© 2013 Pearson Education, Inc. Digestive System Two groups of organs 1. Alimentary canal...

© 2013 Pearson Education, Inc.

Digestive System

• Two groups of organs1. Alimentary canal (gastrointestinal or GI

tract)• Mouth to anus• Digests food and absorbs fragments• Mouth, pharynx, esophagus, stomach,

small intestine, and large intestine


Digestive System

2. Accessory digestive organs• Teeth, tongue, gallbladder• Digestive glands

– Salivary glands– Liver– Pancreas


Figure 23.2 Gastrointestinal tract activities.

Ingestion

Mechanicalbreakdown

Digestion

Propulsion

Absorption

Defecation

Food

PharynxEsophagus• Chewing (mouth)

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

Stomach

Lymphvessel

Small intestineLargeintestine

Bloodvessel

Mainly H2OFeces

Anus

• Churning (stomach)• Segmentation (small intestine)


Figure 23.3 Peristalsis and segmentation.

Frommouth

Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, moving food along the tract distally.

Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving food forward then backward.Food mixing and slow food propulsion occur.


GI Tract Regulatory Mechanisms

1. Mechano and chemoreceptors – Respond to stretch, changes in osmolarity

and pH, and presence of substrate and end products of dig

– Initiate reflexes that• Activate or inhibit digestive glands • Stimulate smooth muscle


Figure 23.4 Neural reflex pathways initiated by stimuli inside or outside the gastrointestinal tract.

External stimuli(sight, smell, taste,

thought of food)

Visceral afferents

Internal(GI tract)stimuli

Chemoreceptors,osmoreceptors, ormechanoreceptors

Long reflexes

Central nervous system

Local (intrinsic)nerve plexus("gut brain")

Effectors:Smooth muscle

or glands

Extrinsic visceral (autonomic)efferents

Short reflexes

Lumen of thealimentary canal

Gastrointestinalwall (site of shortreflexes)

Response:Change in

contractile orsecretory activity


• Peritoneum - serous memb of abd cavity– Visceral peritoneum on surface of organs– Parietal peritoneum lines body wall

• Peritoneal cavity– Between two peritoneums– Fluid lubricates mobile organs – Peritonitis

Abdominal adhesions are bands of fibrous scar tissue that form on organs in the abdomen, causing the organs to stick to one another or to the wall of the abdomen.


Figure 23.5a The peritoneum and the peritoneal cavity.

Abdominopelviccavity

Vertebra

Peritonealcavity

Alimentarycanal organ

Liver

Two schematic cross sections of abdominal cavity illustratethe peritoneums and mesenteries.

Ventralmesentery

Parietalperitoneum

Visceralperitoneum

Dorsalmesentery


Peritoneum and Peritoneal Cavity

• Mesentery - double layer of peritoneum– Routes for BV, lymphatics, and nerves– Holds organs in place; stores fat


Figure 23.5b The peritoneum and the peritoneal cavity.

Alimentarycanal organ

Alimentary canal organ ina retroperitoneal position

Some organs lose their mesentery and move,becoming retroperitoneal, during development.

Mesenteryresorbedand lost


Blood Supply: Splanchnic Circulation

• Branches of aorta– Hepatic, splenic, gastric, mesenteric arteries

• Hepatic portal circulation


Figure 23.6 Basic structure of the alimentary canal.

Intrinsic nerve plexuses

Mucosa

Submucosa

Muscularis externa

Glands insubmucosa

Serosa

LumenMucosa-associatedlymphoid tissue

Duct of gland outside alimentary canal

Gland in mucosa

Lymphatic vesselVein

ArteryNerve

Mesentery

• Myenteric nerve plexus• Submucosal nerve plexus

• Epithelium• Lamina propria• Muscularis mucosae

• Longitudinal muscle• Circular muscle

• Connective tissue

• Epithelium (mesothelium)


Enteric Nervous System

• Intrinsic nerve supply – enteric neurons• Major nerves to GI tract; control motility

– Submucosal nerve plexus• Regulates glands and smooth muscle in mucosa

– Myenteric nerve plexus• Controls GI tract motility

– Sympathetic inhibit dig activities– Parasympathetic stimulate dig activities


Figure 23.7a Anatomy of the oral cavity (mouth).

Palatoglossalarch

Softpalate

HardpalateOral cavityPalatinetonsil

Tongue

Oropharynx

Lingual tonsil

Epiglottis

Hyoid bone

Laryngopharynx

Esophagus

Trachea

Uvula

Sagittal section of the oral cavity and pharynx


Figure 23.7b Anatomy of the oral cavity (mouth).

