BI451-Lecture-5-6-Respiration-F23.txt

Respiration BI451 Lectures 5-6 Sept 2023 Germany 1931  Learning objectives • Internal vs External Gills » adaptive significance • Physical & Chemical Properties of Water Favouring Gills as Respiratory Organ in Fishes • Anatomy & Function of Gills • Why Counter Current Gas Exchange? • Mecha...

Respiration BI451 Lectures 5-6 Sept 2023 Germany 1931  Learning objectives • Internal vs External Gills » adaptive significance • Physical & Chemical Properties of Water Favouring Gills as Respiratory Organ in Fishes • Anatomy & Function of Gills • Why Counter Current Gas Exchange? • Mechanisms of Gill Ventilation • Other Modes of Respiration » cutaneous » air breathing  I. Internal vs External Gills • most fishes have internal gills » covered by operculum » positioned within gill slits » irrigated mainly via buccal-opercular pump • external gills found on few fishes (larval chondrichthyans, juvenile polypterians, and lungfish). » irrigated by movement through water » accessory organ? Fig. 12-6. Hill & Wyse 1989. External Gill African Lungfish Chondrichthyan (Protopterus spp) embryo Polypterus juvenile  II. Physical & Chemical Properties of Water Relative comparison of water versus air as a respiratory medium. [O2] = α PO2 AIR WATER O2 Solubility (αO2) 1 1/30 (ml/L H2O) CO2 Solubility (αCO2) 1 1 (ml/L H2O) O2 Diffusion Co-efficient 1 1/10 000 (cm2/sec) Density 1 800 Viscosity 1 50 Heat Conductivity 1 25 Heat Capacity 1 3 000  Consequences of Water Breathing Greater Ventilatory Flow Required to Deliver O2 to gills. Higher Ventilatory Costs » due to greater density & viscosity Lower O2 consumption (ṀO2) per unit mass in water compared to air-breathers » Limits metabolic scope Low blood PCO2 » readily excrete CO2 due to: • greater ventilatory flow across gills • higher CO2solubility (αCO2) in water » O2 not CO2 primary stimulus for respiration Respiration Dependant Upon Partial Pressure Gradients of O2 & CO2 Units of Pressure • 1 atm = 760 mm Hg = 760 torr = 101.3 kPa Dalton’s Law of Partial Pressure • Patmosphere = PN2 + PO2 + PCO2 + Pwater…+ Pother e.g. O2 21% of air. PO2 = 0.21 x 760 torr = 159 torr Diffusion • O2 & CO2 Diffuse from High Pgas to Low Pgas Δ PO2 Δ PCO2 Relationship Between O2 Content & PO2 in Fresh Water at Cold (5°C) & Warm (35°C) Temperatures Fig. 3.2 Moyle and Cech III. Anatomy & Function of the Fish Gill Most efficient gas exchange organ in vertebrates. Why? Gross Anatomy From Hill & Wyse. 1989. Fig. 12-21a FICK’S LAW of DIFFUSION Gill design Gill Filaments & Lamellae Opercular Cavity Buccal Cavity From Hill & Wyse. 1989. Fig. 12-21c Lamellar Cross-Section Fig. 3.4 Moyle & Cech Control of Branchial Circulation Non-Respiratory Blood • supplied to gills via “venolymphatic” vessels & basal blood vessels Lamellar Blood Flow Control • Environmental Factors » O2 sensed by chemoreceptors on 1st arch (Kinkead & Perry 1989) Lamellar Microcirculation » cholinergic receptors (Acetylcholine)  vasoconstriction (Booth 1979) » adrenergic receptors (Epinephrine)  vasodilation (Booth 1979) » endothelin  contraction of lamellar pillar cells (Sundin & Nilsson 1998) IV. Oxygen Uptake 1. Counter Current Exchange Fig. 12- 21d from Hill & Wyse  IV. Oxygen Uptake 1. Counter Current Exchange • maximizes O2 uptake by maintaining relatively stable ΔPO2 gradient Concurrent Exchange Countercurrent Exchange Fig. 12-8from Hill & Wyse 2. Surface Area • lamellar SA (number) correlated with O2 demand & life style Diffusion Distance • lamellar thickness inversely correlated with O2 demand & life style Moyle & Cech 2004 Cost to higher surface area?  