Respiratory SystemsWhat is a respiratory system? How does it work?What are the functions of respiratory systems?What are the different respiratory strategies that animals use?

DefinitionsRespiration sequence of events that result in the exchange of oxygen and carbon dioxide between the external environment and the mitochondria

External respiration gas exchange at the respiratory surface

Internal respiration gas exchange at the tissues

Mitochondrial respiration production of ATP via oxidation of carbohydrates, amino acids, or fatty acids. Oxygen is consumed and carbon dioxide is produced

Mitochondrial respirationMitochondria consume O2 to produce ATPProduce CO2 in processOrganisms must have mechanisms to obtain O2 from the environment and get rid of CO2

Unicellular and small multicellular organisms rely on diffusion for gas exchangeLarger organisms must rely/depend on a combination of bulk ( large ) flow and diffusion for gas exchange, i.e., they need a respiratory system Respiratory strategies of animals

Respiratory systems - physicsDiffusionDiffusion is the movement of molecules from a high concentration to a low concentration Slow over long distancesFast over short distances

Respiratory strategies of animalsUnicellular and small multicellular organisms rely on diffusion for gas exchangeLarger organisms must rely on a combination of bulk flow and diffusion for gas exchange, i.e., they need a respiratory system

Respiratory StrategiesAnimals more than a few millimeters thick use one of three respiratory strategiesCirculating the external medium through the bodySponges, cnidarians

Diffusion of gases across the body surface accompanied by circulatory transportCutaneous respirationMost aquatic invertebrates, some amphibians, eggs of birds

Diffusion of gases across a specialized respiratory surface accompanied by circulatory transportGills (evaginations) or lungs (invaginations)Vertebrates

Circulating the external medium through the body Parazoa and Cnidaria

Circulating the external medium through the body Tracheal systemSeries of narrow ( sempit ) tubes leading from surface to deep within bodyGases move in the tubes via a combination of diffusion and bulk flow

Cricket spiracle

Most animals have a circulatory systemRespiratory surfaceTissueCirculatory systemExternal mediumDiffusion of gases across a specialized respiratory surface accompanied by circulatory transportO2O2

Cutaneous respirationRespiration through skinFound in some aquatic invertebrates and a few vertebratesSalamanderAnnelidLake Titicaca frog

External gillsGills originate as outpocketings (evaginations)

Advantages: high surface areaDisadvantages: easily damaged, not suitable in airPolychaeteSalamander

Internal gillsAdvantages: High surface areaDisadvantages: not usually suitable in air

LungsOriginate as infoldings (invaginations)

Advantages: High surface area, protected, suitable for breathing airDisadvantages: not suitable in water

Ventilation The active movement of the respiratory medium (air or water) across the respiratory surfaceVentilation of respiratory surfaces reduces the formation of static boundary layers i.e. improves efficiency of gas exchangeTypes of ventilationNondirectional - medium flows past the respiratory surface in an unpredictable patternTidal - medium moves in and outUnidirectional - medium enters the chamber at one point and exits at anotherAnimals respond to changes in environmental oxygen or metabolic demands by altering( mengubah ) the rate or pattern of ventilation

Ventilation and Gas ExchangeBecause of the different physical properties of air and water, animals use different strategies depending on the medium in which they liveDifferences[Oair] 30x greater than [Owater]Water is more dense and viscous than airEvaporation is only an issue for air breathers

StrategiesUnidirectional: most water-breathersTidal: air-breathersAir filled tubes: insects

Ventilation and Gas Exchange in WaterStrategiesCirculate the external medium through an internal cavityVarious strategies for ventilating internal and external gills

Ventilation in water- invertebrates

Sponges and CnidariansCirculate the external medium through an internal cavityIn sponges flagella move water in through ostia and out through the osculumIn cnidarians muscle contractions move water in and out through the mouth