Gingivae (gums)

Palatineraphe

HardpalateSoftpalate

Palatinetonsil

Sublingualfold withopenings ofsublingualducts

Oral vestibule

Lower lip

Uvula

Upper lip

Superiorlabialfrenulum

Palatoglossalarch

Palatopharyngealarch

Posterior wallof oropharynx

Tongue

Lingual frenulum

Opening ofSubmandibularduct

Gingivae (gums)

Inferior labialfrenulum

Anterior view


Figure 23.8 Dorsal surface of the tongue, and the tonsils.

Epiglottis

Palatopharyngealarch

Palatine tonsil

Lingual tonsil

Palatoglossal arch

Terminal sulcus

Foliate papillae

Vallate papilla

Medial sulcus of the tongue

Dorsum of tongue

Fungiform papilla

Filiform papilla


Figure 23.9 The salivary glands.

Tongue

Teeth

Frenulumof tongue

Mylohyoidmuscle (cut)

Anterior belly ofdigastric muscle

Masseter muscle

Body of mandible(cut)

Posterior belly ofdigastric muscle

Serous cellsforming demilunes

Mucous cells

Parotid gland

Submandibularduct

Submandibulargland

Ducts ofsublingualgland

Sublingualgland

Parotid duct


Salivary Glands

• Two types of secretory cells– Serous cells

• Watery, enzymes, ions, bit of mucin

– Mucous cells• Mucus

• Parotid, submandibular glands mostly serous; sublingual mostly mucous


• 97–99.5% water, slightly acidic– 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 microorganismsa

PLAY Animation: Rotating head

Composition of Saliva


Control of Salivation• 1500 ml/day• activated by parasympathetic when

– Ingested food stimulates chemoreceptors and mechanoreceptors in mouth

– Salivatory nuclei in brain stem send impulses along parasympathetic fibers in cranial nerves VII and IX

• Sympathetic inhibits salivation results xerostomia


Teeth

• Primary and permanent dentitions formed by age 21

• 20 deciduous teeth erupt (6–24 months of age)– Roots resorbed, teeth fall out (6–12 years of

age) as permanent teeth develop• 32 permanent teeth

– All but third molars in by end of adolescence• Third molars at 17–25, or may not erupt


Figure 23.10 Human dentition.IncisorsCentral (6–8 mo)

Lateral (8–10 mo)

Canine (eyetooth)(16–20 mo)

MolarsFirst molar(10–15 mo)

Second molar(about 2 yr)

IncisorsCentral (7 yr)

Lateral (8 yr)

Canine (eyetooth)(11 yr)

Premolars(bicuspids)First premolar(11 yr)

Second premolar(12–13 yr)

MolarsFirst molar (6–7 yr)

Second molar(12–13 yr)

Third molar(wisdom tooth)(17–25 yr)

Permanentteeth

Deciduous(milk) teeth


Dental Formulas

• Shorthand indicator of number/position of teeth– Ratio of upper to lower teeth for 1/2 of mouth– Primary:

– Permanent:


Tooth Structure

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

body (calcium salts and hydroxyapatite crystals)• Enamel-producing cells degenerate when tooth

erupts no healing if decay or crack

• Root - portion embedded in jawbone– Connected to crown by neck


Tooth Structure

• Cement - calcified connective tissue – Covers root; attaches to periodontal ligament

• Periodontal ligament– Fibrous joint called gomphosis– Anchors tooth in socket

• Gingival sulcus - groove where gingiva borders tooth


Tooth Structure

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

• Pulp cavity - surrounded by dentin – Pulp - connective tissue, BV, and nerves

• Root canal - as pulp cavity extends to root• Apical foramen at proximal end of root

– Entry for blood vessels, nerves, etc.


Figure 23.11 Longitudinal section of a canine tooth within its bony socket (alveolus).

Enamel

Dentin

DentinaltubulesPulp cavity(containsblood vesselsand nerves)GingivalsulcusGingiva(gum)

Cement

Root canal

Periodontalligament

Apicalforamen

Bone

Crown

Neck

Root


Tooth and Gum Disease

• Dental caries (cavities) - demineralization of enamel and dentin from bacterial action – Dental plaque (film of sugar, bacteria, and

debris) adheres to teeth– Acid from bacteria dissolves calcium salts– Proteolytic enzymes digest organic matter – Prevention: daily flossing and brushing


Tooth and Gum Disease• Gingivitis

– Plaque calcifies to form calculus (tartar)– Calculus disrupts seal between gingivae and

teeth – Bacteria infect gums


Tooth and Gum Disease• Periodontitis -Immune cells attack

• Destroy periodontal ligament• Activate osteoclasts dissolve bone

– Tooth loss; may promote atherosclerosis– Risk factors ?

© 2013 Pearson Education, Inc. Digestive System Two groups of organs 1. Alimentary canal...

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