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PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College

C H A P T E R

Copyright © 2010 Pearson Education, Inc.

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The Digestive System: Part A


Digestive System

• Two groups of organs

1. Alimentary canal (gastrointestinal or GI tract)

• Digests and absorbs food

• Mouth, pharynx, esophagus, stomach, small intestine, and large intestine


Digestive System

2. Accessory digestive organs

• Teeth, tongue, gallbladder

• Digestive glands

• Salivary glands

• Liver

• pancreas

Copyright © 2010 Pearson Education, Inc. Figure 23.1

Mouth (oral cavity)Tongue

Esophagus

LiverGallbladder

Anus

DuodenumJejunumIleum

Small intestine

Parotid glandSublingual glandSubmandibulargland

Salivaryglands

PharynxStomachPancreas(Spleen)

Transverse colonDescending colonAscending colonCecumSigmoid colonRectumVermiform appendixAnal canal

Largeintestine


Digestive Processes

• Six essential activities

1. Ingestion

2. Propulsion

3. Mechanical digestion

4. Chemical digestion

5. Absorption

6. Defecation


FoodIngestion

PropulsionEsophagus

Stomach

PharynxMechanicaldigestion

Chemicaldigestion

• Chewing (mouth)• Churning (stomach)• Segmentation (small intestine)

Smallintestine Largeintestine

Defecation Anus

Feces

Bloodvessel

Lymphvessel

Absorption

• Swallowing (oropharynx)• Peristalsis (esophagus, stomach, small intestine, large intestine)

Mainly H2O


Frommouth

(b) Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving the food forward then backward. Food mixing and slow food propulsion occurs.

(a) Peristalsis: Adjacent segments ofalimentary tract organs alternately contractand relax, which moves food along the tractdistally.


GI tract regulatory mechanisms

1. Mechanoreceptors and chemoreceptors

• Respond to stretch, changes in osmolarity and pH, and presence of substrate and end products of digestion

• Initiate reflexes that• Activate or inhibit digestive glands

• Stimulate smooth muscle to mix and move lumen contents


GI tract regulatory mechanisms

2. Intrinsic and extrinsic controls• Enteric nerve plexuses (gut brain) initiate

short reflexes in response to stimuli in the GI tract

• Long reflexes in response to stimuli inside or outside the GI tract involve CNS centers and autonomic nerves

• Hormones from cells in the stomach and small intestine stimulate target cells in the same or different organs


External stimuli(sight, smell, taste,

thought of food)Central nervous system

and extrinsic autonomic nerves

Afferent impulses Efferent impulses

Long reflexes

Internal(GI tract)stimuli

Chemoreceptors,osmoreceptors, ormechanoreceptors

Local (intrinsic)nerve plexus(“gut brain”)

Effectors:Smooth muscle

or glands

Gastrointestinalwall (site of shortreflexes)

Response:Change in

contractile orsecretory activityLumen of the

alimentary canal

Short reflexes


Peritoneum and Peritoneal Cavity

• Peritoneum: serous membrane of the abdominal cavity• Visceral peritoneum on external surface of

most digestive organs

• Parietal peritoneum lines the body wall

• Peritoneal cavity• Between the two peritoneums

• Fluid lubricates mobile organs

Copyright © 2010 Pearson Education, Inc. Figure 23.5a

Peritonealcavity

Parietalperitoneum

Visceralperitoneum

Ventralmesentery

Abdominopelviccavity

Dorsalmesentery

Vertebra

Alimentarycanal organ

(a) Schematic cross sections of abdominal cavity illustrate the peritoneums and mesenteries.

Liver


Peritoneum and Peritoneal Cavity

• Mesentery is a double layer of peritoneum• Routes for blood vessels, lymphatics, and

nerves

• Holds organs in place and stores fat

• Retroperitoneal organs lie posterior to the peritoneum

• Intraperitoneal (peritoneal) organs are surrounded by the peritoneum

Copyright © 2010 Pearson Education, Inc. Figure 23.5b

Abdominopelviccavity

Mesenteryresorbedand lost

(b) Some organs lose their mesentery and become retroperitoneal during development.

