The Gastrointestinal System II:Small & Large Intestines

Histology SSN

March 7, 2005Presented by:

Anne O’Donnell & Nadia Goodwin

Small & Large Intestines

Small Intestine: principal site for digestion of food and absorption of the products of digestion

Large Intestine: reabsorption of water and elimination of undigested food and waste

4 Layers of Digestive SystemMucosa

- Epithelium

- Lamina Propria

- Muscularis Mucosae

Submucosa- Connective tissue, blood vessels,

submucosal plexus

Muscularis Externa- 2 muscle layers, myenteric plexus

Adventitia / Serosa- Loose connective tissue

Layer 1: Mucosal LayerEpithelium- enterocytes (with microvilli),

- goblet cells,

- paneth cells (SI only),

- entero-endocrine cells,

- M cells

Lamina Propria- loose connective tissue

- Peyer’s Patches

- lacteals

Muscularis Mucosae- Boundary b/t mucosa and submucosa

- 2 layers of smooth muscle

Layer 2: Submucosa & Layer 3: Muscularis Externae

Submucosa:

• Connective Tissue

• Blood vessels

• Submucosal (Meissner’s) Plexus

• (Brunner’s glands in duodenum)

Muscularis Externae:

• 2 smooth muscle layers

• Myenteric (Auerbach’s) Plexus b/t muscle layers

Myenteric Plexus Submucosal Plexus

Layer 4: Adventitia/Serosa

Loose connective tissue

Plicae Circularis vs VilliBoth are present in the small intestine as specializations to

maximize absorptive surface area

Plicae Circularis: circular folds with a core of submucosa. Contains many villi.

Villus: finger-like mucosal projections with a core of lamina propria

Cells of Mucosal Epithelium: Enterocytes

• Absorptive Cells• Columnar cells with basal

nuclei• Microvilli on apical

surface• Digestive enzymes in

microvilli glycocalyx (breakdown sugars & proteins)

• Junctional complexes and terminal web

Cells of Mucosal Epithelium: Enterocytes

Terminal bar

Microvilli

Cells of Mucosal Epithelium: Enterocytes

• Junctional complexes and terminal web

Terminal Bar

Cells of Mucosal Epithelium: Goblet Cells

• Produce mucus• Interspersed among

enterocytes• Appear empty because

mucus is washed out in slide preparation

• (more goblet cells in colon than SI)

Cells of Mucosal Epithelium in SI: Paneth Cells

• Located in Crypts of Lieberkuhn (bases of glands of SI b/t villi)

• Secrete lysozymes• Basophilic base,

eosinophilic granules at apex

• Regulate bacterial flora of gut

Cells of Mucosal Epithelium: Enteroendocrine Cells

• Secrete Hormones– GIP, CCK, Secretin

• Seen with silver stain• (Also in stomach)

Features of Mucosal Lamina Propria in SI

Lamina Propria: loose cellular connective tissue

Contains: 1. Peyer’s Patches: lymph

nodules and immune cells

2. Lacteals: endothelial-lined lymphatic channels w/in villi that uptake lipid droplets

Lipid Absorption

• Triglycerides and other lipids are packaged into droplets

• Droplets are absorbed from lumen, then reach basolateral surface where they are released by excocytosis

• Transported into lacteal

Features of Muscularis Mucosae in SI

• Boundary b/t mucosa and submucosa

• Composed of two thin layers of smooth muscle

Duodenum

Characterized by submucosal Brunner’s Glands (protect duodenum by neutralizing stomach acid)

Duodenum vs Jejunum and Ileum

Submucosal Brunner’s Glands

No Brunner’s Glands

Large Intestine

• Function: Reabsorbs water and electrolytes and eliminates undigested food and waste

Large vs Small Intestine

Similarities• Same Layers

– Mucosa– Submucosa– Muscularis Externa– Adventitia/Serosa

• Same Epithelial Cells– Enterocytes– Goblet cells– Enteroendocrine cells– M cells

BUT

Differences• Large Intestine has NO

plicae circularis and NO villi

• Large Intestine has MORE GOBLET cells

• NO PANETH cells in LI

Large vs Small Intestine

Junction: Rectum and Anal Canal

Rectum -simple columnar epithelium with goblet cells-glands

-No glandsRecto-Anal Junction-stratified columnar/ cuboidal epithelium

Recto-Anal Junction-stratified columnar/cuboidal epithelium

- as move toward anus, more stratified squamous- at perineum, stratified squamous epithelia is keratinized

Stratified Columnar/Cuboidal

Stratified Squamous (non-keratinized)

Hemorrhagic Vessels

Hemorrhagic vessel

These vessels are in the submucosa of the anal canal. When dilated, they are internal hemorrhoids.

Internal Anal Sphincter

Inner circular layer of muscularis externa thickens to form internal anal sphincter

Question 1

The organ shown :a. Digests carbohydrates

and proteins

b. Contains paneth cells

c. Reabsorbs water

d. Conjugates bile

Question 2Villi are present in both images:

a. True

b. False

Question 3Which sequence is the

correct oral to anal order?

B

A

DC