系统字体描述如下：

+ (CGFloat)labelFontSize;//Returns the standard font size used for labels.
+ (CGFloat)buttonFontSize;//Returns the standard font size used for buttons.
+ (CGFloat)smallSystemFontSize;//Returns the size of the standard small system font.
+ (CGFloat)systemFontSize;//Returns the size of the standard system font.

您可以更改字体大小而不使用如下字体系列：

and you can change the font size without the font family like this :

cell.textLabel.font = [UIFont systemFontOfSize:14];