1
Q
How does SA:V ratio affect diffusion?
A
smaller SA:V ratio (ie. larger size) has several effects:
- limits surface area available for diffusion
- increases diffusion distance (thicker)
2
Q
What is Dalton’s Law?
A
pressure exerted by a gas is related to (a) number of moles of the gas, and (b) volume of the chamber
- air is a mixture of gases that each exert its own partial pressure
- sum of all partial pressures is the total pressure of the mixture
- partial pressure is the driving force for gas diffusion
3
Q
What is Henry’s Law?
A
concentration of gas in a liquid is proportional to its partial pressure
- remember that gas molecules in air must first dissolve in liquid in order to diffuse into a cell
4
Q
Partial pressure of a gas (mmHg) also means…
A
potential energy for the gas to move
5
Q
At a given PO2, there is a higher [O2] in air than water because…
A
solubility of O2 in air is 30x greater compared to water
6
Q
What is O2 solubility in air? In water?
A
air: 1000
water: 33.1
(air holds 30x more oxygen)
7
Q
What is the relationship between partial pressure and concentration of O2 in air and water?
A
[O2] is directly proportional to partial pressure – this is Henry’s Law
- air has way more O2 than water, therefore has larger slope
8
Q
What is CO2 solubility in air? In water?
A
air: 1000
water: 930
(air and water hold about the same amount of carbon dioxide)
9
Q
How does CO2 and O2 solubility differ in air?
A
it is the same
10
Q
How does CO2 and O2 solubility differ in water?
A
CO2 is 30x more soluble than O2 in water – has large implications for gas exchange
11
Q
How does air or water flow rate change as you get further from the membrane (cell surface)? Why?
A
increases due to friction and boundary layer effects
- closer to membrane → water moves slower → more time for O2 to be removed before that water leaves that barrier → O2 tension decreases
- faster flow → higher partial pressure
12
Q
When are boundary layer effects more problematic?
A
in more viscous mediums
- air: don’t need to move much to get rid of any boundary layer in water
- water: viscous, therefore need to work harder
13
Q
How are boundary layer problems solved?
A
by changing both flow rates and optimizing gas exchange
14
Q
How does elimination of a boundary layer affect diffusion?
A
–
15
Q
How can a boundary layer be reduced?
A
higher flow rate → air/water is better mixed at the cell surface
16
Q
What is an embryonic rotation?
A
hypoxia-sensitive behaviour that mixes egg capsule fluid, which reduces the boundary layer, to enhance O2 delivery to embryo
17
Q
What are the three main respiratory strategies of small animals?
A
- circulating the external medium through the body
- diffusion of gases across the body surface accompanied by circulatory transport
- diffusion of gases across a specialized respiratory surface accompanied by circulatory transport (internal bulk flow movement)
18
Q
How does diffusion through water occur?
A
O2 diffuses in
19
Q
How does diffusion through air occur?
A
O2 dissolve, then diffuses in
20
Q
How does ventilation reduce the formation of boundary layers?
A
faster ventilation → less boundary layer → less impairment to gas exchange → reduces static boundary layer
(if more stagnant at respiratory surface → less efficient at providing gases)
21
Q
What are the 3 different types of ventilation?
A
- non-directional
- tidal
- unidirectional
22
Q
What is non-directional ventilation?
A
medium flows past the respiratory surface in an unpredictable pattern
23
Q
What is tidal ventilation?
A
medium moves in and out of the chamber
ie. filling/emptying lungs
24
Q
What is unidirectional ventilation?
A
medium enters the chamber at one point and exits at another
25
What influences efficiency of gas exchange? (3)
- contact time: how long it takes for blood to exchange gases with environment
- thickness of membrane: Fick equation indicates there is greater transport when membranes are thinner (but this has the cost of structural integrity)
- directions of flow
26
What value can give you an indication of gas exchange efficiency?
PO2 values in respiratory medium vs. blood, as they pass through the respiratory surface
- ie. PO2 in blood and environment is the same if you can take up as much O2 as provided (100% efficiency)
27
What are the pros of gills and lungs (specialized respiratory surfaces)? (6)
- allows rest of skin to be thick/protected
- protected in body cavity (sometimes) – also allows it to remain moist
- higher effective surface area
- highly vascularized (lower diffusion distance) – efficient blood flow to structure
- highly ventilated
- synchronized with circulatory system – bringing in air to blood that can take away O2
28
What are some of the important physical differences between air and water as they relate to gas exchange? (3)
- O2 solubility in air is 30x greater than in water – much more water must be ventilated than air to remove the same amount of O2, which requires more energy
- CO2 solubility in air is similar to in water – if water breather has sufficient flow for O2 uptake, system very easily gets rid of CO2 (blood CO2 much lower in water breathers than air breathers)
- water is more dense and viscous than air – requires more energy
29
What type of ventilation do most water breathers use and why?
