Human Anatomy 205

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How the Body Works The Digestive System

Digestive System System Outline with multimedia links

Function of digestion is to break down large food molecules to suitable size for absorption into cells
Functional Terms: ingestion, mastication, deglutition, digestion, absorption, peristalsis, defecation. [see terms defined]
Digestion of Carbohydrates [oral cavity & small intestine]
Digestion of fats [small intestine]
Digestion of proteins [stomach & small intestine]

Serous membranes in peritoneal cavity

Lining of abdominal cavity [parietal peritoneum and visceral peritoneum]
Mesenteries
- greater omentum and lesser omentum (supports stomach)
- mesentery (small intestine) and mesocolon (large intestine)

Histology of Digestive Tract [four layers on small intestine model] more information here

See examples of four layers

Mouth and Dentition

Tongue with papillae on dorsum - See slide of papillae
Three types of papillae [circumvallate papillae ] [fungiform papillae and filliform papillae ]
Palate [hard palate & soft with uvula] is the roof of the oral cavity
Glossopalatine arch is boundary between oral cavity & oropharynx
Three main Salivary Glands
1. Parotid [see model]
2. Submandibular [see model]
3. Sublingual
Saliva lubricates and initiates starch digestion
Dentition function in mastication
- Heterodont - 4 types of teeth [incisors, canines. premolars, molars] [torso dentition, lateral view]
- Dental formula: 2/2, 1/1, 2/2, 3/3 = 16 x 2 = 32 permanent teeth
- Tooth regions are crown, neck and root
- Tissues or layers of tooth [dentin] [enamel] [cementum] [pulp cavity]

Pharynx - see [sagittal section]

Has three regions
1. Nasopharynx adjacent to nasal cavity
2. Oropharynx [separated from oral cavity by Glossopalatine arch]
3. Laryngopharynx leads into to larynx & esophagus
Deglutition [swallowing] See Steps of Deglutition
See web site graphics of deglutition with animation

Peristalsis: wave-like contraction of smooth muscles - propels contents through the digestive tract.

Esophagus, from pharynx to stomach, is located in mediastinum

Stomach stores food and initiates digestion of proteins

Four Regions of the stomach
1. cardia is region where esophagus meets stomach
2. fundus is superior dome
3. body is main region
4. pylorus turns upward to meet duodenum
Interacive image of lab torso stomach
Gastric rugae are ridges on internal surface of stomach
Two mesenteries of stomach attached to surface curves
1. Greater omentum attached to greature curvature
2. Lesser omentum atached to lesser curvature
Cells of the stomach mucosa * see histology
- Parietal Cells secrete HCl and intrinsic factor
- Chief Cells secretes enzymes for protein hydrolysis
  [pepsinogen → pepsin]
- Mucus or goblet cells secrete protective mucus
- Enteroendocrine cells secrete gastrin [regulates acid production]
Physiology of stomach
- Acid + protein enzymes initiates digestion of proteins
- See history of physiology [William Beaumont & Alexis St. Martin]

Plica circularis are spiraling ridge-like folds of the mucosa and submucosa
Finger-like projections of the mucosa are villi, which function in absorption.
- Microvilli are cellular projections from the columnar epithelial cells of villi
- See human mucosa with villi
- See cross section of microvilli
Mucosa secrets digestive enzymes and hormones like secretin
Brunners Glands throughout duodenum (alkaline secretions neutralize gastric secretions) [See interactive intestinal wall with villi]
Three regions of small intestine
1. duodenum is 25 cm portion from pylorus to jejunum
2. jejunum is 1 m portion from duodenum to ileum
3. ileum is 2 m portion from jejunum to ascending colon
Mesenteries [mesododenum of duodenum] [mesentery of jejunum and ileum]
Pancreas is dual organ
1. pancreatic acini secrete hydrolytic enzymes [exocrine]
2. alpha & beta cells of pancreatic islets secret glucagon and insulin [endocrine]
Pancreatic digestive enzymes are transported to duodenum by pancreatic duct
See pancreas & duodenum on LMC Lab Torso

Liver

Lobes [right, left, caudate, quadrate] see liver image below.
See LMC torso liver model - [interactive posterior view]
Hepatic portal vien carries all nutrients, absorbed from intestine, to liver.
Nutrient rich hepatic portal blood is distributed through liver lobules.
Anatomy of liver Lobule [hepatic plates] [sinusoids]
Kupffer cells - phagocytic cells along walls of sinusoids - engulf bacteria and cell debris
See the Histology of the Liver Lobule
Liver lobules produce bile and collect bile in hepatic ducts
- Many of the body's waste products are secreted into the bile
- From hepatic duct bile enters gall bladder through cystic duct
- From hepatic duct or cystic duct bile enters duodenum through common bile duct
- Bile ducts and Gall Bladder
- Bile is critical for the digestion and absorption of fats. Bile breaks apart fats into small drops. The physiological term is emulsification

Big torso's interactive colon and Lab digestive system model with colon labeled
Taeniae coli are three longitudinal muscle bands
Haustra (sacculations) are puckered buldges between taeniae coli.
Mesocolon is the mesentery that supports large intestine
Regions of colon are ascending colon ⇑, right colic flexure, transverse colon ⇒, left colic flexure, descending colon ⇓, sigmoid colon
Cecum is on inferior portion of ascending colon.
Vermiform Appendix is vestigial tube extending from caecum
Rectum is a muscular organ that continues medially from sigmoid colon
- Temporarily stores and eliminates feces (defecation).
- Anal Canal is the final 3 cm of rectum [sphincters in wall- external & internal]
- Opening to outside is anus

Practice Tests Games and Crosswords

Crossword on digestive system terms
Try WebAnatomy quizzes on Digestive system or
WebAnatomy Games: Digestive system, stomach, small intestine, large intestine, from the University of Minnesota

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