Transcript Chapter 19: The Heart

Chapter 18: The Heart
Size, location, & orientation
• Heart is about 250-350 grams (less than 1 lb)
• About the size of a persons fist
• Location –
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found in the mediastinum – medial cavity of thorax
2/3 of mass is left of midsternal
Rests on superior surface of the diaphragm
Anterior to the vertebral column
Posterior to the sternum
Flanked by the lungs
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Posterior surface (top)
Broad & flat
9 cm wide
Directed towards right shoulder
• Base –
• Apex –
– Pointed end
– Base of both ventricles
– Point towards the left hip
Coverings
• Heart is enclosed in the pericardium:
– Protects the heart
– Anchors it to surrounding structures (diaphragm)
– Prevents over filling
• Serous pericardium:
– Thin serous membrane
– Two layers:
• Parietal –
– Lines the inside of the pericardium – internal surface
– Tough fibrous connective tissue layer
– Anchors to diaphragm & sternum
• Visceral –
– Covers the external surface of the heart
– Serous layer turns downward to cover the heart
– Part of heart wall – laced with fat
• Pericardial cavity –
– Potential space – space between visceral & serous layer of
parietal pericardium
– Contains pericardial fluid – allows serous membranes to glide
past one another
Layers of the heart wall
• 3 layers:
– Superficial epicardium (viseral pericardium):
• Visceral layer of the serious pericardium
• Infiltrated with fat
– Middle myocardium:
• Mostly cardiac muscle – bulk of the heart
• Layer that actually contracts
• Branching cardiac cells held together by crisscrossing
connective tissue fibers & arranged in bundles
– Connective tissue fibers form network – fibrous skeleton –
reinforcement of heart muscle especially around valve areas
& where vessels attach to the heart
– Deep endocardium:
• White sheet of endothelium resting on connective tissue
layer
• Located – inner myocardial surface, lining of chambers, &
covers connective tissue skeleton of valves
• Continuous w/ the endothelial linings of blood vessels
leaving & entering the heart
Chambers
• 4 chambers – 2 atria & 2 ventricles
• Internal septum –
– divides the atria internally longitudinally
• Interventricular septum –
– divides the ventricle internally
longitudinally
• Right ventricle =
– most of the anterior surface
• Left ventricle =
– inferoposterior aspect & forms most of the
apex
Chambers
• Atria –
– Superior
– Receiving chambers for blood returning to the heart from
circulation
– Small chambers
– Push blood to ventricles
– Auricles – ear-like flap – from outside of each atria – increase
atrial volume
– Internal walls have ridges of muscles – pectinate
– Fossa ovalis – shallow depression in interatrial septum –
residual from fetal heart
– Blood enters the right atrium from –
• Superior vena cava – returns blood from above the diaphragm
(upper body)
• Inferior vena cava – blood returning from below the diaphragm
(below the heart)
• Coronary sinus – collects blood draining from myocardium
– Blood enters the left atrium from –
• 4 pulmonary veins
• Seen from posterior view of the heart
• Transport blood from the lungs
Chambers
• Ventricles –
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Inferior
Most of the mass of the heart
Right ventricle = anterior surface
Left ventricle = apex
Trabecuae carneae –
• irregular ridges of muscles
– Papillary muscles –
• project into the ventricular cavity – play a role in valve function
• (muscle folds = trabeculae carnae – some are stalklike and
attach to valves = papillary muscles)
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Discharging chambers – pumps of the heart
Blood propels out of the heart into circulation
Walls much thicker than atrial walls
Right ventricle – pulmonary trunk – routs blood to lungs
(gass exchange occurs)
– Left ventricle - aorta – body
Blood pathway through heart
• Pulmonary circuit –
– Right side of the heart
– Low pressure
– Blood to and from the lungs
– Blood flow path• Blood in right atrium from body (oxygen poor,
CO2 rich) via superior and inferior venae cavae
• right ventricle
• pumps into lungs (for oxygen pickup) via
pulmonary trunk
• from lungs to heart through pulmonary veins
• left atrium
• left ventricle
Blood pathway cont
• Systemic circuit –
– Left side of the heart
– High pressure
– Supplies body w/ oxygenated blood
– Pathway –
• From lungs
• Pulmonary veins
• Left atrium
• Left ventricle – contracts
• Aorta
• Body
Valves
• Atrioventricular valves (AV) –
– Atrial-ventricular junction
– Prevent backflow into the atria when ventricles are
contracting
– Attached to AV valves – collagen cords – chordae tendineane
– anchor papillary muscles protruding from ventricular walls
– Right AV valve = tricuspid valve
• 3 flaps (tri) – endocardium & connective tissue
– Left AV valve = bicuspid valve
• 2 flaps (bi)
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When heart is relaxed – AV valves hang into ventricle
