Heart Anatomy, Blood Pressure, Cardiac Action Potential and Conduction System

Question 1

When you measure someone’s blood pressure, which arm (light vs left) do you use to measure pressure, and why?

Answer 1

the left arm since that is where the artery is. The artery exists from the left-hand side of the heart.

Question 2

What are the two veins dumbing blood into the right atria?

Answer 2

The superior and inferior vena cava

Question 3

Path of blood flow

Answer 3

low oxygen blood entering the right atria from the superior and inferior vena cava. Atrial pressure starts to slowly build up, passes the tricuspid valve into the right ventricle. Ventricle pressure slowly builds up. Once the pressure in the ventricle is higher than the pressure outside the pulmonary valve, low oxygen blood will now be pushed into the lung through the pulmonary artery.

A parallel pathway:
High oxygenated blood coming from the lung enter the left atria through the pulmonary vein, the bicuspid valves, the left ventricle, the aortic valve into the artery.

Question 4

Heart sound – Lub Dub

Answer 4

Lub - the closing of the tri and bi cusbid valves - starting of systole since that is when ventricle pressure is starting to build up.

Dub - the closing of the pulmonary and aortic valves – starting of diastole since that is when the ventricle starts to relax.

Question 5

What is the name of the condition in which the atria contraction is random and not sufficient? does the heart still work?

Answer 5

Atrial fibrillation

Question 6

what do systole and diastole denote?

Answer 6

• pressure of the ventricle at contraction and relaxation.

Question 7

what is another name for the aortic valve?

Answer 7

mitral valve

Question 8

Blood pressure calculations
- Recall the anatomy and the pathway of blood flow in the heart, what are two types of pressure involved? How do they relate to the blood pressure value that often used in doctor office?

Answer 8

• The systolic pressure – Pressure when the ventricle contracts.
• The diastolic pressure - -Pressure during relaxation.
• Blood pressure is a ratio of systolic pressure and diastolic pressure. The normal range for blood pressure is 90/60 - 120/80

Question 9

Factors that change blood pressure

- What is the mathematical formula that relates blood pressure, systemic resistance and cardiac output?

Answer 9

Cardiac output & peripheral pressure.

BP = CO * VSR

Question 10

The formula for Cardiac Output. Take note of units.

What is cardiac output?

Answer 10

Cardiac output describes the volume of blood that gets pumped out per minute.

CO depends on stroke volume and heart rate.

Stroke volume is the volume of blood pumped at every contraction/ beat. Heart rate is the rate of contraction.

Question 11

Factors that change heart rate

Answer 11

Heart rate is controlled by the autonomous nervous system.

• HR goes up when you’re nervous or when you’re exercising.
• HR goes down when you’re relaxing or sleeping.

Question 12

Factors that change the stroke volume.

• What is stroke volume?
• How is it calculated?

Answer 12

Stroke volume is the amount of blood pushed out of the heart at every contraction.

SV= Volume at relaxation - Volume at contraction
In other words,
SV = end of diastolic volume - End of systolic volume = EDV - ESV

• Stroke volume depends on three factors: preload, heart contractibility, and afterload.
• Preload depends on venous return. You get greater blood return during movement due to leg muscle contraction.
• Stroke volume is also greater with greater heart contractability. This is controlled by the autonomous nervous system.
• the afterload is not a volume value. It’s actually the pressure to which the heart must work against to eject blood into the aorta. Remember that for blood to eject into the aorta, the ventricular pressure must be greater than the aortic pressure? What this means is that high afterload decreases stroke volume. What affects the aortic pressure? How does vasodilation and vasoconstriction affect the aortic pressure?
• simple. In the case of vasodilation, more room for the same blood volume, the pressure is lower or afterload is lower … thus more blood will be ejected into the aorta.
• Stroke volume also depends on the overal blood volume. If there isn’t much blood in the system, the stroke volume would simply be low.

Question 13

Factors that change blood volume

Answer 13

• water, osmosis
• Activity level
• Posture

Question 14

You can experience head lightness if you stand up too abruptly from your bed. You can actually pass out as well, why is that the case?

