<span>A retrovirus is anything of a group of RNA viruses that insert a DNA copy of their genome into the host cell to replicate.
your welcome
</span>
Answer:
Explanation:
1) Excitation brings about contraction.
2) Contraction leads to an increase in blood pressure.
3) Changes in blood pressure results in the opening and closing of the heart valves.
4) The opening and closing of heart valves then regulates the flow of blood and it's volume.
Scar tissue is made of a protein called collagen