Histology lecture II Epithelial tissue (Epithelium) Prepared by Dr. Mohamed Abdalla Eltayeb College of medicine Taibah University 1 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 2 Dr. Mohamed Abdalla Eltayeb Surface layer of keratin without nucleated cells Stratified squamous keratinized epithelium Location:- Basement membrane Skin Connective tissue 3 Dr. Mohamed Abdalla Eltayeb Surface cells are nucleated living squamous cells without keratin Stratified squamous nonkeratinized epithelium Location:- Oral cavity and oesophagus Basement membrane 4 Connective tissue Dr. Mohamed Abdalla Eltayeb 2. Stratified columnar epithelium In stratified columnar epithelium the cells of the surface layer of the epithelium are columnar. This type of epithelium is found in few locations in the body e.g. ducts of salivary glands . Dr. Mohamed Abdalla Eltayeb 5 Stratified columnar epithelium Surface layer of columnar cells Connective tissue 6 Dr. Mohamed Abdalla Eltayeb 3. Transitional epithelium This type of epithelium is found in the urinary system (ureter and urinary bladder). It is protective and impermeable. The cells of the surface layer may be squamous or large dome-shaped. The cells of the surface layer are large with a rounded free border in the contracted urinary bladder The surface cells change to squamous (flat) in a stretched or distended bladder. 7 Dr. Mohamed Abdalla Eltayeb 3. Pseudostratified ciliated columnar epithelium Consists of a single layer formed of two types of cells:- 1. Tall columnar ciliated cells 2. Short cells All cells rest on the basal lamina but the short cells do not reach the surface of the epithelium The nuclei of the tall cells are situated at a higher level than those of the short cells (pseudostratified) Found in the upper respiratory tract. It is protective and secretory. 8 Dr. Mohamed Abdalla Eltayeb 3. Pseudostratified ciliated columnar epithelium (Location: trachea) Tall columnar Cilia ciliated cells Short cells 9 Connective tissue Dr. Mohamed Abdalla Eltayeb 2. Epithelial glands (Glandular epithelium) Glands are epithelial cells specialized for synthesis and secretion of enzymes, hormones or mucus Glands are classified into two groups:- 1. Exocrine glands (with ducts) 2. Endocrine glands (without ducts) Dr. Mohamed Abdalla Eltayeb 10 Exocrine glands Exocrine glands secrete their products into a system of ducts which carry the secretion to the surface of epithelial membrane The secretory units may be in the form of a tubule (tubular gland) or rounded structure called acinus (acinar gland) (alveolus : alveolar gland). 11 Dr. Mohamed Abdalla Eltayeb Classification of exocrine glands There are two types of exocrine glands:- 1. Simple gland: has single unbranched duct 2. Compound gland: has a branched duct Dr. Mohamed Abdalla Eltayeb 12 Types of simple glands Simple tubular gland e.g. colon Simple coiled tubular gland e.g. sweat gland Simple branched tubular gland e.g. stomach Simple acinar gland e.g. urethra Simple branched acinar gland e.g. skin 13 Dr. Mohamed Abdalla Eltayeb Simple glands Sebaceous gland Sweat gland (skin) Colon Stomach (skin) Urethra Simple Simple Simplebranched Simplecoiled Simple tubular acinar tubular tubular branched Compound Glands acinar Duodenum Pancreas Salivary gland Single duct connects the secretory unit to the surface of epithelial membrane Compound tubular Dr. Mohamed Abdalla Eltayeb 14 Compound acinar Compound tubuloacinar Types of compound glands There are 3 types of compound glands:- 1. Compound tubular gland e.g. duodenum 2. Compound acinar (alveolar) gland e.g. pancreas 3. Compound tubuloacinar (tubuloalveolar) gland has both types of secretory units (tubule and acinus) e.g. salivary gland. 15 Dr. Mohamed Abdalla Eltayeb Sebaceous gland Simple Glands Sweat gland (skin) CompoundColon Stomach glands(skin) Urethra The duct is branched inside the gland to Simplecollect the secretion from theSimple secretory units Simplebranched Simplecoiled Simple tubular acinar tubular tubular branched acinar Duodenum Pancreas Salivary gland Compound tubular 16 Compound acinar Compound tubuloacinar Classification of exocrine glands according to the type of secretion There are 3 types according to type of secretion:- 1. Serous gland: secretes a thin watery secretion e.g. pancreas 2. Mucous gland: secretes a thick viscous secretion called mucus e.g. sublingual salivary gland 3. Mixed (mucoserous) gland: secretes a mixture of mucus and serous secretions e.g. submandibular salivary gland. 17 Dr. Mohamed Abdalla Eltayeb Classification of exocrine glands according to method of secretion There are 3 types of glands :- Holocrine gland:- the cells die and the contents become the secretion e.g. sebaceous glands in the skin which secrete oil Merocrine gland:- secretion of enzymes or hormones by exocytosis e.g. pancreas Apocrine gland:- the apical part of the cell containing secretion separates from the cell e.g. secretion of milk lipids in the 18 mammary gland. Dr. Mohamed Abdalla Eltayeb Thank you END Dr. Mohamed Abdalla Eltayeb 19.