Answer 14

When at a standing position, more pressure is required to pump blood to your brain. Abruptedly standing up when your blood volume is low … If your body won’t adapt fast enough … you will pass out.

Question 15

What happens to peripheral resistance and blood pressure when blood vessels restrict or dilate?

Answer 15

• Resistance goes up, blood pressure goes up with restriction of blood vessels.

Question 16

what does the renal vs the cardiovascular system control?

Answer 16

The renal system controls the blood volume whereas the cardiovascular system controls blood pressure.

Question 17

You can pass out if running outside under the heat without sufficient hydration, why?

Answer 17

• low blood volume due to dehydration and sweating. –> low SV, low CO.
• Vasodilation due to the heat. –> low systemic vascular resistance

BP = SVR * CO

Question 18

how do Oxygen and CO2 transport through blood? What is the composition of blood and what does that have anything to do with gas transportation?

Answer 18

The reason we think of blood as only made up of red blood cell is because the red color.

However, red blood cells (hematocrit) only make up 40% of our blood. 5% white blood cells and 45% plasma.

• Plasma is the liquid component of the blood. Anything that is hydrophilic is going to be dissolved here. Water, electrolytes, glucose, hormones, plasma proteins, etc.

Question 19

Are Oxygen and CO2 hydrophobic or hydrophilic? how can they dissolve in blood given their properties?

Answer 19

• They are both very hydrophobic.
• Oxygen binds to hemoglobin which is a protein in the plasma.
• CO2 will be converted into HCO3- which is an ion that can also dissolve into the plasma.

Question 20

what does CO2 have anything to do with pH level?

Answer 20

CO2 + H2) –> H2CO3 (strong acid) –> H+ + HCO3-

High CO2 shifts the equilibrium to the left causing a rise in the concentration of H+, higher acidity.

Question 21

what is the biggest difference between cardiac muscle cell and skeletal muscle cells? why is this such an important difference? *duration and absolute refractory period.

Answer 21

• Frequency of contraction, tetanic contraction

- Contract and relax. Can’t sum because of long refractory period.

Question 22

what are cells that are responsible for triggering the action potential in cardiac mussel cells?

Where can you find them?

How are they different from the cardiac muscle cells? what characteristic allows them to be “autorhythmic”?

Answer 22

• They are the cardiac autorhythmic cells. They are the cells that SA and AV nodes of the heart.
• They rest at higher resting potential. (-50) and they have sodium leak channels, which cause a gradual increase in the membrane potential over time making it easier to reach the threshold potential.
• Recall that: for a neuron to fire an action potential, it must be depolarized to reach the threshold to open the Sodium channels for further depolarization. The Sodium leak channels result in a constant upward drift of membrane potential that triggers the firing.

Question 23

In neuron, after the membrane potential reaches the threshold, Sodium channels open, is this the same for the Cardiac autorhythmic cells?

Answer 23

• no. For the cardiac autorhythmic cell, slow voltage gated Ca2+ channel opens.

Question 24

So we know that the heart has a conduction system, why do we even need this?
- I mean we know cardiac muscle cells are connected via gap junctions. Once the autorhythmic cells fire, the action potential can propagate across the heart cell cause the whole heart to contract. Why need a conduction system?

Answer 24

• The mitral and tricuspid valves are large valves that separate the atria from the ventricles. These valves cannot conduct the action potential.
• Plus, the contraction of the ventricles plays a vital role in pumping blood. The aortic and pulmonary valves are located upward. It won’t get a sufficient pump of blood if you’re squeezing top to bottom. This is why the conduction system is so vital because it allows for the contraction of ventricles bottom-up forcing all the blood out!

Question 25

What are the nodes in the heart? What is the name of the thing that conducts action potential to the bottom of the ventricle?

Answer 25

The SA (sinoatrial) node. 
The AV (Atrial ventricular) Node 

• AV nodes. Bundle branches. The Purkinje fibers.