What is the Difference Between Basal Lamina and Basement Membrane

The key difference between basal lamina and basement membrane is that basal lamina is composed of two layers while basement membrane is composed of three layers.

Epithelial cells are tightly bound into sheets called epithelia. The extracellular matrix is small and thin and underlies the epithelium. This structure is known as basal lamina. The extracellular matrix is composed of a loose meshwork of type I and III collagen, and the adhesion of the extracellular matrix is required for the survival of epithelial cells, metabolism, and nutrient uptake. The extracellular matrix is composed of glycosaminoglycans, adhesive glycoproteins such as laminin, fibronectin, tenascin, and nidogen, and fibrous proteins such as collagen and elastin. Basal lamina and basement membrane are two main layers made up of extracellular matrix.

CONTENTS

1. Overview and Key Difference
2. What is Basal Lamina
3. What is Basement Membrane
4. Similarities – Basal Lamina and Basement Membrane
5. Basal Lamina vs Basement Membrane in Tabular Form
6. Summary – Basal Lamina vs Basement Membrane

What is Basal Lamina?

The basal lamina is a layer made up of an extracellular matrix secreted by epithelial cells. The basal lamina is visible only through an electron microscope. It consists of two layers: lamina lucida and lamina densa. The Lamina lucida layer is an electron-lucid layer that contains glycoprotein laminin. It is light colour layer closer to the epithelium. Lamina lucida is made up of laminin, integrins, entactins, and dystroglycans. The lamina densa layer is an electron-dense layer composed of type IV collagen. It is dark-coloured and is about 30-70 nanometres thick.

The basal lamina contains anchoring fibres made up of type VII collagen. These extend to the underlying reticular lamina and the loop located around collagen bundles. The basal lamina is composed and maintained by cells that reside on it. It acts as a point of attachment for cells. It also acts as a permeability barrier in the glomerulus during urine production and mediates synaptic adhesion in neuromuscular synapses.

What is Basement Membrane?

The basement membrane is a thin sheet-like structure of the extracellular matrix. It provides support to cells and tissues and acts as a platform for complex signalling. The basement membrane lies between epithelial tissues, mesothelium, endothelium and the underlying connective tissues. It is visible under light microscopy. The basal lamina is composed of basal lamina (lamina lucida and lamina densa) and reticular lamina. The lamina lucida contains glycoproteins, and lamina densa is composed of type IV collagen. Reticular lamina contains fibronectin and is synthesized by cells from underlying connective tissues. The lamina lucida and lamina densa sit on top of the reticular lamina.

The main function of the basement membrane is the anchoring of epithelium to its loose connective tissue, which consists of dermis and lamina propria underneath. Anchoring is achieved through cell-matrix adhesions by substrate adhesion molecules (SAMs). Basement membrane also acts as a mechanical barrier by preventing malignant cells from invading deeper tissues. It also aids in angiogenesis, and the basement membrane proteins accelerate the differentiation process of endothelial cells. Examples of basement membranes include Bruch’s membrane, basilar membrane, Descemet’s membrane, and glomerular basement membrane.

What are the Similarities Between Basal Lamina and Basement Membrane?

• Basal lamina and basement membrane are made up of extracellular matrix.
• They are found in cells.
• Both are visible through an electron microscope.
• Both consist of the two-layer lamina lucida and lamina densa.
• They lie close to connective tissues.
• Both constitute collagen.

What is the Difference Between Basal Lamina and Basement Membrane?

The basal lamina is composed of two layers, while the basement membrane is composed of three layers. Thus, this is the key difference between basal lamina and basement membrane.

Basal lamina consists of lamina lucida and lamina densa, while basal membrane consists of lamina lucida, lamina densa, and reticular lamina layers. So, this is another difference between basal lamina and basement membrane. Besides, the basal lamina is located between connective tissue and the basolateral side of the cell layer, whereas the basal membrane is located between the epithelial tissues (mesothelium and endothelium) and underlying connective tissues.

The below infographic presents the differences between basal lamina and basement membrane in tabular form for side-by-side comparison.

Summary – Basal Lamina vs Basement Membrane

Basal lamina and basement membrane are composed of an extracellular matrix. The basal lamina is a layer made up of an extracellular matrix secreted by epithelial cells. It is composed of two layers, namely lamina lucida and lamina densa layers. It is only visible through an electron microscope. Also, the basal lamina is located between the connective tissue and the basolateral side of a cell layer. Whereas, the basement membrane is a thin sheet-like structure of the extracellular matrix. It consists of lamina lucida, lamina densa, and reticular lamina layers. This layer is visible through both light and electron microscopes. Besides, the basement membrane is located between epithelial tissues and underlying connective tissues. So, this summarizes the difference between basal lamina and basement membrane.

Reference:

1. “Basal Lamina.” An Overview | ScienceDirect Topics.
2. “Basement Membrane: What Is It, How It’s Formed, and More.” Osmosis.

Image Courtesy:

1. “Extracellular Matrix v1.001-labeled” By Sagearbor – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Oral mucosa” By Wiki-minor – Own work (CC BY-SA 3.0) via Commons Wikimedia