Tissues and Histology Overview

Study Notes

Tissues

Tissues are groups of cells working together for a specific purpose.
Histology studies tissues microscopically.
Pathologists examine tissues for disease indicators.

Types of Tissues

Four basic tissue types: epithelial, connective, muscular, and nervous.
Epithelial tissue covers surfaces, lines organs/cavities/ducts, and forms glands.
Connective tissue protects and supports, binds organs, stores energy, and provides immunity.
Muscular tissue contracts for movement and heat generation.
Nervous tissue detects changes and responds with nerve impulses.

Epithelial Tissue

Types: Surface epithelium (covers) and glandular epithelium (secreting glands)
Surface epithelium is tightly packed with little intercellular substance.
- Arranged in single or multiple layers.
- Avascular (no blood vessels), but has nerves.
- Regenerative, attached to connective tissue via a basement membrane.
- Simple epithelium: single layer, functions in diffusion, osmosis, secretion, and absorption.
- Stratified epithelium: multiple layers, protective in high wear areas.
- Pseudostratified epithelium: single layer that appears stratified due to nuclei alignment, all cells attach to the basement membrane.
Cell shapes: squamous (flat), cuboidal (cube-shaped), columnar (rectangular), and transitional (variable).
- Columnar cells have cilia or microvilli.
- Transitional cells change shape with organ relaxation/stretching.
Glandular epithelium: found in glands (skin, digestive, endocrine).
- Exocrine glands: release products via ducts (e.g., salivary, sweat).
- Endocrine glands: ductless, release hormones into the bloodstream (e.g., thyroid, pituitary).

Classification of Epithelium

Based on layers and cell shape.
Simple Epithelium:
- Squamous: lining cardiovascular/lymphoid systems, serous membranes, alveoli. Functions in filtration, diffusion, secretion.
  - Endothelium: lines heart, blood vessels, lymphatic vessels.
  - Mesothelium: found in serous membranes.
- Cuboidal: covers ovaries, lines the lens, forms retinal epithelium.
- Columnar: one layer of rectangular cells.
  - Nonciliated: lacks cilia, contains microvilli.
  - Ciliated: contains cilia.
- Pseudostratified columnar: may be ciliated or nonciliated.
Stratified Epithelium:
- Squamous: multiple layers, flat top layer.
  - Nonkeratinized: lacks keratin.
  - Keratinized: contains keratin.
- Cuboidal: multiple layers, cube-shaped top layer.
- Columnar: multiple layers, rectangular top layer.
- Urothelium (transitional): cells change shape based on organ form.

Functions of Epithelium

Protection, secretion, absorption, and excretion.

Description

Explore the essential concepts of tissues and their classifications, including epithelial, connective, muscular, and nervous tissues. This quiz will test your understanding of histology and the role of pathologists in examining tissues. Ideal for students studying biology or related disciplines.