CASE 2 Flashcards
pulmonary circuit
right side receives oxygen-poor blood –> pumps into lungs to pick up O2 and dispel CO2
- blood vessels that carry blood to and from the lungs form the pulmonary circuit
Systemic circuit
left side of the heart receives oxygenated blood from lungs –> pumps this blood throughout body
- blood vessels that carry blood to and from all body tissue form the systemic circuit
mediastinum
medial cavity of the thorax
coverings of the heart
- pericardium, double walled sac
- fibrous pericardium: loosely fitting superficial part of this sac
1. protect the heart
2. anchor it to surrounding structures
3. prevent overfilling of the heart with blood
serous pericardium
- thin, slippery, two-layer membrane that forms a closed sac around the heart.
parietal layer
- lines the internal surface of fibrous pericardium
- at the superior side, parietal layer attaches to the large arteries exiting the heart and then turn inferiorly and continues over the external heart surface as the visceral layer (epicardium)
pericardial cavity
- between parietal and visceral layer
- contains a thin layer of serous fluid
- the serous membranes, lubcricated by the fluid, glide smoothly past each other
heart wall
has three layers
- epicardium
- myocardium
- endocardium
epicardium
- superficial
- visceral (deep) layer of the serous pericardium
myocardium
- composed of cardiac muscle,
- this layer contracts
- connective tissue fibers form the cardiac skeleton, which strenghtens the myocardium internally.
endocardium
- glistening white sheet of squamous endothelium resting on a thin connective tissue layer
- lines heart chambers and covers the valves
chambers and associated great vessels
- two superior atria
- two inferior ventricles
- interatrial septum, seperates atria
- interventricular septum, separates ventricles
Coronary sulcus (atrioventricular groove)
encircles the junction of atria and ventricles like a crown
anterior interventricular sulcus
cradling the anterior interventricular artery, marks the anterior position of the septum separating the right and left ventricles –> continues as the posterior interventricular sulcus –> provides a similar landmark on the heart’s posteroinferior surface
right atrium
- a smooth-walled posterior part
- an anterior portion in which bundles of muscle tissue are. These are called pectinate muscles because they look like the teeth of a comb.
- posterior and anterior are separated by C-shaped ridge, crista terminalis
left atrium
- mostly smooth
- pectinate muscle are only found in the auricle.
- Fossa ovalis, interatrial septum has a little weakness, marks the spot where the foramen ovale existed
atria
- receiving chambers for blood returning to the heart from the circulation.
- thin walled chambers
Blood entering in atria
Right atrium:
- superior vena cava
- inferior vena cava
- coronary sinus: collects blood from myocardium
Left atrium:
- four pulmonary veins, transport blood from lungs back to the heart
Ventricles
- Trabeculae carneae mark the internal walls of ventricular chambers
- papillary muscles, play a role in valve function, project into the ventricular cavity
- discharging chambers
- bigger walls than atria
- right ventricle pumps into the pulmonary trunk
- left ventricle pumps into the aorta
heart valves
- ensure one-way traffic of blood inside the heart
- four types
Atrioventricular valves (AV)
prevent backflow into the atria when the ventricles contract.
- right AV valve, tricuspid valve
- left AV valve, mitral valve
- chordae tendinae, tiny collagen cords which anchor the cusps to the papillary muscles
Semilunar valves (SL)
- right SL valve, pulmonary valve
- left SL valve, aortic valve
- open and close in response to differences in pressure
Coronary circulation
functional blood supply of the heart
coronary arteries
- arise from the base of the aorta and encircle the heart
- left coronary artery runs towards the left side of the heart and divides into two major branches:
1. anterior interventricular artery
2. circumflex artery - right coronary artery runs towards the right side of the heart and divides into two major branches:
1. right marginal artery
2. posterior interventricular artery
coronary veins
- cardiac veins: after passing through the capillary beds of the myocardium, blood is collected here.
- veins join to form an enlarged vessel, called the coronary sinus, which empties the blood into the right atrium. has three tributaries:
1. great cardiac vein
2. middle cardiac vein
3. small cardiac vein
the heart is myogenic
functions in ordered rhytmic fashion because of the inherent properties of cardiac muscle rather than specific neural stimuli
cardiac muscle cells are self-excitable
they can initiate their own depolarization and that of the rest of the heart –> automaticity
Action potentials
cardiac muscle contraction is triggered by action potentials.
Intrinsic conduction system
- ## made up of cardiac pacemaker cells –> have an unstable resting potential that continuously depolarizes –> pacemaker potentials –> trigger heart to its rhythmic contractions
sequence of excitation
cardiac pacemaker cells are found in the: 1. sinoatrial node 2. atrioventricular node 3. atrioventricular bundle 4. right and left bundle branches 5. subendocardial conducting network impulses pass from 1-5
SA node
- right atrial wall
- sets pace for the heart
- the hearts pacemaker –> no other region has a faster depolarization rate
- sinus rhythm determines heart rate
AV node
- wave spreads via gap junctions throughout the atria and via the internodal pathway to the AV node
- located immediately above the tricuspid valve
- impulse is delayed for 0.1 s allowing atria to respond and complete contraction
AV bundle
- also called bundle of His
- superior part of interventricular septum
Right and left bundle branches
- AV bundle splits into two pathways :
1. right bundle branch
2. left bundle branch - go towards the heart apex
Subendocardial conducting network
- also called Purkinje fibers are long strands of barrel-shaped cells with few myofibrils.
