1.Respiratory system a complete guide.pdf

Respiratory System 1
26 September 2021
Respiratory System
ninsiimaherbertizo

26 September 2021 Respiratory System 2
Respiratory System
• Pulmonary Ventilation
• Gas Transfer Across
Alveolar/capillary Membrane
• Transport of O2 & CO2 in Blood
• Regulation of Ventilation

Introduction
• Animal cells obtain energy by
– Oxidative breakdown of nutrients
• Therefore
– They must be continually supplied with
oxygen
– Carbon dioxide must be removed

Introduction
• In lower forms of life
– Simple diffusion is adequate
• In mammals
– Simple diffusion is not adequate
– Had to develop specialized system for
• Oxygen supply
• Carbon dioxide elimination

Introduction
• To achieve this they use two systems
– Respiratory system
– Cardiovascular system
• Respiratory system
– Gas exchanger
– Fragile barrier between external & internal
environment

Introduction
• Fragile barrier protected against
– Trauma, dehydration, freezing
• Fragile membrane imposes
– Small barrier to gas exchange

Respiratory System
• Respiration is the term used to include
– Internal respiration
• Covered during biochemistry course
– External respiration
• Gas exchange
– Ventilation
– Gas transfer (alveolar/capillary)
– Blood gas transport

Respiratory System
• Respiratory system is made
up of
– Gas exchange organ
(lungs)
– The pump that ventilates
the lungs which include
• Chest wall
• Respiratory muscles
• Respiratory center

Respiratory System
• At rest a normal
human breathes
– 12 to 15 times per
minute
– 500 mls of air per
breath
– 6 to 8 liters of air
inspired or expired per
min

Respiratory System
• Gas exchange
organ
– Consists of 2 lungs
• Each divided into
lobes

Structure of Lungs
• The lungs comprise of 2
tree like structures
– Vascular tree made up
of
• Arteries and veins
• Connected by
capillaries
From Textbook of Work Physiology by
Astrand, Rodahl, Dahl & Stromme

Structure and Functions of
Lungs
• Airway tree,
embedded in elastic
connective tissue

From: www.coheadquarters.com/penlibr/myphysiology

The Airways
• The trachea divides into 2
main bronchi
• The bronchi divides
– Many times to form
bronchioles
• Between the trachea and
alveolar sac
– Air ways divides 23 times
• (23 generations)
From: Nunn’s Applied
Respiratory physiology; 5th Ed

The Airways
• The first 3 generations of
conducting zone plus the
trachea
– Contain cartilage to prevent
airway collapse
• Trachea, main bronchi
cartilage is U shaped
• Lobar, segmental bronchi
have small plates
From Jennifer Shaw: PPT “The
Respiratory System”

The Airways
• In the bronchioles
– Cartilage disappears
• The smallest airways in the
conducting zone
– Are the terminal bronchioles
• The bronchioles and
terminal bronchioles
– Suspended by elastic tissues in
the lung parenchyma

The Airways
• The first 16 generation
form
– Conducting zone of the airways
• Transport gas from & to
exterior
– Made up of
• Bronchi
• Bronchioles
• Terminal bronchioles

The Airways
• The remaining 7 generation
form the
– Transitional & respiratory
zone
– Made up of
• Respiratory bronchioles
• Alveolar duct
• Alveoli
– Gas exchange takes place
in this zone

The Airways
• The multiple divisions
– Greatly increase the cross
sectional area of the airways
– 2.5 cm2 in the trachea
– 11,800 cm2 in the alveoli
• Hence the velocity of
airflow
– Decline to very low values in
small airways

Respiratory Zone
• Alveoli
– Surrounded by pulmonary
capillaries
• Alveolar capillary
membrane
– Very thin < 0.5 m
• Alveolar epithelium
• Interstitial fluid
• Capillary endothelium
(From Hassen Taha Sherrif )
Textbook of Physiology CD
Alveoli with
capillary network
Alveolus
Respiratory
bronchiole
Branch of pulmonary
artery
Branch of pulmonary
vein

Respiratory Zone
• There are 300 millions
alveoli in human
• Total Surface Area
• of alveolar wall in
contact with capillary =
75 m2
– Compare skin SA = 1.8
m2
(From Hassen Taha Sherrif )
Textbook of Physiology CD
Alveoli with
capillary network
Alveolus
Respiratory
bronchiole
Branch of pulmonary
artery
Branch of pulmonary
vein

The Respiratory Airways

Alveolar Capillary Membrane

• Made up of
– Alveolar epithelium
• Single layer epithelial cells
– Basement membrane
• Elastic collageneous tissue
– Capillary endothelium
• Single layer endothelial cells
From: www.pdh-odp.co.uk/diffusion.htm

Alveolar-Capillary membrane
• Alveolar capillary
membrane thickness can
increase if
– Basement membrane is
distended with fluid
• Pulmonary oedema
– Fluid accumulates in the
alveolar space

Surface Tension
• Any air – liquid interface develop surface
tension
– When water forms interface with air
• Water molecules on the surface of the water have
strong attraction force for one another
• Water surface attempt to contract

Surface Tension
• In the alveolar the water on the inner side
of alveolar tend to contract
• This causes
– Powerful collapsing tendency of the alveoli
• Surface tension elastic force of lungs

Laplace’s law
– P = (2T)/R
• P = pressure exerted by surface tension of bubble
• T = surface Tension
• R = radius of the bubble (alveolus)
– In the alveoli
• During expiration R decreases
– P increases, tendency to collapse increases

Surfactant
• Surface active phospholipids
• Synthesized by type II alveolar cells
(granular pneumonocytes)
• It is a complex mixture of
– Phospholipids, proteins & Ca++
• Dipalmitoylphosphatidylcholine
• Surfactant apoproteins
• Calcium ions

Surfactant
• Phospholipids
– Responsible for reducing the surface tension
– Does not dissolve uniformly in the water lining
the alveolar surface
• One portion of molecule is hydrophilic
– Dissolves in water
• The other portion is hydrophobic
– Oriented towards air

Surfactant
• Thus a hydrophobic surface is exposed to
the air
– Has a much lower ST

Effects of Surfactant
• The amount of
reduction of ST by
surfactant
– Proportional to
concentration of
surfactant on the
surface

• During inspiration
– Volume of alveolar increases
– With fixed amount of
surfactant
• Conc. of surfactant on surface
decreases
– Increases ST
– Prevent further increase in
surface of alveoli

• During expiration
– Volume of alveoli
decreases
– Conc of surfactant on the
surface increases
• Decreases ST
• Decrease the tendency to
collapse

• Thus
– Stabilizing the alveoli
against tendency to
collapse
– Diminish the force
required for expansion of
the lung
• Reduces the work of
breathing

1.Respiratory system a complete guide.pdf

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1.Respiratory system a complete guide.pdf