Gill Re-modeling in Crucian Carp & Goldfish Normoxia (8°C) Absence of protruding lamellae in normoxic crucian carp Sollid & Nilsson. 2006.  Gill Re-modeling in Crucian Carp & Goldfish - Gill filaments covered by interlamellar cell mass (ILCM) Fish exposed to hypoxia (< 1 mg O2/L) Lamellar SA increased 7.5-fold Sollid et al. 2003. ILCM: interlamellar cell mass Carassius carassius Carassius auratus Sollid et al. 2003. JEB Mitrovic et al. 2009 Am.J.Physiol.  Gill Re-modeling in Crucian Carp & Goldfish. Osmorespiratory compromise. Set point of transformation differs between two species. Sollid & Nilsson. 2006. V. Mechanisms of Gill Ventilation 1. Buccal-Opercular Pump Fig. 12.22 Hill & Wyse 1989. 2.(i) Larval Lampreys - Velar Pump Sediment dwelling filter feeder Branchiopores Oral Hood Petromyzon marinus Velum Fig. 11-14 Kardong 2002. Larval lamprey Unidirectional breather. Vellar pump and compression-recoil of branchial chamber.  2.(ii) Post-Metamorphic Lampreys - Tidal Ventilation Lampreys (Petromyzon marinus) feeding on basking shark (Cetorhinus maximus) (Wilkie et al. 2004). Fig. 11-15 Kardong 2002. Post metamorphic lamprey Contraction of branchial musculature forces water across the gills and out the external branchiopore, followed by elastic recoil which expands branchial pouch to draw in water. Hagfish Unidirectional ventilation using vellar pump. Water inflow through nostril (and mouth?). They do NOT tidally ventilate when feeding. Endure apnea. mo mouth en nostril  3. Elasmobranchs - Buccal-Parabranchial Pump Architecture • Lamella extending from Filament Lamella • Gill arches Filament » 4 holobranch » 1 Hemibranch • Five Gill Slits » covered by flap valve • Spiracle » remnant of first aortic arch » chemosensory » water intake in skates, rays Fig 11-17 Kardong 2002. 3. Elasmobranchs - Buccal-Parabranchial Pump Fig 11-18 Kardong 2002. 4. RAM Ventilation • initiated by rapid swimming » critical velocity mouth opens & water forced through buccal cavity & across gills » generally initiated at 1.0-2.0 body lengths/sec • some respiratory costs transferred to swimming musculature » Striped Bass & Sailfish greater than 8% increase in efficiency • obligate RAM ventilation » tuna, swordfish, some sharks VI. Aquatic Cutaneous Respiration 1. Larval Fish • 96 % of ṀO2 Cutaneous (Rombough & Moroz, 1990) » 50 mg in weight, 3.7 days post-hatch Why? Adult/Juvenile Fish • Skin not an organ of gas exchange in most » poorly vascularized » ṀO2 skin = ṀO2 demands of skin • Scaleless Black Carp » 5 % of MO2 VII. Air-Breathing Fishes • ~ 374 species to date • most retain ability to breath in water (facultative air breathers) • Obligate Air Breathers » drown if denied access to air e.g. South American & African Lungfishes, some Mudskipper P. dolloi Boleophthalmus sp. 1. Why Air-Breath? Aquatic hypoxia Take advantage of O2 at water: air interface e.g. gar pike Desiccation of habitat e.g. lungfishes, walking catfishes Receding Waters e.g. intertidal fishes such as killifish (F. heteroclitus) Overland Migrations » poor water quality e.g. snakehead, walking catfishes » spawning e.g. some lampreys » foraging or habitat selection e.g. American eel 2. Challenges & Solutions for