William A Beresford MA, D Phil ©
Professor of Anatomy
Anatomy Department, West Virginia University, Morgantown, USA
Long, muscular, tubular structure for ingesting food and water, separating
them from the intake of air, breaking the food down mechanically and
chemically (digestion) for absorption, while propelling it anally. Ancillary
glands, liver and pancreas (Chapter 25), are included, since they produce
materials used for digestion or to be excreted via the tube, and they participate
metabolically and in the control systems. Powerpoint
A ORAL STRUCTURES
l Salivary glands
l Generally compound tubulo-alveolar, with intralobular intercalated ducts
and secretory ducts (with basal striations), leading to interlobular
2 Parenchyma is divided by CT septa into lobes and lobules.
3 Saliva is water, salts, and organic materials (mainly mucin and
salivary amylase/ptyalin and maltase), with suspended lymphocytes
(salivary corpuscles), epithelial cells, and bacteria.
4 Mucin is formed by mucous cells (pale in HE staining).
5 Enzymes are formed by serous cells (basophil, with zymogen granules).
6 Parotid gland is serous; submandibular/submaxillary has
serous alveoli, and mixed tubules with serous demilunes/crescents; and the
sublingual gland has mucous and mixed branched tubules, but lacks
intercalated and secretory ducts.( The tubules are long enough to reach the
7 Smaller mucous and mixed glands are in lingual, labial, buccal,
pharyngeal and palatine sites.
8 Chapter 11 gave more details of salivary glandular structure.
l Core of fibro-elastic CT and skeletal muscle.
2 Outside is thin skin with hairs and glands.
3 Transition zone is the red margin/vermilion border, where the skin's
cornified layer thins out; a rich capillary plexus is responsible for the
colour. Glands are absent.
4 Inside is a thick stratified squamous epithelium, with mucous glands
in its lamina propria.
5 The cheek is similar, but has more adipose tissue, and no red margin.
3 Gingiva/gum and raphe of hard palate
Stratified squamous epithelium (partly keratinized) on a dense CT lamina
propria, with deeply penetrating papillae, and fastened tightly to tooth or
4 Soft palate
l Fibrous and skeletal muscle core, with mucous glands;
2 pseudostratified, columnar, ciliated epithelium covers the pharyngeal side,
and stratified squamous the oral surface.
3 Functions in deglutition (swallowing), speech, blowing, coughing, and
l Core is interlaced skeletal muscle bundles oriented in three
directions, with attendant nerves and blood vessels.
2 Covered by stratified squamous epithelium, modified over the
anterior dorsum by being thrown up with the dense lamina propria into
3 papillae of various kinds, with special distributions:
4 Lingual glands - (a) posterior mucous; (b) posterior serous of von
Ebner, opening into the trenches; (c) anterior mixed sero-mucous.
- (a) Filiform - most numerous, spiky, with a partly
keratinized tip which is shed.
- (b) Fungiform - less numerous, larger, with some taste buds
in their smooth tops.
- (c) Circumvallate - least numerous, largest, lie along the terminal
sulcus, each surrounded by a trench, and with taste buds in its wall.
- (d) (Foliate - small ridges on the sides of the tongue, prominent in
rabbit, vestigial in man; also with taste buds in the walls.)
5 Lingual tonsils are stratified squamous epithelium-covered
aggregations of lymphoid nodules, with shallow crypts flushed out by mucous
secretions of the posterior lingual glands.
6 Palatine/faucal tonsils
l Covering is stratified squamous epithelium.
2 Deep, branching, epithelium-lined pits or crypts run down from the
surface into the tonsils, but the epithelium is infiltrated by
3 lymphocytes produced in germinal centres of lymphoid nodules
(often confluent) in the lamina propria, and by macrophages.
4 Immunoglobulins and lysozyme are present.
5 Glands and skeletal muscle lie nearby, outside the underlying CT capsule.
6 The palatine tonsils have substantial depth; the lingual are a narrow
region interposed between the epithelium and the muscular core of the tongue.
l Anatomical features: crown, cervix/neck, root, apical foramen, pulp
cavity, bony alveolus/socket, attaching periodontal ligament and the gingiva.
2 Tooth components
3 Histological details of tooth
- (a) Enamel: covers the crown of the tooth; tall tightly packed
prisms/rods; 96 per cent mineral crystals, 4 per cent organic content; but
- (b) Dentine: supports enamel and acts as the skeleton of
the tooth; hard material of collagen fibrils, impregnated with crystals of
calcium salts; penetrated from the pulp side by dentinal tubules enclosing
long, thin processes of odontoblasts, whose bodies lie outside the dentine
at the pulp.
