Chapter 18 Flashcards
Where is the heart located and describe its position?
- ventral, thoracic, mediastinum, pericardial cavity
- apex points to left hip and base to right shoulder
- two thirds lies left of the midsternal line, between ribs 2 and 5
What is membrane that closes the heart and has 3 layers?
pericardium
What is the pericardium made up of?
- fibrous pericardium
- parietal layer
- visceral layer (epicardium)
What is the function of the fibrous pericardium?
protects, anchors, and prevents overfilling
What is the function of the parietal layer?
lines the internal surface of the fibrous pericardium
What do both parietal and visceral layers produce?
lubricating serous fluid
What is the purpose of the lubricating serous fluid?
reduces fluid
What are the 3 layers of the heart wall?
- epicardium
- myocardium
- endocardium
What type of tissue is the epicardium made up of?
squamous epithelium and connective tissue
What does epicardium contain?
blood, lymph and nerve supply
What is the function of the epicardium?
reduces friction
What is the myocardium made up of?
spiral bundles of cardiac muscle cells
The myocardium is a fibrous network of collagen and elastin fibers. Name 3 purposes they have.
- anchors cardiac muscle fibers
- supports great vessels and valves
- limits spread of action potentials to specific paths
What is the main function of myocardium?
pumps blood throughout the body
What is the innermost layer of the heart wall?
endocardium
What is the main function of the endocardium?
friction free surface for blood to flow over
What do the surface grooves of the heart carry?
coronary blood vessels to heart wall
Name the 3 surface grooves.
- atrioventricular sulcus
2. anterior & posterior interventricular sulcus
Describe the two walls of the atria and what is their function.
ridged by pectinate muscles
function: receiving chambers
When the blood is received in a chamber describe how the blood is moved into the ventricles.
30% pumped and 70% passive movement
What are the purpose of the auricles?
increase atrial volume
Name the 3 vessels that enter the right atrium.
superior and inferior vena cava, coronary sinus
Name the 2 vessels that enter the left atrium.
right and left pulmonary veins
What do the right and left pulmonary veins carry?
oxygenated blood
What is the function of the two ventricles?
discharging chambers
What are the two ventricles separated by?
interventricular septum
What comprises most of the heart?
right and left ventricles
What muscle anchors the chrodae tendonae of valves?
papillary muscles
What forms the ridges in the ventrical walls?
trabeculae carnae
Describe the function of the left ventricle
receives oxygenated blood from pulmonary veins
pumps blood through aorta to systemic unit
Describe the function of the right ventricle.
receives deoxygenated blood from vena cava
pumps blood through pulmonary trunk to pulmonary circuit
Do both left and right sides pump the same volume of blood?
yes
Describe the pulmonary circuit
short, low pressure circulation
moves blood to and from the lungs for gas exchange between air and blood
Name the 9 steps of the pulmonary circuit
- right ventricle
- pulmonary semilunar valve
- pulmonary trunk
- pulmonary arteries
- capillaries of lungs
- pulmonary veins
- left atrium
- left AV valve
- left ventricle
Describe the systemic unit
long, high pressure circuit
moves oxygenated blood to and from tissue for gas exchange between blood and tissue cells
Name the 10 steps of the systemic unit
- left ventricle
- aortic semilunar valve
- aorta
- systemic arteries
- tissue capillary beds
- systemic veins
- vena cava
- right atrium
- right AV valve
- right ventricle
What is the coronary circuit?
function blood supply to the heart muscles itself
muscle has high ATP demand
What does the coronary circuit contain many of?
junctions (anastomoses)
Name the 5 coronary arteries
right and left cononary, marginal, circumflex, anterior interventricular arteries
Name the 3 coronary veins
small cardiac, anterior cardiac, great cardiac veins
What are two hoemostatic imbalances of coronary circulation?
angina pectoris myocardial infarction (heart attack)
What is agina pectoris
acute thoracic pain caused by temporary blockage in blood supply to the myocardium
temporary lack of O2 weakens cells
What is myocardial infarction
heart attack
proglonged coronary blockage -> prolonged lack O2 -> cells die -> repaired with non contractile scar tissue
if cells do not repair and all die = death
What is the purpose of a heart valve?
ensures one way direction of blood flow through the heart
What instigates the opening and closing of of the heart valves
changes in blood pressure
Name the 4 valves of the heart
left and right atrioventricular valves
left and right semilunar valves
What are the other names for the right and left atrioventricular valves?
right = tricuspid left = bicuspid (mitral)
What is the function of the right AV valve?
prevents back flow into the right atrium when the right ventricle contracts
What is the function of the left AV valve?
prevents back flow into the left atrium when the left ventricle contracts
What is the function of the chordae tendinae?
anchors the AV valve cusps to papillary muscles and prevents flaps from being blown into the atria during ventricular contraction
What is the function of the papillary muscles?
contracts just before ventricles to take up the slack in the chordae tendonae and prevent the valves from being pushed open backwards into the atria
What is the function of the semilunar valves?
to prevent back flow into the ventricles when the ventricle relaxes.
