ANAT20006 Gut formation question

[Turtle]

I am just studying my last lecture for the mst.
In lecture 12, last monday's lecture, we spoke about formation of the coelom/gut at one point.

I know the mouth of the fetus forms just after 3 weeks when the oral plate breaks.
I don't know if I missed this, but when does the anus form? Did he say?
I know that the GI tract begins to develop at 1 month, so does the anus form before this?
I know at 3 weeks the proctodeum (which is the pit that forms the anus) has a membrane layer of cells covering it, and that it is not open to the outside world yet.

So my question is, when the oral plate breaks down, and the mouth forms, does the anus form at this time as well? And how does it form? Does the membrane layer of cells break as well like the oral plate?
I have tried looking on google/textbook but it won't tell me, so I would really appreciate a little help.
Thanks for the help

[Russ]

Temporally, oral plate formation is before anus formation. They occur relatively close together, but definitely not simultaneously

[Russ]

If you PM me an email address, I can send you the snippet of my notes I referenced.
Won't let me attach it for some reason

[Turtle]

Thanks Pi, I will PM you now.

[Turtle]

Thanks Pi for that. I understand how the anus forms. I just have 1 quick thing to clarify.

I wrote down that GI tract forms at around 1 month, and that the yolk sac is still connected to the yolk stalk at this point.

The mouth and anus have already formed haven't they, if they form at around 3 weeks, even though the yolk sac hasn't separated at 1 month?

[Russ]

Embryology isn't my field but in the process of the GIT forming, the yolk sac will break off. Initially, as the gut forms, the lumen will be connected to that of the yolk sac but will then separate and the 'pursestring' is lost and you get the distinct sac

[Turtle]

Thanks Russ, much appreciated!
So before the yolk sac breaks off, has the anus already formed? I assume it has since it forms around 3 weeks, and the GI tract forms around a month.
Sorry if I sound stupid, but this topic is really quite confusing.

[Russ]

It depends on what you mean by "anus". At week 4 you get the fore/mid/hindgut which are still attached to the yolk sac. This isn't really an anus per se. There's a pit where it will be, but it can't be considered an anus.