Autocrine and paracrine signalling are signalling and communicating mechanisms. During autocrine signalling, cells secrete substances that bind to the receptors of the same cell from where it was secreted. During paracrine signalling, cells secrete substances which bind to the receptors of the adjacent cells.
Endocrine glands are also known as ductless glands as their secretions are released directly into the bloodstream. Exocrine glands release chemicals into the duct which deliver the chemicals to the site of action.