Lecture 6: Respiratory Systems

Question 1

Partial Pressures of Gases

partial pressure of a gas

Answer 1

pressure that a particular gas exerts when it is in a gas mixture.

Excluding trace gases, the gaseous composition of air on earth is below.

Composition of Air

79. 04 % Nitrogen
80. 93 % Oxygen
81. 03 % Carbon Dioxide

Question 2

Partial Pressures of Gases

air pressure (atmospheric pressure)

Answer 2

is the sum of the partial pressures of all of the gases within
the air plus the partial pressure of water vapour (in the case that relative humidity is anything other
than 0%).

P of air = PN2 + PO2 + PCO2 + PH20

Question 3

Partial Pressures of Gases
At sea level, the atmospheric pressure (with a relative humidity of 0%) is ____

Therefore, in order to calculate the partial pressure of any given gas, you multiply the
atmospheric pressure by the fractional concentration of a particular gas. For example, air is 79%
nitrogen so the fractional concentration of N2 is 0.79.

Answer 3

760 mmHg (millimeters of 
mercury).

PN2 = 0.7904 (760 mmHg) = 601 mmHg 
PO2 = 0.2093 (760 mmHg) = 159 mmHg 
PCO2 = 0.0003 (760 mmHg) = 0.23 mmHg = 0 mmHg

Question 4

Hypoxia

Answer 4

Decreased inspired O2 (PIO2)

Question 5

Hyperoxia

Answer 5

Increased inspired O2

Question 6

Normoxia

Answer 6

Normal inspired O2

Question 7

Increased inspired CO2 (PICO2)

Answer 7

Hypercapnia

Question 8

Decreased inspired CO2

Answer 8

Hypocapnia:

Question 9

Normal inspired CO2

Answer 9

Normocapnia

Question 10

Air versus Water

Air has ____ more oxygen than water.

• Oxygen diffuses _____ faster in air than in water.

• Water breathers need to move more water over their gills than air breathers need to move air over
their lungs in order to extract the same amount of oxygen.

Answer 10

• Air has 30X more oxygen than water.
• Oxygen diffuses 10 000X faster in air than in water.
• Water breathers need to move more water over their gills than air breathers need to move air over
their lungs in order to extract the same amount of oxygen.

Question 11

Air versus Water

• Water is ____ denser than air.
• Water is ____ more viscous than air.
• More energy is required to move water than air over a respiratory surface.

Answer 11

Water is 1000X denser than air.
• Water is 50X more viscous than air.
• More energy is required to move water than air over a respiratory surface.

Question 12

General Forms of Respiratory Organs

There are numerous forms of gas exchange organs.

The most common are ____ although
there are numerous other forms of respiratory (gas exchange) organs used by some air-breathing fish.
Some animals also exchange gases across their skin.

Answer 12

lungs and gills

Lungs are always internal to an animal while gills can either be internal or external.

Question 13

General Forms of Respiratory Organs

Ventilation of a gas exchange organ can either be active or passive.

_____ involves using
muscular contraction to move either air or water across the respiratory exchange surface.

_____ involves diffusion of gases across a respiratory surface with no active movement of water or air.

Answer 13

Active ventilation

Passive ventilation

Lungs and internal gills are actively ventilated while external gills are passively ventilated (i.e.,
they just “flap around” in the water.

Question 14

General Forms of Respiratory Organs

involves moving the respiratory medium in and out of a respiratory organ.

For
example, in the mammalian lung, air goes in and comes out along the same pathway.

Answer 14

Tidal ventilation

Question 15

General Forms of Respiratory Organs

involves moving the respiratory medium in one direction only.

For example, water moves
across the fish gill in a unidirectional manner. It moves in through the mouth and out across the
operculum (see gill structure below). Air flow through the bird lung is also unidirectional; it “loops
around” in a circuit (although it does exit through the same point as it entered).

