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Cardiovascular Physiology > Fewell - Electrical properties of the heart > Flashcards

Fewell - Electrical properties of the heart Flashcards

1
Q

How do physiologist gauge blood pressure

A

by the height it can drive a column of liquid

  • water or mercury
  • normal adult mean blood pressure is around 100mmHg
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2
Q

What causes tissue blood flow

A

-tissue blood flow is caused by the driving pressure (generated from the pumping action of the heart)
across variable resistance

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3
Q

pressure transducer

A

changes pressure into an electrical signal used to measure blood pressure

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4
Q

why is the variable resistance different between organs

A
  • different organs have different blood flow rates but same driving pressure
  • organs regulates its own pressure
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5
Q

Darcy’s Law

A

Change in pressure = flow x resistance

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6
Q

Poiseuille’s Law

A

resistance = (8 x viscosity x length)/(pi x radius^4)

*radius of blood vessels changes to regulate flow but not length

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7
Q

pressure within the systemic & pulmonary blood vessels

A
  • losing pressure over time

- organs receive blood at low pressure contract and than send the blood out at a higher pressure

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8
Q

how is blood pressure described

A

-statolic over diastolic

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9
Q

driving pressure

A

pressure between two spots in the circulatory system (one is higher and one is lower)

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10
Q

transmural pressure

A

inside - outside
(outside is usually 0 but in the heart sometimes external pressure is greater than internal resulting in no flow)
-ex: across a wall of the heart

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11
Q

hydrostatic pressure

A
  • the pressure exerted by a fluid due to the force of gravity
  • gravity causes a hydrostatic pressure when there is a difference in height
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12
Q

giraffe neck vs human neck driving pressure

A

higher in giraffe because it has a longer neck and therefore a bigger heart compared to a human

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13
Q

hydrostatic pressure reference point

A

the heart is at zero height

-varies with bodies position

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14
Q

hydrostatic pressure when recumbent/horizontal

A
  • no need to add or substract hydrostatic pressure to overall intravascular pressure
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15
Q

hydrostatic pressure when upright

A
  • need to add (if below reference point) or substract (if above reference point) hydrostatic pressure to overall intravascular pressure
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16
Q

excitable heart cells

A

the cell of the heart, like neurons, are excitable and generate action potentials

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17
Q

what excites the heart

A

the heart initiates its own continuous succession of contractions

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18
Q

types of heart muscle cells

A

-myocardial contractile cells (99%)
-myocardial excitatory & conductive cells (1%)
>no myofibrils cannot contract

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19
Q

where are electrical stimulus generated in the heart

A

SA node

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20
Q

rate at which SA node depolarizes

A

60-100 times a minute

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21
Q

how is the heart electrical system modulated?

A

ANS modulates heart rate and contraction strength

but heart can function without it

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22
Q

Automaticity

A

the ability to generate its own heart beat

23
Q

rhythmicity

A

the regularity of peacemaking activity

24
Q

Electrical system of the heart

A

-hierarchy from SA node to AV node to AV bundle to right/left bundle branches and purkinje fibers (lose pressure as you go down?)

25
Q

Excitation - contraction coupling

A

because excitation of myocytes triggers contraction, propagation of action potentials must be timed to synchronize atrial and ventricular contraction in order to move blood
***SA node has slow conduction velocity to give atrial time to contract

26
Q

what is cardiac action potential based on the _ of the _

A

the speed of the upstroke therefore action potentials can be slow or fast

27
Q

slow response action potential

A 
-pacemaker
• Sinoatrial (SA) Node
• Atrioventricular (AV) Node
• Lacks early repolarization phase 1
• Lacks stable phase 4
28
Q

fast response action potential

A 
-non-pacemaker
• Atrial & ventricular myocytes
• Common bundle & bundle branches*
• Purkinje fibers of the heart*
• Divided into 5 phases
*can exhibit spontaneous depolarization under special conditions
29
Q

Cardiac Myocyte & Nerve Cell

Action Potentials

A
  • very different

- cardiac myocytes last 250-300ms vs nerve cells have around 5ms

30
Q

fast action potential order of phases

A

depolarizing phase -> initial repolarizing phase -> plateau phase -> final repolarizing phase

31
Q

channels responsible for fast action potential

>depolarizing phase

A

-depolarizing phase: fast voltage-gated Na+ channels open (-90 to +20mV)

