Why is it that valves are found in veins, but not in arteries outside heart?

Question

Also what's the difference between a mechanical and chemical process? Please give an example where each occurs in digestion.

Answer 1

Valves prevents the back flow of blood. In arteries blood flows in high pressure since it comes directly from the heart hence no back flow of  blood therefore there are no valves while in veins blood is in low pressure making it to have valves to prevent back flow of blood..

Answer 2

Arteries have the force of the heart's pump behind them so there is little risk of the blood turning back in an artery. But the vein only has the organ behind it such as the stomach, the bones, spleen, the brain etc. So there is no pump to force the blood in the vein. The vein's internal blood pressure is just derived from the artery's pressure which is behind the organ. So valves are needed so that the blood does not turn back.

Answer 3

Valves are not required in the arteries, as blood is pumped at high pressure, there is little chance of a backflow.  Conversely, in the veins, blood is at low pressure, and so there is greater risk of backflow, hence the need for valves.  Examples of mechanical digestive processes include mastication (i.e. chewing food) and the churning of food in stomach.  Examples of chemical digestive processes include he secretion of digestive enzymes in the small intestines, and the secretion of amylases in the saliva of the mouth.

Answer 4

the mastication(chewing of food) and the churning of food due to the peristaltic movements of the walls of the stomach are examples of of physical process. the digestion of starch by enzyme amylase in the mouth and digestion of proteins by enzyme are the examples of chemical process

Answer 5

This is because blood in arteries, blood coming out form the heart, is at high pressure. Which means that there would not be a back flow of blood. Whereas in the vein, blood pressure is low. Therefore backflow of the blood may occur and valves are needed to prevent this. Valves shuts when a backflows occur....

Answer 6

In short, valves are needed in the veins because there is less pressure in them than arteries.