Physics of Respiratory Systems

Physics of Respiratory Systems

• The respiratory system aids passive diffusion of gases
• Diffusion facilitates molecule movement down a pressure gradient
• For most organisms, diffusion alone is insufficient to supply oxygen to cells and tissues
• A respiratory system provides a surface for gas exchange via diffusion between blood and air or water

Respiratory Surface Requirements

• Must be moist to allow cells to live and facilitate diffusion
• Must be large enough to permit sufficient gas exchange
• Must be thin enough to permit rapid diffusion

Fick's Law of Diffusion

• dQ/dt = D x A x (dC/dx)
• D is the diffusion coefficient
• A is the area of the membrane
• dC/dx represents the gradients
• Rate is maximized when:
  • Diffusion coefficient (D) is large
  • Membrane area (A) is large
  • Gradients (dC/dx) are large
  • Diffusion distance (x) is small
• Gas exchange surfaces are typically thin with a large surface area

Henry's Law and Gas Dissolution

• Henry's law equation: [G] = S x P
• G is the gas concentration in the solution
• P is the partial pressure of the gas in air
• S is the solubility of the gas

Ideal Gas Law

• Ideal gas law is: PV = nRT
• Total pressure exerted by a gas relates to number of moles and volume
• P is the pressure in Pascals (Pa)
• V is the volume in cubic meters (m³)
• n is the amount of substance in moles (mol)
• R is the gas constant 8.314 J/(mol·K)
• T is the temperature in Kelvin (K)
• Volume of a gas is inversely proportional to pressure

Dalton's Law of Partial Pressures

• Air is a mixture of gases: Nitrogen (78%), Oxygen (21%), Argon (0.9%), Carbon Dioxide (.04%)
• In a gas mixture, each gas exerts its own partial pressure, which sums to the total mixture pressure
• Atmospheric pressure = 760 mm Hg: Nitrogen partial pressure = 600 mm Hg, and Oxygen partial pressure = 160 mm Hg

Graham's Law of Diffusion

• Diffusion rate: Directly related to solubility and inversely related to molecular mass
• The rate is proportional to Diffusion ~ solubility / √(molecular weight)
• Factors affecting diffusion: solubility, molecular weight, pressure gradient, surface area, and membrane thickness

Respiratory Strategies: Surface Area and Volume Ratio

• As organisms grow, the ratio of surface area to volume decreases
• This reduces the availability for diffusion and increases diffusion distance

Respiratory Strategies: Diffusion Alone

• Animals must be less than a few millimeters thick
• Exchange occurs through circulatation of the external medium
  • Sponges, cnidarians, and insects
• Gas exchange happens across the body with circulatory transport
  • Cutaneous respiration observed in aquatic invertebrates, some amphibians, birds' eggs
• Exchange across a specialized respiratory surface with circulatory transport
  • Gills (evaginations) or lungs (invaginations) observed in vertebrates

Cutaneous Respiration and Lungless Salamanders

• Observed in nematodes, horsehair worms, tubellarian flatworms
• Oxygen transfer across the body surface is observed in most aquatic invertebrates, terrestrial annelid worms, frogs, and salamanders
• Consists Very thin skin (prone to damage)
• Tradeoff between surface area and skin requirements
• Need to keep skin moist (limits to aquatic or wet habitats)

Specialized Respiratory Surfaces: Gills and Lungs

• Located on terrestrial and aquatic animals
• Gills: Outpockets, usually in water
• Lungs: Infoldings terrestrially
• Air exchange is associated with ventilation: movement of external medium, air can be unidirectional and Tidal

Ventilation and Gas Exchange

• Air and water differences impact animal respiratory strategies
  • Oxygen is 30x greater in air
  • Water is more dense and viscous than air
  • Evaporation is only an issue for air breathers

Ventilation Strategies in Water

• Circulate external medium through an internal cavity
• Ventilate internal and external gills

Ventilation in Sponges and Cnidarians

• Sponges: Flagella move water in througHthe osculum
• Cnidarians: Tissue contractions move water in and out through the mouth

Unidirectional Flow in Molluscs

• Cilia beating on gills moves water unidirectionally across gills

Molluscs Respiration Through Gills and Mantle

• Muscular contractions propel water through the mantle cavity past gills
• Exists in cephalopods
• Blood flow is countercurrent