Alimentarycanal organ

Alimentary canal organ ina retroperitoneal position


Blood Supply: Splanchnic Circulation

• Arteries• Hepatic, splenic, and left gastric

• Inferior and superior mesenteric

• Hepatic portal circulation• Drains nutrient-rich blood from digestive

organs

• Delivers it to the liver for processing


Histology of the Alimentary Canal

• Four basic layers (tunics)• Mucosa

• Submucosa

• Muscularis externa

• Serosa


Glands in submucosa

Submucosa

LumenMucosa-associatedlymphoid tissue

Duct of gland outsidealimentary canal

Gland in mucosa

NerveArteryVein

Lymphaticvessel Mesentery

Intrinsic nerve plexuses• Myenteric nerve plexus• Submucosal nerve plexus

Mucosa• Epithelium• Lamina propria• Muscularis mucosae

Muscularis externa• Longitudinal muscle • Circular muscleSerosa• Epithelium• Connective tissue


Mucosa

• Lines the lumen • Functions• Secretes mucus, digestive enzymes and

hormones• Absorbs end products of digestion• Protects against infectious disease

• Three sublayers: epithelium, lamina propria, and muscularis mucosae


Mucosa

• Epithelium• Simple columnar epithelium and mucus-

secreting cells

• Mucus

• Protects digestive organs from enzymes

• Eases food passage

• May secrete enzymes and hormones (e.g., in stomach and small intestine)


Mucosa

• Lamina propria• Loose areolar connective tissue

• Capillaries for nourishment and absorption

• Lymphoid follicles (part of MALT)

• Muscularis mucosae: smooth muscle that produces local movements of mucosa


Submucosa and Muscularis Externa

• Submucosa• Dense connective tissue

• Blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus


Submucosa and Muscularis Externa

• Muscularis externa• Responsible for segmentation and peristalsis

• Inner circular and outer longitudinal layers

• Myenteric nerve plexus

• Sphincters in some regions


Serosa

• Visceral peritoneum• Replaced by the fibrous adventitia in the

esophagus

• Retroperitoneal organs have both an adventitia and serosa


Glands in submucosa

Submucosa

LumenMucosa-associatedlymphoid tissue

Duct of gland outsidealimentary canal

Gland in mucosa

NerveArteryVein

Lymphaticvessel Mesentery

Intrinsic nerve plexuses• Myenteric nerve plexus• Submucosal nerve plexus

Mucosa• Epithelium• Lamina propria• Muscularis mucosae

Muscularis externa• Longitudinal muscle • Circular muscleSerosa• Epithelium• Connective tissue


Enteric Nervous System

• Intrinsic nerve supply of the alimentary canal• Submucosal nerve plexus

• Regulates glands and smooth muscle in the mucosa

• Myenteric nerve plexus

• Controls GI tract motility


Enteric Nervous System

• Linked to the CNS via afferent visceral fibers

• Long ANS fibers synapse with enteric plexuses• Sympathetic impulses inhibit secretion and

motility

• Parasympathetic impulses stimulate


Mouth

• Oral (buccal) cavity• Bounded by lips, cheeks, palate, and tongue

• Oral orifice is the anterior opening

• Lined with stratified squamous epithelium


UvulaSoft palate Palatoglossal arch

Palatine tonsil

Hard palate

Oral cavity

Tongue

Lingual tonsilOropharynx

EpiglottisHyoid boneLaryngopharynx

Esophagus

Trachea(a) Sagittal section of the oral cavity and pharynx


Lips and Cheeks

• Contain orbicularis oris and buccinator muscles

• Vestibule: recess internal to lips and cheeks, external to teeth and gums

• Oral cavity proper lies within the teeth and gums

• Labial frenulum: median attachment of each lip to the gum


UvulaPalatine tonsil

Sublingual foldwith openings ofsublingual ducts

Tongue

Upper lip

Lower lipVestibule

Gingivae (gums)

Gingivae (gums)

