Ppt chapter 56

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Introduction to the Gastrointestinal System

Introduction to the Gastrointestinal System

Chapter 56


GI System GI System


GI System (cont.)GI System (cont.)• The GI system is the only system in the body open to the

external environment

• Composed of one continuous tube

– Begins at the mouth

– Progresses through the esophagus, stomach, and small and large intestines

– Ends at the anus

• Accessory Organs

– Pancreas

– Liver

– Gallbladder


Major Activities of the GI SystemMajor Activities of the GI System

• Secretion: Of enzymes, acid, bicarbonate, and mucus

• Absorption: Of water and almost all of the essential nutrients needed by the body

• Digestion: Of food into usable and absorbable component

• Motility: Movement of food and secretions through the system


Layers of the GI TubeLayers of the GI Tube• Mucosa

• Muscularis Mucosa

• Nerve Plexus

• Adventitia


Layers of Nerves in the Nerve PlexusLayers of Nerves in the Nerve Plexus

• Submucosal Layer

• Myenteric Layer


Layers of the Gastrointestinal TractLayers of the Gastrointestinal Tract


Control of the GI SystemControl of the GI System

• GI system is controlled by the nerve plexus

– Maintains basic electrical rhythm

– Responds to local stimuli to increase or decrease activity

• Activity of GI tract can be influenced by the autonomic system

• Initiation of activity depends on local reflexes


Types of Secretions of the GI TractTypes of Secretions of the GI Tract• Saliva

• Mucus

• Acid and Digestive Enzymes (Gastrin)

• Secretin

• Sodium Bicarbonate

• Pancreatic Enzymes, Other Lipases, and Amylases

• Bile

• Endocrine Hormones


QuestionQuestion

Please answer the following statement as true or false.

The GI system is controlled by the nerve plexus which maintains basic electrical rhythm.


AnswerAnswer

True

Rationale: GI system is controlled by the nerve plexus, which maintains basic electrical rhythm and responds to

local stimuli to increase or decrease activity.


DigestionDigestion

• Is the process of breaking food into usable, absorbable nutrients

• Begins in the mouth with enzymes in the salvia

• The stomach continues the digestion process

• In the small intestines, the food mixes with bile which breaks down the fat molecules


AbsorptionAbsorption

• Is the active process of removing water, nutrients, and other elements from the GI tract

• Once removed from the GI tract, they are delivered to the bloodstream for use in the body


MotilityMotility

• GI tract depends on an inherent motility to keep things moving through the system.

• In the esophagus, the basic movement is peristalsis.

• The stomach uses its three muscle layers to produce a churning action.

• Small intestines use a process of segmentation.

• Large intestines use a process of mass movement.


Local Gastrointestinal ReflexesLocal Gastrointestinal Reflexes• Gastroenteric Reflex: Stimulation of the stomach by

stretching

• Gastrocolic Reflex: Stimulation of the stomach causing increased activity in the colon

• Duodenal–Colic Reflex: Stimulation of colon activity and mass movement by the presence of food or stretch in the duodenum


Other Local GI ReflexesOther Local GI Reflexes• Ileogastric Reflex

• Intestinal–Intestinal Reflex

• Peritoneointestinal Reflex

• Renointestinal Reflex

• Vesicointestinal Reflex

• Somatointestinal Reflex


Centrally Mediated Reflexes of the GI Tract

Centrally Mediated Reflexes of the GI Tract

• Swallowing Reflex

– Stimulated when a food bolus stimulates pressure receptors in the back of the throat and pharynx

• Vomiting Reflex

– Protects the system from unwanted irritants

– Stimulated by two centers in the medulla


Swallowing ReflexSwallowing Reflex

• Stimulated whenever a food bolus stimulates pressure receptors in the back of the throat and pharynx.

• This send impulses to the medulla, which stimulates a series of nerves.

• Involves more than 25 pairs of muscles

• This reflex can be facilitated in a number of ways if swallowing is a problem.


Stimulation of the Chemoreceptor Trigger Zone (CTZ)

Stimulation of the Chemoreceptor Trigger Zone (CTZ)

• Tactile stimulation of the back of the throat

• Excessive stomach distention

• Increasing intracranial pressure by direct stimulation

• Stimulation of the vestibular receptors in the inner ear

• Stimulation of stretch receptors in the uterus and bladder

• Intense pain fiber stimulation

• Direct stimulation by various chemicals


Maintaining Homeostasis of the GI Tract Maintaining Homeostasis of the GI Tract

• A series of local reflexes within the GI tract helps maintain homeostasis within the system

• Overstimulation can result in:

– Constipation (underactivity)

– Diarrhea (overactivity)


QuestionQuestion

Please answer the following statement as true or false.

When the renal capsule becomes irritated the gastrointestinal tract shuts down.


AnswerAnswer

True

Rationale: Renointestinal Reflex: Irritation or swelling of the renal capsule causes a cessation of movement in the GI tract, again to prevent further irritation to the capsule.

Ppt chapter 56

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