That's the rough ER, and that's the piece that you may not have been familiar with.
In smooth ER, it's something that typically gets less emphasis overall in cell biology courses,
but it's important for us for a number of reasons in pathologic processes.
So, this smooth ER is a continuum of the rough ER without ribosomes.
It's still the same one organelle. It's one topologic space contiguous with the rough ER.
So, here, we have the rough ER. We have the smooth ER that comes off that.
No ribosomes. In there, besides being a packaging site
for all the newly synthesized proteins coming out of the rough ER,
we're also gonna synthesize lipids and cholesterol-based hormones.
So, the smooth ER is a very prominent organelle in the adrenal gland.
We're gonna be making a whole variety of cholesterol-based hormones.
Aldosterone, for example. And the ovary and the testis.
Clearly, the ovaries are gonna be making estrogen. The testis, going to be testosterone.
So, those are cholesterol-based hormones synthesized by the smooth ER.
And so, very important organelle in those tissues.
The smooth ER is also going to be the site where we are going to solubilize lipid-soluble molecules.
The body has a tough time getting rid of hydrophobic waste.
The way that it does it is by turning it into hydrophilic material,
making various modifications of those compounds so they can now be excreted in the urine.
So, we need to make hydrophobic molecules or lipid-soluble molecules hydrophilic.
And that's done on the smooth ER, typically in the liver.
So, we talk about liver detoxification. It's not detoxification, it's solubilization.
It is making something from hydrophobic to hydrophilic so it can be excreted.
It's also in other tissues such as muscle, gonna be the site where we sequester calcium.
So, the sarcoplasmic reticulum is basically just the smooth ER of skeletal muscle,
and that's where we're gonna hold all the calcium in reserve,
so that when we want the muscle to contract, we release it from the smooth ER.
From the sarcoplasmic reticulum. It's also going to be the waste station.
The collection station, the organization station, between the rough ER and the Golgi apparatus.
So, the Golgi is going to be adding on carbohydrates
and doing other modifications on the proteins.
The packaging stuff coming out of the rough ER,
to get it to the right location in the Golgi so then it can be spit out
and sent to the right location within the cell or to the plasma membrane,
happens in the smooth ER. So, this is not just ER without ribosomes.
It has a lot of very important functions.