Download Gas Exchange

RESPIRATION
Respiratory muscles:
1-Diaphragm – which increase and decrease the vertical diameter of the
chest cavity.
2-Internal & External intercostal muscles move the ribs and sternum 
affecting the anteroposterior diameter of the thoracic cavity
Movement of air in and out of the lungs:
1- The lung is formed of an elastic tissue that collapse like a balloon and
inflated and then expel the air out
2- The lungs are surrounded by a very thin layer of pleural fluid inside
pleura that lubricate the movements of the lungs within the cavity
Functions of the respiratory passageways:
The trachea, bronchi, and bronchioles:
the walls are formed of cartilage and the smooth muscle  contraction of the
smooth muscle  narrowing of the airway.sympathetic nervous system
causes dilatation of the bronchi to supply the central area of the lung,
epinephrine and norepinephrine cause dilatation of the bronchial tree.
parasympathetic nerve fibers penetrate the lung parenchyma and secrete
acetylcholine that causes mild to moderate constriction of the bronchioles.
Focal factors that cause bronchiolar constriction:
1-histamine
2-slow reacting substance of anaphylaxis (secreted from the mast cells in
allergic reactions and pollen in the air)
.
Respiratory System Anatomy
Nasopharynx
Oropharynx
Epiglottis
Larynx
Trachea
Carina
Bronchi
Bronchioles
Respiratory System Anatomy
Alveoli •
Air sacs –
Site of oxygen –
and carbon
dioxide
exchange with
blood
Mucous of the respiratory passageways:
Secreted by epithelial cells that lines the respiratory passage:it moisten the
respiratory passages from the nose up to the terminal bronchioles it traps
small particles out of the inspired air – removal of the mucous by movement of
the cilia in the ciliated epithelia that line the entire surface of the respiratory
passages in the lungs it beat upward while in the nose it beat downward
towards the pharynx.
Various pressure in the lungs:
1-pleural pressure :– is the pressure of fluid in the narrow space between the
visceral and parietal pleura, normally slightly negative pressure
-the normal pleural pressure at the beginning of inspiration is –5cm of H2O
- The pleural pressure at the beginning of expiration is –7.5cm of H2O
2- Alveolar pressure:
alveolar pressurep: – is the pressure inside the lung alveoli
during inspiration: is –1cm of H2O (this slight negative pressure is enough
to move about 0.5 liter of air into the lungs
during expiration: it rises to about +1cm of H2O (this forces 0.5 liter of
inspired air out of the lungs
Compliance of the lungs:
Definition:
- the extent to which the lungs expand for each unit increase in
transpulmonary pressure
transpulmonary pressure (pleural pressure minus alveolar pressure) = m~
200ml/cm of H2O (each time, the transpulmonary pressure increase by 1cm
of H2O, the lungs expand 200ml)
the compliance of the lungs are determined by the elastic forces of the
lungs, which can be divided into 2 parts:
1-elastic forces of the lung tissue
2-elastic force caused by surface tension of the fluid that lines the alveoli
- elastic forces of the lung tissue are determined by the elastin and collagen
fibers among the lung tissue (deflated lungs, these fibers contracted and but
when the lung expand it becomes stretched and elongating)
- elastic forces caused by the surface tension accounts for about 2/3 of the
total lung elastic forces and much more complex and it depends on the
“surfactant”
Surfactant surface tension and collapse of the lungs:
when water forms surface with air, the water molecules on the surface of
water have extra attraction force for each other and contract. Also water
surface in the inner surface of the alveoli attempting to contract to force air
out of the alveoli through the bronchi which causes the alveoli to collapse
Surfactant:
- is a substance produce by type II alveolar epithelial cells which reduce the
surface tension of the fluid in the inner surface of the alveoli &keep alveoli
expanded
- it is a mixture of phospholipids, proteins, and ions, the most important
component is phospholipid dipalmitoyl phosphatidylcholine which is
responsible for reducing the surface tension)
Pulmonary volumes and capacities:
Pulmonary volumes (by using spirometer):
1-Tidal volume – is the volume of air inspired or expired with each normal
breath = 500ml in young adult man.
2-Inspiratory reserve volume – is the extra volume of air that can be inspired
over and beyond the normal tidal volume = 3000ml.
3-Expiratory reserve volume – is the extra amount of air that can be expired
by forceful expiration after the end of a normal tidal expiration ~ 1100ml.
4-Residual volume – is the extra volume of air that still remain in the lungs
after the most forceful expiration ~ 1200ml.
-The pulmonary capacities: Comprises more than one volume:
-1-Inspiratory capacity – is the volume of air inspired by a maximal
inspiratory effort after normal expiration = 3500ml = inspiratory reserve
volume + tidal volume.
-2-The functional residual capacity – is the volume of air remaining in the
lungs after normal expiration = 2300ml = expiratory reserve volume +
residual volume.
-3-The vital capacity – is the volume of air expired by a maximal expiratory
effort after maximal inspiration ~ 4600ml = inspiratory reserve volume +
tidal volume + expiratory reserve volume.
-4-Total lung capacity – is the maximum volume of air that can be
accommodated in the lungs ~ 5800ml = vital capacity + residual volume.
-5-Minute respiratory volume – is the volume of air breathed in or out of the
lungs each minute = respiratory rate x tidal volume = 12 X 500ml =
6000ml/min.
