General Organization of the Alimentary Tract Practice Flashcards

A set of vocabulary flashcards covering the histological organization, electrophysiology, neural control, and hormonal regulation of the gastrointestinal tract.

Unitary (visceral, syncytial) smooth muscle

Types of smooth muscle in the gastrointestinal tract containing actin and myosin not arranged in a regular fashion (no striations), with actin filaments attached to dense bodies.

Gap junctions

Connections between cells that enable gastrointestinal smooth muscle to act as a syncytium by allowing electrical signals to pass between them.

Basic electrical rhythm (BER)

Spontaneous rhythmic fluctuations in membrane potential between $-65$ and $-45\,mV$, also known as slow waves.

Interstitial cells of Cajal (ICC)

Pacemaker cells with smooth muscle-like features and long branched processes that initiate the basic electrical rhythm (BER).

Spike potentials

Electrical events occurring at the depolarised phase of the BER caused by $Na^+$ and $Ca^{2+}$ entry, which lead to the contraction of the GI tract.

Myenteric plexus

Part of the enteric nervous system that primarily controls the movements of the entire length of the gut.

Submucosal plexus

Part of the enteric nervous system that controls localised secretions, absorption, and the contraction of submucosal muscles.

Peristalsis

A motility pattern where the stretch of a gut segment causes contraction of the proximal segment and relaxation of the distal segment to propel content distally.

Substance P and Acetylcholine

Neurotransmitters released in a retrograde direction to cause smooth muscle contraction behind a bolus during peristalsis.

NO and Vasoactive Intestinal Polypeptide (VIP)

Substances released in an anterograde direction to cause smooth muscle relaxation ahead of a bolus during peristalsis.

Migrating motor complexes (MMC)

A cycle of regular electrical activity (Phases I, II, and III) that repeats every $90-100$ minutes under fasting conditions to sweep along the length of the intestine.

Gastrin

Hormone secreted by G cells of the antrum, duodenum, and jejunum that stimulates gastric acid secretion and mucosal growth.

Cholecystokinin (CCK)

Hormone secreted by I cells that stimulates pancreatic enzyme secretion and gallbladder contraction while inhibiting gastric emptying.

Secretin

Hormone secreted by S cells in response to acid and fat that stimulates pancreatic and biliary bicarbonate secretion.

Gastric inhibitory peptide (GIP)

Hormone secreted by K cells of the duodenum and jejunum that stimulates insulin release and inhibits gastric acid secretion.

Motilin

Hormone secreted by M cells of the duodenum and jejunum during fasting that stimulates gastric and intestinal motility.