VAN 504 , Lecture 04-2 Systemic histology : Study of microscopic structure of the organs of digestive system

The digestive tract has the following functions:   Prehension (grasping) of food with the lips and mouth Mechanical breaking down of the food by chewing Digestion of foodstuff by enzymatic and chemical reactions Absorption of nutrients and water Elimination of wastes

Most tubular organs consists of four concentric layers which are called tunics. These are from the lumanl surface to the periphery: The tunica mucosa – innermost or luminal coat, consist of three layers i. Lamina Epithelialis mucosae- epithelial layer of an organ ii. Lamina propria muscosae iii.Lamina muscularis mucosae 2. Tunica submucosa 3. Tunica Muscularis i. Lamina Muscularis Interna ii. Lamina Muscularis Externa 4. Tunica Adventitia or tunica serosa

INTRODUCTION BASIC PATTERN: I) Mucosa - Epithelium - Lamina propria - Muscularis Mucosae II) Submucosa III) Muscularis Externa IV) Serous layer / Adventitial layer

mucosa EPITHELIUM: It is columnar (Absorption/secretion) all over except in the Oesophagus and the lower part of Anal canal where it is stratified squamous (Protection). - Numerous folds - Crypts – At numerous places epithelium dips into the Lamina propria and form crypts (Simple tubular glands).

Villi: In Small intestine, Mucosa bears numerous finger-like processes that project in the lumen. Glands: 1. Unicellular secretory cells are scattered among the cells of the lining epithelium. 2. In some parts of GIT, Compound tubulo-alveolar glands are present in the submucosa.

LAMINA PROPRIA: - Made up of Collagen and reticular fibres. - contain blood capillaries, lymph vessels and nerves - In SI, the core of villus is attached to the lamina propria. - Prominent aggregation of lymphatic tissue is seen in Lamina propria (MALT)

MUSCULARIS MUCOSAE - Thin layer of smooth muscle that seperates lamina propria with the submucosa. - Inner layer: Circular - Outer layer: Longitudinal - Contraction of Muscularis Mucosa is important for the local mixing of intestinal contents - It changes the shape of mucosa, that helps in absorption and secretion

SUBMUCOSA This layer consists of loose areolar tissue that connects mucosa to the muscularis externa. Its looseness permits some mobility of mucosa over the muscularis externa. Contain numerous blood vessels, lymphatics and nerve fibres and Meissner’s plexus.

MUSCULARIS EXTERNA It consists of smooth muscles all over GIT except upper part of oesophagus which contain skeletal muscles. Arranged in two layers - Inner layer: Circular - Outer layer: Longitudinal Between the two layers “Auerbach’s plexus (Myenteric plexus)” is present. - Inner circular layer acts as sphincter. Eg: Pyloric sphincter, Internal anal sphincter, Ileo - caecal valve

Serosa /adventitial layer It is merely visceral peritoneum composed of connective tissue and simple squamous epithelium. The oesophagus lies outside the abdominal cavity has a superficial layer called Adventitia which consists of areolar connective tissue

OESOPHAGUS It is a straight muscular tube extending from pharynx to the stomach in abdomen. MUCOSA: Epithelium: Non-Keratinised sratified squamous epithelium Lamina Propria: Thin layer of loose CT. Muscularis Mucosae: - It is thicker than other parts of GIT - It is single layer of longitudinally running smooth muscle fibres.

SUBMUCOSA: - It is a wide layer of irregular, moderately dense connective tissue composed of bundles of collagen and elastic fibres. - Due to elastic fibres mucosa is thrown into folds, hence lumen of oesophagus appears star shaped - Contains blood vessels and branched tubulo- alveolar mucous glands

MUSCULARIS EXTERNA Arranged in two layers: - Inner layer: Circular - Outer layer: Longitudinal * Between the two layers – Myenteric plexus of nerve fibre and ganglion cells are present. It controls peristaltic movement. TYPES OF MUSCLES: Upper 1/3rd – Skeletal muscle Middle 1/3rd – Both skeletal and smooth muscle Lower 1/3rd – purely smooth muscle

SEROSA / ADVEVTITIA It consists of loose areolar connective tissue, which merges with the connective tissue of surrounding structures.

CARDIO-OESOPHAGEAL JUNCTION

STOMACH Stomach is a dilated segment of the digestive tract, that digest food and secrets hormone There are three histological regions: Cardia Fundus and body Pylorus The fundus and body are identical in microscopic structure The mucosa and submucosa of the undistended stomach lie in longitudinally directed folds known as rugae When the stomach is filled with food, folds flatten out

Cardiac region of the stomach Mucosa: Epithelial lining at the cardio-oesophageal junction changes from stratified sq. to simple columnar epithelium Presence of Mucous surface cells and cardiac glands Submucosa: Consists of Meissner’s plexus and blood vessels

Muscularis externa: Inner – Oblique Middle – circular Outer – longitudinal Myenteric plexus between muscle layers Serosa – Simple squamous epithelium resting on a thin layer of connective tissue

Stomach - fundus Mucosa: - Lining Epithelium – Simple columnar epithelium that invaginates to various extents into the lamina propria, forming gastric pits. - These cells are involved in mucus secretion. The mucus protects the epithelial lining from damage due to the presence of acid in the stomach.

Stomach – fundus Lamina propria: - Small tubular fundic/gastric glands are present. - Types of cells: i) Mucous neck cells – Located just below gastric pit. - Columnar in shape - Contain mucinogen granules in apical cytoplasm, while nuclei are basally situated basally. - Produces soluble mucus

Parietal or oxyntic cells: - They are large, ovoid or polyhedral cells with a large central nucleus. - More numerous in the upper half of the gland than in the lower half - Secretes HCL and intrinsic factor. Intrinsic factor combines with vitamin B12 to form a complex necessary for erythrocytes formation.

Chief or zymogenic cells: - Located in the lower 1/3rd of gastric glands. - Contain rough endoplasmic reticulum near the base, secretory granules near their apex and a small golgi apparatus. - Secrete pepsinogen which is converted into pepsin in an acid environment.

Enteroendocrine and APUD cells: - Located in the basal portion of gastric glands - Secretes serotonin, histamine and gastrin. These are endocrine cells which release their products into the blood vessels. MUSCULARIS MUCOSAE: - It consists of two thin layer of smooth muscles. i.e., Outer longitudinal and inner circular

SUBMUCOSA: - Consists of blood vessels, lymphatic vessels and Meissner’s plexus. MUSCULARIS EXTERNA: Inner: Oblique Middle: circular Outer: Longitudinal SEROSA: Outermost layers of the stomach which consists of loose connective tissue covered by mesothelium

MUSCULARIS EXTERNA: Inner: Oblique Middle: circular Outer: Longitudinal Similar to Fundic part, but the circular fibres are much thickened to form pyloric sphincter