An extract made from the dried leaflets on the pods of Cassia angustifolia or Cassia acutifolia with cathartic activity.
Dimeric glycosides in dried senna extract are converted to the active monoanthrones by bacterial action in the colon. Through direct effects on enterocytes, enteric neurons, and muscle, monoanthrones produce giant migrating colonic contractions in addition to water and electrolyte secretion.
As do other stimulant laxatives, monoanthrones may induce a limited low-grade inflammation in the colon through activation of prostaglandin/cyclic AMP and nitric oxide/cyclic GMP pathways and perhaps inhibition of Na+, K+-ATPase.

National Cancer Institute. NCI Drug Dictionary. Internet. September 15, 2009.