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RESPIRATORY SYSTEM
(STRUCTURE AND FUNCTION)
Dr. Mohammed Sharique Ahmed Quadri
Assistant Prof. physiology
Al maarefa college
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Anatomy Of Respiratory System
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Nasal passages (Nose)
Pharynx (Throat )
Larynx (Voice box)
Trachea –Divides into Right main bronchus and Left
main bronchus
Bronchi
Bronchioles—large and small
Terminal Bronchioles
Respiratory Bronchioles
Alveolar Duct
Alveoli
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Important Points
• Trachea divides into Right and Left Bronchi
which enter Right and Left Lungs
• Within each lung, bronchi continue to branch
into narrow (small diameter),shorter and
more numerous airways like branching of a
tree.
• Small braches are known as Bronchioles- lastly
Terminal bronchioles
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Important Points [Cont]
• At the end of Terminal Bronchioles, are
Respiratory Bronchioles , Alveolar duct,
Alveoli.
• Tiny sacs(Alveoli) where gas exchange takes
place between alveolar air and blood
capillaries
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Important Points [Cont]
• Trachea and large bronchi have cartilaginous
rings that prevent these from compressing
• Very small bronchioles have no cartilage to hold
them open. Their wall has smooth muscle
• This smooth muscle is innervated by Autonomic
Nervous System, and is also sensitive to some
hormones and local chemicals, which affect the
air flow in small bronchioles
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Important Points [Cont]
• Sympathetic stimulation causes
bronchodialation by acting on β2(adrenergic)
receptors.
• Parasympathetic stimulation causes
bronchoconstriction by acting on muscarinic
receptors
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FUNCTIONS OF RESPIRATORY SYSTEM
• 1- Breathing Oxygen in, and breathing out
Carbon dioxide
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RESPIRATION TYPES
• Cellular Respiration ( Internal Respiration)
• External Respiration
• Cellular Respiration
– It refers to intracellular metabolic process in the
Mitochondria, which uses O2 and produces CO2
and energy ATP from food.
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CELLULAR
RESPIRATION
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CELLULAR RESPIRATION (CONT)
• On a mixed diet ( Carbohydrate, Fat, Protein ) O2 used
is 250 ml/min and CO2 produced is 200 ml/min.
• We use the Term Respiratory Quotient (RQ)
CO2 produced = 200
RQ =
O2 used
= 250
- On a mixed diet RQ = O.8
-- RQ depends on the type of food used
-- when Carbohydrate is used RQ= 1
-- when Fat is used RQ= 0.7
-- when Protein used RQ=0.8
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EXTERNAL RESPIRATION
• Exchange of O2and CO2 between External
environment and cells of body. It has 4 steps.
• 1 – Gas exchange between the atmosphere and
alveoli.
• 2- Exchange of O2 and CO2 between air in the
alveoli and blood in pulmonary capillaries.
• Transport of O2 and CO2 by the blood to the
tissues.
• 4 – Exchange of O2 and CO2 between system
capillaries and tissue cells
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Non Respiratory Functions of
Respiratory System
• Helps in regulation of pH of blood (Acid –base
balance) , by adjusting the rate of removal of
CO2.
• It is route for water loss and heat elimination.
– (Inspired air is humidified and warmed by the
respiratory airways.)
• Respiratory pump – helps in venous return.
• It enables speech, singing .
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Non Respiratory Functions of
Respiratory System [cont]
• It defends against inhaled foreign material.
• Prostaglandins are inactivated in the lungs.
• Conversion of angiotensinI to angiotensinII
hormone, by ACE ( angiotensin converting
enzyme ).
• Nose– part of respiratory system , organ of
smell.
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Gas Exchange Between Alveoli &
Pulmonary Capillaries
• O2 and CO2 diffuse through alveoli.
• Rate of diffusion depends on thickness of
alveolar membrane, surface area and partial
pressure of O2 and CO2.
• Alveolar wall consists of single layer of
alveolar cells [type I].
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Gas Exchange Between Alveoli &
Pulmonary Capillaries [cont]
• Each alveolus is surrounded by a network of
pulmonary capillaries, which is also single
layer .
• The interstitial space between an alveolus and
capillary is very thin 0.5 µm which facilitates
gas exchange.
• Respiratory Membrane [Alveolar wall and
Capillary wall].
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Gas Exchange Between Alveoli &
Pulmonary Capillaries [cont]
• Lungs contain about 500 million alveoli, each
about 300 µm in diameter [surface area
exposed between alveolar air and pulmonary
capillary blood is about 75 m2, size of tennis
court].
• In alveoli, there are Type II alveolar cells .
They secrete Pulmonary Surfactant.
• Pulmonary Surfactant is a phospholipoprotein
complex that helps in lung expansion.
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Gas Exchange Between Alveoli &
Pulmonary Capillaries [cont]
• Also in alveolar lumen, present are alveolar
macrophages which help in defense
[Phagocytosis].
• Pore of Kohn – are present between adjacent
alveoli. Their presence permits air flow
between adjacent alveoli. This process is
called Collateral Ventilation.
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Lungs & Thoracic Cavity
• Two lungs
– Right lung is divided into 3 lobes [upper, middle,
lower] by oblique and transverse fissure.
– Left lung is divided into 2 lobes [upper, lower and has
lingula] by oblique fissure.
• Lungs – has alveoli, blood vessels and large
quantities of elastic connective tissues.
• Changes in lung volume and alveolar volume are
brought about through changes in dimensions of
thoracic cavity.
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Lungs & Thoracic Cavity [cont]
• The outer chest [Thorax] is formed by 12 pairs of
curved ribs, which join the sternum anteriorly
and thoracic vertebrae posteriorly.
• Diaphragm – forms floor of thoracic cavity.
Diaphragm is sheet of skeletal muscle that
separates thoracic cavity from abdominal cavity.
It is penetrated by esophagus and blood vessels.
• In the lung and chest wall, there is considerable
amount of elastic connective tissue.
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Lungs & Thoracic Cavity [cont]
• Pleura – separates each lung from the thoracic wall.
• Pleura which surround each lung has two layers –
Visceral Pleura [inner layer] which surrounds the lung
and Parietal Pleura [outer layer] which is under thorax.
• Interior of pleural sac(space between parietal and
visceral pleura) is known as Pleural Cavity.
• Surfaces of pleura secrete intrapleural fluid which
lubricates surfaces as they slide on each other during
respiratory movements.
• Clinical application – pleurisy – [inflammation of
pleura]. It causes pain during inspiration and
expiration, and friction rub.
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References
• Human physiology by Lauralee Sherwood,
seventh edition
• Text book physiology by Guyton &Hall,11th
edition
• Text book of physiology by Linda .s
contanzo,third edition
THANK YOU
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