Download respiratory system notes - Kevan Kruger

The Respiratory System
Respiration is the set of processes that are involved with the movement
of oxygen to the tissues and the removal of the waste product CO 2.
There are four aspects to respiration:
1. Breathing: the inspiration and expiration of air.
1. External Respiration: the gas exchange that occurs at the alveoli. Oxygen diffuses
([High] to [Low]) moves into the blood, carbon dioxide diffuses into the alveoli to be
breathed out.
3. Internal Respiration: the gas exchange that occurs at the tissues. The oxygen diffuses
into the tissues, and the carbon dioxide diffuses into the blood.
4. Cellular Respiration: the use of the oxygen by the mitochondria in tissue cells for the
manufacture of ATP, which can be used for metabolism by the cells.
O2 + glucose (C6H12O6)
CO2 + H2O + ATP Energy
I. Respiratory Structures and their Functions:
A) Nasal Sinus: this initial passageway is richly lined with capillary beds and mucous
secreting glands. As this is one of the major entry ways into the body (the other is
through the mouth) there are a number of ‘safeguards’ that have evolved.
1. Nose hairs: with the aid of mucous, these hairs filter and trap particulate matter.
The debris that is trapped in this manner is discharged through the nose.
2. The blood supply allows the presence of large number of basophils (and mast
cells) that will release histamines as an allergic response when foreign irritants
are encountered. This causes an increase in fluid discharge from the sinuses.
B) Pharynx: this is the common passageway for air and food.
C) Epiglottis: this is a flap of tissue that covers the top of the trachea when
swallowing to ensure that food enters the esophagus and not the lungs.
D) Larynx: when the epiglottis is opened, the air is able to pass through the larynx
(voice box) and into the trachea. The larynx contains the vocal cords (two tendons that
adjust the pitch of sounds according to how taut they are).
E) Trachea: the windpipe. This passageway is held
open by the presence of C-shaped rings of cartilage.
This is a protective adaptation. The trachea
conducts air into the bronchi.
F) Bronchi: two major divisions of the trachea
leading to the lungs. These branches also have
cartilage around them, and for the same reason.
The bronchi conducts air into smaller branching
passageways called bronchioles.
G) Bronchioles: The bronchioles are branching
passageways that carry air to its ultimate
destination, the alveoli.
H) Alveoli: these are the blind sac-like endings at the end of
the bronchioles. There are approximately 300 million alveoli
in each human lung. This is the site of O2/CO2 exchange.
Only about 0.2 µm separate the alveoli from the capillaries as
both have very thin walls.
Alveoli are specialized in a number of ways:
1. They are very numerous. The average adult lung contains millions of alveoli. This
provides a great surface area for diffusion of gases.
2. They are very thin-walled. Alveolar walls are only one cell thick. This also aids
gas diffusion.
3. They are supplied with stretch receptors. These are nerve endings that are sensitive
to stretch. During inhalation, these signal when the alveoli are full enough
(stretched). This marks the onset of exhalation.
4. The alveoli have a coating of LIPOPROTEINS (surfactant) on their inner surface.
This helps to maintain surface tension, thus preventing them from collapsing and
sticking together during exhalation.
5. The alveoli are kept moist. This ensures gas exchange is possible. If they dried
out, efficient diffusion would be impossible.
6. The alveolar surfaces have a very rich blood supply from the pulmonary capillaries,
to ensure maximum diffusion of gases.
Three things that make the lungs very efficient at gas exchange
1. Huge surface area
2. Only 2 cell layers separate air in lungs from the blood
3. Moist
I) Diaphragm: a sheet of muscle that separates the chest cavity from the abdominal
cavity.
J) RIBS: bones hinged to the vertebral column and sternum, which
with muscle, define the top and sides of the chest cavity.
K) PLEURAL MEMBRANES: membranes that enclose the lungs.
The outer pleural membrane sticks closely to the walls of the chest
and the diaphragm. The inner pleural membrane is stuck to the
lungs. The two lie very close to each other.
The pressure
between the two membranes is less
that outside air pressure (or else the
lungs would collapse). These
membranes stick the lungs to the
chest cavity walls.
II. Mechanics of Inhalation and Exhalation:
A) INHALATION:
Our control of the breathing process is only voluntary to a point. The medulla
oblongata of the brain is sensitive to
the concentration of carbon dioxide
and hydrogen ions in the blood.
Both of these are products of cellular
metabolism and both need to be
excreted. As CO2 accumulates in the
blood, it means that you’re not
breathing fast enough, and therefore,
are not getting enough oxygen.
When the concentrations of H+ and
CO2 reach a critical level, the
breathing center in the medulla
oblongata is stimulated and sends
nerve impulses to the diaphragm and
the intercostal muscles (that lie between the ribs) to initiate their contraction.