Hard palateSoft palate

Lingual frenulumOpening ofsubmandibular duct

Palatine raphe

Inferior labialfrenulum

Posterior wallof oropharynx

Palatopharyngealarch

Superior labialfrenulumPalatoglossal arch

(b) Anterior view


Palate

• Hard palate: palatine bones and palatine processes of the maxillae• Slightly corrugated to help create friction

against the tongue

• Soft palate: fold formed mostly of skeletal muscle• Closes off the nasopharynx during swallowing

• Uvula projects downward from its free edge


Tongue

• Functions include• Repositioning and mixing food during chewing

• Formation of the bolus

• Initiation of swallowing, speech, and taste

• Intrinsic muscles change the shape of the tongue

• Extrinsic muscles alter the tongue’s position

• Lingual frenulum: attachment to the floor of the mouth


Tongue

• Surface bears papillae

1. Filiform—whitish, give the tongue roughness and provide friction- have keratin in the cells

2. Fungiform—reddish, scattered over the tongue

3. Circumvallate (vallate)—V-shaped row in back of tongue

4. Foliate—on the lateral aspects of the posterior tongue

Note: The Fungiform, Circumvallate and Foliate house taste buds

Go To Taste PowerPoint


Tongue

• Terminal sulcus marks the division between• Body: anterior 2/3 residing in the oral cavity

• Root: posterior third residing in the oropharynx


EpiglottisPalatopharyngealarchPalatine tonsilLingual tonsilPalatoglossalarch

Foliate papillaeCircumvallatepapilla

Terminal sulcus

Dorsum of tongue

Midline grooveof tongue

Filiform papillaFungiform papilla


SALIVA


Salivary Glands (Two groups)

• Extrinsic salivary glands - (parotid, submandibular, and sublingual)

• Intrinsic (buccal ) salivary glands - scattered in the oral mucosa


Saliva Functions

• Cleanses the mouth

• Moistens and dissolves food chemicals

• Aids in bolus formation

• Contains enzymes that begin the breakdown of starch


Extrinsic Salivary Glands

• Parotid gland (Otic Ganglion – CN IX)• Anterior to the ear external to the masseter

muscle

• Parotid duct opens into the vestibule next to second upper molar

• Submandibular gland (Submandibular Ganglion CN VII)• Medial to the body of the mandible

• Duct opens at the base of the lingual frenulum


Salivary Glands

• Sublingual gland (Submandibular Ganglion CN VII)• Anterior to the submandibular gland under the

tongue

• Opens via 10–12 ducts into the floor of the mouth


Teeth

Ducts ofsublingualgland

Sublingualgland

Submandibularduct

Posterior bellyof digastric muscle

Parotid ductMasseter muscleBody ofmandible (cut)

Parotidgland

Tongue

Submandibulargland

(a)

Frenulumof tongue

Mylohyoidmuscle (cut)Anterior belly ofdigastric muscle Mucous

cells (b)

Serous cellsforming demilunes


UvulaPalatine tonsil

Sublingual foldwith openings ofsublingual ducts

Tongue

Upper lip

Lower lipVestibule

Gingivae (gums)

Gingivae (gums)

Hard palateSoft palate

Lingual frenulumOpening ofsubmandibular duct

Palatine raphe

Inferior labialfrenulum

Posterior wallof oropharynx

Palatopharyngealarch

Superior labialfrenulumPalatoglossal arch

(b) Anterior view


Saliva is secreted by serous and mucous cells• Serous cells produce a watery secretion containing

enzymes, ions, and tiny bit of mucin.

• Mucous cells produce mucin – a glycoprotein substance that when mixed with water produces mucous.

• The parotid gland only has serous cells.

• Submandibular and buccal glands produce equal proportions of serous and mucous

• Sublingual glands only produce mucous


Composition of Saliva

• 97–99.5% water, slightly acidic solution containing

• Electrolytes—Na+, K+, Cl–, PO4 2–, HCO3–

• Salivary amylase and lingual lipase

• Mucin

• Metabolic wastes—urea and uric acid

• Lysozyme, IgA, defensins, and a cyanide compound protect against microorganisms


Additional Data on Saliva• Normal flora in the mouth convert food-derived

nitrates into nitrites which in-turn convert to nitric oxide in an acidic environment. This transformation occurs around the gums, where acid producing bacteria tend to cluster, and in the HCl rich secretions of the stomach. This activity acts as bacteriocidal agents in these locations.

