Download Digestive System

Chapter 24 The Digestive System
BIO 211 Lab
Instructor Dr. Gollwitzer
1
• 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
layer’s characteristics
•
•
•
•
Mucosa
Submucosa
Muscularis externa
Serosa
– Begin our discussion of the gastrointestinal tract
components in more detail
• Oral cavity
• Pharynx
• Esophagus
2
Digestive System
• Gastrointestinal (GI) tract = continuous,
muscular tube from mouth to anus
– Oral cavity (mouth)
– Pharynx
– Esophagus
– Stomach
– Small intestine
– Large intestine
– Anus
3
Digestive System
• Accessory digestive organs = any digestive
organ attached to the GI tract
– Teeth
– Tongue
– Glandular organs
• Salivary glands
• Pancreas
• Liver
– Gall Bladder
4
Figure 24-1
5
Histological Organization
• 4 Major layers to wall
– Mucosa
– Submucosa
– Muscularis externa
– Serosa
6
Figure 24-3
7
Mucosa
• Inner lining of digestive tract
• A mucous membrane
• Consists of
– Epithelium - moistened by glandular secretions
– Lamina propria = areolar CT “filler”
8
Mucosa: Digestive Epithelia
• Depend on location, function, stresses
• Simple or stratified
• Columnar or squamous
9
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
10
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
11
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
12
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
13
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 (Peyer’s 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)
14
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)
15
Figure 24-3
16
Figure 24-3
17
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
18
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
19
Figure 24-6
20
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
21
Esophagus
• Hollow, muscular tube
• From posterior laryngopharynx to stomach
• Descends through thoracic cavity posterior to
trachea
• Enters abdominopelvic cavity through
esophageal hiatus in diaphragm
22
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
23
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
24
• 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
25
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
26
Figure 24-13
27
Stomach
• Has expanded J shape
– Lesser curvature = shorter, inner, medial surface
– Greater curvature = longer, outer, lateral surface
28
Figure 24-12b
29
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
30
Stomach
• Rugae
– Folds of gastric mucosa
– Temporary features
– Let gastric lumen expand (almost disappear when
stomach full)
31
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
32
Figure 24-13b
33
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
34
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
35
Figure 24-16
36
Figure 24-17
37
Large Intestine (Bowel)
• 3 Main sections
– Cecum
– Colon (4.5 ft)
– Rectum (6 in.)
38
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
39
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
40
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
41
Figure 24-24a
42
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
43
Figure 24-9a, b
44
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 Flattened
cuspids
crown,
prominent
ridges
Crush/
mash/
grind
1 or 2
Molars
(wisdom
teeth)
6
Posterior to Large,
bicuspids
flattened
crown,
prominent
ridges
Crush/
grind
3 or
more
45
Teeth
• Parts
– Crown – above gum line
– Neck – boundary between crown and root
– Root – below gum line; sits in alveolus
46
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
47
Figure 24-8a, b
48
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 (Stenson’s) 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 (Wharton’s) ducts – open into mouth on either
side of lingual frenulum immediately posterior to teeth
49
Figure 24-7a, b
50
• 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
51
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
52
Fig. 24-18, p. 888
53
Gallbladder
• Hollow, pear-shaped, muscular sac
• Located in recess on posterior surface of
liver’s right lobe
• 3 regions
– Fundus – bottom of pouch
– Body – main region
– Neck – narrow end where cystic duct exits
54
Figure 24-19
55
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
56
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
57
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
58
Figure 24-20
59
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
60
Figure 24-21a, b
61