MolluscsTwo strategies for ventilating their gills and mantle cavityBeating ( gerak ) of cilia on gills move water across the gills unidirectionally Blood flow is countercurrentSnails and clams ( kerang )Muscular contractions of the mantle propel ( mendorong ) water unidirectionally through the mantle cavity past the gillsBlood flow is countercurrentCephalopods (squid)

CrustaceansBarnacles (filter feeding) or small species (copepods) lack gills and rely on diffusionShrimp, crabs, and lobsters, have gills derived from modified appendages located within a branchial cavity Movements of the gill bailer ( lembaran ) propels ( mendorong ) water out of the branchial chamber; the negative pressure sucks water across the gillscopepod

Echinoderms sea stars, sea urchins, sea cucumbersMost sea stars and sea urchins use their tube feet for gas exchangeWater is sucked in and exits through the madreporiteSea stars also have external gill-like structures (respiratory papulae); cilia move water over the surface

Echinoderms, cont.Brittle stars and sea cucumbers have internal invaginationsBrittle stars used cilia to move water into bursae ( kantong )Sea cucumbers use muscular contractions of the cloaca and the respiratory tree to breathe water tidally though the anus

Lamprey and hagfish have multiple pairs of gill sacsJawless Fishes - HagfishHagfishA muscular pump (velum) propels water through the respiratory cavityWater enters the median nostril!!!! and leaves through a gill openingFlow is unidirectionalBlood flow is countercurrent

Ventilation - hagfishGills sacs are arranged for counter current flowWater flow

Jawless Fishes - LampreyLampreyVentilation is similar to that in hagfish when not feeding When feeding the mouth is attached to a prey (parasitic)Ventilation is tidal though the gill openings

Elasmobranchs sharks, skates and raysSteps in ventilationExpand the buccal cavityIncreased volume sucks fluid into the buccal cavity via the mouth and spiraclesMouth and spiracles closeMuscles around the buccal cavity contact forcing water past the gills and out the external gill slitsBlood flow is countercurrent

Water flows in via the mouth, out via the opercular openingTeleost Fishes

Fish GillsFish gills are arranged for countercurrent flow

Ventilation and Gas Exchange in AirTwo major lineages have colonized terrestrial habitatsVertebratesArthropods

Unidirectional ventilation of gills common in water-breathing animalsTidal ventilation of lungs common in air-breathing animals

Ventilation in airInsectsVertebratesMolluscsSpiders

Ventilation terrestrial molluscsThe pulmonate molluscs lack gills (or have highly reduced gillsInstead, mantle cavity is highly vascularized and acts as a lungGarden snails and terrestrial slugs are pulmonatesPumping of the mantle cavity moves air in and out of these lungs

ArthropodsCrustaceans (crabs, woodlice and sowbugs)Chelicerates (spiders and scorpions)Insects

CrustaceansTerrestrial crabsRespiratory structures and the processes of ventilation are similar to marine relatives, butGills are stiff so they do not collapse in airBranchial cavity is highly vascularized and acts as the primary site of gas exchangeMovements of the gill bailer propels air in and out of the branchial chamber

Terrestrial isopods (woodlice and sowbugs)Have a thick layer of chitin on one side of the gill for support and the other side is thin walled and used for gas exchangeAnterior gills contain air-filled tubules (pseudotrachea). Oxygen diffuses down the pseudotrachea and dissolves in the interstitial fluid

Chelicerates - Spiders and scorpionsHave four book lungsConsists of 10-100 lamellaeOpen to outside via spiraclesGases diffuse in and outSome spiders also have a tracheal system series of air-filled tubesOxygen diffuses into the trachea and dissolves in the interstitial fluid before diffusing into the tissues

InsectsHave an extensive tracheal system - series of air-filled tubesTracheoles terminating ends of tubes that are filled with hemolymphOxygen dissolves in the hemolymphOpen to outside via spiraclesGases diffuse in and outHigh diffusion coefficient of oxygen in air allows oxygen to diffuse through the tracheal system

Ventilation in insectsSome species can expand and compress the tracheaChanges in tracheal volume cause changes in pressure, which causes air to flow through the systemImages of insect trachea obtained using X-ray synchrotron radiation

