Digestive System PPT – function and histology

June 17, 2012 | By | Reply More

Digestive System PPT –  function and histology
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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.


consists of:

Muscular, hollow tube (= “digestive tract”)


Various accessory organs



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:

mechanical digestion
chemical and enzymatic digestion
excretion and elimination

Histological Organization 

Tube made up of  four layers.

Modifications along its length as needed.

The 4 Layers of the Gut

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



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


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
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
Submandibular – medial surface of mandible – drain near lingual frenulum drain posterior to lower molars
Sublingual – in floor of mouth – drain near frenulum

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


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


Types and Numbers of Teeth

Dental succession

Deciduous (baby, milk) teeth – 20, replaced by

Permanent teeth – 32 teeth

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


Histology of Stomach

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

1.Parietal cells (produce HCl and intrinsic factor)
2.Chief cells (produce pepsinogen)
3.Enteroendocrine cells – G cells  (several hormones including gastrin which stimulates both parietal and chief cells)
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)

Structure of Small Intestinal  Wall

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


Regions of Large Intestine

Cecum – pocket at proximal end with Appendix


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

Rectum – terminal end is anal canal – ending at the anus –   which has internal involuntary sphincter and external voluntary sphincter

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


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

Microscopic anatomy: Liver lobules and triads



Endocrine or exocrine gland?
Common bile duct and pancreatic duct lead to duodenal ampulla and papilla


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