Cardiac Muscle - PowerPoint PPT Presentation

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Cardiac Muscle

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Title: Cardiac Muscle


1
Cardiac Muscle
  • Found only in heart
  • Striated
  • Each cell usually has one nucleus
  • Has intercalated disks and gap junctions
  • Autorhythmic cells
  • Action potentials of longer duration and longer
    refractory period
  • Ca2 regulates contraction

2
Cardiac Muscle
  • Elongated, branching cells containing 1-2
    centrally located nuclei
  • Contains actin and myosin myofilaments
  • Intercalated disks Specialized cell-cell
    contacts
  • Desmosomes hold cells together and gap junctions
    allow action potentials
  • Electrically, cardiac muscle behaves as single
    unit

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Cardiac myocyte action potential
5
Refractory Period
  • Absolute Cardiac muscle cell completely
    insensitive to further stimulation
  • Relative Cell exhibits reduced sensitivity to
    additional stimulation
  • Long refractory period prevents tetanic
    contractions

6
AP-contraction relationship
  • AP in skeletal muscle is very short-lived
  • AP is basically over before an increase in muscle
    tension can be measured.
  • AP in cardiac muscle is very long-lived
  • AP has an extra component, which extends the
    duration.
  • The contraction is almost over before the action
    potential has finished.

7
Functions of the Heart
  • Generating blood pressure
  • Routing blood
  • Heart separates pulmonary and systemic
    circulations
  • Ensuring one-way blood flow
  • Heart valves ensure one-way flow
  • Regulating blood supply
  • Changes in contraction rate and force match blood
    delivery to changing metabolic needs

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Orientation of cardiac muscle fibres
  • Unlike skeletal muscles, cardiac muscles have to
    contract in more than one direction.
  • Cardiac muscle cells are striated, meaning they
    will only contract along their long axis.
  • In order to get contraction in two axis, the
    fibres wrap around.

10
Circulation circuits
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Heart Wall
  • Three layers of tissue
  • Epicardium This serous membrane of smooth outer
    surface of heart
  • Myocardium Middle layer composed of cardiac
    muscle cell and responsibility for heart
    contracting
  • Endocardium Smooth inner surface of heart
    chambers

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Valve function
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Coronary circulation
23
Cardiac conducting system
24
Pacemaker potential
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EKG
28
Heart sounds
29
Heart Sounds
  • First heart sound or lubb
  • Atrioventricular valves and surrounding fluid
    vibrations as valves close at beginning of
    ventricular systole
  • Second heart sound or dupp
  • Results from closure of aortic and pulmonary
    semilunar valves at beginning of ventricular
    diastole, lasts longer
  • Third heart sound (occasional)
  • Caused by turbulent blood flow into ventricles
    and detected near end of first one-third of
    diastole

30
Cardiac Arrhythmias
  • Tachycardia Heart rate in excess of 100bpm
  • Bradycardia Heart rate less than 60 bpm
  • Sinus arrhythmia Heart rate varies 5 during
    respiratory cycle and up to 30 during deep
    respiration
  • Premature atrial contractions Occasional
    shortened intervals between one contraction and
    succeeding, frequently occurs in healthy people

31
Cardiac Cycle
  • Heart is two pumps that work together, right and
    left half
  • Repetitive contraction (systole) and relaxation
    (diastole) of heart chambers
  • Blood moves through circulatory system from areas
    of higher to lower pressure.
  • Contraction of heart produces the pressure

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Pressure relationships
35
Mean Arterial Pressure (MAP)
  • Average blood pressure in aorta
  • MAPCO x PR
  • CO is amount of blood pumped by heart per minute
  • COSV x HR
  • SV Stroke volume of blood pumped during each
    heart beat
  • HR Heart rate or number of times heart beats per
    minute
  • Cardiac reserve Difference between CO at rest
    and maximum CO
  • PR is total resistance against which blood must
    be pumped

36
Factors Affecting MAP
37
Regulation of the Heart
  • Intrinsic regulation Results from normal
    functional characteristics, not on neural or
    hormonal regulation
  • Starlings law of the heart
  • Extrinsic regulation Involves neural and
    hormonal control
  • Parasympathetic stimulation
  • Supplied by vagus nerve, decreases heart rate,
    acetylcholine secreted
  • Sympathetic stimulation
  • Supplied by cardiac nerves, increases heart rate
    and force of contraction, epinephrine and
    norepinephrine released

38
Heart Homeostasis
  • Effect of blood pressure
  • Baroreceptors monitor blood pressure
  • Effect of pH, carbon dioxide, oxygen
  • Chemoreceptors monitor
  • Effect of extracellular ion concentration
  • Increase or decrease in extracellular K
    decreases heart rate
  • Effect of body temperature
  • Heart rate increases when body temperature
    increases, heart rate decreases when body
    temperature decreases

39
Baroreceptor and ChemoreceptorReflexes
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Cardian innervation
43
Pacemaker regulation
  • Once the pacemaker cells reach threshold, the
    magnitude and duration of the AP is always the
    same.
  • In order to change the frequency, the time
    between APs must vary.
  • The interval can only be changed in two ways.
  • The rate of depolarization can be changed
  • The amount of depolarization required to reach
    threshold can be changed.

