1. DIGESTIVE SYSTEM
Lecture 13

2. Digestive System
• Oral tissues
– lips, oral cavity, teeth, tongue
• Digestive tract
– oral  esophagus  stomach 
small int.  large int.  rectum 
anus
• Accessory glands
– Salivary glands, pancreas, liver

3. The oral cavity
1) Vestibule (the area "outside" the
teeth)
2) Oral cavity proper
• The entire oral cavity - lined by a
stratified squamous epithelium.

4. The epithelial linings have 2 broad types:
• Masticatory epithelium - covers the
surfaces involved in the processing of
food
– Ex: tongue, gingivae (gums) and hard palate.
– The  keratinized epithelium (vary in
degree) = extent of physical forces exerted
on it.
• Lining epithelium - covers the
remaining surfaces of the oral cavity
– Ex: soft palate, cheek walls
– Non-keratinized stratified squamous
epithelium).

5. LIPS
Vestibule portion
• Outer lips
– lined by skin
• Inner lips
– oral mucosa
– Labial vessels
– Nerves
– orbicularis oris muscle (striated)
which shapes the lips
– labial salivary glands. – found within
the 2 lips.

7. Vermilion border (or prolabium)
• the "anatomical" lips
• the entire fleshy fold
surrounding the oral orifice;
• Area of transition from skin
to the oral mucosa.
Aesthetics
- Focus more on proper
proportions and accentuates the
vermillion lip border
- the key to achieving beautiful and
balanced results.

8. Epithelium
• thicker than other parts of facial skin.
Dermal papilla
• extend deep into the epithelium
Labial salivary glands – feel the small nodules in
the oral surface of your lips.
Vermillion border / prolabium

9. Dermal papilla
• extend deep into the epithelium
 vascularized (such close proximity to the
epithelium makes our lips red).

10. TONGUE
• Dorsal surface of the tongue –
Origin: Sulcus terminalis
• Anterior 2/3: oral part (lingual
papillae)
Posterior 1/3: pharyngeal part
(forms irregular surface covering
the lingual tonsils)

11. TONGUE
• a muscular organ covered by oral
mucosa which is specialised for
manipulating food, general sensory
reception and the special sensory
function of taste.
• The tongue is also vital for speech.
• Core: Dense CT covered with epithelium
• Epithelium: Strat. Squamous keratinized

12. Lingual papillae and its types
* Foliate papillae
• rudimentary (not well-developed) in
humans absent in aged individuals

14. Filiform papillae
– The smallest and most numerous papillae.
– surrounding the fungiform papilla
– slender with conical tips, covered by
stratified squamous epithelium that exhibits
partial keratinization.
– Provides the tongue with a rough surface
• aid in the manipulation and processing of
foods.
– Appear as short “bristles”.
• also clean the surfaces of the mouth, in
particular, the teeth.

15. 1- Keratin
2 – Filiform papilla
3 – Skeletal muscle

16. Fungiform (FG)
• scattered among the Filiform (FL) which
are small red globular papillae.

17. Fungiform
• The surface is covered by stratified squamous
epithelium that is not cornified or keratinized.
• exhibits numerous taste buds that are located in
the epithelium on the apical surface of the
papilla
• lamina propria - the underlying connective
tissue core that projects into the surface
epithelium of the fungiform papilla to form
numerous indentations.

18. Circumvalate papilla
• Six to 14 large papillae form a
row immediately anterior to the
sulcus terminalis
• contain most of the taste buds
located in the peripheral
epithelium.
• von Ebner’s gland (VE) –
“rinsing glands” (serous
glands), its excretory ducts
open into the trenches
surrounding the papillae.
– Serous (watery) fluid –
dissolves food & facilitates
taste reception (taste
buds).

20. Taste buds
- oval shaped, elongated cells (modified
columnar) that are arranged perpendicular to the
epithelium
Taste pore

21. Taste buds
• the chemoreceptors for the sense of taste
(gustation)
• open at the surface via the taste pore.
• Four taste modalities are recognised: sweet,
bitter, acid and salt.
• Each modality tends to be principally perceived
in a specific region of the tongue
• The sensations of taste and smell are
closely associated
• loss of olfactory sense is accompanied by
diminished gustatory perception.

22. TEETH
• small, calcified, hard, whitish structures
found in the mouth.
• To mechanically break down items
of food by cutting and crushing them in
preparation for swallowing and digestion.

23. TEETH

24. Histology of the tooth
Two segments
• CROWN - portion which projects into the oral
cavity and is protected by a layer of highly
mineralised enamel which covers it entirely.
– Enamel - an extremely hard, translucent substance
composed of parallel enamel rods or prisms of
highly calcified material cemented together by an
almost equally calcified interprismatic material.
• ROOT – the lower portion that is embedded in
the bony ridge of the jaw.

