Cardiology Unit

How does the blood move through the heart?

superior vena cava —> right atrium —> tricuspid valve —> right ventricle —> pulmonary valve (semilunar valve) —> pulmonary artery —> lungs —> pulmonary veins —> left atrium —> mitral/bicuspid valve —> left ventricle —> aortic valve (SL valve) —> aorta —> the body.

arteries

away from the heart = does not mean only oxygenated blood

vein

toward the heart = does not mean only deoxygenated blood

how does blood oxygen occur/the pathway?

oxygenated blood through the aorta/artery —> arteriole —> capillaries (where O2 exchange happens) —> venule (deoxygenated) —> vein cava vein

how does blood flow through the body?

gradients

what types of gradients are in neurophysiology?

electrochemical gradients

what types of gradients are in cardiovascular?

pressure gradients

what types of pressure are in the aorta and vena cava?

aorta = highest pressure

vena cava = lowest pressure

it’s how/why blood flows from aorta (oxygenated) to vena cava (deoxygenated)

what part has the largest pressure drop?

arterioles have the highest pressure drop b/c they have the highest resistance to blood flow due to their small diameter (decreased SA = increased flow)

what is the equation for flow (Q)

Q = change in pressure / resistance (R)

how is the magnitude of Q determined?

Determined by the size of the pressure difference (change in pressure)

how is the direction of Q determined?

determined by the pressure gradient (high to low)

what is poiseuille’s law?

Resistance = (8nl)/(pir⁴)

what do each of the variables in poiseuille’s law mean?

R = resistance

n = viscosity of blood (constant)

l = length of blood vessel (constant)

r⁴ = radius of blood vessel raised to the fourth power

what is the shortened version of poiseuille’s law/resistance?

R = 1/r⁴

when is viscosity relevant in determining resistance?

• change in volume (such as dehydration)

• change in # of cells (such as polycythemia)

how does dehydration (change in volume) effect viscosity and resistance?

decrease in water = decrease in plasma

decrease in plasma —> increase in blood viscosity —> thicker blood —> increased resistance —> decreased flow

how does polycythemia (change in # of cells) effect viscosity and resistance?

decrease in water = decrease in plasma

decrease in plasma —> increase in blood viscosity —> thicker blood —> increased resistance —> decreased flow

when is length relevant in determining resistance?

always constant

• unless there is an amputation of blood vessel

vessels in series

R_total = R_A+R_a+R_c+R_c+R_v+R_V

• have to go sequentially through each category

vessels in parallel

what is velocity (v)?

distance a given fluid moves within a unit of time (cm/sec)

• how fast per time

• rate of blood flow

what is flow (Q)?

quantity of a given fluid that passes by a certain point within a unit of time (mL/sec)

• how much per time

when is flow preserved?

when the arteries/veins are in series —> blood is preserved should not change

what is the equation for velocity?

v = Q/A

what do the variables for velocity stand for?

v = velocity of blood flow (cm/sec)

Q = flow (mL/sec)

A = cross-sectional area (cm²) = total cross sectional area

what is the vessel diameter range?

capillaries have the lowest, arteries and venae cavae are the highest

what is the total cross-sectional area of vessels range?

capillaries have the highest because it’s not individual, instead based on the cross-sectional area of all capillaries added together

what is the velocity of blood flows range?

the arteries have the highest velocity, the capillaries have the lowest velocity

• higher total SA = slower

ICLICKER: radius plays the greatest role in determining resistance because…

correct: radius can be regulated —> when your being chased the blood gets rerouted

correct: length and viscosity are constants —> equation

correct: radius factors in the equation to the 4th power —> equation

when is flow constant?

when resistance is in series

• pressure will still decrease between 1 and 5

what happens with parallel resistances?

they have the same pressure difference

what is true about pressure for in parallel?

Arteriole 1 P₃-P₄ = Arteriole 10 P₃-P₄

what is true about pressure for in series?

