Pharmacology of intestines



There are four types of drugs which are used in constipation. They are also called purgative, laxative, aperient, or evacuants. They all act mainly on the colon.


Osmotic laxatives


Fecal softeners


Stimulant laxatives


Stool bulking agents

Osmotic laxatives

These are little absorbed and encourage osmosis in the colon (which physiologically allows absorption) with increase in bulk and reduction in viscosity in order to produce a fluid stool. Agents include inorganic salts such as magnesium hydroxide and lactulose, which is a synthetic dissacharide

Fecal softeners (emollients)

These are gentle softeners which disallow hard feces and make the feces soft and are useful in conditions like fistula-in-ano or fissure-in-ano in which hard fecal matter may have caused the tear in the first place. They include docusate sodium and liquid parafiin.

Stimulant laxative

These drugs stimulate gut motility and peristalsis and may cause abdominal cramps. They are contraindicated in pregnancy and intestinal obstruction. They include bisacodyl, sodium picosulphate, gluycerol senna, and danthron. it also include anthraquinone group such as senna, danthron, cascara, aloes and rhiubarb.

Stool bulking agents

These are fibers which absorb water in the large intestine and are insoluble and therefore not digestible by enzymes in the small intestine. They absorb water and therefore increase volume at the same time as reducing viscosity of intestinal content. They produce soft and bulky stool and encourage normal reflexes in the bowel. They include bran, ispaghula, methylcellulose and sterculia.


7-8 liters of fluid are secreted into intestine daily. Absorption of sodium in the  intestine is influenced by the following phenomena

Sodium glucose coupled entry: glucose in the small intestine stimulate the absorption of sodium and water follows together with chloride ions in the solvent drag phenomenon.

Sodium ion coupled entry: Na+ and Cl- enter the epithelial cells either alone or as double exchange  with H+ or Cl- Na- with H+  or Cl- with OH- or HCO3-. Hence oral rehydration solutions should contain sodium, chloride and bicarbonate.

Treatment of diarrhea:

Oral rehydration therapy This contains the oral rehydration salts as follows: sodium chloride, potassium chloride, sodium citrate and anhydrous glucose useful in diarrhea and dehydration .

Antimotility drugs: They act on gut muscles to delay motility in order to allow more time for absorption. In gut infections they may not be necessary. You have codeine, diphenoxylate and loperamide

Increase in viscosity of gut drugs: Kaolin and ispaghula

Drugs used in inflammatory bowel diseases (ulcerative colitis): Aminosalicylates  such as sulfasalazine, mesalazine

There is nothing in anatomy not found in this website

Electronic School of Medicine
Creator: Oluwole Ogunranti




Small intestine explanatory video



























Cell Biology



Gross anatomy

Lymphatic drainage

Organ integration
Clinical anatomy





Chemical Pathology

Anatomical Pathology





Main Subject Course Links

eAnatomy eAnesthesia eBiochemistry eChemical pathology eCommunity Health
eDermatology eENT eGynecology eHematology eImaging
eMedicine eMedical microbiology eObstetrics eOphthalmology ePathology
ePediatrics ePharmacology ePhysiology ePsychiatry    eSurgery/eOrthopedics
eLab eOSCE eProcedures eInvestigations eSchool/Videopage
eOrgans eLocator Anatomy Museum eDissector eFractures/Dissect-it-yourself
All diseases eClerking eTreatment eDoctor ePatient