25. The bulk of the tooth is made up of dentine, a
mineralised tissue which has a similar chemical
composition to bone.
• more inorg. constituents of the matrix of dentine
than that of bone - hydroxyapatite crystals.
• Teeth are thus harder than bone.

26. • From the pulp cavity P,
minute parallel tubules,
called dentine tubules,
radiate to the periphery of
the dentine.
• The root is invested by a
thin layer of cementum
C which is generally thicker
towards the apex of the
root.
• The cementum is an
amorphous calcified tissue
into which the fibers of the
periodontal membrane are
anchored.

27. • Pulp cavity
– pulp chamber: the coronary portion
– root canal: the root portion extending to the apex
of the root.
– apical foramen: an orifice that permits the entrance
and exit of blood vessels, lymphatics, and nerves of
the pulp cavity.
• Periodontal ligament - a fibrous CT with
bundles of collagen fibers inserted into the
cementum and alveolar bone
– Fixes the tooth firmly in its bony socket (alveolus),
permitting limited movement of the tooth.
• Gomphosis – synarthosis joint in the teeth and
gums.

28. Digestive tract
• The alimentary
canal is a long,
tortuous tube
that begins with
the lips and
terminates with
the anus.

29. Common properties of the walls of the alimentary
tract
The wall is composed of the following
layers as follows from the lumen.
1.Mucosa (mucous membrane)
2.Submucosa
3.Muscularis
4.Serosa (serous membrane) or
adventitia

31. Basic Histological Layers
1. Mucosa
a. Epithelium
b. Lamina Propria
c. Muscularis
Mucosae
2. Submucosa
a. glands
b. blood vessels
b. Submucosal plexus
“Plexus of Meissner”
3. Muscularis
a. Layers of smooth M.
b. Myenteric plexus
“Plexus of Auerbach”
4. Serosa
a. CT with bld. vessels
and adipocytes
b. simple squamous
lining

32. MUCOSA
• the most important layer with
various tissue components has
diverse functions:
– Protection
– Secretion
– Absorption

33. Epithelium / lamina epithelialis
• adluminal, covering epithelium
• functions:
– physicochemical barrier between the
lumen and the connective tissue
– selective absorption of the digested
substances
– secretion of digestive enzymes and
lubricating mucins

34. • The types of the epithelium reflects the
special demands of the appropriate
segments of the alimentary canal
• examples:
– oral cavity, esophagus: stratified squamous,
nonkeratinized epithelium
– Stomach: simple columnar epithelium
– small intestine: simple columnar epithelium
with cuticle

35. Lamina propria (LP)
• Loose CT, which contains blood and
lymphatic vessels, nerve fibers and
different kinds of connective tissue cells
• In the LP of most segments of the G.I.T.,
there are tubular glands, such as the
gastric - and intestinal glands
• Elements of the immune system are
present throughout the G.I.T. to defend
the body against possible bacterial
attacks.

36. Muscularis mucosae
• thin layer of smooth muscle, which
is often composed of an inner
circular and outer longitudinal
sublayers
• contributes to the motility of the
mucous membrane; this movement
is independent of the peristaltic
movement of the tract

37. Example

38. SUBMUCOSA
• CT layer with various thickness; here
blood vessels run
• contains plexus of lymphatics
• contains vegetative ganglion cells and
peripheral nerves, which together make
the submucous plexus of Meissner
• may contain glands in the submucosa of
certain segments (esophagus and
duodenum)

39. MUSCULARIS
• Relatively thick layer with two sublayers
of smooth muscle in the vast majority of
cases
– inner circular sublayer (str. circulare)
– outer longitudinal sublayer (str. longitudinale)
• The sublayers are separated by thin
connective
• Tissue containing the myenteric plexus
of Auerbach as well as blood and
lymphatic vessels

40. Local variations of the
MUSCULARIS of alimentary
canal
• There are striated muscles in the
proximal segments of the esophagus,
and also in the anal canal
• There is a third muscular sublayer in
the wall of the stomach: inner oblique
fibers
• In the large intestine, the external
sublayer forms longitudinal bands of
smooth muscle: taeniae coli

41. SEROSA (serous membrane)
• The outermost layer of those segments
of the alimentary canal that are
enveloped by peritoneum
• Has simple squamous epithelium
(lamina epithelialis; mesothelium) and
a thin connective tissue sublayer (lamina
propria serosae)
• The serous membrane is attached to the
muscularis through a subserous
connective tissue

42. TUNICA ADVENTITIA
• Certain segments of the G.I.T. are not
enveloped by peritoneum
• In these segments, the outermost layer
is loose connective tissue (adventitia),
which connects the tract to the its
surroundings