The greatest proportion of blood volume is present within which ONE of the follo
ID: 83751 • Letter: T
Question
The greatest proportion of blood volume is present within which ONE of the following vessel types? Select one: Systemic capillaries Systemic arteries and arterioles Pulmonary blood vessels Systemic veins and venules Heart ich ONE of the following is responsible for the rapid depolarization phase of an action potential within the pacemaker cells? Select one: A decrease in P An increase in P Ca2+ An increase in PK An increase in P Na+ A decrease in P Na+ Which ONE of the following statements about an action potential generated from a sinus nodal fibre is INCORRECT? Select one: The unstable baseline can be partly attributable to a progressive decrease in Ca2 permeability. The resting membrane potential is about -60 mV. o The sudden upstroke (depolarisation) is due to the opening of Ca channels causing a rapid influx of Ca nto the cell. 2+. 2+ Repolarisation is in part due to activation of K channels. The unstable baseline can be partly attributable to a progressive spontaneous reduction in membrane permeability to KExplanation / Answer
1. Systemic veins and venules.
2. an increase in Pca+ [ An increase in PCa2+ allows Ca to flow into the cell causing the rapid depolarization phase of an action potential within the pacemaker cells.]
3.The unstable baseline can be partly attributable to a small progressive increase (not decrease) in Ca2+ permeability due to the opening of T (transient) channels.
4. vessel length is doubled.
5. Starling’s Law dictates that an increase in pre-load, will result in the stimulated ventricular muscle contracting with increased force. Thus more blood will be ejected during contraction, resulting in an increased stroke volume.
6. The pressure in venules would be less than the pressure in large veins.
7. arterioles, resistance [Resistance = Pressure Gradient / Flow. Resistance to flow is highest in arterioles, and this is where the greatest decrease in blood pressure occurs (from 80 to about 30 mmHg)].
8. decreased end-systolic volume and increased stroke volume. [An increase in myocardial contractility will mean a greater proportion of the heart’s content of blood will be ejected during systole. So end-systolic volume will decrease and stroke volume will increase.]
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