-All lung volume and capacity are about 20 to 25% less in women than in
men and are greater in athletic persons than in small and asthenic persons.
•
Alveolar ventilation:
Movement of air between the lung and atmospheric air, in the gas exchange
areas which include the alveoli, the alveolar sacs, the alveolar ducts, and the
respiratory bronchiole.
Dead space:
The respiratory passages where gas exchange does not occur (up to the
terminal bronchioles), normal dead space air in the young adult male =
150ml
Respiratory membrane
The total surface area of the respiratory membrane is ~ 50 to 100 m2 in
normal adult. This large surface area to allow rapid diffusion of gases
through the respiratory membrane
Factors that affect the rate of gas diffusion through the respiratory
membrane:
1.The thickness of the respiratory membrane.  thickness of the respiratory
membrane e.g., edema   rate of diffusion. The thickness of the respiratory
membrane is inversely proportional to the rate of diffusion through the
membrane.
2.Surface area of the membrane. Removal of an entire lung decreases the
surface area to half normal. In emphysema with dissolution of the alveolar
wall   S.A. to 5-folds because of loss of the alveolar walls
3-The diffusion rate of the specific gas. Diffusion coefficient for the transfer
of each gas through the respiratory membrane depends on its solubility in
the membrane and inversely on the square root of its molecular weight. CO2
diffuses 20 times as rapidly as O2
4-The pressure difference between the two sides of the membrane (between
the alveoli and in the blood). When the pressure of the gas in the alveoli is
greater than the pressure of the gas in the blood as for O2, net diffusion from
the alveoli into the blood occurs, but when the pressure of the gas in the
blood is greater than the pressure in the alveoli as for CO2, net diffusion
from the blood into the alveoli occurs
Regulation of respiration:
1-Neural control of respiration
2-Chemical control of respiration
Neural control of respiration:The respiratory center is composed of groups of neurons located bilaterally
in the medulla and pons divided into 3 major collections of neurons:
1-Dorsal respiratory group in the dorsal portion of the medulla and mainly
inspiratory neurons.
2-Ventral respiratory group in the ventralateral part of the medulla which
contains both expiratory and inspiratory neurons
.3-Pneumotaxic center which is located dorsally in the pons, which helps
control both the rate and pattern of breathing.
Chemical control of respiration:
- Excess CO2 or  H+ ions mainly stimulate the respiratory center to
increase the strength of both inspiratory and expiratory signals to the
respiratory muscles
Central chemoreceptors:
-Located on the ventrolateral surfaces of the medulla oblongata (bilaterally).
This area is highly sensitive to changes in either blood PCO2 or H+ ion
concentration. H+ ions can’t cross the blood-brain barrier (BBB). So CO2
cross the BBB and react with H2O to form carbonic acid and then dissociate
into H+ ion and HCO3¯, then the H+ ion which stimulate the chemosensitive
area in the brain.
Gas Exchange
When carbon dioxide diffuses from the cells into the blood, only a
small amount of it (9%) reaching the blood is held in simple solution.
(as dissolved carbon dioxide)
Another 27 % attaches directly to the Hemoglobin to form
carbonamino-hemoglobin.
The remaining 64% combines with water to form bicarbonate
ions and hydrogen ions.
Each time blood passes through the tissues; it picks up large
quantities of carbon dioxide. This then reacts with water to form
Bicarbonate (HCO3-) and Hydrogen Ions (H+). There are many
substances in the blood capable of binding the excess free hydrogen
ions. Hemoglobin is one of the most important of these substances.
When Hydrogen (H+) combines with the hemoglobin (Hb), the Hb
releases some of the oxygen attached to it.
Gas Exchange in Tissues Internal Respiration
1. 1. CO2 diffuses into the blood from the cell
2. 2. CO2 joins with water to make Bicarbonate and Hydrogen
Ions. (Carbonic Anahydrase) – Enzyme that runs this reaction
3. 3. Most of the released H+ is picked up by the combined from
of O2 and hemoglobin. (Oxy-hemoglobin [HbO2-] ) The
binding of H+ by HbO2- (produces HHb) aids in the release of
oxygen. The H+ concentration and the slight increase in
temperature alters the hemoglobin (protein denatures slightly)
and releases oxygen easily.
4. 4. Oxygen then enters the tissue moving from an area of high
concentration to an area of low concentration.
The blood leaving the tissues now contains large quantities of
hemoglobin which is free of oxygen, and is called Reduced
Hemoglobin (HHb) The blood also contains large amounts of
bicarbonate ions (HCO3-). No further changes occur until the blood
reaches the lungs.
Gas Exchange in the Lungs – External Respiration
1. 1. High concentration of Oxygen in lungs. Oxygen diffuses
into blood.
2. 2. Oxygen joins with reduced hemoglobin to form
Oxyhemoglobin and Hydrogen ions.
3. 3. H+ picked up by Bicarbonate to produce CO2 + H2O
4. 4. The CO2 diffuses into lung alveoli where it is expelled by
normal breathing.
***NOTE: H+ does not accumulate because as soon as it is
released from HHB, it combines with HCO3- to release Carbon
dioxide.
Hemoglobin is essential in the blood because it serves as a
carrier for oxygen, carbon dioxide, and hydrogen ions (acts like a
buffer).***
Temperature is cooler which allows hemoglobin to grab oxygen
easier.