Crustacean Respiration

• Filter feeders (barnacles) or small species (copepods) lack gills
• Shrimp, crabs, and lobsters use gills derived from modified appendages within a brachial cavity
• Gill bailer (scaphognathite) movements propel water out of the brachial chamber creating negative pressure

Echinoderm

• Sea stars and sea urchins exchange gas through tube feet
• Water enters and exits through the madreporite
• Cilia move water across external, gill-like structures (respiratory papulae)
• Brittle stars and sea cucumbers have internal invaginations/cilia

Fish Respiration

• Brile stars and sea cucers have internal invagina ons

Jawless Fish (Lampreys and Hagfish)

• Multiple pairs of gill sacs
• Hagfish: Uses a muscular pump (velum) to propel water
• Water enters and leaves through a gill opening
• Flow is unidirectional with countercurrent bloodflow
• Lamprey: Ventilation is similar to hagfish when not feeding, tidal through gill openings,
• They also exist when feeding and attached to prey (parasitic)

Elasmobranch (Sharks and Rays) Respiration

• Steps involved in ventilation include
  • Expanding buccal cavity
  • Increasing volume and drawing water in through spiracles
  • Closing Spiracles and mouth
  • Contracting muscles around the buccal cavity to push water out through gill slits
  • Blood flow is countercurrent

Teleost Fish Respiration

• Gills are located in the operculum-protected cavity
• Ventilation steps: the mouth opens, the buccal cavity floor lowers, volume increases, water is sucked in
• The opercular cavity then expands, pressure and volume decreases, and the mouth closes
• The oral cavity raises, volume decreases and the pressure increases as the water leaves through opercular slit
• Active fish uses ram ventilation

Fish Gills

• Arranged for countercurrent flow
• Operculum covers gills

Ventilation and Ram Ventilation in Water

• Ram ventilation: Flow of H20 across respiratory area through fwd movment
  • Observed in tuna, mackerel and billfish

Vertebrate Air Breathing

• Air breathing has evolved multiple times in fishes

Teleost Fish Air Breathing

• Fish can use reinforced gills that do not have capacity to collapse in air, limited gas exchange but can live out of water
  • Mudskippers
• Accessory breathing: mouth or pharyngeal cavity (highly vascluarized)
• Buccal forces are similar to lungfish
• Specialized pockets are used when they are dal and unlike other fish

Lungfish Anatomy and Physiology

• Lungs are highly developed accessory breathing organs
• Walls of the lung are complex
• Maximized by use of surface area
• Contain Pneumatic ducts
  • Australian lungfish (Neoceratodus): Has a single lung and well-developed gills
  • African lungfish (Protopterus): 2 lungs, reduced gills South America lungfish (Lepidosiren): 2 lungs and reduced gills

Lung features within Alveoli

• Extends the lung wall that is open to common lumen
• Contain, and bind sacs that are at the end of long air passages

Amphibian Respiratory Structures

• Amphibians have simple bilobed lungs or complex structures. Ventilation is tidal using a buccal force pump

Reptile Respiratory Anatomy and Physiology

• Reptiles are Mul cameral lungs fed by bronchi
• Most have lungs
  • In snakes one lung may be reduced or absent
• Ventilation: Tidal and relies on suction pumps dependent on separte feed and muscular breathing
• Use one of serveral chest changing mechanisms

Crocodilian and Bird Respiratory Systems

• Muscular contraction pulls the hepatic septum and liver creating negative flow, acts like a piston
• Have a Hepa c septum on the anterior side of the liver and divives visceral cavity in two
• Ventilation by movements of ribs and sternum

Bird Respiratory System

• Birds use air sacs and parabronchi
• Their Lung do not change and are relatively sf
• The rely on series that are made of flex
• Air capillaries are are very samll and has high of the exchange area to be very effective
• Ventilation Requires 3 cycles of movement with 2 air flows, has continuous flow

Mammalian Respiratory System

• Lungs have two parts
  • upper has a nasal cavity, lower contains bronchi and airways
  • the lung is a site of the Alveoli Both lungs are surrounded by a plural sec

Mammalian Anatomy for Breathing

• Tidal is volume of air in the process, exchange doesnt need to happen, volume is air to the area
• Lung capacity: inhalation for normal breath
• residual volume=what left in the lungs