Pathogenesis of Select Causes of Constipation in Adults and in Elderly • Mechanical (ex. Bowel Obstruction, Stricture) -> Mechanical obstruction in the bowel -> Interrupted flow of bowel contents • Metabolic (ex. Hypercalcemia) -> Incr Ca2+ = Decr Na+ permeability in neurons -> Decr Excitability and tone of bowel smooth muscle -> Decr Peristalsis of the bowel • Endocrine (ex. Hypothyroidism) -> Thyroid hormone deficiency -> Possible mechanisms: hormone receptor changes, neuromuscular disorders, myopathy from infiltration of the intestinal wall -> Decr Peristalsis of the bowel • Neurological (ex. Multiple Sclerosis) -> Demyelination of CNS neurons -> Dysfunction of autonomic nerves that supply involuntary bodily functions -> Decr Digestion and colonic motor response after a meal • Myogenic (ex. Scleroderma) -> Collagen deposits into colonic mucosa, leading to fibrosis of the gut wall -> Atrophy of the smooth muscle wall of the colon -> Decr Ability of the colon to contract • Pelvic Floor Dyssynergia -> Puborectalis muscle and external anal sphincter fail to relax -> Narrowed anorectal angle and Incr pressure of anal canal -> Evacuation of feces is less effective • IBS-C -> Disturbance in the gut-brain interaction -> Mechanism unknown, many pathways -> Visceral hypersensitivity and Decr colonic motility • Drugs (ex. Opioid Analgesics) -> Opioids bind to mu-opioid receptors on gut wall -> Inhibition of excitatory neural pathways within the enteric nervous system -> Decr Peristaltic contractions -> Incr Colonic transit time #constipation #pathophysiology #geriatrics
