the intestinal phase of stomach digestion is triggered by partially digested nutrients filling the pylorus.

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Phases of Digestion

Phases of Digestion

Phases of Digestion Cephalic Phase

The cephalic phase of gastric secretion occurs before food enters the stomach due to neurological signals.

LEARNING OBJECTIVES

Outline the cephalic phase of digestion

KEY TAKEAWAYS

Key Points

The cephalic phase of gastric secretion is initiated by the sight, smell, thought or taste of food.

Neurological signals originate from the cerebral cortex and in the appetite centers of the amygdala and hypothalamus.

This enhanced secretory activity is a conditioned reflex.

This phase of secretion normally accounts for about 20 percent of the gastric secretion associated with eating a meal.

Key Terms

conditioned reflex: A response, to a stimulus, that has been acquired by operant conditioning.cephalic phase: This occurs before food enters the stomach, especially while it is being eaten.

The cephalic phase of gastric secretion occurs before food enters the stomach, especially while it is being eaten. It results from the sight, smell, thought, or taste of food; and the greater the appetite, the more intense is the stimulation.

Neurogenic signals that initiate the cephalic phase of gastric secretion originate from the cerebral cortex, and in the appetite centers of the amygdala and hypothalamus. They are transmitted through the dorsal motor nuclei of the vagi, and then through the vagus nerve to the stomach.

This phase of secretion normally accounts for about 20% of the gastric secretions that are associated with eating a meal. Since this enhanced secretory activity is brought on by the thought or sight of food it is a conditioned reflex—it only occurs when we like or want food. When one’s appetite is depressed this part of the cephalic reflex is inhibited.

The cephalic phase causes ECL cells to secrete histamine and increase HCl acid in the stomach. There will also be an influence on G cells to increase gastrin circulation.

Chain of Events for the Nervous System and Hormone System

Thinking of food (i.e., smell, sight) stimulates the cerebral cortex.

The cerebral cortex sends messages to the hypothalamus, the medulla, and the parasympathetic nervous system via the vagus nerve, and to the stomach via the gastric glands in the walls of the fundus and the body of stomach.

The gastric glands secrete gastric juice.

When food enters the stomach, the stomach stretches and activates stretch receptors.

The stretch receptors send a message to the medulla and then back to the stomach via the vagus nerve.

The gastric glands secrete more gastric juice.

Chemical stimuli (i.e., partially digested proteins, caffeine) directly activate G cells (enteroendocrine cells) that are located in the pyloric region of the stomach to secrete gastrin; this in turn stimulates the gastric glands to secrete gastric juice.

Gastric Phase

The gastric phase is a period in which swallowed food activates gastric activity in the stomach.

LEARNING OBJECTIVES

Outline the gastric phase of digestion

KEY TAKEAWAYS

Key Points

The gastric phase accounts for about two-thirds of gastric secretions.

Ingested food stimulates gastric activity by stretching the stomach and raising the pH of its contents; this causes a cascade of events that leads to the release of hydrochloric acid by the parietal cells that lower the pH and break apart the food.

Gastric secretion is stimulated chiefly by three chemicals: acetylcholine (ACh), histamine, and gastrin.

Below pH of 2, stomach acid inhibits the parietal cells and G cells; this is a negative feedback loop that winds down the gastric phase as the need for pepsin and HCl declines.

Key Terms

gastric phase: The second phase of digestion that follows mastication (chewing) and takes place in the stomach.

The gastric phase is a period in which swallowed food and semi-digested protein ( peptides and amino acids ) activate gastric activity. About two-thirds of gastric secretion occurs during this phase.

Ingested food stimulates gastric activity in two ways: by stretching the stomach and by raising the pH of its contents.

Stretching activates two reflexes: a short reflex is mediated through the myenteric nerve plexus; and a long reflex is mediated through the vagus nerves and brainstem.

Gastric Secretion

Gastric secretion is stimulated chiefly by three chemicals:

Acetylcholine (ACh). This is secreted by the parasympathetic nerve fibers of both the short and long reflex pathways.

Histamine. This is a paracrine secretion from the enteroendocrine cells in the gastric glands.

Gastrin. This is a hormone produced by enteroendocrine G cells in the pyloric glands.

All three of these stimulate parietal cells to secrete hydrochloric acid and intrinsic factor. The chief cells secrete pepsinogen in response to gastrin and especially ACh, and ACh also stimulates mucus secretion.

