Final answer:
Glands are secretory tissues derived from epithelial tissues. Exocrine glands release secretions through ducts, while endocrine glands secrete hormones directly into the fluid and bloodstream. Glands can be classified based on secretion type and structure.
Step-by-step explanation:
Glands are secretory tissues and organs that are derived from epithelial tissues. Exocrine glands release their products through ducts. Endocrine glands secrete hormones directly into the interstitial fluid and blood stream. Glands can be classified based on the type of secretion and their structure. Merocrine glands secrete products as they are synthesized, while apocrine glands release secretions by pinching off the apical portion of the cell. Holocrine glands store their secretions until they rupture and release their contents, with the cell becoming part of the secretion.