Typically veins are generally wider than arteries, and therefore the pressure is lower. Capillaries are tiny vessels, so repsent high resistance to the incoming blood, so the rate of blood flow through will be quite low. All blood from the artery eventually passes through capillaries and into the vein.
Graves' disease. Graves' disease is the most common cause of overactive thyroid. It can run in families and can occur at any age, although it is most common in women aged 20-40 years old. You are more likely to develop Graves' disease if you smoke. Graves' disease is an autoimmune condition.
If you have had your thyroid gland removed or radioactive iodine treatment for an overactive thyroid, this can cause an underactive thyroid. Radiotherapy for thyroid cancer can also lead to an underactive thyroid. Other causes of underactive thyroid include: some medicines, such as lithium and amiodarone.