1. What is SA node???
2. -------------------are the blood vessels that starts in capillaries and ends in capillaries.
3. What is pacemeter?
4.  Only the veins and not the arteriesare provided with valves. Why?????
5. Thearteries are deep seated in the body? why???

1 . SA node  or Sino Atrial Node - the beat originates in the heart itself from a mass of highly specialised muscle tissue called the pace maker or sa node which has some of the properties and characteristics of nerve cells . it regulates the rate of contraction of heart muscle and inities heartbeat.

1. SA node also known as Sinoartrial Node and Sinus Node is the impulse-generating (pacemaker) tissue located in the right atrium of the heart, and thus the generator of normal sinus rythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava. These cells are modified cardiac myocytes. Though they possess some contractile filaments, they do not contract.

•  I think your third question is wrong. If it is 'pacemaker' then the anser is as follows:
• A pacemaker is a medical device that uses electric impulses , delivered by electrodes contacting the heart muscles to regulate the heart beat. The primary purpose of a pacemaker is to maintain an adequate heart rate.

 4. Arteries do not have valves because the heart provides the pressure needed to send blood through the system while the veins have valves because venous pressure is often not great enough (because the blood has to overcome gravity and other forces) to return the blood to the heart.

 5. The Arteries are deep seated in the body so that they can continuously pump oxygenated blood to major organs that lie deep inside the human body.