Introduction of histology.docx

Histology requires use of microscope to view structures in detail and slides needs to be prepared to be viewed such as stain and fix the specimen. 4 basic tissues in the human body Epithelial tissue- covers body surfaces, lines body cavities and forms gland. Connective tissue- supports the other 3...

Histology requires use of microscope to view structures in detail and slides needs to be prepared to be viewed such as stain and fix the specimen. 4 basic tissues in the human body Epithelial tissue- covers body surfaces, lines body cavities and forms gland. Connective tissue- supports the other 3 basic tissues, both structurally and functionally Muscle tissue made up of contractile cells and responsible for movement. Nerve tissue receives, transmits, and integrates information from outside and inside the body to control the activities of the body. Each organ has at least 2 types of tissues and some has all of them. Epithelial tissue Avascular tissue- no blood vessels Covers the exterior body surfaces. Lines internal closed cavities and body tubes such as GI tract. Forms the secretory portion (parenchyma) of glands. Specialised epithelial cells act as receptors for special senses such as hearing, taste, and smell. Functions of epithelial cells includes: Protection (skin) Transport of molecules across epithetical sheets Secretion of mucinogen, hormones, enzymes etc. Absorption of material from lumen such as small intestine. Selective permeability= control of movement of materials between body compartments. Detection of sensations= taste buds, retina in eye and hairs in the ear. Features of epithelial cells Held together by 3 junctional complexes. Tight junction: prevents diffusion of molecules between adjacent cells (near luminal border). Decides what goes from one cell to another. Made of specific protein called claudin. Adherens junctions- continuous belt around the circumference of epithelial cell associated with actin filaments. Desmosomes= exactly same structure as adherens but not associated with actin, instead associated with intermediate filament. Found in epithelial cells subjected to stretching such as skin, uterus etc. Gap junctions- enables exchange of ion in cells with electrical activity. Formed by connexons. Exhibits functional and morphologic polarity. Apical/luminal surface- exposed to the outside of the body or internal cavity its lining L Lateral Lateral surface (junctions are found here) Basal surface- attached to basement membrane (collagen fibres) that anchors it. The basal surface of epithelial cells is attached to a basement membrane that separates epithelial cells from surrounding connective tissues. Classification of epithelial tissues Number of cell layers Simple epithelium- one single layer Stratified epithelium - sheets of epithelial cells Shape of the surface cells Can also have keratinized epithelium meaning the cells on the surface does not have the nucleus anymore and packed with keratin. Function is to impermeabilize. Found in hair, nails etc. *Transitional- only specific to urinary system* Corelation between function and structure of epithelium Apical domain specialization 3 different surface modifications of epithelial cells Microvilli- increases surface area for absorption. Formed by bundle of actin filament. Brush border is seen in optical microscope. Stereocilia- microvilli of unusual length A thick brush borders. Found in male reproductive system- in epididymis that helps with sperm maturation. Also found in the sensory hair of the inner ear and is sensitive to mechanical vibration. Cilia- cytoplasmic processes containing bundles of microtubules. Has 2 functions Motile cilia- transports secretions, proteins Primary cilia- not motile, function as sensory antennae. Cilia is made of microtubules and NOT actin. Epithelial cells can renew. Rate of turnover is specific in different areas (small intestine: 4-6 days) and skin can take up to 47 days). Replacement cells are produced by mitotic divisions of adult stem cells.