Animal Histology
Digestive System Notes Part I.
Note of Caution: It is important to remember that the digestive tract can be thought
of as a long tube extending from the mouth to the anus, remember to think of it as
such. In other words, think about where you are in each part of the digestive tract,
what other organs/structures are nearby, and the function of the organ/structure
you are examining to help you deduce types of tissues you would expect to identify
and find.
1
Oral Cavity:
I.
Lips: the epithelium of the lip will change gradually from Stratified
Squamous Keratinized to Stratified Squamous Non-Keratinized as
you near the inside of the mouth. (see below)
Additionally, along the Stratified Squamous Keratinized Skin (thin skin) of the lip you may
see some SEBACOUS GLANDS and HAIR FOLLICLES which are characteristic of thin
skin. (see below)
(inside of the mouth) lip = Stratified Squamous NonKeratinized epithelium, with NO Hair Follicles,
mucus glands, skeletal muscles and fibroelastic
connective tissue.
Red Free Margin Zone (red flushy portion of
your lip = Stratified Squamous NonKeratinized Epithelium)
2
II. Tongue:
composed a skeletal muscle, glands and lymphatic tissues. Epithelial tissues
gives rise to three types of papillae:
All Papillae are composed of an epithelial layer + connective tissue (Lamina Propria)
3 Papillae:
(NOTE: ONLY Fungiform and Valatae Papillaes contain Taste Buds)
1. Filliform: most numerous; conelike projections of Straitified
Squamous Keratinized Epithelium w/keratinhyaline granules.
2. Fungiform/Foliate: scattered between filliform papillae; have
a toadstool appearance and contains Stratified Squamous NonKeratinized Epithelium and Taste Buds; located on edges of
tongue.
3
Compare: Fungiform (Red) and Filliform (Blue) Papillae:
3. Valate: found on the border of the oral and pharyngeal
portions of the tongue. Largest Papillae on tongue. Contain
Stratified Squamous Non-Keratinized Epithelium, Taste
Buds, Von Ebner’s Glands(cleansing secretions) and deep
“moats”.
4
<><><><><><><><><><><><><><><><><><><>
Taste Buds: (found ONLY in Vallate and Fungiform Papillae)
All Tatse Buds = 3 cell types
1. Sustenacular cells (support)
2. Stem Cells
3. Taste Receptor Cells
5
III.
Teeth:
All teeth contain several tissues:
1. Dentin: calcified tissue
2. Enamel: protective crown of tooth
3. Cementum: covers the root
4. Pulp Cavity: inner of tooth (LCT, Blood Vessels, and Nerves)
Within each tooth there are several cells:
In Dentin:
Odontoblasts (with long projections housed in Dentin Tubules that
project into the dentin)
In Enamel:
Ameloblasts (with long projecttions called Tomes Processes)
6
Digestive Tube:
There are four layers that are present throughout the entire Digestive Tube:
A. Mucus Membrane – composed of three layers :
1. Epithelial Lining
2. Lamina Propria
3. Muscularis Mucosa (Muscularis Interna)
B. Submucosa- contains LCT, blood vessels, connects muscularis mucosa to
muscularis Externa
C. Muscularis Externa- two layers of smooth muscle (one longitudinall one
circularily around the digestive tube)
D. Adventitia or Serosa- (Serosa- when tube is surrounded by a layer of
connective tissue and mesothelium; Adventitiat- when the tube is
connected to another organ and has no mesothelium layer)
7
I.
Esophagus: Contains an Adventita NOT a Serosa!!! (Stratified Squamous
Non-Keratinized Epithelium)
-
Lamina Propria (Mucus Membrane) near stomach =
cardiac glands (mucus glands)
Submucosa: Esophgeal Glands (Mucus Glands)
Muscularis Externa: upper 1/3 = Skeletal Muscle
Lower 2/3 = Smooth Muscle
Junction Between Esophagus and Stomach:
Blue= Esophagus
Yellow = Stomach (Cardiac)
II.
8
II.
