Transcript ANATOMY OF THE RESPIRATORY SYSTEM (OVERVIEW)

INTRODUCTION TO THE
RESPIRATORY SYSTEM
1
IMPORTANT FACTS:
Oxygen and Carbon Dioxide are respiratory
gases
Most cells require continuous oxygen supply
for production of energy.
Without oxygen supply cells die.
Carbon dioxide is a waste product of cellular
metabolism. Its accumulation leads to
acidosis.
Exchange of respiratory gases between cells
and their surrounding for homeostasis is
maintained by Respiration.
Phylogenesis of Respiratory System
In Protozoa, (unicellular organism) oxygen and
carbon dioxide diffuse directly through cell
surfaces.
Metazoa (multicellular organisms) developed
specific respiratory areas and liquid (blood)
transport systems thus providing transportation
of respiratory gases .
Mammals have highly developed respiratory
and circulatory systems.
RESPIRATORY TERMINOLOGY
Respiration: is a complex process of exchange of
respiratory gases (Oxygen & Carbon dioxide) between
an organism and external environment. It requires a
constant supply of fresh air by Breathing in and out.
Breathing: is a process of continuous ventilation of
the lungs when a fresh atmospheric air will replace an
air used for the external (pulmonary) respiration
– Breathing includes two phases:
Inspiration – when air is taken into the lungs and
Expiration – when air is removed from these organs
– Breathing involves skeletal components of thoracic
cage and muscles of respiration, which produce
respiratory movements.
Ventilation and Perfusion
During ventilation of lungs a reciprocal
movement of air is caused by alternately
increasing and decreasing the volume of the
chest in breathing.
Perfusion of lungs is achieved via branches of
pulmonary arteries, which bring deoxygenated
blood to the lungs for its oxygenation
RESPIRATION employs three processes:
External respiration involves the stage of
taking oxygen from the air into the blood and
returning carbon dioxide to the air. It occurs
through the Respiratory Membranes (air-blood
barriers).
Transport of respiratory gases in the blood
throughout the body via the circulatory system.
Internal or cellular respiration is the process
by which glucose or other small molecules
within the cell are oxidized to produce energy:
this requires oxygen and generates carbon
dioxide.
GAS EXCHANGE AT RESPIRATORY MEMBRANE:
Pulmonary ventilation ensures that alveoli are supplied
with oxygen, and it removes carbon dioxide arriving
from bloodstream.
The actual process of gas exchange occurs between
the blood and alveolar air across the respiratory
membrane.
The driving force for exchange of respiratory gases is
defined by a difference of Partial Pressure of Gases in
the air and blood and an ability of their molecules to
diffuse from a gas into a liquid and vice versa.
During gas exchange between air & blood molecules
of each gas diffuse from area with higher pressure to
area with lower pressure (Henry’s Law)
Partial Pressure & Normal Gas Concentration in Air
Inspired air:
–
–
–
–
Nitrogen – 597 (78.6%)
Oxygen – 159 (20.8%)
Carbon Dioxide – 0.3 (0.04%)
Water Vapor – 3.7 (0.5%)
Alveolar air:
–
–
–
–
Nitrogen – 573 (75.4%)
Oxygen – 100 (13.2%)
Carbon Dioxide – 40 (5.2%)
Water Vapor – 47 (6.2%)
Expired air:
–
–
–
–
Nitrogen – 569 (74.8%)
Oxygen – 116 (15.3%)
Carbon Dioxide – 28 (3.7%)
Water Vapor – 47 (6.2%)
Exchange & Transport of Gases
Diffusion of Gases-Fick's Law
Transfer of gases across cell membranes or capillary walls
occurs by simple diffusion. For gases, the rate of transfer by
diffusion (X) is directly proportional to the driving force, a diffusion
coefficient, and the surface area available for diffusion; it is
inversely proportional to the thickness of membrane barrier. Thus,
VX - Volume of gas transferred per unit time
D - Diffusion coefficient of the gas
A - Surface area
ΔP - Partial pressure difference of the gas
ΔX - Thickness of the membrane
Diffusion of Gases-Fick's Law
The driving force for diffusion of a gas is the
partial pressure difference of the gas (ΔP)
across the membrane, not the concentration
difference.
Thus, if the PO2 of alveolar air is 100 mm Hg
and the PO2 of mixed venous blood that enters
the pulmonary capillary is 40 mm Hg, then the
partial pressure difference, or driving force, for
O2 across the alveolar/pulmonary capillary
barrier is 60 mm Hg (100 mm Hg - 40 mm Hg).
Transport of Gases
Transport of Carbon Dioxide
Conditions for Oxygenation of Blood:
Sufficient surface areas (Respiratory Areas) for
gaseous exchange between Atmospheric air
and Blood
Presence of Respiratory Membranes (air-blood
barriers) with a very short diffusion path
between Atmospheric air and Blood
Concentration gradients for diffusion of Oxygen
and Carbon dioxide between the air and blood
Conditions for Oxygenation of Blood:
The surface area available in adult lungs for
gaseous exchange is around 140m², which is
about the area of a single tennis court.
The blood in the alveolar capillaries is
separated from alveolar air by a thin (0.6* in
many places) respiratory membrane (1* = one
thousandth of a mm).
Respiratory Membrane includes:
1. Cell membrane & Cytoplasm of the
covering alveolar epithelial cell, lined with
a layer of Surfactant, which has contact
with an air with a high Oxygen content.
2. Cell membrane & Cytoplasm of
endothelial cell of the adjacent blood
capillary, containing red blood cells with a
high Carbon Dioxide content.