Answer 15

Unidirectional ventilation

Question 16

General Forms of Respiratory Organs

occurs with external gills that are “free-floating” in the respiratory media (i.e., water).

Answer 16

Non-directional ventilation

Question 17

External Gills

such as those seen in tadpoles and axolotols protrude from the side of the animal.

Ventilation is _____ (active/passive) and _____ (non-directional/uni-directional)

Answer 17

generally passive and non-directional

Oxygen diffuses from the water, across the gills
into the blood. CO2 diffuses from the blood, across the gills and into the water.

Question 18

Internal Gills: Aquatic Invertebrates

Squid gills sit within the mantle cavity.

Water is moved across these gills in a ____ when the animal is moving.

Water is sucked into the mantle cavity through an opening at the bottom of the cavity.

Muscular contraction of the mantle cavity closes off this intake opening and causes the water to
be forcefully ejected through a funnel.

This serves to both ventilate the gills and propel the animal forward (its caudal end moves ahead of its rostral (head) end).

Answer 18

tidal manner

Question 19

Internal Gills: Aquatic Invertabrates

Gills in decapod crustaceans such as lobsters arise from the base of the legs and protrude upward under the shell (carapace).

A muscular structure called _____ pumps water forward through the carapace. Water is drawn in from the back and expelled out of the front. This flow of water serves to
ventilate the gills.

Answer 19

scaphognathite

Question 20

Internal Gills: Fish

Fish gills are internal. They sit under a body (or cartilaginous) flap of tissue called the ______.

Water enters through the mouth into the buccal cavity. Water then flows across the gills into the
opercular cavity and exits via the gill slit (or opercular opening).

Answer 20

operculum

Question 21

Internal Gills: Fish

In most fish there are ____ sets of gills on each side of the fish.

The main structure of the gills is the ____.

Coming off each gill arch are two sets of ______.

On all gill filaments there are structures
called ______ with are oriented perpendicular to the gill filament. There are blood vessels that carry deoxygenated blood to the gills and into the gill arches.

Blood then enters the gill filaments,
flows across the secondary lamellae and collects on the opposite side of the filament before returning to a vessel within the arch.

Answer 21

In most fish there are {4 sets of gills} on each side of the fish.

The main structure of the gills is the {gill arch}.

Coming off each gill arch are two sets of {gill filaments}.

On all gill filaments there are structures
called {secondary lamellae} with are oriented perpendicular to the gill filament.

There are blood vessels that carry deoxygenated blood to the gills and into the gill arches.

Blood then enters the gill filaments,
flows across the secondary lamellae and collects on the opposite side of the filament before returning to a vessel within the arch.

Question 22

Internal Gills: Fish

Water flows between the _____.

The direction of water flow between the secondary
lamellae is OPPOSITE to the direction of blood flow within the secondary lamellae.

The lamellae are the site of gas exchange and the mode of gas exchange is referred to as _____
because the water and blood move in opposite directions. This is an extremely efficient arrangement for
gas exchange to occur.

Answer 22

secondary lamellae

countercurrent gas exchange

Question 23

Internal Gills: Fish

As deoxygenated blood enters the secondary lamellae, it encounters oxygenated water flowing across the outside of the lamellae.

Oxygen diffuses across the lamellae into the blood and carbon dioxide diffuses from the blood, across the lamellae and into the water. Oxygenated blood leaves the secondary lamellae and enters a blood vessel in the filament before moving into the vessel in the gill arch.

Answer 23

Review!

Question 24

Countercurrent Gas Exchange in the Fish Gill

Gas exchange in the fish gill is referred to as countercurrent gas exchange.

The reason for this is that the direction of water flow between the secondary lamellae is opposite to the direction of blood flow within the secondary lamellae.

Answer 24

In the example below, water enters the channels between the secondary lamellae with a partial pressure value of 100 (these are arbitrary units).

Blood enters the secondary
lamellae with a partial pressure value of 0 (again; arbitrary units). As water flows between the
secondary lamellae, it “gives up” oxygen to the blood.

