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The Digestive System

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The Digestive System – PowerPoint PPT presentation

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Title: The Digestive System


1
The Digestive System
2
Introduction
  • The digestive system consists of the muscular
    digestive tract and various accessory organs.
  • Digestive functions include ingestion, mechanical
    processing, digestion, secretion, absorption,
    compaction, and excretion.

3
Overview of the digestive Tract
  • The digestive tract includes the oral cavity,
    pharynx, esophagus, stomach, small intestine,
    large intestine, rectum and anus.

4
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5
Histological Organization
  • The epithelium and underlying connective
    tissue,the lamina propria, form the mucosa of the
    digestive tract.
  • Next, outward, are the submucosa, the muscularis
    externa, and the adventitia, a layer of loose
    connective tissue.
  • In the peritoneal cavity, the muscularis externa
    is covered by the serosa, a serous membrane

6
  • Double sheets of peritoneal membrane called
    mesenteries suspend the digestive tract.

7
Movement of Digestive Materials
  • The neurons that innervate the smooth muscle of
    the muscularis external are not under voluntary
    control.
  • The muscularis externa propels materials through
    the digestive tract by means of the contractions
    of peristalsis.
  • Segmentation movements in areas of the small
    intestine churn digestive materials.

8
The Oral Cavity
  • The functions of the oral cavity are
  • Analysis of potential foods
  • Mechanical processing using the teeth, tongue and
    palatal surfaces
  • Lubrication by mixing with mucus and salivary
    secretions
  • Digestion by salivary enzymes

9
  • The oral cavity, or buccal cavity, is lined by
    oral mucosa
  • The hard palate and soft palate form its roof and
    the tongue forms its floor.

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11
The Tongue
  • The primary functions of the tongue include
  • Mechanical processing
  • Manipulation to assist in chewing and swallowing
  • Sensory analysis.

12
The Salivary Glands
  • The salivary glands discharge their secretions
    into the oral cavity
  • Saliva lubricates the mouth, dissolves chemicals,
    flushes the oral surfaces and helps to control
    bacteria.
  • Salivation is usually controlled by the ANS.

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14
Teeth
  • Mastication occurs through the contact of the
    opposing surfaces of the teeth
  • The periodontal ligament anchors the tooth ins a
    bony socket.
  • Dentin forms the basic structure of a tooth
  • The crown is coated with enamel, and the root is
    covered with cementum

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16
The 20 primary teeth or deciduous teeth are
replaced the the 32 teeth of the secondary
dentition during development.
17
The Stomach
  • The stomach has four major functions
  • Bulk storage of ingested food
  • The mechanical breakdown of food.
  • The disruption of chemical bonds by acids enzymes
  • The production of intrinsic factor

18
  • Chyme forms in the stomach as gastric and
    salivary secretions are mixed with food.
  • The four regions of the stomach are the cardia,
    fundus, body and pylorus
  • The pyloric sphincter guards the exit from the
    stomach.
  • In a relaxed state the stomach lining contains
    numerous rugae (ridges and folds)

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20
The Gastric Wall
  • Within the gastric glands, parietal cells secrete
    intrinsic factor and hydrochloric acid.
  • Chief cells secrete pepsinogen which acids I the
    gastric lumen convert to the enzyme pepsin
  • Gastric gland endocrine cells secrete the hormone
    gastrin.

21
The Regulation of Gastric Activity
  • Gastric secretion includes
  • The cephalic phase which prepares the stomach to
    receive ingested materials
  • The gastric phase which begins with the arival of
    food in the stomach
  • The intestinal phase which controls the rate of
    gastric emptying

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23
The Small Intestine
  • The small intestine includes the duodenum, the
    jejunum, and the ileum.
  • The ileocecal valve, a sphincter, marks the
    transition between the small and large intestines.

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25
The Intestinal Wall
  • The intestinal mucosa bears transverse fold
    called plicae, or plicae circulares,
  • and small projections called intestinal villi.
  • They increase the surface area for absorption.
  • Each villus contains a terminal lymphatic called
    a lacteal.

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27
Intestinal Secretions
  • Intestinal glands secrete intestinal juice,
    mucus,and hormones.
  • Intestinal juice moistens the chyme, helps buffer
    acids,and dissolves digestive enzymes and the
    products of digestion.
  • Intestinal hormones include secretin,
    cholecystokinin(CCK) and gastric inhibitory
    peptide.

28
Digestion and the Small intestine
  • The most important digestive and absorptive
    functions occur in the small intestine.
  • Digestive enzymes and buffers are provided by the
    pancreas, liver and gallbladder.

29
The Pancreas
  • The pancreatic duct penetrates the call of the
    duodenum, where it delivers the secretions of the
    pancreas.

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31
  • The pancreas has two functions
  • Endocrine (secreting insulin and glucagon into
    the blood)
  • Exocrine (secreting water, ions, and digestive
    enzymes into the small intestine)
  • Pancreatic enzymes include lipases,
    carbohydreases and proteases.

32
The Control of Pancreataic Secretion
  • When chyme arrives in the small intestine
    secretin triggers the pancreatic production of a
    fluid containing buffers, primarily sodium
    bicarbonate, what help bring the pH of the chyme
    under control.
  • Also CCK is released which stimulates the
    pancreas to secrete pancreatic amylase,
    pancreatic lipase, nucleases and protease
    enzymes.

33
The Liver
  • Largest visceral organ in the body, with over 200
    known functions.

34
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35
Liver Functions
  • The liver performs metabolic and hematological
    regulation and produces bile.
  • The gallbladder stores and concentrates bile for
    release into the duodenum.

36
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37
The large Intestine
  • The main functions of the large intestine are
  • Reabsorb water and compact the feces
  • Absorb vitamins liberated by bacteria
  • Store fecal material prior to defecation.

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39
Three Parts of Large Intestine
  • Cecum collects and stores material from the
    ileum. Vermiform appendix is attached to the
    cecum.
  • Colon larger diameter and thinner wall than sm.
    Intestine/
  • Rectum terminates in the anal canal leading to
    the anus.

40
Physiology of the Large Intestine
  • The large intestine reabsorbs water and other
    substances such as vitamins, bilirubin, bile
    salts, and toxins
  • Bacteria residing in the large intestine are
    responsible for intestinal gas or flatus.

41
Digestion and Absorption
  • The digestive system breaks down the physical
    structure of the ingested material and then
    disassembles the component molecules into smaller
    fragments through hydrolysis.

42
  • Amylase breaks down complex carbohydrates. These
    are broken down into monosaccharides by other
    enzymes and are absorbed by the intestinal
    epithelium through facilitated diffusion and
    cotransport.

43
  • Triglycerides are emulsified into large lipid
    drops. The results interact with bile salts to
    form micelles which diffuse across the intestinal
    epitheliums.
  • Protein digestion involves the gastric enzyme
    pepsin and various pancreatic proteases.

44
Water and Electrolyte Absorption
  • About 2-2.5 liters of water are ingested each day
    and digestive secretion provide 6-7 liters
  • Nearly all is reabsorbed by osmosis.

45
  • Fat-soluble vitamins are enclosed within fat
    droplets are are absorbed with the products of
    lipid digestion.
  • The nine water-soluble vitamins are important as
    cofactors and coenzymes in enzymatic reactions..

46
Aging and the Digestive System
  • Age related changes include a thinner and more
    fragile epithelium to a reduction in epithelial
    stem cell division and weaker peristaltic
    contraction as smooth muscle tone decreases.
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