The Heart as a Pump & ECG Flashcards
What are the first heart sounds?
The AtrioVentricular valves
What are the second heart sounds?
Semilunar valves
What happens to the heart sounds with age?
They can stiffen and start whistling
If they regurgitate they make a gurgling sound
What happens during the first phase of the cardiac cycle?
- Isovolumetric relaxation
- Passive ventricular filling (~75%)
- Atrial systole (priming pump (~25%)
What happens during diastole?
Actin and myosin in venticular cells relax and the heart becomes very elastic allowing it to fill up with blood. This is known as isovolumetric relaxation (because volume doesn’t change) and pressure reduces until AV valves open up which allows for the ventricles to fill up passively and then Atrial systole (Atrial contraction) pushes more blood into the ventricle and back into the veins as well.
Does blood flow backwards at any stage of atrial contraction?
Yes there is a valve only between the atrium and the ventricle
What happens after atrial systole?
Ventricular systole which is the contraction of the ventricles and the sealing of both AV valves. Once enough pressure is produced by the ventricles to overcome the semilunar valves the blood moves into the aorta and the pulmonary trunk.
What happens when both ventricles are contracting and the AV valves are closed?
Isovolumetric contraction because volume is constant until the semilunar valves are open.
What is ventricular ejection?
The rapid ejection of blood under high pressure out of the ventricles and into the aorta + pulmonary trunk
What is cardiac muscle made up of?
Intercalated discs
Gap junctions which transmit action potential (Na K and Ca) (and desmosomes)
What is calcium useful for in cardiac muscle?
Calcium channels are used as part of the action potential. Calcium passes through L type channels on the cardiac muscle when stimulating a contraction. The L-type channel repolarizes the muscle cell in a delayed manner which is important to prevent cardiac muscle from reaching a tetanic contraction (like in skeletal muscle)
How do cardiac muscles contract?
Action potential in cardiac contractile travels down the T - tubule with a small amount of Calcium from the extracellular fluid.
Calcium that enters interacts with ryanadeine receptors causing release of calcium from sarcoplasmic reticulum increasing the cytosolic calcium.
Troponin-tropomyosin complex in thin filaments are pulled aside
Cross-bridge cycling between thick and thin filaments occurs
Thin filaments slide inwards between thick filaments
contraction results
How do RyR2 receptors activate?
calcium receptors bind stimulating more calcium presence.
This is important because any calcium can cause this to occur
How does calcium induce cardiac muscle contraction?
it binds to troponin exposing tropomyosin
How is calcium concentration maintained in the cell after SR action?
a Na/Ca exchangers operates to remove calcium. (sodium diffuses out)
Where does action potential start in the heart?
SA node
How does the SA node start a heartbeat?
Has ion channels known as funny channels because they leak sodium into the cell triggering an action potential. These action potentials spread towards the AV node which creates a time delay for the ventricle to contract from the bottom up
What insulates the atrium from the ventricles to create a delay for ventricle filling?
The annulus fibrosis
What is the funny channel leaky to?
To sodium and potassium but potassium tends to leak in most often
What are leaky channels also known as?
Hyperpolarization - activated cyclic nucleotide-gated (HCN) channels
What are the types of leaky channels?
T (fast)
L (slow)
What is RMP of the SA node?
-50 to -60
What is the threshold potential? Why is this significant?
-40 (it is very similar to the RMP making small fluctuations enough to trigger a potential)
How are internodal pathways different to purkinje fibers?
They are very slow (1m/s)
What happens at the AV node?
It slows down the AP to allow viscous blood to fill up ventricles
How is AP rate different at the purkinje fibers?
Way faster and almost simultaneous and synchronous contraction
How are SA node cells different to atrial cells and ventricular cardiomyocytes?
At SA node there are mainly sodium channels.
Different calcium channels come in for atrial and ventricular cells. The idea is the action potential as a plateau phase that is longer in ventricular cells than in atrial cells.
Ventricle has L-type calcium channels let calcium into a muscle cell which makes it beat harder. Tension is not as necessary in SA node cells or atrial cells.
How often do SA node cells fire without any influence from sympathetic or parasympathetic NS stimuli?
Control chronotropy when autonomic NS is no longer activated the SA node will fire 100 -110 times each minute
How often do AV node cells fire without external influence?
40 - 60 bpm
How often do purkinje fibers act without external influence?
15 - 40 bpm
Are the SA, AV, and purkinje cardiomyocytes able to independently start action potentials?
Yes just at different rates without external influences.
How does SA node stay at 70bpm?
parasympathetic innervation is always in action
Can parasympathetic NS affect muscle tone in heart cells?
No only the rate
Can sympathetic NS affect muscle contraction strength?
Yes as well as rate
What is the electrocardiogram atrial depolrization wave called?
A P wave
What is a QRS complex?
The ventricular depolarization and then repolarization is at the T wave
What can ECG be used for?
Diagnose cardiac myopathies (eg tachycardia, ventricular fibrillation, and atrial fibrillation) and measure heart rate
What is heart block?
failure of stimulation to ventricles following atrial contraction
What is wigger’s diagram?
Describes direct function of the heart using pressure of blood at those locations as well as volume of blood moving around.
What causes the dichrotic notch?
The aortic semilunar valve gets sealed shut causing the bouncing of blood off the aorta to elevate pressure briefly
What causes the heart sounds?
1 Closure of tricuspid and mitral valves
2 Closure of aortic and pulmonary valves
Which circuit gets more blood systemic or pulmonary?
Both get exactly the same amount of blood
