Lecture 9 -Cardiac Physiology I: Structure, function, electrical conductance

Question 1

How can the cardiovascular system be anatomically split up?

Answer 1

The cardiovascular system can be
anatomically subdivided into the heart
and the blood vessels

Question 2

What is the main function of the heart?

Answer 2

The heart’s main function is to pump
oxygenated blood into systemic
circulation (to all body organs) and
deoxygenated blood into pulmonary
circulation (to the lungs)

Question 3

What are blood vessels and how are they split up?

Answer 3

Blood vessels are the distribution
system and are divided into:
Arterial system (oxygenated blood)
Venous system (deoxygenated blood)

Question 4

Design a diagram that splits the circulatory system up between the venae cavae and the pulmonary artery

Question 5

What are systemic and pulmonary circulation?

Answer 5

Systemic circulation: (Both arterial and
venous system)
Blood is pumped from the left site of the
heart (left ventricle) and circulate around
body then returns to the heart through the
right ventricle
(Circuit of vessels carrying blood between
heart and other body systems)

Pulmonary circulation: Where
the blood pumped from the right
ventricle into the pulmonary
artery to the lungs and gets
oxygenated
(Closed loop of vessels carrying
blood between heart and lungs)

Question 6

How is blood divided between the 2 systems?

Answer 6

Systemic circulation:

Pulmonary circulation:

Question 7

How big is the heart and how much does it weigh?

Answer 7

Approximately the size of your fist

Question 8

Where is the heart located?

Answer 8

centre left of chest

– Superior surface of diaphragm
– Left of the midline
– Anterior to the vertebral column, posterior to the sternum

Question 9

What is the myocardium? What is it composed of? What is the thicker side and why?

Answer 9

The heart normally weighs about 300 g in an adult

 The heart (myocardium) is composed of 4 chambers:
2 atria: left (LA) and right (RA) 2 ventricles: left (LV) and right (RV)

The left ventricular
wall is thicker than
that of the right
ventricle because it pumps blood around the body

Question 10

What are the heart valves needed for?

Answer 10

The heart valves are present to aid the unidirectional flow of
blood

Question 11

What are the atria needed for? How does blood enter the atria?

Answer 11

Atria are the receiving chambers of the heart
Blood enters right atria from superior and inferior venae cavae
Blood enters left atria from pulmonary veins

Question 12

What are the ventricles and how does it enter the heart?

Answer 12

Ventricles are the discharging chambers of the heart
Right ventricle pumps blood into the pulmonary artery
Left ventricle pumps blood into the aorta

Question 13

On the right side of the heart what is blood pumped through and why? What happens when the ventricle contracts?

Answer 13

Right side
From the great
veins and right
atrium blood
flows through
the tricuspid
valve (atrioventricular
valve) to fill
the right
ventricle

When the right
ventricle
contracts
blood flows
through the
pulmonary
valve to the
lungs.

Question 14

Where does blood enter from to get into the left atria and what happens when the left atria contracts?

Answer 14

Left side
From the
pulmonary
vein and left
atrium blood
flows through the mitral
valve (atrioventricular
valve) to fill
the left
ventricle

When the left ventricle
contracts
blood flows
through the
aortic valve
to the aorta
and hence
the body.

Question 15

Name all the valves

Answer 15

(right side)
Pulmonary
valve
Tricuspid
valve

(left side)
Aortic
valve
Mitral
valve

Question 16

What is the pericardium? Where is it located and What is it needed for?

Answer 16

Pericardium – a double-walled sac around the heart composed of:
1. A superficial fibrous pericardium
2. A deep two-layer serous pericardium
a. The parietal layer lines the internal surface of the fibrous
pericardium

Question 17

What is the heart wall made up of? What are the 3 layers for?

Answer 17

Epicardium – visceral layer of the serous pericardium

Myocardium – cardiac muscle layer forming the bulk of the heart

Endocardium – endothelial layer of the inner myocardial surface

Question 18

What are the major vessels that return blood to the heart from external anterior view?

Answer 18

Arteries – right and left coronary (in atrioventricular groove),
marginal, circumflex, and anterior interventricular arteries

Veins – small cardiac, anterior cardiac, and great cardiac veins

Question 19

From the anterior view, What are the major vessels that convey blood away from the heart and name the branches of the aorta?

Answer 19

Vessels returning blood to the
heart include:
1. Superior and inferior venae
cavae
2. Right and left pulmonary
veins

Vessels conveying blood away
from the heart include:
3. Pulmonary trunk, which
splits into right and left
pulmonary arteries

4. Ascending aorta (three
   branches) –
   a. Brachiocephalic
   b. Left common carotid
   c. Subclavian arteries

Question 20

Front the posterior view what are the major blood vessels that take blood too and from the heart?

