Lecture 9 -Cardiac Physiology I: Structure, function, electrical conductance Flashcards
How can the cardiovascular system be anatomically split up?
The cardiovascular system can be
anatomically subdivided into the heart
and the blood vessels
What is the main function of the heart?
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)
What are blood vessels and how are they split up?
Blood vessels are the distribution
system and are divided into:
Arterial system (oxygenated blood)
Venous system (deoxygenated blood)
Design a diagram that splits the circulatory system up between the venae cavae and the pulmonary artery
What are systemic and pulmonary circulation?
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)
How is blood divided between the 2 systems?
Systemic circulation:
Pulmonary circulation:
How big is the heart and how much does it weigh?
Approximately the size of your fist
Where is the heart located?
centre left of chest
– Superior surface of diaphragm
– Left of the midline
– Anterior to the vertebral column, posterior to the sternum
What is the myocardium? What is it composed of? What is the thicker side and why?
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
What are the heart valves needed for?
The heart valves are present to aid the unidirectional flow of
blood
What are the atria needed for? How does blood enter the atria?
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
What are the ventricles and how does it enter the heart?
Ventricles are the discharging chambers of the heart
Right ventricle pumps blood into the pulmonary artery
Left ventricle pumps blood into the aorta
On the right side of the heart what is blood pumped through and why? What happens when the ventricle contracts?
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.
Where does blood enter from to get into the left atria and what happens when the left atria contracts?
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.
Name all the valves
(right side)
Pulmonary
valve
Tricuspid
valve
(left side)
Aortic
valve
Mitral
valve
What is the pericardium? Where is it located and What is it needed for?
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
What is the heart wall made up of? What are the 3 layers for?
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
What are the major vessels that return blood to the heart from external anterior view?
Arteries – right and left coronary (in atrioventricular groove),
marginal, circumflex, and anterior interventricular arteries
Veins – small cardiac, anterior cardiac, and great cardiac veins
From the anterior view, What are the major vessels that convey blood away from the heart and name the branches of the aorta?
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
- Ascending aorta (three
branches) –
a. Brachiocephalic
b. Left common carotid
c. Subclavian arteries
Front the posterior view what are the major blood vessels that take blood too and from the heart?
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
When does most blood flow happen and why? Where does most blood flow take place?
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.
How is the heart affected by ischaemia?
when blood flow to the heart muscle is constricted because of an artery spasm
Atherosclerosis is one of the main
causes of myocardial ischemia
What muscles make up the heart muscle and how is the heart contracted?
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
What are pacemaker cells?
Pacemaker cells differentiate
from other cardiomyocytes to
have this specialist function
What are the 3 steps in the cardiac action potential?
- rapid depolarization due to Na+ inflow when voltage-gated fast Na+ channels open
- 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
- repolarization due to the closure of Ca2+ channels and K+ outflow when additional-gated K+ channels open
Why is the SA important?
The cardiac conduction system
regulates the heart rate
and rhythm
How does the action potential spread through the heart?
1 The heart has a natural
pacemaker from where APs
originate - the sinoatrial (SA)
node, also known as the
natural pacemaker
- AP propagates across the atria
and depolarises and excites the
atrial myocardium (muscle) - 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 - 3 The AP then propagates
rapidly down the bundle of
His - The AP next propagates rapidly
down to the left and right
branches of His - The AP next propagates rapidly
down to the left and right
branches of His - then down Purkinje fibre bundles
- Impulse rapidly disperses
throughout the myocardium via
Purkinje fibres - Thus, the ventricular
myocardium is depolarised at
nearly the same time
due to rapid cell-to-cell spread of
impulse through gap junctions
How are action potentials regulated? How many times do they occur per minute?
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
Can the nervous system elicit cardiac action potentials?
BUT – the nervous system cannot
elicit cardiac action potentials:
this can only happen via the SA
node
What does the ECG teach you?
*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
What are the standard limb leads for the heart?
1, 2, 3
How is the p wave developed by a cardiac impulse?
Atrial depolarisation generates
a ‘P wave’ on the ECG
How are QRS impulses developed?
Ventricles invaded by impulse and
depolarised generating a QRS
complex
What can you learn about a rhythm from an ECG?
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
What are the normal ecg values?
P-R interval= 0.12-0.20 sec
QRS width= 0.08-0.12 sec
Q-T interval= 0.35-0.43 sec
How can ECGs be used to measure heart rate?
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.
How can you use ECGs to learn about sinus arrhythmias?
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
How can you spot a myocardial infarction using an ECG?
ST depression of elevation
from the posterior view what vessels supply and drain the heart?
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
