Respiratory System
General description
Respiration is the process of taking oxygen from the air and transporting
it to individual body cells, and the subsequent transportation of carbon
dioxide from the cells back into the air. The respiratory system provides
the route by which oxygen enters the body and by which carbon dioxide
is excreted. This system also plays a role in regulating body temperature.
The major structures of the respiratory system are the nose, pharynx,
larynx, trachea, bronchi and lungs. Breathing is accomplished by the
diaphragm and the muscles of the chest wall.
Trachea and bronchi
The trachea is a semi-rigid tube about 115 mm long and 12 mm in
diameter. Rings of cartilage embedded in fibrous, elastic and smooth
muscle tissue make up the exterior surface, and it is lined with mucous
membrane which has a special ability to trap dust particles and move
them upward toward the pharynx. Near its lower end the trachea
divides into the right and left bronchi, which conduct inspired air into
the right and left lungs. Numerous branches stem from both main
bronchi so that air reaches all segments of the lungs. The smallest
branch of the bronchial tree is known as a bronchiole.
Lungs
The right lung has three lobes (sections) and the left lung has two. Each
lung is connected to the heart by arteries and veins. Lungs are composed
of bronchial tubes, tiny air sacs called alveoli, blood and lymph vessels,
and nerves supported by connective, elastic and muscle tissue. Each
lung is enclosed within a two-layered membranous sac, the pleura.
The outer layer (parietal pleura) adheres closely to the chest wall and
diaphragm whilst the inner (visceral pleura) clings closely to the lungs.
Pleural cavity
Each lung is surrounded by a pleural cavity. The pleural cavity is the space
between the pleural lining of the lungs and the chest wall.
Mechanism of respiration
In the process of inhaling, the lungs are expanded. Air is brought into the
nose and conducted through the passageway previously outlined. The blood
in the body continuously passes through the small vessels (capillaries) in the
lungs. As it does so, blood passes the thin, semipermeable membrane
which separates the tiny vessels from the air sacs (alveoli). The vital
ex- change of gases takes place by diffusion through this membrane.
Venous blood gives up much of the carbon dioxide (CO2) it has picked up
from tissue cells in exchange for oxygen (O2) present in the air sacs.
After the blood has been oxygenated it is returned to the heart for
distribution to body cells.
In effect, there is a two way exchange of two gases in two locations.
- Across tissue cell membranes all over the body
- Across air sac membranes in the lungs.
Carbon dioxide, a by-product of metabolism, is formed in tissue cells.
CO2 crosses the cell membrane and enters the bloodstream as the blood
gives up its oxygen supply to the cells. Carbon dioxide is carried by the
bloodstream back to the lungs where it crosses the membrane of the
air sac in exchange for oxygen, and the cycle begins again.
In the process of exhaling, the lungs are compressed, carbon dioxide is
forced out of the air sacs and upward through the bronchi, trachea and
out of the nose or mouth. About one pint of water is lost daily in the
process of breathing. Consequently, the respiratory system plays a role
in body temperature regulation and control of the water content of the body.
Control of respiration
The mechanism of breathing (respiration) is interrelated with other body
systems. Two brain stem divisions, the medulla oblongata and the pons
alveoli share control of respiration. Nerve impulses from these divisions
pass via the spinal cord and nerves to the muscles of the diaphragm,
abdomen and rib cage. The rate, rhythm, and depth of breathing are
controlled by nerve impulses to meet the varying needs of man
whether he is running or resting. The central nervous system is vital
to proper functioning of the respiratory system, as without its stimuli,
man would not breathe.
Respiratory System
Alveoli and Alveolar Ducts
Glossary of Terms Respiratory System
Alveoli
(al-ve-o’li) Very small air sacs in the lungs through which oxygen and
carbon dioxide are exchanged.
Blood
Fluid which circulates throughout the body carrying nutrients to cells and
removing wastes from cells. Arterial blood (with the exception of the
pulmonary artery) contains a heavy concentration of oxygen while venous
blood (with the exception of the pulmonary vein) contains carbon dioxide in
large amounts.
