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Chapter 24 The Digestive System

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Chapter 24 The Digestive System BIO 211 Lab Instructor Dr. Gollwitzer * Small Intestine 3 Regions Duodenum (10 in.) First part; connects to pylorus Mixing bowl ... – PowerPoint PPT presentation

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Title: Chapter 24 The Digestive System


1
Chapter 24 The Digestive System
  • BIO 211 Lab
  • Instructor Dr. Gollwitzer

2
  • Today in class we will
  • Discuss the gastrointestinal tract and identify
    its components
  • Identify the accessory organs associated with
    the digestive tract
  • The layers that make up the digestive tract wall
    and each layers characteristics
  • Mucosa
  • Submucosa
  • Muscularis externa
  • Serosa
  • Begin our discussion of the gastrointestinal
    tract components in more detail
  • Oral cavity
  • Pharynx
  • Esophagus

3
Digestive System
  • Gastrointestinal (GI) tract continuous,
    muscular tube from mouth to anus
  • Oral cavity (mouth)
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Anus

4
Digestive System
  • Accessory digestive organs any digestive organ
    attached to the GI tract
  • Teeth
  • Tongue
  • Glandular organs
  • Salivary glands
  • Pancreas
  • Liver
  • Gall Bladder

5
Figure 24-1
6
Histological Organization
  • 4 Major layers to wall
  • Mucosa
  • Submucosa
  • Muscularis externa
  • Serosa

7
Figure 24-3
8
Mucosa
  • Inner lining of digestive tract
  • A mucous membrane
  • Consists of
  • Epithelium - moistened by glandular secretions
  • Lamina propria areolar CT filler

9
Mucosa Digestive Epithelia
  • Depend on location, function, stresses
  • Simple or stratified
  • Columnar or squamous

10
Mucosa Digestive Epithelia
  • Nonkeratinized stratified squamous epithelium
  • Where mechanical stress most severe
  • In oral cavity, pharynx, esophagus, rectum
  • Life span 2-3 days
  • Simple columnar epithelium
  • Where absorption and secretion occur
  • (with villi and goblet cells)
  • Stomach, small intestine, most of large intestine
  • Life span 6 days

11
Mucosa Lamina Propria
  • Layer of areolar (loose connective) tissue
  • Contains
  • Blood vessels, sensory nerve endings, lymphatic
    vessels, lymphoid tissue
  • Mucosal glands and glandular secretions
  • Muscularis mucosae/interna
  • Band of smooth muscle and elastic fibers
  • Smooth muscle arranged in 2 concentric layers
  • Inner, circular layer (around lumen)
  • Outer, longitudinal layer
  • Contractions alter shape of lumen and move
    epithelial folds

12
Mucosa Glandular Structures
  • Have secretory function
  • Associated with simple columnar cells and/or
    mucous-secreting cells
  • Goblet cells (exocrine) ? mucus
  • Enteroendocrine cells
  • ? hormones (e.g., G cells ? gastrin)
  • Coordinate activities of digestive tract and
    accessory glands
  • e.g., chief cells, G cells, parietal cells

13
Submucosa
  • Layer of dense, irregular connective tissue
  • Around muscularis mucosae
  • Contains
  • Large blood vessels and lymphatic vessels
  • Exocrine glands ? buffers and enzymes into lumen
  • Submucosal plexus contains nerve fibers and
    neurons

14
Muscularis Externa
  • Dominated by smooth muscle cells
  • Inner, circular layer
  • Outer, longitudinal layer
  • Important role in mechanical processing and
    movement of materials along tract
  • Also contains
  • Lymphoid nodules (Peyers patches)
  • Masses of lymphoid tissue have lymphocytes that
    protect small intestine from bacteria that are
    normal inhabitants of large intestine
  • Myenteric plexus/plexus of Auerbach
  • Network of neurons located between circular and
    longitudinal muscle layers
  • Movements coordinated by enteric nervous system
    (part of ANS)

15
Serosa
  • A serous membrane lines sealed, internal
    subdivisions of ventral body cavity
  • Covers muscularis externa of most of digestive
    tract
  • except oral cavity, pharynx, esophagus, and
    rectum, which have adventitia (a dense collagen
    fibrous sheath)