32
Q

channels responsible for fast action potential

>initial repolarizing phase

A

-initial repolarizing phase: fast voltage-gated Na+ channels close and fast voltage-gated K+ channels open (20-15mV)

33
Q

channels responsible for fast action potential

>plateau phase

A

-plateau phase: L-type voltage-gated Ca 2+ channels open, fast voltage-gated K+ channels close and slow voltage-gated K+ channels partially open (15mV)

34
Q

channels responsible for fast action potential

>final repolarizing phase

A

final repolarizing phase: L-type voltage-gated Ca2+ channels close and slow voltage-gated K+ channels fully open (+15mV–90mV)

35
Q

phases responsible for slow action potential order

A

pacemaker potential -> depolarizing phase -> repolarizing phase

36
Q

channels responsible for slow action potential

>pacemaker potential

A

-pacemaker potential: voltage-gated K+ channels close and F-type Na+ channels open (-60 to -40mV)

37
Q

channels responsible for slow action potential

>depolarizing phase

A

-depolarizing phase: L-type voltage-gated Ca2+ channels open (-40mV to +20mV)

38
Q

channels responsible for slow action potential

>repolarizing phase

A

-repolarizing phase: L-type voltage-gated Ca2+ channels close and voltage-gated k+ channels open (20mV to -60mV)

39
Q

Modulation of the Heart Electrical System

A

Conducted by the ANS

-heart rate and contraction strenght

40
Q

AUTOMATICITY

A

the ability to

generate its own heartbeat

41
Q

RHYTHMICITY

A

the regularity of pace-making activity

42
Q

muscarinic receptors slow action potential & ANS

A 
increase K+ permeability,
which hyperpolarizes the
cell, decreases slope of
phase 4 depolarization,
and slows HR
43
Q

β1-adrenergic receptors slow action potential & ANS

A 
increase Na+
permeability, increases
slope of phase 4
depolarization and
increases HR
44
Q

Relationship among action potential,
refractory period and tension developed in
Skeletal and Cardiac Muscle

A

Cardiac muscle needs a longer refractory period therefore plateau stage. Need to allow the muscles to relax to fill up the heart?

45
Q

Natural exication of the heart

A

-ordered fashion because of excitation system, which is slowed at particular parts to allow ventriculus to fill before they contract and atria to fill before they contract

46
Q

Atrial & Ventricular muscle act as____

A

act as functional syncytia

47
Q

functional syncytium definiton

A

electrical impulses propagate freely
between cells in every direction, so that the myocardium
functions as a single contractile unit.

48
Q

functional syncytium allows _____ of the myocardium

A

This property allows rapid,

synchronous depolarization of the myocardium

49
Q 
Requirements effective pumping of blood
>depolarization must be propagates \_\_
>action potentials must be \_\_
>absence of \_\_
> substantial delay between _
>coordinated _ of _
>_ contraction beging at _ and _
A

-Depolarization propagates through cardiac
muscle very rapidly
-The action potentials of cardiac muscle are
unusually sustained
-Absence of tetany
-Substantial atrial to ventricular delay
-Coordinated contraction of ventricular cells
-Ventricular contraction begins at the apex of the heart,
progressing upwards to eject blood into the great arteries

50
Q

Reason why The action potentials of cardiac muscle are unusually sustained

A

This prevents premature relaxation, maintaining initial
contraction until the entire myocardium has had time
to depolarize and contract.

51
Q

Reason why there is an absence of tetany in the heart

A

After contracting, the heart must relax to fill up again.
Sustained contraction of the heart without relaxation
would be fatal, and this is prevented by a temporary
inactivation of certain ion channels.

52
Q

Why does is there as substantial atrial to ventricular delay

A

This allows the atria to completely empty their contents into the
ventricles; simultaneous contraction would cause inefficient filling and
backflow. The atria are electrically isolated from the ventricles,
connected only via the AV node which briefly delays the signal.

53
Q

Why is there a coordinated contraction of ventricular cells?

A

The ventricles must maximize systolic pressure to force blood through
the circulation, so all the ventricular cells must work together.

54
Q

Why does the Ventricular contraction begins at the apex of the heart,
progressing upwards to eject blood into the great arteries?

A

Contraction that squeezes blood towards the exit is more efficient than a
simple squeeze from all directions. Although the ventricular stimulus
originates from the AV node in the wall separating the atria and
ventricles, the Bundle of His & Bundle Branches conduct the signal to
the apex.

Cardiovascular Physiology (14 decks)

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