Digestive System Chapter

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Questions and Answers

What type of muscles are present in the muscularis externa, except in the upper esophagus and anal sphincter?

Smooth muscle fibers

Striated muscle fibers (correct)

Skeletal muscle fibers

Cardiac muscle fibers

What is the function of the muscularis mucosae in the mucosa layer?

To inhibit peristalsis in the GI tract

To absorb nutrients from the lumen

To contract and throw mucosa into folds and ridges (correct)

To secrete digestive enzymes into the lumen

What is the name of the plexus of nerves found in the submucosa?

Meissner's plexus

Enteric plexus

Auerbach's plexus

Messner's plexus (correct)

Where does the majority of digestion and absorption of carbohydrates and amino acids occur?

Stomach and small intestine Signup and view all the answers

What is the function of the lymphatic vessels in the GI tract?

To transport dietary fat Signup and view all the answers

What is the function of the exocrine pancreas in the GI tract?

To secrete HCO3 into the small intestine Signup and view all the answers

What is the purpose of the muscular valves or sphincters in the GI tract?

To separate the different organs of the GI tract Signup and view all the answers

What is the outermost layer of the GI tract?

Adventitia of the serosa Signup and view all the answers

What is the location of Brunner glands in the duodenum?

Submucosa Signup and view all the answers

What is the primary function of mucosal villi?

Absorption of nutrients into the bloodstream Signup and view all the answers

How do monosaccharides cross the intestinal epithelium?

Active transport via a Na+-sugar coupled uptake mechanism Signup and view all the answers

What is the primary mechanism of amino acid uptake across the intestinal epithelium?

Co-transport with Na+ via a specific mucosal carrier Signup and view all the answers

What is the primary function of PepT1 in the intestinal epithelium?

Transport of oligopeptides across the intestinal epithelium Signup and view all the answers

What is the primary driving force for oligopeptide uptake across the intestinal epithelium?

H+ gradient from lumen to cell Signup and view all the answers

What is the function of the basolateral membrane in the intestinal epithelium?

Exit of nutrients into the bloodstream Signup and view all the answers

What is the primary function of the capillary network in the intestinal villi?

Transport of absorbed nutrients to the bloodstream Signup and view all the answers

What is the maximum rate of saliva flow in humans?

1 ml/min Signup and view all the answers

What is the function of glycoproteins secreted from submandibular, sublingual glands, and buccal glands?

Aid in starch digestion Signup and view all the answers

What is the main function of parasympathetic stimulation via the chorda lingual nerve?

Increase fluid secretion accompanied by increased blood flow and oxygen consumption Signup and view all the answers

What is the arrangement of capillary networks in salivary glands?

Parallel capillary networks Signup and view all the answers

What is the function of the striated or intercalated duct in salivary glands?

Converges into large ducts and opens into main excretory ducts Signup and view all the answers

What is the blood flow in salivary glands compared to contracting skeletal muscle?

10 times more Signup and view all the answers

What is the type of cells that forms the salivary glandular epithelium?

Acinar cells Signup and view all the answers

What is the importance of a 5-10-fold increase in blood flow during neural activation of salivary secretion?

Guarantees sufficient supply of water, electrolytes and nutrients to sustain epithelial cells and active salivary secretion Signup and view all the answers

What is the primary function of the pharyngeal phase of swallowing?

To prevent reflux into the nasopharynx Signup and view all the answers

What is the purpose of intrinsic factor in the stomach?

To combine with vitamin B12 for absorption Signup and view all the answers

What is the function of the myenteric nerve plexus of Auerbach?

To coordinate the contractions of the stomach muscles Signup and view all the answers

What is the function of the mucous cells in the stomach?

To protect the gastric surface with a thin film of mucous Signup and view all the answers

What is the primary function of the muscularis mucosa in the stomach?

To separate the mucosa from the serosa Signup and view all the answers

What is the turnover rate of mucous cells in the stomach?

2-6 days Signup and view all the answers

What is the function of the upper esophageal sphincter?

To relax and allow food to enter the esophagus Signup and view all the answers

What is the function of the palatopharyngeal fold during swallowing?

To move inward to prevent reflux into the nasopharynx Signup and view all the answers

What is the primary function of chief cells in the gastric gland?

Synthesise and secrete pepsinogen Signup and view all the answers

What is the mechanism by which gastrin regulates acid secretion in the stomach?

