Histology of digestive system oesophagus, stomach- fundus & pylorus

1. Histology of digestive systemoesophagus, stomach-fundus & pylorus Dr. Makarchuk Iryna

2. 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).

3. 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)

4. 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

5. 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.

6. 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

7. 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

8. 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.

9. 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

10. 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

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

12. 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

13. 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

14. 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

15. 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.

16. 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

17. 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.

18. 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.

19. 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

20. 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

21. Difference between cardia, fundus & body, and pylorus 21