A&P chapter 5 March 10 2025

Overview of Histology

• Histology: The study of tissues, covered in the second chapter for the upcoming lecture exam.

  • Essential for understanding the organization of living organisms (from atomic level to cells to tissues).

  • Tissues: Collections of cells and products that perform specific functions in the body.

Levels of Organization

• Atoms to Molecules: Atoms bond to form molecules.

• Molecules to Cells: Molecules combine to create cells.

• Cells to Tissues: Similar cells form tissues.

• Tissues to Organs: Different tissues combine to form organs.

Types of Tissues

1. Epithelial Tissues:

   • Line hollow organs and cavities.

   • Function: Control what enters/exits an environment.

   • Forms barriers, covering body surfaces and lining organs and glands (endocrine and exocrine).

2. Connective Tissues:

   • Provide support and protection.

   • Bind organs together and store energy.

3. Muscle Tissues:

   • Responsible for movement.

4. Neural Tissues:

   • Facilitate communication within the body through neurons.

Characteristics of Epithelial Tissues

• Cell Arrangement: Tightly packed cells, minimal extracellular space.

• Anchorage: Epithelial cells anchor to a basement membrane; dependent on connective tissues for nourishment.

• Avascular: Lacking blood vessels; oxygen and nutrients diffuse from underlying tissues.

• High Renewal Rate: Cells frequently undergo mitosis due to environmental abrasion.

• Cell Junctions: Points of contact between cells, including:

  • Tight Junctions: Prevent leakage of substances between cells.

  • Gap Junctions: Allow communication and material transfer between adjacent cells.

  • Desmosomes: Provide mechanical stability by holding cells together.

Basement Membrane

• Composition: Made of two layers: basal lamina (from epithelial cells) and reticular lamina (from connective tissues).

• Functions:

  • Attachment of epithelial cells to underlying structures.

  • Support for epithelial cells, allowing nutrient diffusion.

  • Thickened in conditions like diabetes, affecting nutrient diffusion and leading to complications.

Types of Epithelial Cells

1. Simple Squamous Epithelium:

   • Thin, flat cells allowing diffusion and filtration (e.g. lungs, blood vessels).

2. Simple Cuboidal Epithelium:

   • Cube-shaped cells involved in secretion and absorption (e.g. kidney tubules, glands).

3. Simple Columnar Epithelium:

   • Tall cells often having cilia or microvilli; involved in absorption and secretion (e.g. digestive tract).

4. Pseudostratified Columnar Epithelium:

   • Appears multi-layered but is single-layered with varying cell heights; typically ciliated and secretes mucus (e.g. respiratory tract).

5. Stratified Squamous Epithelium:

   • Many layered, providing protection; keratinized (skin) or non-keratinized (oral cavity, vagina).

6. Transitional Epithelium:

   • Specialized for stretching (e.g. urinary bladder).

Functions of Epithelial Tissue

• Protection: Barriers against pathogens and mechanical damage.

• Absorption: Nutrient uptake via specialized cells (microvilli in SI).

• Secretion: Release digestive enzymes, hormones, and mucus.

• Transportation: Moves substances across surfaces (e.g. in trachea by cilia).

Clinical Application

• Biopsy: Removal and examination of tissue to detect conditions like cancer.

  • Examination includes staining to visualize histological details.

• Pap Smear: Collection of cells from the cervix for cancer screening.

Summary

• Understanding histology is fundamental for recognizing tissue types, functions, and their role in health and disease. Tissue organization leads to functions crucial for survival and plays a key role in medical diagnostics.