Week 11 The respiratory system (introduction & respiratory strategies

Question 1

What is air made of?

Answer 1

Air = mixture of gases
Nitrogen (78%),
Oxygen (21%), 
Argon (0.9%), 
Carbon dioxide (0.03%)

Question 2

What does Dalton’s law dictate?

Answer 2

– 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

Question 3

Calculate the PP of O2 in environment at sea level.

Answer 3

– atmospheric pressure = 760 mmHg (might be given might not, good to know)
21% is Oxygen of that total
-0.21 x 760= 160 mmHg

Question 4

Calculate the PP of O2 in environment at 18,000 ft

Answer 4

– atmospheric pressure = 380mmHg (would be given)

- 0.21 x 380 mmHg= 80mmHg

Question 5

How does atmospheric pressure change with altitude and how does that affect biological organisms? give examples.

Answer 5

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)

Question 6

What adaptations do animals that live in high altitude regions have?

Answer 6

– Able to extract O2 more efficiently from air
– Can tolerate low blood O2
– Can tolerate changes in blood CO2 & pH

Question 7

Why is oxygen necessary for life?

Answer 7

– 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

Question 8

What is cellular respiration?

Answer 8

– process by which mitochondria consume O2 and produce CO2

Question 9

What is external respiration?

Answer 9

– 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

Question 10

How do Unicellular organisms & small organisms (aquatic environments) perform external respiration?

Answer 10

• utilize diffusion gradient – drives gas exchange with environment

Question 11

How do larger animals perform external respiration?

Answer 11

• 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

Question 12

What are the steps of external respiration?

Answer 12

(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

Question 13

What is the formula for rate of diffusion? (alternatively what is rate of diffusion?)

Answer 13

-Fick’s law of diffusion dQ/dt = D x A x (dC/dx)

Question 14

What are Factors that influence rate of diffusion?

Answer 14

– 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

Question 15

What are Factors that influence diffusion when gases dissolved in liquids ?

Answer 15

– gas solubility (proportional)

– molecular weight (indirectly proportional)

Question 16

Summary of ALL factors that affect rate of diffusion.

Answer 16

– 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)

Question 17

How does O2 concentration differ in water and air?

Answer 17

– 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

Question 18

What’s the significance of the respiratory medium?

Answer 18

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

Question 19

What are the main respiratory strategies?

Answer 19

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

Question 20

How do gills and lungs differ?

Answer 20

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

Question 21

How do most animals ventilate?

Answer 21

• 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

Question 22

What is necessary for optimum gas exchange?

Answer 22

• Respiratory medium must be well mixed - availability of fresh O2
• Diffusional distance must be small

Question 23

What is non-directional ventilation?

Answer 23

• medium flows past the GE surface in an unpredictable pattern
• e.g. animals that wave gills through the external medium
• e.g skin breathers

Question 24

What do we need to consider with non-directional ventilation?

Answer 24

-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

Question 25

How does diffusional distance affect gas exchange?

Answer 25

– ↑ diffusional distance ↓ rate of diffusion ↓ GE efficiency

– e.g. cutaneous respiration – skin thicker than lining of gills/lungs

Question 26

What is tidal ventilation and what do we have to consider?

Answer 26

• 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

Question 27

How does tidal ventilation work?/What is it’s significance?

Answer 27

– 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

Question 28

What is unidirectional ventilation?

Answer 28

• 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

Question 29

What do we need to consider with unidirectional ventilation?

Answer 29

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