Chapter 15
Respiratory System
Parts of Respiratory System
• Nasal Cavity
• Pharynx
• Epiglottis  covers the opening to trachea during
swallowing
• Glottis  Opening under the epiglottis
• Larynx  Made of cartilage that contains the voice
box
• Trachea  Breathing tube in the front of neck. Has
cartilage rings that keeps it open
• Trachea branches into two tubes. One tube
goes to the right lung and the other tube goes
to the left lung. These tubes are called the
Bronchi (single is Bronchus).
• The Bronchi then branch into smaller tubes in
the lungs called the Bronchioles.
• The bronchioles end at little sacs called
Alveoli. It is at the alveoli that gas exchange
with the blood is done.
Alveoli
Which direction is the flow of blood?
More Parts of Respiration
• The lungs are in the Thoracic Cavity. The Rib
cage form the top and sides of the thoracic
cavity.
• The bottom of the thoracic cavity is
maintained by the diaphragm. This is a large
dome shaped muscle.
• The Lungs are encased by a membrane called
the Pleural Membrane. The pleural
membrane made up of two membranes.
Problems About Breathing
• This is the most common way for a person to
get germs into their body.
– So therefore the body filters the air before it
enters the lungs.
• Filtering Air
1. Air moves into nasal cavity and thick hairs,
mucus, and cilia.
2. Cilia cover the trachea and move things upward
• Cilia move dust, mucus, and food bits that
went down the breathing tubes up.
• When there is enough debris that has moved
up into the pharynx then it is either swallowed
or spat out.
• Air is warmed and made moist before it gets
too the lungs.
– It is warmed by the blood that moves through the
lungs
– Its is moistened by the wet surfaces of the
passages of the lungs.
So what do the Pleural Membranes
do?
• The pleural cavity has a slightly lower pressure
than the atmosphere.
• Why do the pleural membranes have a lower
pressure?
• Research it Page 290
• The lower pressure in the pleural membranes
create a lower pressure
• This lower pressure stops from lungs from
collapsing.
• A collapsed lung can not get any oxygen.
• If someone has an accident and gets their
pleural membrane broken then a common
thing to happen is a collapsing of a lung
How we breath
• There are two parts that are involved in
breathing
1. Breathing in  Inhalation  Inhale
2. Breathing out  Exhalation  Exhale
Inhalation
• Starts in the Brain in a place called the respiratory
centre in the Medulla oblongata
• There are special nerves that detect chemicals.
These nerves are called chemoreceptors.
• These particular chemoreceptors detect carbon
dioxide (CO2) and hydrogen ion (H+) levels.
• These chemoreceptors are located in in the carotid
arteries (carotid bodies) and are in the aorta (aortic
bodies)
• When carbon dioxide levels and hydrogen ions are at
high levels the chemoreceptors send a message to the
respiratory centre and the rate and depth of breathing
increases.
• The respiratory centre sends a message to the
diaphragm and the muscles of the rib cage.
• The diaphragm contracts and moves down  this
causes the thoracic cavity to increase size
• The rib muscles contract  the external intercostal
muscles contract and this causes the rib cage to
become wider and increases the size of the thoracic
cavity
• This increase in the thoracic cavity size and volume
creates negative pressure ( or a vacum) in the lungs and
air rushes in.  negative pressure because intrapleural
pressure is even less
Exhalation
• The respiratory centre stops sending nervous
signals  this causes the diaphragm and the rib
cage to relax and they return to their normal shapes
• They return to their normal shapes because of
elastic forces  the body pushing in on the lungs
• You can force extra air out if you contract the
internal intercostal muscles. This forces the ribs
cage to become smaller and forces the ‘guts’ to
push up against the diaphragm and therefore
pushes air out
• There are also stretch receptors in the lungs.
• When the lungs are breathing in the alveoli
have stretch receptors and if they get too big
then the respiratory centre stops sending its
signal
Two types of Respiration
1. External Respiration
– This refers to the exchange of gases between the
air in the alveoli and the blood
2. Internal Respiration
– This refers to the exchange of gases between the
blood and Tissues in the body
External Respiration
• The pressure of CO2 in the blood is higher
than that of the air. So CO2 moves from blood
to air.
• Most of the CO2 is carried as bicarbonate ions
(HCO3-)
• Carbonate ions combine with a hydrogen ion
to form hydrogen bicarbonate. This is then
turned into water and carbon dioxide
H+ + HCO3-  H2CO3  H2O + CO2
• This reaction is catalyzed by the enzyme
carbonic anhydrase
• Hemoglobin is carrying no oxygen and is
referred to as deoxyhemoglobin
• Oxygen concentrations are higher than that of
the blood in the lungs so there is a pressure
for oxygen to move into the blood
• Red blood cells take up the O2 and the
hemoglobin is referred to as oxyhemoglobin
Hb + O2  Hb + O2
Internal Respiration
• Oxyhemoglobin gives up its oxygen and it then
moves into tissues
Hb O2  Hb + O2
• Carbon dioxide diffuses into blood from the
tissues because of the pressure difference
• Hemoglobin takes up a small amount of CO2
• The Hemoglobin that takes up CO2 creates
carbaminohemoglobin
Hb + CO2  Carbaminohemoglobin
• Most of the CO2 is taken up by the water in
the plasma and it forms carbonic acid
CO2 + H2O  H2CO3  H+ + HCO3-