16
Figure 24-3
17
Figure 24-3
18
Oral (Buccal) Cavity
  • Space within mouth
  • Lined by oral mucosa (nonkeratinized stratified
    squamous epithelium)
  • Vestibule space between cheeks or lips and
    teeth
  • Labial frenulum fold of mucosa connects lip to
    gum
  • Cheeks lateral walls of oral cavity
  • Mucosae supported by fat pads and buccinator
    muscles
  • Labia (lips)
  • Gingivae (gums)
  • Ridges that surround base of each tooth
  • On alveolar processes of maxillary bones and
    mandible

19
Oral (Buccal) Cavity
  • Palates
  • Hard palate formed by maxillary bones
    (anterior) and palatine bones (posterior)
  • Soft palate fleshy part posterior to hard
    palate
  • Formed from skeletal muscle
  • Posterior margin supports uvula dangling
    process that helps prevent food from entering
    pharynx prematurely
  • Tongue
  • Muscular organ attached to floor of oral cavity
  • Dorsum (superior) surface covered with lingual
    papillae (location of taste buds)
  • Lingual frenulum thin fold of mucous membrane
    that attaches tongue to floor of oral cavity

20
Figure 24-6
21
Pharynx
  • Throat area posterior to nasal and oral cavities
  • Shared by respiratory and digestive systems
  • Extends between internal nares and entrances to
    larynx and esophagus
  • Nasopharynx
  • Posterior portion or nasal cavity
  • Separated from oral cavity by soft palate
  • Contains
  • Pharyngeal tonsils and opening to auditory
    (eustachian) tube
  • Oropharynx
  • Posterior portion of oral cavity
  • Between soft palate and base of tongue
  • Fauces opening between oral cavity and
    oropharynx
  • Laryngopharynx
  • Inferior part
  • Between hyoid bone and entrances to esophagus and
    larynx

22
Esophagus
  • Hollow, muscular tube
  • From posterior laryngopharynx to stomach
  • Descends through thoracic cavity posterior to
    trachea
  • Enters abdominopelvic cavity through esophageal
    hiatus in diaphragm

23
Esophageal Histology
  • Muscularis externa transitions from
  • Skeletal muscle fibers (superior third) to
  • Smooth muscle fibers (inferior third)
  • Adventitia
  • CT outside muscularis externa (no serosa)
  • Anchors esophagus against dorsal body wall

24
Esophageal Sphincters
  • Circular smooth muscles that control
    entrance/exit to esophagus
  • Upper esophageal sphincter
  • In superior 1 in.
  • Prevents air from entering
  • Lower esophageal sphincter
  • At inferior end
  • Prevents backflow from stomach

25
  • Today in class we will
  • Complete our more detailed discussion of the
    gastrointestinal tract components
  • Stomach
  • Small intestine
  • Large intestine
  • Anus
  • Begin our discussion of the 4 accessory
    digestive organs
  • Teeth
  • Tongue
  • Glandular organs
  • Salivary glands

26
Stomach
  • Muscular tube with extra layers of smooth muscle
    cells
  • Strengthen stomach wall
  • Assist in mixing/churning activities required to
    form chyme
  • Muscularis mucosae/interna has extra outer,
    circular layer
  • Muscularis externa has oblique layer

27
Figure 24-13
28
Stomach
  • Has expanded J shape
  • Lesser curvature shorter, inner, medial surface
  • Greater curvature longer, outer, lateral surface

29
Figure 24-12b
30
Stomach
  • Has 4 regions
  • Cardia
  • Smallest region where esophagus enters (at
    gastroesophageal/cardiac sphincter)
  • Fundus
  • Superior hump to left of cardia that contacts the
    diaphragm
  • Body (corpus)
  • Main (middle) region of the stomach between
    fundus and curve
  • Pylorus
  • Last part of stomach that enters the duodenum
    through pyloric sphincter

31
Stomach
  • Rugae
  • Folds of gastric mucosa
  • Temporary features
  • Let gastric lumen expand (almost disappear when
    stomach full)

