Digestive System Function to obtain nutrients Digestive System

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

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

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

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

3. Tunica Muscularis Externa Smooth muscle layers 1) Inner Circular Layer 2) Outer Longitudinal Layer 4. Tunica Serosa (or Adventitia*) Serous membrane – visceral peritoneum * Name depends on location: a) Inside peritoneal cavity = serosa b) Outside peritoneal cavity = adventitia

Histology of the G. I. Tract

Serous Membranes 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

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

Voluntary control Pharynx and Esophagus Deglutition Swallowing Epiglottis closes over larynx

Tunica muscularis has three layers of muscle Fig 25. 11 Tunica mucosa has folds, rugae when empty

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

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

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

Rectum and Anal canal

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

Liver

Bile Ducts

Diagrammatic view of lobular organization.

Pancreas

Et. OH on Liver

Pancreas

Pancreas Exocrine: acini Endocrine: Pancreatic islets Isles of Langerhans