Chapter 4- Tissues & Living Fabric

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Chapter 4
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
Requirements
* 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
Light Microscopy
* 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
1. Protection
2. Absorption
3. Filtration
4. Excretion
5. Secretion
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.

Special Characteristics-
* 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;...
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