diaphragm
膈 refers to the diaphragm, the muscular partition separating the chest and abdominal cavities.
膈 combines the flesh radical ⺼ with 鬲, which likely contributes the sound. The character specifically denotes the diaphragm as a bodily partition.
The flesh radical ⺼ indicates a body part, and 鬲 resembles a partitioned vessel. Picture the diaphragm as a fleshy divider inside the torso, like a membrane separating two chambers.
For カク, imagine a diaphragm contracting with a sharp 'kak' sound during a hiccup: kak -> カク, and the muscle flexes.