Regionals: Digestive

Question 1

Peritoneum – definition

Answer 1

A thin serous membrane that lines the walls of the abdominopelvic cavity and reflects onto the organs, forming a closed sac in males and a nearly closed sac in females.

Question 2

Peritoneum – layers

Answer 2

The parietal peritoneum lines the internal surface of the abdominopelvic walls, while the visceral peritoneum reflects from the wall to cover the abdominal organs.

Question 3

Peritoneal cavity – definition

Answer 3

The potential space between parietal and visceral peritoneum, normally containing only a thin film of lubricating serous fluid that allows organs to move smoothly.

Question 4

Peritoneal vs abdominal cavity

Answer 4

The abdominal cavity is the entire space within the abdominal walls and diaphragm, whereas the peritoneal cavity is only the potential space between parietal and visceral peritoneum inside it.

Question 5

Intraperitoneal – definition

Answer 5

An intraperitoneal organ is almost completely covered by visceral peritoneum and is suspended within the peritoneal cavity by a mesentery.

Question 6

Intraperitoneal – examples

Answer 6

Examples include the stomach, first part of the duodenum, jejunum, ileum, transverse colon, sigmoid colon, spleen, and liver (except bare area).

Question 7

Retroperitoneal – definition

Answer 7

A retroperitoneal organ lies posterior to the parietal peritoneum, between it and the posterior abdominal wall, and is only partially covered by peritoneum on its anterior surface.

Question 8

Primary vs secondary retroperitoneal

Answer 8

Primary retroperitoneal organs develop and remain behind the peritoneum (e.g., kidneys), whereas secondary retroperitoneal organs were initially intraperitoneal and became fixed retroperitoneally after gut rotation (e.g., pancreas, most of duodenum).

Question 9

Retroperitoneal – examples

Answer 9

Primary retroperitoneal: kidneys, ureters, suprarenal glands, abdominal aorta, IVC. Secondary retroperitoneal: pancreas (except tail), most of duodenum, ascending and descending colon.

Question 10

Mesentery – definition

Answer 10

A double layer of peritoneum that suspends an organ from the posterior abdominal wall, providing a neurovascular conduit for vessels, lymphatics, and nerves.

Question 11

Omenta – greater omentum

Answer 11

A large, apron‑like double fold of peritoneum hanging from the greater curvature of the stomach and proximal duodenum, draping over intestines, with roles in fat storage, immune defense, and limiting spread of infection.

Question 12

Omenta – lesser omentum

Answer 12

A double layer of peritoneum extending from the lesser curvature of the stomach and first part of the duodenum to the liver, containing structures of the portal triad in its right free edge.

Question 13

Peritoneal ligaments

Answer 13

Double layers of peritoneum that connect an organ to another organ or the body wall, such as the falciform ligament connecting liver to anterior abdominal wall and diaphragm.

Question 14

Peritoneal reflections – clinical

Answer 14

Peritoneal reflections create recesses and gutters (e.g., hepatorenal pouch, paracolic gutters) where fluid, pus, or blood can collect and spread, influencing symptoms and drainage approaches.

Question 15

Peritonitis

Answer 15

Inflammation of the peritoneum, usually from infection or perforation, causing severe abdominal pain, guarding, and systemic toxicity because the large, richly vascularized surface can rapidly absorb toxins.

Question 16

Enteric nervous system – overview

Answer 16

A complex network of neurons within the wall of the gastrointestinal tract that can coordinate many aspects of gut function independently of the central nervous system, hence called the ‘gut brain’.

Question 17

ENS – plexuses

Answer 17

The myenteric (Auerbach) plexus lies between circular and longitudinal muscle layers and mainly controls motility, while the submucosal (Meissner) plexus lies in the submucosa and regulates secretion and blood flow.

Question 18

ENS – functions

Answer 18

Coordinates peristalsis, regulates glandular secretion and local blood flow, and integrates reflexes such as mixing and segmenting contractions in response to luminal contents.

Question 19

Vagus nerve – GI role

Answer 19

Provides parasympathetic preganglionic fibers to most of the gut up to the proximal two‑thirds of the transverse colon, enhancing motility, secretion, and digestive reflexes.

Question 20

Vagus nerve – effects

Answer 20

Increases peristaltic activity, stimulates secretions of stomach, pancreas, and intestines, relaxes certain sphincters during appropriate phases of digestion, and promotes vasodilation in the gut.

Question 21

Parasympathetic vs ENS

Answer 21

Parasympathetic (mainly vagal) fibers modulate and ‘tune’ enteric circuits, providing excitatory input that enhances ENS‑driven motility and secretion, but many ENS reflexes can still operate without parasympathetic input.

