Three basic rules for building medical words.

Rule #1

A word root links a suffix that begines with a vowel.

hepat/o + itits = hepatitis

liver + inflammation = inflammation of the liver

Rule #2

A combine form (root + O) links a suffix that begines with consonant.

hepat/o + Cyte = hepatocyte

liver + cell = liver cell

Rule #3

 Use a combining form to link a root to another root to form a compound word.  This rule holds true even if the nex root begins with a vowel, as in osteoarthritis.  Keep in mind that the rules for linking multuple roots to each toher are slightly diffrent from the rules for linking roots and combining forms to suffixes.

oste/o + chondr/ + itis = osteochondritis

bone + cartilage + inflammation = inflamaction of bone and cartilage

oste/o + arthr/ + -itis = osteoarthritis

bone + joint + inflammation = inflammation of bone and joint

Define the first part of the word (which may be a word root, combining form, or prefix)

The combining form gastr/o means stomach.

Define the middle parts of the word. 

enter/ means intestine.