As a result, the oxygen level continually
decreases as the water flows along the length of the channel between the secondary lamellae. As blood flows through the secondary lamellae, it is “picking up” oxygen from the water and therefore the blood oxygen levels increase as it proceeds to flow through the secondary lamellae.

Question 25

Countercurrent Gas Exchange in the Fish Gill

Countercurrent refers to the fact that the water and the blood are flowing alongside one
another in opposite directions. There is always exchange of oxygen from the water into the blood.
Compare this to the human lung (see later) in which there is not a constant gradient for oxygen
movement from the air in the lungs to the blood.

Answer 25

The diagram above illustrates that as blood flows through the secondary lamellae, it is constantly
encountering water than has a higher oxygen level than the blood. This means that there is always a
gradient for oxygen to diffuse from the water into the blood. The gradient exists because water enters
with high oxygen levels at one end while blood enters with low oxygen levels at the other end. As a
result of this, oxygen moves from the water to the blood along the entire length of the secondary
lamellae.

Question 26

Air-Breathing in Fish

Not all fish breathe water. Many fish breathe air. Some breath air all of the time and do not breathe
water. These fish are called _______

Answer 26

obligate air-breathers.

Question 27

Air-Breathing in Fish

Some fish breathe water when there is enough
oxygen in the water but switch to breathing air when the oxygen levels in the water are low (i.e., they are hypoxic). These fish are called _______.

Numerous structures and organs (termed
air-breathing organs) have developed to allow fish to breath air.

Answer 27

facultative air-breathers.

Question 28

Air-Breathing in Fish

Some fish use their _____ (also called an air bladder or buoyancy bladder) as an air-breathing
organ.

Answer 28

swimbladder

Air enters the swimbladder and oxygen diffuses across the swimbladder into the blood. 
Arapaima gigas (Piaruchu) is an obligate water-breather as a new-born, a facultative air-breather as juvenile and an obligate air-breather as an adult.

Some fish such as catfish and mudskippers exchange gases across their gut. They will swallow air and then oxygen diffuses across the gut into the blood.

Question 29

Facultative Air-Breathing in Mudskippers

Mudskippers are a good example of facultative air breathing fish.

They will breathe water when there is
sufficient oxygen in the water but switch to breathing air when water oxygen levels fall too low.

These animals can actually walk on land at which time they are breathing atmospheric air. The diagram below shows that mudskippers spend time in their burrows (dark bars) when the tide is in and the burrow entrance is covered with water. When the tide is out and the burrow entrance is open to air (white bars)
they will come out onto the mud flats and walk around on land. When they are in their burrows they
either breathe water (orange bars) or air that is stored in air pockets within the burrow (blue bars).
When they are out on land they breathe atmospheric air (pink bars).

Answer 29

Review!

Question 30

Facultative Air-Breathing in Mudskippers

When the burrow entrance is covered with water, they start out breathing water. However, as they do
so, the level of oxygen (partial pressure of oxygen; PO2) within the water in the burrow decreases (blue
dots). When the oxygen level in the water falls to low, they begin to breathe the air that is stored in the
air pockets (orange dotted line; air-breathing threshold). Once the tide goes out and the burrow entrance
is open to the air, they move onto the mud flats and breathe air from the atmosphere.

Answer 30

Review

Question 31

Lungfish Lungs

From an evolutionary perspective, lungfish are the first animals to have _____.

Their lungs are
sub-divided into numerous compartments which increase the surface area available for gas exchange
between the air in the lung compartments and the blood that flows through capillaries within the lungs.
Lungfish lungs are much more complex (in terms of being subdivided into compartments) than are
amphibian lungs but they are much less complex than mammalian lungs. They resemble reptilian lungs
(see below).

Answer 31

“true lungs”

Question 32

Amphibian Lungs

Amphibians have very simple lungs; they are basically _____ with no subdivisions into smaller
compartments.

