What is the difference in the explanation of the shape of the aggregate demand curve (AD) and a single product demand curve (D).

What is the difference in the explanation of the shape of the aggregate demand curve (AD) and a single product demand curve (D). After all, both demand curves show an inverse relationship between price and quantity?  

What is the difference in the explanation of the shape of the Short Run Aggregate Supply Curve (SRAS) and Long Run Aggregate Supply Curve (LRAS)?