–
30
What type of flow is there in fish gills?
countercurrent
- water flows evenly over gill arches, through different filaments, and over lamellae
- lots of surface area
- highly efficient system
31
Why has air breathing evolved over 70 times independently in fishes?
likely in response to aquatic hypoxia
32
What type of respiratory structures do air-breathing fish have? (5)
- reinforced gills that do not collapse in air
- highly vascularized mouth or pharyngeal cavity
- highly vascularized stomach or intestine
- specialized pockets of the gut
- lungs
33
What are the two major animal lineages that have colonized terrestrial habitats?
- vertebrates: amphibians, reptiles, birds, mammals
- arthropods: crustaceans, chelicerates, insects
34
Discontinuous Gas Exchange in Insects
adaptive value of discontinuous gas exchange is unknown
35
What is the tracheal system of insects?
- air-filled tubes called tracheae open to outside via spiracle
- tracheae branch into tracheoles, which penetrate to within a few cells throughout the body – no cell is more than 5-6 cells away from air
36
What is a disadvantage of the tracheal system?
takes up lots of space (30% of body)
37
How does a lungfish prevent O2 loss across the gills when airbreathing in hypoxic water?
–
38
What types of respiratory structures do amphibians have? (3)
- cutaneous respiration – ie. frogs, salamanders
- external gills – ie. juvenile salamanders, axolotls
- simple bilobed lungs (more complex lungs) – ie. terrestrial frogs and toads
39
What characteristics of reptiles are different from fish and amphibians? (2)
- reptiles use suction pump, while fish and amphibians use buccal pump
- reptiles have separation of feeding and respiratory muscles, while fish and amphibians use buccal pump for feeding and breathing
40
Describe bird lungs.
- lungs are stiff and change little in volume
- located between series of air sacs that act as bellows (posterior and anterior air sacs that drive air through the lung)
41
What do type I alveolar cells do?
make up the thin wall of alveoli
42
What do type II alveolar cells do?
they are surfactant cells that secrete fluid
43
What is the outer surface of alveoli covered in? Why?
dense network of capillaries
- high surface area to efficiently exchange gases and remove CO2
- as blood moves through alveoli and becomes oxygenated, vessels coalesce into pulmonary vein (oxygenated, leaving the lungs)
44
What is the mammalian pleural sac?
sac made up of two layers of cells with a pleural cavity, attached between lung lobe and chest wall, containing pleural fluid that surrounds each lung
- important structure in making sure energy is dissipated equally throughout lung to facilitate lung expansion
45
What is intrapleural sac pressure and what does it do?
slightly subatmospheric
- keeps lung expanded
46
How does the pleural sac and intrapleural sac pressure keep the lungs expanded?
- when chest wall is pulled, pleural sac is also pulled, which will transmit that force (negative pressure) effectively to the lung surface and evenly expand the lung
- water is incompressible, and the force is transmitted evenly throughout the lung
- when everything relaxes, elastic recoil of the lung pulls on the pleural sac, which pulls the chest wall and everything in
47
What occurs during a pneumothorax (lung collapse)?
- pleural cavity punctured
- negative pressure draws air in
- lung itself has elastic recoil for exhalation
- lung collapses
- air is drawn into enlarged pleural sac area, and you cannot breathe
48
What kind of air does the mammalian lung see? Why is this important?
mixed inhalant and exhalant air (due to tidal ventilation) – has implications for efficiency of gas exchange
49
Mammalian Tidal Ventilation – Inhalation
- motor neuron stimulates inspiratory muscles
- contraction of external intercostals and diaphragm
- ribs move outwards
- diaphragm moves downward
- volume of thorax increases
- intrathoracic pressure decreases
- transpulmonary pressure gradient increases
- lungs expand and air is pulled in
50
Mammalian Tidal Ventilation – Exhalation
- nerve stimulation of inspiratory muscles stops
- muscles relax
- ribs and diaphragm return to original positions
- volume of thorax decreases
- intrathoracic pressure increases
- passive recoil of lungs pushes air out
- during rapid, heavy breathing, forced exhalation is by contraction of internal intercostal muscles – allows large lung volume, and removal of as much air as possible to maximize gas exchange
51
What influences the work required to breathe? (3)
- lung elastance
- lung compliance
- airway resistance
52
What is elastance?
how readily a structure returns to its original shape
- high elastance = easy to return to its original form
53
What is compliance?
how easy it is to stretch a structure
- high compliance = easy to stretch (does not take a lot of work)
54
What is the role of surfactants in lung compliance?
increases lung compliance and reduces work required to breathe
- aqueous fluids have substantial surface tension due to hydrogen bonding between water molecules, which would cause walls of alveoli to stick together, and would therefore increase energy needed to inflate lungs
- surfactants produced by type II alveolar cells reduce the surface tension, and make it easier for alveoli to expand
55
How does fibrotic lung disease affect the structure of the lungs?
