Large Intestine, Diarrhoea, Lactose Intolerance

What are the main muscle layers involved in GI tract motility?

Circular, longitudinal muscle layers, and muscularis mucosa; skeletal muscles in mouth, pharynx, upper esophagus, and external anal sphincter.

What is the Enteric Nervous System (ENS)?

A network of ~100 million neurons in the GI tract that can operate independently but is modulated by hormones and extrinsic nerves.

What cells act as pacemakers for the GI tract's slow waves?

Interstitial Cells of Cajal (ICCs).

How does water absorption occur in the intestines?

It is a passive process driven by solute (especially Na+) movement.

What is the cause of secretory diarrhoea like Cholera?

Activation of CFTR channels by cAMP, leading to Cl- and water secretion.

How is lactose intolerance diagnosed?

By diet observation, hydrogen breath test, or lactose tolerance test.

Name two types of laxatives used to treat constipation.

Bulk laxatives (e.g., methylcellulose) and osmotic laxatives (e.g., lactulose).

What role does loperamide play in treating diarrhoea?

It reduces peristalsis and increases fluid absorption with low CNS penetration.

What two plexuses form the Enteric Nervous System?

Myenteric (Auerbach’s) plexus and Submucous (Meissner’s) plexus.

How does parasympathetic innervation affect the GI tract?

Increases secretion, blood flow, and smooth muscle contraction; relaxes sphincters.

What is the main neurotransmitter used by the parasympathetic preganglionic fibres?

Acetylcholine (ACh).

What are the three main types of GI motility patterns?

Peristalsis, tonic contraction, and segmentation.

What drives the Basic Electrical Rhythm (BER) in the GI tract?

Slow waves generated by Interstitial Cells of Cajal.

In which part of the GI tract does segmentation primarily occur?

Small intestine.

How much water typically enters and is absorbed by the GI tract daily?

9.3 liters enter; 8.3 liters absorbed by small intestine; 90% of the rest absorbed in the large intestine.

What defines diarrhoea in terms of fluid loss?

Loss of more than 500 ml of fluid per day from the GI tract.

What is the major cause of traveller’s diarrhoea?

Enterotoxigenic E. coli (ETEC).

Name two second messengers that activate CFTR channels.

cAMP and Ca2+.

What are two common causes of impaired NaCl absorption leading to diarrhoea?

Congenital defects and infections (e.g., norovirus).

What is osmotic diarrhoea often caused by?

Presence of non-absorbable solutes like lactose in lactose intolerance.

What are the symptoms of lactose intolerance?

Bloating, abdominal pain, diarrhoea.

What is the role of oral rehydration salts in diarrhoea?

Exploit Na+/glucose co-transport to enhance water absorption.

What components make up standard oral rehydration salts?

Glucose, sodium chloride, trisodium citrate, potassium chloride.

How do anti-motility agents like diphenoxylate work?

Block acetylcholine release, reducing gut motility.

Name a first-line anti-motility agent for traveller’s diarrhoea.

Loperamide.

List some causes of constipation.

Low fiber diet, sedentary lifestyle, aging, neurogenic disorders, opiates, antidepressants.

What lifestyle changes can help relieve constipation?

Increased water intake, higher fiber intake, regular exercise, proper toilet routine.

How do osmotic laxatives like lactulose work?

Attract water into the bowel, softening stools and stimulating bowel movements.

What is the mechanism of action for stimulant laxatives like senna?

Directly stimulate enteric nerves to increase peristalsis.

What is hypokalaemia in diarrhoea caused by?

Loss of potassium (K+) through excessive fluid loss.