Why do endocrine glands release their secretions into the blood?

Which organ secretes a hormone when the blood sugar rises? Name a digestive enzyme released by this organ.

Which of the following endocrine glands is unpaired?

Why is it advised to use iodised salt in our diet?

$(a)$ Name the hormone which is released into the blood when its sugar level rises. Name the organ which produces this hormone and its effect on blood sugar level. Also, mention the digestive enzymes secreted by this organ with one function of each. $(b)$ Explain the need for chemical communication in multicellular organisms.

Choose the incorrect statement about insulin: