals employ lungs since they can provide more gas exchange to meet higher activity needs

•       lungs contain sacs lined with a moist surface (epithelium); these sacs increase surface area

•       blood transports gases to cells by diffusion

•       Ex: Mammals, birds, reptiles most amphibians 

 

Terrestrial Gas Exchange

Breathing is required to move air in and out of the lungs.

The brain regulates the breathing rate and monitors the volume of air in the lungs. 

  • The muscular diaphragm (the dome muscle at the bottom of the thoracic cavity).

  • The rib muscles (intercostal muscles) control air pressure inside the lungs, and thus inhalation and exhalation.

 

Air Pressure in Lungs

  • Inspiration (inhalation) begins when the intercostal muscles and the diaphragm contract, expanding the thoracic cavity, with the rib cage moving up and out.

Since the cavity is airtight, the volume increases, the gas particles exert less pressure on the walls, and the air pressure inside the lungs decreases.

This results in air from the external environment rushing in to counterbalance the lower pressure inside the lungs.

  • Expiration (exhalation) is the opposite action. The diaphragm and intercostal muscles relax, reducing volume.

The increase in pressure inside the lungs forces the air out.


Spirographs

  • Spirographs represent the amount of air that moves into and out of the lungs with each breath as measured by a spirometer

Spirometers

  • Spirographs are generated from the measurements taken with a spirometer. There are a number of types of spirometers, but they all do the same thing: measure respiratory volumes.

  • A spirometer measures the volume of air that is inhaled and exhaled over a period of time.

    Measuring Respiratory Volume


Tidal volume is the volume of air that is inhaled and exhaled in a normal breathing movement (body is at rest).

Inspiratory reserve volume is the additional volume of air that can be taken into the lungs beyond a regular (tidal) inhalation.

Expiratory reserve volume is the additional volume of air that can be forced out of the lungs beyond a regular (tidal) exhalation.

Vital capacity (total lung volume) is the total volume of gas that can be moved into or out of the lungs.

tidal volume + inspiratory reserve volume + expiratory reserve volume = vital capacity

Residual volume is the amount of air that remains in the lungs and passageways even after a full exhalation.

 

The Human Respiratory System

Since humans are land animals, they use lungs to respire. The respiratory tract allows air to travel into the body to reach the moist lungs. The respiratory tract begins at the nose.

 

Upper Respiratory Tract


  • Air enters the nostrils or through the mouth

  • Inside the nasal passage, thin turbinate bones increase the surface area.

  • The nasal passages warm the air to body temperature with a dense network of capillaries. This protects the more delicate structures of the lower respiratory tract.

  • Air is cleansed of dust and small particles by ciliated cells that also secrete mucus. 

  • Air moves down into the pharynx (throat) and then past the glottis opening and into the larynx.

  • The glottis can be closed by the epiglottis when food is swallowed to prevent the entry of any food into the trachea.

  • The air then moves into the larynx (voicebox), which is made of cartilage and used for sound production in mammals.

  •   Cartilage is a tough, firm connective tissue.

  • Sounds are made as vocal cords in the larynx are moved closer together so pressure from exhaled air causes them to vibrate.

  • Pitch (tone) of sound varies with the length of the cords. The longer the vocal cord, the lower the sound.

  • Next, air enters the 10 to 12 cm long trachea, which is strengthened and kept open by semicircular loops of cartilage.

 

Lower Respiratory Tract

  • The trachea branches into two tubes called bronchi (singular bronchus).

  • One bronchus enters each lung

  • The lungs are surrounded by a pleural membrane.

  • The outer layer of the membrane is attached to the chest wall, and the inner layer covers the lungs.  The thin space between the two contains a lubricating fluid to make moving the lungs during breathing easier.

  • Lungs are divided into regions called lobes.  The left lung has two lobes, and the right lung has three. 

  • Each bronchus divides many times to form a network of microscopic bronchioles.

  • Each bronchiole ends in a microscopic grape-like cluster of tiny sacs called alveoli (singular alveolus).

 

Alveoli

There are about 500 million alveoli per lung. Each one is surrounded by a network of capillaries. The walls of the alveoli and the walls of the capillaries are only one cell thick so that gas exchange can occur quickly by diffusion.

 

Gas Exchange in Detail

The air that enters the alveoli after inhalation has a higher concentration of O2 than the alveolar blood.

Thus, O2 diffuses out of the alveoli and into the blood because the air that enters the alveoli has a higher concentration than the alveolar blood.

The opposite is true for CO2 diffuses out of the blood and into the alveoli, where it is then released into the air in the lungs.

