M04.01.016 Structure of Glands

Glands: Structure and Types

Glands are collections of secretory epithelial cells. This article discusses the structure of the two main types of glands: exocrine and endocrine.

Exocrine Glands

Exocrine glands secrete onto a surface and possess ducts lined with epithelium. They are classified into simple and compound glands:

• Simple Glands: These have a single, unbranched duct. Examples include sebaceous glands, intestinal crypts, and uterine glands.
• Compound Glands: These have multiple, branched ducts. Examples include the salivary glands and the pancreas.

Exocrine glands are further classified by the shape of their secretory units:

• Tubular Glands: These have tube-like secretory units and are found in the uterus, alimentary tract, and sweat glands.
• Acinar (Alveolar) Glands: These have rounded secretory units and are found in the breast.
• Tubuloacinar (Tubuloalveolar) Glands: These have both tubular and acinar shapes and are found in the pancreas and salivary glands.

Exocrine glands can produce different types of secretions:

• Mucous Glands: Secrete a glycoprotein mixture (mucus).
• Serous Glands: Produce a watery fluid containing enzymes.
• Mixed Glands: Secrete both mucous and serous fluids.

Clinical Relevance: Cystic Fibrosis

Cystic Fibrosis is an autosomal recessive genetic disorder caused by a mutation in the CFTR gene, leading to defective chloride channels in exocrine glands. Secretions become hyper-viscous, leading to symptoms such as salty-tasting skin, poor growth, accumulation of thick mucus, coughing, and shortness of breath. There is no cure, and treatment focuses on symptomatic management.

Endocrine Glands

Endocrine glands are ductless and release their secretions (hormones) directly into the bloodstream, forming the endocrine system. Examples include the pituitary gland, pancreas, adrenal glands, thyroid gland, and parathyroid glands.

Pituitary Gland:

The pituitary gland is a crucial part of the endocrine system, secreting hormones that regulate vital body functions and general well-being. Located below the hypothalamus, it consists of the anterior (adenohypophysis) and posterior (neurohypophysis) pituitary.

• Anterior Pituitary Hormones:
  • Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH)
  • Growth Hormone
  • Prolactin
  • Thyroid Stimulating Hormone (TSH)
  • Adrenocorticotrophic Hormone (ACTH)
• Posterior Pituitary Hormones:
  • Oxytocin
  • Antidiuretic Hormone (ADH)

Pancreas:

The pancreas has both endocrine and exocrine functions:

• Endocrine Function: Regulates glucose levels by secreting hormones such as glucagon, insulin, somatostatin, gastrin, and pancreatic polypeptide.
• Exocrine Function: Secretes an alkaline fluid containing enzymes (like trypsinogen and lipase) and bicarbonate ions into the duodenum through the pancreatic duct.

By understanding the structure and function of these glands, we can better appreciate their roles in maintaining homeostasis and overall health.