3. Fused basal laminae of the above two
epithelial cells.
Components of Respiratory Membrane
Alveolar Air
Diffusion gradients are maintained by:
Ventilation (breathing) which renews alveolar
air, maintaining oxygen concentration near that
of atmospheric air and preventing the
accumulation of carbon dioxide.
The flow of blood in alveolar capillaries which
continually brings blood with low oxygen
concentration and high carbon dioxide
concentration to the respiratory membranes.
Sites For External Respiration:
Areas of the body, which may have a
presence of Respiratory Membranes with
a very short diffusion path between
atmospheric air and blood & appropriate
concentration gradients of oxygen and
carbon dioxide in the air and blood, may
perform External Respiration.
Three Types of External Respiration:
Lungs, Skin and Alimentary Canal have
conditions for External Respiration
Pulmonary respiration - 85%;
Cutaneous respiration - 10%;
Intestinal respiration - 5%.
GROSS ANATOMY OF
THE RESPIRATORY
SYSTEM
(OVERVIEW)
THREE COMPONENTS OF THE
RESPIRATORY SYSTEM:
RESPIRATORY TRACT
– Conducting portion
– Respiratory portion
LUNGS & PULMONARY CIRCULATION
ADDITIONAL STRUCTURES INVOLVED IN
PULMONARY VENTILATION
RESPIRATORY SYSTEM
RESPIRATORY TRACT
(AIRWAY)
Its conducting portion is composed of
interconnected hollow organs, thus forming a
branching out passageway, which has hard
elements (bones, cartilages, ligaments) in its
walls. Those elements maintain to keep
lumina of hollow organs patent, because they
prevent collapsing of walls of air passages.
Two Major Subdivisions of
Conducting Portion:
a)
Upper part/airway (nasal cavity with
paranasal air sinuses, oral cavity, nasopharynx,
oropharynx
and
upper
portion
of
laryngopharynx);
b)
Lower part/airway (larynx, trachea,
extrapulmonary
bronchi,
intrapulmonary
bronchi, regular and terminal bronchioles). It
includes bronchial trees.
Subdivisions of Respiratory Tract
Upper & Lower Airway
Pharynx
Nasal Cavity
Oral
Cavity
4
Larynx
5
6
Trachea
RESPIRATORY TRACT
(AIRWAY)
Its respiratory portion – “Respiratory Tree”:
consists of functional units “Acini”, which
include respiratory bronchioles, alveolar ducts,
alveolar atria or vestibules and alveolar sacs
with alveoli. Acini are attached to the smallest
elements of the bronchial tree – the terminal
bronchioles.
Lowest part of Conducting Portion & Respiratory Portion
Outside air:
Varies in temperature. At the alveolar surface it must
be at body temperature
Varies from very dry to very humid. At the alveolar
surface it must be saturated with water vapour
Contains dust and debris. These must not reach the
alveolar wall
Contains micro-organisms, which must be filtered out
of the inspired air and disposed, before they reach the
alveoli, enter the blood and cause possible problems.
It is easy to see that the temperature and humidity of
inspired air will increase as it passes down a long
series of tubes lined with a moist mucosa at body
temperature. The mechanisms for filtering are not so
obvious though the turbulence of inspired air could
play some role in it.
Functions of Nasal Cavity
It is also filtered & cleaned there.
LUNGS
Lungs are paired parenchymatous organs,
which consist of lobes, bronchopulmonary
segments and lobules.
They also include intrapulmonary bronchi,
bronchioles and numerous Respiratory Trees or
functional
units:
Acini,
which
contain
Respiratory Membranes (air-blood barriers).
Latter serve for gas exchange between
atmospheric air and blood. Transport of gases
with the blood to and from lungs is provided via
the pulmonary circulation.
ADDITIONAL STRUCTURES
INVOLVED IN PULMONARY
VENTILATION
They include the:
– Visceral and parietal pleurae
– Two plural cavities (right & left)
– Bones and joints of the thoracic cage
– Muscles of respiration with their blood and
nerve supply)
Mechanism of breathing.
In order to grasp the way in which we breathe we have
to grasp the following facts:
– Each lung is surrounded by a pleural cavity or sac, except
where the plumbing joins it to the rest of the body, rather like
a hand in a boxing glove.
The glove has an outer and inner surface, separated by a layer of
padding. The pleura, similarly, has two surfaces, but the padding is
replaced by a thin layer of fluid.
– Each lung is enclosed in a cage bounded below by the
diaphragm and at the sides by the chest wall and the
mediastinum.
– Breathing works by making the cage bigger: the pleural
layers slide over each other and the pressure in the lung is
decreased, so air is sucked in. Breathing out does the
reverse, the cage collapses and air is expelled.
Arrangement of Pleura
Ribs, Respiratory Muscles, Lungs & Pleurae
Parietal Pleura
Visceral Pleura
Mechanism of breathing.
Breathing movements are sometimes divided into:
– Pump handle movements, the sternal end of rib is elevated
or depressed on its vertebral joints
– Bucket handle movements, the rib rotating on its axis
around anterior and posterior attachments.
With more and more effort put into deeper and deeper
breathing the scalene muscles of the neck contract,
raising the first rib and hence the rest of the cage, then
other neck muscles and even those of the upper limb
become involved.
A patient with difficulty in breathing often grips a table
edge in order to stabilize the limbs so that their
muscles can be used to help in moving the thoracic
wall.
Expansion of Thoracic Cage (Bucket handle action)
Expansion of Thoracic Cage (Pump handle action)
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