Term
| What are the three types of Myocardial cells? |
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Definition
1. Pacemaker cells(generate APs)
2. Specialised conducting fibres
3. Normal contracting myocardial fibres
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Term
| Describe the structure of Arteries. |
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Definition
1. Thick walls
2. Lots of Elastic tissue - little resistance to blood flow
3. Large diameter 0.5-25 millimeters
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Term
| Describe the structure of Arterioles. |
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Definition
1. Lots of smooth muscle - high resistance
2. Thick walls
3. Internal diameter 30-500 micrometers |
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Term
| Describe the structure of capillaries. |
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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 |
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Term
| Describe the structure of Venules. |
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Definition
1. Mainly connective tissue
2. Internal diameter of approximately 20 micrometers
3. Extremely porous |
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Term
| Describe the structure of Veins. |
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Definition
1. Elastic and smooth muscle - large capacitance
2. Can contract and dilate
3. Thin walls
4. Internal diameter of 0.5-30 millimeters |
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Term
| Where is most of the blood in the body? |
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Definition
In the veins.
This is because the elasticity provides little resistance, the internal diameter is large and the vein can dilate. |
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Term
| What is the layer on the internal surface of blood vessels called? |
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Definition
The endothelium.
They line all vessels and reduce the turbulance of blood flow. |
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Term
| The arteries that supply the heart are called? |
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Definition
Coronary ateries.
There are both left and right coronary arteries supplying the heart. |
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Term
| Which side of the heart is thicker and why? |
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Definition
The left side.
It needs to generate greater pressure as to force the bood through the systemic system, hence more muscle. |
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Term
| Name the four valves of the heart and describe their location. |
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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 |
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Term
| How can the ventricular contract virtually simultaneously? |
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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
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Term
| Describe the spread of AP through the heart. |
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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. |
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Term
| Could an AP reach the ventricles if there were no atrioventricular node? |
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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. |
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Term
| Contrast the propagation of APs through the atria with the propagation through the AV node. |
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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. |
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Term
| Decribe the conduction of AP through the Bundle of His, right and left branches and the Purkinje network. |
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Definition
All three consist of fast-conducting Purkinje fibres. Conduction in the Purkinje system is about 30 msec
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Term
| Describe the sequence of ionic movement across the membrane of the myocardial contracting fibre that leads to an AP. |
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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. |
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Term
| Describe the changes in membrane permiability of Na+, K+ and Ca2+ during AP conduction in a myocardial contraction fibre. |
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Definition
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Term
| What are the resting potentials for the pacemaker cells in the SA node and myocardial contracting fibres |
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Definition
Pacemaker cell = -60mV
Contracting fibre = -90mV |
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Term
| Decribe the membrane permiability and movement of ions across the membrane of a pacemaker cell. |
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Definition
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Term
| What is the abolsolute refractory period in cardiac muscle? |
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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. |
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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. |
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Definition
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Term
| How is the ECG recording taken? |
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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. |
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Term
| What is the ECG measuring? |
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Definition
| The ECG is measuring small electrical changes in the skin that result from depolarisation of the heart muscles. |
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Term
| What autonomic nerves can affect SA node AP generation, and what are their resulting effects on heart rate? |
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Definition
1. Cardiac sympathetic nerves - they increase heart rate.
2. Cardiac vagal nerves - they decrease heart rate. |
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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? |
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Definition
1. Cardiac vagal nerves - decrease the gradient of the pacemaker potential.
2. Cardiac sympathetic nerves - increase the gradient of the pacemaker potential. |
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Term
| What are the normal maximum membrane potentials achieved by the pacemaker cells of the SA node and the myocardial contracting fibres? |
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Definition
pacemaker = 0mV
contracting fibre = +30mV |
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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. |
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Definition
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