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【多选题】
Why is the polarity crucial for epithelial function?
A.
The apical and basal faces of an epithelium are different: each contains a different set of molecules that reflect the polarized organization of the individual epithelial cells: each has a top and a bottom, with different properties and functions. This polarity is crucial for epithelial function.
B.
For example, the simple columnar epithelium that lines the small intestine of a mammal. It mainly consists of two intermingled cell types: absorptive cells, which take up nutrients, and goblet cells (so called because of their shape), which secrete the mucus that protects and lubricates the gut lining. Both cell types are polarized.
C.
The absorptive cells import food molecules from the gut lumen through their apical surface and export these molecules from their basal surface into the underlying tissues. To do this, absorptive cells require different sets of membrane transport proteins in their apical and basal plasma membranes. The goblet cells also have to be polarized, but in a different way: they have to synthesize mucus and then discharge it from their apical end only; their Golgi apparatus, secretory vesicles, and cytoskeleton are all polarized so as to bring this about.
D.
For both types of epithelial cells, polarity depends on the junctions that the cells form with one another and with the basal lamina. These cell junctions in turn control the arrangement of an elaborate system of membrane-associated intracellular proteins that create the polarized organization of the cytoplasm.
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【单选题】曲线半径为800m,圆曲线正矢最大最小值差允许偏差作业验收为()mm
A.
4
B.
5
C.
9
D.
15
【简答题】The ______ Approach emphasizes on oral skills use of only the target language in the classroom.
【多选题】货币的职能包括
A.
价值尺度
B.
流通手段
C.
支付手段
D.
贮藏手段
E.
世界货币
【多选题】货币的职能包括
A.
支付手段
B.
流通手段
C.
贮藏手段
D.
价值尺度
【简答题】货币的职能包括( )。
【多选题】货币的职能包括:
A.
价值尺度
B.
流通手段
C.
支付手段
D.
信用手段
【多选题】货币的职能包括 :
A.
价值尺度
B.
流通手段
C.
贮藏手段和支付手段
D.
货币层数
【判断题】各种类型的碳单质几乎拥有地球上所有物质所具有的性质,有的甚至是完全对立的性质。
A.
正确
B.
错误
【简答题】货币的职能包括( )。
【单选题】.– She was in clas on Friday afternoon, but no one has seen her since. ---She _____ an accident.
A.
might have
B.
might have had
C.
may have
D.
ought to have had