BI451 Lecture 8 CardioVascular System F23.pptx

Blood and Circulation Hemoglobins to Hearts BI451 Lectures 8 CH 4 he Fish Circulatory System: Hear Moyle and Cech. Fig.4-9 Comparative Anatomy of the Heart (i) sinus venosus (ii) atrium (iii) ventricle (iv) Conus arteriosus » lampreys & elasmobranchs » contractile » conal valves Bulbous arteri...

Blood and Circulation Hemoglobins to Hearts BI451 Lectures 8 CH 4 he Fish Circulatory System: Hear Moyle and Cech. Fig.4-9 Comparative Anatomy of the Heart (i) sinus venosus (ii) atrium (iii) ventricle (iv) Conus arteriosus » lampreys & elasmobranchs » contractile » conal valves Bulbous arteriosus* » teleosts » non-contractile » single bulbal valve *Elastic chamber to dampen pressure pulses to deliver more continuous flow. Shark Bony Fish onstruction of Ventricular Walls • Cortex » dense compact myocardium » coronary artery » Well developed in Active Fishes and elasmobranchs. » Less associated with sluggish fish. • Spongy Myocardium » universal inner layer » depend upon O2 reserves & nutrients in venous blood Coronaries in shark heart Biphasic filling Cardiac Cycle in Fishes Farrell 2011 Fish Hearts are Myogenic • Electrical signal initiated in islets of “Pacemaker” Cells in Sinoatrial region » other myocardial cells are less myogenic • Atrio-Ventricular Delay » allows atria to completely empty • lacks conducting fibres V. Cardiac Performance · Q = f x SV H H · Cardiac Output (mL/min) Where: = Q fH = heart rate (beats/min) SVH = stroke volume (mL/beat) Chronotropic Effects = Altered fH • positive = tachycardia • negative = bradycardia Inotropic Effects = Altered SVH • positive = greater SVH • negative = lower SVH Regulation of Cardiac Output (i) Routine Activity · than active fish Sluggish lower resting Q (ii) Exercise (a) Burst Swimming · » Q , fH, Arterial Pressure Recovery · »  Q, fH, Arterial Pressure (b) Endurance Swimming · , 50-200 % » Q » mainly greater SVH - 25 to 200 % » fH - 7 to 50 % greater . Regulation of Cardiac Output (Q) (iii) Temperature • · Q increases with temperature » Q10 = 1.6 to 2.4 (iv) Hypoxia • moderate hypoxia (> critical PO2) · maintained »Q • severe hypoxia (< critical PO2) » fH . Control of SVH (stroke volume) SVH = EDV - ESV (i) Frank-Starling Mechanism • ↑ SVH with greater ventricular filling Influenced by: » EDV » Cardiac Filling Pressure Farrell 2011. Control of SVH (stroke volume) • Contractility The change in development of force at a given resting muscle fibre length. » peak isometric tension (ii) SNS (sympathetic nervous system) • Epinephrine increases contractility actors Influencing Cardiac Filling Cardiac Filling Venous Return Effectors 1. Vis-a-tergo forces (from behind- PUSH) • Central Venous Pressure » Skeletal Muscle Pump • Potential Energy & Kinetic Energy in anterior chambe Factors Influencing Cardiac Filling Cardiac Filling Venous Return ffectors 2. Vis-a-fronte forces (in front-PULL) • Aspiration Filling Positive Inotropic Factors • • • • ↑ Temperature adrenergic stimulation Extracellular Ca2+ Peptides » arginine, vasotocin, oxytocin, adenosine, histamine Negative Inotropic Factors • Hypoxia • Acidosis • -adrenergic stimulation in some species (e.g. dogfish) • Extracellular Ca2+ • Acetylcholine (vagus nerve) VI. Autonomic Control of the Fish Cardiovascular System Parasympathetic Sympathetic Nervous System • “rest(PSNS) and digest” Nervous System • “fight or (SNS) flight” • housekeeping • energy conservation • Vagus Nerve » innervates SA region » acetylcholine (Ach) » Ventricle poorly innervated • Adrenergic Innervatio » SA & AV regions » Compacta of ventricle » coronary vessels 1. PSNS Control of fH Intrinsic fH (heart rate) • determined by blocking both adrenergic & cholinergic receptors • Teleost > Elasmobranch > Cyclostomes • Q10 ~ 2.0 Extrinsic control: • “Push-Pull” Modulation (Adrenergic vs Cholinergic tone). » Inhibitory Cholinergic Tone Suppresses fH • hypoxia, burst swimming, visual/olfactory stimuli, cold temperature acclimation 2. SNS Control of fH Sites of EP (epinephrine) & NEP (norepinephrine) Release • Chromaffin tissue outside heart (EP) • Heart in cyclostomes, lungfish (EP) • Adrenergic nerves (NEP, EP) Target Sites • SA & AV regions Action • Most fish hearts » -receptors → + chronotropy • Some fish hearts » -receptors → - chronotropy Summary • Hemoglobin designed to maximize O2 uptake at gill and unloading at the tissues. Intertwined with opposite CO2 transport. (Bohr effect, Root shift and Haldane effect.) • Numerous polymorphisms of Hb in fishes • Fish Heart has 4 chambers (in series) • Cardiac Output » Heart Rate (fH) » Stroke Volume (SVH) • Autonomic Nervous System » SNS & norepinephrine/epinephrine » PSNS & acetylcholine rey Hemoglobin has only 1 heme gr • Deoxygenation causes Hb to aggregate, forming dimers or oligomers • Hb-O2 Affinity Increased when Hb oxygenated • Promotes Hb-O2 unloading to tissues & blood deoxygenated Monomeric Hb O2 Saturation (%) 100 Dimeric/Oligomeric Hb 80 60 40 20 0 P50 10 P50 20 30 40 PO2 (mm 50 60 Wilkie 2011.