Senna Leaf Powder (Cassia senna)

Definition

Senna is the dried leaflet of Cassia senna (Alexandrian senna) or Cassia angustifolia (Tinnevelly senna), family Leguminosae. It is an official pharmacopoeial stimulant laxative. The powder is yellowish-green, odourless, with a nauseous taste.

General / Essential Features

Paracytic (rubiaceous) stomata: two subsidiary cells parallel to guard cells — the most characteristic feature
Unicellular non-glandular trichomes: thick-walled, warty (verrucose) surface, pointed apex — on both leaf surfaces
Calcium oxalate rosette crystals (cluster crystals): in mesophyll parenchyma — diagnostic
Straight-walled palisade mesophyll cells with chloroplasts
Spiral and annular vessels from vascular bundles
Fibres and fibre bundles from midrib region

Sites

Cassia senna: cultivated in Egypt, Sudan, and southern India
Cassia angustifolia: grown primarily in Tamil Nadu, India
Official in British Pharmacopoeia, Indian Pharmacopoeia, and USP
Active constituents: sennosides A and B (dianthrone glycosides) concentrated in leaflets

Pathophysiology

Sennosides are prodrugs converted by colonic bacteria to rheinanthrone, which stimulates propulsive peristalsis by acting on enteric neurons and directly increases electrolyte secretion into the lumen. It inhibits Na+/K+ ATPase in the colon, causing fluid and electrolyte accumulation. Increased colonic motility produces laxative effect 6–12 hours after oral administration.

Etiology

Therapeutic use: constipation, bowel preparation before colonoscopy/surgery, hepatic encephalopathy
Overdose: abdominal cramping, electrolyte disturbance (hypokalaemia)
Chronic overuse: melanosis coli (reversible brown/black discolouration of colon)
Adulterants: Cassia obovata — identifiable by different trichome morphology

Clinical Features

Therapeutic: soft formed stool within 6–12 hours
Abdominal cramping and griping: due to increased peristalsis
Hypokalaemia: electrolyte disturbance with chronic overuse
Melanosis coli: brown/black discolouration of colonic mucosa — reversible on stopping

Diagnosis

Microscopy: paracytic stomata, warty trichomes, rosette crystals — all 3 together are diagnostic
Bornträger test: NaOH turns pink/red with anthraquinone glycosides — chemical identification
TLC: reference standards for sennoside A and B
IP identity tests: both chemical and microscopic tests required

Treatment

Dose: 15–30 mg sennosides at night for constipation
Bowel preparation: higher doses with dietary restriction
Contraindicated: intestinal obstruction, inflammatory bowel disease, appendicitis
Avoid prolonged use to prevent laxative dependency and hypokalaemia

References

Trease, G.E. & Evans, W.C. (2009). Pharmacognosy (16th ed.). Elsevier Saunders.
Indian Pharmacopoeia Commission. (2018). Indian Pharmacopoeia 2018 (8th ed.). Government of India.
Kokate, C.K., Purohit, A.P., & Gokhale, S.B. (2020). Pharmacognosy (56th ed.). Nirali Prakashan.