Lecture 17- Gas exchange in animals Flashcards
Factors which govern gas exchange, adaptations and human lungs (118 cards)
1
Q
What respiratory gasses must animals exchange?
A
Oxygen and carbon dioxide
2
Q
Why must oxygen be obtained by cells?
A
To produce ATP by cellular respiration
3
Q
By what means are respiratory gasses exchanged between internal body fluids of animals and the outside medium?
A
Diffusion
4
Q
How is the diffusion of respiratory gasses driven?
A
Concentration differences- diffusion is the random motion of molecules so net diffusion is always down its concentration gradient.
5
Q
How are the concentrations of gasses in gas mixtures expressed?
A
Partial pressures
6
Q
How is gas pressure measured?
A
A barometer-typically a glass tube closed at one end and filled with Mercury, inverted over a pool of Mercury with the open end under the surface of the mercury.
7
Q
What is the barometric pressure of the atmosphere at sea level?
A
760 mm Hg
8
Q
What is the partial pressure of oxygen at sea level?
A
20.9% 760 mm Hg = 159 mm Hg
9
Q
Why is the measuring the concentration of respiratory gasses in a liquid more complicated?
A
Another factor is involved- the solubility of the gas in the liquid
The actual amount of gas depends on the partial pressure in the gas phase as well as the solubility of that gas
10
Q
What does the diffusion of gas between the gaseous phase and the liquid phase depend on?
A
The partial pressures of the gas in the two phases
11
Q
By what law is gas diffusion described by?
A
Fick’s law of diffusion
12
Q
What is fick’s law?
A
Q=DA (P1-P2)/L Where Q is the rate of diffusion D= diffusion coefficient A= Cross sectional area P1 and P2= partial pressure L= length of diffusion pathway
13
Q
What is the diffusion coefficient?
A
A characteristic of the diffusing substance, the medium and the temperature
14
Q
What is the partial pressure gradient?
A
P1-P2/L
15
Q
Why is it easier to obtain oxygen from air then water?
A
- O2 concentration is higher in air then water
- Oxygen diffuses more rapidly in air
- More energy is required to move water over gas exchange surface than air (water is more dense and more viscous)
16
Q
What does the slow rate of diffusion of oxygen in water limit?
A
- The size and shape of species without internal systems for gas exchange
- The efficiency of oxygen distribution from gas exchange surfaces to the sites of cellular respiration in air-breathing animals
17
Q
How have some animals, such as invertebrates, adapted to maximize gaseous exchange without internal systems for distributing oxygen?
A
- Some are small
- Some have evolved to be flat and thin (large surface area)
- Some have bodies built around a central cavity, through which water circulates
18
Q
What environmental conditions can cause respiratory problems for aquatic animals?
A
High temperatures
19
Q
Why do aquatic animals have respiratory problems in warmer waters?
A
Most are ectotherms
As water temperature rises, body temperature rises
Metabolic rate rises
More oxygen is needed in warmer water
Warmer water does not hold as much dissolved gas
20
Q
What happens to the amount of available oxygen as altitude increases?
A
It decreases
21
Q
Why does available oxygen decrease at higher altitudes?
A
% oxygen remains the same (20.9)
Total amount of gas per unit volume decreases
PO2 decreases
22
Q
How is carbon dioxide lost?
A
Diffusion- the partial pressure of CO2 in the atmosphere is very slow, large concentration gradient
23
Q
How do external gills maximise gas exchange based on their surface area?
A
They are highly branched and folded extensions of the body surface that provide a large surface for gas exchange
24
Q
In what organisms are external gills found?
A
Larval amphibians, larvae of insect species
25
What are the disadvantages to external gills?
Vulnerable to damage, particularly from predators.
26
In what organisms are internal gills found?
Mollusks, arthropods, fishes
27
What are lungs?
Internal cavities for respiratory gas exchange with the air. They are highly divided to give a large surface area and they are elastic to be inflated and deflated
28
What are the most abundant air breathing invertebrates?
Insects
29
What gas exchange system do insects have?
A net work of air filled tubes called tracheae that branch through all tissues in the insects body
30
How is partial pressure gradients maximised across gas exchange surfaces?
- Minimise path length
- Ventilation
- Perfusion
31
What is ventilation and how does it maximise partial pressure gradients?
Actively moving the respiratory medium over the gas exchange surfaces (breathing) exposes those surfaces to regularly fresh respiratory medium containing maximum O2 concentrations and minimum CO2 concentrations
32
What is perfusion and how does it maximise partial pressure gradients?
Circulating blood over the internal side of the exchange surface transports CO2 to those surfaces and O2 away from those surfaces
33
What is an animals gas exchange system made up of?
Gas exchange surfaces and the mechanisms it uses to ventilate and perfuse those surfaces
34
How does respiratory gas diffuse to every cell in insects?
