1.4 The heart as a pump 43-58 Flashcards
Cardiac muscle tissue is composed of what kind of muscle cells:
Striated
How are striated heart muscles cells anchored at their ends?
Intercalated discs
Why is the syncytium of cardiac muscle important?
Allows rapid coordinated contraction/action potential from cell to cell (slowly)
The heart is a demanding tissue that requires:
Extensive capillary density within endomysium to deliver steady supply of O2
Ischemia
Reduction in O2
With would happen without syncytium?
Cell won’t maintain polarized state, will reach action potential and fire out of sequence
A non-regenerating tissue with cells that are capable of hypertrophy (add new myofibrils) when worked hard
Cardiac muscle
Responsive to chronic stresses
Cardiac muscle Ie. Pressure and/or volume loading
Cells that abandoned much of their myofibrillar apparatus for rapid impulse conduction/propagation:
Purkinje cells
What is Purkinje’s system?
Network of Purkinje fibers that carry cardiac impulse from AV node to ventricles of the heart and causes them to contract. Acts as a wiring to get depolarization stimulus everywhere at the right time (as opposed to the normally slower paced propagation between cells due to intercalated disks.)
The action potential of cardiac, contrite cells is very _____ and has 3 basic phases:
Long
- Depolarization
- Plateau
- Repolarization
Rapid influx of Na+ as voltage gates then open Ca2+ channels
Depolarization
Contraction happens at this phase:
Plateau AKA absolute refractory period (ARP)
The phase when the cell is resistant to stimulation, cytosolic Ca2+ rises and induces SER release of Ca2+ reserves
Plateau / absolute refractory period
This phase consists of a variable sensitivity period known as relative refractory period
Repolarization
When K+ is relocated to the interior, as at rest
Repolarization
The end of the relative refractory period (RRP) has a period of
Supranormal excitability period (SNP)
Where stimulation easily causes another depolarization and contraction
Supranormal excitability period (SNP)
As a cell is _____ during relaxation, it tends to produce a stronger contraction in the next cycle
Lengthened
Action potentials are ____ depending upon the particular cardiac muscle cell examined (form, duration, timing)
Variable
Nodal tissue tends to be ___ to depolarize but ___ to repolarize.
Slow; quick
Spontaneous action potentials are called
Auto-rhythmicity
In auto-rhythmicity, membranes are:
Leaky to inward movement of ions
Are nerves needed in auto-rhythmicity?
No. Though may modulate action
Cardiac muscle cells are complexly covered with
Receptors
What renders cardiac cells sensitive to some hormones and neurotransmitters from the autonomic nervous system?
Receptors
What two broad category receptors are on the cardiac muscle?
Adrenergic receptors
Cholinergic receptors
Receptors that bind adrenergic agonists such as sympathetic neurotransmitter norepinephrine and circulating hormone epinephrine
Adrenergic
What Adrenergic receptor is sensitive to norepinephrine and released from the axons of sympathetic fibers?
β1 receptors
What receptor increases excitability, strength and rate of contraction by hypo-polarizing the plasma membrane of the cell through G-protein signaling?
Adrenergic receptors (primarily β1 receptors)
Adrenergic receptors bind to
Norepinephrine and epinephrine
What receptor works by decreasing excitability, strength and rate fo contraction by tending to hyperpolarize the membranes (through G-protein signalin)
Cholinergic receptors
How does cholinergic receptors work
Ach “muscarinic” receptors sensitive to acetylcholine released from axons of parasympathetic fibers
Describe the flow of blood through the heart starting with the IVC/SVC
Right atrium —> Right ventricle —> Pulmonary trunk, arteries —> lungs —> pulmonary veins —> Left atrium —> left ventricle —> ascending aorta, etc.
Name the valves that prevent retrograde (backwards) flow of the blood
Atrioventricular (AV) valves
Tricuspid and Bicuspid/Mitral valves
Semilunar valves: aortic and pulmonic
Both the left and right ventricles must pump the ____ amount of blood per unit time.