- (c) Cementum: a thin layer of bone-like material, with cementocytes
(like osteocytes), but no Haversian systems, covers the root. Sharpey's
collagen fibres of the periodontal ligament insert into cementum, and
also into the bone of the alveolus, thus attaching the tooth to the jaw.
- (d) Pulp: jelly-like ground substance, with CT cells, blood and
lymphatic vessels and nerves, on a network of fine collagenous fibres;
dentine's pulp-surface is covered with the columnar odontoblasts.
(a) Decalcification for sectioning destroys mature enamel. It can be studied
in the ground section.
(b) Enamel prisms have a spiral curvature to better withstand masticatory
(c) Bands/striae of Retzius are growth/incremental lines across the enamel;
Owen's contour lines are analogous features in dentine.
(d) Interglobular areas are poorly mineralized regions in the dentine.
(e) Dentinal tubules branch, and may penetrate a little way into the enamel as
(f) Von Korff's 'fibres' seen in the pulp by young odontoblasts are either
collagen awaiting incorporation into the matrix of the dentine, or are an
artefact of silver impregnation.
(g) Secondary dentine (sometimes reparative) may be formed later to
increase the thickness of the dentine.
(h) Epithelial attachment is a cuff-like extension of the gingival
epithelium, attached to the neck of the tooth by glycoprotein.
(i) Acellular cementum lacks cementocytes.
4 Tooth development
(a) Two stages with (i) 20 deciduous/milk teeth, (ii) followed by 20
successional teeth and l2 permanent or accessional molars,
totalling 32. Powerpoint
(b) Involves complex inductive processes:
- (i) Migrating neural crest cells become 'mesectoderm,'
- (ii) and induce overlying ectoderm to thicken and grow down producing a
- (iii) dental lamina, under which 'mesectoderm' cells group,
- (iv) These induce the ectodermal dental lamina above to separate into
tooth germs, and to provide for each an enamel/dental organ, with
its stellate reticulum and inner and outer epithelia. The inner epithelium of
the enamel organ, in its turn, induces
- (v) 'mesectodermal' cells of the dental papilla to become
odontoblasts, which form dentine.
- (vi) The dentine acts as a stimulus to inner epithelium to become
functional ameloblasts and deposit enamel on the dentine.
Ameloblasts and odontoblasts are tall, columnar, secretory cells.
- (vii) The enamel organ's epithelium extends down as Hertwig's root
sheath, determining the form, size, and number of the roots.
- (viii) The root sheath perforates, and, through the holes, cells of
the surrounding mesectodermal dental sac approach root dentine
and lay down cementum. Other sac cells become fibroblasts forming
the periodontal ligament.
8 Functions of oral structures
l Obtaining, approving, masticating, and swallowing food and water.
2 General exploration of the environment.
3 Vocalization and communication. (Many systemic diseases have oral signs).
4 Preening, mating, fighting, etc, where chewing, licking, grasping or
biting is needed.
5 Oral glands contribute to digestion, and the lymphoid tissues to protection.
6 Breathing in exercising, and when the nose is blocked; coughing, and blowing.
B GASTROINTESTINAL TRACT
l General plan
l Mucosa (innermost)
2 GI submucosa
- (a) Of epithelium, lamina propria and smooth muscle muscularis
- (b) The epithelium in most places takes a glandular form, with
simple tubular glands and a secreting surface epithelium.
- (c) Some parts have discrete compound glands lying in the mucosa.
- (d) Single lymphoid nodules can occur anywhere.
3 GI muscularis externa
- (a) Of fairly dense CT, with blood and lymphatic vessels, and having a plexus
of unmyelinated autonomic nerve fibres - Meissner's submucosal plexus.
- (b) Glands are present in a few places.
4 GI serosa or adventitia/fibrosa (outermost)
- (a) Two or more helical layers of smooth muscle: the inner, tight
'circular'; the outer, loosely coiled 'longitudinal'.
- (b) Served by a nerve fibre plexus - Auerbach's myenteric plexus,
whose parasympathetic ganglion cells lie between the muscle layers.
- (c) Circular coat is more developed at sphincters and valves.
- (a) Of loose CT, with collagen and elastic fibres, nerves and vessels.