Question 22

Sympathetic chain – GI role

Answer 22

Preganglionic fibers from thoracic and upper lumbar spinal cord synapse in prevertebral ganglia, and postganglionic fibers follow arterial branches to the gut, generally inhibiting motility and secretion and constricting vessels.

Question 23

Sympathetic – effects

Answer 23

Decreases peristalsis and glandular secretion, contracts sphincters (e.g., internal anal sphincter), and causes vasoconstriction of splanchnic vessels to shunt blood away during stress.

Question 24

Pain vs reflex pathways

Answer 24

Visceral pain afferents from the gut often travel with sympathetic fibers to spinal cord segments, whereas reflex afferents involved in physiological regulation commonly travel with parasympathetic fibers (especially the vagus).

Question 25

Foregut innervation – summary

Answer 25

Parasympathetic: vagus nerve. Sympathetic: greater splanchnic nerves (T5–T9) via the celiac ganglion and plexus supplying esophagus (distal), stomach, proximal duodenum, liver, gallbladder, pancreas, and spleen.

Question 26

Midgut innervation – summary

Answer 26

Parasympathetic: vagus nerve. Sympathetic: lesser splanchnic nerves (T10–T11) mainly via the superior mesenteric ganglion and plexus supplying distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, and proximal two‑thirds of transverse colon.

Question 27

Hindgut innervation – summary

Answer 27

Parasympathetic: pelvic splanchnic nerves (S2–S4). Sympathetic: lumbar splanchnic nerves via the inferior mesenteric ganglion and plexus supplying distal one‑third of transverse colon, descending and sigmoid colon, and upper rectum.

Question 28

Swallowing – phases

Answer 28

The oral (voluntary) phase forms and propels the bolus to the oropharynx, the pharyngeal (involuntary) phase rapidly protects the airway and moves the bolus through the pharynx, and the esophageal (involuntary) phase uses peristalsis to deliver it to the stomach.

Question 29

Oral cavity structures in swallowing

Answer 29

Key structures include lips, cheeks, teeth, hard palate, soft palate, tongue, floor of mouth, salivary glands, and the muscles of mastication and facial expression that help form and control the bolus.

Question 30

Tongue – role in swallowing

Answer 30

The tongue shapes and positions food during mastication, then elevates and presses the bolus against the hard palate, sweeping it posteriorly into the oropharynx to initiate the pharyngeal phase.

Question 31

Soft palate – function in swallowing

Answer 31

The soft palate elevates and moves posteriorly to contact the posterior pharyngeal wall, closing off the nasopharynx and preventing regurgitation of food into the nasal cavity.

Question 32

Pharynx – regions in swallowing

Answer 32

The oropharynx and laryngopharynx are the main regions involved, forming a muscular passageway that directs the bolus from the oral cavity to the esophagus while the nasopharynx is sealed off.

Question 33

Pharyngeal constrictor muscles

Answer 33

Sequential contraction of the superior, middle, and inferior pharyngeal constrictors propels the bolus downward through the pharynx toward the esophagus.

Question 34

Larynx – protection during swallowing

Answer 34

The larynx elevates and moves anteriorly, bringing the airway under the tongue base, tightening the laryngeal inlet, and helping the epiglottis deflect the bolus away from the airway.

Question 35

Epiglottis – function

Answer 35

The epiglottis acts as a passive flap that is pushed posteriorly over the laryngeal inlet during the pharyngeal phase, directing the bolus toward the esophagus and away from the trachea.

Question 36

Upper esophageal sphincter (UES)

Answer 36

A high‑pressure zone at the junction of pharynx and esophagus (mainly cricopharyngeus muscle) that relaxes briefly during swallowing to allow the bolus to enter the esophagus and then contracts to prevent air entry and reflux.

Question 37

Lower esophageal sphincter (LES)

Answer 37

A physiologic sphincter at the gastroesophageal junction formed by smooth muscle tone and diaphragmatic support that relaxes during swallowing to allow bolus entry into the stomach and prevents reflux of gastric contents.

Question 38

Esophagus – muscular composition

Answer 38

The upper third contains skeletal muscle, the middle third a mix of skeletal and smooth muscle, and the lower third predominantly smooth muscle, enabling voluntary initiation and then involuntary peristalsis.

Question 39

Peristalsis – definition

Answer 39

A coordinated wave of muscular contraction and relaxation that propagates along the esophagus, pushing the bolus toward the stomach during the esophageal phase of swallowing.

Question 40

Swallowing – neural control

Answer 40

Swallowing is coordinated by a central pattern generator in the medulla (swallowing center) and involves cranial nerves V, VII, IX, X, and XII for sensory input and motor output to the oropharyngeal and laryngeal muscles.