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UNIT 6 NOTES
THE RESPIRATORY SYSTEM
Respiration Flow Chart:
Nostrils/mouth → nasal cavity/oral cavity → pharynx → epiglottis → glottis → larynx → trachea → bronchi → bronchioles
→ alveolus
(alveolus & pulmonary capillaries → gas exchange of O2/CO2 occurs)
What is the difference between respiration and breathing?
} Respiration = breathing (inspiration & expiration), transport of gases in blood, and cellular respiration (ATP
production)
Pathway of Air:
} enters through nose via the nostrils & leads to two nasal cavities
} the nasal cavities function to:
1. Filter are via hair and mucus (99%)
All 3 used to protect the
2. Moisten air via mucus
delicate lungs
3. Warm air via capillaries
→warm, moist air results in better gas exchange
4. tear ducts, cranial sinuses and ears empty into the nasal cavities
Pharynx / Throat
• This is the common passageway for air and food
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.
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 (2 bands of elastic ligaments)
Trachea - Aka windpipe.
• held open by the presence of C-shaped rings of cartilage.
• Lined with cilia & mucous glands to trap & sweep out debris
• The trachea conducts air into the bronchi.
Bronchi
• The trachea splits into two bronchi (bronchus = singular)
• Each have cartilage rings and cilia
• Each bronchi branches into smaller passageways called bronchioles
Bronchioles
• Ciliated but no cartilaginous rings
• They carry air to its ultimate destination, the alveoli.
Alveoli - Singular = alveolus
• sac-like endings at the end of the bronchioles.
• site of gas exchange
Why are the alveoli so special??
1. NUMEROUS: Each adult lung contains millions of alveoli. This provides lots of surface area for the gases to
be exchanged.
2. THIN WALLS: walls of alveoli are only one cell thick.
3. STRETCH RECEPTORS: signal when the alveoli are full enough (stretched). They send a message to the
brain to start exhalation.
4. MOIST: They are very moist which helps with gas exchange.
5. VERY RICH BLOOD SUPPLY: many blood capillaries so oxygen and carbon dioxide can be exchanged
efficiently.
6. LINED WITH A LAYER OF LIPOPROTEINS on their inner surface which helps prevent them from collapsing
and sticking together during exhalation.
Diaphragm
• a dome-shaped muscle that separates the chest cavity from the abdominal cavity.
• When you inhale it moves down.
• When you exhale it moves up.
Ribs and Muscles
• Ribs are the bones that are connected to the vertebral column and sternum.
• There are INTERCOSTAL muscles located between the ribs, which help to move the ribs:
1. Up and out when we inhale.
2. Down and in when we exhale.
The Lungs
The lungs are suspended in the thoracic cavity which is an airtight space surrounded by the ribcage
– The right lung has 3 lobes
– The left lung has 2 lobes
Pleural Membranes
• These are double membranes that enclose the lungs.
• The outer pleural membrane sticks closely to the walls of the chest & the diaphragm.
• The inner pleural membrane is stuck to the lungs. The two lie very close to each other.
Ø The INTRAPLEURAL fluid, between the 2 membranes, allows the surface of the lungs to slide over
the body wall easily, without abrasion.
• The pleura seals off the thoracic cavity so when the lungs inflate, a negative air pressure is created and this
causes air to rush in.
• These membranes also hold the lungs to the chest cavity walls, so when the ribs move out, so do the lungs.
MECHANISMS OF BREATHING
Air always moves from an area of high pressure to low pressure (a pressure gradient)
MEDULLA OBLONGATA
• 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
+
• 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.
INHALATION aka inspiration or inspiring
• Is an active process: requires ATP
To Inhale:
• When the brain realizes there is too much CO2 in our blood, it sends a message to the intercostal muscles and
diaphragm to contract.
• The ribs move up and out, the diaphragm moves down/flattens.
• This creates more space in the lungs (negative air pressure)
• Atmospheric pressure is now greater than lung pressure and air rushes in to fill that space.
• This is called inhalation.
⇒ negative pressure breathing
EXHALATION aka expiration or expiring
• Passive process: no ATP needed
To Exhale:
• When the alveoli get too stretched (full of air), they send a message to the brain to stop inhaling.
• The brain stops sending a stimulatory message, therefore, all the muscles relax causing:
• ribs to move back down and in, &
• diaphragm resumes dome shape
• This decreases the amount of space in the lungs & the lungs recoil
• Lung pressure increases compared to atmospheric pressure (creating a pressure gradient) and the air is pushed
out.
• This is called exhalation.
