Define the following:
$(a)$ Exocrine gland,
$(b)$ Endocrine gland,
$(c)$ Hormone.

(N/A) Exocrine gland is a gland that pours its secretion on the surface or into a particular region by means of ducts for performing a metabolic activity,e.g.,sebaceous glands,sweat glands,salivary glands,and intestinal glands.
$(b)$ Endocrine gland is an isolated gland (separates even from the epithelium forming it) which secretes informational molecules or hormones that are poured into venous blood or lymph for reaching the target organ because the gland is not connected with the target organ by any duct. Therefore,an endocrine gland is also called a ductless gland,e.g.,thyroid gland.
$(c)$ Hormone is a substance that is manufactured and secreted in very small quantities into the blood stream by an endocrine gland or a specialized nerve cell and regulates the growth or functioning of a specific tissue or organ in a distant part of the body,e.g.,insulin.