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Vascular physiology
46
Peripheral Circulatory System
  • Systemic vessels
  • Transport blood through most all body parts from
    left ventricle and back to right atrium
  • Pulmonary vessels
  • Transport blood from right ventricle through
    lungs and back to left atrium
  • Blood vessels and heart regulated to ensure blood
    pressure is high enough for blood flow to meet
    metabolic needs of tissues

47
Blood Vessel Structure
  • Arteries
  • Elastic, muscular, arterioles
  • Capillaries
  • Blood flows from arterioles to capillaries
  • Most of exchange between blood and interstitial
    spaces occurs across the walls
  • Blood flows from capillaries to venous system
  • Veins
  • Venules, small veins, medium or large veins

48
Structure of Arteries and Veins
  • Three layers except for capillaries and venules
  • Tunica intima (interna)
  • Endothelium
  • Tunica media
  • Vasoconstriction
  • Vasodilation
  • Tunica adventitia (externa)
  • Merges with connective tissue surrounding blood
    vessels
  • Note mistake on figure

49
Structure of Arteries
  • Elastic or conducting arteries
  • Largest diameters, pressure high and fluctuates
  • Muscular or medium arteries
  • Smooth muscle allows vessels to regulate blood
    supply by constricting or dilating
  • Arterioles
  • Transport blood from small arteries to capillaries

50
Structure of Veins
  • Venules and small veins
  • Tubes of endothelium on delicate basement
    membrane
  • Medium and large veins
  • Valves
  • Allow blood to flow toward heart but not in
    opposite direction
  • Atriovenous anastomoses
  • Allow blood to flow from arterioles to small
    veins without passing through capillaries

51
Blood Vessel Comparison
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Capillaries
  • Capillary wall consists mostly of endothelial
    cells
  • Types classified by diameter/permeability
  • Continuous
  • Do not have fenestrae
  • Fenestrated
  • Have pores
  • Sinusoidal
  • Large diameter with large fenestrae

56
Capillary Network
  • Blood flows from arterioles through
    metarterioles, then through capillary network
  • Venules drain network
  • Smooth muscle in arterioles, metarterioles,
    precapillary sphincters regulates blood flow

57
Muscular contractions aid venous return
58
Pulmonary Circulation
  • Moves blood to and from the lungs
  • Pulmonary trunk
  • Arises from right ventricle
  • Pulmonary arteries
  • Branches of pulmonary trunk which project to
    lungs
  • Pulmonary veins
  • Exit each lung and enter left atrium

59
Systemic Circulation Arteries
  • Aorta
  • From which all arteries are derived either
    directly or indirectly
  • Parts
  • Ascending, descending, thoracic, abdominal
  • Coronary arteries
  • Supply the heart

60
Systemic Circulation Veins
  • Return blood from body to right atrium
  • Major veins
  • Coronary sinus (heart)
  • Superior vena cava (head, neck, thorax, upper
    limbs)
  • Inferior vena cava (abdomen, pelvis, lower limbs)
  • Types of veins
  • Superficial, deep, sinuses

61
Dynamics of Blood Circulation
  • Interrelationships between
  • Pressure
  • Flow
  • Resistance
  • Control mechanisms that regulate blood pressure
  • Blood flow through vessels

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Blood Pressure
  • Measure of force exerted by blood against the
    wall
  • Blood moves through vessels because of blood
    pressure
  • Measured by listening for Korotkoff sounds
    produced by turbulent flow in arteries as
    pressure released from blood pressure cuff

64
Pressure and Resistance
  • Blood pressure averages 100 mm Hg in aorta and
    drops to 0 mm Hg in the right atrium
  • Greatest drop in pressure occurs in arterioles
    which regulate blood flow through tissues
  • No large fluctuations in capillaries and veins

65
Blood Pressure Measurement
66
Pulse Pressure
  • Difference between systolic and diastolic
    pressures
  • Increases when stroke volume increases or
    vascular compliance decreases
  • Pulse pressure can be used to take a pulse to
    determine heart rate and rhythmicity

67
Blood Flow, Poiseuilles Lawand Viscosity
  • Blood flow
  • Amount of blood moving through a vessel in a
    given time period
  • Directly proportional to pressure differences,
    inversely proportional to resistance
  • Poiseuilles Law
  • Flow decreases when resistance increases
  • Flow resistance decreases when vessel diameter
    increases
  • Viscosity
  • Measure of resistance of liquid to flow
  • As viscosity increases, pressure required to flow
    increases

