Chapter 27.2 Digestive System Regulation

This textbook is designed specifically for Kansas State's Biology 198 Class. The course is taught using the studio approach and based on active learning. The studio manual contains all of the learning objectives for each class period and is the record of all student activities. Hence, this textbook is more of a reference tool while the studio manual is the learning tool.
Authors: Robert Bear, David Rintoul, Bruce Snyder, Martha Smith-Caldas, Christopher Herren, and Eva Horne
Kansas State University Libraries
New Prairie Press
Bear, Robert; Rintoul, David; Snyder, Bruce; Smith-Caldas, Martha; Herren, Christopher; and Horne, Eva, "Principles of Biology" (2016). Open Access Textbooks. 1. https://newprairiepress.org/textbooks/1
The textbook was originally published and is also available to download at http://cnx.org/contents/[e-mail] is licensed under a Creative Commons Attribution License 4.0 license.

Episode Transcript

(00:00):
Welcome to Principles of Biology. Thisbook was written by the Open Alternative Textbook
Initiative at Kansas State University and isbeing released as a podcast and distributed under
the terms of the Creative Commons AttributionLicense. Today's episode is Chapter twenty seven
point two Digestive system Regulation. Allhyperlinks, images and sources can be found

(00:22):
at the link to the book.In the description, the digestive canal is,
in its task, a complete chemicalfactory. The raw material passes through
a long series of institutions in whichit is subjected to certain mechanical and mainly
chemical processing, and then through innumerableside streets it is brought into the depot
of the body. Aside from thisbasic series of institutions along which the raw

(00:46):
material moves, there is a seriesof lateral chemical manufactories which prepare certain reagents
for the appropriate processing of the rawmaterial. Ivan Petrovitch Pavlov speech to the
Society of Russian Physicians, December eighteenseventy four. Povlov's pioneering work showing that
dogs can associate the ringing of abell with the imminent delivery of food pointed

(01:07):
the way toward our current understanding ofthe coordinated responses that regulate the digestive system.
The brain is the control center forthe sensation of hunger and satiety.
The functions of the digestive system areregulated through neural and hormonal responses. Neural
responses to food in reaction to thesmell, sight, or thought of food

(01:29):
like that shown in figure. Thefirst hormonal response is that of salivation.
The salivary glands secrete more saliva inresponse to the stimulus presented by food in
preparation for digestion. Simultaneously, thestomach begins to produce hydrochloric acid to digest
the food. Recall that the peristalticmovements of the esophagus and other organs of

(01:51):
the digestive tract are under the controlof the brain. The brain prepares these
muscles for movement as well. Whenthe stomach is full, the part of
the brain that detects satiety signals fullness. There are three overlapping phases of gastric
control, the cephalic phase, thegastric phase, and the intestinal phase.
Each requires many enzymes and is underneural control as well. Photo shows plates

(02:15):
of food on a dinner table.Seeing a plate of food triggers the secretion
of saliva in the mouth and theproduction of HCl in the stomach. Credit
Kellie Bailey. Digestive phases. Theresponse to food begins even before food enters
the mouth. The first phase ofingestion, called the cephalic phase, is

(02:36):
controlled by the neuro response to thestimulus provided by food. All aspects such
as sight, scents, and smelltrigger the neural responses, resulting in salivation
and secretion of gastric juices. Thegastric and salivary secretion in the cephalic phase
can also take place due to thethought of food right now. If you
think about a piece of chocolate ora crispy potato chip. The ink reason

(03:00):
salivation is a cephalic phase response tothe thought. The central nervous system prepares
the stomach to receive food. Thegastric phase begins once the food arrives in
the stomach. It builds on thestimulation provided during the cephalic phase. Gastric
acids and enzymes process the ingested materials. The gastric phase is stimulated by one

(03:23):
distension of the stomach, two adecrease in the pH of the gastric contents,
and three the presence of undigested material. This phase consists of local hormonal
and neural responses. These responses stimulatesecretions and powerful contractions. The intestinal phase
begins when kim enters the small intestine, triggering digestive secretions. This phase controls

(03:49):
the rate of gastric emptying. Inaddition to gastric emptying, when kim enters
the small intestine, it triggers otherhormonal and neural events that coordinate the activities
of the intestine, anal tract,pancreas, liver, and gall bladder hormonal
responses to food. The endocrine systemcontrols the response of the various glands in

(04:09):
the body and the release of hormonesat the appropriate times. One of the
important factors under hormonal control is thestomach acid environment. During the gastric phase,
the hormone gastron is secreted by Gcells in the stomach in response to
the presence of proteins in the stomachcontents. Gastron stimulates the release of hydrochloric

(04:30):
acid HCl, which aids in thedigestion of the proteins. However, when
the stomach is emptied, the acidicenvironment no longer needs to be maintained and
a hormone called somatostatin stops the releaseof hydrochloric acid. This is a good
example of a negative feedback system.Proteins in the stomach cause a response that
results in elimination of proteins from thestomach contents via the actions of two counteracting

(04:54):
hormones in the duodenum. Digestive secretionsfrom the liver, pancrea and gallbladder play
an important role in digesting kime duringthe intestinal phase. In order to neutralize
the acidic chime, a hormone calledsecretein stimulates the pancreas to produce alkaline bicarbonate
solution and deliver it to the duodenum. Secretin acts in tandem with another hormone

(05:16):
called cholecystic kinin CCK. Not onlydoes cc K stimulate the pancreas to produce
the requisite pancreatic juices, it alsostimulates the gallbladder to release bile into the
duodenum. This is another negative feedbackloop what parameters are being sensed and regulated.
Another level of hormonal control occurs inresponse to the composition of food.

(05:41):
Foods high in lipids take a longtime to digest. A hormone called gastric
inhibitory peptide, is secreted by thesmall intestine to slow down the peristaltic movements
of the intestine to allow fatty foodsmore time to be digested and absorbed.
Understanding the hormonal control of the digestivesystem is an important area of ongoing research.
Scientists are exploring the role of eachhormone in the digestive process and developing

(06:05):
ways to target these hormones. Advancescould lead to knowledge that may help to
battle the obesity epidemic. This podcastwill be released episodically and follow the sections
of the textbook in the description Fora deeper understanding, We encourage you review
the text version of this work voiceby voicemaker Donayanne. This was produced by

(06:29):
Brandon Casturo as a creative Common Senseproduction.