A quick glance about human respiratory system for paramedical students.

1. Respiratory system
CHAPTER-8
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2. INTRODUCTION
Respiration is the process by which oxygen is taken in
and carbon dioxide is given out.
The first breath takes place only after birth. Fetal lungs
are non-functional. So, during intrauterine life the
exchange of gases between fetal blood and mother’s
blood occurs through placenta.
After the first breath, the respiratory process continues
throughout the life. Permanent stoppage of respiration
occurs only at death.
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3. TYPES OF RESPIRATION
Respiration is classified into two types:
1. External respiration that involves
exchange of respiratory gases, i.e. oxygen
and carbon dioxide between lungs and
blood
2. Internal respiration, which involves
exchange of gases between blood and
tissues.
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4. PHASES OF RESPIRATION
Respiration occurs in two phases:
1. Inspiration during which air enters the lungs
from atmosphere
2. Expiration during which air leaves the lungs.
During normal breathing, inspiration is an
active process and expiration is a passive
process.
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5. ANATOMY OF RESPIRATORY TRACT
The respiratory system consists of the
NOSE
PHARYNX (THROAT)
LARYNX (VOICE BOX)
TRACHEA (WIND PIPE)
BRONCHUS
LUNGS
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6. 6

7. Structurally, the respiratory system
consists of two parts:
The upper respiratory system includes
the nose, pharynx, and associated
structures.
The lower respiratory system includes
the larynx, trachea, bronchi, and lungs.
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8.  Functionally, the respiratory system also consists of two parts:
 (1) The conducting zone consists of a series of interconnecting
cavities and tubes both outside and within the lungs.
 These include the nose, pharynx, larynx, trachea, bronchi,
bronchioles, and terminal bronchioles; their function is to filter,
warm, and moisten air and conduct it into the lungs.
 (2) The respiratory zone consists of tissues within the lungs where
gas exchange occurs .
 These include the respiratory bronchioles, alveolar ducts,
alveolar sacs, and alveoli; they are the main sites of gas
exchange between air and blood.
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9. right
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10. FUNCTION OF RESPIRATORY SYSTEM
1. Provides for gas exchange-intake of O2 for delivery
to body cells and elimination of CO2 produced by
body cells.
2. Helps regulate blood pH.
3. Contains receptors for the sense of smell, filters
inspired air, produces vocal sounds (phonation), and
excretes small amounts of water and heat.
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11. NOSE
The nose can be divided into external and
internal noses.
The external nose is the portion of the nose
visible on the face.
The frontal bone, nasal bones, and maxillae
form the bony framework of the external nose
On the undersurface of the external nose are
two openings called the external nares or
nostrils.
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12. External nose have three functions such
as
(1) warming, moistening, and filtering
incoming air;
(2) detecting olfactory stimuli; and
(3) modifying speech vibrations as they
pass through the large, hollow resonating
chambers.
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13. The internal nose is a large cavity beyond
the nasal vestibule in the anterior aspect of
the skull that lies inferior to the nasal bone
and superior to the mouth;
Anteriorly, the internal nose merges with the
external nose, and posteriorly it
communicates with the pharynx through
two openings called the internal nares or
choancae.
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14. Ducts from the paranasal sinuses (which drain
mucus) and the nasolacrimal ducts (which
drain tears) also open into the internal nose.
Skull bones containing the paranasal sinuses
are the frontal, sphenoid, ethmoid, and
maxillae.
The space within the internal nose is called
the nasal cavity
The anterior portion of the nasal cavity just
inside the nostrils, called the nasal vestibule.
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15. LARYNX
The larynx (voice box), is a short passageway that connects the
laryngopharynx with the trachea.
It lies in the midline of the neck anterior to the oesophagus and
the fourth through sixth cervical vertebrae (C4–C6).
The wall of the larynx is composed of nine pieces of cartilage.
Three occur singly (thyroid cartilage, epiglottis, and cricoid
cartilage), and three occur in pairs (arytenoid, cuneiform, and
corniculate cartilages).
