Lecture 7 Flashcards
At what point is the mean arterial blood pressure? What levels would be considered hyper and hypotension?
Mean is slightly below the mid point because the heart spends more time in diastole, hypertension is a max blood pressure above 140, hypotension is a minimum blood pressure below 50.
Which comes first, the pressure wave or the blood wave?
The pressure wave comes first.
What are the two types of cells in the heart and relative proportion, appearance and function?
Electrical cells make up 1% of the cells in the heart, they have a pale, striated appearance (not as much as contractile) and have low amounts of actin and myosin, these could be purkinje cells or nodal cells and function to rapidly send signals throughout the heart.
Contractile cells make up 99%, they have a more striated appearance (high actin and myosin), they act to contract, but can also spread an electrical signal, just slower than electrical cells.
How do electrical signals spread?
Action potentials propogate along the cardiac cells via gap junctions in the intercalated disks, this starts at the sinoatrial node and spreads to neighbouring cells, increasing the Ca2+ in the cells to spread the signal and also causing contraction in contractile cells.
What are the main three factors which cause an increased speed of impulse throughout the heart and cause millions of cardiac cells to behave as one (What is this called?)
The signal travels along a conduction pathway of electrical cells, this spreads from the electrical cells to contractile cells and then between the contractile cells.
The millions of cardiac cells behaving as one is known as a functional syncytium.
What is the pathway of the electrical signal of the heart?
Starts at the sinoatrial node, stimulating the right atrium (as this is where the SA node is), the signal spreads to the left atrium via the interatrial bundle and fibers, the original signal from the SA node then travels through the internodal vundle and fibers to the atrioventricular node, this travels through the AV bundle to the left and right AV bundle branches down the septum (depolarising it) and the subendocardial branches (purkinje fibers) which depolarise the lateral wall of the ventricles.
What is the interaction between the SA node and AV node? What can the AV node do without the SA node?
The AV node pauses the signal from the SA node to allow the atria to contract before the ventricles. Without the SA node the AV node can also act as a much slower beating pacemaker.
what are the stages of exitation and conduction?
- Quiescence (no depolarisation or repolarisation)
- SAN pulse (excitation of the intra and interatrial conduction pathways (both atria starting to depolarise)
- both atria fully depolarise.
- AVN pulse (excitation of the AV bundle and purkinje fibers (atria starting to repolarise and the ventricles starting to depolarise at septum and apex).
- atria finishing repolarisation, ventricles fully depolarising.
- start of ventricle repolarisation
- complete ventricular repolarisation.
- quiescence.
What is an ECG? What are the major peaks?
an electrocardiography lets us measure the electrical signal from the heart via electodes places on specific spots on the body. Each depolarisation and repolarisation leads to a peak.
P wave: SAN pulse and atrial depolarisation
QRS complex: ventricular depolarisation
T wave: ventricular repolarisation.
What are some major links between the many graphs of different heart functions?
Systole is R, S and T while P and Q are in diastole. The pressure spikes in the ventricles immediately prior to systole and rapidly lowers after systole (after T wave), the blood volume in the ventricles increases during diastole and decreases during systole despite pressure being roughly the same, this means the ventricles are supplying more pressure. Aortic pressure increases during systole also and decreases as diatole starts (slight peak immmediately after diastole). The Lubb of the heart is heard slightly after the QRS complex (Av valves close), the Dupp is head slightly after the T wave (semilunar valves close).
