CGIER 4 - The Heart, structure, physiology; Cardiac cycle; Arterial blood pressure

Question 1

Where is the heart located in the body?

Answer 1

The heart is located in its own cavity in the thorax called the pericardium.

Question 2

What is the pericardium lined with?

Answer 2

The pericardium is lined with mesothelium, which helps make up the pericardial membrane.

Question 3

What is the outer covering of the heart called?

Answer 3

The outer covering of the heart is called the epicardium and is also lined with mesothelium.

Question 4

Explain the direction of blood flow through the heart, including the names of veins, arteries, and valves the blood passes through.

Answer 4

Inferior & Superior Vena Cava –> Right Atrium –> Tricuspid Valve (right atrioventricular valve) –> Right Ventricle –> Pulmonary Valve –> Left & Right Pulmonary Arteries –> Lungs –> Left & Right Pulmonary Veins –> Left Atrium –> Bicuspid Valve (Left atrioventricular valve) –> Left Ventricle –> Aortic Semilunar Valve –> Aorta

Question 5

How is cardiac muscle arranged for proper heart function?

Answer 5

Cardiac muscle is striated but arranged into different cells separated by intercalated discs, with many gap junctions as well to allow the free diffusion of ions from cell to cell.

Question 6

Name three features of cardiac muscle that allow it time proper heart beats.

Answer 6

Cardiac muscle is:

1. myogenic - can contract rhythmically and continuously without nervous system stimulation
2. functions as a syncytium - with action potential moving from cell to cell
3. has a refractory period of 0.25 - 0.3sec

Question 7

Where is heart rate regulated in the brain?

Answer 7

Heart rate is regulated by the medulla oblongata which responds to pressure receptors in the walls of blood vessels.

Question 8

Which has a lower heart rate, larger or smaller mammals?

Answer 8

Larger.

Question 9

List heart stats for a healthy human.

Answer 9

• normal: 72 beats/min
• stress: 192 beats/min
• in life a heart beats: 2,600 million times

Question 10

What does the sino-atrial node (pacemaker) consist of?

Answer 10

The sino-atrial node consists of three things:

1. modified cardiac muscle
2. sympathetic nervous fibers (discharge at a slow rate can increase heart beat by up to 100%)
3. parasympathetic nervous fibers (can reduce heart beat by 30%)

Question 11

Explain the excitatory & conductive system of the heart.

Answer 11

1. The sino-atrial node spontaneously contracts to send a wave at 0.3m/s from the node to the entire atrial muscle mass, eventually causing the atria to contract like a single cell.
2. Since the atria are separated from the ventricles by a ring of connective tissue called the Annulus Fibrosus, the contraction wave stops and causes a 0.11 delay between the contraction of the atria and the contraction of the ventricles.
3. The impulse continues to the atrioventricular node (at the center of the heart) which transmits an impulse to the muscles of the ventricles via the Purkinje Fibers or Bundle of His at a rate of 4m/s, causing the ventricles contract immediately and simultaneously.

Question 12

Explain systole vs. diastole.

Answer 12

Systole is the contraction of the heart chambers.

Diastole is the relaxation of the heart chambers.

Question 13

Define cardiac cycle.

Answer 13

The cardiac cycle is the period from the end of one contraction to the end of the next.

Question 14

How do the atria act as a primer pump for the ventricles?

Answer 14

Since blood is continuously flowing into the atria, 70% of the blood just flows directly into the ventricles, while 30% is kept in the atria before atrial systole occurs.

Question 15

Explain ventricular diastole and ventricular systole.

Answer 15

During ventricular diastole the ventricles fill with a volume of 120ml of blood in each, then ventricular systole creates a pressure increase causing the quick closing of the atrioventricular valves and then 0.02 secs later the opening of the semilunar valves.

Question 16

What is stroke volume?

Answer 16

The amount of blood ejected out of the heart with each contraction. Typically, a person’s stroke volume is 80ml, leaving 40ml in the ventricles called the End-systolic volume.

Question 17

What is cardiac output?

Answer 17

Cardiac Output = stroke volume (ml/beat) x heart rate (beats/min) = 5L min

Question 18

What is an electrocardiogram?

Answer 18

An ECG describes the electrical activity of the heart:
P - depolarization of the atria, atrial contraction
QRS - depolarization of the AV node and conduction of the impulse through the purkinje fibres to the ventricle muscles.
R - ventricular systole
T - repolarization of ventricles
P to R - time required for impulse to travel from SA node to ventricles

Question 19

Explain heart sounds.

Answer 19

The ‘Lub’ sound is caused by the closing of the tricuspid and bicuspid valves, during ventricular systole.
The ‘Dub’ sound is caused by the closing of the semilunar valves, during ventricular diastole.
Damaged valves, such as heart murmurs, can be detected by listening to the sounds.

Question 20

What is Frank-Starling Law?

Answer 20

Frank-Starling Law is the heart’s intrinsic ability to adapt to changing loads of inflowing blood

Question 21

Explain blood pressure as it flows through the circulatory system.

Answer 21

Aorta (100 mmHg) –> arteries –> arterioles (85 mmHg) –> metarteriols (30 mm Hg) –> precapillary sphincters –> aterial capillaries (25 mmHg) –> venous capillaries (10 mmHg) –> venules –> veins –> vena cava (0 mmHg)

Question 22

What instrument is used to measure arterial blood pressure?

Answer 22

A sphygmomanometer.

Question 23

What is an incisura?

Answer 23

A sharp drop in systolic pressure after ventricular diastole.