Understanding Respiration

• Respiration involves the exchange of oxygen (O2) and carbon dioxide (CO2).
• O2 deprivation is fatal for animals.
• Animals constantly need O2 to produce energy in the form of ATP through metabolic processes.

Aerobic vs Anaerobic Respiration

• Anaerobic respiration: C6H12O6 → 2CH3COCOOH + 4H, produces 2CH3CHOHCOOH + 4ATP
• Aerobic respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + 34ATP
• Vital physiological processes rely on ATP which requires oxygen.
• Respiratory gases, like O2, need constant production; animals can't store them.

Types of Respiration

• External respiration transports O2 into the body and CO2 out involving the body and external environment.
• Internal respiration transports O2 into cells and CO2 out, involving the body and internal environment.
• Cellular respiration features intracellular catabolic reactions converting stored energy to ATP where oxygen is used (oxidative phosphorylation).

External Respiration

• External respiration moves O2 and CO2 to/from the gas-exchange membrane.
• A gas-exchange membrane is a thin layer of one/two simple epithelia separating internal tissues from the environment (air/water).
• External respiration includes environmental O2 to membrane to tissues, and dissolved CO2 from membrane to the environment, following the laws of physics and chemistry.
• Diffusion facilitates physiological movement.

Physics of Diffusion

• Diffusion: the transport of masses or solutes influenced by concentration gradients.
• Fick's Law determines rate: J = D * A * (C1 - C2) / X
• C1 & C2 represent regions of high and low solute concentration
• A stands for diffusion area & X is the distance separating concentration regions
• D is the diffusion coefficient, affected by temperature + solute properties.

Application of Fick's Law

• Gases aren't always high to low
• States J = D * A * (P1 - P2) / X
• P1 and P2 are regions of high+low partial pressure.

Diffusion Limits

• Vertebrate muscle requires O2 partial pressure ~40 mmHg
• Atmospheric O2 partial pressure = 160 mmHg
• For large vertebrates, diffusion is a slow process.
• Diffusion alone suffices for tiny animals like rotifers because the minimum O2 partial pressure reaches ~1 mm
• Need for a gas exchange respiratory membrane

Diffusion and Organism Size

• Oxygen needs increase with mass, diffusion alone is not enough
• As organisms get bigger, diffusion distance goes up.
• Decreases in surface area are relative to size
• Organisms often need respiratory organs that have a shorter diffusion distance and higher surface area
• Surface area to volume ratio is important (S/A:Vol)

Surface Area to Volume Ratio Examples

• Bacterium (1 µm): SA 6 x 10^-12 m², Vol 10^-18 m³, S/A:Vol 6,000,000:1
• Amoeba (100 µm): SA 6 x 10^-8 m², Vol 10^-12 m³, S/A:Vol 60,000:1
• Fly (10 mm): SA 6 x 10^-4 m², Vol 10^-6 m³, S/A:Vol 600:1
• Dog (1 m): SA 6 x 10^0 m², Vol 10^0 m³, S/A:Vol 6:1
• Whale (100 m): SA 6 x 10^4 m², Vol 10^6 m³, S/A:Vol 0.06:1

Adaptations to Prevent Diffusion limitations

• Animals use the direct relationship between body weight and area to avoid becoming diffusion limited, by:
• Increasing gas exchange membrane area vs body size
• Decreasing the thickness of the gas exchange membrane relative to body size.

Respiration Steps in Larger Animals

• In larger animals ventilation diffuses oxygen via the respiratory epithelia.
• A circulatory system + pulmonary system are required, including system capillaries

What Influences Respiratory System Structure

• Animal requirements and the medium are key
• Air vs water depends on the animal

Physical Properties of Gases

• Understanding the properties of gases, mixtures and aqueous solutions is needed for respiration
• Dalton’s Law Total pressure exerted by a gas mix is the sum of pressures exerted by each gas.
• Partial pressure means the individual pressure of a gas, diffusion rate is linked to its partial pressure in the total mix.
• O2 and CO2 will flow from high to low pressure

Air as a Respiratory Medium

• Air composition includes 79% N2 and 21% 02
• PN2 partial pressure of atmospheric air is ≅ 600 mm Hg
• P02 partial pressure of atmospheric air is ≅ 160 mm Hg
• The total pressure is ≈ 760mmHg at sea level

High Altitude Effects

• Higher elevations reduce the inspired oxygen pressure and not the percent of oxygen in the atmosphere
• At 5100m in La Rinconada, Peru there are 30,000 inhabitants.
• Bar Headed Geese can fly at >8000m altitude.

