Comparative Physiology- Renner Lecture 16
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| since simple diffusion isn't enough to provide adequate gas exchange, animals have evolved mechanisms that increase rate of diffusion, what are they | 1. increase surface area for exchange (respiratory surfaces)
2. forced movement of gas or bulk transport of gas (ventilation and circulation)
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| adaptations to enhance surface area include | 1. tracheal system in insects
2. gills and lungs
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| internally, how is surface area accomplished ? | by extensive capillary networks
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| what helps enhance pressure gradient ? | the use of hemoglobin and bicarbonate/carbonic acid, interconversion between diffusible and bound gas
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| gas in this form does not contribute to pressure gradient because it prevents equilibration and maintain gradient | bound form
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| why do bound gases not contribute to pressure gradient | because they prevent equilibration and maintain gradient
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| what are the three general forms of respiration? | tracheal system in insects
gills in fish
lungs in terrestrial vertebrates
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| how is gas transport mediated in insects? | by an exchange organ that is in close proximity to the cells
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| how is the proximity of the gas exchange organ to the cells is achieved in insects? | by a series of highly branched tubes that are intermittently open to the outside
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| segmentally located openings along the thoracic or abdominal lateral body wall of insects | spiracles
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| in insects, spiracles are open or closed via | spiracular muscles
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| when are spiracles open? | spiracles open in response to high CO2 and low pH of body fluids
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| when are spiracles closed? | in dry conditions, closing limits loss of water
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| define trachea | air conduits that branch extensively throughout the body and terminate in tracheoles
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| why are trachea lined with cuticle | to prevent collapse
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| define tracheoles | blind ended tubules that provide the major site for gas exchange
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| diameter of tracheoles | 0.1 micron
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| cells are present within ____________ of any tracheole ending. Tracheoles are _____________ cells distant | 30 microns, 2-3
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| where are tracheoles densely distributed? | tissues with high metabolic requirement
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| the ends of tracheoles are _____________________ | fluid filled
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| what is the purpose of having the tracheoles be fluid filled? | it represents a balance between hydrostatic and osmotic pressure
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| in insects, at rest, where is tracheole fluid favored? | hydrostatic pressure favors fluid in, osmotic pressure favors fluid out
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| in insects, when activity is increased, how does that affect the fluid in the tracheoles? | osmotic pressure decreases fluid level in the tube
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| why is fluid decreased in the tracheole by osmotic pressure during activity? | because a gaseous environment favors faster diffusion relative to diffusion in liquid
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| mechanism that aids in respiration found in larger insects and during flight to provide bulk gas transport | ventilation
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| ventilation is accomplished by the presence of | air sacs that are associated with the larger trachea
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| at rest most insects do not rely on ventilation of tracheal system and simply rely on ________________ for gas exchange | simple diffusion
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| how do bees ventilate during flight? | air sacs are compressed and expanded in response to muscle contraction/relaxation. That cycles during activity
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| what are benefits of ventilating during flight in bees? | 1. cycles of air sacs compressing/expanding relative to muscle contraction/relaxation during activity
2. reduces diffusion distance by bringing in fresh air and removing "old" air from trachea
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| how does ventilation reduce diffusion distance ? | by bringing in new air and removing "old" air from trachea
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| most aquatic insects use __________________ with adaptations for living in an aquatic environment | an air filled tracheal system
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| what are the two adaptation in aquatic insects regarding the tracheal system? | 1. using direct air intake by having spiracles located an one end of the body
2. using air bubbles as gas gills. Bubbles are trapped by hydrofuge hairs (hydrophobic) and are in contact with spiracles
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| how are air bubbles used as gas gills? | bubbles are trapped against spiracles, bubbles contain O2. As O2 is used, its concentration in the bubble is decreased. O2 diffuses from the water into the bubble
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| how does CO2 not accumulate in the air bubble ? | CO2 entering the bubble diffuses readily into the water due to it being more soluble than O2
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| how longs are air bubbles good for? | ~ 7 hours
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| what are some limitations of water as a respiratory medium? | 1. Gas diffusion in air much faster than in water
2. water is more viscous increasing the energetic cost of ventilating
3. low solubility of O2 in water
4. O2 tension varies in bodies of water
5. presence of sediments and decaying matter depletes O2
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| why is water more viscous than air | at atmospheric pressure:
mass of air/mL=0.0012g/mL
water= 1g/mL
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| why does water respiration cost more energy? | due to the low solubility of O2 in water, more water has to be moved across the respiratory system than air to obtain equivalent O2
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| 1L of water has _______ of O2 1 L of air contains _________ of O2 | 7mL
209mL
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| respiration in humans costs ________ of metabolism for gas exchange in fish, it costs _________ of metabolism for respiration | 1-3%, 10-20%
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| what are the sources of O2 in water? | 1. from atmosphere
2. photosynthesis
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| where is the highest O2 tension present in bodies of water? | O2 tension near the surface is greater than in deep water
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| why is deep water low in oxygen? | dark
no photosynthesis
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| why are lakes more likely to encounter O2 depletion? | due to thermal stratification
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| what is thermal stratification? | Temp in upper water increases, decreasing density which decreases layer mixing. Also known as summer fish kill
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| why does ag runoff, fertilizers, and sewage cause O2 depletion? | because it increases bacteria, fungi and algae which consume O2 in water causing fish kill
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| the outer covering of the gill structures | operculum
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| function of the operculum | protecting the gills
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| what is beneath the operculum | rows of gill filaments on four arches that form V
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| these structures are perpendicular to the gill filament | secondary lamellae
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| these are 10-40 mm and form sieve between oral and operculum cavity increasing the surface area for gas exchange | lamellae
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| functional unit in gas exchange | lamellae
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| how are the lamellae equipped to function in gas exchange? | thin walls
dense capillary network
both of these provide minimum barrier for diffusion ~ DeltaX= 0.6-6 microns
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| direction of water flow in teleost fish | mouth>buccal cavity>across gills>out the operculum
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| how is water forced across the gills in teleost fish | buccal floor raises increasing pressure in buccal cavity
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| what happens when the opercular cavity expands? | pressure in the opercular cavity decreases to below pressure in buccal cavity driving water from buccal cavity across gills to opercular cavity
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| how does water from the outside not enter the opercular cavity when P is decreased | blocked by valves
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| how is H2O discharged from the operculum | by raising the floor of buccal cavity to increase pressure which will instantly increase pressure in the opercular cavity which will open the valves in opercular cavity causing H2O to exit
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| rate of the continuous ventilation is determined by | activity level
O2 tension in water, increase in low O2 tension in H2O
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