Tissue: The Living Fabric
4.1 What are tissues?
* Groups of cells that are similar in structure and perform a common or related function * There are four basic types of tissues:
1) Epithelial (covering)
2) Connective (support)
3) Muscle (movement)
4) Nervous (communication and control)
* The study of tissues is known as histology
4.2 Preparing Human Tissue for Microscopy
* Specimen must be fixed (preserved)
* Specimen must be cut into sections (slices) thin enough to transmit light or electrons * Specimen must be stained to enhance contrast
* The stains used consist of negatively or positively charged molecules that bind within the tissue to macromolecules of the opposite charge * The stains distinguish different anatomical structures because different parts of cells and tissues take up different dyes Transmission Electron Microscopy
* Tissue sections stained with heavy metal salts
* Metal salts deflect electrons in the beam to different extents * Shades of gray, color is a property of light, not electron waves Scanning Electron Microscopy
* Provides three-dimensional pictures of an un-sectioned tissue surface 4.3 Epithelial Tissue
* Epithelial tissue or an epithelium, is a sheet of cells that covers a body surface or lines a body cavity * It occurs in the body in two ways
1. Covering and lining epithelium- Forms outer layer of skin and lines organs 2. Glandular epithelium- fashions glands of body (secretion) * Functions
6. Sensory Reception
-The epithelium of the skin protects underlying tissues from mechanical and chemical injury and bacterial invasion and contains nerve endings that respond to various stimuli acting at the skin surface.
* Polarity: the cell regions near the surface differ from those near the base in structure and function * Specialized Contacts: tight junctions help keep proteins in the apical region of the plasma membrane from diffusing into the basal region, and thus help to maintain epithelial polarity * Supported by Connective Tissue: The Basement Membrane is composed of the Basal lamina of epithelium and Reticular lamina of epithelium; reinforces the epithelial sheet, helping it to resist stretching and tearing forces, and defines the epithelial boundary. * Avascular but innervated: supplied by nerve fibers, contains no blood vessels * Regeneration: reproduce rapidly
Homeostatic Imbalance- An important characteristic of cancerous epithelial cells is their failure to respect the basement membrane boundary, which they penetrate to invade the tissues beneath.
Classification of Epithelia-
* Each epithelium is given two names:
1) The first indicates the number of cells present:
Simple- One cell layer
Stratified – Composed of two or more cell layers
2) The second describes the shape of the cell:
Squamous cells- Flattened and scalelike
Cuboidal Cells- Box-like, generally as tall as they are wide Columnar Cells- Tall and column shaped
Types of Epithelia|
NAME| DESCRIPTION| FUNCTION| LOCATION| VISUAL|
Simple Squamous Epithelium| Single layer of flattened cells with flat nuclei and sparse cytoplasm| Allows passages of materials through Diffusion and Filtration in sites where protection isn’t important.| Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity (serosae)| | Simple Cuboidal Epithelium| Single layer of cubelike cells with round nuclei| Function in secretion and absorption| Kidney tubules, ducts and small glands, ovary surface| | Simple Columnar Epithelium| Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus-secreting unicellular glands (goblet cells)| Absorption;...