Week 11 The respiratory system (introduction & respiratory strategies Flashcards
What is air made of?
Air = mixture of gases Nitrogen (78%), Oxygen (21%), Argon (0.9%), Carbon dioxide (0.03%)
What does Dalton’s law dictate?
– In a gas mixture, each gas exerts its own partial pressure (PP)
– The sum of PPs of all gases in a mixture gives total pressure
– PP of a gas is proportional to the number of gas molecules
Calculate the PP of O2 in environment at sea level.
– atmospheric pressure = 760 mmHg (might be given might not, good to know)
21% is Oxygen of that total
-0.21 x 760= 160 mmHg
Calculate the PP of O2 in environment at 18,000 ft
– atmospheric pressure = 380mmHg (would be given)
- 0.21 x 380 mmHg= 80mmHg
How does atmospheric pressure change with altitude and how does that affect biological organisms? give examples.
With increasing altitude, atmospheric pressure ↓ (decreases)
• air becomes thinner at higher altitudes
• summit of Everest - air has 1/3 of the O2 content per unit volume
– Humans – cant survive high altitudes > only few hrs without supplemental O2
– Many other animals reach higher altitudes with no ill effects
– E.g. pikas (genus Ochotona), jumping spiders (family Salticidae)
What adaptations do animals that live in high altitude regions have?
– Able to extract O2 more efficiently from air
– Can tolerate low blood O2
– Can tolerate changes in blood CO2 & pH
Why is oxygen necessary for life?
– animals depend on cellular respiration to supply ATP
– mitochondria oxidise nutrients → produce ATP
– consume O2 & produce CO2
= must obtain O2 from environment & dispose of CO2 to meet metabolic needs
What is cellular respiration?
– process by which mitochondria consume O2 and produce CO2
What is external respiration?
– sequence of events associated with exchange of O2 & CO2 between external environment & mitochondria within cells
– mitochondria consume O2 & ↓ local O2 concentration
=concentration gradient – low O2 in cell, high O2 in blood
How do Unicellular organisms & small organisms (aquatic environments) perform external respiration?
• utilize diffusion gradient – drives gas exchange with environment
How do larger animals perform external respiration?
• diffusion & bulk flow used to obtain O2 from environment & deliver to cells
- utilise diffusion to transport gases across short distances
- utilise bulk flow to transport gases over long distances
What are the steps of external respiration?
(x 4 steps)
1. Ventilation (bulk flow)
– respiratory medium (air/water) moved across respiratory surface
2. Exchange of O2 & CO2
– exchange between respiratory surface & blood
3. Transport of O2 & CO2 (bulk flow)
– transport between respiratory surface/blood interface & tissues by CS
4. Exchange of O2 & CO2
– exchange between blood & tissues across systemic capillaries
What is the formula for rate of diffusion? (alternatively what is rate of diffusion?)
-Fick’s law of diffusion dQ/dt = D x A x (dC/dx)
What are Factors that influence rate of diffusion?
– Diffusion coefficient (D)
• index of ease of diffusion of particular substance through given medium
– Area of the membrane (A)
– Concentration or energy gradient (dC/dx or ∆Pgas)
• difference in concentration per unit distance – energy gradient
• when applied to gases the energy gradient - pressure difference
What are Factors that influence diffusion when gases dissolved in liquids ?
– gas solubility (proportional)
– molecular weight (indirectly proportional)
Summary of ALL factors that affect rate of diffusion.
– factors that affect rate of diffusion of a gas in fluid (at constant temp): Directly proportional: – diffusion coefficient (D) – cross-sectional area (A) – PP gradient (dC/dx or ∆Pgas) – solubility of the gas in fluid (Sgas)
Indirectly proportional:
– diffusional distance (X)
– molecular weight of the gas (MW)
How does O2 concentration differ in water and air?
– Gases are not very soluble in aqueous solution
– concentration of O2 dissolved in water < conc of O2 in air
Sea level – molar concentration of O2 in air = 9mM
Sea level – molar concentration of O2 in water = 3mM
What’s the significance of the respiratory medium?
Water
• ↑ energy cost
• more fluid must be moved across respiratory surface to obtain same O2
Air
• ↓ energy cost
• less air must be moved across respiratory surface to obtain same O2
What are the main respiratory strategies?
x 3 major respiratory strategies
1. Circulating external medium through body
• Sponges, cnidarians, many terrestrial arthropods
2. Diffusion of gases across all/most of body surface
+ transport of gases in CS (circulatory system)
• Cutaneous respiration, limitations ++ (need large SA, thin skin and capillaries near skin, however thin skin dangerous etc)
• Aquatic invertebrates, terrestrial annelid worms, some vertebrates (frogs), bird eggs
3. Diffusion of gases across specialised respiratory surface
+ transport of gases in CS(circulatory system)
• Classified as gills or lungs
How do gills and lungs differ?
Gills
• Originate as outpocketings (evaginations) of body surface
• External or located within respiratory cavity
• Protected by flap or other covering - oberculum
+Commonly used for GE (Gas exchange) in water
Lungs
• Originate as infoldings (invaginations) of body surface
• Form an internal body cavity that contains the external
medium
+Commonly used for GE(gas exchange) in air
How do most animals ventilate?
• most animals ventilate the respiratory surface
– move external medium across the surface by bulk flow
– when blood meets GE surface it depletes air/water of O2
– creates boundary layer of O2
-depleted medium =static boundary layer
• these animals also have CS that moves fluid/blood by bulk flow
through body
• movement of blood through respiratory surface important for GE Efficiency
What is necessary for optimum gas exchange?
- Respiratory medium must be well mixed - availability of fresh O2
- Diffusional distance must be small
What is non-directional ventilation?
- medium flows past the GE surface in an unpredictable pattern
- e.g. animals that wave gills through the external medium
- e.g skin breathers
What do we need to consider with non-directional ventilation?
-Respiratory medium - poorly mixed
– when blood meets GE surface it depletes respiratory medium of O2
– creates boundary layer of O2
-depleted medium =static boundary layer
How does diffusional distance affect gas exchange?
– ↑ diffusional distance ↓ rate of diffusion ↓ GE efficiency
– e.g. cutaneous respiration – skin thicker than lining of gills/lungs
What is tidal ventilation and what do we have to consider?
• external medium moves in/out of respiratory chambers (back/forth motion)
• e.g. animals with internalised gills or lungs
Considerations:
• animals cannot completely empty respiratory cavity
How does tidal ventilation work?/What is it’s significance?
– Animal breathes in
– Incoming medium mixes with residual O2
-depleted medium
– PO2 in respiratory cavity < external environment
– PO2 of blood exiting GE surface same as that in exhaled medium
What is unidirectional ventilation?
• respiratory medium enters respiratory chamber at one point & exits at another
• medium flows in single direction across respiratory surface
• Blood can flow in 3 ways relative to external medium
• Countercurrent flow MOST efficient in terms of gas exchange
– blood & medium flow in OPPOSITE directions =Countercurrent flow
What do we need to consider with unidirectional ventilation?
Blood & medium flow in OPPOSITE directions
– as blood flows through GE surface
– blood progressively more oxygenated
– medium progressively more deoxygenated
– PP gradient always favours diffusion of O2 into blood
-PO2 of blood leaving GE surface similar to that of inhaled medium
-Efficiency depends on flow rates - most efficient when flow rate SLOW
