DIGESTIVE SYSTEM part 1 Oral cavity, esophagus

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DIGESTIVE SYSTEM part 1Oral cavity, esophagus
stomach
LECTURE
Department of histology, cytology and embryology
KhNMU
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General description and significance

• The digestive tract is
• a long tube extending from oral cavity to the
  anus and
• associated glands.
• Main functions are ingestion, fragmentation,
  digestion, absorption of nutrients and
  elimination of waste products.

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Classification and embryogenesis

• 3 compartments
• Anterior Oral cavity, pharynx, esophagus
• Middle Gastrointestinal tract
• Posterior Last 1/3 rectum, anus

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Embryogenesis
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Embryogenesis Gut from endoderm,
stomatodaeum, proctodaeum from
ectoderm Connective tissue, muscles are from
mesoderm
amnion
yolk sac
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Embryogenesis
foregut
hindgut
midgut
Cloacal Plate
Oral Plate
Allantois
Heart
Yolk Sac
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General plan of structure

• FOUR principal membranes
• Mucosa Epithelium
• Lamina propria
• Muscularis mucosae
• Submucosa
• Muscularis externa
• Serosa or adventitia

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3a
1a
2a
1b
1c
2
2b
4
3b
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Mucosa 1.epithelium (buccal)
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Mucosa 2. lamina propria con.t.
nutrition, support, protection
(GALT), absorption, secrition
(glands), villi 3. muscularis mucosae

• Submucosa - con.t. - big bl.vessels, glands,
  nerve plexuses, lymphatic nodules,
• provides motility of mucosa
• Muscularis externa circular, longitudinal
  layers
• Serosa or adventitia

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Oral Cavity

• consists of a number of suborgans
• Functions
• Ingestion,
  STRUCTURE
• Fragmentation 1. Mucosa
• Moistening 2. Submucosa
  
• Speech (not
  always present ! )
• Facial expression 3. Muscularis
  ext.
• Sensory reception (facial
  muscles)
• Breathing 4.
  Adventitia
• (absent)

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skin side
skin
oral side
oral
ss
ts
Lip
ts
lp
bv
sk
sg
ss
sk
sk
low mag.

• The outer surface (skin) of the lip is covered
  by thin skin (ts).
• The inner surface (oral) is lined by a mucosa
• The transitional zone

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Lip
ss
red area
p
bv

• Vermilion - red transitional zone
• In newborn there are small villi for sucking
  (Krok).
• The cheek is similar to the lip.

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Tongue
f
C
E
SM
G

• Epithelium (E) underlying ct.
• Skeletal muscle (SM) runs in 3 planes. Embedded
  in the skeletal muscle lie glands (G).
• Papillae. Most numerous are conical, keratinized
  filiform (f) papillae function general
  sensation
• fungiform and foliate papillae are scattered.
• At the sulcus terminalis, lie 8 -12 large
  circumvallate papillae (C).
• - Taste sensation

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Tongue, filiform fungiform papillae
ss
ss
fungi
fili
nss
fili
ct
ct
Circumvallate papilla
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Tongue
fp
high
tb
med

• papilla with taste buds

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Hard Palate
Maxilla
unerupted tooth
b
hard palate
epithelium
ss
m
low
med

• The mucosa (m) is tightly bound to the bone (b).
  The epithelium (ss) is disturbed in chewing and
  swallowing and so tends to be keratinized, and
  lamina propria forms deep papillae, protruding in
  the epithelium.

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Soft palate
Epithelium
sm
sg
oral cavity

• Its upper surface faces the respiratory passages
  - pseudostratified epithelium.
• Facing oral cavity epithelium is stratified
  squamous. Krok !

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Lingual Tonsil
c
ss
T
mg
sk

• Lingual tonsil (T) locates on the dorsum of the
  tongue.
• Together with palatine, pharyngeal tonsils form
  "ring".
• At time of chronic inflammation may undergo
  tonsilectomy.

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TOOTH

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Toothdevelopment

• Enamel organ (epith)
• Ameloblasts
• Enamel
• Dental papilla
• Odontoblasts
• Dentine
• Dental sac cementum,
• pulp

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SALIVARY GLANDS

• Saliva water, mucus, amylase, lysozyme, a/b,
  ions
• I. Large salivary glands 3 pairs parotid,
  submandibular, sublingual
• function - IN RESPONce
  TOPARASYMPATHETIC ACTIVITY
  
• II. Minor salivary glandsfunction -
  CONTINUOUSLY

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General structure

• Compound branched acinar or acino-tubular glands
• Connective tissue capsule
• Lobulated structure
• Lobules contain secretory units and small ducts
• Interlobular connective tissue with ducts and
  vessels

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5 Intercalated duct
Serous acinus
Striated duct, Next are interlobular and general
Mucous acinus

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Secretory unit
Myoepithelial cells (contractile) surround
secretory portions and small ducts
intercalated and striated
Nucleus
Myoepithelial cells
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Parotid
su
sd

• The parotid is a serous gland secreting amylase.
  
• Secretory unit (su) is acinar.
• Pyramidal acinar cells have round basally-placed
  nuclei (n) with abundant basal RER

RER
n
high
low
low
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Sublingual gland
itd
id
med
me
sd
d
msu
low
id
me

• This gland has mucous mixed secretory units
  but
• mostly mucous.

n
high

• Mixed acinus with a
• Serous demilune

msu
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Submandibular gland
lobule
m/s
low
id
ed
sa
high
med

• It is predominantly serous gland shows blue,
  pure serous acini (sa) pale, mucous and mixed
  with serous demilunes (m/s).

