What is the source of energy for your heart

Hummingbirds drink nectar from flowers, while robins eat plant seeds. what does this reduce?

When does the circulatory system work with the respiratory system? a. during blood cell formation b. during cellular respiration c. during intestinal digestion d. during a viral infection

What is an endocrine function? (apex) a. esophageal glands release mucus into the esophagus b. salivary glands release saliva into mouth c. swear glands release sweat to the skin d. the pineal gland releases melatonin into the bloodstream