**Question:** Basement membrane consists of all except:

**Core Concept:** Basement membrane is a specialized type of extracellular matrix that provides structural support and acts as a semi-permeable barrier for cells and molecules. It is found in various tissues throughout the body, such as blood vessels, epithelia, and connective tissue.

**Why the Correct Answer is Right:** The correct answer, **D**, refers to the fact that basement membranes are composed primarily of type IV collagen and laminin proteins, along with other glycoproteins and proteoglycans. These components form a network structure that contributes to the membrane's structure and function.

A, B, and C are incorrect because they represent essential components of basement membranes. A: **A. laminin** is a key protein that contributes to the membrane's strength and stability. B: **lamycin** is a hypothetical protein that does not exist and is included for distraction. C: **fibronectin** is another glycoprotein found in basement membranes, contributing to cell adhesion, migration, and tissue repair.

**Why Each Wrong Option is Incorrect:**

A: **Laminin** is a critical component of basement membranes, providing structural support to the membrane and facilitating cell adhesion, migration, and tissue repair.
B: **Lamycin** is a fictitious protein that does not exist. Including it distracts from the correct answer, D.
C: **Fibronectin** is an essential glycoprotein found in basement membranes that aids in cell adhesion, migration, and tissue repair.

**Clinical Pearl:** Understanding the components of basement membranes is crucial for understanding tissue architecture, cell adhesion, and tissue repair processes in various organs and structures.

**Correct Answer:** D. Basement membranes are composed mainly of collagen IV, laminin, and entactin (nidogen). These proteins form a complex network that contributes to the membrane's structure and function, including providing strength, elasticity, and acting as a semi-permeable barrier.