32
Stomach
  • Gastric pits
  • Depressions that open onto gastric surface
  • Each communicates with several gastric glands
  • Mucous cells line neck
  • Gastric glands
  • In fundus and body of stomach
  • 2 types of secretory cells
  • Parietal cells
  • Chief cells

33
Figure 24-13b
34
Small Intestine
  • 3 Regions
  • Duodenum (10 in.)
  • First part connects to pylorus
  • Mixing bowl
  • Receives chyme from stomach and secretions from
    pancreas and liver
  • Curves in a C that encloses head of the pancreas
  • Jejunum (8 feet)
  • Middle part
  • Site for most of chemical digestion and nutrient
    absorption
  • Ileum (12 feet)
  • Last part
  • Connects to large intestine via ileocecal valve

35
Small Intestine
  • Plicae circulares
  • inner folds in intestinal lining
  • Permanent feature -- do not disappear when small
    intestine fills
  • Wall
  • Mucosa
  • Intestinal epithelium
  • Simple columnar epithelium covers villi (pl
    singular villus)
  • Villus capillaries/villus capillary network
  • Lacteals
  • Intestinal glands (goblet cells, enteroendocrine
    cells)
  • Muscularis mucosae/interna
  • Submucosa, muscularis externa, and serosa as
    described previously

36
Figure 24-16
37
Figure 24-17
38
Large Intestine (Bowel)
  • 3 Main sections
  • Cecum
  • Colon (4.5 ft)
  • Rectum (6 in.)

39
Large Intestine (Bowel)
  • Cecum
  • Pouch-like structure that connects to ileum (at
    ileocecal valve)
  • Vermiform appendix small, worm-like appendage
    of lymphoid tissue attached to cecum

40
Large Intestine (Bowel)
  • Colon
  • Ascending colon along right side takes right
    turn at superior end right colic/hepatic
    flexure
  • Transverse colon crosses from R to L takes
    right turn downward at left end left
    colic/splenic flexure
  • Descending colon along left side curves
    medially at sigmoid flexure
  • Sigmoid colon S-shaped empties into rectum
  • Haustra
  • Pouches caused by longitudinal bands of
    muscularis externa (taeniae coli)
  • Permit expansion and elongation of colon

41
Large Intestine (Bowel)
  • Rectum
  • Anal canal last portion
  • Contain small longitudinal folds (anal columns)
  • Anus/anal orifice exit of anal canal
  • Contains 2 sphincters
  • Internal anal sphincter smooth muscle,
    involuntary control
  • External anal sphincter skeletal muscle,
    voluntary control

42
Figure 24-24a
43
Teeth
  • Located in alveoli (bony sockets) on alveolar
    processes of maxillary bones and mandible
  • Number
  • Primary (deciduous)
  • 5/side/jaw 20
  • Secondary
  • 3 molars/side/jaw 32
  • Replace primary teeth

44
Figure 24-9a, b
45
Tooth Type No./ Jaw Location Shape Function No. Roots
Incisors 4 Center front Blade Clip/cut 1
Cuspids/ Canines 2 Lateral to incisors Conical w/sharp ridge, pointed tip Tear/ slash/ shear 1
Bicuspids/ Premolars 4 Posterior to cuspids Flattened crown, prominent ridges Crush/ mash/ grind 1 or 2
Molars (wisdom teeth) 6 Posterior to bicuspids Large, flattened crown, prominent ridges Crush/ grind 3 or more
46
Teeth
  • Parts
  • Crown above gum line
  • Neck boundary between crown and root
  • Root below gum line sits in alveolus

47
Teeth
  • Layers/Regions
  • Outer
  • Enamel
  • Thin, white layer that covers crown
  • Hardest biologically manufactured substance
  • Cementum
  • Thin layer that covers root protects and helps
    anchor tooth
  • Inner
  • Dentin
  • Makes up bulk of tooth
  • Mineralized matrix (CaPO4 crystals) similar to
    bone, except acellular
  • Pulp cavity
  • Central region
  • Receives blood vessels and nerves from root canal
  • Root canal
  • Narrow tunnel at root/base of tooth
  • Blood vessels and nerves enter through apical
    foramen

