Adaptations for Respiratory Gas Exchange

Now that we know the physical factors that influence the rates of diffusion of respiratory gases between an animal and its environment, let's take a look at some of the adaptations animals have evolved for maximizing their respiratory gas exchange. They include adaptations for increasing the surface area over which diffusion of gases can occur, maximizing partial pressure gradients, and minimizing the diffusion path length through an aqueous medium.

Respiratory organs have large surface areas

Many anatomical adaptations maximize the specialized body surface area (A) over which respiratory gases can diffuse. External gills are highly branched and folded extensions of the body surface that provide a large surface area for gas exchange with water (Figure 48.3a). External gills are found in larval amphibians and in many insect species. Because they

(a) External gills

(b) Internal gills

(a) External gills

(b) Internal gills

Adaptation For Respiratory Gas Exchange

(d) Tracheae

(d) Tracheae

consist of thin, delicate tissues, they minimize the length of the path (L) traversed by diffusing molecules of O2 and CO2. Because external gills are vulnerable to damage and are tempting morsels for carnivorous organisms, protective body cavities for gills have evolved. Many mollusks, arthropods, and fish have internal gills in such cavities (Figure 48.3b).

Air-breathing vertebrates also have large surface areas for gas exchange. Lungs are internal cavities for respiratory gas exchange with air. Their structure is quite different from that of gills (Figure 48.3c). Lungs have a large surface area because they are highly divided, and they are elastic so that they can be inflated and deflated with air.

The most abundant air-breathing invertebrates are insects, which have a respiratory gas exchange system consisting of a highly branched network of air-filled tubes called tracheae that branch through all tissues of the insect's body (Figure 48.3d). The terminal branches of these tubes are so numerous that they have an enormous surface area.

Transporting gases to and from the exchange surfaces optimizes partial pressure gradients

Fick's law of diffusion points to other possible adaptations besides increasing the surface area for gas exchange. Animals can maximize the partial pressure gradients (P1 - P2/L) that drive the diffusion of respiratory gases across their gas exchange surfaces in several ways:

► Very thin tissues in gills and lungs reduce the diffusion path length (L).

► Breathing actions move the respiratory medium past the environmental side of the exchange surfaces. This process, called ventilation, supplies the exchange surfaces with fresh respiratory medium that has maximum O2 and minimum CO2 concentrations.

► Circulatory systems transport respiratory gases to and from the internal side of the exchange surfaces. This process, called perfusion, helps maintain the lowest possible 02 concentration and the highest possible C02 concentration on the inside of the exchange surfaces.

An animal's gas exchange system is made up of its gas exchange surfaces and the mechanisms it uses to ventilate and perfuse those surfaces. The following sections describe four

48.3 Gas Exchange Systems Large surface areas (blue in these diagrams) for the diffusion of respiratory gases are common features of animals. Both external (a) and internal (b) gills are adaptations for gas exchange with water. Lungs (c) and tracheae (d) are organs for gas exchange with air.

Air sacs Trachaea

Air sacs Trachaea

Air Sacs Insect

48.4 The Tracheal Gas Exchange System of Insects

(a) In insects, respiratory gases diffuse through a system of air tubes (tracheae) that open to the external environment through holes called spiracles. (b) The spiricles of a sphinx moth larva run down its sides and are visually obvious. (c) A scanning electron micrograph shows an insect trachea dividing into smaller tracheoles and still finer air capillaries.

gas exchange systems. First we'll look at the gas exchange system of insects. Then we'll describe two remarkably efficient systems: fish gills and bird lungs. Finally, we'll discuss human lungs.

insect tracheae. Respiratory gases can diffuse through air most of the way to and from every cell of an insect's body. This diffusion is achieved through a system of air tubes, or tracheae, that communicate with the outside environment through gated openings called spiracles in the sides of the abdomen (Figure 48.4a,b). The spiracles can open to allow gas exchange, and then close to decrease water loss. The tracheae branch into even finer tubes, or tracheoles, until they end in tiny air capillaries (Figure 48.4c). In the insect's flight muscles and other highly active tissues, no mitochondrion is more than a few micrometers away from an air capillary.

Some species of insects that dive and stay under water for long periods make use of an inter esting variation on diffusion. These insects carry with them a bubble of air. A small bubble may not seem like a very large reservoir of O2, yet these insects can stay under water for a long time with their small air supplies. The secret has to do

Gill arches (under opercular flap)

Water flow Water flow

Gill arches (under opercular flap)

Turbinate Countercurrent Exchange

Water flow Water flow

Each filament is folded into many thin, flat gas exchange surfaces called lamellae.

Deoxygenated blood enters (O2 low)

Oxygenated blood leaves (O2 high)

Each filament is folded into many thin, flat gas exchange surfaces called lamellae.

