Human Anatomy Epithelial Tissue Quiz

Basic Tissue Types

• The human body has four main tissue types: epithelial, connective, muscular, and nervous.
• Each tissue type contains specialized cells performing specific functions.
• Each tissue type has its own unique ECM (extracellular matrix).

Characteristics of Connective, Muscle, and Nervous Tissues

• Connective tissue is characterized by cells producing abundant ECM.
• Muscle tissue is composed of elongated cells for contraction and movement.
• Nervous tissue comprises cells with long processes for receiving, generating, and transmitting nerve impulses.

Parenchyma and Stroma in Organs

• Organs are composed of parenchyma and stroma.
• Parenchyma contains cells responsible for the organ's specialized functions.
• Stroma is mainly connective tissue, supporting the parenchyma (except brain and spinal cord).

Composition and Function of Epithelial Tissues

• Epithelial tissues are composed of closely grouped, polyhedral cells.
• They adhere strongly to each other and a thin ECM layer.
• They form sheets lining body cavities and surfaces.
• Substances entering or leaving an organ must cross epithelial tissue.

Principal Functions of Epithelial Tissues

• Covering, lining, and protecting surfaces (e.g., skin epidermis).
• Absorption (e.g., intestinal lining).
• Secretion (e.g., glandular cells).
• Some epithelial cells are contractile (myoepithelial cells) or specialized sensory cells (e.g., taste buds).

Characteristic Features of Epithelial Cells

• Epithelial cells vary in shape (columnar, cuboidal, squamous).
• Cell morphology relates to cell function.
• Cell nuclei shapes depend on cell morphology (elongated nuclei for columnar cells, flattened nuclei for squamous cells).
• Microscopically, light microscopy often identifies cells by the stained nuclei.

Epithelial Tissue Adjacency to Connective Tissue

• Epithelia are usually adjacent to blood-vessel-containing connective tissues for oxygen and nutrient supply.
• Thick epithelia generally do not have blood vessels.
• The underlying connective tissue is called lamina propria.
• Increased contact between epithelial and connective tissues is ensured by papillae.
• This arrangement is often found in friction-prone epithelial tissues.

Polarity and Structural Aspects of Epithelial Cells

• Epithelial cells display polarity, with unequal organelle distribution.
• The basal pole of cells faces the ECM and connective tissue.
• The apical pole generally faces external space or a cavity.
• Lateral surfaces of cells often have folded membranes to maximize surface area, enhancing functional capacity.

Basement Membranes in Epithelial Tissues

• The basal surface of epithelial cells rests on the basement membrane.
• This is a thin ECM sheet with a basal lamina (electron-dense, close to cells) and a reticular lamina (deeper, more fibrous layer).
• The basement membrane acts as a semipermeable filter.
• It plays a role in regulating exchange processes and attaching epithelia to connective tissue.
• Contains glycoproteins.

Reticular Lamina and Collagen Types

• The reticular lamina contains type 3 collagen.
• It's connected to the basal lamina via anchoring fibrils (type 7 collagen).
• Components of the reticular lamina are produced by connective tissue cells.
• Components of the basal lamina are produced by epithelial cells.

Functions of Basement Membranes

• Acts as a filter for substances.
• Supports epithelial cells.
• Connects epithelia to the underlying connective tissue.
• Assists in cell polarity organization and other functions (endocytosis, signal transduction).

Intercellular Adhesion and Junctions in Epithelial Cells

• Epithelial cells adhere strongly using intercellular junctions.
• Lateral surfaces of epithelial cells have specialized intercellular junctions.
• Tight, adherent, and gap junctions are common types.

Types of Intercellular Junctions

• Tight junctions form a seal between adjacent cells.
• Adherent junctions facilitate strong cell adhesion.
• Gap junctions allow communication between adjacent cells.

Order and Structure of Junctions in Epithelia

• Junctions (tight junctions, adherens junctions, desmosomes) are arranged with tight junctions forming the apical barrier.
• Other anchoring junctions appear below the tight junctions.
• The specific types and arrangement of these junctions vary depending on the epithelial tissue's specific needs.

Function of Tight Junctions in Epithelial Transport

• Tight junctions limit paracellular transport.
• The extent of permeability is determined by the number of sealing strands, which vary between epithelial tissue types.

Function of Epithelial Tight Junctions as Membrane Fences

• Tight junctions restrict lipid and protein movement between the different cell surfaces of an epithelium (apical, lateral, and basolateral).
• They maintain two distinct membrane domains.

Adherens Junctions (Zonula Adherens)

• Adherens junctions anchor cells to neighbors, located below tight junctions.
• Cell adhesion is mediated by cadherins.
• Cadherins bind to catenins, anchoring to actin filaments.

Desmosomes (Macula Adherens)

• Desmosomes are disk-shaped anchoring junctions.
• They consist of desmogleins and desmocollins (cadherin family members).
• They provide strong cellular adhesion, especially notable in tissues that experience friction and stress.

Gap Junctions and Intercellular Communication

• Gap junctions mediate communication between cells.
• Transmembrane proteins (connexins) form connexons.
• These channels allow small molecules to pass between cells.
• These junctions facilitate coordinated activities (e.g., rhythmic contractions in heart muscle).

Hemidesmosomes and Basal Epithelial Attachment

• Hemidesmosomes anchor epithelial cells to the basal lamina.
• They are similar to half-desmosomes and involve integrins that bind to the lamina's laminin.

Focal Adhesions in Epithelial Repair and Reorganization

• Focal adhesions are basal anchoring junctions.
• These junctions link integrins to actin filaments.
• They are involved in epithelial repair and reorganization processes.

Specializations of the Apical Cell Surface in Epithelial Cells

• Apical cell specializations often reflect a cell's specific function.
• Microvilli are common in absorptive epithelia, increasing surface area.
• The brush border on epithelial cells is a dense array of microvilli.