The extrinsic muscles of the larynx connect the cartilages to other
structures in the throat; the intrinsic muscles connect the cartilages
to one another.
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16. TRACHEA
The trachea or windpipe, is a tubular passageway for
air that is about 12 cm (5 in.) long and 2.5 cm (1 in.) in
diameter.
It is located anterior to the oesophagus and extends
from the larynx to the superior border of the fifth thoracic
vertebra (T5), where it divides into right and left primary
bronchi.
The layers of the tracheal wall, from deep to superficial,
are the (1) mucosa, (2) submucosa, (3) hyaline cartilage,
and (4) adventitia (composed of areolar connective
tissue).
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17. The mucosa of the trachea consists of an
epithelial layer of pseudostratified ciliated
columnar epithelium and an underlying
layer of lamina propria that contains
elastic and reticular fibers.
Pseudostratified ciliated columnar
epithelium consists of ciliated columnar
cells and goblet cells that reach the
luminal surface, plus basal cells.
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18. BRONCHUS
At the superior border of the fifth thoracic vertebra, the
trachea divides into a right primary bronchus windpipe),
which goes into the right lung, and a left primary
bronchus, which goes into the left lung.
The right primary bronchus is more vertical, shorter, and
wider than the left. As a result, an aspirated object is more
likely to enter and lodge in the right primary bronchus
than the left..
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19.  BRANCHING OF BRONCHIAL TREE
 Trachea
 Primary bronchi
 Secondary bronchi
 Tertiary bronchi
 Bronchioles
 Terminal bronchioles
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20. Larynx
Trachea
Left primary bronchus
Left secondary bronchus
Left tertiary bronchus
Left bronchiole
Left terminal bronchiole
Diaphragm
Pleural cavity
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21. Larynx
Trachea
Right primary bronchus
Right secondary bronchus
Right tertiary bronchus
Right bronchiole
Right terminal bronchiole
Diaphragm
Pleural cavity
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22.  At the point where the trachea divides into right and left primary
bronchi an internal ridge called the carina.
 On entering the lungs, the primary bronchi divide to form smaller
bronchi—the secondary (lobar) bronchi, one for each lobe of
the lung. (The right lung has three lobes; the left lung has two.)
 The secondary bronchi continue to branch, forming still smaller
bronchi, called tertiary (segmental) bronchi, that divide into
bronchioles.
 Bronchioles in turn branch repeatedly, and the smallest ones
branch into even smaller tubes called terminal bronchioles.
 This extensive branching from the trachea resembles an inverted
tree and is commonly referred to as the bronchial tree.
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23. Lungs
The lungs ( lightweights, because they float) are paired cone-
shaped organs in the thoracic cavity.
They are separated from each other by the heart and other
structures in the mediastinum, which divides the thoracic cavity
into two anatomically distinct chambers.
As a result, if trauma causes one lung to collapse, the other
may remain expanded. Each lung is enclosed and protected
by a double-layered serous membrane called the pleural
membrane.
The superficial layer, called the parietal pleura, lines the wall of
the thoracic cavity; the deep layer, the visceral pleura, covers
the lungs themselves
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24. Apex
Superior lobe
Inferior lobe
Base
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25.  STRUCTURE OF RESPIRATORY UNIT
 Respiratory unit starts from the respiratory bronchioles.
 Each respiratory bronchiole divides into alveolar ducts. Each alveolar duct enters an
enlarged structure called the alveolar sac.
 Space inside the alveolar sac is called antrum. Alveolar sac consists of a cluster of
alveoli. Few alveoli are present in the wall of alveolar duct also.
 Thus, respiratory unit includes:
 1. Respiratory bronchioles
 2. Alveolar ducts
 3. Alveolar sacs
 4. Antrum
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26. Terminal
bronchiole
Pulmonary
arteriole Lymphatic
vessel
Respiratory
bronchiole
Alveolar
ducts
Alveolar
sac
Alveoli
Alveoli
Pulmonary
venule
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27. Blood Supply to the Lungs
The lungs receive blood via two sets of arteries:
pulmonary arteries and bronchial arteries.