 

Transporting Gases

  • Oxygen

  • About 99% of O2 that reaches cells is carried by hemoglobin, a protein in red blood cells.

  •   The remaining 1% is carried by dissolving in the water of the blood plasma.

 

Carbon Dioxide

  • About 23% of CO2 is carried by hemoglobin

  • The remaining 77% is carried in the blood fluids (plasma)

    Disorders of the upper respiratory tract

  • Laryngitis

  • Tonsillitis

Tonsillitis

•        a bacterial or viral infection of the tonsils, which are in the pharynx at the back of the throat and function to keep bacteria and other harmful substances out of the respiratory system

•        symptoms include red and swollen tonsils, sore throat, fever, and swollen glands

•       tonsils can be removed surgically

Laryngitis

•       inflammation of the larynx caused by infection or overstraining the voice

•       usually clears up after a few days  


Disorders of the lower respiratory tract

  • Pneumonia

  • Bronchitis

}  Asthma

}  Emphysema


Pneumonia

•       inflammation and fluid build-up in the alveoli

•       Interferes with gas exchange starving the body of oxygen

•       types are lobular and bronchial

•       Can be viral or bacterial, with viral pneumonia generally being less severe

•       treatments include antibiotics (bacterial), anti-virals, and vaccines 

 

Bronchitis

•       Inflammation, redness, and extra mucus in the membranes of the bronchi

•       Mucus expelled by coughing

•       Short term (acute): caused by a bacteria

•       Long term (chronic): caused by regular exposure to concentrations of dust, chemical compounds, or cigarette smoke, which gradually destroy the cilia

•       Without the cleansing of the cilia bronchi grow increasingly inflamed and vulnerable to infection.

Mucus accumulates causing a person to develop a persistent cough. This is known as COPD (chronic obstructive pulmonary disease)

•       can be treated (but not cured) by medications, quitting smoking, and special exercise programs

 

 

Asthma

•       inflammation of the bronchi and bronchioles

•       triggered by inhaled irritants including

•       pollen, dust, and smoke

•       narrows air passages and reduces airflow

•       symptoms include wheezing, coughing, tightness in the chest, and shortness of breath

•       Often starts in childhood

•       cannot be cured but can be managed

•       treatments include inhalers and muscle-relaxing medications that reduce inflammation

 

 

Emphysema

•        walls of the alveoli lose their elasticity

•       reduces respiratory surface for gas exchange

•       breathing is laboured due to collapsed bronchioles

•       a class of COPD that is incurable

•       symptoms can be treated with inhalers or low-flow oxygen tanks

•       causes include smoking and airborne irritants

 

 

Cystic Fibrosis

•       Due to a genetic condition, cells lining the airways release thick, sticky mucus that clogs the lungs

•        Person has difficulty breathing, more bacterial infections.

•       Can be relieved by mucus-thinning medications and antibiotics, but there is no cure

•        Gene therapy has been used since 1993 in an attempt to provide the correct DNA to the cells that line the

Lung Cancer

•      Uncontrolled cell division

•       A mass called a carcinoma (tumour) forms and can grow large enough to reduce respiratory surface area

•       Tumour can break away and form more elsewhere (metastasis)

•       Symptoms include persistent cough, difficulty breathing, chest pain, and loss of appetite

•       Difficult to detect in early stages, and challenging to treat.

•       Leading cause of cancer deaths in Canada; more than 80% diagnosed die within five years

•       Main cause is smoking, but there are others


Treating Lung Cancer

There are three main techniques; choice depends on the type and extent of the cancer, and the age and health of the person:

•             radiation: uses X rays or other radiation to destroy cancer cells

•             chemotherapy: uses drugs administered by mouth or injection to destroy cancer cells

•             laser surgery: removal of the area of the lung that contains tumours with a yttrium aluminum garnet (YAG) laser

 Diagnostic Tool: CT Scanning

•       Main diagnostic tool for respiratory disorders is a special X ray machine called a computed axial tomography scanner (CT or CAT scan)

•       Rotating X ray device takes 360°images of body’s interior

•       Sometimes a dye is also used

•        Produces a clear, detailed view of blood vessels and internal tissues in chest cavity

•        Good for detecting early lung cancer and finding internal injuries

Diagnostic Tool: Two-Photon Microscopy

•        Two-photon microscopy (TPM) is an imaging tool in which microscopes emit photons of light that highlight tissue that has been fluoresced with a marker

•       Produces a 3-D image without extracting a sample

•       Can also show biochemical processes such as how different drugs applied to the skin are absorbed and used by the tissues

Diagnostic Tool: Bronchoscopy

•       Bronchial endoscopy uses a special type of endoscope to examine the trachea and lungs.