- scarring thickens walls of lungs
- reduces lung compliance
- makes inhalation difficult, more work to breathe
56
How does emphysema affect the structure of the lungs?
- walls of alveoli break down
- increases lung compliance, but reduces lung elastance
57
How is airway resistance related to radius?
resistance is inversely proportional to radius to the 4th power
- small changes in radius have large impact on resistance, and therefore flow
58
What is bronchoconstriction caused by?
stimulation of parasympathetic nervous system
- histamine
- irritants
59
What is bronchodilation caused by?
stimulation of sympathetic nervous system
- circulating epinephrine – binds to beta-2 receptors
- high alveolar PCO2 – CO2 should not be high, and is probably because flow is not high enough
60
What is asthma?
excessive bronchoconstriction
- inhalers stimulate beta-2 receptors to relax muscle and dilate
61
What is tidal volume (VT)?
volume of air moved in one ventilatory cycle (difference between inhalant and exhalant)
62
What is dead space (VD)?
air that does not participate in gas exchange
63
What is anatomical dead space?
volume of trachea and bronchi – there are no capillaries here
64
What is alveolar dead space?
volume of alveoli that are not perfused (blood is not going to it)
65
Do animals with long necks have small or large amount of dead space?
have very large dead space
- need to move a lot of air before you get some exchange
- need narrow trachea to reduce dead space, otherwise they will never get air to the lung (BUT the thinner the trachea, the more resistance to flow there is)
66
What is VA:Q matching and why is it important?
ventilation perfusion ratio
- VA: alveolar ventilation
- Q: cardiac output
- required for efficient gas exchange at respiratory surface
67
What is the VA:Q ratio of birds and mammals?
air and blood of birds and mammals have about the same O2 content, therefore VA:Q ratio of 1 matches O2 delivery at the gas exchanger, with the ability to transport O2 away from the gas exchanger
68
What does a drop in PO2 from the lung to blood indicate?
indicates thickness of diffusion barrier
- each step has drop in potential energy for gas to move to tissues
- larger diffusion barrier → larger drop in PO2 across the barrier
69
How is oxygen transported in the blood? Why?
bind to metalloproteins (respiratory pigments)
- solubility of O2 in aqueous fluids is low
therefore animals have evolved transport pigments to increase carrying capacity of blood
70
What are metalloproteins (respiratory pigments)? What do they do?
proteins containing metal ions which reversibly bind to O2
- increase oxygen carrying capacity by 50-fold
71
What are the 3 types of metalloproteins (respiratory pigments)?
- hemocynanin
- hemoerythrin
- hemoglobin
72
What are hemocyanins? In what organisms are they found?
- contain copper
- usually dissolved in hemolymph
- appears blue when oxygenated
found in arthropods and molluscs
73
What are hemoerythrins? In what organisms are they found?
- contains iron directly bound to protein
- usually found inside coelomic cells
- appears violet-pink when oxygenated
found in sipunculids, priapulids, brachiopods, some annelids
74
What are hemoglobins? In what organisms are they found?
- globin protein bound to heme molecule containing iron
- often 2 α and 2 β chains, each with around 145 amino acids – tetrameric molecule
found in vertebrates, nematodes, some annelids, crustaceans, and insects
75
What is myoglobin?
type of Hb found in muscles
- monomeric molecule (1 α and 1 β chain)
76
What do red blood cells (RBCs) do?
encapsulate Hb, and transports O2 and CO2
- 30-60% of blood consists of red blood cells (RBCs)
77
Why do RBCs contain Hb?
containing Hb in RBCs allows fine-tuning of the microenvironment around Hb to optimize function – Hb only sees what is in that particular RBC
78
Why is Hb termed an honorary enzyme?
due to way that 3D conformation changes when an amino acid is changed, or when oxygenated vs. deoxygenated, and its association on affecting oxygen affinity
- single amino acid substitutions in Hb can have profound effects on function
- Hb is model protein for understanding structure-function relationships
79
Ice fish of Antarctica lack RBCs and Hb (have pure plasma only). Their blood cannot transport a lot of O2. How do they adapt? (3)
- live in very cold water, which has higher solubility of O2 relative to tropical environments
- large heart that can pump lots of blood
- low metabolic rate, do not use lots of O2
80
What is P50 of the blood and why is it important?
