(BIO 271) Chapter 4 Tissue Level of Organization

Tissue

Groups of cells/extracellular products that carry out a common function.

Histology

The study of tissues + their relationships with organs.

Epithelial Tissue

A type of tissue that covers body surfaces and lines cavities of organs, body, ducts and vessels, forming protective barriers. Also used to make up glands.

Epithelium

composed of one or more layers of closely packed cells.

4.1A Characteristics of Epithelial Tissues: CELLULARITY

Composed entirely of cells, bound closely together by a variety of intercellular junctions.

Characteristics of Epithelial Tissues: Polarity

3 structural asymmetrical domains: Apical(exposed), Lateral(contain intracellular junctions and located on the sides that face and connect to neighboring epithelial cells) and Basal surfaces (bottom surface attached to underlying connective tissue.

Characteristics of Epithelial Tissues: Attachment to basement Membrane

Epithelial tissue are attached to a thin layer called the basement membrane connected to the underlying connective tissue.

Characteristics of Epithelial Tissues: Avascularity

All Epithelial tissues contain no blood vessels.

Characteristics of Epithelial Tissues: Innervation

Epithelia contain lots of nerve endings to detect the environment, most are located underneath the tissue.

Characteristics of Epithelial Tissues: High regeneration capacity

Apical surface are frequently damaged but replace fast thanks to stem cells found near the basement membrane.

4.1B Functions of Epithelial Tissue: Physical Protection

Protects internal surfaces from dehydration, abrasion and destruction by physical, chemical and biological agents.

Functions of Epithelial Tissue: Selective Permeability

Epithelial act as “gate keepers”, exhibiting impermeable to some and assisting other molecules by absorption and Secretion.

Functions of Epithelial Tissue: secretion

Some epithelial cells may form a gland to produce specific secretions.

Functions of Epithelial Tissue: Sensations

Contain nerve endings that detect environmental changes concerning touch, pressures temperature and pain collectively known as sensation.

4.1C specialized structures of Epithelial Tissue: basement membrane

Provides support, Anchor, and barrier from movement for the epithelium, and the underlying connective tissue.

4.1D classification of epithelia tissue: Simple epithelium

One cell layer thick direct contact with basement membrane : can be located internal linings intestine and blood vessels

classification of epithelia tissue: stratified epithelium

Two or more layers of cells making it strong against stress applied and are located in esophagus, pharynx or vagina.

classification of epithelia tissue: pseudostratified

Cells appear layered but are all attached to basal surfaces therefore is classified under simple epithelium (Ciliated pseudo stratified epithelium make up the linings of the nasal cavity

Classification by cell shape: squamous cells

Cells are flat, wide, and irregular in shape.

Classification by cell shape: cuboidal cells

They are as tall as they are wide and irregular in shape,

Classification by cell shape: columnar cells

are slender and taller than they are wide found common in the basal layer.

Classification by cell shape: transitional

Readily change their shape depending on now stretched the epithelium becomes. Found in the lining of the bladder wich fills ruin and expels it (swells to relax state).

4.1E TYPES OF EPITHELIUM: SIMPLE squamous epithelium

Single layer, irregular flattened cells, appear lightly bound together.

• Found in moist surfaces such as the lung air sacs

• Specialized for rapid membrane transport processes

4.1E TYPES OF EPITHELIUM: SIMPLE cuboidal epithelium

Single layer of tall/wide cells.

• Makes up the walls of kidney tubules, ovary and thyroid gland.

• Functions for absorption and secretion

  
  

4.1E TYPES OF EPITHELIUM: SIMPLE columnar epithelium

Single layer cells that are tall and narrow.

• Located within the basal surface

• Active absorption ans secretion

• Has two forms: Ciliated and no-ciliated

• Non-ciliated SCE have microvilli and goblet cells, located in the lining of the digestive tract.