Newbie question about "other" components

[theoldwizard1]

While typically not shown in heat pump functional diagrams, frequently heat pump systems have "other" components such as

• receiver
• dryer
• accumulator

1. Where do these component fit in the overall heat pump system ?
2. What is the function of each ?
3. Why do some designs have them and others do not ?
4. Any other components I have missed ?