PO2 at which 50% of the hemes are saturated with O2
- maximal unloading occurs at P50
81
Why do animals alter P50 of Hb?
to optimize O2 loading and unloading
- depends on environment it lives in, and what it wants to do
82
Amount of O2 dissolved in plasma follows what law?
Henry's Law
total O2 dissolved (concentration) = PO2 x solubility
83
During stress (such as exercise, hypoxia or diving), how can Hb levels be increased?
RBCs can be released from the spleen, which greatly elevates hematocrit and Hb levels
- this has advantages to enhance O2 uptake and delivery
84
What is a disadvantage of having too much Hb?
viscosity increases with hematocrit
85
What is the ideal situation for O2 transport?
high affinity at gas exchanger, and low affinity at tissues
- high Hb affinity (low P50) maximizes O2 uptake – can bind O2 with little O2 in environment
- low Hb affinity (high P50) maximizes tissue O2 delivery
86
What are the T (tense) and R (relaxed) states?
as Hb molecule is oxygenated, it goes from “T” (tense) state (where oxygenation is difficult) to “R” (relaxed) state (where O2 can be added more easily)
87
How does the transition from T to R state occur?
associated with weakening or breaking of salt bridges within Hb molecule (and also some hydrogen bonds)
- T state: many bonds that make the molecule rigid, and make it hard for O2 to bind to iron
- R state: salt bridge breaks and makes the molecule more relaxed, and makes it much easier for O2 to move in and bind to iron
88
What does the tetrameric characteristic of Hb influence?
influences how O2 is bound and released
- once the first O2 binds, salt bridges break, making it much easier for the rest of the oxygens to bind and fill the tetramer
89
What is the main organic phosphate in mammals? Birds? Reptiles, amphibians, and fish?
mammals: 2,3-DPG
birds: IP5
reptiles, amphibians, and fish: ATP or GTP
90
When do organic phosphate levels alter Hb-O2 affinity?
during exposure to hypoxia, and development
91
What was the discovery of organic phosphates and their applied use important for?
extending the life of blood in blood banks from days to months
92
Why are organic phosphates important for P50?
important for fine-tuning blood P50 – without them, P50 would be very low (2-4 mmHg)
cannot make artificial blood due to this issue
93
What does the amount of O2 stored in blood depend on? (2)
- PO2 of plasma: amount of “pressure” that O2 can bring to bear on the system (how much O2 “trying” to be loaded) – potential energy for oxygen to diffuse and bind
- Hb-oxygen affinity: affinity (ability) of the carrier (Hb) to carry O2 in any particular set of circumstances – ie. P50 is PO2 at which 50% of hemoglobin is saturated
94
What is the swim bladder?
gas-filled sac (in many bony fishes) that helps maintain neutral buoyancy
- fill with gas to increase buoyancy
- remove gas to decrease buoyancy
- in most species this gas is O2
95
Fish that migrate vertically need mechanism to regulate swim bladder volume. What are the two different mechanisms?
- gulping air (physostomus) – there is a direct connection between the mouth and swim bladder, therefore animal can go to surface to take gulp of air and inflate swim bladder, then return to the depth it needs to be at
- utilizing root effect in conjunction with gas gland and countercurrent exchanger (physoclistus swim bladder) – no connection between the mouth and swim bladder, therefore need to excrete O2 from blood to physically inflate bladder
96
How does a physoclistus swim bladder work?
- bladder is perfused by blood – rete mirabile (network) where arterial blood comes in, venous blood exits
- gas gland produces lots of acid/CO2 to acidify blood – this is the site where you can drive O2 off Hb and physically inflate swim bladder
- oval removes O2 from swim bladder to reduce volume – if you need to go to surface but have a full swim bladder, bladder will continue to inflate, so you need to get rid of O2 by extracting it at oval
97
What is in the swim bladder lumen?
gas
98
What is the rete mirabile?
- consists of countercurrent arterial and venous capillaries, in close proximity, to localize the acidosis near the swim bladder
- where acid is recovered and recirculated
(similar structure also exists in eyes of fishes and ensures O2 delivery to this structure)
99
What happens in a catastrophic decompression?
if neutrally buoyant fish is 200 m down in depth and fisherman pulls it up to surface, fish cannot dump the O2 in their bladder fast enough
- all the gas expands (according to Boyle’s Law, P1V1 = P2V2)
- swim bladder system prevents neutral buoyancy anywhere you are
- reduces amount of energy needed to expend to fight against gravity
- important traits that have allowed teleosts to adapt – combination of system to the eye, and ability to regulate swim bladder volume
100
Why is carbon monoxide “poisonous”?
