Lecture note : Epithelium summarized for viva examination

 Epithelium

Characters/features  of epithelial tissue

1. Avascular
2. Cell are closely apposed and adhere to one another by cell junctions
3. Basal surface of cells are attached to an underlying basement membrane
4. Cells of epithelium has surface domain:a free surface or apical domain, a lateral domain &a basal domain.
5. This tissue has nerve supply.
6. They derived from all three germ layers ****

•          from ectoderm: epidermis of skin

•          from mesoderm: endocardium of heart

•          from endoderm: lining epithelium of gastrointestinal tract

Functions of epithelium:

•       Covering and lining of surfaces –(skin, intestines), Absorption - (intestines), Secretion- (glands)

•       Sensation-(gustative and olfactory neuroepithelium), Contractility- (myoepithelial cells)

•       Transport –(pseudostratified ciliated columnar epithelium)

  Classification of epithelium:

    Epitheliums are two types

    1. covering epithelium and 2. glandular epithelium

 Covering epithelium                                             Glandular epithelium is developed from covering epithelium

 

Classification of covering epithelium

 

They are two types:

simple epithelium (cells are arrange in single layer )	Stratified epithelium (cells are arrange in multiple layer)
1.       Simple Squamous epithelium 2.       Simple Cuboidal epithelium 3.       Simple columnar epithelium 4.       Pseudo-stratified ciliated columnar epi.	1.       Stratified Squamous epithelium a)keratinized stratified squamous epithelium b) non-keratinized stratified squamous epithelium 2.       Stratified Cuboidal epithelium 3.       Stratified columnar epithelium 4.       Transitional epithelium

Distribution of different types of simple epithelium

Types of epithelium	Features and Location
Simple Squamous epithelium	Flat cells rest on basement membrane Centrally placed flat nuclei  endothelium (inner lining of vessels) endocardium (inner most layer of heart) mesothelium (lining  of peritoneum)
Simple Cuboidal epithelium	Height  & breath of cells are equal Round nuclei & centrally placed Thyroids follicles, surface of ovary
Simple columnar epithelium	Height of cells are more than the breath of the cell Oval nuclei are basally placed Lining epithelium of stomach, small intestines, colon
Pseudostratified ciliated columnar  epi.	Why is it look like stratified epithelium ? some cells are larger & some are smaller so nuclei of this epithelium are situated at different level so it looks like stratified epithelium  Ex: lining epithelium  of trachea, bronchi, epididymis, vas deferens

Distribution of different types of stratified epithelium

Types of epithelium	Features and Location
Stratified Squamous epithelium 1)non-keratinized stratified squamous epithelium                   2) keratinized stratified squamous epithelium	1.        Many layers of cells are present . from basal to apical region cells size are gradually decreases 2.        basal region is irregular &  3.        cells of basal region are larger but apical cells layer are squamous in shape 4.        Surface cells are alive ,nucleated and squamous in shape 5.        It found in wet surface Ex: lining epi of esophagus and vagina, oral cavity 1.        Many layers of cells are present . from basal to apical region cells size are gradually decreases 2.        basal region is irregular &  3.        cells of basal region are larger but apical cells layer are squamous in shape  4.        no nucleated live cells are present at the  surface 5.        it found in dry surface EX: epidermis of skin
Stratified Cuboidal epithelium	Sweat glands duct, large ducts of exocrine glands
Stratified columnar epithelium	Ocular conjunctiva, large ducts of salivary glands, penile part of male urethra
Transitional epithelium	·         Surface cells are dome shaped ·         In empty urinary bladder, they are 5-6 layers ·         But in during distended bladder they are 3-4 layer Ex: Ureter, urinary bladder