(a) What is an exocrine gland? Name two exocrine glands. (b) What is an endocrine gland? Name two endocrine glands?

(a) Exocrine glands are glands that secrete their products through ducts (tubes) directly to specific target locations rather than into the bloodstream. These secretions are released onto body surfaces (like skin) or into body cavities (like the digestive tract) where they perform specific local functions. The term "exocrine" comes from Greek words meaning "to secrete outward." These glands produce a wide variety of substances including enzymes, mucus, sweat, saliva, and milk, each serving distinct purposes in digestion, cooling, lubrication, or nourishment.

Two important examples of exocrine glands are: (1) Salivary glands, which produce saliva containing enzymes (like amylase that begins breaking down starches), mucus for lubrication, and antimicrobial substances. Saliva is released through ducts into the mouth, facilitating chewing, swallowing, taste, and initiating digestion. There are three pairs of major salivary glands: parotid, submandibular, and sublingual. (2) Sweat glands (also called sudoriferous glands), which produce perspiration that is released through ducts opening as pores on the skin surface. Sweat helps regulate body temperature through evaporative cooling and excretes small amounts of waste products like urea and salts. Other common exocrine glands include sebaceous glands (producing skin oils), mammary glands (producing milk), lacrimal glands (producing tears), and digestive glands like the pancreas (in its exocrine function, producing digestive enzymes), liver (producing bile), and gastric glands (producing stomach acid and enzymes).

(b) Endocrine glands are ductless glands that secrete their products—hormones—directly into the bloodstream rather than through ducts. The term "endocrine" means "to secrete within." These hormones travel through the circulatory system to reach distant target organs or tissues throughout the body, where they regulate various physiological processes. Endocrine glands form a communication network that controls growth, metabolism, reproduction, stress responses, and maintains homeostasis (internal balance).

Two important examples of endocrine glands are: (1) The thyroid gland, a butterfly-shaped gland located in the front of the neck below the larynx. It produces thyroid hormones (T3 and T4) that regulate metabolic rate, growth, development, body temperature, and heart rate. It also produces calcitonin, which helps regulate calcium levels in the blood. Thyroid disorders like hypothyroidism, hyperthyroidism, and goitre are among the most common endocrine problems. (2) The pituitary gland, often called the "master gland," is a pea-sized structure at the base of the brain controlled by the hypothalamus. Despite its small size, it regulates many other endocrine glands and produces numerous hormones including growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin, and antidiuretic hormone (ADH). Other major endocrine glands include the pancreas (producing insulin and glucagon), adrenal glands (producing cortisol, adrenaline, and aldosterone), parathyroid glands (producing parathyroid hormone for calcium regulation), and gonads—testes in males and ovaries in females (producing sex hormones). Some organs have both endocrine and exocrine functions; for example, the pancreas produces digestive enzymes (exocrine function) and hormones like insulin (endocrine function).