Deoxygenated blood passes through the pulmonary
trunk, which divides into a left pulmonary artery that
enters the left lung and a right pulmonary artery that
enters the right lung.
(The pulmonary arteries are the only arteries in the
body that carry deoxygenated blood.)
Return of the oxygenated blood to the heart occurs by
way of the four pulmonary veins, which drain into the left
atrium
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28. Mechanism of respiration
The process of gas exchange in the body,
called respiration, has three basic steps:
1. Pulmonary ventilation or breathing
2. External (pulmonary) respiration
3. Internal (tissue) respiration
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29.  1. Pulmonary ventilation or breathing, is the inhalation (inflow)
and exhalation (outflow) of air and involves the exchange of
air between the atmosphere and the alveoli of the lungs.
 2. External (pulmonary) respiration is the exchange of gases
between the alveoli of the lungs and the blood in pulmonary
capillaries across the respiratory membrane. In this process,
pulmonary capillary blood gains O2 and loses CO2.
 3. Internal (tissue) respiration is the exchange of gases between
blood in systemic capillaries and tissue cells. In this step the
blood loses O2 and gains CO2. Within cells, the metabolic
reactions that consume O2 and give off CO2 during the
production of ATP are termed cellular respiration.
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30. LUNG VOLUME
Lung volumes are the volumes of air breathed by an
individual. Each of these volumes represents the volume
of air present in the lung under a specified static
condition (specific position of thorax).
Lung volumes are of four types:
1. Tidal volume
2. Inspiratory reserve volume
3. Expiratory reserve volume
4. Residual volume.
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31. TIDAL VOLUME
Tidal volume (TV) is the volume of air breathed in and out of
lungs in a single normal quiet respiration. Tidal volume signifies the
normal depth of breathing.
Healthy adult averages 12 breaths a minute, with each
inhalation and exhalation moving about 500 mL of air into and out
of the lungs. The volume of one breath is called the tidal volume
(TV).
The minute ventilation (MV )—the total volume of air inhaled and
exhaled each minute is respiratory rate multiplied by tidal volume:
MV = 12 breaths/min X 500 mL/breath
= 6 liters/min
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32. INSPIRATORY RESERVE VOLUME
Inspiratory reserve volume (IRV) is an additional volume
of air that can be inspired forcefully after the end of
normal inspiration.
Normal Value is 3,300 mL (3.3 L).
EXPIRATORY RESERVE VOLUME
Expiratory reserve volume (EVR) is the additional
volume of air that can be expired out forcefully, after
normal expiration.
Normal Value is 1,000 mL (1 L).
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33. RESIDUAL VOLUME
Residual volume (RV) is the volume of air remaining in
lungs even after forced expiration.
Normally, lungs cannot be emptied completely even by
forceful expiration. Some quantity of air always remains in
the lungs even after the forced expiration.
Residual volume is significant because of two reasons:
1. It helps to aerate the blood in between breathing
and during expiration
2. It maintains the contour of the lungs.
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34.  The apparatus commonly used to measure the volume of
air (lung volume) exchanged during breathing and the
respiratory rate is a spirometer or respirometer.
 The recording is called the spirogram.
 Inhalation is recorded as an upward deflection, and
exhalation is recorded as a downward deflection.
 Lung volumes measured by spirometry include tidal volume,
minute ventilation, alveolar ventilation rate, inspiratory
reserve volume, expiratory reserve volume, and FEV1.0.
Other lung volumes include anatomic dead space, residual
volume, and minimal volume.
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35. LUNG CAPACITY
Lung capacities are the sum of two or more lung
volumes such as include inspiratory, functional,
residual, vital, and total lung capacities.
 lung capacities are of four types:
1. Inspiratory capacity
2. Vital capacity
3. Functional residual capacity
4. Total lung capacity.
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36.  Total lung capacity (TLC) is the volume of air present in lungs
after a deep (maximal) inspiration. It includes all the volumes.
 TLC = IRV + TV + ERV + RV.
