Which of the following pairs of organs includes only the endocrine glands?
Parathyroid and adrenal
Endocrine glands do not have ducts (ductless glands) and their secretions (hormones) are directly released into the blood and transported to the target organ. Eg: Ovary (estrogen and progesterone), testes (testosterone), pancreas (insulin and glucagon).
Exocrine glands have ducts and their secretions are released to target organs by their ducts. Eg: Sweat glands, salivary glands, mammary glands.
Some organs such as the pancreas (enzymes to break down lipids, proteins and sugars and insulin), ovary (estrogen and ovum) and testes (testosterone and sperm) function as both exocrine and endocrine glands.
Hence, option b is correct as parathyroid and adrenal glands are exclusively endocrine.