As dietary protein is digested, it breaks down into smaller peptides and amino acids that directly stimulate the G cells to secrete even more gastrin: this is a positive feedback loop that accelerates protein digestion.

Small peptides also buffer the stomach acid so the pH does not fall excessively low. As digestion continues and these peptides empty from the stomach, the pH drops lower and lower. Below pH of 2, stomach acid inhibits the parietal cells and G cells: this is a negative feedback loop that winds down the gastric phase as the need for pepsin and HCl declines.

Source : courses.lumenlearning.com

Associate Degree Nursing Physiology Review

Digestive System Content

Digestive System Anatomy

Basic Organization of the Digestive Tract

Functions of the GI Tract

Peristalsis/Segmentation

Regulation of Digestion

Intrinsic/Neuronal/Extrinsic Controls

Digestion

Oral Cavity Functions

Saliva

Deglutition (Swallowing)

Functions of the Stomach

Regulation of Gastric Secretion

Regulation of HCl Secretion

Gastric Contractile Activity

Regulation of Gastric Emptying

Digestion in Stomach

Small Intestine

Hormones That Regulate Digestion

Duodenum Liver Gallbladder

Regulation of Bile Release

Pancreas

Digestion in the Small Intestine

Absorption of Nutrients Occurs in the Small Intestine

Control of Intestinal Motility

Large Intestine Rectum

Chemical Digestion and Absorption of Carbohydrates/proteins/lipids/fatty acid/nucleic acids

Absorption of Water

Absorption of Electrolytes

Digestive System

The digestive system is the system of the body that mechanically and chemically breaks down food.

It takes about 12 to 24 hours to completely break down food.

The digestive organs are usually divided into two main groups:

the gastrointestinal tract

the accessory organs

Click here for an animation that provides an overview of the digestive system organs and function.

Practice questions follow the animation.

Gastrointestinal (GI) tract (also called alimentary canal or digestive tract)

The GI tract is a continuous tube running from the mouth to the anus. It measures about 9 m (30 ft) in length. The GI tract digests and absorbs food.

It includes the following organs:

mouth pharynx esophagus stomach small intestine large intestine

Accessory Digestive Organs

Includes the following organs:

teeth tongue gallbladder salivary glands liver, and pancreas

Basic Organization of the Digestive Tract

The digestive tract from the esophagus to the large intestine is made up of the same 4 basic tissue layers:

1. Mucosa (Mucous Membrane)

Innermost layer

Lines the lumen of the digestive tract

Is a mucous membrane made of epithelium, connective tissue, and a very thin layer of smooth muscle

Has many blood and lymphatic vessels to absorb nutrients

Has lots of lymphatic nodules to fight pathogens.

2. Submucosa

Made of connective tissue

Has lots of blood and lymphatic vessels that receive absorbed food molecules

Has lymphatic tissue.

Has a nerve plexus that regulate movements and secretions of the digestive tract

In the esophagus and duodenum the submucosa also has mucin-secreting glands

3. Muscularis Externa

Made of skeletal muscle or smooth muscle.

The mouth, pharynx, and superior and middle parts of the esophagus, and anus contain skeletal muscle.

The lower part of the esophagus and the rest of the GI tract contain 2 or 3 layers of smooth muscle.

Has a nerve plexus here that controls the frequency and strength of contraction of smooth muscle.

4. Adventitia or SerosaAdventitia = areolar connective tissue with dispersed collagen and elastic fibers (retroperitoneal organs, e.g. ascending colon)Serosa = same as adventitia but covered by a visceral peritoneum (intraperitoneal, e.g. stomach)Functions of the GI Tract

The GI tract is a “disassembly” line,  nutrients become more available to the body in each step:

Ingestion

taking in of food through the mouth

Mechanical Digestion

Physical breakdown of solid foods

Masses of food are broken into smaller parts

tongue and teeth physically break down the food

stomach mixes the food.

small intestine also physically breaks down food when the secretion of bile emulsifies or breaks up fat globules into smaller droplets

Propulsion (motility)

swallowing and peristalsis

Secretion

release of hormones and enzymes

Chemical Digestion

Chemical breakdown of food by enzymes into smaller components that can be absorbed by the epithelium of the digestive tract

For example starch is broken down into the disaccharide maltose in the oral cavity. Later the disaccharides are broken down into monosaccharides in the small intestine.

