Transcript Chapter_025.ppt

Chapter 25
Anatomy of the Digestive System
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Slide 1
Overview of the Digestive System
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Role of the digestive system
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Prepares food for absorption and use by all the
cells of the body
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Food material not absorbed becomes feces that is
eliminated

Digestion depends on both endocrine and
exocrine secretions and the controlled movement
of ingested food materials through the
gastrointestinal (GI) tract
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Slide 2
Overview of the Digestive System

Organization of the digestive system (Figure 25-1)

Organs of digestion
• Main organs of the digestive system form the GI tract that
extends through the abdominopelvic cavity
• Ingested food material passing through the lumen of the GI
tract is outside the internal environment of the body

Wall of the GI tract (Figure 25-2)
• Layers—GI tract is made of four layers of tissues: mucosa,
submucosa, muscularis, and serosa
• Modifications of layers—layers of the GI tract have various
modifications to enable it to perform various functions
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Slide 3
Mouth

Structure of the oral cavity (buccal cavity)
(Figure 25-3)

Lips—covered externally by skin and internally by
mucous membrane; junction between skin and
mucous membrane is highly sensitive; when lips
are closed, line of contact is oral fissure

Cheeks—lateral boundaries of oral cavity,
continuous with lips and lined by mucous
membrane; formed in large part by buccinator
muscle covered by adipose tissue; contain
mucus-secreting glands
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Slide 4
Mouth

Structure of the oral cavity (buccal cavity) (cont.)
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Hard and soft palates
• Hard palate consists of portions of four bones: two maxillae and two
palatines
• Soft palate forms partition between the mouth and the nasopharynx
and is made of muscle arranged in an arch
• Suspended from midpoint of posterior border of the arch is the uvula

Tongue—solid mass of skeletal muscle covered by a mucous
membrane; extremely maneuverable (Figure 25-4)
•
•
•
•
Important for mastication and deglutition
Has three parts: root, tip, and body
Papillae located on dorsal surface of tongue
Lingual frenulum anchors tongue to floor of mouth
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Slide 5
Mouth

Salivary glands—three pairs of compound tubuloalveolar
glands (Figure 25-6) secrete approximately 1 liter of
saliva each day; buccal glands contribute less than 5%
of total salivary volume but provide for hygiene and
comfort of oral tissues

Parotid glands—largest of the paired salivary glands; produce
watery saliva containing enzymes

Submandibular glands—compound glands that contain enzyme
and mucus-producing elements

Sublingual glands—smallest of the salivary glands; produce a
mucous type of saliva
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Slide 6
Mouth

Teeth—organs of mastication

Typical tooth (Figure 25-7)
• Crown—exposed portion of a tooth, covered by enamel; ideally
suited to withstand abrasion during mastication
• Neck—narrow portion that joins the crown to the root; surrounded
by the gingivae
• Root fits into socket of alveolar process and is suspended by
fibrous periodontal membrane
• Outer shell contains two additional tissues: dentin and cementum

Dentin makes up the greatest portion of the tooth shell; at crown,
covered by enamel, and at neck and root, covered by cementum

Pulp cavity—located in dentin, contains connective tissue, blood,
and lymphatic vessels and sensory nerves
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Slide 7
Mouth

Teeth (cont.)
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Types of teeth (Figure 25-8)
• Deciduous teeth—20 baby teeth, which appear early in life
• Permanent teeth—32 teeth, which replace the deciduous teeth
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Slide 8
Pharynx

Tube through which a bolus passes when
moved from the mouth to the esophagus by
the process of deglutition
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Slide 9
Esophagus
(Figure 25-9)

Tube that extends from the pharynx to
the stomach
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First segment of digestive tube
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Slide 10
Stomach (Figure 25-10)

Size and position of the stomach

Size varies according to factors such as gender and amount of
distention
• When no food is in stomach, it is about the size of a large sausage
• In adults, capacity ranges from 1.0 to 1.5 liters


Stomach location: upper part of abdominal cavity under liver and
diaphragm
Divisions of the stomach
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Fundus—enlarged portion to the left and above opening of
esophagus into stomach
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Body—central portion of stomach
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Pylorus—lower part of stomach
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Slide 11
Stomach


Curves of the stomach
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Lesser curvature—upper right curve of stomach
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Greater curvature—lower left curve of stomach
Sphincter muscles—circular fibers arranged so that
there is an opening in the center when relaxed and
no opening when contracted

Lower esophageal sphincter (LES) or cardiac sphincter
controls opening of esophagus into stomach

Pyloric sphincter controls outlet of pyloric portion of stomach
into duodenum
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Slide 12
Stomach

Stomach wall

Gastric mucosa
• Epithelial lining has rugae marked by gastric pits
•
•
•

(Figures 25-11 and 25-12)
Gastric glands—found below level of the pits; secrete most
of gastric juice
Chief cells—secretory cells found in gastric glands; secrete the
enzymes of gastric juice
Parietal cells—secretory cells found in gastric glands; secrete
hydrochloric acid; thought to produce intrinsic factor needed for vitamin
B12 absorption
Endocrine cells—secrete gastrin and ghrelin
•
Gastric muscularis—thick layer of muscle with three distinct
sublayers of smooth muscle tissue arranged in a crisscrossing
pattern; this pattern allows stomach to contract strongly at
many angles
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Slide 13
Stomach

Functions of the stomach



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
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Reservoir for food until it is partially digested and
moved further along GI tract
Secretes gastric juice to aid in digestion of food
Breaks food into small particles and mixes them
with gastric juice
Secretes intrinsic factor
Limited absorption
Produces gastrin and ghrelin
Helps protect body from pathogenic bacteria
swallowed with food
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Slide 14
Small Intestine