INSPIRATORY CAPACITY
 Inspiratory capacity (IC) is the maximum volume of air that is
inspired after normal expiration (end expiratory position).
 It includes tidal volume and inspiratory reserve volume.
 IC = TV + IRV
 = 500 + 3,300 = 3,800 mL
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37. VITAL CAPACITY (VC)
Vital capacity (VC) is the maximum volume of air
that can be expelled out forcefully after a deep
(maximal) inspiration. VC includes inspiratory
reserve volume, tidal volume and expiratory
reserve volume.
VC = IRV + TV + ERV
= 3,300 + 500 + 1,000 = 4,800 mL
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38. TOTAL LUNG CAPACITY
Total lung capacity (TLC) is the volume of
air present in lungs after a deep (maximal)
inspiration.
It includes all the volumes.
TLC = IRV + TV + ERV + RV
= 3,300 + 500 + 1,000 + 1,200 = 6,000 mL
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39. REGULATION OF RESPIRATION
Spontaneous respiration is produced by rhythmic discharge of motor
neurons that innervate the respiratory muscles.
This discharge is totally dependent on nerve impulses from the brain;
breathing stops if the spinal cord is transected above the origin of the
phrenic nerves.
The rhythmic discharges from the brain that produce spontaneous
respiration are regulated by alterations in arterial Po2, PCO2, and
H+
concentration.
Two separate neural mechanisms regulate respiration. One is
responsible for voluntary control and the other for automatic control.
The voluntary system is located in the cerebral cortex and sends
impulses to the respiratory motor neurons via the corticospinal tracts.
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40.  Contd…
 The automatic system is driven by a group of pacemaker cells
in the medulla.
 Impulses from these cells activate motor neurons in the
cervical and thoracic spinal cord that innervate inspiratory
muscles.
 The main components of the respiratory control pattern
generator responsible for automatic respiration are located in
the medulla. Notes taken from
 http://accessmedicine.mhmedical.com/content.aspx?
bookid=393&sectionid=39736784&jumpsectionID=39741437
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41. DISORDERS OF RESPIRATORY SYSTEM
Bronchial asthma or asthma
Cyanosis
Caisson’s disease
Mountain sickness
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42. Bronchial asthma or asthma
Bronchial asthma is the respiratory disease
characterized by difficult breathing with wheezing.
Wheezing refers to whistling type of respiration. It is due
to bronchiolar constriction, caused by spastic
contraction of smooth muscles in bronchioles, leading to
obstruction of air passage.
Obstruction is further exaggerated by the oedema of
mucus membrane and accumulation of mucus in the
lumen of bronchioles.
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43.  Because of difficulty during expiration, the lungs are not
deflated completely, so that the residual volume and
functional residual capacity are increased.
 There is reduction in:
 i. Tidal volume
 ii. Vital capacity
 iii. Forced expiratory volume in 1 second (FEV1)
 iv. Alveolar ventilation
 v. Partial pressure of oxygen in blood.
 Carbon dioxide accumulates, resulting in acidosis, dyspnoea
and cyanosis.
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44. CYANOSIS
Cyanosis is defined as the diffused bluish coloration of skin and
mucus membrane.
It is due to the presence of large amount of reduced
haemoglobin in the blood.
Quantity of reduced haemoglobin should be at least 5 to 7 g/dL
in the blood to cause cyanosis.
CONDITIONS WHEN CYANOSIS OCCURS
1. Any condition which leads to arterial hypoxia and stagnant
hypoxia.
2. Conditions when altered haemoglobin is formed. Due to
poisoning, haemoglobin is altered into methemoglobin or
sulfhemoglobin, which causes cyanosis.
3. Conditions like polycythemia when blood flow is slow.
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45. MOUNTAIN SICKNESS
Mountain sickness is the condition characterized by
adverse effects of hypoxia at high altitude.
It is commonly developed in persons going to high
altitude for the first time. It occurs within a day in these
persons, before they get acclimatized to the altitude.
