HOM is a Java program written to teach and simulate human physiology. The current version (1.61) is FREE and can be obtained on the Download page.

Users' comments:

"Thanks again for your work on the program, which the students are very much enjoying in these classes!"
"What you have done with this is excellent, and it will be very useful for our class."
(Staff at Department of Physiology, University of Cambridge)
Amazing. Exactly what I was hoping to find to play with! Greatly appreciated.
(Medical Student at University of Toledo College of Medicine)

Source code on GitHub

HOM is written in Java. You can edit the code, compile to a jar file using 

jar -cfm com
and run the Jar in your browser with the help of CheerpJ.