Download 2. Gaseous exchange SJW

Learning Outcomes
1. Explain how carbon dioxide and
oxygen are exchanged
2. Explain / describe how oxygen and
carbon dioxide is transported around
the body
Video Clip Summary
Gaseous exchange
There are two sites for gaseous exchange
in the body:
1. Between the air in the alveoli of the
lungs and blood in the surrounding
alveolar capillaries
2. Between the tissues/muscles of the
body and surrounding blood capillaries
External Respiration
External respiration
Gaseous exchange at the alveoli
The object is to convert deoxygenated blood
returning from the body into oxygenated blood.
As the blood circulates through alveolar capillaries,
oxygen is picked up from the alveoli and carbon
dioxide is lost to be expired.
Gases flow from an area of high pressure to an area of low pressure
Called Diffusion
Diffusion
The movement of gases from a higher partial pressure to a
lower partial pressure until equilibrium is reached.
Partial Pressure
The pressure that is exerted by an individual gas when
it exists within a mixture of gases
Partial pressure (pp):
The actual pressure of a gas as it exists in a mixture of gases.
For example:
Atmosphere pressure is composed of three main gases:
Nitrogen (approx 79%)
Oxygen (approx 21%)
Carbon Dioxide (approx 0.03%)
Together they exert a pressure of 760mmHg
(mm of mercury to measure the partial pressure of a gas)
Respiration in exercise
GAS TRANSPORT
GAS TRANSPORT ACROSS THE RESPIRATORY MEMBRANE
oxygen diffuses from alveolus across the alveolar wall,
respiratory membrane, and capillary wall towards red blood cells
carbon dioxide diffuses in the opposite direction from the red
blood cell and from blood plasma to the alveolus
Video 1
video gaseous exchange
Respiration
The partial pressure of 02 in the alveoli (alveolar / found in the lungs) is
higher than the partial pressure of the 02 in the blood vessels surrounding
the lungs
Atmosphere air
Atmosphere air
From heart
To heart
Alveolus
C02
High pressure
02
Direction
Of blood
flow
Direction
Of blood
flow
Low pressure
• Blood returning from the body is low in oxygen because it
has been removed by the tissues. (to fuel movement)
• The difference in pressure is even greater during exercise
as more oxygen diffuses into the muscle tissue.
• The difference between the two pressures is known as the
diffusion gradient.
• Oxygen moves from areas of high pressure (alveoli) to
areas of low pressure (blood vessels surrounding lungs).
The greater the gradient the faster the diffusion
When we exercise the gradient will be
greater: therefore faster
Features that Facilitate Diffusion at the
Alveolar
1. Alveolar membrane is very thin = short diffusion
distance between the air in alveoli and the blood
2. Numerous (millions) of alveoli creates a VERY LARGE
surface area for diffusion to take place
3. Alveoli are surrounded by a vast (large) network of
capillaries = huge surface area for diffusion
4. The diameter of the capillaries is slightly narrower than
the area of a red blood cell. This forces the blood flow
slowly in single file.
Internal respiration
Gaseous exchange at the tissues
At the tissue-capillary membranes
surrounding the muscles, the p02 in the
capillary is higher than in tissues, therefore
oxygen moves into the muscle tissue.
Gaseous exchange at muscles
and tissues
Capillary walls just one cell thick – with thin
membranes so a short distance to travel
Myoglobin within the muscle cell attracts oxygen
to it
Diameter of capillaries is narrow which forces
blood cells to travel through them slowly in
single file maximising diffusion
Extensive network of capillaries provide huge
surface area for exchange of O2 & C02
Carbon dioxide moves into blood
Increases in Lactic Acid
Increases in CO2
Increases in blood and muscle
temperature
Decreases in pH thus acidity levels
increase.
These changes mean that the body needs
oxygen quickly.
Altitude
At high altitude (above 1500m) the PP of oxygen in the atmospheric
air is significantly reduced.
At altitude pO2 is less which means that haemoglobin cannot carry
as much o2 as at sea level, therefore reducing the ability to perform
physical work (hypoxia)
This results in a decreases O2 transport in the blood causing a
reduction in the O2 available to working muscles.
It thus decreases VO2 max or aerobic capacity also can increase
breathing which leads to hyperventilation. Can also lead to
dehydration quicker.
EFFICIENCY OF GAS PROCESS
GOOD LUNG
VENTILATION
(efficient breathing
musculature)
VAST SURFACE AREA
of LUNG ALVEOLI
EFFICIENCY OF
GAS PROCESS
MOIST LINING
CONSTANT BLOOD
FLOW
SHORT DISTANCE
BETWEEN ALVEOLAR
LINING AND BLOOD
(only 0.5 microns)
STATE OF FITNESS
AND HEALTH
The Bohr Effect
During exercise muscles
need more oxygen so the
dissociation (release) of
oxygen from haemoglobin
happens more readily
Dissociation
curve shifts to
the RIGHT
This is known as the Bohr
effect and frees up more
oxygen = used by working
muscles
Factors shifting the dissociation curve to the right are:
•1. Increase in blood and muscle temperature
•2. Decreases in PP oxygen within muscle increasing the oxygen
diffusion gradient.
