digestive system function: to obtain nutrients

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Digestive SystemFunction:

to obtain nutrients

Digestive SystemFunction: obtaining nutrients

Activities of Digestion system:• Ingestion – taking food or liquid into the mouth (eating or drinking).• Movements

•Peristaltic and Segmentation• Digestion

•Mechanical• mastication• churning

• Chemical•Enzymes and acids

•Absorption – movement of substances into the body (across epithelium).• Elimination – involves compaction to eliminate waste from body

The Digestive System

Layers of Gastrointestinal Tract

• Four layers:– Know layers and their composition

• Tunic mucosa– Epithelial– Propria– Muscularis mucosae

• Tunic submucosa• Tunica muscularis externa• Tunica serosa-visceral peritoneum

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•Lines digestive tract•Moistened by glandular secretions•Simple or stratified depending on area of tract•Pleated for expansion (Surface Area)

Tunic Mucosa

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A Mucous membrane1) Epithelium2) Lamina propria 3) Muscularis mucosae

2. Tunic Submucosa

1. Tunic Mucosa

•Areolar Connective Tissue •Innervation•May have glands

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Smooth muscle layer capable of plasticityAbility to tolerate stretching

Visceral smooth muscle

Muscularis Mucosa

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3. Tunica Muscularis Externa

4. Tunica Serosa (or Adventitia*)

Smooth muscle layers

1) Inner Circular Layer 2) Outer Longitudinal Layer

Serous membrane – visceral peritoneum

* Name depends on location:a) Inside peritoneal cavity = serosab) Outside peritoneal cavity = adventitia

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Histology of the G.I. Tract

The Peritoneum: Two layersVisceral peritoneum (a.k.a serosa)Parietal peritoneum

Lines inner surfaces of body wall

Mesenteries: Fused double sheets of peritoneal membrane – to suspend portions of digestive tract:

Greater omentumLesser omentumMesentery properTransverse mesocolonSigmoid mesocolon

Serous Membranes

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Retroperitoneal Structures – these are attached to posterior abdominal wall

Ascending colonDescending colonDuodenumPancreas

Salivary glands

• Parotid• Sublingual• Submandibular

– Slightly different secretions– Release enzymes - amylase– Lubrication oral cavity

Fig

25.6

Fig

25.7

Only example of gomphosis joint

Incisors -clipping/cutting

Canines -tearing/slashing

Premolars - mashing/grinding

Molars mashing/grinding

Teeth

Regions:CrownNeckRoot

Layers:EnamelDentinPulp Cavity with Pulp

CementumApical foramenRoot canalPeriodontal membrane

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Pharynx and Esophagus

Deglutition

Swallowing

Epiglottis closes over larynx

Voluntary control

Fig

25.11

Tunica muscularis has three layers of muscle

Tunica mucosa has folds, rugae when empty

Secretin and cholecystokininInhibit gastric secretion

Histology of Gastric glandsChief - Pepsinogen; Parietal - HCl; Neck/Mucous Cells

Lacteal (terminal lymphatic) for lipid absorption

Small IntestineDuodenum

Jejunum

Ileum

Increase Surface Area for Absorption

Intestinal glandsGoblet cellsStem cells

Plicae CircularesIntestinal villiMicrovilli

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Diagrammatic view highlighting the distinguishing features of each region of the small intestine.

Duodenum:Duodenal (Brunner’s) glands produce:

•secretin •CCK•Alkaline mucus

Ilieum: lymphatic aggregations (Peyer’s patches)

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Secretin

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CCK

Large intestine

Functions of large intestineReabsorb water and compact fecesAbsorb vitaminsStore fecal matter

CecumIleocecal valveCollects material from small intestineVermiform appendix

Colon - ascending, transverse, descending and sigmoidRectum

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Histology of Large Intestine

Large Intestine:Lack of villiAbundance of goblet cellsMucous-secreting intestinal glandsMuscularis reduced to Taenia coliFatty appendices

Rectum and Anal canal

Horizontal section through the upper abdomen showing the position of the liver relative to other visceral organs.

Other digestive organs

Liver

Bile Ducts

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Diagrammatic view of lobular organization.

Pancreas

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EtOH on Liver

Pancreas

Exocrine: acini

Endocrine:

Pancreatic islets

Isles of Langerhans

Pancreas