There are a few ridges or partitions on the inner wall but these are very small and really
don’t do anything to increase the surface area of the lung. It is quite unlike the mammalian lung which is subdivided into many small alveoli with the subdivisions being so small that the mammalian lung, in cross section, appears to be a solid mass.

Amphibians have no trachea (see below for the human lung).

The lungs are directly connected to the mouth via a muscular opening called the _____

Answer 32

“bags-of-air”

glottis.

Question 33

The Mechanics of Breathing in Amphibians

Amphibian breathing involves:

Answer 33

NBGL (not big girl lungs)

1) The nostrils (or nares)
2) the buccal cavity (or mouth)
3) the glottis (the opening to the lungs)
4) the lungs.

Question 34

The Mechanics of Breathing in Amphibians

1. In the first phase of a breathing cycle, the nares are open and the glottis is closed. The floor of the
   buccal cavity is lowered and this causes air to flow from the external environment, through the open
   nares and into the lower region of the mouth.
2. In the second phase, the glottis opens and air that was previously being held in the lungs exits the
   lungs via the glottis, flows across the upper regions of the mouth and leaves the animal via the open
   nares.
3. In the third phase, the nares close and the floor of the buccal cavity is raised. This causes air to be
   pumped from the bottom regions of the buccal cavity, through the open glottis and into the lungs. This
   type of breathing mechanism is therefore called a buccal force pump.
4. In the fourth phase, the glottis closes trapping air in the lungs and the nares open.

Answer 34

Review!

Question 35

Reptilian Lungs and Breathing

Reptilian lungs are more complex than amphibian lungs. While they are still no where near as complex as a mammalian lung, we do begin to see numerous subdivisions into smaller chambers. The purpose of subdividing a lung into smaller and smaller chambers is to increase the surface area available for gas exchange. They are similar to lungfish lungs in complexity.

Answer 35

Subdivisions and more complexity

Question 36

Reptilian Lungs and Breathing

Reptilian lungs are ______. Unlike the amphibian buccal force pump, in which muscular
contraction causes the floor of the buccal cavity to move up and “pump air into the lungs, in reptiles, a
negative pressure is developed which causes air flow in-and-out of the lungs.

i.e. In snakes, muscles compress the lungs during expiration. During inspiration the lungs passively expand
causing air to be sucked into them.

In lizards and crocodiles, muscles actively expand the lungs during inspiration and then the lungs recoil
back passively during expiration.

Answer 36

suction lungs

Question 37

Bird Lungs

Bird lungs are very different from amphibian, reptilian or mammalian lungs. They are more like
dinosaur lungs than lungs of any current extant species. The lungs are rigid and do not change in
volume when the animal inspires and expires.

Rather, there are a series of _____ that function as pumps or bellows that move the air through the lungs during the course of a respiratory cycle.

There are a series of anterior, posterior and thoracic air sacs. The thoracic air sacs can also be divided into anterior and posterior thoracic sacs.

Answer 37

air sacs

Question 38

Bird Lungs

Air enters through a trachea which becomes a primary bronchus. The lungs themselves consist of a series of tubes called bronchi.

Answer 38

Review!

Question 39

Bird Lungs

It takes _____ complete cycles of inspiration and expiration to move air through the lungs.

FIRST
In the first inspiration, air moves from the trachea into the posterior air sacs.

During the first expiration, air moves from the posterior air sacs into the lungs (the bronchi).

SECOND
During the second inspiration, air
moves from the lungs into the anterior air sacs.

Finally during the second expiration, air moves from the anterior air sacs, into the trachea and out into the atmosphere.

Answer 39

two

So, during any one inspiration, air moves from the trachea into the posterior air sacs and from the lungs
into the anterior air sacs.

During any one expiration, air moves from the posterior air sacs into the lungs and from the anterior air
sacs into the trachea (and then out of the animal).

Question 40

Bird Lungs

There are a series of air capillaries that branch off from the bronchi (labeled parabronchus in the
diagram below).