48
Figure 24-8a, b
49
Salivary Glands
  • Outside oral cavity, but secrete into oral cavity
  • 3 pairs
  • Parotid glands
  • Extend from mastoid process of temporal bone
    across outer surface of masseter muscle
  • Parotid (Stensons) duct from parotid through
    buccinator to oral cavity
  • Sublingual glands
  • Under the floor of the mouth
  • Many small sublingual (Rivinus) ducts open along
    side of lingual frenulum
  • Submandibular glands
  • Along inner surfaces of mandible
  • Submandibular (Whartons) ducts open into mouth
    on either side of lingual frenulum immediately
    posterior to teeth

50
Figure 24-7a, b
51
  • Today in class we will
  • Complete our discussion of the 4 accessory
    digestive organs
  • Glandular organs
  • Pancreas
  • Liver
  • Histology
  • Bile duct system
  • Gall bladder
  • Trace the path of food through the digestive
    system

52
Pancreas
  • Lies posterior to stomach, extends laterally from
    duodenum toward spleen
  • Covered by thin, CT capsule
  • 3 regions
  • Head burrowed in loop of duodenum
  • Tail tapered end against spleen
  • Body slender middle region
  • Ducts deliver digestive enzymes and buffers to
    duodenum
  • Main pancreatic duct (of Wirsung) large, main
    duct ? major duodenal papilla with common bile
    duct ? duodenal ampulla (chamber)
  • Accessory pancreatic duct (of Santorini) may
    branch from pancreatic duct ? minor duodenal
    papilla ? duodenal ampulla

53
Fig. 24-18, p. 888
54
Gallbladder
  • Hollow, pear-shaped, muscular sac
  • Located in recess on posterior surface of livers
    right lobe
  • 3 regions
  • Fundus bottom of pouch
  • Body main region
  • Neck narrow end where cystic duct exits

55
Figure 24-19
56
Liver
  • Largest visceral organ
  • Covered by tough, fibrous capsule
  • Divided into 4 lobes
  • Right lobe largest, in right hypochondriac
    region
  • Left lobe narrow part extending into left
    hypochondriac region
  • Caudate lobe on inferior side superior, near
    IVC
  • Quadrate lobe inferior to caudate, near
    gallbladder
  • Falciform ligament on anterior surface between
    R and L lobes

57
Liver Histology
  • Hepatocytes liver cells simple cuboidal cells
  • Each liver lobe divided into lobules
  • Liver lobule basic functional unit of liver
  • Has hexagonal shape (6 corners)
  • Hepatic triad at each corner contains
  • Branch of hepatic portal vein
  • Branch of hepatic artery
  • Branch of bile duct
  • Separated by interlobular septa
  • Each has a central vein
  • Hepatocytes
  • Form 1-cell wide plates arranged like spokes
    around a wheel around central vein
  • Plates are separated by sinusoids modified
    blood vessels for large solutes can pass out
    of/into blood stream

58
Liver Histology
  • Branches of hepatic portal vein (from intestine
    to liver) and hepatic artery (to liver from
    systemic circulation) ? sinusoids
  • Hepatocytes absorb solutes and secrete materials
    (plasma proteins) into sinusoids
  • Blood leaves sinusoids and enters central vein of
    lobule
  • Central veins ? ? hepatic veins ? IVC ? heart
  • Kupffer cells
  • Phagocytic cells (lymphatic cells)
  • Functions
  • Engulf pathogens, cell debris and damaged blood
    vessels
  • Store iron, lipids, heavy metals absorbed by
    digestive tract

59
Figure 24-20
60
Bile Duct System
  • Hepatocytes ? bile ? bile canaliculi ? bile
    ductules ? R and L hepatic ducts ? common hepatic
    duct
  • Common hepatic duct cystic duct (to/from
    gallbladder) ? common bile duct
  • Common bile duct meets pancreatic duct at
    duodenal ampulla ? duodenal papilla
  • Hepatopancreatic sphincter - encircles
  • Common bile duct, pancreatic duct, and duodenal
    papilla

61
Figure 24-21a, b
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