Tissue Level of Organization, Exams of Histology

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Chapter 4

The Tissue Level of Organization

• Group of similar cells
  • common function
• Histology
  • study of tissues
• Pathologist
  • looks for tissue changes that indicate disease

4 Basic Tissues (1)

• Epithelial Tissue
  • covers surfaces because cells are in contact
  • lines hollow organs, cavities and ducts
  • forms glands when cells sink under the surface
• Connective Tissue
  • material found between cells
  • supports and binds structures together
  • stores energy as fat
  • provides immunity to disease

Epithelial Tissue -- General Features

• Closely packed cells forming continuous sheets
• Cells sit on basement membrane
• Apical (upper) free surface
• Avascular---without blood vessels
  • nutrients diffuse in from underlying connective tissue
• Rapid cell division
• Covering / lining versus glandular types

Basement Membrane

• holds cells to connective tissue

Classification of Epithelium

• Classified by arrangement of cells into layers
  • simple = one cell layer thick
  • stratified = many cell layers thick
  • pseudostratified = single layer of cells where all cells don’t reach apical surface - nuclei at found at different levels so it looks multilayered
• Classified by shape of surface cells
  • squamous =flat
  • cuboidal = cube-shaped
  • columnar = tall column
  • transitional = shape varies with tissue stretching

Simple Squamous Epithelium

• Single layer of flat cells
  • lines blood vessels (endothelium), body cavities (mesothelium)
  • very thin --- controls diffusion, osmosis and filtration
  • nuclei centrally located
• Cells in direct contact with each other

Simple Cuboidal Epithelium

• Single layer of cube-shaped cells viewed from the side
• Nuclei round and centrally located
• Lines tubes of kidney
• Absorption or secretion

Example of Simple Cuboidal

• Sectional view of kidney tubules

Ex. Simple Columnar

• Section from small intestine

Stratified Squamous Epithelium

• Several cell layers thick
• Surface cells flat
• Keratinized = surface cells dead and filled with keratin - skin (epidermis)
• Nonkeratinized = no keratin in moist living cells at surface - mouth, vagina

Papanicolaou Smear (Pap smear)

• Collect sloughed off cells of uterus and

vaginal walls

• Detect cellular changes (precancerous

cells)

• Annually for women over 18 or if sexually

active

• Multilayered
• Surface cells varying in shape from round to flat if stretched
• Lines hollow organs that expand from within (urinary bladder)

Transitional Epithelium

Connective Tissues

• Cells rarely touch due to extracellular matrix
• Matrix(fibers & ground substance secreted by cells)
• Consistency varies from liquid, gel to solid
• Does not occur on free surface
• Good nerve & blood supply except cartilage & tendons

Cell Types

• Blast type cells = retain ability to divide & produce

matrix (fibroblasts, chondroblasts, & osteoblasts)

• Cyte type cells = mature cell that can not divide or

produce matrix (chondrocytes & osteocytes)