These air capillaries are the site of ___.

n the diagram below, air is flowing
through the bronchi (parabronchus) and air capillaries in the direction of bottom to top. The blood
vessels that supply the lungs have capillaries that run between an afferent blood vessel and an efferent
blood vessel. These capillaries run perpendicular to the direction of air flow in the bronchi and the air
capillaries. This arrangement gives rise to a type of gas exchange called crosscurrent gas exchange.

Answer 40

gas exchange

Question 41

Crosscurrent Gas Exchange

Crosscurrent gas exchange is

Answer 41

It shows the blood flowing in a
perpendicular orientation from the air flow in the bronchi / air capillaries. In this example, air enters the
lungs with a partial pressure value of 100. Blood enters the lung with a partial pressure value of zero.

These values are arbitrary for this example.

Question 42

Crosscurrent Gas Exchange

As air flows through the bronchi / air capillaries, oxygen diffuses from the air into the blood. This
causes oxygen levels in the air to decrease as it flows through the lungs. Blood entering at the start of
the lungs and moving upward through the initial perpendicular blood vessels encounters air with a
relatively high level of oxygen (i.e., around 100). This blood picks up oxygen and becomes relatively
well oxygenated (i.e., 89 and 77). Blood that flows through the perpendicular blood vessels further on
in the lung encounters air with progressively less-and-less oxygen in it (because the air has given up
oxygen to the capillaries near the start of the lungs; i.e., 74 and 48). Therefore the blood that leaves
these capillaries does not have as much oxygen (i.e., 65, 53 and 41) as blood leaving the capillaries at
the beginning of the lung.

When you “average” the levels of oxygen leaving all of the capillaries together at the end of the lung,
the final oxygen level in blood leaving the lung reflects the mixing of the blood that moved through all
of these capillaries. In this case the overall oxygen level in the blood leaving the lungs is 65.

Answer 42

Example!

Question 43

Crosscurrent Gas Exchange

Recall the countercurrent exchange earlier in the fish gill. In that case, blood left the gills with an
oxygen level of 75. Here, blood is leaving the bird lung (crosscurrent exchange) with an oxygen level
of 65. If you look below you will see that blood leaves the mammalian lung (concurrent gas exchange)
with an oxygen level of 52.

Therefore, in terms of gas exchange efficiency, the fish gill is ____ than
the bird lung which in turn is ____ than the mammalian lung

Answer 43

better, better

Question 44

The Mammalian / Human Lung

Mammals have a left and a right lung.

In humans, the left lung has ____ lobes and the right lung has ____ lobes.

The right lung is _____ than the left lung (due to the curvature of the diaphragm to
accommodate the liver) but the right lung is ____ than the left lung (due to the cardiac notch
which accommodates the left-side positioning of the heart).

Overall, left lung capacity is _____ than
right lung capacity.

Answer 44

2 lobes in left lung, 3 lobes in right

right lung is shorter and narrower than the left lung

capacity of left lung is greater than right lung

Question 45

The Mammalian / Human Lung

Air enters the mouth/nose and moves through the pharynx and the larynx before entering the trachea.
The glottis is the opening to the trachea. The epiglottis is the flap/valve that covers the glottis during
the swallowing reflex. It blocks the opening to the trachea and prevents food from entering the trachea
and the lungs. The trachea is relatively rigid; it is supported by rings of cartilage that helps prevent it
from collapsing. The trachea branches to form primary, secondary, tertiary, etc. bronchi. Ultimately
they form small bronchioles that terminate in alveolar sacs which are aggregates of alveoli. The
alveoli are the site of gas exchange (oxygen moving from the air in the alveoli into the blood and
carbon dioxide moving from the blood into the alveolar air).

Answer 45

air -> pharynx -> larynx -> trachea (glottis opening with epiglottis with covers the glottis during swallowing) -> bronchi -> alveli (site of gas exchange

Question 46

The lungs (and heart) are protected by the \_\_\_\_\_ which contains the ribs, sternum (breast bone), 
thoracic vertebrae as well as the internal and external intercostal muscles that sit between the ribs. 

