Lecture 16: Ventilation and Gas Exchange in Animals

Question 1

What are the 3 key characteristics of an efficient gas exchange surface?

Answer 1

1. large surface area (branching, projections, etc)
2. thin
3. moist (diffusion is faster if gas is dissolved in a thin film of water)

Question 2

Define ventilation. What is its role in facilitating gas exchange?

Answer 2

the movement of respiratory medium (air or water) across a respiratory surface.

aka, the way the air or water gets into and over the gas exchange surface.

Question 3

How does gas exchange occur in cnidarians? How does it relate to its environment and method of locomotion?

Answer 3

Respiratory surface: their body walls, inside and out

Medium: the surrounding water

Cnidaria are either sessile, floating or energy-efficient swimmers, so they do not need a complex respiratory system. Gasses exchange directly between water and the cells of their body surface and gastrovascular cavity lining.

Question 4

How does gas exchange occur in platyhelminthes? Include respiratory surface and medium?How does it relate to its environment and method of locomotion?

Answer 4

Respiratory surface: their body walls, inside and out

medium: the surrounding water

Flatworms are only a few cell layers thick with fluid filled gastrovascular cavities. gasses exchange directly with water environment or host fluids (for parasites)

Question 5

How does gas exchange occur in insects? Include respiratory surface and medium? How does it relate to its environment and method of locomotion?

Answer 5

Insects have a tracheal system.
Respiratory surface: Tracheae

Medium: air, terrestrial animals.

the tracheae are air-filled tubes that branch throughout the insect body and open to the external environment at various points. O2 and CO2 can rapidly diffuse through the entire body. If the insect is larger, they have a series of air sacks to ventilate throughout the body.

A very efficient system, which makes sense for an animal that is very active and has a high metabolism rate.
Especially in insects that fly (high energy use) - flying insects ventilate air sacs using flight muscles (movement of wings)

1. air diffuses into trachea through openings along the exoskeleton called SPIRACLES
2. gasses exchange directly between fine branches of trachea and body cells
   OR
   larger insects can use muscle contractions (expand) to inflate their air sacs by pulling air in (with negative pressure) and (contract) pushing air out (with positive pressure) through the spiracles along the side of the exoskeleton.

Question 6

How does gas exchange occur in amphibians? Include respiratory surface and medium? How does it relate to its environment and method of locomotion?

Answer 6

Tadpoles have gills for breathing in water, as individuals mature, they lose gills and develop lungs.

respiratory surface tadpoles: gills; medium: water

Respiratory surface in adults: lungs, skin, and lining of oral cavity.
medium in adults: air

Adult amphibians on land conduct most gas exchange across their skin (because it is always moist) and across the lining of their mouths.

Lungs used for respiration while on land, gas exchange occurs in alveoli.

POSITIVE PRESSURE BREATHING VIA LUNGS:
Inhalation:
1. glottis closed, mouth closed, nostrils open
2. mouth cavity expands by dropping to the floor, creating negative pressure inside the mouth and pulling air in through nostrils
3. nostrils close, glottis opens, mouth cavity contracts and becomes smaller to push air into the lungs

exhalation:
1. mouth cavity expands and drops to floor, creating negative pressure and pulling air out of the lungs
2. lungs contract
3. glottis closes, nostrils open and mouth cavity contracts to push air out of mouth.

Question 7

How does gas exchange occur in mammals? Include respiratory surface and medium? How does it relate to its environment and method of locomotion?

Answer 7

respiratory surface: alveoli
Respiratory medium: air

1. air enters through the nostrils and passes through nasal cavity, pharynx, larynx and into the TRACHEA
2. Trachea branches into 2 BRONCHI, 1 leading to each lung
3. Bronchi divide increasingly into fine tubes called BRANCHIOLES
4. Branchioles terminate in thin air sacs, ALVEOLI, that inflate when air enters and deflate when air exits
5. Alveoli are the gas exchange sites
   - O2 and CO2 diffuse down their concentration gradients between the air inside the alveoli and blood inside the capillaries

Question 8

How does gas exchange occur in birds? Include respiratory surface and medium? How does it relate to its environment and method of locomotion?

Answer 8

Respiratory surface: Parabronchi in lungs
Medium: air

Birds have 8 or 9 air sacs located above and below their lungs to move air through the parabronchi.
The air sacs are NOT respiratory surfaces, they just expand and contract to bring air in and out of the bird body.