Name the two semilunar valves?
right pulmonary SL valve
left aortic SL valve
What does the lub dub pause sound represent
closing of heart valves
What does the 1st sound in the heart beat represent
closing of AV valves - start of ventricular contraction (systole)
What does the 2nd sound in the heart beat represent
closing of the SL valves - start of ventricular relaxation (diastole)
What are heart murmurs
abnormal heart sounds representing valve problems
What is auscultation
listening to heart sounds - valves closing
can clost a sightly different times
LAV closes before RAV
Aortic SL closes before pulmonary SL
What are two homeostatic imbalances in valve function
- leaky valves - produce murmurs
2. stenosis - narrowing of valves - impedes flow - caused by stiffening of valve flap
Describe the cardiac muscle cell
striated, short, fat, branched, uninucleate and interconnected by intercalated discs
What connects the fibrous skeleton in the muscles cells?
connective tissue matrix (endomysium)
What is the difference between sarcoplasmic reticulum and t-tubules in cardiac muscle vs. skeletal muscle?
in cardiac muscle t-tubles are wide but less numerous and sarcoplasmic reticulum is simpler than in skeletal muscles
What makes up 25-35% of the cardiac muscle cell volume?
mitochondria
What is the difference in the sarcomere between the cardiac and skeletal muscle?
they are more irregular in the cardiac muscle
What are intercalated discs?
junctions between cells
What do the intercalated discs contain and what is their function?
desmosomes - hold cells together during contraction
gap junctions - ions can pass quickly from cell to cell
What does it mean when they say a heart behaves as a functional syncytium unit?
contracts as a single unit
Describe the physiology and events of contraction in the heart
1% made up of pacemaker cells
99% made up of pumping cells (contractile)
gap junctions ensure heart contracts as a single unit
long refractory period enables pumping
Describe the process of the pacemaker cells
- > specialized cardiac cells initiate impulses, ensuring heart depolarizes in an orderly fashion
- > autorhythmic cells have an unstable resting potential that continuously depolarize (pacemaker potential)
- > slow depolarization from -60mv (resting potential) to -40mv (threshold) happens due to slow sodium channels opening
- > once -40mv reached fast calcium gates open and calcium rushes in
- > membrane continues depolarization until an action potential is generated
- > calcium gates shut and potassium gates open and potassium leaves the cell and repolarization occurs
- > action potential is transmitted to rest of myocardium via intrinsic conduction system
- > heart contracts; first the atria then the ventricles
What is the intrinsic conduction system
- > coordinates and synchronizes heart activity
- > causes heart to beat faster, without it impulses would move much slower and contraction would not be synchronous
Name the 5 autorhythmic cardiac cells in order of impulse transfer
- Sinoatrial SA Node - primary pacemaker
- internodal pathway to…
- AV Node node
- AV bundle
- right and left bundle branches
- purkinje fibers
What is the rate called that the SA node sets and how fast?
sinus rhythm at about 75 bpm
Why does the SA node set the pace for the heart?
because no other region of the conduction system of the myocardium has a faster depolarization rate
Describe the AV node… what makes it delay impulses and for how long, depolarization rates, fibers and junctions
smaller diameter fibers and fewer gap junctions
depolarizes at about 60 x per minute and delays impulse approx 0.1 second
What is the rhythm called in the AV node?
junctional rhythm
What is the function of the AV bundle? Where does it branch into? What else can it be called?
connects the atria to the ventricle - is the only electrical connection between them
branches into the purkinje fibers
bundle of His
What are the right and left bundle branches?
two pathways in the interventricular septum that carry the impulses toward to apex of the heart
What is the function of the purkinje fibers? how fast do they depolarize?
complete the pathway into the apex and ventricular walls
depolarize only 30 x per minute
Name the sequence of stimulation and contraction in the intrinsic conduction system
- > SA node develops pacemaker potential
- > transmitted to walls of atria
- > atria begin to contract
- > impulse delayed at AV node - atria completes contraction
- > impulse transmitted from AV node to walls of ventricles
- > ventricles contract
- > produces normal sinus rhythm
What are arrythmias?
irregular heart rhythms
What is fibrillation?
rapid, irregular contractions; useless for pumping blood
What would happen if the SA node became defective?
the AV node would take over and would result in a junctional rhythm of 40-60 bpm.