Change in P₃-P₄ is NOT EQUAL to P₂-P₃

ICLICKER: are left and right sides of heart in series or in parallel?

correct: series

incorrect: parallel

incorrect: impossible to tell

• everything needs to go into the right side of the heart to get into the lungs and so forth —> IN SERIES

as fluid moves through the branching system of pipes, what happens to the flow rate?

flow is constant because they are in parallel so the change in pressure is the same

as fluid moves through the branching system of pipes, what happens to the velocity of flow?

v=Q/A

• don’t know how A changes

ICLICKER: which are true of flow and velocity of flow in the cardiovascular system?

correct: flow remains constant from aorta to capillaries

• only the flow within the aorta is not constant = in parallel

• in series = constant

correct: velocity is inversely proportional to total cross-sectional area

• v=Q/A

correct: velocity of flow is lowest in the capillaries

• we want a lot of exchange for oxygen

ICLICKER: a large artery branches into two arterioles. arteriole A is 2x longer than arteriole B, but the radius of arteriole B is ½ that of arteriole A. which arteriole offers less resistance to flow? explain using poiseuille’s equation.

WORK IT OUT

which has less resistance: A

ICLICKER: Suppose one dilates and the other constricts. what happens to flow in each arteriole?

WORK IT OUT

increases in A, decreases in B

1. is it in parallel or in series?

   1. does all the blood need to go through A to go through B

   2. no b/c they’re not connected in that way —> they’re parallel

2. if in parallel —> their pressure drop is the same

ICLICKER: what is the pressure difference (P₁-P₂) of vessel A vs the pressure difference (P₁-P₂) vessel C?

• vessels are in parallel —> pressure drop is the same

• A=C

how does asthma affect your airways?

for an asthmatic airway: decrease radius —> increase resistance = decrease of flow

what consistent of muscle cells?

• contractile cells (99%)

• conducting (1%)

what do contractile cells do?

produce force and contraction

what does conducting cells consist of?

• autorhythmic cells

  • SA node

  • AV node

  • bundle of His

  • purkinje fibers

• conducting fibers

  • internodal fibers

  • R and L bundle branch

conduct action potentials and/or initiate action potentials

what location is followed by the rhythm of the fastest node?

the sinoatrial node (SA node)

location of the nodes

sinoatrial node (SA node) = 70-80 impulses/min

atrioventricular node (AV node) = 40-60 impulses/min

bundle of His = 40 impulses/min

purkinje fibers = 15-20 impulses/min

how do pacemaker and contractile cells compare?

pacemaker cells = conduct action potentials and/or initiate action potentials

contractile cells = produce force and contraction

ICLICKER: pacemaker cells are BLANK in origin

muscle cells

• muscles cells that have electrical properties

pacemaker cells

• does NOT have a true RMP

• have a calcium ion action potential

• I_f channels open at -60 mV

contractile cells

• have a RMP —> -90 mV

• spread signals via gap junctions

• have a plateau —> K+ leave is equal to Ca²⁺ coming in

what are funny channels?

1. non-specific, can let in Na⁺ and K⁺, but hey favor Na⁺

2. Can be activated when the cell’s hyperpolarize

• activated at -60 mV hyperpolarized-activated

• I_f can produde a signal w/o a stimulus for pacemaker cells

Important parts of the pacemaker cell figure:

• I_f channels are activated at -60mV - hyperpolarized-activated.

• when I_f channels open, increase permeability of BOTH Na⁺ and K⁺

• However, Na⁺ going in the cell is greater than K⁺ going out of the cell (Na⁺ into the cell > K⁺ out of the cell).

• At -50mV, T Type Ca²⁺ channels activated

• At -40mV, voltage gated Ca²⁺ channels activated called L Type Ca²⁺ channels.

T type Ca²⁺ channels

activated at -50 mV

• only activate during this time

• role = help the funny channel out in bringing the membrane potential more positive —> easier to achieve the threshold faster.