Birds use two cycles of breath and the air flows in ONE direction.

First inhale:
- air sacs below lungs expand creating negative pressure and bringing air in

First exhale:
- air sacs contract to push air into the lungs

second inhale:
- second set of air sacs expand and pull air out of the lungs from the top

second exhale:
- second set of air sacs contracts and push air out of the bronchus and trachea, pushing it out of the body

rapid diffusion of O2 into the blood stream makes sense for animals that are extremely active and expend a lot of energy in flight. As well, there is less O2 availability at higher altitudes

Question 9

How does gas exchange occur in fish? explain the countercurrent mechanism. How does it relate to its environment and method of locomotion?

Answer 9

Respiratory surface: gills
Medium: water

O2 dissolved in water flows across gills and diffuses into blood vessels

*Water flows countercurrent to the blood in the capillaries in order to maximize contact with fresh water that has a higher [O2] and ensures a steep concentration gradient all the way across the capillary.
1. low [O2] blood enters the capillaries on the right
2. high [O2] water enters on the left and passes over capillaries
= O2 will rapidly diffuse into the capillary all the way down the capillary as the water flows in the opposite direction of the blood. this ensures a steep concentration gradient and efficient diffusion.

Question 10

Define negative pressure breathing

Answer 10

When muscles expand and create a larger space, air is PULLED in because air moves from areas of high to low pressure

Question 11

Define positive pressure breathing

Answer 11

When muscles contract and create a smaller space, air is PUSHED out of that area because air moves from high to low pressures.

Question 12

How does human ventilation compare to frogs? include use of N. Pressure breathing & P. pressure breathing.

Answer 12

Similarity: While both humans and adult frogs use their lungs as a respiratory surface for the same respiratory medium, air, frog ventilation through lungs is much more limiting than in humans.

Differences:

1. Frogs have fewer alveoli with less surface area compared to mammal lungs because while on land, they can also conduct gas exchange across their skin and mouth lining, which humans cannot.
2. Frogs also do not have ribs or diaphragms to create the negative pressure to pull air into their lungs like humans do, so instead they PUMP air from their mouths into their lungs using POSITIVE PRESSURE.
3. Humans breathe through negative pressure (chest expands and creates space to pull air into lungs), whereas frogs force air into their lungs using positive pressure (pulling air into mouth and forcing it into lungs).

Question 13

Describe the location, structure, and function of the parts of the human respiratory system

Answer 13

• nostrils allow air to enter system
• pharynx, larynx, and trachea direct air to the lungs
• trachea branches into two bronchi (one for each lung)
• bronchi branch into increasingly smaller tubes called branchioles
• bronchioles end in the alveoli
• alveoli are covered in capillary nets where gas exchange occurs

Question 14

Describe and explain the reciprocal exchange of gases between the alveoli and the blood and between the blood and body cells in humans

Answer 14

O2 will diffuse down its concentration gradient from inside the air in the alveoli (high [O2]) into the the blood in the capillaries (low [O2]).

CO2 will diffuse down its concentration gradient from the blood in the capillaries (high[CO2]) into the air in the alveoli (low [CO2]).

Question 15

describe how O2 is transported in human blood

Answer 15

O2 moves down its concentration gradient into the blood (from the alveoli) and binds to hemoglobin molecules of red blood cells in the capillaries of the lungs where it is transported to body cells that require O2.

Question 16

T or F: if an animal uses lungs for gas exchange, it also requires a circulatory system. Why/why not?

Answer 16

TRUE because lungs are not in contact with the entire body, they are centralized, so the gases need to be transported to other body cells because ALL LIVING CELLS CONDUCT CELLULAR RESPIRATION

Question 17

T or F: lungs expand and contract on their own? why/why not?

Answer 17

FALSE. Lungs do not expand and contract on their own because they are very thin structures that DO NOT HAVE MUSCLES

Question 18

How do lungs expand and contract?

Answer 18

Lungs do not have muscles, so the diaphragm and the muscles around the ribs expand and contract to pull in and push out air.

Question 19

Describe lungs

Answer 19

elastic air-filled tubes (respiratory organ) that are not in contact with the entire body, but are contained in one centralized location

Question 20

How do lungs expand and contract?

Answer 20

Lungs do not have muscles, so the diaphragm and the muscles around the ribs expand and contract to pull in and push out air.

Question 21

what is the thoracic cavity?

