Epithelia are connected to underlying connective tissues by
A) protein filaments embedded in glycoprotein only.
B) a basal lamina only.
C) a basement membrane and protein filaments embedded in glycoprotein only.
D) a basement membrane only.
E) a basement membrane, protein filaments embedded in glycoprotein, and a basal lamina.
The correct answer and explanation is :
The correct answer is D) a basement membrane only.
Explanation:
Epithelial tissues are anchored to the underlying connective tissue by a structure called the basement membrane. This specialized structure plays a crucial role in providing support, promoting cell signaling, and controlling the movement of molecules between the epithelium and the connective tissue.
Structure of the Basement Membrane:
The basement membrane is a thin, dense sheet of extracellular matrix that lies between the epithelial cells and the underlying connective tissue. It is composed of two main layers:
- Basal Lamina: This is the upper layer, secreted by the epithelial cells. It consists mainly of proteins such as collagen IV, laminin, and entactin, which provide structural support and help in cell adhesion. The basal lamina acts as a selective filter, controlling the movement of substances between the epithelium and the connective tissue below.
- Reticular Lamina: This layer is produced by the connective tissue cells (such as fibroblasts) and is made of collagen fibers, particularly collagen III, which integrate with the basal lamina. The reticular lamina helps anchor the basement membrane to the connective tissue.
Function of the Basement Membrane:
- Anchorage: The basement membrane physically attaches the epithelium to the underlying connective tissue, preventing the epithelial layer from detaching.
- Barrier Function: It acts as a selective barrier, controlling the exchange of molecules between the epithelial and connective tissues.
- Cell Signaling: The basement membrane influences cellular behavior, such as cell differentiation, migration, and growth, through interactions with integrins and other receptors on the epithelial cell surface.
Why Other Choices Are Incorrect:
- A) Protein filaments embedded in glycoprotein are part of the extracellular matrix but don’t form the primary connection between epithelium and connective tissue.
- B) The basal lamina is part of the basement membrane, but it’s not the only structure connecting epithelia to connective tissue.
- C) The basement membrane and protein filaments are part of the connective tissue’s extracellular matrix but are not the exclusive way epithelia are connected.
- E) While the basement membrane contains the basal lamina and reticular lamina, it is primarily the basement membrane that connects epithelia to the underlying tissue, not the combination of the individual components listed.
Thus, the basement membrane is the key structure that anchors epithelia to the underlying connective tissue, making D) a basement membrane only the correct answer.