Aquatic insectsMost aquatic insects breathe airMosquito larvae have snorkel

Water beetle (Dytiscus)Water beetles carry scuba tanks (air bubbles)

Air breathing vertebratesAir breathing evolved in fishesAquatic habitats can become hypoxicUnder these conditions, the ability to breathe air is a substantial benefit

VertebratesFishAmphibiansReptilesBirdsMammals

Evolution of air breathingSome fish use aquatic surface respiration when hypoxicSwim to the surface and ventilate gills with water from the thin well-oxygenated water layer near surfaceSome fish can gulp air into mouth (buccal cavity)Buccal cavity highly vascularized for gas exchange

FishAir breathing has evolved multiple times in fishesTypes of respiratory structuresReinforced gills that do not collapse in airMouth or pharyngeal cavity for gas exchange (highly vascularized)Vascularized stomachSpecialized pockets of the gutLungsVentilation is tidal using buccal force similar to other fish

Amphibians - ventilationAmphibians have simple sac-like lungsForm as outpocketings of the gut

AmphibiansTypes of respiratory structuresCutaneous respirationExternal gillsSimple bilobed lungs; more complex in terrestrial frogs and toads

Amphibians external gillsAdvantages: high surface area, exposed to mediumDisadvantages: easily damaged, not suitable in airPolychaeteSalamander

Amphibians

ReptilesMost have two lungs; in snakes one lung is reduced or absentCan be simple sacs with honeycombed walls or highly divided chambers in more active speciesMore divisions result in more surface areaVentilationTidalRely on suction pumpsResults in the separation of feeding and respiratory musclesTwo phases: inspiration and expirationUse one of several mechanisms to change the volume of the chest cavity

Reptiles: mechanisms to change the volume Snakes and lizards: use intercostal muscles. Contraction of the intercostals moves the ribs forward and outward, increasing the volumeTurtles and tortoises: Use abdominal muscles that expand and compress the lungsCrocodilians: Hepatic septum is attached to the anterior side of the liver. Paired diaphramaticus muscles run from the hepatic septum to the pelvic girdle. Diaphramaticus muscles contract which decreases the volume in the abdominal cavity and increases the volume of the lungs. As a result pressure in the lungs decreases

Reptiles

Ventilation in birds and mammals

BirdsLung is stiff and changes little in volumeRely on a series of flexible air sacsGas exchange occurs at parabronchi

Bird lungs crosscurrent flowOxygen extraction efficiency high (up to 90%)

Bird VentilationRequires two cycles of inhalation and exhalationAir flow across the respiratory surfaces is unidirectional

Bird Ventilation

MammalsTwo main partsUpper respiratory tract: mouth, nasal cavity, pharynx, tracheaLower respiratory tract: bronchi and lungsAlveoli are the site of gas exchangeBoth lungs are surrounded by a pleural sac

Mammalian lungs

Mammalian lungs - alveoliType I cells gas exchange

Type II cells surfactant secretion

Airways:

LarynxTracheaBronchiiBronchiolesAlveoliMammalian lungs

Mammal Ventilation

StepsInhalationSomatic motor neuron innervationContraction of the external intercostals and the diaphragm Ribs move outwards and the diaphragm moves downVolume of thorax increasesAir is pulled inExhalationInnervation stopsMuscle relaxRibs and diaphragm return to their original positionsVolume of the thorax decreasesAir is pushed out via elastic recoil of the lungsDuring rapid and heavy breathing, exhalation is active via contraction of the internal intercostal muscles

Mammals

Mammalian lungs - ventilationAir moves into and out of the lungs along pressure gradients that are the result of volume changes

Dead SpaceTidal volume total volume of air moved in one ventilatory cycleDead space air that does not participate in gas exchangeTwo componentsAnatomical dead space volume of the trachea and bronchiAlveolar dead space volume of any alveoli that is not being perfused with blood