L type Ca²⁺ channels

• voltage-gated Ca²⁺ channels

• activated at -40 mV

all pacemakers have ______ properties

similar

pacemakers are origin of ______ heartbeat

myogenic

SA node sets the pace because

it is the node w/ the fastest rhythm

if a pacemaker other than the SA node is setting the pace, then…

• it is an ectopic pacemaker

• the SA node is likely damaged

• this is when you know something is wrong

contractile myocardium mV graph

• threshold for v-gated Na⁺ channels = -60 mV

• threshold for v-gated L type Ca²⁺ channel = -40 mV

• threshold for V-gated K⁺ channels = -20 mV

what is the RMP of contractile myocardium?

-90 mV

what is the reasoning behind the plateau of the contractile myocardium cell?

the amount of K⁺ going out of the cell is balanced by the amount of Ca²⁺ coming into the cell

which cell has an absolute and relative refractory period?

the contractile myocardium

what is the structure of the myocardial muscle cells? 

• branched

• have a single nucleus

• attached by specialized junctions (intercalated disks)

what do gap junctions do in contractile cells?

depolarizations of autorhythmic cells (pacemaker cells) rapidly spread to adjacent contractile cells through gap junctions.

what is a syncytium?

organ that is made up of different cells but because of gap junctions they act like one big cell

what does the membrane potential of pacemaker cells look like?

what is the membrane potential of contractile cells?

how do the pacemaker cells and contractile cells connect?

depolarizations of autorhythmic cells rapidly spread to adjacent contractile cells through gap junctions

which cell type controls force of contraction?

contractile cells

which controls rate of contraction?

pacemaker cells

stimulation by parasympathetic nerves ____ heart rate

decreases

stimulation by sympathetic nerves ______ heart rate

increases

parasympathetic neuron (ACh on Muscarinic receptor) steps

1. cardiovascular control center in medulla oblongata

2. parasympathetic neurons (ACh)

3. muscarinic receptors of autorhythmic cells

4. increase K⁺ efflux; decrease Ca²⁺ influx

5. hyperpolarizes cell and decreases rate of depolarization

6. decrease heart rate

why did the parasympathetic neurons (ACh) lead to a decreased heart rate?

led to a decrease in cAMP —> increase K⁺ permeability and decrease Ca²⁺ permeability

• this makes it harder to make threshold —> decrease HR

sympathetic neurons (NE)

1. cardiovascular control center in medulla oblongata

2. sympathetic neurons (NE)

3. B₁-receptors autorhythmic cells

4. increase Na⁺ and Ca²⁺ influx

5. increase rate of depolarization

6. increase heart rate

why did the sympathetic neurons (NE) lead to a increased heart rate?

The sympathetic neuron leads to an increased cAMP —> increase in Na and Ca into cell

• more positive —> easier to meet threshold

• dec polymerization rate

• increase HR

parasympathetic stimulation mV graph

sympathetic stimulation mV graph

what does a normal mV graph look like?

what does a sympathetic stimulation look like?

what does parasympathetic stimulation look like?

ICLICKER: the internodal pathways take the signal to the:

Atrial muscle (atrial contractile cells)

AV node

what is the typical signal pathway?

1. SA node

2. internodal pathways

3. AV node

4. AV bundle (bundle of His)

5. bundle branches

6. purkinje fibers

7. ventricular contractile cells (cells in the ventricle)

how did the small local current flow in ECF reflect the ICF?

• the ECF mirrors what is happening in the ICF of the cardiac contractile cells

what is the direction of the current flowing in the heart / electrical axis of the heart?

• from the Right Atrium to the Left Ventricle

• average value of 60 degrees from horizontal

electrocardiography

process of recording potential changes at skin surface

electrocardiogram (ECG or EKG)

record of potential changes

• SUM of electrical activity

Not an action potential

action potential

a single cell recording ICF reading

lead I

right arm —> left arm

lead II

right arm —> left leg

lead III

left arm —> left leg

what lead most represents the heart?

lead two —> it is parallel to the heart

depolarization wave towards POS

upward deflection

repolarization wave towards NEG

upward deflection

depolarization wave toward NEG

downward deflection

repolarization wave towards POS

downward deflection

depolarization wave = 90 degrees / parallel

no deflection

repolarization wave = 90 degrees / parallel

no deflection

ICLICKER: overall strongest upward deflections produced by:

lead II