heart physiology Flashcards
blood flow around the heart
from body to lung:
- vena cava into right atrium
- tricuspid valve open to let deoxygenated blood into right ventricle
- when r ventricle full and ready to contract, tricuspid closes and pulmonary semilunar valve opens so blood flow into pulmonary artery
from lung to body:
- pulmonary vein into left atrium
- bicuspid valve open to let oxygenated blood into left ventricle
- when l ventricle full and ready to contact, bicuspid closes and aortic valve opens to let blood flow into aorta
fossa ovalis
- shallow depression in the right atrium
- remnant of foramen ovale (fetal circulation)
- which allow blood to flow from r atrium to l atrium, bypassing the units to reach baby
coronary sinus
- located on posterior side of heart, within the AV sulcus
- drains blood from the coronary veins (drains deoxygenated blood from myocardium after its supplied heart muscle with nutrient and oxygen)
chordae tendineae
“heart strings”
- prevent AV valves from inverting
- originate on the cusps of the valves and insert onto the papillary muscle (on inner walls of the ventricles)
papillary muscles
- anchor the chordae tendineae
- 3 on right
- 2 on left
- prevent inversion
inter ventricular septum
- thick muscular wall
- needs to be able to withstand pressure of the blood
- separates the ventricles and prevent blood mixing
diastolic phase
ventricle relax
fill with blood
valves of the heart
prevent backflow of blood
- open and close in response to pressure changes
coronary artery circulation
heart muscle supplied with blood from left and right c arteries
- arise for aortic sinuses within aorta
- located on posterior side of heart within AV sulcus
- provides oxygen and nutrient to myocardium
variation in coronary artery circulation
larger left than right
- dominant c artery gives rise to the posterior interventicular branch
coronary venous circulation
blood drains into right atrium via coronary sinus
layers of the heart wall
endocardium
myocardium
epicardium
endocardium
- inner layer
- simple squamous endothelium on thin layer of connective tissue
- smooth lining for chambers of heart
- SURROUND INDIVIDUAL CHAMBERS
myocardium
- middle layer
- cardiac muscle tissue
- bundles organised diagonally around heart
- generates pumping action of heart
- SURROUNDS ENTIRE HEART
epicarium
- outer layer
MADE UP OF:
- areolar connective tissue
- mesothelium
- gives smooth surface to outside of heart
- contains blood vessels
- adheres tightly to
pericardium
triple layered sac- surrounds and protects the heart
fibrous pericardium: (OUTER)
- tough inelastic, dense irregular connective tissue
- protects heart ans prevent overstretch
- anchor heart in medaistnim
parietal pericardium: MIDDLE)
- fused to fibrous pericardium
visceral layer (INNER):
- epicardium
PERICARDIAL FLUID BETWEEN PAR AND VIS:
- reduce friction as heart beat
skeletal and cardiac muscle
S:
- under voluntary control
C:
- striated appearance
- under involuntary control
- branching structure
- cells are shorter in S= MORE MITOCHONDAIR
- one nucle per cell
electrical activity of the heart
- doesn’t require external stimuli’s for cardiomyocyte contraction
- AUTORHYTHMIC CELLS:
- auto generate action poteion that triggers heart contraction
- specialised cardiomyocytes
- found in SA (sinoatrial) node
SA node action potential
- no stable resting potential
- repeatedly depolarise to threshold required to trigger action pot
what and where is the SA node
right atrium
primary pace maker
the conducting system
- SA node activity and atrial activation begins
- stimulus spreads across atrial surfaces and reaches AV node
- there is a 100 msec delay at the AV node. atrial contraction begins
- impulse travels down the interventricular septum within AV bundle and the bundle branches into the purkinje fibres via moderator band to the papillary muscles of th right ventricle
- impulse is distributed by purkinje fibres and relay throughout the ventriclar myocardium
ATRIAL contraction is done and VENTRCULAR begins
cardiac muscle action potential
- cardiomyocytes have different shape action potentials compared to skeletal muscle
- longer action potential allows for prolonged contraction in coordinated fashion
- refractory period between depolarisation and re polarisation where another action potential can’t be formed
- give time for chambers to fill with blood
excitation contraction coupling in cardiomyocytes
- action potential enters from adjacent cell
- L type voltage-gated calcium ions channel open and calcium ions enter the cell
- calcium from outside the cell binds to ryanodine receptor
- entry of ions trigger the release of ions from sarcoplasmic reticulum (most calcium ions comes from SR)
- calcium ions bind to troponin to initiate contraction
conduction of cardiac action potential
- cardiac muscle cells connected by intercalated discs
- secured by desmosomes
- linked by gap junctions
- allow for transfer of ions between cells
- local changes in currents
mechanics of cardiac contraction
P reload
A fterload
C ontrctlity
E art rate
cardiac output equation
CO= HR X SV
heart rate x stroke volume
stroke volume
- EDV-ESV
- EDV= volume before contraction
- ESV= volume after contraction
- increase in blood coming back to heart (EDV) leads to increase in contractility
- due to increased Ca ion release and sensitivity
after load
- the pressure in which the heart has to pump against to eject blood
- higher the pressure in aorta= more force required by the heart (systemic circulation)
- as afterload increase= cardiac output decreases
contractility
the ability to contract the heart
to increase contractility you need positive ionotropic agents
- promote calcium ion influx or sensitivity during cardiac action potential
- sympathetic nervous stimulation of ventricular muscle fibres
- hormonal control
eart rate
neuronal and endocrine regulation of SA node
increase HR: positive chronotropic factors (adrenaline and noradrenaline)
decrease HR: negative chronotrpic factors (acetylcholine)
sympathetic increases HR
parasympathetic decreases HR