Deoxygenated blood enters (O2 low)

Oxygenated blood leaves (O2 high)

Exchange Surface Insect

Lamella

Water flow

Water enters, O2 is high.

O2 diffuses from water into the blood over the entire length of a lamella.

Blood flow through the lamellae is countercurrent to the flow of water over the lamellae.

Afferent blood vessel

Efferent ' blood vessel

Oxygenated blood

Afferent blood vessel

Efferent ' blood vessel

Oxygenated blood

Lamella

Water flow

Water enters, O2 is high.

O2 diffuses from water into the blood over the entire length of a lamella.

Blood flow through the lamellae is countercurrent to the flow of water over the lamellae.

48.5 Fish Gills (a) Water flows unidirectionally over the gills of a fish. (b) Gill filaments have a large surface area and thin tissues. (c) Blood flows through the lamellae in the direction opposite (left to right, in this depiction) to the flow of water (right to left) over the lamellae.

with the Po2 in the bubble. When the insect dives, the air bubble contains about 80 percent nitrogen and 20 percent O2. As the insect consumes the O2 in its bubble, the bubble shrinks a little. The bubble doesn't disappear, however, because it consists mostly of nitrogen, which the insect does not consume.

When the PO2 in the bubble falls below the PO2 in the sur-

rounding water, O2 diffuses from the water into the bubble. The bubble acts as an auxiliary lung, and for these small animals, the rate of O2 diffusion into the bubble is enough to meet their O2 demand while they are under water.

fish gills. The internal gills of fish are supported by gill arches that lie between the mouth cavity and the protective opercular flaps on the sides of the fish just behind the eyes (Figure 48.5a). Water flows unidirectionally into the fish's mouth, over the gills, and out from under the opercular flaps, so that the gills are continuously bathed with fresh water. This constant, one-way flow of water moving over the gills maximizes the Po2 on the external surfaces. On the internal side, the circulation of blood minimizes the Po2 by sweeping the O2 away as rapidly as it diffuses across.

The gills have an enormous surface area for gas exchange because they are so highly divided. Each gill consists of hundreds of leaf-shaped gill filaments (Figure 48.5b). The upper and lower flat surfaces of each gill filament are covered with rows of evenly spaced folds, or lamellae. The lamellae are the actual gas exchange surfaces. Their delicate structure minimizes the path length (L) for diffusion of gases between blood and water. The surfaces of the lamellae consist of highly flattened epithelial cells, so the water and the fish's red blood cells are separated by little more than 1 or 2 |m.

The flow of blood perfusing the inner surfaces of the lamellae, like the flow of water over the gills, is unidirectional. Afferent blood vessels bring blood to the gills, while efferent blood vessels take blood away from the gills (Figure 48.5c). Blood flows through the lamellae in the direction opposite to the flow of water over the lamellae. This countercurrent flow optimizes the Po2 gradient between water and blood, making gas exchange more efficient than it would be in a system using concurrent (parallel) flow (Figure 48.6).

Some fish, including anchovies, tuna, and certain species of sharks, ventilate their gills by swimming almost constantly with their mouths open. Most fish, however, ventilate their gills by means of a two-pump mechanism. The closing and contracting of the mouth cavity pushes water over the gills, and the expansion of the opercular cavity prior to opening of the opercular flaps pulls water over the gills.

These adaptations allow fish to extract an adequate supply of O2 from meager environmental sources by maximizing the surface area (A) for diffusion, minimizing the path length (L) for diffusion, and maximizing the Po2 gradient by means of constant, unidirectional, countercurrent flow of blood and water over the opposite sides of their gas exchange surfaces.

bird lungs. As we saw at the beginning of this chapter, birds can sustain extremely high levels of activity much longer than mammals can—even at very high altitudes, where mammals cannot even survive. Yet the lungs of a bird are smaller than the lungs of a similar-sized mammal. How can this be? Another unusual feature of bird lungs is that they expand and contract less during a breathing cycle than mammalian lungs do. To make things even more puzzling, bird lungs contract during inhalation and expand during exhalation!

The structure of bird lungs allows air to flow unidirec-tionally through the lungs, rather than having to flow in and

