The Circulatory System 3 & 4 (2023-24) PDF

WEEK WEEK 26 19 MPharm Programme Normal Systems The Circulatory System 3 Dr G Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 The Circulatory System WEEK 19 General Properties of Cardiac Cells Refractoriness inability of more than enough stimulus to eli...

WEEK WEEK 26 19 MPharm Programme Normal Systems The Circulatory System 3 Dr G Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 The Circulatory System WEEK 19 General Properties of Cardiac Cells Refractoriness inability of more than enough stimulus to elicit an action potential occurs for some time after a previously elicited AP gives rise to absolute/effective (ARP/ERP) & relative refractory periods (RRP) protects against premature excitation & tetany time for recovery of excitability (i.e. duration of the refractory period) differs for fast & slow response cells fast response – faster recovery of excitability slow response – slower recovery of excitability   risk of conduction block Slide 73 of 154 MPharm PHA112 The Circulatory System WEEK 19 Refractory Periods in a Ventricular Muscle Cell Slide 74 of 154 MPharm PHA112 The Circulatory System WEEK 19 Cardiac APs & Refractoriness Fast Response Slow Response Slide 75 of 154 MPharm PHA112 The Circulatory System WEEK 19 Refractory Period & Muscle Contraction in a Ventricular Muscle Cell Slide 76 of 154 MPharm PHA112 The Circulatory System WEEK 19 General Properties of Cardiac Cells Automaticity Ability of some cardiac cells to initiate / fire APs spontaneously Called automatic or pacemaker activity Normal cardiac automatic or pacemaker cells: SA node AV node specialised conducting tissue – His-Purkinje system Primary vs latent or subsidiary pacemakers Basis of automaticity – If current & spontaneous phase 4 depolarisation Intrinsic & extrinsic control of automaticity Slide 77 of 154 MPharm PHA112 The Circulatory System WEEK 19 Autonomic Innervation of the Heart Slide 78 of 154 MPharm PHA112 The Circulatory System WEEK 19 Control of SA nodal Pacemaker Activity & Heart Rate by Autonomic Nervous System Slide 79 of 154 MPharm PHA112 The Circulatory System WEEK 19 Electrical Activity of the Heart The Natural Pattern of Excitation of the Heart The heart beats spontaneously & rhythmically throughout life Triggered by spread of action potentials (electrical impulse) across muscle cell membranes Action potentials are cyclically initiated & conducted in an orderly sequence through the heart by the electrical or autorhythmic cells SA node  Atria  AV node  Bundle of His  Purkinje fibres  Ventricles AV conduction delay allows ventricles to be relaxed while atria are contracting Slide 80 of 154 MPharm PHA112 The Circulatory System WEEK 19 The Natural Pattern of Excitation of the Heart Slide 81 of 154 MPharm PHA112 The Circulatory System WEEK 19 The Natural Pattern of Excitation of the Heart Slide 82 of 154 MPharm PHA112 The Circulatory System WEEK Electrical Activity of the Heart 19 The Electrocardiogram (ECG or EKG) Electrical currents are generated by cardiac muscle during depolarization & repolarisation Conducted through body fluids & into tissues around the heart They can be detected on body surface & recorded as the Electrocardiogram (ECG or EKG) The ECG – a summation of overall spread of electrical activity throughout the heart during depolarization & repolarisation Standard 12-lead ECG recording six limb leads (I-III, aVR, aVL & aVF) six chest leads (V1-V6) Slide 83 of 154 MPharm PHA112 The Circulatory System WEEK 19 Slide 84 of 154 The Electrocardiogram Leads MPharm PHA112 The Circulatory System WEEK 19 The Electrical Activity of the Heart The Electrocardiogram (ECG or EKG) A normal ECG has three distinct waveforms The P wave represents atrial depolarization The QRS complex represents ventricular depolarization The T wave represents ventricular repolarisation Slide 85 of 154 MPharm PHA112 The Circulatory System WEEK 19 Slide 86 of 154 The Waveforms of the ECG MPharm PHA112 The Circulatory System WEEK 19 Slide 87 of 154 The Waveforms of the ECG MPharm PHA112 The Circulatory System WEEK 19 ECG Waveforms & Corresponding Electrical Status of the Heart Slide 88 of 154 MPharm PHA112 The Circulatory System WEEK 19 Slide 89 of 154 Sequence of Cardiac Excitation & Associated ECG Waveforms MPharm PHA112 The Circulatory System WEEK 