Stomach: Contains a Serosa NOT and Adventitia!!! (Simple Columnar
Secretive Epithelium)
- contains a thick mucus membrane filled with tubular glands.
- each of the muscularis layers is composed of 3 layers of smooth muscle.
- the inside of the stomach muscle is also arranged in large folds called Rugae.
- contains Gastric Glands and Gastric Pits.
Pay Attention to the Size of the Pits and Glands of the Stomach to Help You Identify
Which Part of the Stomach you are in!!!
9
Three Main Areas of the Stomach:
1. Cardiac (near esophagus)
2. Fundic (body of stomach)
3. Pyloric (distal end of stomach)
A. Cardiac Stomach- Pits/Glands about the same size
Contains:
mostly mucus secreting cells ; tubular secreting glands
10
B. Fundic Stomach- Short Pits/ Long Glands (more FUN than the Pyloric Stomach)
Contains:
mucus secreting cells
parietal cells (fried egg appearance) – secrete HCl
chief cells (basophilic zymogen cells) – secrete pepsinogen (gets
converted to pepsin by HCl)
Blue- Gastric Glands; Red- Mucus Membrane;
White- Muscularis Interna ; Green- Submucosa;
Black- Gastric Pits
11
C. Pyloric Stomach- Long Pits/ Short Glands
Contains:
NO chief cells/ few parietal cells
mucus secreting cells
gastrin cells – secrete gastrin (activates parietal cell secretions/
contraction of stomach muscl)
Blue- Muscularis Externa; Red- Mucus
Membrane; White- Muscularis Interna ;
Green- Submucosa; Black- Deep Gastric
Pits ; Yellow- Muscularis Interna
12
III.
Small Intestine (SI):(Simple Columnar Secretive/Absorptive Epithelium)
SI is organized as a hierarchy of folds:
Plicae Circularis (folds of submucosa)  Villi forming Crypts of Lieberkuhn
(folds of lamina propria)  Microvilli (found on columnar epithelium of mucus
membrane)
<><><><><><><><><<><><><><><><><><><><><><><><><><><><><><><><>
3 Main Parts of the SI (from stomach to colon):
1. Duodenum
2. Jejunum
3. Ileum
All Parts of the SI have: Goblet Cells and Oligomucus Cells!!
(will only need to differentiate between the ileum and duodenum of the SI for LAB)
Stomach/Duodenum Junction:
Blue –Mucus Membrane of Duodenum; Red- Mucus Membrane of Stomach; Black arrow Deep Gastric Pits; Orange - Submucosa of Duodenum; Yellow - Brunner's Glands; Green
arrow - Pyloric Sphincter
13
A. Duodenum:
- Submucosa- Glands of Brunner (large mucus glands)
Blue – Mucss Membrane (giving rise to
Villi and Crypts of Lieberkuhn) ; Red –
Submucosa; Green - Muscularis Externa;
Yellow- Plicae Circularis; Black arrows Intestinal Villi
14
C. Ileum :
- Mucus Membrane- within epithelium/ crypts of Lieberkun = paneth cells
(cells that secrete digestive enzymes)
- Submucosa – Peyer’s Patches (non-encapsulatyed lymphatic nodule)
Blue – Lacteal; Red - Crypts of
Lieberkuhn; Black arrows - Goblet cells
15
IV. Large Intestine (Colon): Contains NO Villi!!! Only Plicae Circularis!!!
- All layers of the Colon resemble the SI
- Has an increased number of goblet and oligomucus cells!!!
Red – Goblet Cells
16
IV.
Rectum and Anal Canal:
Colon (simple columnar epithelium)  Rectum (simple columnar
epithelium)  Anal Canal (stratified squamous non-keratinized to keratinized
epithelium (thin skin))
<><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
Rectum: resembles the colon except: mucus membrane is flat/ Crypts of Lieberkuhn
are straight and parallel (will see lots of goblet and mucus secreting cells)
Rectal Anal Junction:
Red – Anus; Blue- Rectum
17
Anus: (transition from non-keratinized to keratinized stratified squamous
epithelium)
18