Histology Notes

HISTOLOGY: EPITHELIAL TISSUE o Human body composed of 4 basic types of tissue: epithelial, connective, nervous and muscular o Formed by cells and molecules of the extracellular matrix o Connective tissue: characterized by the abundance of extracellular fluid o Organs can be divided by parenchyma (composed of cells for main function of organ) and stroma ( supporting tissue) o Except in brain and spinal cord stroma made of connective tissue o Epithelial tissue: covering, lining protecting surfaces ex: skin, absorption (intestines), secretion (epithelial cells of glands), contractility (myoepithelial cells) o Characteristic features of epithelial cells: o Forms and dimensions range from high columnar to cuboidal to low squamous o Epithelial cells have distinctu nuclei from spherical to elongated or elliptic o Most epithelial lay on connective tissue o In epithelia that line cavity of internal organs, layer of connective tissue called lamina propina. Lamina propina serves to support epithelial tissue and provide nutrition o Connective tissues has small evaginations called papillae. Occur most frequently in epithelial tissues subject to friction ex: covering of skin/tongue o Polarity in epithelial cells
 Region of cell facing connective tissue: basal pole
 Region facing open space: apical side
 Regions on the side called: lateral sides o Basal laminae and basement membrane: o Basal lamina: sheet of extracellular material on basal surface of cells (where it comes into contact with connective tissue) o Consists of dense layer or lamina dense o Basal lamina may have electron lucent layers or lamina lucida o where epithelia are w/o connective tissue basal lamina is thicker due to fusion of basal laminae from each epithelial layer o components of basal lamina:
 laminin: large glycoproteins. Form lace like sheet below basal cells where they are held in place by transmembrane integrins
 type IV collagen: form felt like sheet associated with