LOWER RESPIRATORY TRACT
CONDUCTING ZONE RESPIRATORY ZONE
1) THICKER WALL 1) THINNER WALL
2) LARGER DIAMETER 2) SMALLER DIAMETER
3) SMOOTH MUSCLES IN WALLS 3) ABSENT
4) TOTAL AREA OCCUPIED 4) MORE
WITHIN THE LUNG IS LESS
5) VELOCITY OF AIR MOVEMENT* 5) SLOW
• Atria are
• The number of alveoli present in each lung is 300
• An average diameter of each alveolus is 0.2mm.
• The alveoli of both lungs provide a combined surface
area of 80 sq.meters.
• The trachea undergoes 23 levels of branching to produce
the bronchial tree or respiratory tree.
2) Weighing 550 grams
3) Divided into two lobes namely
superior & inferior by an oblique
4) Has a cardiac notch to
accommodate the tip of the heart
2) Weighing 650 grams
3) Divided into three lobes namely
superior, middle & inferior lobes
by oblique and horizontal fissures
4) It is absent
• Lungs are surrounded by two pleural membranes. They
● Inner visceral/pulmonary
● Outer parietal
• It is the painful infection involving inflammation of
pleura and overproduction of pleural fluid.
CELL SURFACE RESPIRATION
• It is the direct exchange of gases between cells and the
Example; Sponges, coelenterates and protistans
• Skin functions as respiratory surface Example;
Earthworm, leech and frog
• This system consists of network of white shining tubes
called tracheae. Tracheae communicate to the outside
through lateral holes called spiracles or stigmata.
It occurs in insects and myriapods.
• It is the exchange of gases with the help of gills. They
occur in aquatic animals.
• There are two kinds of gills
• It occurs with the help of lungs and
• Examples; All land vertebrates
including birds and mammals. (Even
PULMONARY SAC RESPIRATION
• It is seen in molluscs.
• Here the mantle or glandular membrane of molluscs is
modified in many cases to function as respiratory sac or
• It is seen in frog and some related animals where the
buccopharyngeal surface functions as respiratory
• It is seen in some turtles.
• Some turtles, especially those specialized in diving,
are highly reliant on cloacal respiration during dives.
They accomplish this by having a pair of accessory air
bladders connected to the cloaca, which can absorb
oxygen from the water.
• In zoological anatomy, a cloaca is the posterior
opening that serves as the only such opening for
the intestinal, urinary, and genital tracts of certain
animal species. The word comes from Latin, and means
"sewer". All birds, reptiles, and amphibians possess
this orifice, by which they simultaneously evacuate both
urine and feces
• The walls of the alveoli are extremely thin, being composed
primarily of a single layer of squamous epithelial cells called type
I cells. Scattered among them are cuboidal cells called type II
cells or Septal cells or surfactant cells. In addition to these cells,
there are roaming phagocytic cells called alveolar macrophages
or dust cells. They are involved in defence.
• These type II cells secrete a fluid called surfactant.
• It forms a coating to the inner surface of an alveolus.
• It lowers the surface tension of alveoli. If the surface tension is
not kept low, the alveoli become smaller during expiration and
• They are also known as auditory tubes and
• This tube connect the pharynx with the cavity of the
• They are the internal nostrils or nares
• During swallowing of food, it is closed by Uvula.
GUARDIAN OF AIRWAYS
• Nasal chamber is differentiated into three regions
namely vestibular, respiratory and olfactory parts.
● Vestibular part; It is the anterior most region, lined
by pseudostratified ciliated epithelium, meant for
● Respiratory tract; It is the middle region, lined
by glandular and vascular epithelium, meant for
warming up of air.
● Olfactory part; It is the posterior region, lined by
sensory epithelium, meant for olfaction.
• The bronchial tree divides 23 times.
• The first 16 generations form the conducting zone.
It includes bronchi, bronchioles and terminal
• The remaining 7 generations form the transitional
and respiratory zones. They are made up of
respiratory bronchioles, alveolar ducts and alveoli.
• The muscles of diaphragm are called phrenic muscles.
• The tonsils are the 2 oval masses of lymphoid tissue
lying in the side walls of the oral pharynx. The tonsils
forms part of a ring of lymphoid tissue guarding the
alimentary and respiratory tracts against bacteria.
CARTILAGES OF LARYNX
• The wall of larynx is supported by 9 pieces of cartilages.
● 3 of them are unpaired and 3 of them are paired.
● The three unpaired pieces are thyroid cartilage (Adams
apple), epiglottic cartilage (epiglottis) and cricoid cartilage.
● Paired ones are the arytenoids, corniculate and cuneiform
PRESSURES INVOLVED IN
It is the pressure
surrounding air on
It is 760 mm Hg.
It is a positive
It is the pressure
exerted within the
It is 760 mm Hg.
It is a positive
It is the pressure
exerted within the
It is 756 mm Hg.
It is a negative
RESPIROMETER OR SPIROMETER
• It is a device to measure the amount of air exchanged
during breathing. Its recording is called a “spirogram”.
• Spirometer is also called pulmometer.
• Measurement of lung capacity with the help of
spirometer is called spirometry.
• The instrument used in
measuring and recording
the volume of air exchanged
during breathing is called
spirometer or respirometer.
▪ Normal breathing rate in a new-born baby is 32/ minute.
▪ In a child of 6 years of age , it is about 26/minute.
▪ It is 12-15/minute in a man of 25-30 years of age.
▪ It is 18/minute in a man of 50 years of age.
• Tidal volume: - It is the amount of air move in
and out of lungs during normal breathing. It is
approximately 500 ml of air for an average person.