SpirometryMethod for measuring pulmonary function

Gas transportBulk flowVentilationDiffusionBulk flowCirculationDiffusion

Respiratory pigmentsRespiratory pigments help to increase the amount of O2 in bloodOxygen-binding moleculesContain metal ionsGives them a strong colour (e.g. hemoglobin red)Oxygen binds reversibly to the metal ionBind to the pigment at the lungsReleases from the pigment at the tissues

Types of respiratory pigmentHemoglobin - vertebrates, nematodes, some annelids, some crustaceans, some insects Hemerythrin - sipunculids, priapulids, brachiopods, and one family of annelids Hemocyanin - arthropods and molluscs

Respiratory PigmentsMetalloproteins are referred to as respiratory pigmentsThree major typesHemoglobinsMost commonVertebrates, nematodes, some annelids, crustaceans, and insectsConsist of a protein globin bound to a heme molecule containing ironUsually located within blood cellsAppears red when oxygenatedMyoglobin is a type of hemoglobin found in musclesHemocyaninsArthropods and molluscsContain copperUsually dissolved in the hemolymphAppears blue when oxygenatedHemerythrinsSipunculids, priapulids, brachiopods, some annelidsContains iron directly bound to the proteinUsually found inside coelomic cellsAppears violet-pink when oxygenated

HemoglobinVertebrate hemoglobins are tetramersTwo alpha chainsTwo beta chainsEach contains a heme groupEach heme group can bind 1 molecule of oxygenTherefore 1 Hb molecule can bind 4 oxygen molecules

Myoglobin (Mb)Type of hemoglobin found in vertebrate muscleMonomerEach Mb molecule binds one molecule of oxygen

HemocyaninArthropods & molluscsContain copper instead of ironCopper is complexed directly to amino acids in the proteinMultimeric (up to 48 subunits)Blue when oxygenated

HemerythrinsSipunculids, priapulids, brachiopods, and one family of annelidsDo NOT contain hemeIron is bound directly to amino acids in the protein subunits (usually 2 iron molecules per subunit)Molecules are usually trimeric or octomericVery pretty violet colour when oxygenated, colorless when deoxygenated

Swim bladderFish Many bony fish have a swimbladder that helps to maintain neutral buoyancyGas-filled sacFill with gas to increase buoyancyRemove gas to reduce buoyancyIn most species this gas is oxygen

Swim bladderGas gland excretes lactic acid Acidity causes hemoglobin of the blood to lose its oxygen Oxygen diffuses into the bladder while flowing through a complex structure known as the rete mirabile

Carbon Dioxide TransportCarbon dioxide is more soluble in body fluids than oxygenHowever, little CO2 is transported in the plasmaSome CO2 binds to proteins (carbaminohemoglobin) Most CO2 is transported as bicarbonateCO2 + H2O H2CO3 (carbonic acid) HCO3- (bicarbonate) + H+Carbonic anhydrase catalyzes the formation of HCO3-

Vertebrate Red Blood Cells and CO2 TransportCarbonic anhydrase is located within RBCsReactions to synthesize HCO3- occur in the RBCs even though most of this HCO3- is carried in the plasma

Carbon dioxide transport at tissuesCO2 is produced by aerobic metabolismRapidly diffuses out of tissues and into red cellCarbonic anhydrase catalyzes formation of bicarbonatethe H+ formed by this reaction binds to Hbthe bicarbonate ions are moved out the the RBC by a transporter protein (band III)Bicarbonate does not readily diffuse through membranesif it were not removed, build up within red cell would inhibit CA reactionBand III exchanges HCO3- for Cl- (Chloride shift)

Carbon dioxide transport at respiratory surfacePCO2 of air/water is lower than bloodCO2 diffuses out of plasma across respiratory surfaceCO2 diffuses out of RBC into plasmaEquilibrium of CO2-bicarbonate reaction is shiftedBicarbonate ions move from plasma into RBCs (reverse-chloride shift)Bicarbonate and H+ from carbonic acid and then CO2CO2 diffuses out of RBC into plasma and then across respiratory surface

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