The diaphragm is the primary respiratory muscle in mammals. It is a curved-shaped muscle that sits
below the lungs. The _____ is the “border” between the chest (thoracic cavity) and the
abdominal cavity.

Answer 46

chest wall (ribs, sternum/breast bone, and thoracic vertebrae, and internal and external intercostal muscles)

diaphragm is the border

Question 47

The Mammalian / Human Lung

During inspiration, the diaphragm _____(contract/relax) and moves _____ (down/in).

This causes the chest wall to
expand as the ribs move ____ (down/up) and (in/out).

This creates a ____ (positive/negative) pressure in the lungs that causes air to be drawn (sucked) from the atmosphere, into the lungs.

During expiration, the diaphragm _____(relax/contract) and the
chest moves _____(inward/outward) while the ribs move ____ (up/down) and inward.

The lungs contract and air moves out of the
lungs into the atmosphere.

Answer 47

During inspiration, the diaphragm CONTRACTS and moves DOWNWARD. This causes the chest wall to
EXPAND as the ribs move UP and OUT.

This creates a NEGATIVE pressure in the lungs that causes air to be drawn (sucked) from the atmosphere, into the lungs.

During expiration, the diaphragm RELAXES and the
chest moves INWARD while the ribs move DOWN and INWARD. The lungs contract and air moves out of the lungs into the atmosphere.

Question 48

Concurrent Gas Exchange

Air movement in and out of the mammalian lung is ____. Air moves through the same pathway on its
way in as it does on its way out.

Answer 48

tidal

Question 49

Concurrent Gas Exchange

Gas exchange in the mammalian lung is considered to be concurrent gas exchange. The easiest way to think of the anatomical arrangement of air and blood flow is to think of them flowing in the same direction through the lungs.

This is opposite to the countercurrent gas exchange in the fish gill in which
water and blood were flowing in opposite directions.

Answer 49

The diagrams below show that air enters the lung with an oxygen level of 100 while blood enters with
an oxygen level of zero. This means that the blood with no oxygen initially encounters the air with very
high levels of oxygen. At the beginning of the lung there is a very large gradient for oxygen to diffuse
from the lung gas into the blood. This means that oxygen levels in the air quickly decrease as oxygen is
given up to the blood, in which oxygen levels rapidly increase.

It doesn’t take long before the oxygen levels in the blood and air become very similar. In this case the
gradient for oxygen diffusion across the lung gets smaller and smaller as we progress from the start of
the lung to the end of the lung. Compare this to the countercurrent situation in fish where the gradient
for oxygen diffusion remained constant along the entire length of the gill. In this situation (the
mammalian lung), blood leaves the lung with an oxygen level of 48. This is vastly inferior to the gill
and bird lung in which final oxygen levels were 75 and 65 respectively.

Question 50

The Insect Tracheal System

Insects do not have lungs or gills. Instead, they have a series of ____ that penetrate from
the surface of the animal deep into the tissues (even penetrating directly into muscles).

The external
openings of this tracheal system are _____ . These are valves on the surface that open into the
trachea.

Oxygen diffuses from the atmosphere, through the trachea which ultimately branch into small
tracheoles just before coming in contact with internal tissues. Carbon dioxide leaves the animal via these tracheoles, trachea and spiracles.

Answer 50

tubes (or trachea)

spiracles

Question 51

The Insect Tracheal System

Just as many vertebrate species breathe ____, so to do insects with their tracheal system.
The trace below illustrates CO2 release from the spiracles.

There are periods when the spiracles are
completely closed and no carbon dioxide is leaving. This is the closed (C) phase. There are times when
the spiracles are open (O) and large amounts of CO2 are being released. There is also a flutter phase
(F) when there are small but continuous bursts of CO2 being released.

Answer 51

discontinuously