HISTOLOGY Gastrointestinal & Nutrition Block GNT 223 Histology of the Esophagus and Stomach By Dr. Einas Yousef 2018/2019

Objectives By the end of this lecture, the student should be able to discuss the microscopic structure, in correlation with the function, of the following organs: Esophagus. Stomach. 17-11-19

Introduction Digestive system is consists of digestive tract and its associated gland. 17-11-19

Histology of the Digestive Tract The wall of the gastrointestinal tube is formed of four layers. From the lumen outwards these layers are: 1. Mucosa (Epithelium, Lamina propria, Muscularis mucosa) 2. Submucosa 3. Muscularis externa (Musculosa) 4. Serosa or adventitia 17-11-19

Histology of the Digestive Tract (LS) L.S= longitudinal section 17-11-19

Histology of the Digestive Tract (TS) T.S.= Transverse section 17-11-19

1- Mucosa A- Epithelium: B- Lamina propria (Corium): The type of epithelium varies in different type of GIT depending on the function. Function for protection (esophagus), Secretion (stomach), Absorption of nutrients (intestine). B- Lamina propria (Corium): Loose connective tissue with nourishing and absorbing capillaries. It contains most of mucosa-associated lymphoid tissue C- Muscularis mucosae Thin layer of muscle arranged as inner circular and outer longitudinal. Produce movements of the mucosa.

2- Submucosa Loose areolar connective tissue containing blood and lymphatic vessels Submucosal nerves plexus “Meissner Plexus”. Contain Glands in some parts. Contain many elastic fibers so gut can regain shape after food passes 17-11-19

3- Muscularis Externa Two layers of involuntary smooth muscle that arranged as: A) Inner circular layer (circumferential): in some places forms sphincters (act as valves). B) Outer longitudinal layer: shortens gut In between these two layers, there is Myenteric nerve plexus (Auerbach’s Plexus) , blood and lymph vessels These muscles responsible for peristalsis and segmentation of the digestive tract.

4- Adventitia or Serosa Adventitia Serosa Certain segments of the GIT are not enveloped by peritoneum. In those segments, the outermost layer is loose connective tissue (Adventitia) containing blood vessels, lymphatics & nerve fibers. Adventitia connects the digestive tract to its surroundings. Serosa It is the adventitia that is covered by peritoneum. Thin layer of loose connective tissue covered with simple squamous epithelium (mesothelium)

Esophagus Esophagus is a muscular tube through which food is carried from the pharynx to the stomach. Descends through thorax and enter the abdomen through the esophageal opening of diaphragm Esophagus has to be protective, as it is open to the outside. The esophagus also has to accommodate a wide variety of food and drink (hot, cold, spicy etc). Esophagus 17-11-19

Histology of Esophagus Mucosa: Epithelium: Non-keratinized stratified squamous. Lamina Propria (Corium) Muscularis Mucosae: two thin layers, inner circular (IC) and outer longitudinal (OL). Submucosa: Loose CT, Plexus of Meissner, Mucous esophageal glands Muscularis externa (Musculosa): 2 layers; inner circular, outer longitudinal. Upper 1/3: striated (skeletal) muscle. Middle 1/3: mixed skeletal and smooth muscles. Lower 1/3: only smooth muscles. Serosa or adventitia: All esophagus is covered by adventitia except the intraabdominal part of the esophagus which has a serosal coat. Skeletal muscle of the esophagus is involuntary controlled by the autonomic nervous system.

Histology of Esophagus Mucosa Muscularis externa IC OL Submucosa Diagram of esophagus Section of esophagus 17-11-19

Stomach Anatomically, stomach is divided into four regions: Cardiac region, Fundus, Body and Pyloric region. Histologically, three regions only are described based on the nature of the glands of the lamina propria: Cardiac region, Fundic region (Fundus and Body) and Pyloric region. Fundic region Cardiac region Pyloric region

Histology of Stomach The inner surface of the stomach is thrown into folds called rugae that include both mucosa and submucosa. Mucosa: Thick mucous membrane, the surface is characterized by invaginations of the lining epith. into the lamina propria forming gastric pits Epithelium: Simple columnar epithelium Lamina Propria: contains gastric glands Muscularis Mucosae: sometimes 3 layers.