68
Critical Closing Pressure, Laplaces Law and
Compliance
  • Vascular compliance
  • Tendency for blood vessel volume to increase as
    blood pressure increases
  • More easily the vessel wall stretches, the
    greater its compliance
  • Venous system has a large compliance and acts as
    a blood reservoir
  • Critical closing pressure
  • Pressure at which a blood vessel collapses and
    blood flow stops
  • Laplaces Law
  • Force acting on blood vessel wall is proportional
    to diameter of the vessel times blood pressure

69
Physiology of Systemic Circulation
  • Determined by
  • Anatomy of circulatory system
  • Dynamics of blood flow
  • Regulatory mechanisms that control heart and
    blood vessels
  • Blood volume
  • Most in the veins
  • Smaller volumes in arteries and capillaries

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Cross-Sectional Area
  • As diameter of vessels decreases, the total
    cross-sectional area increases and velocity of
    blood flow decreases
  • Much like a stream that flows rapidly through a
    narrow gorge but flows slowly through a broad
    plane

72
Laminar and Turbulent Flow
  • Laminar flow
  • Streamlined
  • Outermost layer moving slowest and center moving
    fastest
  • Turbulent flow
  • Interrupted
  • Rate of flow exceeds critical velocity
  • Fluid passes a constriction, sharp turn, rough
    surface

73
Aging of the Arteries
  • Arteriosclerosis
  • General term for degeneration changes in arteries
    making them less elastic
  • Atherosclerosis
  • Deposition of plaque on walls

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Capillary Exchange andInterstitial Fluid Volume
Regulation
  • Blood pressure, capillary permeability, and
    osmosis affect movement of fluid from capillaries
  • A net movement of fluid occurs from blood into
    tissues. Fluid gained by tissues is removed by
    lymphatic system.

77
Fluid Exchange Across Capillary Walls
78
Vein Characteristics andEffect of Gravity on
Blood Pressure
  • Vein Characteristics
  • Venous return to heart increases due to increase
    in blood volume, venous tone, and arteriole
    dilation
  • Effect of Gravity
  • In a standing position, hydrostatic pressure
    caused by gravity increases blood pressure below
    the heart and decreases pressure above the heart

79
Control of Blood Flow by Tissues
  • Local control
  • In most tissues, blood flow is proportional to
    metabolic needs of tissues
  • Nervous System
  • Responsible for routing blood flow and
    maintaining blood pressure
  • Hormonal Control
  • Sympathetic action potentials stimulate
    epinephrine and norepinephrine

80
Local Control of Blood Flow by Tissues
  • Blood flow can increase 7-8 times as a result of
    vasodilation of metarterioles and precapillary
    sphincters in response to increased rate of
    metabolism
  • Vasodilator substances produced as metabolism
    increases
  • Vasomotion is periodic contraction and relaxation
    of precapillary sphincters

81
Nervous Regulation of Blood Vessels
82
Short-Term Regulation ofBlood Pressure
  • Baroreceptor reflexes
  • Change peripheral resistance, heart rate, and
    stroke volume in response to changes in blood
    pressure
  • Chemoreceptor reflexes
  • Sensory receptors sensitive to oxygen, carbon
    dioxide, and pH levels of blood
  • Central nervous system ischemic response
  • Results from high carbon dioxide or low pH levels
    in medulla and increases peripheral resistance

83
Baroreceptor Reflex Control
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Local mechanisms affect MAP
86
Effects of pH and Gases
87
Long-Term Regulation of Blood Pressure
  • Renin-angiotensin-aldosterone mechanism
  • Vasopressin (ADH) mechanism
  • Atrial natriuretic mechanism
  • Fluid shift mechanism
  • Stress-relaxation response

88
General control of MAP
89
Renin-Angiotensin-AldosteroneMechanism
90
Vasopressin (ADH) Mechanism
91
Long Term MechanismsWhich Lower Blood Volume
  • Fluid shift
  • Movement of fluid from interstitial spaces into
    capillaries in response to decrease in blood
    pressure to maintain blood volume
  • Stress-relaxation
  • Adjustment of blood vessel smooth muscle to
    respond to change in blood volume
  • Atrial natriuretic factor
  • Hormone released from cardiac muscle cells when
    atrial blood pressure increases, simulating an
    increase in urinary production, causing a
    decrease in blood volume and blood pressure

92
Chemoreceptor Reflex Control
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Shock
  • Inadequate blood flow throughout body
  • Three stages
  • Compensated Blood pressure decreases only a
    moderate amount and mechanisms able to
    reestablish normal blood pressure and flow
  • Progressive Compensatory mechanisms inadequate
    and positive feedback cycle develops cycle
    proceeds to next stage or medical treatment
    reestablishes adequate blood flow to tissues
  • Irreversible Leads to death, regardless of
    medical treatment

95
Fetal circulation
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