GI Control and Digestion Notes

What are the primary mechanisms of control for GI structures?

Nervous control (primarily vagus nerve using acetylcholine) and Hormonal control (peptides exerting endocrine, paracrine, and neurocrine effects).

Describe the location and primary function of the Myenteric (Auerbach's) plexus?

Located between longitudinal and circular muscle layers of the muscularis externa; primarily stimulates muscle movement.

What is the main characteristic of a paracrine hormone action? Provide an example.

Hormone released into lamina propria, affecting adjacent cells (e.g., histamine from ECL cells stimulating parietal cells).

Where does carbohydrate digestion begin and what enzyme is primarily involved?

Begins in the oral cavity with salivary amylase.

Name the final products of carbohydrate digestion in the small intestine.

Glucose, galactose, fructose.

How are glucose and galactose primarily transported across the apical surface in the small intestine during secondary active transport?

Via SGLT1 (sodium-glucose cotransporter 1) with sodium.

What are the symptoms of lactose intolerance and what causes them?

Increased gas, bloating, flatulence, loose stools, diarrhea, cramps, caused by fermentation of undigested lactose by commensal bacteria in the large intestine.

Where does protein digestion begin, and what enzyme is active there?

Begins in the stomach with pepsin (active in acidic pH).

Which GI hormone stimulates gallbladder contraction and pancreatic enzyme secretion, and what are its stimuli?

CCK (Cholecystokinin); stimulated by fatty acids and amino acids.

What is the primary function of Secretin, and where is it stimulated?

Stimulates bicarbonate secretion; stimulated by acidic pH in the small intestine (S cells).

Which vitamin and mineral absorption primarily occurs in the duodenum?

Iron, Calcium, Zinc.

Describe the pathway of chylomicron transport after they are formed in enterocytes.

Transported via lacteals into cisterna chyli, then thoracic duct, and finally into the left subclavian vein (lymphatic system).

What are the primary mechanisms of control for GI structures?

Nervous control (primarily vagus nerve using acetylcholine) and Hormonal control (peptides exerting endocrine, paracrine, and neurocrine effects).

Describe the location and primary function of the Myenteric (Auerbach's) plexus?

Located between longitudinal and circular muscle layers of the muscularis externa; primarily stimulates muscle movement.

What is the main characteristic of a paracrine hormone action? Provide an example.

Hormone released into lamina propria, affecting adjacent cells (e.g., histamine from ECL cells stimulating parietal cells).

Where does carbohydrate digestion begin and what enzyme is primarily involved?

Begins in the oral cavity with salivary amylase.

Name the final products of carbohydrate digestion in the small intestine.

Glucose, galactose, fructose.

How are glucose and galactose primarily transported across the apical surface in the small intestine during secondary active transport?

Via SGLT1 (sodium-glucose cotransporter 1) with sodium.

What are the symptoms of lactose intolerance and what causes them?

Increased gas, bloating, flatulence, loose stools, diarrhea, cramps, caused by fermentation of undigested lactose by commensal bacteria in the large intestine.

Where does protein digestion begin, and what enzyme is active there?

Begins in the stomach with pepsin (active in acidic pH).

Which GI hormone stimulates gallbladder contraction and pancreatic enzyme secretion, and what are its stimuli?

CCK (Cholecystokinin); stimulated by fatty acids and amino acids.

What is the primary function of Secretin, and where is it stimulated?

Stimulates bicarbonate secretion; stimulated by acidic pH in the small intestine (S cells).

Which vitamin and mineral absorption primarily occurs in the duodenum?

Iron, Calcium, Zinc.

Describe the pathway of chylomicron transport after they are formed in enterocytes.

Transported via lacteals into cisterna chyli, then thoracic duct, and finally into the left subclavian vein (lymphatic system).

What stimulates Gastrin secretion and what are its primary actions?

Stimulated by peptides, amino acids, distension, and vagal stimulation (GRP); stimulates gastric acid secretion and mucosal growth.

What is the primary function of Somatostatin in the GI tract?

Inhibits gastric acid and pepsinogen secretion, pancreatic exocrine secretion, and gallbladder contraction (general inhibitor).

Describe the location and primary function of the Submucosal (Meissner's) plexus?

Located in the submucosa; primarily regulates secretion, absorption, and local blood flow.

Where does the majority of chemical fat digestion occur, and which enzymes are primarily responsible?

In the small intestine; pancreatic lipase and colipase.

What are the primary mechanisms of control for GI structures?

Nervous control (primarily vagus nerve using acetylcholine) and Hormonal control (peptides exerting endocrine, paracrine, and neurocrine effects).

Describe the location and primary function of the Myenteric (Auerbach's) plexus?

Located between longitudinal and circular muscle layers of the muscularis externa; primarily stimulates muscle movement.

What is the main characteristic of a paracrine hormone action? Provide an example.

Hormone released into lamina propria, affecting adjacent cells (e.g., histamine from ECL cells stimulating parietal cells).

Where does carbohydrate digestion begin and what enzyme is primarily involved?

Begins in the oral cavity with salivary amylase.

Name the final products of carbohydrate digestion in the small intestine.

Glucose, galactose, fructose.

How are glucose and galactose primarily transported across the apical surface in the small intestine during secondary active transport?

Via SGLT1 (sodium-glucose cotransporter 1) with sodium.

What are the symptoms of lactose intolerance and what causes them?

Increased gas, bloating, flatulence, loose stools, diarrhea, cramps, caused by fermentation of undigested lactose by commensal bacteria in the large intestine.

Where does protein digestion begin, and what enzyme is active there?

Begins in the stomach with pepsin (active in acidic pH).

Which GI hormone stimulates gallbladder contraction and pancreatic enzyme secretion, and what are its stimuli?

CCK (Cholecystokinin); stimulated by fatty acids and amino acids.

What is the primary function of Secretin, and where is it stimulated?

Stimulates bicarbonate secretion; stimulated by acidic pH in the small intestine (S cells).

Which vitamin and mineral absorption primarily occurs in the duodenum?

Iron, Calcium, Zinc.

Describe the pathway of chylomicron transport after they are formed in enterocytes.

Transported via lacteals into cisterna chyli, then thoracic duct, and finally into the left subclavian vein (lymphatic system).

What stimulates Gastrin secretion and what are its primary actions?

Stimulated by peptides, amino acids, distension, and vagal stimulation (GRP); stimulates gastric acid secretion and mucosal growth.

What is the primary function of Somatostatin in the GI tract?

Inhibits gastric acid and pepsinogen secretion, pancreatic exocrine secretion, and gallbladder contraction (general inhibitor).

Describe the location and primary function of the Submucosal (Meissner's) plexus?

Located in the submucosa; primarily regulates secretion, absorption, and local blood flow.

Where does the majority of chemical fat digestion occur, and which enzymes are primarily responsible?

In the small intestine; pancreatic lipase and colipase.

What is the primary function of Motilin and what stimulates its secretion?

Stimulates gastric and intestinal motility during fasting (Migrating Motility Complex); stimulated periodically by neural mechanisms.

What is the main action of Glucose-dependent Insulinotropic Peptide (GIP) and what stimulates its release?

Stimulates insulin release from pancreatic beta cells in response to glucose and fat in the small intestine; also inhibits gastric acid secretion.

Which cells are responsible for secreting hydrochloric acid (HCl) in the stomach and what is HCl's primary role?

Parietal cells; sterilizes ingested food, denatures proteins, activates pepsinogen to pepsin.

Describe the absorption process of Vitamin B_{12} in the small intestine.

Requires intrinsic factor (secreted by parietal cells) for absorption in the terminal ileum via specific receptors.