• Inspiratory reserve volume: - It is the amount of air
inspired forcefully over and above the tidal volume.
It is about 3000ml for a normal person.
• Expiratory reserve volume: - It is the amount of air
that can be forcefully expired over and above the
tidal volume. It is about 1200 ml on the average.
• Vital capacity: - It is the maximum amount of
air a person can move in and out of his lungs.
It is equivalent to the sum of the tidal volume +
inspiratory and expiratory reserve volumes.
The vital capacity of an average person is about
• Residual volume: - Even after a maximum
expiration about 1200 ml of air remains in the
lungs. This is known as the residual volume.
• It is 500ml
• It consists of 150ml of dead space volume and 350 ml of
CARRYING CAPACITY OF BLOOD
• 20ml of oxygen and 3-7ml of CO2/100 ml of blood
OXYGEN CARRYING CAPACITY OF
• There is about 15gm of haemoglobin in 100 ml of blood,
which can transport about 20 ml of oxygen.
RESPIRATORY MINUTE VOLUME
• It is the product of tidal volume and normal breathing
rate per minute i.e. 500 x 12 =6000ml/minute
• Functional residual capacity; It is sum total of ERV+
residual volume i.e. 1200+1200= 2400
• Total lung capacity; Maximum amount of air the lungs
can hold after forceful inspiration. It is 6000ml. It is the
sum of IRV+ERV+TV+RV
ANATOMICAL DEAD SPACE AIR
• It is the volume of air, present in the conducting zone of
human respiratory system.
• It is not used for exchange of gases
• It is 150 ml
• A respiratory cycle includes one inspiration and one
• An average period taken by one respiratory cycle is 5
• Out of 5 seconds, 2 seconds are for inspiration and 3
seconds for expiration. It is calculated by multiplying
tidal volume and respiratory rate per minute. (500ml x
• It is the production of sound. It is the non-respiratory
function of larynx
• When a person living on plains ascends and stays on a
mountain about 8000 feet from sea level, he develops
mountain sickness. Its symptoms are nausea, headache,
breathlessness, dizziness, mental fatigue and a bluish
tinge on skin, nails and lips.
• Rate of breathing increases with altitude. Hill people
have more RBC’s.
MECHANISM OF RESPIRATION
• External respiration
• Transport of gases by blood
● Transport of CO2
• In the form of carbonic acid
• In the form of ions and bicarbonates
• In the form of carbaminohaemoglobin
● Transport of O2
• As solution in plasma
• Through RBC as oxyhaemoglobin
• Internal respiration and cellular oxidation
• The alveolar-capillary membrane acts as the air-blood
barrier. This is due to the membrane with air on the
alveolar side and blood on the capillary side
• He described gaseous exchange in blood.
CHRISTIAN BOHR (1904)
• He put forth Bohr’s effect in 1909
• According to this” the affinity of haemoglobin to O2
reduces with increased concentration of CO2”
• Carbaminohaemoglobin is produced more readily when
the haemoglobin is deoxygenated. Therefore binding of
O2 to Hb reduces its affinity for CO2. This effect is called
• Hay fever is even known by the name rose fever or
Rhinitis or Pollenosis.
▪ It is one of the diseases along with bronchitis and asthma,
coming under COPD (chronic obstructive pulmonary
▪ The meaning of emphysema is fully blown out.
▪ It is a disorder of the pulmonary system characterized by
destructive changes of alveolar walls resulting in loss of
lung elasticity and reduces the ventilation of alveoli.
• Emphysema and smoke inhalation makes the lungs to
loose their elasticity. The lungs become permanently
inflated. To adjust to the increased lung size, size of
thoracic cavity also increases. This condition is called as
• It is a technique of detecting abnormal malignant cells in
• It is a state in which malignant tumour cells move from
the site of formation to other parts through transport
system (blood and lymph)
• Reduced supply of oxygen to the tissues.
• Types of hypoxia;
● Hypoxic hypoxia; It is a state where PO2 of the arterial blood is
● Anemic hypoxia; It is a state where the arterial PO2 is normal but
the amount of haemoglobin available to carry O2 is reduced.
● Stagnant or Ischemic hypoxia; It is a state where the blood flow to
a tissue is so low, that adequate O2 is not delivered to it inspite of
normal PO2 and haemoglobin concentration.
● Histotoxic hypoxia; It is a state where the amount of O2 delivered to
a tissue is adequate but because of the action of toxic agents, cells
cannot make use of the O2. Cyanide poisoning leads to histotoxic
hypoxia, as the poison blocks electron transport chain.
• An absence of oxygen supply to the tissues is known as
• Increased concentration of CO2 in blood is known as
• The complete cessation of breathing is known as apnoea
• The forceful breathing (i.e. difficulty in breathing) is
known as dyspnoea.
• It is the process of normal breathing
• Rapid i.e. increased breathing caused by emotions,
ASPHIXIA (BREATHING ARREST)
• Paralysis of respiratory centre due to excessive CO2.
• It is commonly due to irreversible combination of CO
with haemoglobin to form carboxyhaemoglobin. It
results in death.
• It is common in closed rooms with coal burning, kerosine
• Nose bleeding
• It may be due to scratching of nasal membranes or
• It is a terrestrial respiratory organ similar to the purse
with a number of compartments.
• It occurs in spiders and scorpions
• It is an aquatic respiratory organ found in Limulus. It
consists of a number of leaf-like structures , between
which water circulates.
• The lymph flows in lymphatic vessels very slowly. Only
about 10-20 liters of lymph passes into the blood in a
• Inspiratory spasm caused by sudden contraction of
diaphragm accompanied by loud closure of glottis.