Answer 21

the chest

Question 22

Describe alveoli

Answer 22

Alveoli are the gas exchange sites in mammal lungs. They have a ton of surface area and are wrapped in capillaries that form nets and that is where gas exchange occurs

Question 23

What are capillaries?

Answer 23

fine blood vessels that do gas exchange with alveoli

where oxygen is being taken up or unloaded

Question 24

When mammals/humans inhale, is [O2] higher in or outside of the alveoli than in the capillaries?
How about [CO2]?

Answer 24

When mammals inhale, [O2] is higher in the air inside the alveoli than it is in the blood inside the capillaries.

When mammals inhale, [CO2] is higher in the blood inside the capillaries than it is in the air inside the alveoli

Question 25

When mammals/humans exhale, is [O2] higher inside or outside the alveoli than in the blood in the capillaries?
How about [CO2]?

Answer 25

When mammals exhale, [O2] is higher in the blood in the capillaries than in the air in the alveoli.

When mammals exhale, [CO2] is higher in the air in the alveoli than in the blood in the capillaries

Question 26

Describe the 3 ways CO2 is transported in human blood

Answer 26

1. Some CO2 will dissolve into the blood plasma
2. Most CO2 will react with water to form Bicarbonate (HCO3) which will then dissolve into the blood plasma
3. Some of the HCO3 will bind to hemoglobin and travel inside red blood cells to the lungs and get converted back into CO2.

Question 27

T or F: fresh inhaled air has high concentration of O2 and low concentration of CO2.

Answer 27

TRUE

Question 28

Describe the structure of lungs. How does this explain how air moves into and out of lungs?

Answer 28

Lungs are surrounded by a double membrane: the inner membrane layer adheres to the lungs; the outer membrane layer adheres to the thoracic cavity (chest cavity).
the membranes stick together because of the surface tension of the fluid between them.

This is why when the muscles surrounding the lungs contract and the thoracic cavity expands, it pulls to the outer layer which pulls on the inner layer which pulls the lungs open to accept air.

Question 29

Describe the mechanics of mammal ventilation

Answer 29

Inhalation:

• rib muscles contract, thoracic cavity expands
• diaphragm contracts and moves down to create more volume in thoracic cavity
• NEGATIVE PRESSURE pulls air in (air moves from high to low pressures)

Exhalation:

• rib muscles relax
• diaphragm relaxes
• less space in thoracic cavity pushes air out of the lungs

Question 30

T or F: Birds do not have alveoli

Answer 30

TRUE

Question 31

What do birds have instead of alveoli?

Answer 31

Small tubes within their lungs called PARABRONCHI

Question 32

Describe the structure of parabronchi in birds?

Answer 32

They are the gas exchange surface in birds

they are not elastic, so their lungs cannot expand or contract

Question 33

How many directions does air flow in birds?

Answer 33

Air flows in ONE direction through parabronchi

Question 34

How many directions does air flow in mammals?

Answer 34

two directional

Question 35

How many cycles of breath does it take for air to pass through a bird respiratory system?

Answer 35

TWO

Question 36

What is the advantage of having a one way gas exchange system? Which animals have this?

Answer 36

Gas exchange will occur very quickly because there is steep concentration gradients because there is only fresh air circulating.

Question 37

T or F: diffusion efficiency depends on the concentration gradient. why/why not?

Answer 37

TRUE.
Birds have an extremely efficient respiratory system because there is a steep concentration gradient through their unidirectional air flow.

Whereas, mammal lungs have two-way air flow so the fresh air in the alveoli, mixes with the used air that is lower in O2, which reduces the concentration gradient

Question 38

What is the advantage of having a one way gas exchange system? Which animals have this?

Answer 38

Gas exchange will occur very quickly because there is steep concentration gradients because there is only fresh air circulating.

In the parabronchi, one-way air flow ensures all the used/low [O2] air is flushed out of the system before the next inhalation.
This ensures there is always a steep concentration gradient for O2 to diffuse into blood more rapidly.

Question 39

Is breathing in fish more similar to birds or humans? why?

Answer 39

Birds, because in fish, the air flow is unidirectional, which means that there is a steep concentration gradient for O2 to diffuse into the blood stream.

Question 40

Which has a higher density: water or air? And therefore, which is harder to do gas exchange in?

Answer 40

Water has a much higher density and is much harder to conduct gas exchange in. Much more energy is required to do gas exchange in water.