Cardiac Output Control Flashcards
What is unique about the cardiac myocyte structure?
These possess intercalated discs with a gap junction allow for a spontaneous depolarisation through the tissue, allowing a corridor for the action potential to rapidly fly through. Hence why it beats like one entire functional unit.
What is spontaneous rhythmicity or intrinsic cardiac control?
The ability of cardiac muscle to generates its own electrical impulse through specialised myocardial cells. If you were to take away surrounding nervous tissue, it can still beat - but really fast.
How does the medulla oblongata regulate heartbeat through the Sympathetic Nervous System (Fight or Flight)?
- Use of norepinephrine (NE)
- Increase heart rate
- Increase force of contraction
- Stimulates SA node, AV node and myocardium
- Coronary arteries dilate
How does the medulla oblongata regulate heartbeat through the Parasympathetic Nervous System (Rest and Digest)?
- Use of acetylcholine
- Slow heart rate
- Acting on the SA node via the vagus nerve
What does adrenaline do for the heart and what’s another name for it?
Epinephrine - released by the adrenal medulla, increases HR and force of contraction.
How does the MO know when to deploy SNS responses and what happens?
The MO detect the need for a faster HR through chemoreceptors (CO2 levels) and baroreceptors (blood pressure)
How does the MO know when to deploy PNS responses and what happens?
The MO signals the vagus nerve, which releases ACh which binds to muscarinic receptors in the heart.
Name 5 key structures of intrinsic cardiac control
Sinoatrial Node (SA), Atrioventricular Node (AV), Bundle of His (AV Bundle), Right / Left Bundle Branches, Purkinje fibres
What is depolarisation?
Cell becomes positive inside (Na+ and Ca2+ rush in), triggering contraction.
What is repolarisation?
Cell returning to its negative resting state (K+ moving out), triggering relaxation.
What is a polarised state?
Resting state - the cell is at rest, ready for the next cycle.
What is the first step of the heart beat?
Atrial depolarisation. The SA node fires, atria depolarise (P Wave). The atria then contract, and push blood into ventricles - there is no sound just yet.
What is the second step of the heart beat?
Ventricular depolarisation. The umpulse reaches the AV node which then sends it to the Bundle of His and Purkinje fibres, resulting in depolarisation (QRS complex). Ventricles contract, pressure builds, AV valves (tricuspid and mitral) slam shut.
What is the third step of the heart beat?
Ventricular repolarisation. As ventricles relax (T wave), the pressure drops, semilunar valves slam shut (aortic and pulmonary).
Risk of all-cause and cardiovascular mortality based on heartbeat / min
Results suggest the risk of all-cause and cardiovascular mortality increased by 9% and 8% for every 10beats/min increment of resting heart rate.
Could you describe the sequence of flow of blood in the heart?
First, deoxygenated blood flows into the right atrium via the superior and inferior vena cavae. From here, via the tricuspid valve, the deoxygenated blood flows into the right ventricle. Then, through the pulmonary artery, it flows into the lungs, where it is oxygenated and then flows through to the pulmonary vein, going into the left atrium. From the left atrium, the blood flows to the left ventricle via the bicuspid valve. It then leaves the heart via the aorta.