Blood into atria & into ventricle (through open AV valve)
Ventricle contracts
Ventricular pressure rises – forces blood (superiorly) against AV
valve
• Valve edges meet – closing the valve
• Chordae tendineae & papillary muscles – anchor valves while
they are closed
Valves
• Semilunar (half moon) valves –
– Major arteries leaving the heart
– Prevent backflow into the ventricles
– Aortic semilunar –
• Valve at the base of the aorta
– Pulmonary semilunar –
• Valve at the base of the pulmonary trunk
– No chordae tendinae – valve movement
caused by force of blood
• Heart is relaxed – valves are closed
• Heart contracts – valves are forced open
Microscopic anatomy
• Cardiac muscle –
– Striated, short fat, branched, & interconnected muscle
– One or two nuclei
– Intracellular space filled w/ loose connective tissue matrix &
capillaries – connected to fibrous skeleton – allows cardiac
cells to exert force
• Contraction occurs via sliding filaments
– Adjacent muscles interconnect @ intercalated discs
• Disc contains desmosomes (hold cardiac cells together) & gap
junctions (allow ions to pass from cell to cell)
• Allow cardiac cells to electrically behave as a unit
– High concentration of mitochondria
• Metabolize fatty acids for ATP
• Can switch nutrient pathways to use whatever nutrient supply
that is available
– Depends on a continual supply of oxygen
• Aerobic respiration – can’t have oxygen deprivation & still
operate
Heart contraction
• Sodium & calcium needs:
– Sodium ions enter cardiac muscle cells from
extracellular fluid (sodium ion channels)
– Causes a depolarization that causes the
sarcoplasmic reticulum (specialized ER) to
release calcium
– Calcium enters the sarcoplasm (cytoplasm
of cardiac cells)
– Calcium signals myofilaments (individual
muscle fibers) to contract
– Cardiac muscles contract as a unit or not at
all
Electrical events
• Intrinsic cardiac conduction system –
made up of specialized cardiac cells –
nodal system
• Initiate & distribute impulses
• Ensures that the heart depolarizes in
sequential order
• Contracts because of gap junction
(allows signals to pass between cells)
Electrical events
• Sequence of excitation –
– 1. SA node –
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Sinoatrial
Pacemaker - sets pace for the heart
In right atrial wall
Minute cell mass
Depolarizes 70-80 times per min
Called sinus rhythm – determines heart rate
– 2. AV node –
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Atrioventricular
In interatrial septum – above the tricuspid valve
Depolarization spreads via gap junctions
From SA node to AV node
Impulse delayed 1 sec to allow atria to completely contract
– 3. AV bundle –
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Atrioventricular
“Bundle of His”
Superior part of interventricular septum
Connects atria & ventricles electronically
Sequence of excitation cont.
– 4. right & left bundles –
• Along interventricular septum toward apex of the heart
• Conduct signal through ventricles
– 5. ventricular walls –
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Penetrate the heart apex
Turn superiorly into ventricular walls
Bundle branches excite septal cells
Contraction depends on cell-to-cell transmission via gap
junctions
• Total elapsed time from SA node to
ventricular node = .22 sec
• Ventricles contract w/ wringing motion
beginning at apex, moving toward atria
Nodes
Excitation
http://www.youtube.com/watch?v=MGxxR
yJTmwU&feature=related
Heart sounds & CO
• Lub –
– 1st heart sound
– AV valves close
– Beginning of systole (ventricular pressure rises above atrial
pressure)
• Dup –
– 2nd heart sound
– Closure of semilunar valves
– During ventricular diastole
• Cardiac output (CO) –
– Amount of blood pumped out each ventricle in one minute
(one cycle)
– CO = HR x SV
• Stroke volume (SV) –
– Volume of blood pumped by a ventricle with each beat
(during one contraction)
– Correlated w/ force of ventricular contraction
Defects
• Murmurs –
– Abnormal heart sounds
– Indicate valve problems
• Tachycardia –
– Abnormally fast heart rate
– Over 100 beats per min
• Arrhythmias –
– Uncoordinated contractions
– Irregular heart rhythms
• Fibrillation –
– Rapid, irregular, out of phase contractions
– Heart is useless
– Must be defibrillated immediately before brain death (electric
shock)
• Abnormal pacemaker –
– Ectopic pacemaker
– AV node may take over – but at a slower pace
– Caffeine can cause irregular rhythms separate from the SA
node
Cardiac cycle
• Ventricular filling –
– Flows passively through atria into ventricles (70%
of blood)
– Atria contract propelling left over blood into
ventricles
• Ventricular systole –
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Atria relax
Ventricles contract
Pressure rises closing the AV valves
Semilunar valves forced open
Blood passes into the aorta & pulmonary trunk
• Isovolumetric relaxation –
– Ventricular pressure drops
– Closes the semilunar valves
– Blood rebounds off the valves & continues its path