Purines have 2 rings pyrimidines have 1 ring.
interphase is the first phase of mitosis
Much of the coordination of vertebrate body functions via chemical signals is accomplished by the endocrine system.
The endocrine system is an information system composed of hormonal feedback loops that are secreted directly into the circulatory system by the body's endocrine glands and regulate distant target organs.
In vertebrates, the hypothalamus is the centre of neuromodulation of all endocrine systems. The main endocrine glands in humans are the thyroid and adrenal glands.
The study of the endocrine system and its disorders is called endocrinology.
The glands that send signals to each other in sequence are often referred to as the hypothalamic-pituitary-adrenal axis.
In addition to the specialized endocrine organs mentioned above, many other organs that are part of other body systems have secondary endocrine functions such as bones, kidneys, liver, heart and gonads.
For example, the kidneys secrete the endocrine hormone erythropoietin. Hormones are amino acid complexes, steroids, eicosanoids, leukotrienes, or prostaglandins.
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