CO binds to Hb with an affinity 250x that of O2 for Hb – competes with oxygen for binding to Hb
- Hb becomes 100% saturated with CO at PCO = 0.6 mmHg
- can completely displace all oxygen – decreases the effective oxygen carrying capacity of blood
101
How is CO2 transported from the tissues to the environment? (3)
- small amounts of CO2 gas are transported in plasma, physically dissolved (about 5%) – CO2 is more soluble in body fluids than O2
- some CO2 binds to hemoglobin (about 5-23%) – ie. carbaminohemoglobin
- most CO2 is transported as bicarbonate (HCO3-)
102
Effect of Acidosis on OEC
example: when blood PO2 = 150 mmHg and blood is 100% saturated, only 2% is physically dissolved and 98% is bound to Hb
- if you draw 2% more off Hb and now have 4% in solution, that O2 has nowhere to go but to increase partial pressure – partial pressure doubles from 150 to 300 mmHg
- if blood is acidified such that you drive 10% of O2 off Hb, there is now 5x more O2 in solution that has nowhere to go, and PO2 will increase to 800 mmHg
103
What is the Bunsen solubility coefficient (𝛼)?
CO2 solubility
104
How does CO2 move across membranes?
as the physically dissolved CO2 form
- HCO3- is not very permeable across membranes
105
How is the Bohr effect and Haldane effect related?
they are mirror images of the same phenomenon – both based on H+ being bound or released from Hb when it is oxygenated or deoxygenated
106
What is the Bohr effect?
refers to oxygen-related traits
- reducing pH right shifts OEC and increases O2 unloading
107
What is the Haldane effect?
- increasing O2 unloading allows binding of more CO2 – can bind more H+, which is good for CO2 transport and excretion
108
For a given PCO2, the more H+ buffered (bound, and no longer contributing to pH), the _________.
greater the total CO2 (physically dissolved CO2 + HCO3-)
109
Vertebrate RBCs Create a Microenvironment to Enhance O2 and CO2 Transport
- Hb levels in RBCs are very high, on the verge of solubility
- regulation of organic phosphates and pH values optimize blood P50 for efficient O2 uptake and delivery
- CA is located within RBCs at very high levels to rapidly and reversibly convert CO2 to HCO3- and vice versa
- RBCs have high levels of HCO3-/Cl- exchangers to allow most CO2 to be transported in the plasma as HCO3-
- strong interaction between O2 and CO2 transport at the level of Hb within RBC due to Bohr and Haldane effects
- O2 uptake facilitates CO2 removal at gas exchanger (Haldane effect) and CO2 removal from tissues enhances O2 unloading from blood (CO2 removal acidifies blood, stabilizes T state, and right shifts curve)
110
How do changes in ventilation affect body fluid pH?
- hyperventilation causes PCO2 ↓
- hypoventilation causes PCO2 ↑
111
How does PCO2 affect body fluids?
affects [HCO3-] and pH of body fluids
- as PCO2 ↑: [HCO3-] ↑, and pH ↓ (ie. [H+ ] ↑)
- as PCO2 ↓: [HCO3-] ↓, and pH ↑ (ie. [H+ ] ↓)
112
In air breathers, what is the predominant regulator of acid-base balance?
respiratory, by modulating blood CO2 levels
- kidney (or gills) is important in regulating HCO3- levels
113
What is respiratory alkalosis?
hyperventilation blows off CO2 and increases pH
114
What is respiratory acidosis?
hypoventilation permits CO2 to accumulate and decreases pH
115
What is metabolic acidosis?
acidosis during anaerobic respiration when lactate levels become elevated
116
How do vertebrates regulate respiratory systems? (3)
- regulate ventilation (frequency and depth of breath)
- regulate O2 carrying capacity and affinity – can change hematocrit and total O2 carrying capacity, but also need to be careful about viscosity effects (too much Hb = very viscous), can change P50 of blood
- regulate tissue perfusion
117
What regulates ventilation?
rhythm generators (central pattern generators in medulla)
- Pre-Botzinger complex: important respiratory rhythm generator in mammals
118
What are the sources of input that modify ventilation rate? (7)
- peripheral chemoreceptors in aortic arch
- central chemoreceptors in brain
- receptors in muscles and joints
- irritant receptors
- stretch receptors in lungs
- higher brain centres – cerebral cortex-voluntary control over breathing
- other receptors (ie. pain) and emotional stimuli acting through hypothalamus
119
Where are central chemoreceptors located?
in medulla
120
Where are peripheral chemoreceptors located?
in carotid and aortic body
121
What do central chemoreceptors detect?
pH (related to CO2) of cerebrospinal fluid
122
What do peripheral chemoreceptors detect?
primarily sense low PO2
123
What are the two types of peripheral chemoreceptors in mammals?
- aortic body (blood going to body)
- carotid body (blood going to brain)
124
What is the primary regulator in air-breathers?
CO2 is primary, O2 is secondary
- central chemoreceptors detect pH (related to CO2) of cerebrospinal fluid
- mammals have 2 peripheral chemoreceptors that primarily sense low PO2
- hyperventilation results in lower CO2 levels, and pH increases
- hypoventilation results in higher CO2 levels, which dissociates into H+ and HCO3-, and pH decreases
125
What is the primary regulator in water-breathers?
O2
- internal PO2 sensors within gills (and in gill cavity and on gill surface) – can sense the environment
- also PCO2/pH sensors in gills (environmental, not physiological?)
126
What is hyperoxia?
higher than normal PO2 in environment, blood, or organ system
- rare terrestrial environmental condition – mostly aquatic
- ie. plants and algae photosynthesize during the day, producing O2
127
What is hypoxia?
lower than normal PO2 in environment, blood, or organ system
128
What is hypoxemia? What is it caused by?
lower than normal arterial blood O2 content
caused by:
- environmental hypoxia – ie. high altitude, burrows
- inadequate ventilation (hypoventilation)
- reduced blood hemoglobin content (anemia)
129
What is hypercapnia?
higher than normal PCO2 in environment or blood
- common in aquatic systems
- ie. plants consume O2 at night, producing CO2
- ie. animals in burrows consume O2 and produce CO2
130
What is hypocapnia?
lower than normal PCO2 in environment or blood
ie. hyperventilate and blow CO2
131
Are burrows often hyperoxic or hypoxic? Hypercapnic or hypocapnic?
often hypoxic and hypercapnic
- deal with low O2 and high CO2, and modify the way they breathe to compensate
132
How does PO2 change as you get higher in altitude? What does this cause?
barometric pressure drops ∴ PO2 drops
- decreases driving force for gas diffusion
- results in hypoxia
133
What other adaptations (other than O2, the biggest problem) does altitude present?
- low temperature adaptation
- adaptation to low relative humidity
134
How does relative humidity change as you get higher in altitude? Why?
water levels are low (dry air) at high altitude because pressure cannot hold as much water vapour, and we also lose lots of water
- ie. we humidify our lungs with every breath, therefore we are more likely to lose more water
135
How does PO2 change with an increase in altitude?
How does PO2 change with an increase in depth?
- PO2 decreases with altitude because air is compressible
- PO2 is constant because water is not compressible
136
What is the pressure during a clear, sunny day?
What is the pressure on a cloudy day?
- clear, sunny day is a higher pressure day – blows away clouds
- cloudy day is a lower pressure day
this can be what makes the difference between a successful and unsuccessful climb to the summit without supplemental O2
137
What happens to blood when altitude is elevated?
increase hematocrit and RBC levels
- ie. athletes train at high altitudes – when they come down, they have higher hematocrit and Hb
138
What does high hematocrit cause?
increases viscosity of blood, and therefore increases pulmonary arterial pressure
- causes right ventricular hypertrophy (thicker, more muscular because it is working harder) and congestive heart failure
- polycythemia: largely linked to high viscosity of blood, causes Monge’s disease (chronic mountain sickness)
139
How can acute mountain sickness be alleviated?
by administration of drug acetazolamide (carbonic anhydrase inhibitor)
140
What does acetazolamide do? (2)
majority of CO2 that is excreted is HCO3- in plasma that has to enter RBC, and in presence of CA get converted to CO2 that we excrete
- if you inhibit CA, CO2 excretion is impaired – even if you breathe more, PCO2 will not decrease because you are not secreting enough, therefore CSF pH does not change, and ventilation rate can increase
kidney normally absorbs HCO3- – excrete acid into urine, which combines with HCO3- to form CO2
- if you inhibit CA, you urinate HCO3-
141
Which P50 (lower P50, higher affinity, left-shifted /OR/ higher P50, lower affinity, right-shifted) is more beneficial during exposure to environmental hypoxia and why?
both are important – BUT mostly see left shift because most important thing is to get O2 in
- higher affinity of Hb for oxygen → easier O2 uptake
- but left-shifted curve inhibits O2 unloading to tissues
- need to find sweet spot that is left-shifted enough to get O2 in, but not so left-shifted that it becomes a problem for delivering oxygen
142
Do animals adapted to higher altitudes have higher or lower P50? Why?
