Epithelial tissue (Epithelium)

Transcription

1 Histology lecture I Epithelial tissue (Epithelium) Prepared by College of medicine Taibah University 1

2 1.Epithelial tissue (epithelium) Epithelial tissue is one of the 4 basic tissues of the body. Epithelial tissue exists in two forms:- 1. EPITHELIAL MEMBRANES 2. EPITHELIAL GLANDS 2

3 Epithelial membranes (epithelium) Epithelial membranes are continuous sheets of cells in contact with air (e.g. skin and respiratory system) or with fluid (e.g. stomach and urinary bladder). The cells of the epithelial membrane are attached together by cell junctions Epithelial membranes are avascular. They receive nutrition from blood capillaries present in the undrlying connective tissue. 3

4 Basal lamina and basement membrane Epithelial cells secrete a glycoprotein layer called basal lamina which separates them from the connective tissue. The basal lamina is seen only with the electron microscope (EM) and is not visible with the light microscope. The connective tissue close to the basal lamina is called basement membrane seen with the light microscope (LM). 4

5 Classification of epithelial membranes According to the number of cell layers:- 1. Simple:- single layer of epithelial cells. 2. Stratified:- more than one layer of cells. 3. Pseudostratified:- single layer of tall & short cells. 5

6 Classification of simple epithelium According to shape of cells in histological sections:- 1. Simple squamous epithelium: single layer of flattened cells e.g. peritoneum. 2. Simple cuboidal epithelium:- single layer of squared cells e.g. kidney. 3. Simple columnar epithelium:- single layer of rectangular cells e.g. stomach. 4. Simple columnar epithelium with goblet cells e.g. small intestine 6

7 Simple squamous epithelium Location:- Blood vessels (Called endothelium) Body cavities (Called mesothelium) Kidney Lung Function:- Diffusion, Secretion, Transport Single layer of squamous cells with flat nuclei Connective tissue 7

8 Simple cuboidal epithelium Single layer of cuboidal cells(squares) with round nuclei Thyroid gland Ducts in the kidney Ducts of exocrine glands Location:- Function:- Secretion and absorption 8

9 Simple columnar epithelium Single layer of columnar cells (rectangular) with oval nuclei Connective tissue Basement membrane Location:- Stomach and gall bladder Function:- Secretion and absorption 9

10 Goblet cell A goblet cell is a unicellular gland which synthesizes and secretes mucin. Mucin is stored in the cytoplasm until it is secreted and changed to mucus on the surface of the epithelium. Mucus protects against foreign material Goblet cells are found in the epithelium of the intestine and upper repiratory tract 10

11 Simple columnar epithelium with goblet cells Nuclei of columnar cells Goblet cells Basement membrane Nucleus of goblet cell 11

12 Stratified epithelium Stratified epithelium consists of 2 or more layers of epithelial cells. According to the shape of cells of the surface layer there are 3 types of stratified epithelia:- 1. Stratified squamous epithelium 2. Stratified columnar epithelium 3. Transitional epithelium 12

13 1. Stratified squamous epithelium The surface layer consists of squamous cells. It is a protective epithelium. There are two types of stratified squamous epithelium:- 2. Stratified squamous keratinized epithelium : the cells of the surface layer are dead cells consisting of keratin which is a type of protein e.g. skin 1. Stratified squamous non-keratinized epithelium: the cells of the surface layer are nucleated living cells and do not form keratin e.g. oesophagus 13

14 Surface layer of keratin without nucleated cells tratified squamous keratinized epithelium Basement membrane Connective tissue Location:- Skin 14

15 The rest of this lecture is uploaded as Histology lecture II 15