Click here for an animation that reviews how enzymes (such as sucrase) can break down foods (such as a disaccharide).

Secretion

Release of water, acids, enzymes, and buffers by the digestive tract and by the accessory organs into the lumen of the digestive tract

Absorption

Movement of small organic molecules, electrolytes, vitamins, and water across the digestive epithelium and into the blood and lymph

Excretion (Defecation)

Removal of waste products which are first compacted and then discharged during defecation

Source : www.austincc.edu

Chapter 23 Anatomy Flashcards

Start studying Chapter 23 Anatomy. Learn vocabulary, terms, and more with flashcards, games, and other study tools.

Chapter 23 Anatomy

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Which major process involves the removal of water from intestinal contents?

mechanical breakdown

defecation absorption ingestion

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absorption

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Where does the process of segmentation occur?

anus esophagus stomach small intestine

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small intestine

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1/40 Created by ryan_moran77

Terms in this set (40)

Which major process involves the removal of water from intestinal contents?

mechanical breakdown

defecation absorption ingestion absorption

Where does the process of segmentation occur?

anus esophagus stomach small intestine small intestine

How would you classify chewing food?

digestion ingestion propulsion

mechanical breakdown

mechanical breakdown

Which of the following functions is NOT correctly matched with its description?

-mechanical breakdown: churning movements in the GI tract

-absorption; passage of digested nutrients into the blood or lymph

-propulsion: physical breakdown of ingested food in the GI tract

-ingestion: intake of food nutrients

-propulsion: physical breakdown of ingested food in the GI tract

Which of the following is NOT a means of mechanically breaking down food?

mastication segmentation peristalsis churning peristalsis

Which organ of the digestive tract is the body's major digestive organ?

liver stomach large intestine small intestine small intestine

Which layer of the alimentary canal is constructed from either stratified squamous or simple columnar epithelium?

mucosa serosa submucosa muscularis externa mucosa

Which layer of the alimentary canal is responsible for segmentation and peristalsis?

muscularis externa serosa submucosa mucosa muscularis externa

The __________ is the serous membrane that lines the abdominal organs.

visceral peritoneum omenta mesentery parietal peritoneum visceral peritoneum

Which layer of the digestive tract controls digestive propulsion?

mucosa submucosa serosa muscularis externa muscularis externa

The uvula is an extension of the __________.

oral vestibule lingual frenulum soft palate

palatopharyngeal arch

soft palate

Which of the following is NOT a function of saliva?

-Saliva moistens food and helps compact it into a bolus.

-Saliva cleanses the mouth.

-Saliva contains enzymes that begin the chemical breakdown of proteins.

-Saliva dissolves food chemicals so that they can be tasted.

-Saliva contains enzymes that begin the chemical breakdown of proteins.

Which of the following inhibits salivation?

the sight or smell of food

being stressed or frightened

relaxing after a meal

ingestion of spicy foods

being stressed or frightened

How many total permanent teeth should an adult have, assuming none have been lost or removed?

8 16 20 32 32

The deciduous dentition consists of __________ teeth.

10 16 20 32 20

Which digestive process does NOT occur in the mouth?

segmentation

mechanical breakdown

digestion ingestion segmentation

Which layer of the stomach contains the gastric pits that secrete mucous, acid, and digestive enzymes?

serosa mucosa submucosa muscularis externa mucosa

Which of these structures is found in the stomach but nowhere else in the alimentary canal?

a circular muscle layer

an oblique muscle layer

a lining of columnar epithelium

mucus-forming cells

an oblique muscle layer

Which area of the stomach adjoins the small intestine?

body cardia pylorus fundus pylorus

Which of the following constitute a portal triad?

-three lobules sharing a common central vein

-the hepatic artery and two hepatic veins

-a bile duct along with a portal venule and arteriole

-the porta hepatis

a bile duct along with a portal venule and arteriole

Which of the following best describes the capillary wall structure found in the liver lobules?

-The walls are continuous, only allowing small molecules and water to pass through.

-The walls have windows that allow small proteins to pass through but not cells.

-The capillary walls have openings that allow large proteins and small cells to pass through.

-The walls only allow water to pass through.

-The capillary walls have openings that allow large proteins and small cells to pass through.

Source : quizlet.com