• Saliva tests for HIV antibodies, oral cancer and diabetes are available

• Quick assessments of body hormones can be performed on saliva


Control of Salivation (1)• Intrinsic glands continuously keep the mouth moist

• Extrinsic salivary glands produce secretions when • Ingested food stimulates chemoreceptors and

mechanoreceptors in the mouth – chemoreceptors are activated more strongly by acids like vinegar and citrus juice – mechanoreceptors are stimulated by any object in the mouth

• Sight or smell of food is enough to get juices flowing

• Irritations of lower GI by bacterial toxins, spicy foods or hyperacidity especially when associated feeling of nausea – also increases salivation


Control of Salivation (2)

• Salivatory nuclei in the brain stem (Pons and Medulla) send impulses along parasympathetic fibers in cranial nerves VII and IX

• Strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia)

• Average output of saliva is 1 to 1 ½ liter per day


Teeth

• Primary and permanent dentitions are formed by age 21• 20 deciduous teeth erupt (6–24 months of

age)• Roots are resorbed, teeth fall out (6–12 years

of age) as permanent teeth develop• 32 permanent teeth• All except third molars erupt by the end of

adolescence


Deciduous teeth Permanent teeth(b)


Classes of Teeth

• Incisors• Chisel shaped for cutting

• Canines • Fanglike teeth that tear or pierce

• Premolars (bicuspids) and molars • Have broad crowns with rounded cusps for

grinding or crushing


IncisorsCentral (6–8 mo)

IncisorsCentral (7 yr)

Canine (eyetooth)(16–20 mo)

Canine (eyetooth)(11 yr)Premolars(bicuspids)First premolar(11 yr)

MolarsFirst molar(10–15 mo)

MolarsFirst molar (6–7 yr)

Lateral (8–10 mo) Lateral (8 yr)

Second molar(about 2 yr)

Second molar(12–13 yr)Third molar(wisdom tooth)(17–25 yr)(a)

Permanentteeth

Deciduous(milk) teeth Second premolar

(12–13 yr)


Dental Formulas

• A shorthand way of indicating the number and relative position of teeth• Ratio of upper to lower teeth for one-half of the

mouth

• Primary: 2I,1C, 2M

• Permanent: 2I,1C, 2PM, 3M


Tooth Structure

• Crown: the exposed part above the gingiva (gum)• Covered by enamel—the hardest substance in

the body (calcium salts and hydroxyapatite crystals)

• Root: portion embedded in the jawbone• Connected to crown by neck


Tooth Structure

• Cementum: calcified connective tissue • Covers root and attaches it to the periodontal

ligament

• Periodontal ligament• Forms fibrous joint called a gomphosis

• Gingival sulcus: groove where gingiva borders the tooth


Tooth Structure

• Dentin: bonelike material under enamel• Maintained by odontoblasts of pulp cavity

• Pulp cavity: cavity surrounded by dentin

• Pulp: connective tissue, blood vessels, and nerves

• Root canal: extends from pulp cavity to the apical foramen of the root


Crown

Neck

Root

EnamelDentinDentinal tubulesPulp cavity (containsblood vessels and nerves)Gingiva (gum)

CementumRoot canalPeriodontalligament

Apical foramen

Bone


Tooth and Gum Disease

• Dental caries (cavities): gradual demineralization of enamel and dentin • Dental plaque (sugar, bacteria, and debris)

adheres to teeth

• Acid from bacteria dissolves calcium salts

• Proteolytic enzymes digest organic matter

• Prevention: daily flossing and brushing



• Gingivitis• Plaque calcifies to form calculus (tartar)

• Calculus disrupts the seal between the gingivae and the teeth

• Anaerobic bacteria infect gums

• Infection reversible if calculus removed



• Periodontitis• Immune cells attack intruders and body tissues

• Destroy periodontal ligament

• Activate osteoclasts

• Consequences

• Possible tooth loss, promotion of atherosclerosis and clot formation in coronary and cerebral arteries

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