CONTROL OF BREATHING:
Inhalation:
+
1. medulla oblongata, brain’s respiratory centre, has chemoreceptors that detect increases in CO2 and H levels
(NOT O2 levels)
+
∼ [H ] increases when [CO2] increases - Why?
+
∼ chemoreceptors directly detect a drop in blood pH ([H ]) along with an increase in [CO2]. This sends a
stimulatory message to the rib & diaphragm muscles to contract
• Response: this causes a decrease in the [H+] level→ so the medulla oblongata is
inactivated
2. Indirect response to O2: Chemoreceptors in the carotid bodies (carotid arteries) and aortic bodies (in aorta)
detect decreases in [O2] & provide an immediate increase in the rate & depth of breathing (hyperventilation).
Result? increase in the amount of CO2 exhale
Exhalation:
3. stretch receptors in the alveoli send an impulse to the medulla oblongata to stop the stimulatory contraction
messages
– Exhalation is caused by relaxing the diaphragm and intercostal muscles
– this ↓ thoracic volume, & ↑ lung air pressure)
RESPIRATORY SYSTEM:
• Respiration is the set of processes involved with the conduction of oxygen to the tissues and the removal of
the waste product CO2.
• There are four aspects to respiration:
1. Breathing: the inspiration and expiration of air.
2. External Respiration: gas exchange at the alveoli.
3. Internal Respiration: gas exchange at the tissues.
4. Cellular Respiration: mitochondria turning O2 and glucose into CO2, H2O and ATP energy.
EXTERNAL RESPIRATION:
• Happens at the lungs.
• This involves the diffusion of O2 into the pulmonary capillaries and the diffusion of CO2 and water into the alveoli to
be exhaled
} Because there is a lot of CO2 returning to the lungs, and not very much in the alveoli, the CO2 diffuses from
[High] to [Low] down its concentration gradient and moves into the alveoli to be breathed out.
} Because there is a lot of O2 in the fresh air in the alveoli, and not much in the deO2 blood, the oxygen
diffuses from [H] to [L] down its concentration gradient and into the blood.
Conditions in the blood at the alveoli are:
Basic: pH of ~ 7.4
Cool: ~ 37°C
Low (negative) pressure
• Under these conditions, hemoglobin lets go of CO2 and starts to love oxygen.
• As it leaves the lungs, 99% of the hemoglobin is occupied with oxygen. It is called oxyhemoglobin
O2 + Hb
HbO2
•
Hemoglobin transports oxygen to the tissue cells.
INTERNAL RESPIRATION:
• Happens at the tissues
• It is the diffusion of O2 into the tissue cells, and the diffusion of CO2 and water into the blood capillaries
• The CO2 is then returned to the heart and sent to the lungs to be removed during exhalation.
Conditions in the blood at the tissues are:
Acidic: pH of ~ 7.3
Warm: ~38°C
High pressure
+
• Under these conditions, hemoglobin lets go of O2 and starts to love CO2 and H .
HbO2
Hb + O2
• The oxygen diffuses into the tissue spaces along with the water that is forced from the plasma due to blood
pressure.
• At the venule end of the capillary bed, when water is drawn back into the blood by osmotic pressure, CO2
enters the blood.
• Carbon dioxide can be transported in three ways:
1. Dissolved gas in blood plasma,
2. Carbaminohemoglobin (HbCO2)
3. Bicarbonate ion (HCO3 )
• Because the hemoglobin now loves the CO2, they join to form carbaminohemoglobin
CO2 + Hb
•
•
HbCO2
CO2 also joins with water to make the bicarbonate ion.
There is an enzyme in the red blood cells called CARBONIC ANHYDRASE which catalyzes this reaction.
CO2 + H2O
Carbonic anhydrase
•
•
H2CO3
Carbonic anhydrase
HCO3
-
+
H
+
The extra hydrogen ion from the water is now free. This is BAD since it is ACIDIC and can eat through the
blood vessel walls.
So, hemoglobin acts as a buffer and joins with the hydrogen ion to form reduced hemoglobin.
+
H + Hb
HHb
EXTERNAL RESPIRATION:
+
• When the blood returns to the lungs, the conditions change again, and hemoglobin dumps CO2 and H & wants to
pick up O2 again.
.
•
So all of the reactions happen in reverse
HbCO2
CO2 + Hb
+
HHb
H + Hb
+
H + HCO3
H2CO3
CO2 + H2O
Carbonic anhydrase
•
•
•
Carbonic anhydrase
At this point, all that is left to be excreted at the lungs is water and CO2.
So 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 blood plasma