Fewell - Electrical properties of the heart

Question 1

How do physiologist gauge blood pressure

Answer 1

by the height it can drive a column of liquid

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

Question 2

What causes tissue blood flow

Answer 2

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

Question 3

pressure transducer

Answer 3

changes pressure into an electrical signal used to measure blood pressure

Question 4

why is the variable resistance different between organs

Answer 4

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

Question 5

Darcy’s Law

Answer 5

Change in pressure = flow x resistance

Question 6

Poiseuille’s Law

Answer 6

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

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

Question 7

pressure within the systemic & pulmonary blood vessels

Answer 7

• losing pressure over time

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

Question 8

how is blood pressure described

Answer 8

-statolic over diastolic

Question 9

driving pressure

Answer 9

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

Question 10

transmural pressure

Answer 10

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

Question 11

hydrostatic pressure

Answer 11

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

Question 12

giraffe neck vs human neck driving pressure

Answer 12

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

Question 13

hydrostatic pressure reference point

Answer 13

the heart is at zero height

-varies with bodies position

Question 14

hydrostatic pressure when recumbent/horizontal

Answer 14

• no need to add or substract hydrostatic pressure to overall intravascular pressure

Question 15

hydrostatic pressure when upright

Answer 15

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

Question 16

excitable heart cells

Answer 16

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

Question 17

what excites the heart

Answer 17

the heart initiates its own continuous succession of contractions

Question 18

types of heart muscle cells

Answer 18

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

Question 19

where are electrical stimulus generated in the heart

Answer 19

SA node

Question 20

rate at which SA node depolarizes

Answer 20

60-100 times a minute

Question 21

how is the heart electrical system modulated?

Answer 21

ANS modulates heart rate and contraction strength

but heart can function without it

Question 22

Automaticity

Answer 22

the ability to generate its own heart beat

Question 23

rhythmicity

Answer 23

the regularity of peacemaking activity

Question 24

Electrical system of the heart

Answer 24

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

Question 25

Excitation - contraction coupling

Answer 25

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

Question 26

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

Answer 26

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

Question 27

slow response action potential

Answer 27

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

Question 28

fast response action potential

Answer 28

``` -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 ```

Question 29

Cardiac Myocyte & Nerve Cell | Action Potentials

Answer 29

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

Question 30

fast action potential order of phases

Answer 30

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

Question 31

channels responsible for fast action potential | >depolarizing phase

Answer 31

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

Question 32

channels responsible for fast action potential | >initial repolarizing phase

Answer 32

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

Question 33

channels responsible for fast action potential | >plateau phase

Answer 33

-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)

Question 34

channels responsible for fast action potential | >final repolarizing phase

Answer 34

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

Question 35

phases responsible for slow action potential order

Answer 35

pacemaker potential -> depolarizing phase -> repolarizing phase

Question 36

channels responsible for slow action potential | >pacemaker potential

Answer 36

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

Question 37

channels responsible for slow action potential | >depolarizing phase

Answer 37

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

Question 38

channels responsible for slow action potential | >repolarizing phase

Answer 38

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

Question 39

Modulation of the Heart Electrical System

Answer 39

Conducted by the ANS | -heart rate and contraction strenght

Question 40

AUTOMATICITY

Answer 40

the ability to | generate its own heartbeat

Question 41

RHYTHMICITY

Answer 41

the regularity of pace-making activity

Question 42

muscarinic receptors slow action potential & ANS

Answer 42

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

Question 43

β1-adrenergic receptors slow action potential & ANS

Answer 43

``` increase Na+ permeability, increases slope of phase 4 depolarization and increases HR ```

Question 44

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

Answer 44

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

Question 45

Natural exication of the heart

Answer 45

-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

Question 46

Atrial & Ventricular muscle act as____

Answer 46

act as functional syncytia

Question 47

functional syncytium definiton

Answer 47

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

Question 48

functional syncytium allows _____ of the myocardium

Answer 48

This property allows rapid, | synchronous depolarization of the myocardium

Question 49

``` Requirements effective pumping of blood >depolarization must be propagates __ >action potentials must be __ >absence of __ > substantial delay between _ >coordinated _ of _ >_ contraction beging at _ and _ ```

Answer 49

-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

Question 50

Reason why The action potentials of cardiac muscle are unusually sustained

Answer 50

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

Question 51

Reason why there is an absence of tetany in the heart

Answer 51

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.

Question 52

Why does is there as substantial atrial to ventricular delay

Answer 52

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.

Question 53

Why is there a coordinated contraction of ventricular cells?

Answer 53

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

Question 54

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

Answer 54

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.