Animal Tissues

• A tissue consists of a group of similar cells performing specialized activities

• The four types of tissues are epithelial, connective, muscular, and nervous

Animal Tissues

• Animal tissues are classified into 4 main types: Epithelial tissue, Muscular tissue, Connective tissue and Nervous/Neural tissue

• Epithelial tissue can be further classified into: simple squamous epithelium, stratified squamous epithelium, columnar epithelium, ciliated columnar epithelium, cuboidal epithelium and glandular epithelium

• Muscular tissue can be further classified into: striated muscle, non-striated muscle and cardiac muscle

• Connective tissue can be further classified into: connective tissue proper, supportive connective tissue and fluid connective tissue

• The connective tissue proper is: areolar tissue, adipose tissue and fibrous tissue

• The supportive connective tissue is: cartilage and bone

• The fluid connective tissue is: blood and lymph

Epithelial Tissues

• Epithelial cells cover or line all body surfaces, cavities, and tubes

• Epithelial tissue consists of closely packed cells without intervening intracellular substance

General Characteristics of Epithelial Tissues

• Epithelial tissues cover and line/cavity walls

• Epithelial tissues form boundaries

• Epithelial tissues are bound to adjacent cells by cell junctions, offering physical strength and mediating the exchange of information and metabolites

Special Characteristics of Epithelial Tissues

• Epithelial tissues are closely attached to each other

• Epithelial exhibit polarity with an apical surface that is open to the outside of the body or inside an internal organ cavity

• Epithelial exhibit polarity with a basal surface that is attached to underlying connective tissue

• Epithelial tissues are avascular but innervated

• Epithelial tissues are supported by connective tissues and cells

• Epithelial tissues are attached to a basement membrane

• Epithelial tissue can regenerate, examples include skin burn and skinned knee

Functions of Epithelial Tissues

• Epithelial tissues provides protection against mechanical injury, pathogens and fluid loss

• Epithelial tissues secretes enzymes, hormones, mucus, and sweat

• Epithelial tissues perform absorption of nutrients and respiratory gases

Classification of Epithelial Tissues

• Epithelial tissues are classified based on the number of cell layers and the shape of the cells

• Cell layers can be simple composed of one layer or compound composed of 2 or more

• The cell shape can be squamous, cuboidal or columnar cells

Simple Epithelia

• Simple epithelia consist of a single layer of cells

• Simple epithelia are found at interfaces involved in selective diffusion, absorption and secretion

• Simple epithelia provide little protection against mechanical abrasion

• Simple epithelia range in shape from flattened to tall

• Flattened epithelial cells are suited for diffusion

• Columnar cells are present in highly active epithelial cells to accommodate the correct organelle

Simple Squamous Epithelium

• Simple squamous epithelium consists of a single layer of thin, flattened, irregularly shaped cells

• Simple squamous epithelium looks like a fried egg

• Simple squamous epithelium is easily damaged

• Simple squamous epithelium forms a continuous surface known as pavement epithelium

• Simple squamous epithelium is common at sites of filtration, diffusion, and osmosis, and can cover surfaces

• Locations of simple squamous epithelium include: air sacs of lungs, wall of capillaries and linings of blood and lymph vessels

• Simple squamous epithelium limit membranes

• Simple squamous epithelium enables fluid transport

• Simple squamous epithelium allows gaseous exchange

• Simple squamous epithelium allows lubrication and reduces friction

Simple Cuboidal Epithelium

• Simple cuboidal epithelium consists of a single layer of cube shaped cells, with a centrally located nucleus

• Simple cuboidal epithelium provides secretion, absorption and surface barriers

• Simple cuboidal epithelium is found on the surface of the ovaries, lining the kidney tubules, and linings of ducts of certain glands

Simple Columnar Epithelium

• Simple columnar epithelium consists of a single layer of cells that are longer than they are wide and elongated nucleus located near the basement membrane

• Simple columnar epithelium can be ciliated or non-ciliated

• Some simple columnar epithelium have microvilli

• Some simple columnar epithelium contains Goblet cells which secrete mucus

• Simple columnar epithelium is found in the linings of the uterus, stomach, and intestines

• Simple columnar epithelium enables transportation, absorption, secretion and protection

Pseudostratified Columnar Epithelium

• Pseudostratified columnar epithelium appears stratified, however its nuclei are at 2 or more levels

• Pseudostratified columnar epithelium is not stratified because all cells touch basement membrane

• Pseudostratified columnar epithelium is often ciliated

• Pseudostratified columnar epithelium has goblet cells

• Pseudostratified columnar epithelium allows protection, secretion and movement of mucus

• Pseudostratified columnar epithelium is found in the linings of respiratory systems

Stratified Epithelia

• Stratified epithelia consists of two or more layers of cells

• Stratified epithelia protect regions of wear and tear

• The nature and degree of stratification of stratified epithelia are related to the kinds of physical stresses to which the surface is exposed

• Stratified epithelia is poorly suited for absorption due to thickness

• Stratifed epithelia classification can be done based on the appearance of the top layer of the cells

Stratified Squamous Epithelium

• Stratified squamous epithelium has many layers of flattened cells

• Stratified squamous epithelium regenerates rapidly

• Stratified squamous epithelium experiences sloughing off of old cells and replaced by new cells

• Stratified squamous epithelium provides protection and is located in the outer layer of skin, in the lining of the oral cavity and throat, in the lining of vagina and in the lining of the anal canal

Stratified Cuboidal Epithelium

• Stratified cuboidal epithelium consists of 2 or 3 layers of cuboidal cells

• Stratified cuboidal epithelium provides protection

• Stratified cuboidal epithelium is found in the linings of large ducts of mammary glands, sweat and salivary glands, and in the pancreas

Stratified Columnar Epithelium

• Stratified columnar epithelium: top layer consists of columnar cells

• Stratified columnar epithelium provides protection

• Stratified columnar epithelium is found in the vas deferens, part of the male urethra and part of the pharynx

Transitional Epithelia

• Transitional epithelia can stretch and provides distensibility (stretching) and protection

• Transitional epithelia in non-distended state consist of 4-5 cell layer thick

• Transitional epithelia in stretched state consist of 1-3 layer thickness, but the number of layers remains constant; appearance due to flattening of intermediate and surface layers

• Transitional epithelia basal cells: cuboidal

• The intermediate cells in the transitional epithelia are polygonal

• Surface cells of transitional epithelia are large, rounded and may contain 2 nuclei

• Transitional epithelia provides protection and stretchability

• Transitional epithelia is located in the inner lining of urinary bladder as well as the lining of ureters, and part of urethra