I got this great question from one of you and I’m so glad that person brought this up – because it means: a) that person is really understanding things, and b) there’s an error in my slides I need to fix!

Here’s the question

“On the slides, it states that basal lamina anchors epithelium to underlying connective tissue. I am confused as I thought it would be considered the whole basement membrane that does this? If it were to get more specific than just the basement membrane my guess would have been reticular lamina as that is beneath the basal lamina and actually touching the connective tissue.”

SUCH a good question! The student is referring to slide 8, bullet point one:

Here’s the answer.

First: “Basal lamina” is not the same thing as “basement membrane”

I mentioned in lecture (on slide 14) that “basal lamina” is NOT equivalent to “basement membrane.” The basement membrane contains the basal lamina and the reticular lamina, as shown here on slide 12:

Second: there’s this misleading phrase that just won’t die

There’s a phrase that is commonly used in books and in other lectures and at weird cocktail parties: “The epithelium is connected to the underlying connective tissue by the basal lamina.”

That’s not exactly right, and not exactly wrong – but it is misleading, I think – and I certainly should NOT put it in my slides!! And I’ll remove it posthaste.

It’s not exactly right, because it implies there is no reticular lamina – that basal lamina just connects epithelium to any old connective tissue that happens to be underneath it.

It’s not exactly wrong, because the reticular lamina is basically connective tissue (it’s got collagen fibers and extracellular matrix in it!), as shown here on slide 13:

So what’s the take-away short answer?

Epithelial cells sit on a basement membrane. The basement membrane is composed of two layers: a basal lamina (right under the epithelial cells) and a reticular lamina (right under the basal lamina). Underneath the reticular lamina, there is usually some kind of connective tissue.

Oh, and I need to remove that stupid phrase from my slide! Thank you so much to the student who brought this up!