Digestive System_Part 1

8/7/2019 Digestive System_Part 1

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Digestive Systemy Two groups of organs

1. Alimentary canal (gastrointestinal or GI tract)

Digests and absorbs food

Mouth, pharynx, esophagus, stomach, small intestine, andlarge intestine

2. Accessory digestive organs

y Teeth, tongue, gallbladder

y Digestive glands

y Salivary glands

y Liver

y Pancreas


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Copyright 2010 Pearson Education, Inc. Figure 23.1

Mouth (oral cavity)

Tongue

Esophagus

Liver

Gallbladder

Anus

DuodenumJejunumIleum

Small

intestine

Parotid glandSublingual glandSubmandibular

gland

Salivary

glands

PharynxStomachPancreas(Spleen)

Transverse colonDescending colonAscending colonCecumSigmoid colonRectumVermiform appendix

Anal canal

Large

intestine


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Digestive Processesy Six essential activities

1. Ingestion

2. Propulsion

3. Mechanical digestion4. Chemical digestion

5. Absorption

6. Defecation


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Food

Ingestion

PropulsionEsophagus

Stomach

PharynxMechanicaldigestion

Chemicaldigestion

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

SmallintestineLargeintestine

Defecation Anus

Feces

Bloodvessel

Lymphvessel

Absorption

Swallowing(oropharynx)

Peristalsis(esophagus,

stomach,small intestine,large intestine)

Mainly H2O


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From

mouth

(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 of

alimentary tract organs alternately contract

and relax, which moves food along the tract

distally.


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GI tract regulatory mechanisms2. Intrinsic and extrinsic controls

Enteric nerve plexuses (gut brain) initiate short reflexesin response to stimuli in the GI tract

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

Hormones from cells in the stomach and small intestinestimulate target cells in the same or different organs


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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, or

mechanoreceptors

Local (intrinsic)

nerve plexus

(gut brain)

Effectors:

Smooth muscle

or glands

Gastrointestinal

wall (site of short

reflexes)

Response:Change in

contractile or

secretory activityLumen of the

alimentary canal

Short reflexes


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Peritoneum and Peritoneal Cavity

y Peritoneum: serous membrane of the abdominal cavity

y Visceral peritoneum on external surface of most digestive

organs

y

Parietal peritoneum lines the body wall

y Peritoneal cavity

y Between the two peritoneums

y Fluid lubricates mobile organs


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Copyright 2010 Pearson Education, Inc. Figure 23.5a

Peritoneal

cavity

Parietal

peritoneum

Visceral

peritoneum

Ventral

mesentery

Abdominopelvic

cavity

Dorsal

mesentery

Vertebra

Alimentary

canal organ

(a) Schematic cross sections of abdominal cavity

illustrate the peritoneums and mesenteries.

Liver


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Copyright 2010 Pearson Education, Inc. Figure 23.5b

Abdominopelvic

cavity

Mesenteryresorbed

and lost

(b) Some organs lose their mesentery and

become retroperitoneal during development.

Alimentary

canal organ

Alimentary canal organ in

a retroperitoneal position


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Blood Supply: Splanchnic Circulation

y Arteries

y Hepatic, splenic, and left gastric

y Inferior and superior mesenteric

y Hepatic portal circulation

y Drains nutrient-rich blood from digestive organs

y Delivers it to the liver for processing


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Histology of the Alimentary Canal

y Four basic layers (tunics)

y Mucosa

y Submucosa

y Muscularis externay Serosa


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Mucosay Lines the lumen

y Functions

y Secretes mucus, digestive enzymes and hormones

y Absorbs end products of digestiony Protects against infectious disease

y Three sublayers: epithelium, lamina propria, andmuscularis mucosae


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Mucosay Epithelium

y Simple columnar epithelium and mucus-secreting cells

y Mucus protects digestive organs from enzymes and eases food passage

y May secrete enzymes and hormones (e.g., in stomach and smallintestine)

y Lamina propria

y Loose areolar connective tissue

y Capillaries for nourishment and absorption

y Lymphoid follicles (part of MALT)

y Muscularis mucosae: smooth muscle that produces local movements

of mucosa


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Submucosa and Muscularis Externa

