Introduction into Histology PDF

Introduction into Histology By Dr.Alaa Al-sahlany M.Sc. Dermatology Boston, USA Nov. 08, 2021 1 Tissues are groups of cells organized to perform one or more specific functions There are four basic types of tissue: Epithelium (epithelial tissue) covers body sur...

Introduction into Histology By Dr.Alaa Al-sahlany M.Sc. Dermatology Boston, USA Nov. 08, 2021 1 Tissues are groups of cells organized to perform one or more specific functions There are four basic types of tissue: Epithelium (epithelial tissue) covers body surfaces, lines body cavities, and forms glands. Muscle tissue is made up of contractile cells and is responsible for movement Nerve tissue receives, transmits information to control the activities of the body Connective tissue underlies or supports the other three basic tissues 2  Epithelial tissue Epithelium covers body surfaces, lines body cavities, and constitutes glands The cells that make up epithelium have three principal characteristics: (1)They adhere to one another by cell junctions (2)They exhibit polarity: apical polarity, a lateral polarity, and a basal polarity. (3) Their basal surface is attached to an underlying basement membrane 3  Basement membrane Is a specialized structure located next to the basal part of epithelial cells and the underlying connective tissue stroma. Composed of: (a) basal lamina (amorphous substance) – product of epithelium (b) reticular lamina (reticular fibres) – product of connective tissue. 4 Epithelium is made of either single layer(simple) or many layers of cells(stratified). Epithelial cells are adherent to each other by means of intercellular junctions(junctional complexes). The deep surface (basal) of the epithelium rests on a basement membrane, which separates it from the vascular connective tissue. No blood vessels nor lymphatics are found in the epithelium; nourishment is provided by diffusion from the adjacent supporting connective tissues. Epithelium has good regenerative capacity. Its nuclear shape corresponds to cell shape (nuclei are oval in columnar cells, round in cuboidal , and flat in squamous cells). Epithelium can invaginate and subsequently grows into glands. 5 Epithelium may undergo morphological and functional changes from one type to another type(metaplasia) Epithelium is derived from all three germ layers: Skin – ectoderm Respiratory and digestive systems – endoderm Cardiovascular system – mesoderm 6  Metaplasia Smoking cause chronic irritation of respiratory epithelium and consequently cause metaplasia The superficial surface (apical) of the epithelium is free and exposed to air or fluid and often shows modifications (i.e. presence of microvilli or cilia) depending upon the function it is destined to perform Surface modifications are listed in the next table 7  Surface Functions modifications 1. Glycocalyx ▪ Surface coat over the absorptive epithelium of small intestine( (cell coat) rich in polysaccharides and hydrolytic enzymes). ▪ Acts as receptor sites for hormones and enzymes. 2.Microvilli (brush ▪ minute finger-like projections of the cell membrane border) ▪ Increase the surface area for absorption (intestine) 3. Stereocilia ▪ Very long, thick microvilli, non-motile, ▪ Increase the surface area (inner ear) 4. Cilia ▪ long hair-like projections of cell membrane ▪ Move towards one direction, thereby moving the entangled particles (beat towards pharynx in respiratory tract and towards uterus in uterine tube) Microvilli Cilia Motility Non-motile Motile Composition Composed of Composed of microtubules microfilament Function Absorption Moving the particles in one direction Example Intestinal epithelium Respiratory tract Kidney Uterine tube 8  Primary ciliary dyskinesia Not included in the exam Celiac disease Gluten sensitivity Atrophy of microvilli cause decreased intestinal absorption and chronic diarrhea Not included in the exam 9  INTERCELLULAR JUNCTIONS (JUNCTIONAL COMPLEXES) Name of junction Type of junction Function Zonula occludens (tight junction) Occluding junction Seals adjacent cells between cells together Zonula adherens Anchoring junction Couple between cells microfilaments to basement membrane at site of cell-cell adhesion Name of junction Type of junction Function Macula adherens Anchoring junction Couple the intermediate (desmosomes) between cells filaments to basement membrane at site of cell- cell adhesion Gap junction(nexus) Communicating junction Create a conduct for between cells passage of ions and molecules between adjacent cells 10  Pemphigus Skin disease due to damage in macula adherens Not included in the exam 11