There are two types (maybe three) of difficult classes: Classes with a lot of material making the class difficulty due to the volume, Classes with difficult concepts and the third is when these two factors are combined.

Anatomy is an example of a difficult class because of the sheer volume of material that needs to be memorized. Calculus is an example of a class being difficult because the concepts are hard for most people to grasp. Biochemistry is an example of a class with a tremendous volume and contains relatively complicated math. So biochemistry is difficult because it is a combination of volume and subject matter.

While I have never taught calculus or anatomy I have taught multiple levels of biochemistry. It is difficult to teach because for the classes I was teaching it was required by the students and less than a favorite. My goal for the students was to make the class as relevant as possible and to try to keep them engaged.

When I was teaching biochemistry to medical students I would make references to clinical maladies and relate biochemical changes to clinical manifestations. Quite simply every chemical reaction in the human body is needed for normal bodily function. If defective or absent medical problems often occur and bringing in such examples make the class and lecture more interesting for the students.

Teaching with real life examples or case studies is a common teaching method, but the down side is that it can take up a lot of time. So the choices for such examples need to be chosen carefully. This is especially poignant because of the large volume of material that must be covered. As discussed earlier this is a classic example of combining volume of material with complicated subject matter makes the class hard for the students and difficult to teach.

Without being overly formulaic I would either introduce the clinical study at the beginning of the class and let the students ponder it as I go through the lecture and close the lecture with the conclusion of the clinical example. Alternately I would go through the lecture and give a clinical case study from the days lecture as I close. After multiple years of giving the lectures coming up with examples was not a problem and there are multiple texts available for cross referencing as well. Either way it is a lot of effort to get information across and keep it interesting and it is still a very hard class and unpopular with students.