Physiology Revision - Cardiovascular system

Question 1

How are the pulmonary and systemic circulations connected to the heart?

Answer 1

Pulmonary - connected to the heart in series

Systemic - connected to the heart in parallel

Question 2

What is Darcey’s Law?

Answer 2

Darcey’s law states that:

Flow = Pressure difference / Resistance

Question 3

How is resistance related to flow?

Answer 3

They are inversely proportional i.e flow increases, resistance decreases

Question 4

How does AP signal propagation work in cardiac muscle? Where does the AP originate from?

Answer 4

Gap junctions allow electrical signals to propagate from fiber to fiber in an organized manner

The AP originates from the Sinoatrial (SA) Node and is autorhythmic with an intrinsic rate of about 100bpm. These pacemaker conducting cells initiate cardiac contraction alone.

Question 5

Describe how sympathetic and parasympathetic activity affects the SA node.

Answer 5

Parasympathetic activity (valgus nerves secrete Ach) causes the membrane potential to become hyperpolarized and the drifting potential to have a decrease in slope. This serves to slow the heart rate

Sympathetic activity (thoracic nerves releasing epinephrine and channels become more permeable to Na+) causes the membrane potential to become depolarized quicker as the slope of the membrane potential increases. This serves to increase the heart rate.

Sympathetic stimulation also:

• Shortens the AV node delay
• Shortens myocyte action potential
• Increases the speed of relaxation

Question 6

What causes the drifting membrane potential in pacemaker cells (SA node)?

Answer 6

The constant influx of Na+ causes the drifting membrane potential and it is responsible for the rhythmic activation of pacemaker cells

Question 7

What is the pericardium ?

Answer 7

It is a layer of fibrous tissue that protects the heart by providing lubrication during movement and anchors the heart against the diaphragm and the spine

Question 8

What side of the heart takes in deoxygenated blood? Which vein?

Answer 8

The right side of the heart i.e the superior and inferior vena cava. Then through to the tricuspid valve to the pulmonary arteries

Question 9

Which side of the heart sends oxygenated blood away from the heart? Which artery?

Answer 9

The left side of the heart. The aorta and other arteries

Question 10

What are the 4 valves of the heart and what do they separate? What is the main function of a valve? How does pressure affect valves?

Answer 10

Tricuspid valve (separates R atrium and R ventricle), pulmonary valve (separates R ventricle and pulmonary artery), Mitral valve (separates the L atrium and R ventricle), aortic valve (separates R ventricle and aorta)

Valves main function is to open and close to ensure that blood doesn’t move backwards in the vessels. Increased pressure opens a valve, decreased pressure closes it.

Question 11

What are the electrical transmission event in the heart? What waves would appear on the ECG?

Answer 11

1. SA node initiates AP
2. AP propagates across atria (P wave)
3. Electrical activity is delayed at the atrioventricular (AV) node in order for the atria to fully empty.
4. Signal then travels through the Bundle of His and into the ventricles down the interventricular septum via the two bundle branches (this process of ventricular excitation is the QRS wave)
5. Once the stimulus has depolarized the entire muscle via the Purkinje fibers, ventricular relaxation occurs, producing the T wave

Question 12

Describe the events of systole and diastole of the heart.

Answer 12

Systole; consists of isometric ventricular contraction - when the ventricles contract but valves are closed so no blood is ejected yet, and ventricular ejection - when the pressure in the ventricle exceeds the pressure in the pulmonary trunk and aorta, valves open

Diastole; consists of isometric ventricular relaxation - ventricles relax and the pulmonary/aortic valves close, and ventricular filling - AV valves open and blood flows in from the atria (80% of ventricular filling occurs through gravity)

Question 13

What is stoke volume?

Answer 13

The volume of blood ejected from each ventricle

Question 14

What 2 factors is stoke volume regulated by?

Answer 14

1. The force by which the muscle contracts
2. The arterial pressure against which muscle cells have to eject the blood

Question 15

What two factors is the force of contraction regulated by?

Answer 15

1. Length-tension relationship of myocyte cells i.e “Starling’s Law of the Heart” or the “Frank Starling mechanism”
2. Effects of hormones on myocyte cells i.e sympathetic stimulation of circulating epinephrine increases the force of contraction

Question 16

What do arteries do to counteract the pressure oscillations produced through systole and diastole?

Answer 16

Arteries and veins are pulsatile, meaning they stretch and compress depending on blood volume to maintain a constant, steady blood flow.

Question 17

What is systolic and diastolic pressure?

Answer 17

Systolic pressure - the maximum arterial pressure during peak ventricular contraction

Diastolic pressure - the minimum arterial pressure just before ventricular ejection begins

Question 18

What is MAP and what is the formula?

Answer 18

MAP is the average pressure during the cardiac cycle.

Diastole lasts twice as long as systole so MAP is closer to the diastolic value. Thus:

MAP = Diastole + ( (Systole - Diastole) / 3)

or

MAP = (Heart rate x SV) x TPR