(a) Concurrent flow

% Saturation Gill lamellae ff /

Blood flow

Water flow 100%

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Responses

  • Fastred
    How insect tracheal system maximise the efficiency of gaseous exchange?
    7 years ago
  • PHILIPP
    Has exchange in insects?
    7 years ago
  • rasmus
    Are highly branched folds of the body surface that maximise gas exchange?
    7 years ago
  • Dominik
    What is the process of moving the respiratory medium past the sites of gas exchange?
    7 years ago
  • Kenneth
    What are some adaptations that increase surface area in animal system?
    7 years ago
  • Nicholas
    What are all the adaptations that increase surface area in animal systems?
    7 years ago
  • markus eichelberger
    Why are fish gills continually bathed in fresh water?
    7 years ago
  • gioele
    Do any fish use concurrent flow?
    7 years ago
  • aziz
    How to maximize gas exchange?
    7 years ago
  • Chilimanzar
    Why the gas exchange system of insects and mammals are similar?
    7 years ago
  • Caden Gibson
    How does insects moves gases over the gas exchange surface>?
    7 years ago
  • HAYLEY
    What structures provide a large surface area for gas exchange in frogs?
    7 years ago
  • Ulrich
    What minimizes the diffusion distance for o2 and co2?
    7 years ago
  • Joshua
    How do exchange gases fish?
    7 years ago
  • Dorotea Dellucci
    Why do gill membranes have large surface area?
    6 years ago
  • alide
    What is the flow of water through a fish?
    6 years ago
  • casimiro
    How do the respiratory surfaces adaptions make for efficient gas exchange?
    6 years ago
  • Aziza
    What specialized adaptations do fish have for maximize gas exhange?
    6 years ago
  • robur tunnelly
    What are some adaptations that help increase gas diffusion in animals?
    6 years ago
  • jasmine
    How insect highly developed gases exchange?
    6 years ago
  • lexi
    What are the three adaptations that enhance the function of a respiratory surface?
    5 years ago
  • MULU
    Are highly branched folds of the body surface that maximize gas exchange?
    5 years ago
  • drew
    Do any fish have tracheae?
    5 years ago
  • Melissa
    How Do Respiratory Adaptations Minimize Diffusion Distances?
    5 years ago
  • jessica
    Which of the following is not an adaptation for gas exchange?
    5 years ago
  • cheryl swan
    What adaptations do fish have to allow this exchange?
    5 years ago
  • semret brhane
    How do lamallae minimize the diffusion length in fish?
    5 years ago
  • dina bruno
    What adaptations do fish have to enhance gas exchange?
    4 years ago
  • michael
    Which of the following is not an adaptation for respiratory gas exchange?
    4 years ago
  • ritva virrankoski
    What adaptations do lungs have to maximise diffusion?
    2 years ago
  • COSIMO SANDHEAVER
    What is the adaptation of the following gaseous exachange surface Gills?
    2 years ago
  • danait
    What is the adaption of gas exchange on the body surface?
    2 years ago
  • cesio
    What are adaptation of gills in acting as gaseous exchange?
    2 years ago
  • christopher
    What would speed up the rate of gaseous exchange in insects?
    2 years ago
  • hildibrand
    What are the adaptive features of respiratory surface?
    2 years ago
  • dawit
    How respiratory surface adapt to its function?
    1 year ago
  • Asfaha
    What is adaptation for respiratory media in animal?
    1 year ago
  • antero
    Why are lungs and gills highly folded?
    1 year ago
  • may
    How are the gills adapted to gaseous exchange?
    1 year ago
  • teighan
    How are the lungs and gill structures adapted to their function?
    1 year ago
  • Tim
    How is the respiratory surface in fish adapted to its functions?
    1 year ago
  • emma
    Why are lungs and gills highly foilded?
    1 year ago
  • Virpi
    WHO DOES A MOSQUITO LARVAE USE FOR GASEOUS EXCHANGE?
    1 year ago
  • adalfredo
    Which respiratory surfaces are adapted for gaseous exchange?
    1 year ago
  • gerda
    How are respiratory surface in mammals adapted to their functions?
    1 year ago
  • camilla
    How the different characteristics of respiratory surface?
    1 year ago
  • franziska
    How are respiratory surface in mammals adapted to their function?
    1 year ago
  • tom
    How are gases transported in insect bodies?
    1 year ago
  • franziska meister
    How the gill filaments are adapted to their function?
    1 year ago
  • Lorena
    How respiratory surfaces in animals adapted to functions?
    1 year ago
  • fesahaye
    What adaptation are found in the surface during respiration for gases exchange?
    12 months ago
  • jaiden
    What makes respiratory adapt to its function?
    11 months ago
  • MARTIN
    How can air sacs adapt to respiration?
    9 months ago
  • tony spence
    How the tracheal system is adapted to its funsion?
    9 months ago
  • girma
    Why is the gaseous exchange surfaces very thin?
    9 months ago
  • ivy
    How is the respiratory surface in man adapted to carry out its function?
    8 months ago
  • timoteo palerma
    What are the adaptative features of gills for respiration?
    8 months ago
  • Patricia Roye
    Why do mammals use gaseous respiration and not aqueous respiration?
    7 months ago
  • madihah teodros
    How respiratory surface is adopted to their function?
    7 months ago
  • leanna
    How are gills adapted to breathing?
    6 months ago
  • justiina
    How are the respiratory surfaces in animals adapted to their function?
    6 months ago
  • Regina
    How an insect is suited for gaseous exchange?
    5 months ago
  • vanessa
    How are gaseos exchange surface of a frog adapted on the function?
    3 months ago

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