Epithelium PDF

Epithelium Dr/ Mohammed Ghazy  Tissues  There are 4 primary tissue types in the human body: 1. Epithelial (covering/lining) 2. Connective (support) 3. Muscle (movement) 4. Nervous (control) Epithelial Tissue  Covers the surface of the body, lines...

Epithelium Dr/ Mohammed Ghazy  Tissues  There are 4 primary tissue types in the human body: 1. Epithelial (covering/lining) 2. Connective (support) 3. Muscle (movement) 4. Nervous (control) Epithelial Tissue  Covers the surface of the body, lines the body cavities, forms the external and internal linings of most organs, and constitutes the bulk of most glands.  Functions include: 1. Protection 4. Absorption 2. Secretion 5. Filtration 3. Sensory reception  General Features : - Maximum cell-to-cell contact. - Minimum extracellular material. - Cell junctions: Several types of junctional unite (tight junctions, desmosomes and gap junctions). - Supported by basement membrane (basal lamella). - Avascular: There are no blood vessels within the epithelial layer. - Derived from all embryonic germ layers, including endoderm, mesoderm and ectoderm With the exception of endocrine glands  All epithelia have one free surface, called the apical surface, which is exposed at the body surface or at the lumen of the body cavity, duct, tube or vessel.  The basal surface of epithelium rests on a basement membrane: a non-living adhesive material secreted by the epithelium and the underlying connective tissue.  These cells are often characterized by frequent cell division because they are exposed to wear and tear and injury, necessitating replacement.  How to classify epithelia 1- Number of cell layers present  one layer of cells =simple.  more than one layer = stratified. 2- Shape of the cells in the apical layer. There are 3 cell shapes: 1. Squamous = flat, scale-like 2. Cuboidal = cube-shaped 3. Columnar = column-shaped Types of epithelium tissues 1- simple - Simple squamous. - Simple cuboidal. - Simple columnar. - Simple columnar ciliated. - Pseudostratified columnar. 2- Stratified - Stratified squamous keratinized. - Stratified squamous non-keratinized. - Stratified cuboidal. - Stratified columnar. - Stratified columnar ciliated. - Transitional epithelium.  Simple Squamous Epithelium  Appearance:  Single layer of flattened cells.  Functions:  Friction Reduction  Filtration  Secretion  Location  Alveoli of lungs  Kidneys  3P (peritoneum, pericardium and pleura).  Endothelium of blood vessels.  Stratified Squamous Epithelium  Microscopic Appearance:  Multiple cell layers with cells becoming flatter toward surface.  keratinized stratified Dead cells at surface  Nonkeratinized stratified squamous This is keratinized stratified squamous No dead cells at epithelium from the sole of the foot. It surface extends the length of the blue line on the left. Notice the multiple layers of clear, dead, enucleated cells.  Location of keratinized version:  Epidermis of skin.  Locations of non-keratinized version:  all opening on the skin (male and female), as oral cavity and esophagus, anal canal, vagina, cornea of the eye and so on. Which of these is keratinized and which is non- keratinized stratified squamous epithelium?  Simple Cuboidal Epithelium  Appearance:  Single layer of square or round cells.  Centrally-placed spherical nuclei.  Locations: a) None ciliated; as thyroid follicles, kidney tubules (proximal and distal). b) Ciliated; lining central canal of spinal cord. Simple Cuboidal Epithelium Cross-Section of a kidney tubule Stratified Cuboidal Epithelium  Microscopic Appearance:  2 or more layers of cells.  Surface layers are square or round (cuboidal).  Locations:  1) Lines ducts of sweat gland.  2) Lines ducts of the mammary gland (breast).  Functions  PROTECTION  Secretion = Sweat and Hormones  Simple Columnar Epithelium  Appearance:  Single layer of tall, narrow cells.  Oval basal nuclei.  Locations: a)Ciliated: as Fallopian tube and uterus. b) Non ciliated: for absorption as in small intestine and others cells can secrete as stomach or protection as in gall bladder  Stratified Columnar Epithelium  Microscopic Appearance:  2 or more layers of cells.  Surface cells tall and narrow with basal nuclei.  Locations:  In penile urethra, main ducts of salivary glands, fornix of conjunctiva and terminal part of the rectum. NB: Uncommon type (stratified columnar ciliated) can present in fetal esophagus.  Pseudostratified Columnar Epithelium  Appearance:  Mixture of Cells Nuclei are at several levels, cilia, goblet cells  Functions: Trap dust, secrete mucus  Locations:  Respiratory tract from nasal cavity to bronchi.  Transitional Epithelium  Appearance:  Layered  Typically 5-6 cell layers thick when relaxed and 2-3 cell layers thick when stretched.  Some cells are binucleate, i.e., they have 2 nuclei.  Locations:  In the urinary passage (called urothelium) as renal pelvis, ureter, urinary bladder and prostatic part of the urethra.  Glandular epithelium - Generally formed by down growth of surface epithelium into underlying connective tissue, and separated from connective tissue by basal lamina.  Classification of glands: 1- According to presence or absence of ducts: - Exocrine glands (have duct system) - Endocrine glands (ductless) secrete hormones glands. 2- According to Nature of secretion: - Serous secretion: secret watery fluid rich in protein (parotid glands) - Mucous secretion: secret mucus; poor in protein (goblet cells) - Muco-serus secretion: as in mixed salivary glands - Milky secretion: mammary gland - Wax secretion: glands in external ear - Fatty secretion: sebaceous glands - Watery secretion: sweat glands - Cellular secretion: ovary and testis. 3- According to mode of secretion: - Apocrine glands: a small portion of the apical cytoplasm discharged with the secretory products. e.g. Mammary glands and some sweat glands. - Holocrine glands: discharge whole cell; sebaceous glands (sebum). - Merocrine glands: in which secretion occurs by exocytosis; i.e. no cellular changes as parotid glands.  Modes of Glandular Secretion What is lost during secretion? Apocrine Merocrine Holocrine  Apocrine Secretion Cytoplasm & secretion are excreted Figure 4–6b  Merocrine Secretion Secretory products secreted via vesicular exocytosis – Most common form of secretion – often continuous – Ex: Pancreatic cells, sweat, saliva Figure 4–6a  Holocrine Secretion Entire cell lost with secretion. – Stem cells divide to replace lost cells – Ex: Sebaceous glands Figure 4–6c 4- According to Number of cells: - Unicellular glands (goblet cells) secrete mucus. - Multicellular glands that can be further classified according to the shape of secretory portion into: - A- Simple tubular gland: large intestine. B- Simple coiled tubular gland: sweat glands. C- Simple acinar (alveolar) gland: (rounded secretory unit) mucus-secreting glands of penile urethra D- Simple branched tubular gland: stomach. E- Simple branched acinar gland: sebaceous gland F- Simple branched tubulo-alveolar glands: glands of oral cavity. G- Compound tubular gland: liver, kidney H- Compound acinar (alveolar) gland: mammary gland I- Compound tubulo-acinar gland: pancreas