Respiratory system Physiology powerpoint.pptx

03/18/2025 1
Respiratory Physiology
Tekle H. (MSc in Medical Physiology)
By Tekle H

03/18/2025 By Tekle H 2
Introduction
Breathing:
 Mechanical process which alternately draws & expels air into &
out of the lungs
Respiration:
 Is the exchange of gases b/n atmosphere and body
 Mainly deals with the scientific concepts of gas exchange
 Normal respiratory rate varies from 12-20 times/minute
 Rate can increases during active work /exercise

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Respiratory system has respiratory and non-
respiratory functions
A. Respiratory function
 Is maintaining appropriate gas exchange
◦ Obtain oxygen for use by body cells
◦ Eliminate CO2 that the cells produce

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 Such respiratory functions involve 4 stages:
◦ Pulmonary ventilation
 Inflow and outflow of air between atmosphere & lung alveoli
◦ Alveolar ventilation
 Diffusion of O2 & CO2 b/n alveoli & pulmonary capillary
blood
◦ Transport of such gases in the blood
◦ Exchange in tissue bed – b/n systemic capillaries &
cells

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B. Non respiratory functions
1. A route for water & heat loss
2. Enhances venous return
3. Maintenance of normal - acid base balance
4. It enables vocalization: speech, singing, ….
5. Defense against foreign matter
◦ Alveolar macrophages

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6. The lung produces angiotensin converting
enzyme which is used to
Convert angiotensin I angiotensin II
7. Olfaction
 Olfactory receptors are in the mucus membrane
lining the upper nostril

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Physiologic anatomy of respiratory system
The conducting zone (air ways)
◦ Nasal cavities (oral cavity)
◦ Pharynx
◦ larynx
◦ Trachea
◦ Bronchi (primary, secondary, tertiary)
◦ Terminal bronchioles
The exchange zone (air space)
◦ Respiratory bronchioles
◦ Alveolar ducts
◦ Alveolar sac
◦ Alveoli
The chest cage
◦ Lungs
◦ Pleural cavity
◦ Blood and nerve supply

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The nose and the nasal cavity
 The primary air passageway
 Promote filtration of air
 Contain epithelial cell lining that have
◦ Cilia
 Beat 10-20x/sec, move mucus at rate of 2 cm/min
◦ Goblet cells inside the epithelial lining
 Secrete mucus used to trap dusts, smokes, pollen, bacteria,
toxins, ….
 The epithelial lining also used to humidify
(moisten) & warm the air

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The Pharynx
 Extends from base of skull to junction with esophagus and
trachea
 It has 3 different areas
◦ Nasopharynx- has only respiratory function
 Behind the posterior nasal openings
 Above the Soft palate.
◦ Oropharnynx-
 It is behind the mouth cavity
 Extends from Soft palate to the upper border of the Epiglottis.
◦ Laryngopharynx: -
 Extends from the upper border of the epiglottis TO the lower border
of the cricoid cartilage
 Protective reflex during swallowing

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Larynx (voice box)
 Extends from C-3 to C-6
 Includes; epiglottis, vocal cords, thyroid and cricoid
cartilages
 Connects the pharynx to trachea
 Functions of the Larynx
◦ Its vocal folds provide: control of airflow and production of
sound.
◦ Acts as a switching mechanism to route air and food into the
proper channels
◦ Contracts rapidly, to prevent food and liquids from entering
the airway.

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Trachea
 A tube of 10-12 cm in length and 2 cm width
 Contains ciliated pseudostratified columnar
epithelium
 Surrounded by C – shaped cartilages that extend
anterior 5/6th
of trachea
 Protect the tracheal wall and prevent it from
collapse
 Trachea bifurcates in to two primary bronchi

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Bronchial Tree
 Starts at right and left primary bronchi
 Continue branching into smaller branches up to
tiny air sacs called alveoli
 As the branching continues the cartilage in the
walls decreases
 Finally, absent in the bronchioles
 As we go down the respiratory tract, the amount
of smooth muscle increases

