If a person has lost a significant amount of blood but still maintains a normal blood pressure it does not necessarily mean that the person is maintaining adequate perfusion. which of the following best explains why this is so?
blood vessels are constricting causing greater peripheral resistance.
the heart has increased its rate to increase cardiac output.
the sympathetic nervous system has increased its nervous impulses.
the heart has increased its contractile force increasing cardiac output.

Blood vessels are constricting causing greater peripheral resistance

Explanation:

When the body experiences a significant amount of blood loss, the body will constrict the blood vessels to compensate for the blood loss. This results in the blood flow and pressure remaining in at a normal level. This does also result in your a decrease of the amount of blood your heart pumps to areas outside of the centre or your body, which causes the skin to lose heat and become paler.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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