Gastrointestinal Physiology Chapter 6

Questions and Answers

What is the primary function of the muscularis mucosa in the GI tract?

Contraction for altering surface area (correct)

Secretion of digestive enzymes

Transportation of nutrients

Absorption of water

Which part of the autonomous nervous system primarily influences GI tract functions in an excitatory manner?

Intrinsic nervous system

Parasympathetic nervous system (correct)

Peripheral nervous system

Sympathetic nervous system

Which plexus is responsible for integrating motility, secretory, and endocrine functions in the GI tract?

Celiac plexus

Submucosal plexus

Myenteric plexus

Both submucosal and myenteric plexuses (correct)

What role do afferent fibers play in the GI tract?

Carrying sensory information to the CNS Signup and view all the answers

Which nerve innervates the esophagus, stomach, pancreas, and upper large intestine?

Vagus nerve Signup and view all the answers

What type of muscle primarily controls the motility of the gastrointestinal smooth muscle?

Myenteric plexus Signup and view all the answers

Which of the following is NOT considered an official GI hormone?

Insulin Signup and view all the answers

What is the primary function of the submucosal plexus (Meissner plexus)?

Control of blood flow and secretion Signup and view all the answers

During which phase is little gastrin secreted?

In response to a meal Signup and view all the answers

Which section of the gastrointestinal tract includes the lamina propria?

Mucosa Signup and view all the answers

What is the effect of the sympathetic nervous system on gastrointestinal functions?

Inhibitory Signup and view all the answers

Where do postganglionic sympathetic adrenergic fibers synapse?

Myenteric and submucosal plexuses Signup and view all the answers

What inhibits gastrin release in the stomach?

H+ in the lumen Signup and view all the answers

What is one of the main actions of gastrin?

Stimulates growth of gastric mucosa Signup and view all the answers

Which amino acid sequence is essential for the biologic activity of CCK?

C-terminal heptapeptide Signup and view all the answers

Which of the following is a potent stimulus for gastrin secretion?

Tryptophan Signup and view all the answers

Which action is NOT performed by CCK?

Increases gastric acid secretion Signup and view all the answers

What stimulates the release of CCK?

Small peptides Signup and view all the answers

Where is gastrin secreted in the gastrointestinal tract?

G cells of the stomach Signup and view all the answers

What inhibits the secretion of gastrin?

Somatostatin Signup and view all the answers

Which of the following hormones is homologous to glucagon?

Secretin Signup and view all the answers

Which of the following hormones stimulates gallbladder contraction?

CCK Signup and view all the answers

What is an action of secretin?

Stimulates HCO3- secretion from the pancreas Signup and view all the answers

What is the primary action of secretin?

Stimulates pancreatic HCO3- secretion Signup and view all the answers

What stimulates the release of secretin from the S cells of the duodenum?

H+ in the lumen of the duodenum Signup and view all the answers

Which hormone contains 42 amino acids and is homologous to secretin and glucagon?

GIP Signup and view all the answers

Which hormone is responsible for increasing insulin secretion?

GIP Signup and view all the answers

Which of the following is a common effect of CCK?

Stimulates gallbladder contraction Signup and view all the answers

Gastrin secretion is stimulated by which of the following conditions?

Distention of the stomach Signup and view all the answers

What is the role of fatty acids in gastric physiology?

Stimulating gastrin secretion Signup and view all the answers

Study Notes

Structure and Function of the GI Tract

The GI tract is designed for secretion and absorption, with specialized epithelial cells.
Muscularis mucosa changes surface area for secretion/absorption.
Circular muscle contraction reduces lumen diameter; longitudinal muscle contraction shortens GI tract segments.
Enteric nervous system consists of the submucosal plexus (Meissner plexus) and myenteric plexus, coordinating GI motility and secretions.

Innervation of the GI Tract

Autonomic nervous system (ANS) includes extrinsic and intrinsic components.
Efferent fibers relay commands from the brain to the GI tract; afferent fibers send sensory info back.

Extrinsic Innervation

Parasympathetic Nervous System:
- Primarily excitatory; mediated via the vagus and pelvic nerves.
- Preganglionic fibers synapse in the myenteric and submucosal plexuses.
- Vagus nerve innervates upper GI areas; pelvic nerve innervates lower intestine.
Sympathetic Nervous System:
- Generally inhibitory; fibers originate between T8 and L2.
- Preganglionic fibers synapse in prevertebral ganglia before activating the myenteric and submucosal plexuses.

Intrinsic Innervation (Enteric Nervous System)

Regulates GI functions autonomously, even without extrinsic input.
Myenteric plexus predominantly controls motility.
Submucosal plexus mainly manages secretion and blood flow.

GI Hormones and their Functions

Four key hormones recognized as GI hormones: gastrin, CCK, secretin, GIP.
Gastrin:
- 17-amino acid form increases H+ secretion and stimulates gastric mucosa growth.
- Secreted from G cells in response to small peptides and amino acids, specifically phenylalanine and tryptophan.
CCK (Cholecystokinin):
- Contains 33 amino acids; stimulates gallbladder contraction and pancreatic enzyme secretion.
- Released from I cells of the duodenum in response to fatty acids, small peptides, and monoglycerides.
Secretin:
- Has 27 amino acids, stimulates secretion of bicarbonate from the pancreas and liver in response to H+ and fatty acids in the duodenum.
GIP (Glucose-dependent Insulinotropic Peptide):
- 42 amino acids; unique for being released in response to fats, proteins, and carbohydrates.
- Stimulates insulin secretion from pancreatic β cells.

Feedback and Regulation

High H+ concentration in the stomach inhibits gastrin release, ensuring regulation of acidity.
When gastrin is secreted excessively (e.g., Zollinger-Ellison Syndrome), it leads to hypertrophy of the gastric mucosa.
Somatostatin and histamine modulation affect gastric secretions and hormone activities.

Neurocrines and Paracrines

Neurocrines:
- Include vasoactive intestinal peptide (VIP), which relaxes smooth muscle and stimulates pancreatic HCO3- secretion.
- GRP stimulates gastrin release; enkephalins cause contraction of GI smooth muscle.
Paracrines:
- Somatostatin inhibits GI hormones and gastric H+ secretion; histamine increases gastric H+ secretion.

Appetite Regulation

Hypothalamus regulates appetite through satiety and feeding centers.
Anorexigenic (POMC) neurons decrease appetite, while orexigenic (neuropeptide Y) neurons increase it.
Hormones like leptin, insulin, and GLP-1 suppress appetite, while ghrelin raises it; peptide YY inhibits ghrelin.

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Description

Dive into Chapter 6 of Gastrointestinal Physiology, where we explore the structure and innervation of the GI tract. Understand the roles of epithelial cells, muscularis mucosa, and circular muscle in secretion and absorption processes. Test your knowledge on the complexities of the gastrointestinal system.