here's a table showing difference bwtween alopecia vs trichotillomania
Here's a GREAT video explaining ultrasound findings of pregnancy. @9:57 is a great picture so far with labels of the yolk sac, gestational sack, fetal pole, and amnion. One thing the person explaining said that I thought would be good to keep in mind is that the yolk sac looks like a cheerio inside the gestational sac. Also, this site has a bunch of pictures as well: https://radiopaedia.org/articles/first-trimester?lang=us.