1. Histology of Digestive Tract
Dr. Nabil Khouri

2. General Structure of Digestive Tract
Common Characteristics:
Hollow tube composed of a lumen whose diameter varies.
Surrounded by a wall made up of 4 principal layers:
Mucosa
Epithelial lining; A lamina propria of loose connective tissues rich in blood, lymph vessels and smooth muscle cells; Muscularis mucosae.
Submucosa
Dense connective tissues with many blood and lymph vessels.
Muscularis
Contains smooth muscle cells, divide into 2 layers; internal (circular); external (longitudinal)
Serosa
Thin layer of loose connective tissue rich in blood and lymph vessels and adipose and single squamous covering epithelium (mesothelium)

4. Basic Mucosal Forms in GI
. Protective mucosa –
Found in oral cavity, pharynx, esophagus, anal canal
Type – stratified sqaumous epithelium.
. Secretory mucosa –
Found only in stomach
Type – glandular epithelium (packed tubular), Simple branched.
. Absorptive mucosa –
Found in the Entire small intestine
Arranged in a fingerlike projection manner – villi
Duodenum only – sub-mucosal mucus Brunner’s glands – crypts - extend into the muscularis mucosa
. Absorptive/protective mucosa –
Found in large intestine
Type – glandular epithelium (packed tubular), Strait, cells specialized for water and mucus absorption - Goblet cells

5. Esophagus

6. The Stomach Wall

7. Histology of the Stomach
Mucosa
Epithelial lining is composed of
Simple columnar, cells with round or oval nucleus at the base with granules
Goblet cells that produce a coat of alkaline mucus
Mucosa is folded to form gastric pits
Gastric pits (GP) containing gastric glands (Open into the bottom of GP) that secrete:
Gastric glands secrete gastric juice
Mucus – protects stomach wall from pepsin
Pepsin – splits protein
Hydrochloric acid – needed for pepsin to work
Intrinsic factor – aids in absorption of vitamin B12

10. Small Intestine
Duodenum
Jejunum
Ileum

11. Microscopic Anatomy of the Small Intestine
Structural modifications of the small intestine wall increase surface area
Plicae circulares: Characteristics of the jejunum
Transverse folds of the intestinal lining (deep circular folds of the mucosa and submucosa) semi lunar, Circular or spiral form
Villi:
fingerlike extensions of the mucosa (epithelium and lamina propria)
Microvilli:
tiny projections of absorptive mucosal cells’ plasma membranes
Lacteals
Terminal lymphatic in villus
Intestinal glands
Lined by entero-endocrine, goblet and stem cells

12. Small intestine

13. The Intestinal Wall

14. The Intestinal Villi Simple columnar epithelium
Enterocytes
Tall columnar cells
W microvilli form the
brush border
Produces
Mucin
- Paneth cells found at the base of the crypt
Lymphatic
vessels
Central lacteal (lymphatic vessel)
Core capillaries
Core of connective tissue
Epithelial cells – Tall columnar with striated border

15. Small Intestine: Histology of the Wall
The epithelium of the mucosa is made up of:
Absorptive cells and goblet cells
Interspersed T cells (intraepithelial lymphocytes), and
Entero-endocrine cells
Intestinal crypts cells secrete intestinal juice
Peyer’s patches are found in the submucosa
Whereas, Brunner’s glands are found only in the duodenum and secrete alkaline mucus

16. Duodenum M G V Mucosa (M)-Villous form Glands- Coiled and branched
Crypts of LieberKuhn.
Brunner glands
Tall columnar cells.
Basally located nucleus
Secret alkaline mucus
Lysozyme and EG Factor
Ducts pass through the MM and openinto the crypts
Muscularis mucosa (MM)
Extends between the glands M
ucosa G

17. Mucosa of the Small Intestine
The mucosal surface is folded into villi
Increases surface area for absorption
Interior contains blood vessels and a lacteal
The mucosa and submucosa are thrown into circular folds Plicae Circulares PC
Microvilli are present on the luminal surface of the enterocytes.
Prominent future Peyer’s Patches – lymphoid tissue aggregates – Lamina propria
Intestinal Glands
Secrete intestinal juice
Contains enzymes that break down proteins, carbohydrates, fats

18. Differences between duodenum, jejunum & ileum
Epithelium
Columnar
Striated border
Few goblet cells
goblet cells+
goblet cells++
Villi
Broad
Spatula Shaped
Closely packed
Tongue-shaped
Different heights
Few thin finger-shaped
Lamina Propria
Crypts+
No Peyer’s patches
Diffuse infiltration of lymphocytes
Peyer’s patches extend into submucosa
Submucosa
Mucus secreting Brunner’s glands
Only connective tissues and blood vessels
Peyer’s patches

19. Small Vs Large Intestine
Small intestine
Large intestine
Villi
Crypts shallow
Goblet cells less
Absence of villi
Crypts deeper, More Goblet cells
Longitudinal muscle coat of muscularis externa
Uniformly thick
Three bands of Taenia coli