•       Under general anesthesia, the endoscope is inserted down the mouth or nose and special attachments can collect mucus or tissue to diagnose disorders (such as asthma), remove tumours, and repair damaged tissues.

 

  The Need for Oxygen

•  All animals and plants need oxygen to survive

•  Oxygen is used in aerobic cellular respiration, which is the processes of using oxygen and other substances to create energy

•  The basic equation is:

      glucose  + oxygen → carbon dioxide  +  water  + energy

      C6H12O6 +  6O2      →          6CO2           +   6H20   + energy


Energy - ATP

•  Most of the energy is released as thermal energy, while the rest is stored in a molecule called adenosine triphosphate (ATP)

•  Cells use ATP to power almost all energy-requiring processes, such as growth and movement

•  ATP is used in the breakdown of glucose through cellular respiration

Four stages of Respiration

•   Breathing - the process by which air enters and leaves the lungs (inspiration and expiration)

•   External respiration- the exchange of oxygen and carbon dioxide between the inside of the lungs and the blood that occurs simultaneously

•   Internal respiration - the exchange of oxygen and carbon dioxide between the blood and the body’s tissue cells that occurs simultaneously

•   Cellular respiration – the complex series of chemical reactions that involve the release of energy from carbohydrates in the presence of oxygen, occurring in the mitochondria of every cell

 

Respiratory Surfaces

•  There are two requirements for respiratory surfaces

  • They must be large enough for gas exchange to occur quickly enough to meet the body’s needs

  • They must be moist so gases can dissolve

•  Various types of respiratory surfaces and systems have evolved in different animals.

•  However, ventilation, the process of drawing or pumping an oxygen-containing medium over the respiratory surface, is common for all.

 

 

Using the Outer Skin as a Respiratory Surfaces

•  Do not have specialized gas exchange organs, but use their entire outer skin

•  Diffusion from skin into thin-walled capillaries where O2 and CO2 move in and out of cells from blood

•  Organism must live in moist environments  and have a high surface to body volume ratio.

•  Ex: Worms



Respiratory System in Fish - Gills

•  Gills are extensions of folds in the body surface that increase surface area available for gas exchange

•  Oxygen from water diffuses across gill surfaces into capillaries, and CO2 diffuses out

•  All gill breathers live in aquatic environments, ensures respiratory surface is moist.

•   Counter Current Flow

•   Fish also employ a counter-current exchange system where O2 and CO2 flow in the opposite direction to the flow of oxygen rich water

 

Tracheal Respiration - Insects

•  Internal system of branching respiratory tubes called tracheae

•  Tracheae connect the body cells directly to the environment for gas exchange (blood is not required) via spiracles (even smaller tubes)

•  Oxygen enters through spiracles and diffuses into tracheae, CO2 moves in opposite direction

•  Rhythmic contractions of abdomen help this to occur

 

Lungs – Mammals and Birds

•  Large animals employ lungs since they can provide more gas exchange to meet higher activity needs

•  Lungs contain sacs lined with a moist surface; these sacs increase surface area

•  Blood transports gases to cells by diffusion

  

Reptiles and Amphibians

•  Frogs ventilate their lungs by movement of muscles in the nostrils (nares), mouth, and abdomen

•  Also use skin gas exchange, so they must remain close to water and  humid conditions

•  Snakes and other reptiles rely exclusively on internal lungs, so they are not confined to areas near water

Birds

•  Flying high energy activity, so birds require LOTS of O2

•  Birds have a two-cycle breathing process, with AIR SACS in addition to their lungs

•  Air sacs move fresh air through the lungs during inhalation AND exhalation

•  On inhalation, both sets of air sacs inflate.

•  Inhaled air bypasses the lungs and fills up the posterior air sacs.

•   At the same time, the anterior air sacs fill with stale air from the lungs.

•   On exhalation, both sets of air sacs deflate, forcing fresh air from the posterior sacs into the lungs and stale air from the anterior sacs out through the trachea. 

•   Air takes two cycles of inhalation and exhalation to pass through the system

•   Mammalian Lungs

•  Unlike the other systems we’ve looked at, mammals use NEGATIVE pressure to move air — a pump sucking air in

•  Air moves through a series of tubes to alveoli, tiny moist sacs where gas exchange actually occurs

•  Alveoli are surrounded by tiny blood vessels called capillaries

•  Oxygen diffuses across the alveoli to the capillary and into the blood stream