Same
The systemic circulation is ______ while the pulmonary circulation is ______
Large; small
Contraction and ejection of blood
Systole
Relaxation and filing of blood
Diastole
The full action of the heart per beat is usually presented as a classic, integrated, display of all relevant activity of the heart and is known as
Cardiac cycle
In the cardiac cycle, atrial pressure supplies
additional filling to the ventricles (not important for us)
In the cardiac cycle, the heart sounds are called
phonocardiogram, clinically important
In the cardiac cycle, the thing that gets it all going
electrocardiogram (ECG)
In the cardiac cycle, the “bottom line” product of contraction
ventricular volume
In the cardiac cycle, the arterial blood pressure (left side output)
aortic pressure
In the cardiac cycle, the source of most initial ∆P
ventricular pressure
Memorize Wiggers diagram (sketch it out)
check your work
25% of ventricular filling is done by _____. The other 75% is done by:
atrial systole (at rest)
blood pouring straight from great veins through atria into ventricles.
Ventricular diastole subphases:
- isovolumetric relaxation
- rapid inflow (75% passive filling)
- diastasis
- atrial systole (25% active filling)
Ventricular systole subphases:
- isovolumetric contraction
- ejection
end-diastolic volume (EDV) = the volume at end of diastole
~130 ml
end-systolic volume (ESV) = volume end of systole
~60 ml
stroke volume (SV) equation
SV = EDV - ESV
average stroke volume
~70 ml
a useful indicator of heart performance
ejection fraction
ejection fraction equation
SV/EDV
an event occurring in early systole during which the ventricles contract with no corresponding volume change
period of isovolumetric contraction (AKA isovolumic or isometric)
once ventricular pressure exceeds aortic pressure, then aortic valve opens and the ____ begins
period of ejection
systolic pressure (systolic BP) should be
~120 mm Hg
diastolic pressure (diastolic BP) should be
~80 mm Hg
a secondary upstroke in the descending part of a pulse tracing corresponding to the transient increase in aortic pressure upon closure of the aortic valve
dicrotic notch
2 principle heart sounds, S1 is described as the:
LUB
2 principle heart sounds, S2 is described as the:
DUB
S1 is the closure of __________ while S2 is the closure of ___________
AV valves; semilunar valves
What is the valvular abnormality due to difficulty pushing blood through aortic valve. Loud and strong murmur during LEFT ventricular ejection heard throughout systole that is sometimes be felt as a “thrill.”
aortic stenosis
What is the valvular abnormality that is regurgitation, when the valve fails to prevent backflow into the left ventricle. Often heard as a “blowing” murmur or higher pitch swishing sound through diastole.
aortic insufficiency
What is the valvular abnormality that is due to difficulty pushing blood through mitral valve? Creates a weak/low-pitched murmur sound heard in the 2nd half of diastole but especially the later aspect (atrial systole)
mitral stenosis
What is the valvular abnormality that is regurgitation, occurring when the valve allows blood back into the left atrium? Creates a blowing, swishing murmur heard throughout systole.
mitral insufficiency
All valvular abnormalities due to stenosis or insufficiency usually _________ the net stroke volume
reduce
extra strain due to stenosis, the cardiac muscle will usually
hypertrophy
serious overload on the heart leads to chamber ___
dilation
cardiac output for resting adult is about
5000 ml/min
name the 2 basic mechanisms to regulate cardiac output
intrinsic autoregulation (self-regulated)
reflex / extrinsic control (nervous)
The law states that the stroke volume of the heart increases in response to an increase in the volume of blood in the ventricles, before contraction (the end diastolic volume), when all other factors remain constant
law of the heart
AKA frank-starlin mechanism
law of the heart is sometimes stated simply as _____ in venous return leads to _____ in cardiac output
an increase; an increase
peripheral factors, which affect returning blood flow, are more important than
cardiac factors
blood pressure does/does not normally affect cardiac output
does not
sympathetic innervation include numerous nerves from
spinal sympathetic chain
parasympathetic innervation includes
2 vagus cranial nerves
conduction speed
dromotropic effect
rate of contraction
chronotropic effect
strength of contraction
inotropic effect
What serves as landing site for neurotransmitter norepinephrine from sympathetic innervation on the heart? (also epinephrine from adrenal glands)
β1 adrenergic receptors
How do β1 adrenergic receptors affect dromotopism, chronotropism and inotropism?
positive (by opening Na+ and Ca2+ channels)
a heart rate greater than or equal to 100 bpm is perfectly normal in many situations but not at rest
tachycardia
some cardiac myocytes respond to this parasympathetic neurotransmitter ____ because it displays receptors for it
acetylcholine
how does acetylcholine affect dromotropism (conduction speed), chronotropism (rate of contraction), inotropism (strength of contraction)?
makes them negative
a heart rate less than or equal to 60 bpm is sometimes perfectly normal, sometimes abnormal
bradycardia
reflex control is
rapid and anticipatory
