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Cardiac Physiology 1
Lecture 1
28
Physiology
Undergraduate 2
06/07/2011

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Cards

Term
What are the three types of Myocardial cells?
Definition

1. Pacemaker cells(generate APs)

2. Specialised conducting fibres

3. Normal contracting myocardial fibres

 

Term
Describe the structure of Arteries.
Definition

 

1. Thick walls
2. Lots of Elastic tissue - little resistance to blood flow
3. Large diameter 0.5-25 millimeters

 

Term
Describe the structure of Arterioles.
Definition

1. Lots of smooth muscle - high resistance

2. Thick walls

3. Internal diameter 30-500 micrometers

Term
Describe the structure of capillaries.
Definition

1. Very thin walls- just one layer of endothelial cells thick

2. Very small internal diameter - the D of one red blood cell

3. Leaky - Gases, nutrients and waste can pass in and out

Term
Describe the structure of Venules.
Definition

1. Mainly connective tissue

2. Internal diameter of approximately 20 micrometers

3. Extremely porous

Term
Describe the structure of Veins.
Definition

1. Elastic and smooth muscle - large capacitance

2. Can contract and dilate

3. Thin walls

4. Internal diameter of 0.5-30 millimeters

Term
Where is most of the blood in the body?
Definition

In the veins.

This is because the elasticity provides little resistance, the internal diameter is large and the vein can dilate.

Term
What is the layer on the internal surface of blood vessels called?
Definition

The endothelium.

They line all vessels and reduce the turbulance of blood flow.

Term
The arteries that supply the heart are called?
Definition

Coronary ateries.

There are both left and right coronary arteries supplying the heart.

Term
Which side of the heart is thicker and why?
Definition

The left side.

It needs to generate greater pressure as to force the bood through the systemic system, hence more muscle.

Term
Name the four valves of the heart and describe their location.
Definition

1. Pulmonary valve - between the right ventricle and the pulmonary artery

2. Aortic valve - between the left ventricle and the aorta

3. Right AV valve - between the right atrium and ventricle

4. Left AV valve - between the left atrium and ventricle

Term
How can the ventricular contract virtually simultaneously?
Definition

1. low resistance junctions -INTERCALATED DISKS- between muscle fibres which allow AP to pass into adjacent muscle fibres easily.

2. Specialised conducting muscle fibres which facilitate rapid and co-ordinated spread of AP

 

Term
Describe the spread of AP through the heart.
Definition

1. Sinoatrial node (right atrium)

2. Internodal pathway to the right ventricle OR interatrial pathway to the left atrium.

3.Atrioventricular node

4. Bundle of His - Left branch serves left side and the converse for the right branch

5. Purkinje fibres.

Term
Could an AP reach the ventricles if there were no atrioventricular node?
Definition
No. The wave of depolarisation cannot reach the ventricles as there is a seperation of the atria and the ventricles by non-conductive connective tissue.
Term
Contrast the propagation of APs through the atria with the propagation through the AV node.
Definition
The propagation through the atria is rapid (40msec) whereas propagation is delayed in the AV node (100msec). This is because the fibres of the AV node are narrow and branching. 
Term
Decribe the conduction of AP through the Bundle of His, right and left branches and the Purkinje network.
Definition

All three consist of fast-conducting Purkinje fibres. Conduction in the Purkinje system is about 30 msec

 

Term
Describe the sequence of ionic movement across the membrane of the myocardial contracting fibre that leads to an AP.
Definition

1. Na+ moves into the cell fast and raises the membrane potential above threshold to +30mV

2. Transient movement of Cl- into the cell, decreasing the membrane potential slightly.

3. Membrane potential plateaus (around 0mV) due to weak inward flow of Ca2+ and slow outward flow of K+ driven by the concentration gradient.

4. Voltage dependent K+ channels open and there is a rush of K+ outwards, bring the potential below threshold

5. Na+/K+ pump moves Na+ outwards and K+ inwards.

Term
Describe the changes in membrane permiability of Na+, K+ and Ca2+ during AP conduction in a myocardial contraction fibre. 
Definition
[image]
Term
What are the resting potentials for the pacemaker cells in the SA node and myocardial contracting fibres
Definition

Pacemaker cell = -60mV

Contracting fibre = -90mV

Term
Decribe the membrane permiability and movement of ions across the membrane of a pacemaker cell.
Definition
[image]
Term
What is the abolsolute refractory period in cardiac muscle?
Definition

Approximately 250msec.

This is the period, following an AP, in which a new AP cannot be generated. This prevents re-excitation of  the heart, preventing tetanic contractions.

Term
Draw an ECG trace and label the segments, indicate where there is depolarisation or repolarisation and label where there is diastole or systole of atria and ventricles. 
Definition
[image]
Term
How is the ECG recording taken?
Definition
By use of recording electrodes placed on the skin. Usually there is more than 2 electrodes but there must be measurements taken from both sides of the heart.
Term
What is the ECG measuring?
Definition
The ECG is measuring small electrical changes in the skin that result from depolarisation of the heart muscles.
Term
What autonomic nerves can affect SA node AP generation, and what are their resulting effects on heart rate?
Definition

1. Cardiac sympathetic nerves - they increase heart rate.

2. Cardiac vagal nerves - they decrease heart rate.

Term
What are the two possibles affects on the gradient of the pacemaker potential mediated by autonomic nerves, and what are the nerves responsible for these changes?
Definition

1. Cardiac vagal nerves - decrease the gradient of the pacemaker potential.

2. Cardiac sympathetic nerves - increase the gradient of the pacemaker potential.

Term
What are the normal maximum membrane potentials achieved by the pacemaker cells of the SA node and the myocardial contracting fibres?
Definition

pacemaker = 0mV

contracting fibre = +30mV

Term
Draw a graph of a normal pacemaker membrane potential over time, and include the resulting traces where there is cardiac sympathetic stimulation and cardiac vagal stimulation.
Definition
[image]
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