Cardio - Cardiac Function Flashcards
What are atrial and ventricular contractile muscle fibres similar to?
Skeletal muscle fibres but are structurally different
What other cells are present in the heart?
Specialized excitatory and conductive cardiac cells
What aren’t the specialized cardiac cells good at doing?
Contract very weekly because the contain very dew contractile elements (myofibrils)
What are the specialized cardiac cells good at doing?
They have special properties of self excitability
-they are able to spontaneously generate an AP
Are able to rapidly conduct these impulse to atrial and ventrical muscles
Over all the specialized cells provide what as a whole?
A self excitatory system for the heart to generate impulses and a transmission system for rapid conduction of impulses throughout the heart
Why are the 2 types or myocardial cells?
- Contractile (muscle) cells
2. Specialized nodal and conducting cells
What are the similarities between myocardial contractile cells and skeletal muscle cells?
- Striated banding pattern of cells (caused by thin and thick myofilament arrangements)
- Contain similar contractile proteins (actin+myosin)
- Ca++ released from SR triggers the contraction
What is the difference in myocardial cells compared to skeletal muscle cells?
- Short and branched
- 1/3 of their volume is mitochondria (ATP production)
- Extract 80% of the O2 from the blood that goes by
- Joined by intercalated disks that contain gap junctions
What do the gap junctions at the intercalated disks allow?
Allow the movement of ionic currents (APs) between cells.
-when one contractile cell contracts, so do all the others
What is the difference between skeletal muscle movement and myocardial cell movement?
Skeletal needs neurons to move
Myocardial excites itself to move
What are the main purposes of the nodal and conducting cells?
Contains 4 important contractile proteins
Self excitable: spontaneously generate APs
Rapidly conduct AP through the heart
What are the 2 nodal cells?
Found in the SA node
Found in the AV node
What are the 2 conducting cells?
Bundle of His
Purkinjo fibres
What is the SA node?
The Sinoatrial node is the self excitatory impulse that triggers the heart to beat
-origin
Where is the SA node located?
Upper posterior wall of the RA
What is the normal beats/min?
70 contractions/beats/ min
Do all cardiac cels have the potential to be self excitatory?
Yes, this eventually leads to automatic rhythmic contractions
Why is the SA node the origin of the “heart beat”
Because it has the fastest spontaneous generation fo the action potential compared to all other areas of the heart
-therefore the SA node controls the rate of the heart beat
What is the nickname of the SA node?
The pacemaker
What are the 2 main characteristics of the SA node largely responsible for the self excitability?
- Cells of the SA node have greater permeability fo Na+ and Ca+ compared to other heart cells.
- K+ permeability of the SA node cells decreases (less K+ leaves) during diastole
- both 1 and 2 cause the SA nodal cells to spontaneously depolarize to threshold
SA nodal cells do not contain…..?
RMP because of their properties
What is the pacemaker potential?
The slow depolarization to threshold by cells
-slow spontaneous generation of action potentials determines the heart rate
What are the sequence of events of a typical SA nodal action potential?
- Slow spontaneous depolarization caused by increased permeability of Na+ and Ca++ and decrease permeability of K+
- Depolarizing phase- at threshold (-40mV) CA++ voltage gated channels open and Ca++ flow into the SA nodal cells where membrane potential reaches -15mV
- Repolarizing phase- Ca++ voltage gated channels start to come and K+ voltage gated channels start to open and K+ leaves the cell. The membrane potential returns to -60mV and the K+ channels begin to close
Why is there a rounded curve on the graph for this cycle?
Due to the overlap of the Ca++ voltage gated channel open along with the K+ voltage gated channels open
How are APs in the heart sent?
They are sent from the top of the heart down because you want to push the blood from the top down into the ventricles
Why are contraction movements from the bottom up?
Because we want to push the blood up and out into either the pulmonary valve and the aorta
What and where is the AV node?
Above the tricuspid valve
-it slows down the AP because we want the atrium to contract and push the blood down before the ventricles contract
How are APs spread throughout the heart?
Gap junctions
What is the atrial ventricular ring?