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Bronchioles
 Continuation of bronchial tree
◦ Terminal bronchioles – no gas exchange
◦ Respiratory bronchioles – involved in gas exchange
 The walls lack cartilaginous supports
◦ But dominated by smooth muscle tissue
 The ANS regulates the activity of smooth muscle
layer
◦ Sympathetic activation - Bronchodilation
◦ Parasympathetic stimulation - Bronchoconstriction

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Alveoli
 A one cell layer thick diffusion barrier to respiration
 No muscle around the alveoli
 Has extremely thin alveolar wall that is important for
gas exchange
 Between the alveoli is an almost solid network of
interconnecting capillaries
◦ Capillaries cover – 90% of the alveolar surface
 There are about 300 million alveoli in both lungs

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 The alveoli are lined by two types of epithelial cells.
◦ Type I cells - are the primary lining cells of the alveoli,
 95% of the alveolar epithelial surface area
 Involved in gas exchange
◦ Type II cells (granular pneumocytes)
 A primary function of these cells is to secrete surfactant
 Make up about 5% of the surface area
◦ The alveoli also contain other specialized cells, including
 Pulmonary alveolar macrophages
 Lymphocytes, plasma cells, mast cells.
 The mast cells contain heparin, histamine, and various
proteases that participate in allergic reactions

Respiratory unit or the
respiratory zone
 Site of gas exchange in
the respiratory tree
 Which is composed of:
◦ Respiratory bronchioles
◦ Alveolar ducts
◦ Alveolar sacs
◦ Alveoli
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Respiratory Membrane
 Layer of membranes that gases cross during alveolar
respiration
Is composed of
 Alveolar walls:
Fluid and Surfactant layer
Single cell layer of alveolar epithelium
Epithelial basement membrane
 Interstitial space
 Capillary walls:
√Basement membrane
√Capillary endothelium

If the partial pressure is greater in the gas phase
(alveoli), as is normally true for oxygen, then more
molecules will diffuse into the blood than in the
other direction.
Alternatively, if the partial pressure of the gas is
greater in the dissolved state in the blood, which is
normally true for CO2, then net diffusion will occur
toward the gas phase in the alveoli.
03/18/2025 By Tekle H 24

Surfactant
Fluid in the alveolar fluid which is mixture
of protein and lipid complex
Secreted by type II alveolar cells
Reduces the surface tension on the surface
of the alveoli.
Prevents the alveoli from collapsing
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Anatomically, the respiratory tract is divided into 2
parts:
1. Upper respiratory tract
Nose, nasal cavity, paranasal sinuses, pharynx, and larynx
2. Lower respiratory tract
Trachea to alveolar ducts and alveoli
Physiologically, respiratory tract is divided into 2 zones:
3. The conducting zone
Only passage of air
From the nasal cavity up to the terminal bronchioles
Filters, warms, and humidifies the incoming air
4. The respiratory zone
 Involved in gas exchange, walls are thin
 Respiratory bronchioles, alveolar ducts, sacs, & alveoli

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Conducting zone
16 generations
Respiratory zone
7 generations

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Dead space
It is the amount of air in the respiratory passage which
does not take part in exchange of gases.
Two types;
Anatomical dead space
 The volume of air in the conducting zone of the respiratory
passage i.e. from nose and mouth up to terminal bronchioles
where exchange of gases does not take place.
Physiological dead space
 It includes anatomical dead space and the volume of air
in the alveoli which does not take part in the exchange
of gases.

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Functions of dead space
 Purification of air
◦ Removal of solid particles of various size from air
 Air-conditioning function
◦ Warming, humidification, … of air

03/18/2025 By Tekle H 30
Lungs
 Principal organs of respiration and we do have two lungs;
◦ Right lung:Three lobes
◦ Left lung:Two lobes
 Right lung is a little bit shorter b/se of liver pushes from below
 Left lung has cardiac notch

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Pleural cavity
 Space found between the parietal and visceral pleura
 Has pleural fluid produced by pleural membranes
◦ That acts as lubricant

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Nerve supply of the lungs
Lungs receive autonomic nerve supply
Sympathetic nerves:
Supply bronchial smooth muscles – bronchodilation.
Blood vessels – vasoconstriction.
Parasympathetic nerves:
Bronchoconstriction and
Vasodilation of the blood vessels.