The tracheal system extends to all tissues in the insect body
35
How does the insect respiratory system communicate with the outside environment?
Gated openings called spiracles in the sides of the abdomen
36
Why do spiracles open and close?
Open to allow gas exchange
| Close to decrease water loss
37
Describe the branching of the tracheal system in insects.
Spiracles open into tubes called tracheae.
Tracheae branch into finer tubes- tracheoles
Tracheoles end in tiny air capillaries
38
What system do fish use to maximize gas exchange across their gills?
Countercurrent flow
39
Describe the structure of internal fish gills.
Gills are supported by gill arches that lie between the mouth cavity and protective opercular flaps on the sides of the fish behind the eyes
40
How does water flow into a fish mouths?
Unidirectionally,
| Through the fish's mouth, over the gills, out of the opercular flap
41
How is the partial pressure gradient maintained on the surface of fish gills?
Constant, one-way flow of water moving over gills maximises partial pressure of oxygen on external gill surfaces
42
How is the partial pressure gradient maintained within fish gills?
Circulation of blood minimises the partial pressure of oxygen by sweeping away oxygen rapidly as it diffuses across
43
How is the surface area of gills maximised?
High amount of division
Each gill consists of hundreds of leaf shaped gill filaments, upper and lower surface of each gill filament is covered in rows of evenly spaced folds called lamellae
44
What does the surface of lamellae consist of?
Highly flattened epithelial cells (1-2micrometers thick)
45
What type of blood vessels bring blood to the gills?
Afferent blood vessels
46
What type of blood vessels take blood away from the gills?
Efferent blood vessels
47
What is countercurrent flow?
Blood flows through the lamellae in the direction opposite to the flow of water over the lamellae to optimise PO2 gradient to make the gas exchange system more efficient then concurrent flow would be
48
What types of fish ventilate their gills by swimming with their mouths constantly open?
Anchovies, tuna, certain species of sharks
49
How do most fish ventilate their gills?
A two pump mechanism
50
Describe the two-pump mechanism of gill ventilation.
The closing and contracting of the mouth cavity prior to opening of the opercular flaps pulls water over the gills
51
What method of ventilation do birds use to maximise gas exchange?
Unidirectional ventilation
52
What does the structure of birds lungs allow?
Air to flow unidirectionally through lungs, as opposed to bidirectionally
53
What is dead space inside lungs?
Air that cannot be emptied during exhalation, lung volume that can not be ventilated with fresh air
54
How do birds minimise dead space?
Continuous, unidirectional airflow
55
In addition to lungs, what other structures do birds have?
Air sacs interconnected with each other, lungs and air spaces within bones. These are not a site of gaseous exchange.
56
What structure does air enter initially in birds?
The trachea
57
What does the trachea divide into?
Bronchi
58
Within birds, what do the bronchi divide into?
Parabronchi that run parallel to each other through the lungs
59
What do parabronchi have branching off of them?
Air capillaries- the site of gas exchange
60
How do air capillaries provide a large surface area for gas exchange?
They are numerous
61
What do parabronchi coalesce into?
Larger bronchi that take air out of the lungs and back into the trachea
62
Explain how the hypothesis that birds breath in a tidal manner can be disproven experimentally.
Place oxygen sensors at different locations in a birds respiratory system
Give the bird a breath of pure O2 followed by normal air.
Record oxygen pulse reaching each sensor.
63
Explain how air moves through a birds respiratory system.
Breath enters trachea and enters the posterior air sac
During exhalation, the breath flows into the lungs
During the next inhalation, the breath flows from the lungs into the anterior air sacs
During the next exhalation, oxygen is expelled
64
What role do air sacs play in the respiratory system of birds.
They act as belows, expanding and compressing
65
How did lungs first evolve in 'air-gulping' vertebrates?
Outpocketings of the digestive tract
66
Why can air flow in human lungs not be unidirectional?
They are dead-end sacs- air flow must be tidal
67
What does tidal air flow mean?
Air flows in and exhaled gas flows out by the same root
68
What device measures the volume of air a person breathes in and out?
A spirometer
69
What is tidal volume?
The amount of air that moves in and out per breath when at rest
70
What is the average tidal volume of a human adult?
500 ml
71
What is inspiratory reserve volume?
The additional amount of air that can be inhaled
72
What is expiratory reserve volume?
The additional amount of air that can be forcefully exhaled
73
What is vital capacity volume?
The sum of the tidal volume, the inspiratory reserve volume and expiratory reserve volume
74
What is residual volume?
The air that cannot be fully expelled from lungs
75
What is the sum of residual volume and vital capacity?
Residual air volume
76
What makes tidal breathing inefficient?
Reduces PO2- fresh air is not moving into the lungs during part of the breathing cycle
Incoming fresh air mixes with stale air that was not previously expelled
Does not permit countercurrent gas exchange
77
How are the inefficiencies of tidal breathing in mammals offset?