y Submucosa

y Dense connective tissue

y Blood and lymphatic vessels, lymphoid follicles, and

submucosal nerve plexus

y Muscularis externa

y Responsible for segmentation and peristalsis

y Inner circular and outer longitudinal layers

y Myenteric nerve plexus

y Sphincters in some regions


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Serosay Visceral peritoneum

y Replaced by the fibrous adventitia in the esophagus

y Retroperitoneal organs have both an adventitia and serosa


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Glands in submucosa

Submucosa

Lumen

Mucosa-associated

lymphoid tissueDuct of gland outside

alimentary canal

Gland in mucosa

NerveArtery

Vein

Lymphatic

vesselMesentery

Intrinsic nerve plexuses

Myenteric nerve plexus Submucosal nerve plexus

Mucosa

Epithelium Lamina propria Muscularis

mucosae

Muscularisexterna

Longitudinalmuscle

Circular muscleSerosa

Epithelium Connective

tissue


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Enteric Nervous Systemy Intrinsic nerve supply of the alimentary canal

y Submucosal nerve plexus

y Regulates glands and smooth muscle in the mucosa

yMyenteric nerve plexusy Controls GI tract motility

y Linked to the CNS via afferent visceral fibers

y

Long ANS fibers synapse with enteric plexusesy Sympathetic impulses inhibit secretion and motility

y Parasympathetic impulses stimulate


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Functional Anatomy: Mouthy Oral (buccal) cavity

y Bounded by lips, cheeks, palate, and tongue

y Oral orifice is the anterior opening

yLined with stratified squamous epithelium


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Uvula

Soft palatePalatoglossal arch

Palatine tonsil

Hard palate

Oral cavity

Tongue

Lingual tonsilOropharynx

Epiglottis

Hyoid bone

Laryngopharynx

Esophagus

Trachea

(a) Sagittal section of the oral cavity and pharynx


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Uvula

Palatine tonsil

Sublingual fold

with openings of

sublingual ducts

Tongue

Upper lip

Lower lip

VestibuleGingivae (gums)

Gingivae (gums)

Hard palate

Soft palate

Lingual frenulum

Opening of

submandibular duct

Palatine raphe

Inferior labial

frenulum

Posterior wallof oropharynx

Palatopharyngeal

arch

Superior labialfrenulum

Palatoglossal arch

(b) Anterior view


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Palatey Hard palate: palatine bones and palatine processes of the

maxillae

y Slightly corrugated to help create friction against the tongue

y Soft palate: fold formed mostly of skeletal muscle

y Closes off the nasopharynx during swallowing

y Uvula projects downward from its free edge


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Tongue

y Functions include

y Repositioning and mixing food during chewing

y Formation of the bolus

y Initiation of swallowing, speech, and taste

y Intrinsic muscles change the shape of the tongue

y Extrinsic muscles alter the tongues position

y Lingual frenulum: attachment to the floor of themouth


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Tongue

y Surface bears papillae

1. Filiformwhitish, give the tongue roughness and

provide friction

2. Fungiformreddish, scattered over the tongue3. Circumvallate (vallate)V-shaped row in back of

tongue

y These three house taste buds

4. Foliateon the lateral aspects of the posterior tongue


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Tonguey Terminal sulcus marks the division between

y Body: anterior 2/3 residing in the oral cavity

y Root: posterior third residing in the oropharynx


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Epiglottis

Palatopharyngeal

archPalatine tonsil

Lingual tonsil

Palatoglossal

arch

Foliate papillae

Circumvallate

papilla

Terminal sulcus

Dorsum of tongue

Midline grooveof tongue

Filiform papilla

Fungiform papilla


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Salivary Glandsy Extrinsic salivary glands (parotid, submandibular, and

sublingual)

y Intrinsic (buccal) salivary glands are scattered in the oral

mucosa

y Secretion (saliva)

y Cleanses the mouth

y Moistens and dissolves food chemicals

y Aids in bolus formation

y Contains enzymes that begin the breakdown of starch


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Salivary Glandsy Parotid gland

y Anterior to the ear external to the masseter muscle

y Parotid duct opens into the vestibule next to second upper

molar

y Submandibular gland

y Medial to the body of the mandible

y Duct opens at the base of the lingual frenulum

y Sublingual gland

y Anterior to the submandibular gland under the tongue

y Opens via 1012 ducts into the floor of the mouth


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Teeth

Ducts of

sublingual

gland

Sublingual

gland

Submandibular

duct

Posterior belly

of digastric

muscle

Parotid ductMasseter muscle

Body of

mandible (cut)

