8 Electrical and Molecular Mechanisms Flashcards
When a cell has a resting membrane potential, is the inside of the cell more positive or more negative than the outside?
More negative
Which ions move out of cardiac myocytes to maintain the resting membrane potential?
K+ ions
What is Ek?
ie what does it represent?
Equilibrium reached- no net movement of K+
( - 95mV )
Fill in the missing gaps in the image below:
Identify what type of cell each of these action potentials are showing.
Fill in the missing gaps in the following image:
What is the normal plasma concentration of K+?
3.5 - 5.5 mmol/L
What happens to the Ek if the plasma [K+] increases?
Ek becomes less negative
What happens to Na+ channels if the Ek becomes less negative?
Some Na+ channels are inactivated
What can happen to the heart if a patient is hyperkalaemic?
Asystole- heart stops
(may initially get increase in excitiability)
What are the values for mild, moderate and severe hyperkalaemia?
Mild: 5.5-5.9 mmol/L
Moderate: 6.0-6.4 mmol/L
Severe: > 6.5 mmol/L
How is hyperkalaemia treated (if heart hasn’t already stopped)?
- Calcium gluconate
- Reduces the risk of ventricular fibrillation
- Insulin and glucose
- Insulin administered with glucose: Facilitates the uptake of glucose into the cell, which results in an intracellular shift of potassium.
Explain how hypokalaemia can cause ventricular fibrillation.
Hypokalaemia- longer action potentials
Delayed repolarisation- depolarisation happens to early- repolarisation not complete
What part of the blood vessels facilitates the control of tone of the blood vessels?
Circular smooth muscle in tunica media
Differentiate between the contraction pathways of cardiac myocytes and smooth muscle.
How do cardiac myocytes relax after contraction?
How do smooth muscle cells relax?
