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Dr. Nabil Khouri
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)
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
Esophagus
The Stomach Wall
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
Small Intestine
Duodenum
Jejunum
Ileum
Microscopic Anatomy of the Small Intestine

Structural modifications of the small intestine wall increase
surface area
 Plicae circulares: Characteristics of the jejunum


Villi:


Transverse folds of the intestinal lining (deep circular folds of the
mucosa and submucosa) semi lunar, Circular or spiral form
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

Small intestine
The Intestinal Wall
The Intestinal Villi
Simple columnar epithelium
Produces
Mucin
Enterocytes
Tall columnar cells
W microvilli form the
brush border
- Paneth cells found at the base of the crypt




Central lacteal (lymphatic vessel)
Core capillaries
Core of connective tissue
Epithelial cells – Tall columnar with striated border
Lymphatic
vessels
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
V
Duodenum



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
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

Differences between duodenum, jejunum & ileum
Duodenum
Jejunum
Ileum
Epithelium
Columnar
Striated border
Few goblet cells
Columnar
Striated border
goblet cells+
Columnar
goblet cells++
Villi
Broad
Spatula Shaped
Closely packed
Tongue-shaped
Different heights
Few thin fingershaped
Lamina Propria
Crypts+
No Peyer’s patches
Crypts+
Diffuse infiltration of
lymphocytes
No Peyer’s patches
Crypts+
Peyer’s patches
extend into
submucosa
Submucosa
Mucus secreting
Brunner’s glands
Only connective
tissues and blood
vessels
Peyer’s patches
Small Vs Large Intestine
Small intestine
Large intestine
Villi
1. Crypts shallow
2. Goblet cells less
1. Absence of villi
2. Crypts deeper,
More Goblet
cells
Longitudinal
muscle coat of
muscularis
externa
1. Uniformly thick
1. Three bands of
Taenia coli