- (b) The serosa has a smooth mesothelial covering, and that part of the
tract is suspended on a mesothelium-covered tissue fold - omentum or
- (c) Mesothelial cells bear microvilli, are well attached, and secrete
lubricants to allow viscera to move freely.
(If mesothelium is lost during inflammation or operations, and is replaced by
the fibrous scar tissue of an adhesion, function is lost, e.g.,
uterine tubal adhesions can cause infertility.)
To avoid knots and obstruction, the plan for the GI tract is fasten, loosen,
fasten, and so forth, so that only the small intestine and transverse colon
have long stretches of mobile tube: fastening requires an adventitia,
mobility, a serosa. [ Powerpoint story on when a
serosa rather than an adventitia is found.]
l Mucosa has stratified squamous epithelium ending sharply, but along a jagged line,
at the gastric junction, creating a white-red distinction between proximal and
distal sides of the Z-line in endoscopy. Here, abnormalities of the oesophageal
epithelium and the position of the epithelial junction are quite common - Barrett's
oesophagus, where the stratified squamous epithelium is replaced metaplastically by
simple columnar epithelium with some or all of the small-intestinal cell types.
2 Muscularis mucosae - longitudinal smooth muscle.
3 Cardiac glands - make neutral mucus and are branched tubular, in the
mucosa near the gastric cardia, and in mucosa of the upper oesophagus; inconsistently
4 Oesophageal glands - acidic mucous, compound, tubulo-alveolar, and lying in
the submucosa, less numerous in the middle segment of the oesophagus.
5 Circular and longitudinal external muscle coats of skeletal muscle in the
upper fifth or so give way progressively to only smooth muscle in the lower
6 Outermost coat is CT adventitia, except on a small piece below the
7 Function - rapid passage of food to (and from) the stomach.
l General structure
2 Stomach mucosa
- (a) Anatomical regions - cardia, fundus, corpus, pyloric antrum and
pyloric canal: the regions are histologically distinct.
- (b) Outer covering is a serosa, from which hang omenta.
- (c) Muscular coat of three smooth muscle layers - outer,
longitudinal; middle, circular; inner, oblique. The middle layer is more
developed to form a sphincter at the pylorus. The muscle churns the
contents (chyme), and passes them periodically in regulated amounts to the
- (d) Submucosa - no glands; CT carries vessels and the nerve plexus.
- (e) Muscularis mucosae - two layers, with the inner circular one
sending a few muscle fibres up towards the lumen.
- (f) Mucosa is deep and glandular, with only a little lamina propria
tissue; produces acid and enzymes for digestion, and undertakes some
absorption, e.g., of water and alcohol.
3 Gastric secretions and cell types responsible
- (a) Empty stomach's lining is folded in ridges - rugae.
- (b) Surface is pitted by recesses - gastric pits/foveolae gastricae.
- (c) Long tubular glands extend from the muscularis mucosae up to
empty into the pits. A gland has a base, neck and isthmus.
- (d) The surface of the stomach and the pits are lined by simple, columnar,
special mucous epithelial cells.
- (e) Gastric glands throughout the body and fundus of the stomach
are simple, branched tubules with these cells:
- (i) Chief/zymogenic/peptic serous cells: in the majority; basophilic,
with 'zymogen' granules and rich granular ER.
- (ii) Parietal/oxyntic cells: occur peripherally and singly; large
and eosinophil; packed with mitochondria and smooth ER; have long
secretory canaliculi, lined by microvilli, and opening to the gland's
- (iii) Mucous neck cells: concentrated near the neck of the gland.
- (iv ) Endocrine/enteroendocrine/argentaffin/enterochromaffin/
Kultschitsky cells: few in number, seen with EM, silver methods, or cytochemistry,
but may be recognized from their empty look with H & E, and their rarity.
- (f) In the narrow cardiac region lie cardiac glands - compound tubular,
with mucous and a few parietal cells.
- (g) In the pylorus, pits are much deeper, and glandular tubules are
wider and more branching. The main kind of glandular cell present is pale and
resembles fundic mucous neck cells.
(a) Surface mucous cells - mucus, to prevent auto-digestion
of the mucosa, and bicarbonate ions held in the mucus.
(b) Chief/zymogenic cells - enzymes, e.g., pepsin, rennin, gastric
(c) Oxyntic/parietal cells - Cl-/HCO3- is
exchanged basolaterally to balance the apical Na+/H+
proton pump used to form the hydrochloric acid of the digestive juice.