“Ectopic focus” = abnormal pacemaker takes over
What would a defective AV node result in?
partial or total heart block
- > few or no impulses from the SA node would reach the ventricles
- > ventricles would beat at different rate from atria
What is the result of too much coffee or nicotine?
premature ventricular contraction - extra systole
Describe what happens when initially the membrane is polarized (contraction of contractile cells)
- > inside is more negative than outside
- > potential difference is maintained by active transport pumps
- > sodium is pumped out and potassium is pumped in
- > both ions are positively charged but more sodium is outside than potassium inside
Describe what happens in an action potential from the pacemaker cells to the contractile cells.
- > sodium gates open, sodium rushes into cell, positive feedback, depolarization
- > fast calcium gates open, calcium enters cell, triggers opening of slow calcium gates in SR
- > sodium gates shut, SR releases calcium into cell
- > calcium binds to troponin
- > crossbridges form, myofilaments slide, etc = contraction
- > slow calcium gates stay open, keeps calcium high, prolongs contraction, depolarization plateau
- > potassium gates open, potassium moves out of cell = repolarization
- > long absolute refractory period - maintained by slow calcium gates, prevents tetany
Where is calcium store in the cardiac muscle vs. the skeletal muscle?
calcium is stored in the SR and outside the cell
Name 3 things the heart depends on
- aerobic respiration for adequate ATP
- good supply of oxygen and fuel
- adequate blood supply
What is ischemia?
blockage of coronary arteries that leads to deficient O2 supply to the myocardium
In terms of fuel what is the limiting factor for the heart?
oxygen supply = limiting factor
can use glucose, fatty acids, lactic acid - whatever is available
What is an ECG
composite of all action potentials generated by nodal and contractile cells at a given time
What are the three deflection waves and what do they represent
P wave = depolarization of Atria
QRS complex = depolarization of ventricles
T wave = repolarization of ventricles
Describe the 3 segments of the ECG
PR interval = beginning of atrial excitation to beginning of ventricular excitation
ST segment = complete depolarization of ventricular myocardium
QT interval = beginning of ventricular depolarization to repolarization
What is contraction of atria triggered by?
depolarization of SA node
What is contraction of ventricles triggered by?
purkinje fibers
How is the cardiac cycle described?
all events associated with blood flow through the heart during one complete heartbeat
What are contraction and relaxation called?
systole = contraction
diastole = relaxation
What are the four phases of the cardiac cycle?
- ventricular filling
- ventricular systole
- isovolumetric relaxation
- quiescent period
When does ventricular filling take place?
mid to late diastole
What happens during ventricular filling?
- AV valves are open
- 70% of blood passively flows into ventricles
- 30% of blood is pumped in during atrial systole
- EDV (end diastolic volume) occurs: volume of blood in each ventricle at end of ventricular diastole
What happens during ventricular systole?
- atria relax and ventricles begin to contract
- rising ventricular pressure results in closing of AV valves
- isovolumetric contraction phase - all valves are closed
- ejection phase, ventricular pressure exceeds pressure in the large arteries forcing SL valves open
- ESV (end systolic volume): volume of blood left in ventricles
What happens during isovolumetric relaxation?
- ventricles relax
- backflow of blood in aorta and pulmonary trunk closes SL valves and causes dicrotic notch (brief rise in aortic pressure)
What happens during the quiescent period? How long is it?
both atria and ventricles are relaxed - lasts for 0.4 sec
What is the length of the cardiac cycle with a heart rate of 75bpm?
atrial systole: 0.1 sec
ventricular systole: 0.3 sec
quiescent: 0.4 sec
Total: 0.8 sec
What is cardiac output?
volume of blood pumped by each ventricle in 1 minute
What is cardiac output the product of?
heart rate and stroke volume
define HR, SV and CO
heart rate = number of beats per min
stroke volume = volume of blood pumped by one ventricle with each beat
cardiac output = HR x SV
At rest what is the average CO?