•3. An increase in carbon dioxide during exercise, increasing the
carbon dioxide gradient.
•4. Bohr effect – increase in acidity (lower pH)
•These factors increase during exercise. The effect is that the working
muscles:
•Generate more heat when working
•Use more oxygen to provide energy, lowering the PP oxygen
•Produce greater carbon dioxide as a by-product
•Increase lactic acid levels which increase muscle/blood acidity
Transport of oxygen
3% dissolves in plasma. 97% combines with haemoglobin to
form oxyhaemoglobin
At the tissues, oxygen dissociates from haemoglobin due
to the lower pressure of oxygen that exists there. In the
muscle, oxygen is transported by myoglobin.
Myoglobin has a high affinity for oxygen and transports the
oxygen from the capillaries to the mitochondria (where
aerobic respiration takes place, power house of the cell).
• oxygen moves from haemoglobin to myoglobin.
Iron based protein
Similar to Hb
•In the muscle oxygen is transported by myoglobin.
•Myoglobin has a high affinity for oxygen.
•It stores oxygen and transports it from the capillaries to
the mitochondria.
•Mitochondria are the centres in the muscle where aerobic
respiration takes place.
Much
higher
affinity
For 02 than
Hb
Arterial-venous oxygen difference
(a-vo2 diff)
The amount of oxygen removed from the blood by muscles
This represents how much oxygen is actually
extracted and used by the muscles
Measured by:
Analysing the difference in oxygen content of the blood in
the arteries leaving the lungs and that in the mixed venous
blood returning to the lungs
Control of Respiration
Breathing happens automatically and is
under the influence of the Respiratory
Control centre (RCC) located in the
medulla oblongata of the brain.
Inspiratory control centre (ICC) – basic rhythm of
breathing
Expiratory control centre (ECC) – passive process
Control of Ventilation
The nervous system can increase or
decrease the rate, depth and rhythm of
breathing. The respiratory centre located
in the medulla oblongata of the brain
controls breathing.
Neural Control
AT REST
Inspiratory centre is responsible for rhythmic cycle of inspiration and
expiration to produce a respiratory rate of 12-15 breaths a minute.
Impulses are sent and when stimulated muscles contract, increasing
the volume of the thoracic cavity, causing inspiration (active)
When their stimulation stops, the muscles relax, decreasing the
volume of thoracic cavity, causing expiration (passive)
The expiratory centre is inactive during quiet/resting breathing. It is
passive as a result of the relaxation of the diaphragm and external
intercostals.
Activity
Put the sentences in the correct order…
DURING EXERCISE
Pulmonary ventilation increases during exercise, which
increases both the depth and rate of breathing. This is
regulated by:
1. The Inspiratory Centre which:
(a) increases the stimulation of the diaphragm and
external intercostals
(b) stimulates additional inspiratory muscles for
inspiration, the sternocleidomastoids, scalenes and
pectoralis minor, which increase the force of
contraction and therefore the depth of inspiration.
DURING EXERCISE
2. The Expiratory Centre which:
(a) stimulates the expiratory muscles, internal
intercostals, rectus abdominus and obliques, causing
a forced expiration which reduces the duration of
inspiration.
(b) the inspiratory centre immediately stimulates the
inspiratory muscles to inspire, which results in an
increase in the rate of breathing.
Control of ventilation
Chemo receptors
-detect changes in
blood acidity pH
-detect decrease 02
Proprioceptors
-detect movement
Thermo receptors
-detect increase in
blood temperature
Respiratory Control Centre (RCC)
Located in the Medulla Oblongata
-determines basic rate
and depth of breathing
Baro receptors
-detect increase in
blood pressure
Stretch receptors
-prevent over-inflation of the lungs
by sending impulses to
the expiratory centre (Hering-Bruer reflex)
Chemoreceptors
(detect changes in
blood acidity)
Stretch receptors (prevent over
inflation of the lungs; if these start to
get excessively stretched they send
impulses to the expiratory centre to
induce expiration (Hering Breur reflex))
Thermoreceptors
Baroreceptors
(detect
changes in
blood
pressure)
Proprireceptors
(detect movement)
Expiratory Centre
Respiratory Centre
Inspiratory Centre
(Medulla Oblongata)
Phrenic
Phrenic nerve
nerve
Diaphram and
external
intercostals
Increase
breathing rate
Intercostal nerve
Abdominals
and internal
intercostals
Increase
expiration
Hering-Breuer Reflex
•
Expiratory centre acts as a safety mechanism in the lungs to ensure they
are never over inflated.
•
Stretch receptors in the lungs detect when the depth of breathing
increases and stimulate the RCC to inhibit the inspiratory centre and
stimulate the expiratory muscles.