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Intercalated duct
Demilune
demilune
Parotid gland
sublingual gland
Sublingual gland Compare!
Striated duct
Demilune
Striated duct
Submandibular gland
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Esophagus ( Pharynx)

• 6-7 longitudinal folds.
• The muscularis externa.
• The upper 1/3rd is composed of skeletal muscle
  the lower 1/3rd - smooth muscle the middle 1/3rd
  shows a blending of the two varieties of muscle.
• Epithelium is stratified squamous nonkeratinized

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• Esophagus
• 1) Mucosa-epithelium, lamina
• propria muscularis mucosae,
• 2) Submucosa,
• 3) Muscularis
• externa
• 4) Adventitia

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Esophagus
ss
mg
lp
sm
mm
me

• Mucosal cardiac glands (mg) are in the lamina
  propria (lp) (mm) in the upper and lower thirds
  of the esophagus.
• If they are not fully effective, the excessive
  reflux results in pyrosis (heartburn) the rise
  of the gastric contents upward toward the neck.

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Esophagus
mm
mg
s
me

• A mucous esophageal glands proper (mg)
• lie in the submucosa (s).

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• Esophagus,
• middle 1/3rd - med. mag.
• .

m
L
sub
sm
me
sk

• muscularis externa (me). smooth (sm) skeletal
  muscle (sk).
• lymphatic nodules (L) are in the mucosa (m).

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Esophagus
submucosal gl.
med
lymphatic nodule
M'
high
lumen
str.sq.epi
musc. muc.
A'
high
submuc.
muscul. externa.

• The enteric nervous system is extensive and its
  neurons and fibers form in the submucosa
  (Meissners plexus) (M') and in the muscularis
  externa (Auerbachs plexus) (A').

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E
1
S
gp
sc
2
low
sc
3
E
S
gp
med
high

• Esophagus/Stomach junction. -
• Epithelium is changed from stratified squamous
  to
• simple columnar (sc).

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Stomach - general

• The process of digestion essentially begins in
  the stomach little absorption and excretion also
  occur here.
• The stomach is composed of a mucosa, submucosa,
  muscularis externa serosa.
• The mucosal lining is a simple columnar secretory
  epithelium (mucous).
• Folds (rugae), gastric pits, mammilated areas.
• Glands vary in different regions of the stomach.

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Stomach

• mucosa
• epithelium
• lamina propria gastric glands
• muscularis mucosae both circular and
  longitudinal layers of SM.
• submucosa
• muscularis the inner oblique layer, circular
  layer and longitudinal layer of SM.
• serosa

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sc
gp

• Stomach, mucosal lining gastric pits
• Gastric pits (gp) are invaginations of a simple
  columnar epithelium
• The mucus blanket which protects the lining from
  stomach acids is present here.

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• Lamina propria contains glands
• fundic glands (in the body, fundus) secrete the
  enzymes and acid of the stomach. While cardiac
  and pyloric glands predominantly secrete mucus.
• The fundic glands are simple tubular.
• They contain 4 cell types

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1. Mucous neck cells2. Chief cells , or
zymogenic cells

• columnar and basophilic cells - in the body of
  the glands.
• produce pepsinogen and lipase.
• 3. Parietal cells
• secrete hydrochloric acid ( HCL ) and intrinsic
  factor. The latter is necessary for absorption of
  vitamin B12 in the ileum

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4. Enteroendocrine cells (APUD)

• 20 different types
• 4 principal hormones
• Gastrin Hcl secretion
• Secretin, cholecystokinin (CCK), gastric
  inhibitory peptide (GIP) pancreatic and
  gallblader activity and gastric secretion

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Pernicious anemia follows the absence of parietal
cells (i.e. loss of epithelium due to gastric
ulcer)

• Disturbance of different cells may call the
  different pathology.
• Digestion of different substances begins in
  different regions.

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Fundic stomach
r
gp
m
sm
me
fg
low
2
sm
mm
me
med

• The lowest mag. shows the mucosa (m), submucosa
  (sm) with folds called rugae (r)
• the muscularis externa (me). At higher mag.
  gastric pits (gp), fundic glands (fg),
  muscularis mucosa (mm) comprises the mucosa.
  Outside is the submucosa (sm) and muscularis
  externa (me).

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Fundic stomachmucosa
gastric pit
Isthmus Neck Base
fundic gland

• In fundic stomach, gastric pits occupy about 1/5
  the mucosa fundic glands comprise the remaining
  3/4ths.

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sc

• Cardiac Stomach,
• Gastric pits occupy ½ of mucosa.
• Gastric glands are simple tubular and slightly
  branched
• Cells are mucus-secreting and
• occational endocrine

gastric pit
cardiac glands
mm
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Stomach, pyloric
gastric pit
gastric gland
mn
low

• Gastric pits occupy 3/4ths the depth of the
  mucosa the remaining 1/4th are pyloric glands
  short and branched.
• The major cell of the gland is the pale mucous
  (mn) parietal cells are absent as the pyloric
  stomach nears the intestine.

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smooth muscle
outer
inner
m
middle
fundic glands
submucosa
muscularis externa
artery
musc. mucosa
s
vein

• Fundic Stomach, nerve supply, - med high mag
• Elements of the submucosal (s) and myenteric (m)
  nerve plexuses are present.