Which of the following endocrine glands is unpaired?

$(a)$ Name the hormone which is injected to a diabetic patient.
$(b)$ Why should we use iodised salt in our diet?
$(c)$ If iodine is insufficient in one's diet,what might be the deficiency disease and its symptoms?

Which disease is caused by high levels of sugar in the blood and urine?

Which hormone regulates the rate of metabolism of carbohydrates,proteins,and fats?

How is the timing and the amount of hormone secreted by a gland regulated? Explain with an example.

Which mechanism controls the timing and amount of hormone released?