Answer 20

Vessels returning blood to
the heart include:
1. Right and left
pulmonary veins
2. Superior and inferior
venae cavae

Vessels conveying blood
away from the heart
include:
3. Aorta
4. Right and left
pulmonary arteries

Question 21

When does most blood flow happen and why? Where does most blood flow take place?

Answer 21

Most of the blood flow through the coronary
arteries occurs when the heart is relaxed.
The contraction of the heart is so powerful it closes
the
arteries during this time.

Question 22

How is the heart affected by ischaemia?

Answer 22

when blood flow to the heart muscle is constricted because of an artery spasm

Atherosclerosis is one of the main
causes of myocardial ischemia

Question 23

What muscles make up the heart muscle and how is the heart contracted?

Answer 23

Heart muscle (cardiac myocytes) :
– Is stimulated by nerves and is self-excitable (automaticity)
– Contracts as a unit
– Has a long (250 ms) absolute refractory period

the heart is conducted by:
autorythmic fibres in the SA node, located in the right atrial wall act as the hearts pacemaker.
-The hearts pacemaker initiates cardiac action potentials that cause contractions of the hearts chanbers

Question 24

What are pacemaker cells?

Answer 24

Pacemaker cells differentiate
from other cardiomyocytes to
have this specialist function

Question 25

What are the 3 steps in the cardiac action potential?

Answer 25

1. rapid depolarization due to Na+ inflow when voltage-gated fast Na+ channels open 2. plateau of membrane potential (a maintained depolarization) due to Ca2+ ions flowing in when voltage-gated slow Ca2+ channels open and K+ outflow when some K+ channels open 3. repolarization due to the closure of Ca2+ channels and K+ outflow when additional-gated K+ channels open

Question 26

Why is the SA important?

Answer 26

The cardiac conduction system regulates the heart rate and rhythm

Question 27

How does the action potential spread through the heart?

Answer 27

1 The heart has a natural pacemaker from where APs originate - the sinoatrial (SA) node, also known as the natural pacemaker 2. AP propagates across the atria and depolarises and excites the atrial myocardium (muscle) 3. 2 The AP reaches the atrioventricular (AV) node - the only electrical connection between atria and ventricles *The AP is delayed at the AV node. This allows the atria to be excited (and contract) before the ventricles 4. 3 The AP then propagates rapidly down the bundle of His 5. The AP next propagates rapidly down to the left and right branches of His 6. The AP next propagates rapidly down to the left and right branches of His 7. then down Purkinje fibre bundles 8. Impulse rapidly disperses throughout the myocardium via Purkinje fibres 9. Thus, the ventricular myocardium is depolarised at nearly the same time due to rapid cell-to-cell spread of impulse through gap junctions

Question 28

How are action potentials regulated? How many times do they occur per minute?

Answer 28

Usually there are ~75-80 AP generated per min This can be regulated externally: * Heart is stimulated by the sympathetic cardioacceleratory centre * Heart is inhibited by the parasympathetic cardioinhibitory centre

Question 29

Can the nervous system elicit cardiac action potentials?

Answer 29

BUT – the nervous system cannot elicit cardiac action potentials: this can only happen via the SA node

Question 30

What does the ECG teach you?

Answer 30

*The electrocardiogram (ECG) is a body surface recording of the overall cardiac electrical activity with time. * It is not a direct recording of actual electrical activity of heart

Question 31

What are the standard limb leads for the heart?

Answer 31

1, 2, 3

Question 32

How is the p wave developed by a cardiac impulse?

Answer 32

Atrial depolarisation generates a ‘P wave’ on the ECG

Question 33

How are QRS impulses developed?

Answer 33

Ventricles invaded by impulse and depolarised generating a QRS complex

Question 34

What can you learn about a rhythm from an ECG?

Answer 34

the rhythm of the heart is usually determined by the difference between the R peaks (the regular RR interval) Each QRS complex is preceded by a P wave

Question 35

What are the normal ecg values?

Answer 35

P-R interval= 0.12-0.20 sec QRS width= 0.08-0.12 sec Q-T interval= 0.35-0.43 sec

Question 36

How can ECGs be used to measure heart rate?

Answer 36

R-R interval can be used to measure the heart rate (HR). *Measure the distance between the peaks of 2 consecutive QRS complexes at a known recording speed. *Heart rate = 1/R-R interval; Normal range 55-75 beats/minute.

Question 37

How can you use ECGs to learn about sinus arrhythmias?

Answer 37

Sinus Rhythm- normal spacing Sinus Bradycardia- very large gaps in the RR peaks Sinus Tachycardia- very small gaps in the RR peaks- more AP being fired

Question 38

How can you spot a myocardial infarction using an ECG?

Answer 38

ST depression of elevation

Question 39

from the posterior view what vessels supply and drain the heart?

Answer 39

Arteries – right coronary artery (in atrioventricular groove) and the posterior interventricular artery (in interventricular groove) Veins – great cardiac vein, posterior vein to left ventricle, coronary sinus, and middle cardiac vein