When these muscles contract, the diaphragm
moves down and the rib cage moves up and
out.
This increases the volume of the thoracic
cavity and creates a negative pressure,
which causes air to be drawn in to the lungs
through the trachea. The air is sucked in!
The surface of the lungs is covered with a pleural membrane, as is the inside of the thoracic
cavity.
1. It allows the surface of the lungs to slide over
the body wall easily, without abrasion.
a. It seals off the thoracic cavity, so when the
lungs inflate a negative air pressure is created
and the air rushes in.
b. It also keeps the lungs from collapsing, as the
lungs are ‘stuck’ by the cohesion of water to
the thoracic cavity by the pleural membranes
(like two ‘wet plates’ stuck together).
A puncture to the chest wall, piercing the pleural membrane (even without damaging
the lung itself), will result in a pneumothorax, or collapse of the lung. In a situation
like this, the negative pressure effectively draws air in through the puncture wound,
putting pressure on the surface of the lung instead of inside it and the lung collapses.
B) EXHALATION
When the stretch receptors detect that the alveoli are stretched open enough, they
respond by signaling the medulla to stop the contraction of the diaphragm and
intercostals muscles.
When the diaphragm relaxes,
it bows upwards. When the
rib muscles relax, the rib
cages moves in and down.
The combined effect of these
actions is to put pressure on
the expanded thoracic cavity.
The thoracic cavity therefore
relaxes and gets smaller, and
this causes the outward
movement of air – exhalation.
The air is ‘forced out’.
*The aortic arch and carotid arteries also contain chemoreceptors that are sensitive to the
oxygen content in the blood. If it is critically low, they will help initiate the inhalation
response. Note, however, that this is a secondary mechanism. The primary mechanism
that triggers inhalation is still an elevated concentration of carbon dioxide and
hydrogen ions.
C) LUNG VOLUMES
1. Tidal Volume: the normal volume of air you breathe in and out at rest.
2. Inspiratory reserve: the maximum air you can inhale after the tidal volume.
3. Expiratory Reserve: the maximum amount of air you can exhale after exhaling
your tidal volume.
4. Vital Capicity: the maximum air you can inhale and exhale (Tidal volume plus
inspiratory and expiratory reserves).
5. Residual air: the air in the lungs that cannot be exhaled.
III. Conditioning of Inhaled Air:
Several things happen to the air on its journey into the alveoli. The air is:
1. Cleansed of debris in a 2 part process. The initial cleaning is by the nose hairs and
mucous in the nasal passageways. The second part of the process occurs in the trachea
and bronchi which are both lined with mucous and cilia. Any material other than the
gases of the inhaled air will get caught in the mucous. The cilia (microscopic protein
filaments) are in constant motion, beating the debris-laden mucous up towards the
pharynx. When this material is detected at the back of the mouth, it is swallowed or
coughed up and expectorated (spit out). *Note: cilia do not filter!
2. Adjusted to body temperature (~37 degrees Celsius). The more contact the air has
with moist tissues at 37o C, the closer the temperature of the inhaled air gets to body
temperature. By the time the air arrives at the alveoli there is no difference in its
temperature than that of the surrounding tissues.
3. Adjusted to 100% humidity. The air in the lungs is saturated with water. One of the
things that happens to inhaled air is that as it passes over the mucous passageways, it
becomes saturated with water.
Respiratory System: Part 2
IV. External and Internal Respiration:
 External respiration is the diffusion of oxygen into the pulmonary capillaries and the
diffusion of carbon dioxide (and the movement of some water) out into the air to be
exhaled.
Alveoli: Oxygen concentration is high (~20% of air)
Carbon dioxide concentration is low (~ 0.5% of air)
In the Blood: Oxygen concentration is low (has been ‘used’ to make ATP)
Carbon dioxide concentration is high (produced in tissues)
These gases diffuse down their concentration gradients from [H] to [L], so the
oxygen moves into the blood, and the carbon dioxide into the alveoli to be exhaled.
Conditions in the blood at the alveoli are:
 pH of ~7.4
 Temperature of ~37o C (relatively cooler)
 Relatively low pressure
Under these conditions, hemoglobin is not transporting
anything and is free to combine with oxygen. When the
blood leaves the alveoli, 99% of the bonding sites of
hemoglobin are occupied.
The combination of hemoglobin and oxygen is called
OXYHEMOGLOBIN (HbO2). Hemoglobin increases the
oxygen-carrying capacity of the blood between 65 and 70 times.
Each red blood cell has about 200-250 million hemoglobin
molecules. It is in this manner that oxygen is transported to the
tissues where internal respiration takes place.
Hb + O2
HbO2
 Internal respiration is the gas exchange that occurs at the tissues, as oxygen diffuses
into the tissue cells, and the waste product of cellular respiration, carbon dioxide,
diffuses back into the blood to be returned to the lungs.