Bronchial tubes; bronchi
(brong’ke-al; brong’ki) Main branch passageways extending from the distal trachea.
Diaphragm
(di’ah-fram) The musculomembranous “partition” between the chest
cavity and abdominal cavity which acts as a bellows in breathing.
Diffusion
(di-fu’zhun) The intermixing of molecules of a liquid or gas so that they
are equally concentrated.
Exhale
(eks-hale’) To expel CO2 from the lungs by breathing.
Larynx
(lar’inks) The organ of voice.
Lobe
A section of an organ separated from neighbouring parts by fissures.
Lung
Major organ of respiration; consists of spongy, porous, elastic tissue.
Medulla oblongata
(me-dul’lah ob-lon-ga’ta) An area of the brain which shares concern for
respiratory function with the pons varolii.
Mucous membrane
(mu’kus) Thin layer of smooth tissue which lines many cavities and has
special ability to secrete a slimy fluid called mucous.
Nasopharynx
(na-zo-far’inks) Upper part of the back of the throat where the nasal
cavity opens into the pharynx.
Olfactory receptors
(ol-fak’to-re) Nerves in the upper part of the nasal cavity concerned
with the sense of smell.
Oxygen
(ok’si-jen) Colourless, odourless gas essential to the life of human tissue cells.
Pharynx
(far’inks) Area in the back of the mouth which serves as passageway for air from
nasal cavity to larynx and for food from mouth to oesphagus
Pleura
(ploor’ah) Membranous sac which encloses the lungs and lines the chest cavity. Parietal pleura lines the chest cavity and visceral pleura adheres closely to the lungs.
Pons varolii
(ponz) An area of the brain which shares concern for respiratory
function with the medulla oblongata.
Respiratory system
(re-spi’rah-to-re) The organs and structures which provide the route by which oxygen gains entry to the body and the route by which carbon diox- ide is excreted.
Trachea
(tra’ke-ah) Passageway for air between larynx and bronchi.
Vocal cords
(vo’kal cords) Folds of mucous membrane which function to produce voice.
Exercises on the Respiratory System
A. Write in the table below the medical terms for the numbered items
in the diagram. Then check your answers against the fully labelled
diagram in this section.
B. Read the definition of terms below. Each describes an organ, part or
function of the respiratory system. You may refer to the preceding text
to assign the appropriate word or phrase.
Definiton
- The gas which is drawn into the lungs where it is taken up by the blood.
- The gas which passes from the blood into the lungs to be excreted.
- The process of taking oxygen from the air and transporting it to individual body cells, and the subsequent transportation of carbon dioxide from the cells back into the air.
- A semi-rigid tube about 115 mm long, lined with mucous membrane which has the ability to move particles upward.
- Three of the major structures of the respiratory system.
- The smallest branch of the bronchial tree.
- The air sacs where the gas exchange takes place.
- The number of lobes in the right lung.
- The number of lobes in the left lung.
- Encloses each lung within its two layered membranous sacs.
- A musculomembranous wall which separates the chest cavity from the abdominal cavity, and acts as a bellows in breathing.
C. Use a medical dictionary to look up the following terms which are
commonly found in case notes of individuals with respiratory disease.
adenoid
anoxia
anthracosis
aphonia
asbestosis
asthma
atelectasis
auscultation
bronchiectasis
bronchitis
bronchoscopy
Cheyne Stokes respiration
coryza
dyspnoea
emphysema
epistaxis
expiration
haemoptysis
haemothorax
hyperpnoea
hypoxia
influenza
Laryngitis
laryngospasm
orthopnoea
percussion
pertussis
pleural effusion
pleurisy
pneumoconiosis
pneumonia
pneumonitis
pneumothorax
pulmonary embolism
rale
rhinitis
rhinoplasty
sinusitis
sputum
stridor
submucous resection
tonsil
tracheostomy
tracheotomy