(The stimulated active parietal cell has greatly extended canaliculi.)
(d) Mucous neck cells - mucus and enzymes, e.g., dipeptidases.
(e) Endocrine cells - hormones and amines; e.g., a
hormone - gastrin - produced by the pyloric antral G cells controls
the release and formation of acid from parietal cells, and of digestive enzymes
from chief cells.
(f) Parietal cells - intrinsic factor - to assist in the absorption
of vitamin B12: this role is upset when the parietal cells' proton pump is an
autoimmune target in pernicious anaemia, leading to the cells' destruction.
4 Gastric protective mechanisms
4 Small intestine
- (a) Digestive secretions (survived by typhoid and other bacilli,
and eggs of parasites, which do their damage in the gut, and by Helicobacter pylori).
H. pylori, resident in many stomachs, may cause intestinal metaplasia -
a pre-malignant state - or peptic/gastric ulcers, in some people.
- (b) Mucous and bicarbonate outer coating of the epithelium.
- (c) A film of surfactant-like lipid secreted by the epithelium.
- (c) Regenerative power of the epithelium, by cell proliferation and
migration (normally renewed every few days).
- (d) Lymphoid nodules and lymphocytes, and other leucocytes, in the
mucosa and submucosa.
- (e) Tight junctions between the epithelial cells.
- (f) Vomiting.
l General structure
2 Cytology of small-intestinal mucosa
- (a) Three regions - duodenum, jejunum and ileum,
anatomically and histologically distinguishable.
- (b) Serous coat over all except part of the duodenum and the
terminal ileum, which are fixed to the abdominal wall.
- (c) Suspended on a mesentery carrying blood and lymphatic vessels,
lymph nodes and nerves.
- (d) Muscularis externa has two complete layers.
- (e) Submucosa - occupied by Brunner's mucous, compound
tubular glands in the duodenum; elsewhere is CT as for the rest of the tract.
- (f) Muscularis mucosae - inner, circular, and outer, longitudinal
- (g) Mucosa has:
.. (i) Villi - finger- or leaf-like projections.
.. (ii) Crypts of Lieberkühn - simple tubular glands.
.. (iii) Lamina propria forming the core of each villus and lying between
the gland tubules.
.. (iv) Covering of simple columnar epithelium.
3 Functions of small-intestinal mucosa
- (a) Enterocytes are columnar absorptive epithelial cells on the
villi; with a brush border (many microvilli); are held apically by
junctional complexes; the many vesicles at the base of the microvilli
communicate with agranular ER.
- (b) Goblet cells, with the nucleus, GER and Golgi apparatus basally,
stored mucigen droplets apically.
- (c) Paneth cells, with eosinophil granules holding defensin and enzymes;
remain at the base of the crypts.
- (d) Enteroendocrine cells (other names 3.2.e.iv. above), with
hormone- and serotonin-containing basal granules.
- (e) Undifferentiated columnar crypt stem cells: few microvilli;
able to divide, migrate, differentiate into the other kinds, function, and
be extruded at the villus tip, over approximately four days.
- (f) Villus core has the basal lamina for the epithelium, a central
lymphatic capillary (lacteal), blood vessels, smooth muscle fibres.
The loose stroma of reticular and elastic fibres is heavily infiltrated by
WBCs, e.g., CD4+ helper-inducer lymphocytes and eosinophils, and plasma cells.
- (g) Ileum has Peyer's patches of extensive lymphoid tissue, erasing
villi, breaking into the epithelium, and interrupting the muscularis
mucosae to invade the submucosa. Elsewhere, only solitary lymphoid nodules
are to be seen. The epithelium domed over the Peyer's-patch follicles is
specialized, with M cells, which transport antigen and otherwise assist
- (a) Secretory
.. (i) Goblet cells give mucus.
.. (ii) Columnar cells make disaccharidases and other digestive enzymes
which, as ecto-enzymes, remain tethered in the microvillous membrane, so
constituting one component of the glycocalyx.
.. (iii) Paneth cells form defensins, etc, for defence.
.. (iv) Endocrine cells produce hormones to coordinate the functions
of the gut, liver and pancreas.
.. (v) Simple tubular intestinal glands/glands of Lieberkühn also contribute
to the enteric juice.
These secretions are additional to those already present from:
.. (vi) Salivary and oesophageal glands.
.. (vii) Stomach mucosa.
.. (viii) Pancreas and liver, introduced into the duodenum.
