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Digestive System Chapter 23 - PowerPoint PPT Presentation

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Digestive System Chapter 23. Overview. Digestive Processes. Functional Concepts. Mechanical and Chemical Stimuli Intrinsic and extrinsic Controls Two types of reflexes Short =enteric (local) Long =CNS and autonomic nerves. Digestive Anatomy Overview. Hepatic portal system 4 layers

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Digestive System

Chapter 23

Functional concepts
Functional Concepts

  • Mechanical and Chemical Stimuli

  • Intrinsic and extrinsic Controls

  • Two types of reflexes

    • Short =enteric (local)

    • Long =CNS and autonomic nerves

Digestive anatomy overview
Digestive Anatomy Overview

  • Hepatic portal system

  • 4 layers

    • Mucosa -mucous membrane

    • Submucosa -areolar tissue with blood and lymphatic vessels

    • Muscularis Externa -circular and longitudinal muscle layers

    • Serosa -areolar and simple squamous

  • Enteric Nervous System

    • Submucosal plexus

    • Myenteric plexus


  • Greater than 97% water

  • PH 6.75-7.0

  • Electrolytes

  • Enzymes: Salivary amylase and lingual lipase

  • Mucin -glycoprotein

  • Immune proteins: Lysozyme, definsin, IgA

  • Urea and Uric acid

  • Naturally occurring bacteria

    • http://www.textbookofbacteriology.net/normalflora.html

Salivary control
Salivary Control

  • Intrinsic salivary glands keep mouth moist

  • Extrinsic glands moisten food

    • Food entering mouth activates

    • Parasympathetic innervation triggers enzyme rich saliva

    • Sympathetic triggers thick saliva (mucin rich)

  • Chemical and mechanical stimulate nuclei in pons and medulla

  • Sight and smell of food also activate

  • Lower GI irritation, spicy food, acidic food increase saliva production

Teeth and gums
Teeth and Gums

  • Mechanical breakdown of food

  • Oral disease may cause:

    • Atherosclerotic plaques

    • Clotting within coronary and cerebral arteries

Pharynx and esophagus
Pharynx and Esophagus

  • Pharynx contains friction free stratified squamous epithelia

  • Esophagus is a muscular tube

    • GERD

    • Hiatal hernia

Digestive process mouth to esophagus
Digestive Process:Mouth to Esophagus

  • Mechanical breakdown

  • Deglutition (swallowing) uses 22 muscle groups

    • Buccal phase -voluntary movement within mouth

    • Pharyngeal-esophageal phase -involuntary movement controlled by pons and medulla


  • Simple columnar epithelium -secretes thick alkaline mucous

  • Gastric pits and glands

    • Secretions depend upon location

    • Mucous neck cells -thin mucous

    • Parietal cells -secretes H+, Cl-, intrisic factor

    • Chief cells -pepsinogen and lipases

    • Enteroendocrine cells -histamine, serotonin, somatostatin, gastrin

Homeostatic imbalances
Homeostatic Imbalances

  • Gastric Ulcers

    • 90% caused by Helicobacter pylori

    • 10-20% of infected show symptoms

    • Inhibit or lessen HCl production

    • Damage stomach epithelium

    • Disrupt cell junctions

    • Promote chronic inflammation

Digestive processes in the stomach
Digestive Processes in the Stomach

  • Protein digestion begins

  • Alcohol and aspirin absorb into blood stream

  • Secretion of intrinsic factor

    • Required for absorbtion of vitamin B12

    • B12 is needed for RBC production

Regulation of gastric secretion
Regulation of Gastric Secretion

  • Neural mechanisms

  • Hormonal mechanism

  • Stimuli act on brain, stomach, intestine

  • Three phases: cephalic, gastric, intestinal

    • Not mutually exclusive phases

Cephalic reflex phase
Cephalic (Reflex) Phase

  • Short, lasting only minutes

  • Prepares stomach to receive food

  • Sight and smell of food are the trigger

  • Stimulates mucous, chief, parietal and G cells

  • Conditional response

  • Special senses → hypothalamus → medulla → vagus → enteric plexus → stomach glands

Gastric phase
Gastric Phase

  • 3-4 hours

  • Neural and hormonal response

  • Triggers

    • Distension of stomach

    • Increase in pH (decrease in acidity)

    • Presence of undigested materials (proteins)

Gastric phase1
Gastric Phase

  • Neural response

    • Produces mixing waves

    • Stretch and chemoreceptors trigger short (myenteric) reflexes

    • Ach from parsympathetic neurons stimulates parietal and chief cells

      • Increase in HCl and Pepsinogen

    • Proteins, alcohol, caffine stimulate chemoreceptors

Gastric phase2
Gastric Phase

  • Hormonal response

    • Increasing gastrin levels stimulates parietal and chief cells

      • Gastrin enters blood stream circulates back to stomach

    • Increase in HCl and Pepsinogen

    • Decrease in pH (acidity)

    • Increase in gastric motility

  • Alkaline tide

Intestinal phase
Intestinal Phase

  • Very long, lasting hours

  • Controls gastric emptying

  • Neural and hormonal responses

  • Neural Responses

    • Chyme leaving stomach relieves distension

      • No-longer stimulating stretch receptors

    • Distension of duodenum by chyme stimulates intestinal stretch receptors =enterogastric reflex

      • Inhibits medulla (gastrin secretions) and local reflexes (gastric contractions)

      • Stimulates contraction of pyloric sphincter

    • Mucous production stimulated in duodenum to protect intestine

Intestinal phase1
Intestinal Phase

  • Hormonal response

  • Triggered by the arrival of chyme in duodenum

  • Arrival of lipids and carbohydrates

    • Stimulates cholesystokinin (CCK) and gastric inhibitory peptide (GIP)

    • CCK inhibits gastric secretion of acids and enzymes

    • GIP inhibits gastric secretion and rate of contraction

    • Meals low in fat enter intestine quicker than those high in fat

      • Allows more time for lipids to be broken down by intestine

  • Decrease in ph stimulates enteroendocrine cells to release secretin

    • Secretin inhibits parietal and chief cells

    • Stimulates pancreas to produce bicarbonate

    • Stimulates liver to secrete bile

  • Partially digested proteins in duodenum stimulate G cells in duodenal wall.

    • G cells produce gastrin which circulates back to stomach increasing acid production

  • Gastric processing meets digestive requirements of specific meals

Gastric motility and emptying
Gastric Motility and Emptying

  • Response to distension of stomach

  • Gastric Contractile Activity

  • Smooth muscle pacemaker cells

    • Interstitial cells of Cajal set basic electrical rhythm (BER)

    • Set maximum rate of contraction

    • Do not initiate contractions

  • Regulation of Gastric Emptying

    • Stomach and duodenum work in conjunction