Heart Flashcards
Where does the AP in the heart start?
In the SA node
What does the AV node ensure?
That the atrium contracts first
How are the muscle cells connected?
Gap junctions (electrical synapses) at the intercalated disc
What ion channels are responsible for the APs in the SA and AV nodes?
I_K (outward), I_f (inward) and I_Ca (inward)
Describe how the ion channelsare involved in the AP.
I_f open when the Vm is hyperpolarized –> Na+ influx –> Vm depolarizes –> I_f close, I_Ca open –> Vm hyperpolarizes slowly (plateau) –> I_K open –> K+ efflux –> Vm hyperpolarizes quickly
How does the para- and sympathetic systems work on the heart?
On I_f channels
Sym: more I_f are activated –> quicker depolarization –> increase in heartrate
Para: Vm needs to be hyperpolarized more before I_f opens –> slower depolarization –> decrease in heartrate
What other channels are important for the regulation of the heart rythm?
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels:
Activated by [cAMP] increase stimulated by 5-HT, ANP and NA, and inhibited by ACh and ADO
What are the frequencies of APs in the SA-, AV-node and in the purkinje fibers ventricular myocyte, and which dominates?
SA: 60-100
AV: 40-60
PFVM: 20-40
Higher frequency always win
How does the para- and sympathetic systems work on the nodes and the contraction?
Sym: works on both the nodes (increase pace) and the contraction (indirectly increase contractilty)
Para: works only on the nodes (decreases the pace)
Describe how the sympathetic system influences the contraction of the heart.
Sym stimulates troponin C release, which increases the Ca2+ sensitivity. Also increases [Ca2+]i.
Frank Starlings law: The longer apart the muscle fibers are the more sensitive to Ca2+ (–> increases the energy of contraction)
What is an ECG?
Electrocardiogram, a summation of the different ion fluxes: PQRST - P = atrial depolarization, Q-T = ventricular depolarization-repolarization
What can an ECG be used for?
Determining if there are any clogs in the heart (where it is), or if the pacemaker cells are functional
Disorders of impulse formation, and disorders of impulse conduction can be determined
How is the direction of de- and repolarization determined?
If the P and T are positive: moving toward positive electrode
P and T are negative: moving away from positive electrode
What are some common causes of arrythmias?
Normal, not dangerous: Inhalation –> heart beat increases a bit, exhale –> heart beat decreases a bit
Wolf-Parkinson-White syndrome: The signal travels in a loop from the AV-node to the rest of the heart, but not SA node => not regulated
Myocardial infarction: damaged cells –> blocked conduction –> elevation of ST segment (can create an ectopic pacemaker by creating a loop)
What causes the heart to contract in different directions?
The direction of the fibers
What is increased with the contractility?
The stroke volume
Which ionotropic substances are stimulated by the symapathetic system, and contributes to the increased storke volume?
Cardiac glycosides, phosphordieasterase III inhibitors, beta-adrenergic receptor agonists
How is the pressure differences in the heart?
Right side: lower
Left side: higher (very high in aorta)
What are the function of arteries, microcirculations (capillaries), and veins?
Arteries (away from heart): distribution of gasses and nutrients
Microcirculations: diffusion and filtration
Veins (toward the heart): collection
How does the pressure change throughout the branching of the blood vessels?
It drops with each branch (artery –> arteriole –> capillary –> vein)
What does the pressure depend on, and how is it regulated?
Resistance, which depend on vascular smooth muscle cells:
Vasoconstriction: increase in resistance, pressure rises
Vasodilation: decrease in resistance, pressure drops
What are the nutritional and the non-nutritional substances transported via the blood?
Nutritional: glucoes, gasses, amino acids, waste and water
Non: hormones, immune factors, temperature regulation
Decribe the cellular mechanisms of vasoconstriction.
[Ca2+]i rises –> Ca2+ binds to calmodulin –> Ca2+-calmodulin binds to MLCK –> active calmodulin-MLCK complex phosphorylates myosine via ATP –> contraction
What is compliance?
The ability of the blood vessel to increase the volume (flexibility)
C = delta-V/delta-P
The steeper the slope, the easier it is to increase the volume (=> higher compliance)
Which has a higher compliance, veins or arteries?
Veins
What happens to the compliance with ageing?
It lowers, as the vessles stiffens
Explain why a high compliance is good.
Stiff arteries are not optimal, as it highers the blood pressure
What is a normal blood pressure?
80 (diastole)/120 (systole)
How does the ACh and NE work on the heart?
Vagus nerve innervate SA –> ACh (para) –> activation of Gi –> decrease in cAMP formation and concentration –> decrease HR and contractility
Sympathetic nerve innervate SA –> NE (sym) –> activation of Gs –> increase in [cAMP]i –> increase of HR and contractility
How does para- and sympaticus work on the arteries?
Para: salivary –> indirect vasodilation
Sym: NE –> binds to alpha2R –> [Ca2+]i increase –> decrease [cAMP]i and [cGMP]i –> vasoconstriction
Describe how the different adrenergic receptors signal.
Alpha1 (smooth muscles): –> [Ca2+]i increase –> [cGMP]i increase
Alpha2 (smooth muscles): –> [Ca2+]i increase –> [cAMP]i and [cGMP]i decrease
Beta1 (heart and smooth muscles): –> increase HR
Beta2 (heart and smooth muscles): –> increase [cAMP]i
Vasodilation
Describe hos ACh works on adrenergic neurons, and how NE works on cholinergic neurons.
ACh inhibits NE and adranaline release via M2 receptors
NE inhibits ACh release via alpha2R
Describe how NE and ACh constantly affects the arterial tone and the HR.
NE: keeps the arterial tone
ACh: keeps the heart cool (lowers HR, SA spontaneous rythm is high)
Describe how feedback from the cell regulates NT release.
ATP released from cell –> adenosine –> inhibits NT release
What are baroreceptors, and where are they found?
Pressure sensing cell, found in the carotid sinuses and aortic arch
Describe how baroreceptors work.
Low pressure –> inactive –> sympathetic activation (normally inhibited by baro) –> NA release –> increased pressure (HR and CO)
High pressure –> active –> parasympathetic activation –> ACH release –> decreased pressure (HR, CO)