The symptoms are loss of appetite, nausea and
vomiting, increased heart rate, increased force of
contraction of heart, pulmonary oedema
(breathlessness), headache, depression, disorientation,
irritability, lack of sleep, weakness and fatigue
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46. CAISSON’S DISEASE
Caisson’s disease is the disorder that occurs when a person returns
rapidly to normal surroundings (atmospheric pressure) from the area
of high atmospheric pressure like deep sea.
It is also known as dysbarism, compressed air sickness,
decompression sickness, bends or diver’s palsy.
High barometric pressure at deep sea leads to compression of
gases in the body. Compression reduces the volume of gases.
Among the respiratory gases, oxygen is utilized by tissues. Carbon
dioxide can be expired out. But nitrogen, which is present in high
concentration, i.e. 80% is an inert gas. So, it is neither utilized nor
expired
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47.  When nitrogen is compressed by high atmospheric
pressure in deep sea, it escapes from blood vessels
and enters the organs.
 As it is fat soluble, it gets dissolved in the fat of the
tissues and tissue fluids. It is very common in the brain
tissues.
 As long as the person remains in deep sea, nitrogen
remains in solution and does not cause any problem.
 But, if the person ascends rapidly and returns to
atmospheric pressure, decompression sickness
occurs.
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48.  Due to sudden return to atmospheric pressure, the nitrogen is
decompressed and escapes from the tissues at a faster rate.
Being a gas, it forms bubbles while escaping rapidly.
 The bubbles travel through blood vessels and ducts. In many
places, the bubbles obstruct the blood flow and produce air
embolism, leading to decompression sickness.
 Underground tunnel workers who use the caissons (pressurized
chambers) also develop decompression (caisson disease)
sickness.
 Pressure in the chamber is increased to prevent the entry of
water inside.
 Decompression sickness also occurs in a person who ascends up
rapidly from sea level in an airplane without any precaution.
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49.  Symptoms are:
 1. Severe pain in tissues, particularly the joints,
 2. Sensation of numbness, tingling or pricking (paresthesia) and itching
 3. Temporary paralysis due to nitrogen bubbles in the myelin sheath of
motor nerve fibers
 4. Muscle cramps associated with severe pain
 5. Occlusion of coronary arteries followed by coronary ischemia, caused
by bubbles in the blood
 6. Occlusion of blood vessels in brain and spinal cord also
 7. Damage of tissues of brain and spinal cord because of obstruction of
blood vessels by the bubbles
 8. Dizziness, paralysis of muscle, shortness of breath and choking occur
 9. Finally, fatigue, unconsciousness and death.
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50. COUGH REFLEX
 The function of both the cough reflex and the sneeze reflex is
to dislodge foreign matter or irritating material from
respiratory passages.
 The bronchi and the trachea contain sensory receptors that
are sensitive to foreign particles and irritating substances.
 The cough reflex is initiated with the sensory receptors detect
these substances and initiate action potentials that pass
along the vagus nerves to the medulla oblongata, where the
cough reflex is triggered.
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51.  The movements resulting in a cough occur as follows:
about 2.5 litters (L) of air are inspired, the epiglottis
closes, and the vestibular folds and vocal cords close
tightly to trap the inspired air in the lung; the
abdominal muscles contract to force the abdominal
contents up against the diaphragm; and the muscles
of expiration contract forcefully.
 As a consequence, the pressure in the lungs increase
to about 100 mm Hg. Then the vestibular folds, the
vocal cords, and the epiglottis open suddenly, and
the air rushes from the lungs at a high velocity,
carrying foreign particles with it.
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52. SNEEZE REFLEX
 The sneeze reflex is similar to the cough reflex, but it differs in
several ways.
 The source of irritation that initiates the sneeze reflex is in the nasal
passages instead of in the trachea and bronchi, and the action
potentials are conducted along the trigeminal nerves to the
medulla, where the reflex is triggered.
 During the sneeze reflex the uvula and the soft palate are
depressed so the air is directed primarily through the nasal
passages, although a considerable amount passes through the
oral cavity.
 The rapidly flowing air dislodges particulate matter from the nasal
passages and propels it a considerable distance from the nose.
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