Digestion B

What does cholecystokinin (CCK) do?

Released by jejunal mucosa in response to fats; increases gallbladder contraction (bile release) and decreases stomach motility.

What does secretin do?

Released by duodenal mucosa in response to acid; mildly inhibits GI motility to allow acid neutralization.

What does gastric inhibitory peptide (GIP) do?

Released from upper small intestine in response to fats; decreases gastric motility when intestine is full.

What are the two types of GI movement?

• Propulsive – Peristalsis (forward movement)

• Mixing – Local churning/contractions to enhance absorption

What stimulates peristalsis?

Distension (2–3 cm); involves circular and longitudinal muscle coordination.

What nerves coordinate swallowing?

CN IX (Glossopharyngeal) & CN X (Vagus)

What are the steps of swallowing?

• Nasopharynx closes, breathing stops

• Glottis closes, larynx elevates

• UES relaxes → pharyngeal peristalsis → food enters esophagus

Length and location of esophagus?

~25–30 cm long; starts at C6 (cricoid cartilage); ends below diaphragm at stomach (cardia)

What are the 3 esophageal narrowings?

• Upper sphincter (air prevention)

• Aortic arch crossing

• Diaphragmatic hiatus (T10)

What is the esophageal blood supply & innervation?

Sympathetic + Vagus nerve (CN X); blood via esophageal arteries

Steps of food propulsion through the esophagus?

• UES relaxes → food enters

• UES contracts → prevent reflux

• Primary peristalsis behind bolus

• Secondary peristalsis clears residue

• LES relaxes (via VIP)

• Receptive relaxation of orad stomach

What is achalasia?

LES fails to relax due to myenteric plexus degeneration → dysphagia, dilated esophagus, high LES pressure

What is GERD?

Reflux due to weak LES tone → heartburn

What is esophageal atresia?

Closed distal esophagus; often with tracheoesophageal fistula → aspiration risk in newborns

What is a sliding hiatal hernia?

Cardia + fundus slide through diaphragm → reflux/heartburn common

What is a paraesophageal hernia?

Fundus herniates, cardia stays in place → usually no reflux

What is Nissen fundoplication?

Fundus wrapped around LES to strengthen anti-reflux barrier

What is radiofrequency treatment for GERD?

Causes scar tissue to tighten LES via endoscopic burns

What are the 4 parts of the stomach?

• Cardia

• Fundus

• Body

• Pyloric part (antrum + canal → pyloric sphincter)

What are the 2 curvatures of the stomach?

Lesser and greater curvature

What are the main functions of the stomach?

• Food reservoir

• Mechanical digestion (chyme formation)

• Controlled emptying into duodenun

What are the muscle layers of the stomach?

• Outer longitudinal

• Inner circular

• Oblique (unique to stomach)

What cells are found in gastric glands?

• Goblet cells – Mucus

• Parietal cells – HCl, intrinsic factor

• Chief cells – Pepsinogen

• ECL cells – Histamine, serotonin

• G cells – Gastrin

• D cells – Somatostatin

What is gastric juice made of?

Exocrine secretions + 2–4 L of water/day → highly acidic

What stimulates gastric secretion?

• Nervous phase: Vagus nerve (sight, smell, taste)

• Gastric phase: Food in stomach

What is receptive relaxation?

Orad stomach relaxes (vagovagal reflex, CCK mediated) to accommodate food

What is retropulsion?

Wave of contraction that propels food backward for mixing

What mediates migrating myoelectric complex?

Motilin; occurs every 90 mins to clean stomach during fasting

What factors slow gastric emptying?

• Fat (via CCK)

• H+ in duodenum (via neural reflex)

When is gastric emptying fastest?

When contents are isotonic

What is the “peristaltic pump”?

Powerful waves force chyme through the pylorus in bursts

What is the parasympathetic supply to the stomach?

Vagus nerve → increases motility, secretions, blood flow

What is the sympathetic supply?

Splanchnic nerves → inhibit peristalsis, increase LES tone, convey pain