.. (ix) Brunner's duodenal glands (alkaline mucus led into the bottom of
- (b) Gut mucosal absorption of materials degraded by the secretions.
- (i) Membrane transports, active and passive, of many kinds, with
appropriate pumps, channels, and transporters. The tricky part is to get
lipid in across a barrier based on lipids - the cell membrane, and back out
- (ii) Pathway, through the absorptive cell, from the lumen to
the lacteal capillary lumen for lipid:
.. (a) hydrolysis, by mostly
pancreatic lipase, of the dietary
.. (b) interaction of the resulting free fatty acids and monoacylglycerol with
bile, to form micelles for solubilization;
.. (c) in this form, the lipids can be transported through the enterocyte's
.. (d) in the apical smooth ER, the lipids are re-acylated, and bound
to a protein for intracellular transport.
.. (e) Meanwhile, the GER is producing proteins to which some lipid is added -
apolipoproteins - which meet up with the apically reacylated lipid at the
Golgi complex, where
.. (f) the apoplipoprotein is used as a kind of cage, into the core/interior
of which increasing amounts of lipid are introduced, as the lipid droplet -
the chylomicron - is assembled,
.. (g) before its basolateral secretion by exocytosis from the Golgi complex
into the baso-lateral intercellular space.
.. (g) The chylomicrons and similar smaller lipid bodies pass through the
basal lamina to enter the lacteal lymph capillary, giving the gut and
mesenteric lymphatic vessels their white colour, and constituting chyle.
- (iv) Devices for increasing the effective gut surface area for
.. (a) the long length of the gut;
.. (b) villi;
.. (c) microvilli on absorbing cells;
.. (d) plicae circulares/valves of Kerckring (high folds of mucosa and submucosa)
.. (e) contractions of villus muscle, muscularis mucosae, and two main muscle
coats; (microvilli can slowly elongate, but not contract and relax.)
4 Changes within small intestine during descent:
(a) Goblet cells increase in number.
(b) Villi become more finger-like.
(c) Lymphoid tissue increases.
(d) Plicae circulares diminish.
5 Protective mechanisms of the gut:
- (a) alkaline mucus of Brunner's glands;
- (b) lubricating and protective goblet-cell mucus;
- (c) immune responses by APCs, lymphocytes and plasma cells;
- (d) rapid reactions of eosinophils, macrophages, and neutrophils
- (e) lysozyme and other antimicrobial contributions of Paneth cells;
- (f) barrier of tight junctions between the enterocytes;
- (g) diarrhoea;
- (h) rapid regeneration by the epithelium.
5 Large intestine
l General features
2 Regional details of large intestine
- (a) Crypts, but no villi or plicae circulares.
- (b) Columnar epithelial cells are: (i) undifferentiated; (ii)
goblet (numerous); (iii) colonocytes, absorbing, with microvilli,
for water, and some products of bacterial metabolism of the faeces;
(some excretion occurs). Endocrine cells are also present.
- (c) Dehydrating faeces need lubrication, hence many goblet cells are
present in the simple columnar epithelium.
- (a) Colon and caecum: outer longitudinal muscle coat is
gathered into three bands - taeniae coli - which pucker or sacculate
the tube, forming haustrations.
- (b) Appendix: continuous muscle coats; few crypts; the mucosa is
mainly occupied by lymphoid tissue; the muscularis mucosae may be
deficient and lymphoid tissue seen in the submucosa. The wall may be
thick. With age the lumen may be blocked off/occluded by fibrosis.
- (c) Rectum: outer longitudinal muscle is one continuous sheet.
- (d) Anal canal
.. (i) Morgagni's anal columns are 6-10 vertical mucosal folds.
.. (ii) Dentate line lies at the level of the bases of the columns, where
there are tiny flaps and pockets - anal valves and sinuses.
.. (iii) The histological epithelial anal transitional zone (ATZ)
lies between unbroken simple columnar colo-rectal epithelium and lower
stratified squamous epithelium.
.. (iv) The ATZ - the common site of anal cancers - is very variable in its
extent and outline, in its kinds of epithelia, and the number of crypts.
.. (v) Submucosal veins display periodic dilations. Deterioration of their
supporting connective tissue permits enlargement and prolapse - haemorrhoids.
.. (vi) The complex anal musculature includes external skeletal-muscle and
internal smooth-muscle sphincters. (The muscles and their innervation are
particularly at risk of stretching and damage in women giving birth.)