Lecture Notes: Tissues, Glands, Membranes, and Skin

Overview

• Transitioning from chemistry and cell biology to tissues and simple organs.
• Focus on glands, membranes, and eventually the skin.
• Tissues will not be covered in depth; assumed background knowledge.

Learning Objectives

• Describe glands based on structure and function.
• Reference: Saladin's textbook, Section 5.5 (pages 160-166), Chapter 5 (histology).
• Importance of photomicrographs and diagrams in Saladin’s text.

Glands

• Derived from Epithelial Tissue: Glands originate from epithelial tissue, which acts as a covering or lining.
• Types of Glands:
  • Unicellular: Single cells that secrete products, e.g., goblet cells secreting mucus.
  • Multicellular: Multiple cells working together.
• Products: Can be secreted into ducts/surfaces or into the bloodstream (hormones).

Gland Classification

1. Endocrine Glands
   • Products (often hormones) are secreted into the bloodstream.
   • No ducts (ductless glands).
   • Example: Thyroid gland secretes hormones into blood.
2. Exocrine Glands
   • Products are secreted into ducts or onto surfaces.
   • Example: Sebaceous glands secrete oil (sebum) onto hair.

Structural Classification of Exocrine Glands

• Based on number of ducts and shape of acini.
• Not emphasized in detail but important for future reference.

Mechanisms of Secretion

1. Merocrine Secretion
   • Product released via exocytosis.
   • Majority of glands use this method.
2. Holocrine Secretion
   • Cells synthesize product and disintegrate, releasing product and cell fragments.
   • Example: Sebaceous glands; disruption can lead to pimples.
3. Apocrine Secretion
   • Cell fragments pinch off without cell death.
   • Historically associated with apocrine sweat glands; now known to use exocytosis (merocrine).

Next Topic

• Brief discussion on membranes to follow.