Digestive System Function: to obtain nutrients

Digestive System Function: 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

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

A Mucous membraneMucous membrane 1) Epithelium 2) Lamina propria 3) Muscularis mucosae 2. Tunic Submucosa 1. Tunic Mucosa Areolar Connective Tissue Innervation May have glands

Smooth muscle layer capable of plasticity Ability to tolerate stretching Visceral smooth muscle Muscularis Mucosa

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 = serosa b)Outside peritoneal cavity = adventitia

Histology of the G.I. Tract

The Peritoneum: Two layers Visceral 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 omentum Lesser omentum Mesentery proper Transverse mesocolon Sigmoid mesocolon Serous Membranes

Retroperitoneal Structures – these are attached to posterior abdominal wall Ascending colon Descending colon Duodenum Pancreas

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: Crown Neck Root Layers: Enamel Dentin Pulp Cavity with Pulp Cementum Apical foramen Root canal Periodontal membrane

Pharynx and Esophagus Deglutition Swallowing Epiglottis closes over larynx Voluntary control

Fig Tunica muscularis has three layers of muscle Tunica mucosa has folds, rugae when empty

Secretin and cholecystokinin Inhibit gastric secretion Histology of Gastric glands Chief - Pepsinogen; Parietal - HCl; Neck/Mucous Cells

Lacteal (terminal lymphatic) for lipid absorption Small Intestine Duodenum Jejunum Ileum Increase Surface Area for Absorption Intestinal glands Goblet cells Stem cells Plicae Circulares Intestinal villi Microvilli

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)

Secretin

CCK

Large intestine Functions of large intestine Reabsorb water and compact feces Absorb vitamins Store fecal matter Cecum Ileocecal valve Collects material from small intestine Vermiform appendix Colon - ascending, transverse, descending and sigmoid Rectum

Histology of Large Intestine Large Intestine: Lack of villi Abundance of goblet cells Mucous-secreting intestinal glands Muscularis reduced to Taenia coli Fatty 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

Diagrammatic view of lobular organization.

Pancreas

EtOH on Liver

Pancreas

Exocrine: acini Endocrine: Pancreatic islets Isles of Langerhans Pancreas