Air vs Water Properties in Respiratory Gases

• Water has less O2 vis a vis its environment
• Air (20°C): Oxygen diffusion coefficient (20,300), Oxygen solubility (1000), Viscosity (0.02)
• Water (20°C) Oxygen diffusion coefficient (2.1), Oxygen solubility (33.1), Viscosity (1)

Temperature + Dissolved O2

• Temperature alters dissolved 02 levels in water

Summary

• Respiratory gas exchange occurs through diffusion, following partial pressure differences between the environment and the animal's body.
• Larger animals face diffusion, needing special membranes that have larger areas and lower thickness
• Since water is less soluble than oxygen, breathing underwater requires more adaptations

Water vs Air Breathing

• Respiration for insects includes air breathing.
• There's less O2 in water+larger medium

Water Breathers - Gills

• Gills consist of invaginations, branched+folded to assist surface area
• Cilla beating or muscle contractions allow water to flow over gills

Types of Gills

• External gills can be extended outside the body without protective coverings
• Internal gills are in the body and protected by chambers, and water is directly put over them

Pumping Mechanisms

• Bony fish and cartilaginous fish have double pumping mechanisms that aren't universal
• A pressure gradient across gills helps the Buccal cavity to increase in volume and move water out
• Pelagic fish like sharks and mackerel often just swim with their mouths open because there are no double pump mechanisms

Gill Arches + Blood Flow

• Fish have 4 pairs of gill arches with countercurrent flow, in which blood and water flow in opposite directions.
• Filamentous gill projections promote a high level of oxygen absorption and extract oxygen from poor mediums.

Water and Blood flow

• Concurrent flow = O2 with blood (same direction) becomes at equilibrium too soon
• Countercurrent flow = O2 with conc gradient allows for diffusion, creating higher and efficient gas exchange

Fish Gills are Highly Efficient

• PaO2 is higher than PeO2
• It uses a pressure gradient along the secondary lamella
• This gives high efficiency.

Water Temperature

• Killifish have gills
• The benefit of diffusion is that O2 increases
• warmer water is more efficient
• This causes dense tissue to appear

Insect Tracheal Systems

• Tracheas = windpipes from the outter surface/skin that branch.
• Spiracles are openings on either side of the exoskeleton that air uses to enter/leave
• Tissues connect with extracellular fluid present where tissues are in contact with
• Gas passes in/out via diffusion of/to cells

Insect gas transport

• Diffusion path limits tissue size
• Small insects may just passively diffuse
• Larger insects ventilate using air supply and tracheal systems

Avian Lungs

• Avian species do not inflate or deflate
• They're connected to air sacs, small lungs, which pass out air.
• They uses different cycles
• They have unidirectional air flow
• The lungs have increased capillaries within with muscles

Adaptations to High Altitude

• Includes unidrectional lungs plus flight muscle vessels
• Crosscurrent exchange exists

Mammalian Respiratory System

• It includes a 2 way flow system, thus having a high PO2 which reduces how fast gas goes intot he blood

Lungs

• Alveoli have increased surface area
• Gas exchange happens between oxygen and carbon dioxide
• The diaphragm facilitates breathing/lung movement as well as intercostal muscles
• Reflexes prevent inhalation causing damage to areas such as trachea

Mammalian Lung Structure

• trachea
• Bronchi.
• Bronchioles
• Alveoli

Pressire

• According to Boyle's Law: P1 x V1 = P2 x V2

Inhalation

• Diaphragm contracts
• Volume expands

Exhalation

• Diaphragm relaxes
• Rib cage contracts

Lung volumes

• TV (Tidal Volume): Volume of air inhaled or exhaled during quite breathing
• IRV (Inspiratory Reserve Volume): The additional volume of air that can be inhaled
• ERV (Expiratory Reserve Volume): The additional volume of air that can be exhaled
• RV (Residual volume) Volume of air remaining in lungs after forced expiration, so lungs do not collapse

Lung Capacities

• IC (Inspiratory Capacity): V+IRV Amount of air that can be inspired after a normal tidal expiration.
• VC (Vital Capacity): V+IRV+ERV Maximum amount of exchangeable air.
• FRC(Functional Residual capacity): ERV+RV Amount of air left in lungs after a quite expiratoin.
• TLC(Total Lung Capacity):V+ERV+IRVV Total amount of air lungs can hold.

Tidal Ventilation

• During breathing air mixes
• air contains oxygen
• Lower respiratory membrane allows exchange and diffusion

Hemoglobin

• oxygen is low
• Partial pressire allows

Hemoglobin

• Can be compared to oxygen

PH Hemoglobin

• Releases oxygen in tissue
• Is used by the cardiovascular system
• is located in the arterial and peripheral circulation

Regulation

• Air that's based on oxygen goes into blood
• and it travels throughout the body