Size and position of the small intestine—tube
approximately 2.5 cm in diameter and 6 m in
length; coiled loops fill most of abdominal
cavity

Divisions of the small intestine
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Duodenum—uppermost division; approximately
25 cm long, shaped roughly like the letter C
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Jejunum—approximately 2.5 m long

Ileum—approximately 3.5 m long
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Slide 15
Small Intestine
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Wall of the small intestine (Figure 25-13)
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Intestinal lining has plicae with villi
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Villi—important modifications of mucosal layer
• Each villus contains an arteriole, venule, and lacteal
• Covered by a brush border made up of 1,700 ultrafine
microvilli per cell
• Villi and microvilli increase surface area of small intestine
hundreds of times
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Slide 16
Large Intestine
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
Size of the large intestine—average diameter, 6 cm;
length, approximately 1.5 to 1.8 m
Divisions of the large intestine (Figure 25-16)
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Cecum—first 5 to 8 cm of large intestine, blind pouch located in
lower right quadrant of abdomen
Colon
• Ascending colon—vertical position on right side of abdomen;
•
•
•
•
ileocecal valve prevents material passing from large intestine into
ileum
Transverse colon passes horizontally across abdomen, above small
intestine; extends from hepatic flexure to splenic flexure
Descending colon—vertical position on left side of abdomen
Sigmoid colon joins descending colon to rectum
Rectum—last 7 or 8 inches of intestinal tube; terminal inch is anal
canal with opening called the anus (Figure 25-17)
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Slide 17
Large Intestine
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Wall of the large intestine (Figure 25-19)
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Intestinal mucous glands produce lubricating
mucus that coats feces as they are formed
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Uneven distribution of fibers in the muscle coat
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Slide 18
Vermiform Appendix
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Accessory organ of digestive system; 8 to 10
cm in length; communicates with cecum
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Slide 19
Peritoneum
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Large, continuous sheet of serous membrane
(Figure 25-20)
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Made up of parietal and visceral layers
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Mesentery—projection of parietal peritoneum;
allows free movement of each coil of the
intestine and helps prevent strangulation of
the long tube (Figure 25-21)
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Transverse mesocolon—extension of
peritoneum that supports transverse colon
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Slide 20
Liver

Location and size of the liver (Figure 25-22)—largest
gland in body, weighs approximately 1.5 kg; lies
under diaphragm; occupies most of right
hypochondrium and part of epigastrium
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Liver lobes and lobules—two lobes separated by
falciform ligament
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Left lobe—forms about one sixth of liver
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Right lobe—forms about five sixths of liver; divides into right
lobe proper, caudate lobe, and quadrate lobe
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Hepatic lobules—anatomical units of liver; small branch of
hepatic vein extends through the center of each lobule
(Figure 25-23)
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Slide 21
Liver
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Bile ducts (Figure 25-25)
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Small bile ducts form right and left hepatic ducts
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Right and left hepatic ducts immediately join to
form one hepatic duct
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Hepatic duct merges with cystic duct to form
common bile duct, which opens into duodenum
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Slide 22
Liver

Functions of the liver
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Detoxification by liver cells—ingested toxic substances and
toxic substances formed in intestines may be changed to
nontoxic substances
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Bile secretion by liver—bile salts are formed in liver from
cholesterol and are the most essential part of bile; liver cells
secrete approximately 1 pint of bile per day
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Liver metabolism carries out numerous important steps in the
metabolizing of proteins, fats, and carbohydrates
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Storage of substances such as iron and some vitamins
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Production of important plasma proteins
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Slide 23
Gallbladder (Figure 25-25)

Size and location of the gallbladder—pear-shaped sac
from 7 to 10 cm long and 3 cm wide at its broadest point;
holds 30 to 50 ml of bile; lies on undersurface of liver
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Structure of gallbladder—serous, muscular, and mucous
layers compose the gallbladder wall; mucosal lining has
rugae
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Functions of gallbladder:
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Storage of bile
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Concentration of bile fivefold to tenfold
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Ejection of the concentrated bile into duodenum
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Slide 24
Pancreas

Size and location of the pancreas—grayish pink–colored
gland; 12 to 15 cm long; weighs approximately 60 g; runs
from duodenum and behind stomach to spleen

Structure of the pancreas (Figure 25-27)—composed of
endocrine and exocrine glandular tissue
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Exocrine portion makes up majority of pancreas; has a
compound acinar arrangement; tiny ducts unite to form main
pancreatic duct, which empties into duodenum
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Endocrine portion—embedded between exocrine units; called
pancreatic islets; constitute only 2% of total mass of pancreas;
made up of alpha cells and beta cells; pass secretions into
capillaries
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Slide 25
Pancreas

Functions of the pancreas
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Acinar units secrete digestive enzymes
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Beta cells secrete insulin
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Alpha cells secrete glucagon
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Slide 26
Cycle of Life: Digestive System
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Changes in digestive function and structure are age-related
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Result in diseases or pathological conditions
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May occur in any segment of intestinal tract
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Changes involve accessory organs: teeth, salivary glands, liver,
gallbladder, and pancreas
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Infants—immature intestinal mucosa; intact proteins can
pass through epithelial cells lining the tract and trigger
allergic response

Lactose intolerance affects infants who lack the enzyme
lactase
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Slide 27
Cycle of Life: Digestive System
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Young age—mumps common in children;
appendicitis more common in adolescents
and then decreases with advancing age
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Middle age—ulcers and gallbladder disease
common
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Old age—decreased digestive fluids, slowing
of peristalsis, and reduced physical activity
lead to constipation and diverticulosis
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Slide 28