What are the consequences of this?
have lower P50 (higher affinity) in their blood – OEC shifted left
- helps with O2 loading at lungs
- but tissue PO2 is necessarily lower
- must have some other adaptation to allow them to unload O2 – increase capillary density, more myoglobin
143
How do humans adapt to higher altitude?
humans hyperventilate at altitude, resulting in CO2 decrease and elevated blood pH, which left-shifts OEC for easier O2 uptake
- humans elevate organic phosphate levels – 2,3-DPG binds to Hb and right-shifts OEC
- overall, there is not much difference – partly because we really need to be able to unload O2 to tissues
144
How is the O2 transport cascade modified in high altitude birds?
- ventilation
- pulmonary O2 diffusion
- circulatory O2 delivery
- muscle O2 diffusion
- muscle O2 utilization
- muscle ATP turnover
adaptations to enhance O2 flux occur at each level of O2 transport cascade in order to adapt to new environment – be able to get O2 from environment to tissues, and get metabolically-produced CO2 out to environment
- ventilation: enhanced hypoxic ventilatory response and more effective breathing pattern
- pulmonary O2 diffusion: larger lungs increase surface area for diffusion (predicted with Fick equation)
- circulatory O2 delivery: Hb with higher O2 affinity, multiple cardiac specializations
- muscle O2 diffusion: (a) even higher capillarity/density (b) mitochondria are redistributed closer to capillaries to reduce diffusion distance – predicted with Fick equation; the smaller the distance O2 has to diffuse, the more likely it will
- muscle O2 utilization: sometimes greater aerobic capacity in flight muscle
- muscle ATP turnover: greater respiratory control by mitochondrial creatine kinase
145
How does blood P50 change with adaptation to aquatic hypoxia?
in general, aquatic organisms exposed to hypoxia exhibit similar physiological changes to terrestrial vertebrates at altitude
- left shift of OEC due to decrease in ATP:Hb ratio
- fish use ATP/GTP inorganic phosphate (humans use 2,3-DPG)
- hypoxia-tolerant fish generally have low P50
146
How and why does gill surface area change in some fish exposed to aquatic hypoxia?
- increase surface area → increase oxygen uptake
- under normal conditions (normoxia), lamellae of crucian carp are packed with cells, therefore lamellae are not available for gas exchange – BUT during hypoxia, cells between lamellae disappear and surface area available for gas exchange increases
147
What two things occur to a fish when exposed to aquatic hypoxia?
What do these changes cause?
- increase in total surface area of gills (lamellae)
- reduction in blood-water diffusion distance (thickness)
these changes that facilitate gas exchange during hypoxia negatively affect ion regulation, resulting in progressive drop in plasma ion levels
148
What is the osmorespiratory compromise?
trade-off between gas exchange and ion regulation – increase in surface area needed for O2 uptake is also an increase in surface area for losing ions to water
- fish are normally in freshwater where they are actively taking NaCl from water to maintain high levels in blood, but increasing surface area and breathing to get O2 in comes at a cost
149
What is dive duration related to?
in part related to O2 supply vs. O2 demand
150
O2 supply that is available for divers can be estimated by measuring... (3)
- blood volume – contains Hb to transport O2
- lung volume
- muscle mass – contains myoglobin that can store O2 that gets released to tissues
151
What are the two components of the integrated dive reflex?
- diving bradycardia: selective slowed heart rate
- selective peripheral vasoconstriction: selective reduction in tissue blood flow (resistance increases and prevents flow to tissues)
152
What organisms have the integrated diving reflex?
- present in all mammals
- well-developed in diving mammals
153
What is the goal of the integrated diving reflex?
to meter out O2 to most essential organs while minimizing cardiac expenditure
154
Diving Bradycardia
How does heart rate change during and after a dive?
What does the magnitude of bradycardia depend on?
- selective slowed heart rate during submersion
- heart rate comes back up during emersion, and gets higher than it was before submersion because the organism needs to replenish the O2 consumed during the dive
- magnitude of bradycardia depends on species and anticipated dive duration – dive duration depends on combination of stress and conscious control
155
How does blood flow to tissues change during a dive?
blood flow to non-essential tissues is reduced to meter out O2 stores
156
Selective Peripheral Vasoconstriction
How does MAP change during and after a dive?
stays relatively constant – there is a slight increase at emersion, but then it goes back down quickly
- tissues that need blood flow have the same pressure to provide flow, while tissues that do not need flow constrict to stop flow
157
What is mean arterial pressure (MAP)?
blood pressure of arterial system
158
Selective Peripheral Vasoconstriction
How does blood flow to extremities change during and after a dive?