Composed of a bundle of fibre connective tissue that electrically isolates the atrial muscle from the ventricular muscles
What is the bundle of His
Takes the AP from the apex of the heart more towards both ventricles
What are the Purkinje fibres?
Delivers the AP to contractile cells and propagates the AP through the gap junctions from the bottom up
Why do we use an ECG?
Electrocardiograms are used because body fluids are god conductors of electricity to measure cardiac impulses generated at the SA node. Small portions of the electrical current spread to the surface of the body
ECG definition?
Is the sum of all the electrical events in the heart
On the graph, what does the P wave represent?
The depolarization of the atrial muscle
On the graph, what does the QRS complex represent?
Depolarization of ventricle muscles
-bigger because the ventricles are bigger
On the graph what does the T wave represent?
Depolarization of ventricular muscle
On the graph why don’t we see the repolatization of the atrial muscle?
Because it is too small and gets lost in the QRS complex
What can the ECG tell you about the health of the heart?
- The exact and type of disturbances of rythm or conduction
- The approximate extent and location of the myocardial change
- Heart rate
What is the cardiac cycle?
Shows all the mechanical and electrical events during a single contraction of the heart
What does the cardiac cycle include at rest?
Pressure changes in the aorta, LA and LV
Volume changes in the LV
Valves opening and closing
ECG
What are the 2 periods in the carload cycle?
Ventricular systole (contraction) Ventricular diastole (relaxation)
What has 1/10th of a delay in the heart?
At the level of the AV node before the impulse is passed from the atria to the ventricles
Why is there 1/10th of a delay?
Allows the atria to contract ahead of the ventricles and empty the blood into the ventricles prior to the strong ventricular contraction which forces the blood into the pulmonary and systematic circulation
What are the 5 phases of the cardiac cycle?
- Atrial Systole (medium length)
- Early ventricular systole - isovolumetric ventricular contraction (short length)
- Ventricular systole - rapid ejection period (long)
- Early ventricular diastole - Isolvolumetric ventricular relaxation (short)
- Late ventricular diastole - ventricular filling (long)
What are the 3 characteristics of the Atrial systole phase?
- P wave represents the depolarization of the atria causing the atria to contract
- Atrial pressure is greater than ventricular pressure. AV valves are ALREADY open
- Ventricles continu to fill with blood. This is the last 30% of ventricular filling producing the end diastolic volume(EDV)
What are the 3 characteristics of the Early ventricular systole phase?
- QRS complex represents depolarization of the ventricles, and ventricles begin contracting causing pressure to build up in ventricles
- Ventricular pressure exceeds atrial pressure causing the AV valve to close
- No change in ventricular volume because aortic valve has not yet opened. (aortic pressure is still greater than ventricular pressure)
What are the 4 characteristics of the Ventricular systole?
- ventricles continue to contract
- Ventricular pressure finally exceeds aortic pressure causing aortic valves to open. Blood leaves ventricles(ejection)
- Ventricular volume decreases. Not all blood leaves ventral. Left with end systolic volume (ESV)
- T wave occurs near the end of phase 3
What are the 3 characteristics of the Early ventricular diastole phase
- Ventricles start to relax causing ventricular pressure to drop.
- Blood in aorta tries to flow back into ventricles causing aortic valve to close
- Ventricular pressure is still greater than atrial pressure so the AV valves remain closed. No blood can enter ventricles so no change in ventricular volume
What are the 3 characteristics of the Late ventricular diastole phase?
- Ventricles continue to relax
- Pressure in the ventricles drops below pressure in the atria and the AV valve opens
- Blood enter ventricles (70% of filling takes place during this phase)
What % of the blood enters the ventricles when they relax?
70-80% during late ventricular diastole
-not when the atria contracts
What % blood does the atrial systole (Atria contract) to ventricular filling?
20-30%
What happens to blood flow when pressure in the atria exceeds the pressure in the ventricles?
Blood flows passively into the ventricles
When does the pressure gradient begin?
In the late ventricular diastole phase
-when ventricles are relaxing
When doesn’t the pressure gradient end?
Continues until the atria have finished contraction
-end of atrial systole