Blood circulation
In the lung there are two types of circulation:
1. Pulmonary circulation
Blood movement from heart to lung and back to heart for
oxygenation
Blood flow via the lung is essentially equal to cardiac
output
Factors that control cardiac output regulate pulmonary BF
2. Bronchial circulation
Blood supply to surrounding tissues of the lung
Accounts for 1-2% of cardiac output
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Phases and Mechanisms of
Respiration

Phases of respiration
 External respiration
◦ Exchange of gases (O2 and CO2) between atmosphere and
pulmonary capillary beds
◦ Includes:
 Pulmonary ventilation
 Between atmosphere and lung
 Alveolar ventilation
 Between alveoli and pulmonary blood
 Internal (Cellular) respiration
oGas exchange between systemic capillaries & cells
 O2 diffuses to the cells and utilized for metabolic activities
 CO2 produced due to metabolic activities diffuse to blood
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Mechanisms of respiration
 Refers to the ways of inspiration and expiration
 The Rhythmic breathing at rest is known as Eupnoea
 Different structures are involved in these processes;
◦ Ribs and Intercostal muscles, diaphragm, Abdominal
and many other muscles

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Mechanism of inspiration
 Inspiration is active process
 Contraction and descent of the diaphragm
 Movement of the ribs outward and upward (when
the external intercostal muscle contact)
 The thorax increases in size
 Pressure in lungs must be less than atmospheric
pressure

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MUSCLES OF INSPIRATION
The primary muscles
 Diaphragm – MAIN muscle
of inspiration
 External intercostals
(Operate during quiet breathing)
Accessory muscles
(Operate only in forceful respiration)
 Scalene
 Sternocleidomastoid
 Serratus anterior
 Pectoralis minor

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 Inhaling means
breathing in.
 The brain sends
signals to the rib
muscles and
diaphragm to
contract
 The ribs are pulled
up and out, and the
diaphragm flattens
downwards;
 The volume of the
chest increases, so
air pressure
drops and more air
is drawn into the
lungs and alveoli.

03/18/2025 By Tekle H 42
Mechanism of expiration
 Lung pressure must be greater than atmospheric
pressure
 In quite breathing expiration is passive
• Resulting from elastic recoiling of lung
• Surface tension due to alveolar fluid
 Becomes active only when forceful exhalation occurs
 During forced expiration muscles of expiration
contracts
◦ Anterior abdominal muscles
◦ Internal intercostal muscles

03/18/2025 By Tekle H 43
Exhalation :
 External intercostal
muscles relax
 Ribs are lowered &
the chest moves
inwards
 Diaphragm muscles
relax & curves
upwards
 Thoracic cavity
becomes smaller
 Air is forced out
from the lungs.

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Lung FunctionTests (LFT)
Method of measuring and studying
pulmonary volumes and capacities
 Method of study – Spirometry
 Apparatus used – Spirometer
 Record obtained – Spirogram

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PulmonaryVolumes
 Tidal volume
◦ Volume of air inspired or expired during a normal inspiration or
expiration
 Inspiratory reserve volume
◦ Amount of air inspired forcefully after inspiration of normal tidal
volume
 Expiratory reserve volume
◦ Amount of air forcefully expired after expiration of normal tidal
volume
 Residual volume
◦ Volume of air remaining in respiratory passages and lungs after the
most forceful expiration

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Pulmonary Capacities
 Inspiratory capacity
◦ Tidal volume plus inspiratory reserve volume
 Functional residual capacity
◦ Expiratory reserve volume plus the residual volume
 Vital capacity
◦ Sum of inspiratory reserve volume, tidal volume, and expiratory
reserve volume
 Total lung capacity
◦ Sum of inspiratory and expiratory reserve volumes plus the tidal
volume and residual volume