- penetrate into heart apex and then turn superiorly into the ventricular walls
Total time of impulse is
- from SA node to last of ventricular muscle cells is 0.22 s (220 ms)
Cardioinhibitory center
- sends impulses to the parasympathetic dorsal vagus nucleus in the medulla –> sends inhibitory impulses to heart via vagus nerves
Cardiac cycle
- systole, period of contraction
- diastole, period of relaxation
- includes all events associated with the blood flow through the heart during one complete heartbeat
Ventricular filling, mid to late diastole
- pressure in heart is low
- blood flows through atria and open AV valves into ventricles, aortic and pulmonary valves are closed.
- atria contract, compressing blood in their chambers –> rise in arterial pressure –> propels residual blood out of the atria into the ventricles
Ventricular systole, atria in diastole
- atria relax –> ventricles begin contracting
- ventricular pressure rises rapidly, closing AV valves.
Isovolumetric contraction phase
split-second period when the ventricles are completely closed and blood volume in chambers remains constant as the ventricles contract
Isovolumetric relaxation, early diastole
- ventricles relax
- ventricular pressure drops because the blood remaining in their chambers, end systolic volume (ESV) is no longer compressed.
heart sound
phonocardiogram
- first sound is tricuspid and mitral valves closing
- second sound is pulmonary and aortic valve closing
Pressure volume diagram
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- D-A phase is diastole
- B-C phase is systole
1. mitral valve opens
2. mitral valve closes
3. aortic valve opens
4. aortic valve closes
Stroke volume
- volume of blood pumped out of our heart per beat
- EDV (end diastolic volume) - ESV (end systolic volume)
isovolumic
volume stays the same
stroke volume depends on 3 factors
- contractility, inotropy
- preload, left ventricular wall stress at end diastole
- afterload, pressure required to open aortic valve
Contractility, inotropy
- ability of heart muscle to contract
- increasing influx calcium –> increasing contractility
- increases the slope and shifts the end-systolic pressure- volume relationship (ESPVR) to the left –> ventricle generates more pressure at a given left ventricular volume.
- increases pressure development and ejection velocity –> increases stroke volume and ejection fraction and decreases ESV
- decreasing inotropy increases ESV and decreases stroke volume and ejection fraction
Preload
- left ventricular wall stress at end diastole.
- increase in preload –> increase in stroke volume –> increase in cardiac output and arterial pressure –> afterload on ventricle increases.
- decrease in preload –> reduces stroke volume –> ESV decreases slightly
Afterload
- pressure required to open aortic valve.
- increased –> stroke volume is reduced –> end-systolic volume increased
- decreased –> stroke volume increases –> end systolic decreases
Blood volume
- determined by amount of water and sodium ingested + excreted by kidneys + lost through the GI-tract, lungs and skin.
- mainly regulated by kidneys
Changes in bloodvolume
- affect arterial pressure by changing cardiac output.
- increase blood volume –> increase central venous pressure –> increases right arterial pressure, right ventricular end-diastolic pressure and volume.
- increase in ventricular preload increases ventricular stroke volume by the Frank-Starling mechanism.
- increase in right ventricular stroke volume –> increases pulmonary venous blood flow to left ventricular –> increasing left ventricular preload and strok volume –> increase cardiac output and arterial blood pressure.
Frank-Starling mechanism
- by increasing blood volume the heart will contract harder
effects of autonomic nervous system (ANS)
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Nicotinic acetylcholine receptors (parasympathetic)
- respond to neurotransmitter acetylcholine
- also respond to nicotine
- they are primary receptor in muscle for motor nerve-muscle communication that controls muscle contraction
- activation of these receptors –> depolarization of plasma membrane
Muscarinic acetylcholine receptor (parasympathetic)
- acetylcholine receptors which work with G-proteins
- act as main end-receptor stimulated by acetylcholine released from postganglionic fibers in the parasympathetic nervous system
- activation of these –> inhibition of postsynaptic neurons
Adrenergic receptors or adrenoceptors
- alfa and beta receptors
- targets of noradrenaline and adrenaline
- stimulate SNS, responsible for fight-or-flight response
Alfa receptors
- vasoconstriction
- decreased motility of smooth muscle in GI-tract
Beta 1- receptors
- increase cardiac output by increasing heart rate, conduction velocity, stroke volume and rate of relaxation of myocardium by increasing calcium ion concentration
Dobutamine effect on heart
direct stimulation of B1-adrenergic receptors of SNS, causing threshold to be reached more quickly –> SA node fires more rapidly –> heart starts beating faster –> increase in cardiac output and heart rate
