Download MBBS Digestive System II Lecture PPT

DIGESTIVE SYSTEM II


GIT OR ALIMENTARY CANAL

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? This is in the form of tube.
? Extend from oral cavity to

anus.

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? Parts of GIT--
? Oral cavity
? Pharynx
? Oesophagus

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? Stomach
? Small intestine
? Colon
? Rectum
? Anal canal

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INTRODUCTION

? GENERAL HISTOLOGY OF ALIMENTARY CANAL

? It is tubular structure

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? Four layers in the wall
? Layers from deep to superficial:--

I) Mucosa

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- Epithelium
- Lamina propria
- Muscularis Mucosae

II) Submucosa

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III) Muscle layer

IV) Serous layer / Adventitial layer

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MUCOSA

? Innermost layer of alimentary canal.

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? Epithelium

It is simple columnar (Absorption/secretion) all

over

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except in the Oesophagus and the lower part of

Anal canal where it is stratified squamous

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(Protection).
Organ

Epithelium

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Mouth

Nonkeratinized Stratified Squamous

Pharynx

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Nonkeratinized Stratified Squamous

Esophagus

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Nonkeratinized Stratified Squamous

Stomach

Simple Columnar

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Small Intestine

Simple Columnar

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Large Intestine

Simple Columnar

Anus

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Nonkeratinized Stratified Squamous
? Lamina propria

? Layers of loose connective tissue

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? Supports the epithelium
? Contains blood and lymphatic vessels
? It also contain glands (gastric glands)
? It also contains mucosa associated lymphoid

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tissue (MALT).
? Muscularis mucosae

- Thin layer of smooth

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muscle that separates

lamina propria with the

submucosa.

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- Inner layer: Circular
- Outer layer: Longitudinal
- It changes the shape of

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mucosa, that helps in

absorption and secretion
SUBMUCOSA

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? Consists of dense connective tissue rich in

collagen and elastic fibres.

? Contain numerous blood vessels, lymphatics

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and nerve fibres and Meissner's plexus.

? It also contains glands (oesophagus and

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duodenum)
MUSCLE LAYER

? It consists of smooth muscles all over GIT except

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upper part of oesophagus which contain skeletal

muscles.

? Arranged in two layers

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- Inner layer: Circular
- Outer layer: Longitudinal
Between the two layers "Auerbach's plexus

(Myenteric plexus)" is present.

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This plexus controles motility of tract.
SEROSA /ADVENTITIA

? It is merely visceral peritoneum composed of

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connective tissue and simple squamous

epithelium.

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? The oesophagus lies outside the abdominal

cavity has a superficial layer called Adventitia

which consists of areolar connective tissue

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OESOPHAGUS

? It is a straight muscular tube extending from pharynx

in neck to the stomach in abdomen.

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? MUCOSA:

Epithelium: Non-Keratinised sratified squamous

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epithelium
Lamina Propria: Thin layer of loose connective tissue.
Muscularis Mucosae:
- It is thicker than other parts of GIT
- It is single layer of longitudinally running smooth

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muscle fibres.
? SUBMUCOSA:

? It is a wide layer of, dense connective tissue

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composed of bundles of collagen and elastic

fibres.

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? Due to elastic fibres, submucosa is thrown into

folds, hence lumen of oesophagus appears star

shaped

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? Contains blood vessels and branched tubulo-

alveolar mucous glands
? MUSCLE LAYER

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? Arranged in two layers:
- Inner layer: Circular
- Outer layer: Longitudinal
* Between the two layers ? Myenteric plexus of

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nerve fibre and ganglion cells are present. It

controls peristaltic movement.

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TYPES OF MUSCLES:
Upper 1/3rd ? Skeletal muscle
Middle 1/3rd ? Both skeletal and smooth muscle
Lower 1/3rd ? purely smooth muscle
? SEROSA / ADVEVTITIA

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? It consists of loose areolar connective tissue,

which merges with the connective tissue of

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surrounding structures.

HISTOLOGY OF STOMACH
INTRODUCTION

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? On the basis of histological structure, stomach is

divided into three region:--

? i)Cardiac region

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? ii)Fundic(or body) region
? iii)Pyloric region
? The stomach wall exhibits four general regions:--
? Mucosa-- a) Lining epithelium, b) Lamina propria,

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c) Musularis mucosae

? Submucosa
? Muscle layer and
? Serosa .

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FUNDIC OR BODY REGION

? Mucosa

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? a)Lining epithelium
? Simple columnar

epithelium that

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invaginates to various

extents into the lamina

propria, forming gastric

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pits.

- These cells are involved in

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mucus secretion. The

mucus protects the

epithelial lining from

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damage due to the

presence of acid in the

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stomach.
? b)Lamina propria--
? Small tubular fundic/gastric glands are present.

Types of cells:

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i) Mucous neck cells ? Located just below gastric pit.

- Columnar in shape
- Contain mucinogen

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- Produces soluble mucus

? Parietal or oxyntic cells:
? Large ,rounded or pyramidal in shape
? Found in upper half of gastric gland.

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? Secretes HCL and intrinsic factor. Intrinsic

factor combines with vitamin B12

? Chief or zymogenic cells:

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? - Located in the lower 1/3rd of gastric glands
? - Secrete pepsinogen which is converted into

pepsin in an acid environment.

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? Enteroendocrine and APUD cells:

- Located in the basal portion of gastric glands
- Secretes serotonin, histamine and gastrin.

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These are endocrine cells which release their

products into the blood vessels.

c)Mucularis mucosae--

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It consists of two thin layer of smooth muscles.

Outer longitudinal

inner circular

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SUBMUCOSA:
Consists of blood vessels, lymphatic vessels

and Meissner's plexus.

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MUSCLE LAYER:
Inner: Oblique
Middle: circular
Outer: Longitudinal
SEROSA:

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Outermost layers which consists of loose

connective tissue covered by mesothelium

DUODENUM

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? Mucosa--villi (finger like mucosal projection)
--Intestinal gland (crypts of lieberkuhn)

? Submucosa--Duodenal gland (Brunner's gland)

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present

? Secrete alkaline mucus that protect the mucosa

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from acid secreted by stomach.

? Also secretes human epidermal growth factor

(which decreases HCL sec ).

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JEJUNUM

? Villi are tongue

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shaped and long

? Absence of

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Brunner's

glands.

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ILEUM

? Presence of

lymphoid

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aggregations in

lamina propria

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known as Peyer's

patches.

? Villi are short &

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finger like
LARGE INTESTINE

? It consists of: appendix, colon, rectum and anal canal.

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? Mucosa: Absence of Plicae circulares and villi
Presence of Microvilli
Presence of Crypts of Lieberkuhn
Presence of Goblet cells in large number
? Submucosa

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? Muscle layer:
Inner circular layer - thin compared to small intestine.
Outer longitudinal layer- forms Taenia coli.
? Adventitia: Appendices epiploicae (peritoneum forms

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pouch like processes filled with fat)
APPENDIX

? A small blind-ending diverticulum.
? Large accumulations of lymphoid tissue in

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lamina propria which may extend into submucosa.

? Intestinal villi are usually absent.
? Crypts are poorly formed.

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? Muscularis externa is thin.
? Absence of taenia coli.

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