Title: Cardiac Muscle
1Cardiac 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
2Cardiac 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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4Cardiac myocyte action potential
5Refractory Period
- Absolute Cardiac muscle cell completely
insensitive to further stimulation - Relative Cell exhibits reduced sensitivity to
additional stimulation - Long refractory period prevents tetanic
contractions
6AP-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.
7Functions 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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9Orientation 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.
10Circulation circuits
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14Heart 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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19Valve function
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22Coronary circulation
23Cardiac conducting system
24Pacemaker potential
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27EKG
28Heart sounds
29Heart 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
30Cardiac 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
31Cardiac 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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34Pressure relationships
35Mean 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
36Factors Affecting MAP
37Regulation 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
38Heart 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
39Baroreceptor and ChemoreceptorReflexes
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42Cardian innervation
43Pacemaker 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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45Vascular physiology
46Peripheral 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
47Blood 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
48Structure 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
49Structure 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
50Structure 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
51Blood Vessel Comparison
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55Capillaries
- 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
56Capillary Network
- Blood flows from arterioles through
metarterioles, then through capillary network - Venules drain network
- Smooth muscle in arterioles, metarterioles,
precapillary sphincters regulates blood flow
57Muscular contractions aid venous return
58Pulmonary 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
59Systemic Circulation Arteries
- Aorta
- From which all arteries are derived either
directly or indirectly - Parts
- Ascending, descending, thoracic, abdominal
- Coronary arteries
- Supply the heart
60Systemic 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
61Dynamics of Blood Circulation
- Interrelationships between
- Pressure
- Flow
- Resistance
- Control mechanisms that regulate blood pressure
- Blood flow through vessels
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63Blood 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
64Pressure 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
65Blood Pressure Measurement
66Pulse 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
67Blood 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
68Critical 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
69Physiology 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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71Cross-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
72Laminar 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
73Aging 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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76Capillary 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.
77Fluid Exchange Across Capillary Walls
78Vein 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
79Control 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
80Local 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
81Nervous Regulation of Blood Vessels
82Short-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
83Baroreceptor Reflex Control
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85Local mechanisms affect MAP
86Effects of pH and Gases
87Long-Term Regulation of Blood Pressure
- Renin-angiotensin-aldosterone mechanism
- Vasopressin (ADH) mechanism
- Atrial natriuretic mechanism
- Fluid shift mechanism
- Stress-relaxation response
88General control of MAP
89Renin-Angiotensin-AldosteroneMechanism
90Vasopressin (ADH) Mechanism
91Long 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
92Chemoreceptor Reflex Control
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94Shock
- 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
95Fetal circulation
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