This is an example of a drop-down question, similar in style to that in the mid-sem quiz. However, the questions in the quiz will not be as long as this one! Maximising surface area A key function of the small intestine is to absorb nutrients from digested food. There are a number of specialisations of the small intestine that allow it to do this. Firstly, the small intestine (duodenum, jejunum and ileum) is very long. Secondly, there are a number of smaller and larger projections of cells and tissues that increase the surface area. Particularly noticeable in the jejunum are Blank 1 Question 3[select: , Plicae ciculares, Brush border, Villi, Microvilli] that are folds of the second layer of the gastrointestinal tissue (the Blank 2 Question 3[select: , Muscularis mucosa, Mucosa, Submucosa] ). On top of these are finger-like projections of the Blank 3 Question 3[select: , Muscularis mucosa, Mucosa, Submucosa] called Blank 4 Question 3[select: , Plicae ciculares, Brush border, Villi, Microvilli] .  On the enterocytes (absorptive cells) of the epithelial layer are many projections of the cell membrane called Blank 5 Question 3[select: , Plicae ciculares, Brush border, Villi, Microvilli] .  This is also called a Blank 6 Question 3[select: , Plicae ciculares, Brush border, Villi, Microvilli] .  It is formed from intracellular projections of Blank 7 Question 3[select: , actin microfilaments, microtubules, intermediate filaments] .多重下拉选择题