19 Contractile Activity of the Heart Cardiac muscle fibres as the basic functional unit of heart pump Individual cardiac muscle cells interconnected to form branching fibres Adjacent cells joined end to end at specialized structures known as intercalated discs Two types of membrane junctions are present within an intercalated disc desmosomes – cell to cell anchoring junctions gap junctions – cell to cell communication junctions Muscle mass forms a functional syncytium – become excited & contract as a single unit Slide 90 of 154 MPharm PHA112 The Circulatory System WEEK 19 The Structure of Cardiac Muscle Slide 91 of 154 MPharm PHA112 The Circulatory System WEEK 19 The Structure of Cardiac Muscle Slide 92 of 154 MPharm PHA112 The Circulatory System WEEK 19 The Structure of Cardiac Muscle Gap Junction & Rapid Excitation Slide 93 of 154 MPharm PHA112 The Circulatory System WEEK 19 The Structure of Cardiac Muscle Fibre Slide 94 of 154 MPharm PHA112 The Circulatory System WEEK 19 The Ultrastructure of Cardiac Muscle Fibre (a) (b) (d) (c) Slide 95 of 154 MPharm PHA112 The Circulatory System WEEK 19 Slide 96 of 154 Excitation Contraction Coupling MPharm PHA112 The Circulatory System WEEK 19 Slide 97 of 154 Excitation Contraction Coupling MPharm PHA112 The Circulatory System WEEK WEEK 26 19 MPharm Programme Normal Systems The Circulatory System 4 Dr G Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 The Circulatory System The Cardiac Cycle WEEK 19 Rhythmic pumping action of the heart Triggered by spread of excitation through the heart Two alternate phases or periods Systole Phase of ventricular contraction & emptying Two sub-phases or periods isovolumetric contraction & ejection periods Diastole Phase of ventricular relaxation & filling Two sub-phases or periods isovolumetric relaxation & filling periods Slide 99 of 154 MPharm PHA112 The Circulatory System WEEK 19 Slide 100 of 154 The Cardiac Cycle MPharm PHA112 The Circulatory System WEEK 19 Phases of the Cardiac Cycle Systole Slide 101 of 154 MPharm PHA112 The Circulatory System WEEK 19 Phases of the Cardiac Cycle Diastole Slide 102 of 154 MPharm PHA112 The Circulatory System Heart Sounds WEEK 19 1st Heart Sound (lub) closure of AV valves at the start of ventricular contraction 2nd Heart Sound (dub) due to closure of aortic & pulmonary valves at the end of ventricular systole 3rd Heart Sound heard in early diastole due to inrush of blood during rapid ventricular filling 4th Heart Sound (dub) heard immediately before 1st sound (in late diastole) due to ventricular filling Slide 103 of 154 MPharm PHA112 The Circulatory System WEEK 19 Slide 104 of 154 Cardiac Cycle – Composite Events MPharm PHA112 The Circulatory System WEEK 19 Blood Vessels Slide 105 of 154 MPharm PHA112 The Circulatory System Blood Vessels WEEK 19 Also called the ‘Vascular System or Tree’ A closed system of vessels Direct the flow of blood from the heart to organs & tissues and back to the heart Consists of Arteries – carry blood away from heart to tissues Arterioles – smaller branches of arteries within organs Capillaries – smaller branches of arterioles within organs; facilitate exchanges between blood & surrounding cells Venules – formed when capillaries re-join; return blood to heart Veins – formed when venules re-join; return blood to heart Slide 106 of 154 MPharm PHA112 The Circulatory System WEEK 19 Slide 107 of 154 The Vascular System MPharm PHA112 The Circulatory System WEEK Structure of Blood Vessels 19 Walls composed of up to 3 ‘tunics’: Tunica externa (adventitia) Outer layer comprised of connective tissue (& elastin fibres) Tunica media Middle layer composed of smooth muscle Tunica interna (intima) Innermost lining of squamous endothelium Basement membrane Layer of elastin Slide 108 of 154 MPharm PHA112 The Circulatory System WEEK 19 Slide 109 of 154 Structure of Blood Vessels MPharm PHA112 The Circulatory System Arteries WEEK 19 Main Functions serve as rapid-transit conduits for blood from heart to organs act as pressure reservoirs – provide the driving force for blood during diastole Two Main Types Elastic arteries – e.g. aorta & pulmonary artery Numerous layers of elastin fibres in vessel wall Expand when pressure of the blood rises (during ventricular systole) & act as a recoil system when the ventricles relax Muscular arteries – e.g. femoral & coronary arteries Less elastic but thicker layer of smooth muscle Diameter changes only slightly as BP rises & falls Slide 110 of 154 MPharm PHA112 The Circulatory System WEEK 19 Slide 111 of 154 Structure & Function of Arteries MPharm PHA112 The Circulatory System Arterioles WEEK 19 Smaller branches of arteries within organs Contain highest % smooth muscle in the vessel wall Major resistance vessels Large pressure drop facilitates blood flow to organs Vessel radius supplying individual organs can be adjusted independently to: Distribute cardiac output among systemic organs – depending on the body’s momentary needs Help regulate arterial blood pressure Control of the tone (constriction or dilatation) of arterioles mediated via nervous & chemical mechanisms Slide 112 of 154 MPharm PHA112 The Circulatory System WEEK 19 Slide 113 of 154 Control of Arteriolar Tone by the Sympathetic Nervous System MPharm PHA112 The Circulatory System WEEK 19 Nervous & Chemical Control of Arteriolar Tone Slide 114 of 154 MPharm PHA112 The Circulatory System WEEK Capillaries 19 Smaller & dense branches off arterioles & metarterioles within organs the sites for exchange of nutrients & wastes between blood and surrounding tissue cells exchange of materials largely occurs via diffusion very thin walls – consist of single layer of flat endothelial cell & thin basement membrane Walls perforated by water-filled pores – permit passage of small, water-soluble substances Precapillary sphincters regulate blood flow via capillaries Three main types – depending on size of water-filled pores Slide 115 of 154 MPharm PHA112 The Circulatory System WEEK 19 Control of Capillary Blood Flow by Precapillary Sphincters Slide 116 of 154 MPharm PHA112 The Circulatory System WEEK Types of Capillaries 19 Continuous Endothelial cells are continuous or closely joined Narrow intercellular pores (~ 4 nm) permit passage of molecules Skeletal & cardiac muscle, lungs & adipose tissue Fenestrated Have larger holes (20-100 nm) in addition to narrow pores Provide greater permeability & rapid exchange Kidneys, intestines & endocrine glands Discontinuous (sinusoidal) Endothelial cells are discontinuous  very large intercellular pores & leaky capillaries Liver, spleen & bone marrow Slide 117 of 154 MPharm PHA112 The Circulatory System WEEK 19 Slide 118 of 154 Types of Capillaries MPharm PHA112 The Circulatory System WEEK 19 Slide 119 of 154 Types of Capillaries MPharm PHA112 The Circulatory System WEEK 19 Exchange of Materials across a Continuous Capillary Wall Slide 120 of 154 MPharm PHA112 The Circulatory System WEEK Capillary Exchange 19 Two mechanisms of capillary exchange between blood & surrounding tissues: Passive diffusion movement of solutes down their concentration gradient Bulk flow ultrafiltration & reabsorption of protein-free plasma Determinants of bulk flow Capillary blood pressure (PC) – outward pressure Plasma-colloid osmotic pressure (πP) – inward pressure Interstitial fluid hydrostatic pressure (PIF) – inward pressure Interstitial fluid colloid osmotic pressure (πIF) – outward pressure Slide 121 of 154 MPharm PHA112 The Circulatory System WEEK 19 Capillary Exchange of Solutes by Passive Diffusion Slide 122 of 154 MPharm PHA112 The Circulatory System WEEK 19 Capillary Exchange of Fluid by Bulk Flow Slide 123 of 154 MPharm PHA112 The Circulatory System WEEK 19 Capillary Exchange of Fluid by Bulk Flow Slide 124 of 154 MPharm PHA112 The Circulatory System WEEK Veins & Venules 19 Venous system – low resistance system that returns blood from tissues to the heart Comprises Venules Small veins Large, systemic veins Systemic veins Large radius  low resistance to flow Thin walls with little smooth muscle or elastin  high distensibility & little elastic recoil Serve as blood reservoir or capacitance vessels one-way valves & ‘skeletal muscle pump’ ensure blood flow toward the heart Slide 125 of 154 MPharm PHA112 The Circulatory System WEEK Structure of Veins 19 A Slide 126 of 154 B MPharm PHA112 C The Circulatory System WEEK 19 Factors That Facilitate Venous Return Slide 127 of 154 MPharm PHA112 The Circulatory System WEEK 19 Pressures throughout the Systemic Circulation Slide 128 of 154 MPharm PHA112 The Circulatory System WEEK 19 Slide 129 of 154 Main Features of Blood Vessels MPharm PHA112 The Circulatory System