In the Blood: Oxygen concentration is high (carried as HbO2) (before capillary fluid
exchange) Carbon dioxide concentration is low
Tissues: Oxygen concentration is low (always used up to make ATP)
Carbon dioxide concentration is high (produced as a waste product)
These gases diffuse down their concentration gradients from [H] to [L], so the
oxygen moves into the tissues, and the carbon dioxide into the blood to be taken to
the lungs and exhaled.
Conditions in the blood at the tissues are:
 pH of ~ 7.3 (relatively more acidic)
 Temperature of ~ 38oC (relatively warmer)
 Relatively high pressure
Under these conditions, hemoglobin readily releases the oxygen at the arteriole side of
capillary beds. The oxygen diffuses into the tissue spaces along with the water that is forced
from the plasma due to blood pressure. Once again, hemoglobin is free to transport.
HbO2
Hb
+
O2
At the venule side of the capillary bed, when water is drawn back into the blood by osmotic
pressure, carbon dioxide also enters the blood. Carbon dioxide can be transported in three
ways:
1. With these temperature and pH conditions, most of the CO2 reacts with water in the
plasma under the influence of the red blood cell enzyme CARBONIC ANHYDRASE
to be transported as bicarbonate ions.
Bicarbonate ion
Carbonic anhydrase
CO2 + H2O
Carbonic anhydrase
H2CO3
HCO3-
H+
+
 The products, bicarbonate ions and hydrogen ions, have different fates.
 Bicarbonate ions are one of the most widely recognized buffers in the
Hb
human body. They are transported freely in the blood plasma carrying
the CO2.
HHb
 In contrast, hydrogen ions would cause a decrease in the pH if
transported freely in plasma. As a result, they bond onto hemoglobin
and are transported as reduced hemoglobin (HHb). Because of this, hemoglobin is
often considered as a buffer in the blood as it counteracts an otherwise inevitable drop
in pH.
2. Some carbon dioxide bonds onto Hb itself and is transported as carbaminohemoglobin
(HbCO2).
Hb + CO2
HbCO2
3. The rest of the carbon dioxide (very little) it transported as a dissolved gas in the
plasma.
The deoxygenated blood arriving in the alveolar capillaries has the following
characteristics:
 It is transporting bicarbonate ions and a little carbon dioxide gas.
 The hemoglobin is transporting either CO2 or Hydrogen ions.
 Due to the conditions of the blood at the alveoli, (cold temperature, neutral pH, and
low pressure), two things occur:
1. The hemoglobin lets go of the CO2 and H+
HHb
Hb + H
HbCO2
Hb + CO2
2. The enzyme carbonic anhydrase catalyses the reverse reaction that it did before:
HCO3- + H+
H2CO3
CO2 + H2O
 At this point, all that is left to be excreted at the lungs is water and
CO2.
 The CO2 diffuses into the alveoli and is exhaled.
 The water will either:
1. Be exhaled in the air
2. Enter the alveoli to keep them moist
3. Remain in the plasma
EXHALED
 Once again, the chemoreceptors recognize the high level of CO2 in the blood, and this
triggers inhalation. And the process continues…
AT THE LUNGS
Relatively cooler temperature (37o)
Relatively more basic pH (7.4)
Relatively lower pressure
AT THE TISSUES
Relatively warmer temperature (38o)
Relatively more acidic pH (7.3)
Relatively higher pressure
O2 + glucose (C6H12O6)
CO2 + H2O + ATP Energy
V. Diseases of the Respiratory System: (FYI)
 Asthma narrows the airways by causing allergy-induced spasms of surrounding
muscles or by clogging the airways with mucus.
 Bronchitis is an inflammatory response that reduces airflow and is caused by
long-term exposure to irritants such as cigarette smoke, air pollutants, or allergens.
 Cystic fibrosis is a genetic defect that causes excessive mucus production that
clogs the airways.
 Although the automatic breathing regulation system allows you to breathe while you
sleep, it sometimes malfunctions. Apnea involves stoppage of breathing for as long as
10 seconds, in some individuals as often as 300 times per night. This failure to respond
to elevated blood levels of carbon dioxide may result from viral infections of the brain,
tumors, or it may develop spontaneously. A malfunction of the breathing centers in
newborns may result in SIDS (sudden infant death syndrome).
As altitude increases, atmospheric pressure decreases. Above 10,000 feet decreased oxygen
pressures causes loading of oxygen into hemoglobin to drop off, leading to lowered oxygen
levels in the blood. The result can be mountain sickness (nausea and loss of appetite).
Mountain sickness does not result from oxygen starvation but rather from the loss of carbon
dioxide due to increased breathing in order to obtain more oxygen.