- Enormous surface area
| - Very short diffusion pathway
78
By what route does air enter the human lungs?
1. Nasal passage/oral cavity
2. Pharynx
3. Larynx
4. Trachea
5. Bronchi
6. Bronchioles
7. Alveoli
79
Describe the structure of the trachea.
2cm diameter
| C shaped bands of cartilage prevent walls collapsing when pressure changes during breathing cycle.
80
Describe the structure of the bronchi
Bronchi branch repeatedly to generate a tree-like structure of progressively smaller airways- after 4 branches, the cartilage support disappear
81
Describe the branching of bronchioles
After 16 branchings, the bronchioles are less than a millimeter in diameter and thin walled air sacs (alveoli) appear
82
Where is the site of gas exchange in the lungs?
Alveoli
83
What type of bronchioles sprout alveoli?
Respiratory bronchioles
84
What type of bronchioles occur before the appearance of alveoli?
Conducting bronchioles
85
How many branches of bronchioles occur after alveoli appear?
6- the bronchioles then end in a cluster of alveoli
86
Why are the airways considered dead space?
They conduct air to and from the alveoli- they do not participate in gas exchange themselves
87
How many alveoli are there in the human lungs?
~300 million
88
What is the combined surface area of alveoli?
70m^2
89
Describe the structure of an alevolus
Made of very thin cells, surrounded by blood capillaries which themselves have very thin walls
90
What is emphysema?
Condition in which inflammation destroys the alveoli
4th largest cause of death in the US
Caused by genetics and/or smoking
91
What two secretions do mammalian lungs produce to aid the ventilation process?
Mucus, surfactant
92
What is the function of mucus in the lungs?
To capture particles and microorganisms that are inhaled. Cells with cilia sweep the mucus towards the pharynx where it is swallowed or spat out
93
What is the name of the phenomenon that sweeps mucus up, towards the pharynx?
The mucus escalator
94
What factors adversely effect the mucus escalator?
Inhaled pollutants- smoking can immobilize the cilia
| Cystic fibrosis affects the respiratory mucus
95
What is a surfactant?
A substance that reduces the surface tension of a liquid
96
What is surface tension?
Surface tension give the surface of a liquid such as water, the properties of an elastic membrane as a result of attractive forces working between molecules
97
What contributes to the elasticity of the lungs?
A thin film of fluid covering the air-facing surfaces of the alveoli with surface tension that contributes to the elasticity of the lungs
98
What forces have to be overcome in order to inflate the lungs?
The elasticity of the lung tissue and the surface tension in the alveoli
99
What type of molecule is lung surfactant?
Fatty acid
100
What is the purpose of surfactant in the lungs?
Reduce the amount of work necessary to inflate the lungs
101
What may happen inside the lungs if a baby is born prematurely?
The cells may not yet be able to produce surfactant when stretched- difficulty breathing due to the enormous effort to stretch the alveoli
102
What is the name of the condition that occurs as a result of a premature baby not being able to produce surfactant?
Respiratory distress syndrome- can lead to exhaustion and death from not enough O2
103
How is respiratory distress syndrome treated?
- Respirator to assist breathing
- Hormones to speed lung development
- Apply surfactant to the lungs via aerosol
104
What are human lungs suspended inside of?
The thoracic cavity
105
What is the throatic cavity bound by at the bottom?
A sheet of muscle called the diaphram
106
What are the lungs covered by?
A pleural membrane that also lines the thoracic cavity
107
What is the space between the pleural membrane of the lung and the pleural membrane of the thoracic cavity?
The pleural space
108
What is in the pleural space?
A thin film of fluid that lubricates the inner surfaces
109
What changes does breathing involve?
Changes in the volume of the thoracic cavity
110
What is the diaphragm?
A sheet of muscle at the bottom of the thoracic cavity
111
What happens when the volume of the thoracic cavity increases?
A sub-atmospheric pressure inside the pleural space occurs because the pleural membranes are attached to the walls of the thoracic cavity
112
How is breathing initiated?
The contraction of the diaphragm pulling down and expanding the thoracic cavity and pulling on the pleural membranes
113
What happens when the diaphragm pulls on the pleural membranes?
Pressure in the pleural space decreases, the pleural membranes pull on the lungs. The lungs are an open cavity, so they expand in volume.
114
What happens when the diaphragm relaxes?
Elastic recoil of lung tissues pull the diaphragm up and pushes air out of the airways- this is a passive process
115
What other muscles change the volume of the thoracic cavity?
Intercostal muscles
116
What muscles (other than the diaphragm) expand the thoracic cavity?
External intercostal muscles
117
How do external intercostal muscles expand the thoracic cavity?
They lift the ribs up and outwards
118
What do the internal intercostal muscles do?
Decrease volume of thoracic cavity by pulling the ribs down and inwards