HR 75 bpm x SV 70 ml/beat = CO 5.25 L/min
What is cardiac reserve?
the difference between maximal CO and resting CO
What can maximal CO reach in a trained athlete?
35 L/min
What is the formula to determine the regulation of stroke volume?
SV = EDV - ESV
What is EDV?
end diastolic volume = maximum volume in the ventricle prior to contraction
What is ESV?
end systolic volume = volume left in ventricle at the end of a contraction
What are the 3 factors affecting SV?
Preload
Contractility
Afterload
What is preload?
the degree of stretch of cardiac muscle cells before they contract
What is the Frank-Starling law of the heart
the more the heart stretches prior to contraction the harder it will contract
greater the EDV, the greater the force of the contraction
What is EDV increased and decreased by?
increased: slower heart beat and excercise (increases venous return)
decreased: rapid heart rate and decreased blood volume (eg. blood loss, dehydration)
What is contractility?
increase in force of contraction independent of muscle stretch and EDV
What is contractility caused by?
more calcium ions from SR and extracellular fluid: more cross bridges form and more complete ejection of blood increasing SV
What increase and decrease contractility?
positive inotropic agents and negative inotropic agents
What does the sympathetic system release that is a positive inotropic agent?
norepinephrine
What are a few negative inotropic agents?
acidosis increased hydrogen
increased extracellular potassium ions
drugs called calcium channel blockers
What is afterload?
pressure that must be overcome for ventricles to eject blood
back pressure that arterial blood exerts making it harder for ventricles to empty
What is afterload caused by?
hypertension
What are the factors called that regulate heart rate? and describe
positive chronotropic = factors that increase HR
negative chronotropic = factors that decrease HR
What is the heart rate modified by?
Autonomic Nervous System Regulation (ANS)
Where are the cardiac centres located, what are they called and describe.
located in medulla oblongata
cardioacceleratory centre = innervates SA and AV nodes, heart muscle and coronary arteries thru sympathetic neurons
cardioinhibitory centre = inhibits SA and AV nodes thru parasympathetic fibers in the vagus nerves
What is the sympathetic nervous system activated by and describe
activated by emotional or physical stressors “fight or flight”
positive chronotype = increases HR
mediated by norephinephrine = stimulates SA node
What is the parasympathetic system and describe
opposes the sympathetic effects
negative chronotype = slows heart rate
mediated by acetycholine = inhibits SA node
What do the vagus nerves do and what happens if these nerves are cut?
carries parasympathetic fibers to the heart
if vagus nerves cut would increase about 25 bpm
What are baroreceptors called? and what do they do?
atrial bainbridge reflex
stretching of atrial walls stimulates SA node and sympathetic reflexes
increase venous return -> increase atrial pressure -> stimulates stretch receptors -> sympathetic nervous system -> increase HR and force of contraction
How does epinephrine regulate heart rate? and where does it come from?
enhances heart rate and contractility
comes from adrenal medulla
How does thyroxine regulate heart rate?
increases heart rate and enhances effects of norepinephrine and epinephrine
What effects to hypercalcemia and hypocalcemia have on the heart?
hypercalcemia = increase HR
hypocalcemia = decrease HR
What effects to hyperkalemia and hypokalemia have on the heart?
hyperkalemia - leads to heart bloc and arrest
hypokalemia - feeble heart rate
What effect does hypernatremia have on the heart?
decreased HR
Name 4 other factors that can influence heart rate?
age, gender, exercise, body temperature
What is tachycardia?
abnormally fast heart rate
may lead to fibrillation; decreases venous return -> decreased CO
What is bradycardia?
heart rate lower than 60 bpm
inadequate blood circulation
What is congestive heart failure?
progressive condition where CO is so low that blood circulation cannot meet tissue needs
What are four factors that cause congestive heart failure? and describe
- coronary atherosclerosis - blockage of arteries with fatty deposits
- persistent high blood pressure - weakens heart; heart has to pump against greater resistance
- multiple myocardial infarcts - contractile cells replaced by scar tissue
- dilated cardiomyopathy - flabby ventricles; ventricles enlarge but lose the ability to contract
What does left sided heart failure cause?
pulmonary congestion
blood accumulates around lungs and fluid leaks into lungs
What does right sided heart failure cause?
system congestion - edema
blood accumulates in extremities; fluid leaks into interstitial spaces in tissues