Histology of Stomach Submucosa: no gland except in pyloric region. Muscularis externa (Musculosa): 3 layers of smooth muscle, inner oblique, middle circular and outer longitudinal. In pylorus, the circular muscle layer is thickened to form the pyloric sphincter. Serosa: loose CT covered with peritoneum. Gastric pit Gastric gland 5/2/2019

Gastric glands They are located in the lamina propria of the mucosa of the stomach. Their opening on the surface of the stomach called gastric pit which is shallow in the cardiac region and deep in the pyloric region. Gastric glands possess: Isthmus: upper part of the gland connect the gland to the bottom of the gastric pit. Neck: is the middle part. Base: is the deep part. Parts of gastric glands Gland

Cells of the gastric glands 1- Surface mucous cells: Simple columnar cells with basal oval nuclei. Site: In the isthmus and are continuous with the lining epithelium of the gastric pits. Function: They secret neutral mucous which protects against HCL in gastric lumen and lubricate the surface. 2- Mucous neck cells Low columnar cells with basal flattened nuclei. They have numerous mitochondria, RER, Golgi apparatus, many apical mucous secretory granules. Site: in the neck of the glands. Function: They secret acid mucous & lysosome enzyme. 5/2/2019

Cells of the gastric glands 3- Parietal (Oxyntic) cells: Rounded or triangular cells with acidophilic cytoplasm and central rounded nucleus. They do not reach the lumen of the gland They contain few RER and ribosomes, numerous mitochondria, well developed SER, many intracellular canaliculi with numerous long microvilli on surface. Site: Mainly in the isthmus and neck regions of the glands. Function: Secretion of HCL & intrinsic factor (Vit. B12 absorption). Parietal=جدارى

Cells of the gastric glands 4- Chief (zymogenic or peptic) cells They are the most numerous cells. Pyramidal cells with basal rounded nuclei. They have well developed RER, supranuclear Golgi apparatus and apical secretory zymogenic granules. Site: Mainly in the base of the glands. Function: production of the main gastric enzymes: pepsinogen, renin and gastric lipase. N.B. Zymogen is a proenzyme which is an inactive precursor of an enzyme which require biochemical changes to become active.

Cells of the gastric glands 5- Enteroendocrine (Argentaffin, APUD) cells Pyramidal cells with darkly stained nuclei. Site: Mainly in the base of the glands and also in the small and large intestine. Function: Secretion gastrointestinal hormones such as gastrin, serotonin, endorphin in blood (Endocrine). 6- Regenerative (stem) cells They are small cells with oval basal nuclei. They are located mostly in the neck, isthmus and gastric pits. They are capable of replacing all cells in the gastric gland. APUD= amine precursor uptake and decarboxylation 5/2/2019

Gastric glands Cardiac gland Fundic gland Pyloric gland Other name Zymogenic glands Mucoparietal glands Gastric pits Medium sized pits Short and narrow (Smallest gastric pits) Deep and wide Type of the gland Short, Simple, branched, coiled tubular glands Simple, branched, straight tubular glands Simple, branched, coiled tubular glands cells Possess all types of cells except chief cells Surface mucous cells. Mucus neck cells. Undifferentiated stem cells. Chief cells, oxyntic cells APUD cells

Functions of the Stomach It is an efficient mixer that transforms the ingested food into a viscous mass called chyme. HCL secretion which dissolves many of the foods we eat, helps the immune system to fight infections. Secretion of mucus which protects the stomach wall from HCL. Secretion of pepsin, renin and lipase the begin the digestion of food. Secretion of enzyme lysosome which is bactericidal . Secretion of some hormones (Mixed endocrine and exocrine gland).

References Junqueira C., Carneiro J. (2005). Basic Histology, Text & Atlas, 11th ed. Gartner LP (2016). Color Textbook of Histology. 4th ed. Philadelphia: Saunders WB. Young B, O' Dowd G, Woodford P (2013). Wheater‟s Functional Histology. 6th ed. London: Churchill Livingstone. 17-11-19

Any Question 17-11-19