1. Ch25: Digestive System Objectives:
Discuss the general functions and anatomy of the digestive tract
Describe the individual organs of the system, including a discussion of the gross and microscopic anatomy.

2. Digestive System consists of:
Muscular, hollow tube (= “digestive tract”) +
Various accessory organs

3. Function ingestion mechanical digestion
The function of the system as a whole is processing food in such a way that high energy molecules can be absorbed and residues eliminated.
Individual parts function in:
ingestion
mechanical digestion
chemical and enzymatic digestion
secretion
absorption
compaction
excretion and elimination

4. Histological Organization
Tube made up of four layers.
Modifications along its length as needed. 1 2
Muscularis
externa 3 4

5. The 4 Layers of the Gut 1) Mucosa
Fig 25.2
1) Mucosa
Epithelium – usually simple columnar with goblets; may be stratified squamous if protection needed
Lamina propria - connective tissue deep to epithelium
Muscularis mucosae -produces folds - plicae (small intestine) or rugae (stomach)
2) Submucosa – made up of loose connective tissue contains submucosal plexus and blood vessels
3) Muscularis externa – smooth muscle, usually two layers (controlled by the myenteric plexus ) -
outer layer: longitudinal
inner layer: circular
4) Serosa
visceral layer of mesentery or adventitia depending on location

6. Membranes Peritoneum - generic serous membrane in abdominal cavity
Mesenteries - double sheets of peritoneum, surrounding and suspending portions of the digestive organs
Greater omentum - "fatty apron", hangs anteriorly from stomach, double layer encloses fat
Lesser omentum - between stomach and liver
Mesentery proper - suspends and wraps the small intestine
Mesocolon - suspends and wraps the colon, parts are
i. transverse mesocolon
ii. sigmoid mesocolon
Fig. 25.4

7. Oral Cavity
Also called buccal cavity - lined with oral mucosa (type of epithelium ?)
Hard and soft palates - form roof of mouth
Tongue - skeletal muscle
Salivary glands - three pairs
Teeth

8. Three pairs of Salivary Glands
1-1.5 l / day for
digestion (?)
lubrication (swallowing) moistening (tasting)
Parotid – lateral side of face, anterior to ear, drain by parotid duct to vestibule near 2nd upper molar
mumps
Submandibular – medial surface of mandible – drain near lingual frenulum drain posterior to lower molars
Sublingual – in floor of mouth - drain near frenulum

9. Mumps Effective vaccine since 1967
Swollen, painful salivary glands on one or both sides of the face
Fever and sometimes orchitis, pancreatitis etc.
About 1/3 of infected people do not show symptoms
Effective vaccine since 1967

10. Structure of Teeth Crown - exposed surface of tooth
Neck - boundary between root and crown
Enamel - outer surface
Dentin – bone-like, but noncellular
Pulp cavity - hollow with blood vessels and nerves
Root canal - canal length of root
gingival sulcus - where gum and tooth meet
Fig 25.7
Enamel: Calcium phosphates. Hardest biological material produced.

11. Types and Numbers of Teeth
Dental succession
Deciduous (baby, milk) teeth - 20, replaced by
Permanent teeth - 32 teeth

12. Gross Anatomy of the Stomach
Lesser curvature
Greater curvature
Cardia - end under the heart
Fundus - bulge above the esophageal opening
Body - largest region
Pylorus - J curve, inferior end, terminates in
Cardiac and Pyloric sphincters (importance?)
Rugae – highly extendable interior folds
Figs 25-10/11

13. Histology of Stomach
Fig 25.13
Type of epithelium lining stomach?
Gastric pits – shallow pits, external half rapidly reproduces for replacement
Gastric glands – deep in lamina propria, 3 types of cells
Parietal cells (produce HCl and intrinsic factor)
Chief cells (produce pepsinogen)
Enteroendocrine cells – G cells (several hormones including gastrin which stimulates both parietal and chief cells)

14. Regions of Small Intestine
SI is longest part of dig. tube
Duodenum (short, 12 inches)
fixed shape & position
Mixing bowl for chyme & ?
Jejunum (2.5 m long)
Most of digestion
Ileum (longest at 3.5 m)
Most of absorption, ends in
Ileocecal valve – slit valve into large intestine (colon)

15. Structure of Small Intestinal Wall
Fig 25.15
Plicae circulares – circular pleats around the interior of the small intestine
Villi – minute finger-like projections, contain capillaries & lacteals
Microvilli – sub-microscopic size, projections on single cells
Function of all three?
Intestinal glands (crypts)
intestinal juice production
Cell regeneration
Histology in lab

16. Regions of Large Intestine
Cecum – pocket at proximal end with Appendix
Colon
Ascending colon - on right, between cecum and right colic flexure
Transverse colon - horizontal portion
Descending colon - left side, between left colic flexure and
Sigmoid colon - S bend near terminal end
Fig 25-17
Rectum – terminal end is anal canal - ending at the anus - which has internal involuntary sphincter and external voluntary sphincter

17. Histology of Large Intestine
1. Mucosa - abundant goblet cells, stratified squamous epithelium near anal canal
2. No villi
3. Longitudinal muscle layer incomplete, forms three bands or taenia coli
4. Circular muscle - forms pockets or haustra between bands
Fig 25.19

18. Liver
On right under diaphragm, largest organ made up of 4 lobes (left and right, caudate, and quadrate)
Hilus (porta hepatis) – underside "entry" point
Extremely versatile: Know a few functions?
Gall bladder
Blood supply to liver
makes bile, stores excess nutrients, makes plasma proteins, detoxifies harmful materials, stores iron & fat soluble vitamins
Fig 25.20
Fig 25.21
Microscopic anatomy: Liver lobules and triads

19. Pancreas Retroperitoneal Endocrine or exocrine gland?
Common bile duct and pancreatic duct lead to duodenal ampulla and papilla
Compare to Figs / 23

20. The End