Air Breathing Problems: Solutions: 1. Thicker, Widely Spaced lamellae • walking catfishes 2. Retain Gills in Moist Microenvironment • burrows, modified opercular chambers (e.g. mudskippers) • greater “internalization” of gill (eg. American Eel) 3. Limit Migrations to Moist Periods • American eels migrate through moist grass 4. Use Other Mechanisms of Aerial Respiration Accessory Air Breathing Organs (ABO)s • Cutaneous respiration » skin, buccal cavity • Swallow Air • Specialized Swim Bladders • Lungs Gill Area to Body Mass & SA Estimates for Air Breathing & Water Breathing Fishes Gills generally reduced in air- breathers. Why? gill Lung H from Graham 1997. 3. Mechanisms of Air Breathing (i) Cutaneous Respiration • ~ 15 Species Studied » European Eel - 10-40 % via skin mudskipper » Mudskippers - 36-76 % via skin » Swamp eel - 31-94% via skin (ii) Mouth • well vascularized buccal cavity » large SA due to papillae/folds (ABO) » reduced gills which retain ability to shed CO2 e.g. electric eels, climbing perch, African catfish African catfish climbing perch 3. Mechanisms of Air Breathing (iii) Gut • Swallow Air • O2 Delivery in Specialized Gut Regions • CO2 excreted at gills TEM x-sections Intraepithelial capillaries. stomach stomach Reduced gastric glands Surfactant secreting cells. 3. Mechanisms of Air Breathing (iv) Lungs or Swimbladders • lungfishes (Obligate air breathers) • Some Facultative Airbreathers » gars, bowfin, bichirs Lungfish dissection Mechanism of Lung/Swimbladder Ventilation BUCCAL PUMP (again) Fig 11-20 Kardong 2002.  Arapaima gigas Pirarucu Ventilates it lung by aspiration Fish horizontal Back archs to breath at surface Ribs flex outward Vertebral ribs column → Negative pressure in lungs → Air sucked into lungs  REVIEW Fish O2 Requirements Fig. 3-56 Randall et al. 1997.  REVIEW Allometric Scaling (allo = different) • Systematic changes in body proportions with increasing body size • Changes in volume & surface area are not necessarily proportionate • Most groups of animals follow allometric scaling » inter-species comparisons » development within same species » cellular level Whole Animal vs Mass Specific Metabolic Rate • Whole animal MR » proportional to body mass (M) • Mass specific MR » inversely proportional to body mass (M) Factors Affecting O2 Consumption (ṀO2) 1. Life Stage • eggs have low ṀO2, increases post-hatch • ṀO2 juveniles > ṀO2 adult Body Size • Allometric Scaling Within a species Across species Sockeye salmon Brett 1964 Svendsen et al. 2017 Factors Affecting O2 Consumption (ṀO2) Feeding • Specific Dynamic Action (SDA) Activity Level Moyle & Cech 2004 Factors Affecting O2 Consumption (ṀO2) Activity Level • ṀO2 proportional to Red Muscle Activity Factors Affecting O2 Consumption (ṀO2) Temperature • Greater BMR at higher T • Q10 = change in MR for every 10ºC Acclimation Temperature (C) Factors Affecting O2 Consumption (ṀO2) Lowered Dissolved Oxygen • Ventilation initially increases to sustain ṀO2 • ṀO2 reduced below Critical PO2  Summary • Water has very low O2 Solubility • Gills very effective at O2 extraction » Large exchange SA due to numerous lamellae » Counter-Current Exchange » Dual-Pumps » RAM ventilation • Accessory Breathing Organs most important in facultative & obligate air-breathers • ṀO2 Influenced by water quality, feeding, behaviour & activity level, temperature, life stage, body size, and numerous other factors