Parotid

gland

Tongue

Submandibulargland

(a)

Frenulum

of tongue

Mylohyoid

muscle (cut)Anterior belly of

digastric muscle Mucous

cells

(b)

Serous cells

forming

demilunes


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Composition of Saliva

y Secreted by serous and mucous cells

y 9799.5% water, slightly acidic solution containing

y ElectrolytesNa+, K+, Cl, PO4

2, HCO3

y Salivary amylase and lingual lipase

y Mucin

y Metabolic wastesurea and uric acid

y

Lysozyme, IgA, defensins, and a cyanide compoundprotect against microorganisms

PLAY Animation: Rotatable head


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Control of Salivation

y Intrinsic glands continuously keep the mouth moist

y Extrinsic salivary glands produce secretions when

y Ingested food stimulates chemoreceptors and

mechanoreceptors in the mouth

y Salivatory nuclei in the brain stem send impulses along

parasympathetic fibers in cranial nerves VII and IX

yStrong sympathetic stimulation inhibits salivation andresults in dry mouth (xerostomia)


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Teethy Primary and permanent dentitions are formed by age 21

y 20 deciduous teeth erupt (624 months of age)

y Roots are resorbed, teeth fall out (612 years of age) as

permanent teeth develop

y 32 permanent teeth

y All except third molars erupt by the end of adolescence


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Deciduous teeth Permanent teeth(b)


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Classes of Teethy Incisors

y Chisel shaped for cutting

y Canines

y Fanglike teeth that tear or pierce

y Premolars (bicuspids) and molars

y Have broad crowns with rounded cusps for grinding orcrushing


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Incisors

Central (68 mo)

IncisorsCentral (7 yr)

Canine (eyetooth)

(1620 mo)

Canine (eyetooth)

(11 yr)

Premolars(bicuspids)

First premolar(11 yr)

Molars

First molar(1015 mo)

Molars

First molar (67 yr)

Lateral (810 mo)Lateral (8 yr)

Second molar

(about 2 yr)

Second molar

(1213 yr)Third molar

(wisdom tooth)(1725 yr)

(a)

Permanent

teeth

Deciduous

(milk) teeth Second premolar

(1213 yr)


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Dental Formulasy A shorthand way of indicating the number and relative

position of teeth

y Ratio of upper to lower teeth for one-half of the mouth

y

Primary: 2I,1C, 2My Permanent: 2I,1C, 2PM, 3M


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Tooth Structurey Crown: the exposed part above the gingiva (gum)

y Covered by enamelthe hardest substance in the body (calcium

salts and hydroxyapatite crystals)

y Root: portion embedded in the jawboney Connected to crown by neck

y Cementum: calcified connective tissue

y Covers root and attaches it to the periodontal ligament

y Periodontal ligament

y Forms fibrous joint called a gomphosis

y Gingival sulcus: groove where gingiva borders the tooth


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Tooth Structurey Dentin: bonelike material under enamel

y Maintained by odontoblasts of pulp cavity

y Pulp cavity: cavity surrounded by dentin

y Pulp: connective tissue, blood vessels, and nerves

y Root canal: extends from pulp cavity to the apical foramenof the root


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Crown

Neck

Root

Enamel

Dentin

Dentinal tubulesPulp cavity (contains

blood vessels and

nerves)

Gingiva (gum)Cementum

Root canal

Periodontal

ligament

Apical foramen

Bone


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Tooth and Gum Diseasey Dental caries (cavities): gradual demineralization of

enamel and dentin

y Dental plaque (sugar, bacteria, and debris) adheres to teeth

y

Acid from bacteria dissolves calcium saltsy Proteolytic enzymes digest organic matter

y Prevention: daily flossing and brushing


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Tooth and Gum Diseasey Gingivitis

y Plaque calcifies to form calculus (tartar)

y Calculus disrupts the seal between the gingivae and the

teeth

y Anaerobic bacteria infect gums

y Infection reversible if calculus removed


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Tooth and Gum Diseasey Periodontitis

y Immune cells attack intruders and body tissues

y Destroy periodontal ligament

y Activate osteoclasts

y Consequences

y Possible tooth loss, promotion of atherosclerosis and clotformation in coronary and cerebral arteries

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Digestive System_Part 1