- State the principle characteristics of epithelial tissue
- Cell junctions – The cells closely adhere to each other through cell-to-cell adhesion molecules that form junctions
- Polarized – Exhibit polarity in 3 distinct domains. The properties of which are determined by specific lipids and integral membrane proteins.
- Apical domain
- Lateral domain
- Basal domain
- The basal surface is attached to an underlying basement membrane
- Describe the apical specialization of epithelial tissue and give examples of their respective locations
- Microvilli: Cytoplasmic projections containing a core of actin filaments. Locations: Intestinal epithelium, Brush border of kidney cells
- Stereocilia: Unusually long, immotile microvilli. Locations: Epididymis, Vas deferens, Sensory (Hair) cells of the inner ear
- Cilia: Cytoplasmic projections containing bundles of microtubules
- Motile cilia: 9 + 2 (Axoneme) arrangement of microtubules. Function to transport secretions, proteins, foreign bodies or cells on their surface. Locations: Oviduct, Trachea, Bronchial Tree, Brain ependyma, Olfactory epithelium
- Primary cilia (Monocila): 9 + 0 pattern of microtubules. A single cilium functioning as a chemoreceptor, osmoreceptor or mechanosensor. Location: Almost all cells of the body, Particularly kidney ducts, bile duct epithelium, thyroid gland, thymus, neurons, Schwann cells, chondrocytes, fibroblasts, adrenal cortex, pituitary cells
- Nodal cilia: 9 + 0 pattern of microtubules. Found in the bilaminar disc of the embryo, in cells concentrated around the primitive node (hence the name) – Establish left-right asymmetry of internal organs.
- Describe lateral specialization of epithelial tissue and their respective functions
- Occluding junctions (Cell-Cell)
- Zona Occludens (Tight Junctions): Seals adjacent cells together, controlling permeability between them
- Anchoring junctions (Cell-Cell)
- Zonula adherens: Joins actin filaments of adjacent cells to the plasma membrane at points of contact
- Macula adherens (Desmosomes): Joins intermediate filaments of adjacent cells to the plasma membrane at points of contact
- Anchoring junctions (Cell-Extracellular Matrix)
- Hemidesmosomes: Joins intermediate filaments of cells to the laminins and collagens of the extracellular matrix
- Communicating Junction (Cell-Cell)
- Gap junction: Creates a channel between 2 adjacent cells for passage of small ions and micromolecules
- Occluding junctions (Cell-Cell)
- State the layers of the basement membrane ***From superficial to deep. Note that some literatures refer to the Basal Lamina and Reticular Lamina collectively as the Basement membrane.
- Basal Lamina
- Lamina lucida: An artefact of chemical fixation as the epithelial cell shrink away from the basal lamina. Contains the cell adhesion molecules fibronectin and laminin receptors.
- Lamina densa: The structural attachment site for the overlying epithelial cells and underlying connective tissue. Electron dense region between the epithelial cells and adjacent connective tissue (Hence the name). In non-epithelial cells (such as muscle cells) it is known as the external lamina. Contain collagen type IV and laminin
- Reticular lamina: A layer of reticular fibers below the basal lamina. Anchors the basement membrane through Type II collagen fibrils
- Basal Lamina
- State three roles of the basement membrane
- Anchors the epithelium to the connective tissue
- Acts as a diffusion barrier, as in the kidneys where the numerously negatively charged molecules prevent the diffusion of negatively charged plasma proteins
- The basement membrane guides cell migration during tissue repair
- Distinguish between basement membrane and basal lamina
- Basement membrane: A description used in light microscopy for the interface between epithelial cells and connective tissue. Includes Basal lamina and the underlying Reticular lamina.
- Basal lamina: A description used in electron microscopy for the layer between epithelia tissue and the underlying reticular lamina.
- Glands can be classified based on mode of secretion. Give examples of the following: Merocrine glands, Apocrine glands, Holocrine glands
- Merocrine glands: Pancreatic acinar cells
- Apocrine glands: Mammary glands
- Holocrine glands: Sebaceous glands of the skin
- Define epithelial metaplasia and give 2 examples
- Epithelial Metaplasia is defined as a reversible conversion of one mature epithelial cell type to another mature epithelial cell type, generally as a response to stress, chronic inflammation, or other abnormal stimuli.
- Columnar-to-squamous (Squamous metaplasia): Occurs in the trachea and bronchi in response to cigarette smoke
- Squamous-to-columnar: Barret’s oesophagus as a result of Gastroesophageal Reflux
- Epithelial Metaplasia is defined as a reversible conversion of one mature epithelial cell type to another mature epithelial cell type, generally as a response to stress, chronic inflammation, or other abnormal stimuli.