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Forced vital capacity (FVC)
The maximum volume of air which can be
breathed out as forcefully and rapidly as
possible following a maximal inspiration.
FEV1(Forced ExpiratoryVolume 1)
Forced expiratory volume in 1 second
Normal : 80% of FVC
Clinically important in diagnosing different
pathologic conditions

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FEV2
Forced expiratory volume in 2 seconds
Normal: 95% of FVC
FEV3
Forced expiratory volume in 3 seconds
Normal: 98-100 % of FVC

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Transport of oxygen and carbon
dioxide

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Oxygen transport
 98% - combined with hemoglobin (Hgb)
◦ Each gram of Hgb carry 1.34 ml of Oxygen
 2% - transported dissolved in the plasma
◦ When the arterial pO2 gets higher more
oxygen will be found in the dissolved form

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 Oxygen binds at the four haem sites in hemoglobin
 4 molecules of oxygen can be transported in one
hemoglobin molecule

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CO2 transportation
 In dissolved form - 0.3ml = 7%
 It goes to solution as CO2 in the plasma
 As bicarbonate - 3ml = 70%
 CO2 + H2O H2CO3 HCO3
-
+ H+
 Combined with Hgb (as carbaminohemoglobin
compounds) - 0.7ml = 23%
 Hgb – CO2

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 Normal respiratory rate = 16 + 4 times/min
 Spontaneous respiration; is due rhythmic discharge
of motor neurons that innervates the respiratory
muscles.
 This discharge is totally dependent on the nerve
impulses from the brain
 Under normal conditions, inspiration is an active
process and expiration is a passive process

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Two sets of regulation
◦ Nervous regulatory mechanism
◦ Chemical regulatory mechanism

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1. Nervous regulation of respiration
Two systems are involved:
 Automatic control of respiration – by the brain
stem (Upper medulla and pons)
◦ Also called the Respiratory center
 Voluntary control of respiration - cerebral cortex

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A. Automatic control of respiration – by the respiratory
center
 Dorsal respiratory group
◦ Receives afferents from airways & chemoreceptors
◦ Stimulates inspiratory movements
 Ventral respiratory group
◦ Responsible for stimulates expiratory movements
◦ Totally inactive during quiet respiration
 Pre-Bötzinger complex – part of ventral respiratory group
◦ Coupled pacemaker cells (produce rhythmic discharges in
phrenic nerves)
◦ Respiratory pattern generator
By Tekle H

03/18/2025 By Tekle H 63
 Apneustic center
◦ Activate inspiratory neurons of medulla
◦ Favors long and deep inspiration
◦ Increase tidal volume
◦ Inhibited by vagal input and Pneumotaxic center
 Pneumotaxic center
◦ Inhibit neurons of Apneustic center
◦ Limits inspiration
◦ Lesion in the area will prolong respiration

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B. Voluntary control - through the cerebral cortex
 Conscious control of respiration
 Rate and depth can be modified for limited duration
 Voluntary hyperventilation, breath holding, etc
 Via Corticospinal tract ending on motor neurons
innervating respiratory muscles

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2. Chemical regulation
 Functions by detecting blood levels of CO2 monitoring it
through the concentration of H+
 It is a form of negative feedback control
◦ Sensory signal is sent to the integrator (medulla and pons) then
◦ Correction measure is taken by the effectors (respiratory muscles)
2 types of chemoreceptors:
 Central chemoreceptors
 Peripheral chemoreceptors

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 Central chemoreceptors
◦ Located on the ventrolateral surface of medulla
oblongata
◦ Detect changes in the pH of spinal fluid
 Peripheral chemoreceptors
◦ Include receptors in:
 Aortic body (that detect blood O2 and CO2 levels),
and
 Carotid body (that detect blood O2, CO2 and pH
levels)

03/18/2025 By Tekle H 67
Peripheral chemoreceptors –
Carotid and Aortic bodies

03/18/2025 By Tekle H 68
THANKYOU

Respiratory system Physiology powerpoint.pptx

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