Epithelial Tissue Thursday, November 22, 2018

Characteristics Polarity Apical surface – faces the lumen or outside environment Have microvilli Absorb or secret substances Ex: lining of kidney tubules & intestines Basal surface – attaches to basement membrane Basal lamina – thin sheet of connective tissue

Characteristics Specialized contacts Fit tightly together to form sheets Tight junctions – Keep cells close together, and proteins on the apical side of the membranes Desmosomes – attach the cells

Characteristics Supported by connective tissue Basement membrane: - reinforces epithelial membrane and helps prevent stretching and tearing Avascular and innervated No blood vessels Has nerve endings Regeneration High regenerative capacity Can divide very quickly and very often

Classification of Epithelial Cells 1. By the number of cell layers simple – one layer stratified – more than one layer 2. By the shape of the cells squamous cuboidal columnar

Simple Squamous Epithelium A single layer of flat cells Lines the body cavities Lines the lungs and capillaries

Simple Squamous Epithelium Endothelium Friction-reducing lining Lymphatic vessels & blood vessels Mesothelium In serous membranes Membranes that line ventral cavity & cover the organs

The green arrow points directly at the nucleus of an endothelial cell The green arrow points directly at the nucleus of an endothelial cell. What type of cell does the purple arrow indicate? 11/22/2018

Simple Cuboidal Epithelium A single layer of cube-like cells Seen in many types of smaller glands and their ducts Also seen in the walls of kidney tubules

Cross-Section of a kidney tubule Lumen Cross-Section of a kidney tubule Above, we have a longitudinal section of a kidney tubule. Notice the almost square-shaped cells . One cell is highlighted for you in red. 11/22/2018

Simple Columnar Epithelium A single layer of tall cells Common modifications: 1 goblet cells – cells that produce mucus that coats the epithelial membrane 2. cilia 3. microvilli Associated with stomach, intestine, uterine, and respiratory tract

Simple columnar epithelium lining the lumen of the gallbladder. 11/22/2018

Pseudostratified Columnar Epithelium A single layer of irregularly shaped columnar cells that appear to be stratified due to the cells having varying heights and the nuclei being at various locations. Often have cilia Found in the lining of the respiratory tract and the male urethra

Pseudostratified Columnar Epithelium 11/22/2018

Stratified Squamous Epithelium Cells at the free edge are squamous and cells closer to the basement membrane are cuboidal or columnar May be keratinized Found in places where friction is common: Outer layer of skin Bottom of feet Throat

Non-keratinized stratified squamous epithelium This is keratinized stratified squamous epithelium from the sole of the foot. It extends the length of the orange line on the left. Notice the multiple layers of clear, dead, enucleated cells.

11/22/2018

Stratified Cuboidal and Columnar Epithelium Rare in the human body Found mainly in ducts of large glands Stratified cuboidal cells from a sweat gland.

Transitional Epithelium Modified, simple squamous epithelium The shape of the cells depends on the amount of stretching Found in urinary bladder

Transitional Epithelium

Identify the following Epithelial tissues. Simple cuboidal Stratified squamous 11/22/2018

Identify the following Epithelial tissue. Transitional Epithelium Distended 11/22/2018

Identify the following Epithelial tissues. Simple columnar Pseudo-stratified columnar 11/22/2018