The Tissue Level of Organization Group of similar

The Tissue Level of Organization • Group of similar cells – common embryonic origin – common function – bound together by intercellular substance • Histology – study of tissues

The Origin of Tissues Morula Blastula Gastrula

4 Basic Tissues Categories • • Epithelial Connective Muscle Nervous

Epithelial Tissue -- General Features • Cover surfaces, line cavities and form glands • FUNCTION – To create tissue that line, cover, protect, secrete. Tend to act as a barrier or covering. • Attached to underlying connective tissue by a basement membrane. • Cells are tightly packed together, to form tight network. • Avascular---without blood vessels – nutrients diffuse in from blood vessels in underlying connective tissue – What does this mean for especially thick epithelia like skin? • Rapid cell division; responsive to environmental stresses. • Named according to the SHAPE and ARRANGEMENT of cells.

Epithelial Tissues and Their Basement Membrane

Simple Squamous Epithelium • Single layer (= SIMPLE) of flat cells (Squamous). – lines blood vessels, form capillary walls, form alveoli. – VERY THIN LAYER--. What is the primary function of this tissue?

Examples of Simple Squamous Epithelium • Surface view of lining of peritoneal (abdominal) cavity • Section through lungs • Why would simple squamous be a good design for alveoli ?

Simple Cuboidal Epithelium • Single layer of cube-shaped cells viewed from the side. • Cuboidal cells usually are found lining/forming gland ducts.

Example of Simple Cuboidal Epithelium • Sectional view of kidney tubules.

Nonciliated Simple Columnar • Unicellular glands =goblet cells secrete mucus – lubricate GI, respiratory, reproductive and urinary systems. • Microvilli = fingerlike cytoplasmic projections on the cell membrane’s top surface. Microvilli are designed to increase surface area to increase absorption.

Example Nonciliated Simple Columnar Epithelium • Section from small intestine The term “brush border” is often used to describe this tissue. Why is having increased surface area along surface of small intestine a good design?

Ciliated Simple Columnar Epithelium • Single layer of rectangular cells with cilia, cilia are locomotive structures that consist of a 9 +2 arrangement of microtubules that are covered with cell membrane. • Mucus from goblet cells moved along by cilia. • Why would we want the bronchi and bronchioli lined with this type of tissue?

Example Ciliated Simple Columnar Epithelium • Section of fallopian tube. • Why would we want this structure lined with cilliated columnar cells?

Stratified Squamous Epithelium • Several cell layers thick • Surface cells flat • Keratinized = surface cells dead and filled with Keratin protein – Examples include the skin (epidermis) and mucous membranes (non-keratinized) What do you think the primary function of this type of epithelium is all about?

Example of Stratified Squamous • Section of vagina

Stratified Cuboidal Epithelium • Multilayered • Surface cells cuboidal – rare (only found in sweat gland ducts & male urethra)

Stratified Columnar Epithelium • Multilayered • Surface cells columnar • Rare (very large ducts & part of male urethra)

Transitional Epithelium • Multilayered • Surface cells varying in shape from round to flat if stretched • Lines hollow organs of the urinary tract that expand from within. • Perfect example is the urinary bladder

Pseudostratified Columnar PSEUDO = FALSE • Single cell layer • All cells attach to basement membrane but not all reach free surface • Nuclei at varying depths Non-Ciliated version found in part of male Urethra and in Vas Deferens Ciliated version found in Trachea

EPITHELIAL Tissues