Paracrine mechanism, releasing histamine from enterochromaffin-like cells Signup and view all the answers

What is the primary agonist that stimulates acid secretion in the stomach?

Histamine Signup and view all the answers

What is the effect of PGE2 on gastric acid secretion?

Inhibits acid secretion by inhibiting histamine's action at a site distal to the histamine receptor Signup and view all the answers

What is the characteristic feature of parietal cells in the gastric gland?

Specialised intracellular canaliculi extending from lumen to basal cytoplasm Signup and view all the answers

What is the function of the microvilli on the luminal and canaliculi walls of parietal cells?

Increase the surface area for HCl secretion Signup and view all the answers

What is the mechanism by which histamine stimulates acid secretion in the stomach?

Histamine binds to receptors on the basolateral membrane of parietal cells Signup and view all the answers

What is the concentration of HCl secreted by parietal cells in the gastric gland?

0.1 N HCl Signup and view all the answers

Study Notes

Digestive System Overview

The digestive system consists of four major organs: esophagus, stomach, small intestine, and large intestine.
The organs are separated by muscular valves or sphincters, and the digestive tract is lined with a mucosal layer.
Digestion of carbohydrates begins in the oral cavity through amylase, and the majority of digestion and absorption of carbohydrates and amino acids occurs in the stomach and small intestine.
Secretions from the exocrine pancreas and liver pass directly into the small intestine.
Lymphatic vessels are distributed throughout the tract and are involved in intestinal absorption of dietary fat.

Histological Organization of the Digestive Tract

The digestive tract, except for the oral cavity, has four concentric layers of muscle: mucosa, submucosa, muscularis, and adventitia of the serosa.
The mucosa consists of superficial epithelium, underlying stroma with vascularized loose connective tissue rich in immunocompetent cells, and a relatively thin layer of smooth muscle (muscularis mucosae).
The muscularis mucosae is subdivided into an inner circular and outer longitudinal layer, and contractions of this layer throw the mucosa into folds and ridges.
The submucosa contains large blood vessels, lymphatic vessels, and nerves that send fibers into the mucosa and muscularis layers.
The muscularis externa consists of two layers of smooth muscle, except in the upper esophagus and anal sphincter, where striated muscle fibers exist.

Digestion and Absorption

Monosaccharide transport occurs through a Na+-sugar coupled uptake mechanism at the mucosal interface, with energy provided by the Na+/K+-ATPase pump.
Amino acid transport occurs through specific mucosal and basolateral carriers, with mucosal uptake via co-transport depending on the Na+ gradient.
Di-, tri-, and tetra-peptide transport occurs through a H+/oligopeptide cotransporter referred to as PepT1.
The basolateral entry mechanisms are primarily Na+-independent facilitated transport proteins and provide a nutrient supply for epithelial renewal.

Salivary, Gastric, and Pancreatic Secretions

Salivary glands are compound organs that secrete electrolytes and proteins (e.g., amylase) as a fluid into the oral cavity.
Saliva lubricates food for swallowing, and glycoproteins secreted from submandibular, sublingual, and buccal glands aid in starch digestion.
The salivary glandular epithelium is comprised of specialized groups of cells called acinar cells, arranged as endpieces surrounding small central lumina.
Parasympathetic stimulation mediated via the chorda lingual nerve evokes a marked fluid secretion accompanied by increased blood flow and oxygen consumption.

Gastric Secretion

The stomach is an exocrine organ that secretes a large acid volume after a meal, containing pepsin, which initiates protein digestion.
The gastric surface is protected by a thin film of mucous constantly produced by surface epithelial cells.
Intrinsic factor, a glycoprotein, is also secreted by the stomach and combines with vitamin B12, aiding absorption in the ileum.
The stomach layers consist of a thin layer of smooth muscle (muscularis mucosa), a dense connective tissue (submucosa), and three primary layers of muscle (muscularis).
Parietal or oxyntic cells secrete 0.1 N HCl, and chief cells secrete protein in a manner similar to salivary/pancreatic acinar cells.
Gastrin released by G cells of the antral mucosa and first part of the duodenum stimulates the parietal cells to secrete HCl.

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Description

This quiz covers the structure and function of the digestive system, including the subdivision of the GI tract and its common features, and the process of digestion.