- drop throughout the dive/submersion
- flow returns to tissue at emersion (after dive) to replenish O2 consumed
159
Selective Peripheral Vasoconstriction
How does blood flow to the brain change during and after a dive?
maintained during dive
- need to have proper brain function
160
Why do animals need to vasoconstrict during diving?
to minimize pressure/perfusion changes that would occur due to drop in heart rate (HR)
161
What is the aerobic dive limit?
how long animal can dive while staying completely aerobic – no anaerobic metabolism needed
- dive time at which lactate begins to accumulate as a result of switch to anaerobic metabolism
- can calculate how long animal can dive before it needs to incur anaerobiosis
162
What happens to...
- heart rate
- cardiac output
- blood O2
- blood CO2
- blood lactate
...during a dive?
- heart rate decreases
- cardiac output decreases
- blood O2 decreases – gets depleted as it’s being used
- blood CO2 increases
- blood lactate is low
163
What happens to...
- heart rate
- cardiac output
- blood O2
- blood CO2
- blood lactate
...after a dive?
- heart rate increases
- cardiac output increases
- blood O2 level returns to normal
- blood CO2 level returns to normal
- blood lactate spikes high – once animal returns to surface and is breathing again, they release lactate
164
When is blood lactate produced?
produced and contained in tissues if dive is anaerobic
- no lactate produced if dive is not anaerobic
- most diving vertebrates do NOT exceed durations where dive requires anaerobic metabolism
165
When dive is anaerobic and lactate is produced, what happens to the lactate?
most lactate is not removed until after the dive
166
Change in PO2 (and PN2) in lungs is directly proportional to...
pressure (which changes with depth)
167
In scuba divers, how does lung volume and total gas pressure (PO2 and PN2) change with depth?
- lung volume remains constant at different depths
- total gas pressure (PO2 and PN2) increases in proportion to depth, and lungs are continuously perfused
ie. at 30 m of depth, gas tensions are 4 times atmospheric (PO2 = 600 mmHg, PN2 = 2400 mmHg)
168
Based on Henry's Law and Boyle's Law...
What happens to PO2 and PN2 with descent/depth?
inhaled PO2 and PN2 increase, and tissues will equilibrate with this
169
Based on Henry's Law and Boyle's Law...
What happens to PO2 and PN2 with ascent? What does this cause?
inhaled PO2 and PN2 decrease, and excess N2 and O2 leave the blood and tissues
- O2 is metabolized (not an issue), but N2 is inert (not metabolized)
- N2 pressure is high, everything is in solution – when you equilibrate it with atmospheric pressure, N2 comes out of solution and forms bubbles (this is the basis of the bends)
170
How does decompression sickness and "the bends" occur?
- as you ascend, gases in tissues are supersaturated relative to lungs
- if you ascend at a rate faster than blood can excrete gases into lungs (ie. if amount of gas in system is greater than solubility), then small bubbles of gas will form spontaneously
- if bubbles occur in wrong place (basically anywhere in body) – “the bends” – it is extremely painful, potentially fatal
- gas bubbles need nucleus to form (to come out of solution), but then can expand rapidly
171
What are the consequences of bubbles causing blockages of blood flow?
- blockage of blood flow to joints by bubbles causes pain
- blockage of blood flow to nervous tissue can cause paralysis or stroke
172
What do dive machines do?
know how long you have been down, and how much pressure you were at, therefore can tell you what rate you should come up to the surface to avoid this problem
173
How does a decompression chamber work?
- hyperbaric chamber is sealed up and pressurized (greater pressure)
- bubbles that were in tissue come out of solution because pressure allows them to dissolve
- take more gases in because of higher pressure
- then pressure is reduced at very slow rate, so all gases are coming out at rate that is sufficient to prevent bubble formation
174
Can fish get the “bends”?
- below waterfalls and downstream of hydroelectric dams, air bubbles are taken to depth and equilibrate at depth (dissolve)
- when that water moves to the surface, it is supersaturated with gases
- supersaturated waters can result in gas bubble trauma in fish – this is of concern downstream of hydroelectric dams
175
Countercurrent Blood Flow in Fish Gills
- blood moves past lamellae from left to right, water moves from right to left
- venous blood entering gill has low PO2 b/c all of the extra O2 is being extracted at tissues
- blood PO2 increases as it moves through lamellae b/c it is taking O2 from the medium
- when blood exits lamellae, it equilibrates with incoming fresh water, and blood PO2 is close to inhalant PO2
- PO2 not exactly equal due to thickness of barrier
+ BIOL 364
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