GIT Histology and Embryology Handout for PC II 2024 PDF

MODULE X: NUTRITION, METABOLIC DISEASES AND GIT Histology and embryology of digestive system  Learning objectives:  Histology of digestive system:  Histology of oral cavity  Hist.Of Esophagus and Gastro-intestinal tract (GIT)  Development of digestive syste...

MODULE X: NUTRITION, METABOLIC DISEASES AND GIT Histology and embryology of digestive system  Learning objectives:  Histology of digestive system:  Histology of oral cavity  Hist.Of Esophagus and Gastro-intestinal tract (GIT)  Development of digestive system:  Development of foregut  Development of mid gut  Development of hindgut HISTOLOGY of DIGESTIVE SYSTEM 1  OVERVIEW OF THE DIGESTIVE SYSTEM – Digestive system is composed of the alimentary canal (digestive tract) and the accessory digestive organs. – The alimentary canal (digestive tract) is a continuous tube that extends from the mouth to the anus – Organs of the alimentary canal include the mouth (oral cavity), most of the pharynx, esophagus, stomach, small intestine, and large intestine. – The accessory digestive organs include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. – alimentary canal (digestive tract) and accessory digestive organs. – For deductive purposes, histology of digestive system divided into three parts: I. Oral cavity: boundaries and its contents (Oral histology) II. Esophagus and Gastro-intestinal tract (GIT): esophagus, stomach, small intestine and large intestine. III. Extrinsic /Extramural glands of digestive system: – major salivary glands (parotid, submandibular & sublingual glands) – Liver and gall bladder and – pancreas  DIGESTIVE SYSTEM I: HISTOLOG Y OF ORAL CAVITY ANDITS CONTENTS 1  GROSS ANATOMY OF THE ORAL CAVITY/MOUTH – The oral cavity is where food is ingested and prepared for digestion in the stomach and small intestine.  Boundaries of the Oral Cavity 1. Anteriorly: Lips 2. Sidewalls: formed by cheeks 3. Roof (superior boundary): formed by palate 4. Floor (inferior boundary):formed by myelohyoid muscle 5. posteriorly: communicates with the oropharynx through fauces  Divisions of the Oral Cavity – Subdivided into two regions by the upper and lower dental arches consisting of the teeth and alveolar bone that supports them, which communicate posteriorly behind the last molar (wisdom) tooth when the mouth is closed. – The oral vestibule: a slit like space between dental arches and the deep surfaces of the cheeks and lips – Mouth cavity Proper which is enclosed by the dental arches.  GROSS ANATOMY OF THE ORAL CAVITY/MOUTH… Contents of oral cavity: 1. Tongue 2. Teeth 3. Salivary glands in its wall and 4. Tonsils  HISTOLOGY OF THE ORAL CAVITY/MOUTH – lined by the oral mucosa that consists of surface epithelium (oral epithelium) and lamina propria.  epithelium: stratified squamous epithelium  It can be keratinized or nonkeratinized, depending on the region. lamina propria: is a connective tissue of varying thickness depending on the region.  It may contains sero-mucous glands, blood vessels, nerves, lymphatic vessels and adipose tissue. keratinized stratified squamous epithelium nonkeratinized stratified squamous epithelium  Types of Oral Mucosa – Three types of oral mucosae line oral cavity: 1. Masticatory mucosa, 2. Lining mucosa, and 3. Specialized mucosa 1. The Masticatory Mucosa – is found on the gingivae (gums), the hard palate – has a keratinized and, in some areas parakeratinized stratified squamous epithelium. – Parakeratinized epithelium is similar to keratinized epithelium except that the superficial cells do not lose their nuclei and their cytoplasm does not stain intensely with eosin. Stratified squamous epithelium of the hard palate. This photomicrograph shows a transition in the oral mucosa from a orthokeratinized stratified squamous epithelium (on the right) to a parakeratinized stratified squamous epithelium (on the left). The flattened surface cells of the keratinized epithelium are devoid of nuclei. The layer of keratohyalin granule–containing cells (stratum granulosum) is clearly visible in this type of epithelium. The flattened surface cells of the parakeratinized epithelium display the same characteristics as the keratinized cells, except they retain their nuclei, i.e., they are parakeratinized. In addition, note the paucity of keratohyalin granules present in the subsurface cells  2. Lining mucosa found on the lips, cheeks, floor of the mouth, inferior surfaces of the tongue, and soft palate. the epithelium of the lining mucosa is NKSSE  3. Specialized mucosa Found on the dorsal surface of the tongue. has a keratinized and, in some areas nonkeratinized stratified squamous epithelium. It contains papillae and taste buds responsible for generating the chemical sensation of taste. – LIPS/LABIA Are fleshy fold of tissues forming the anterior boundary of oral cavity. – Each lip on its internal surface is attached to its respective gingiva by a fold of mucosa known as labial frenulum. – The upper lip is attached to the gingiva of the upper jaw by frenulum of the upper lip. – The lower lip is attached to the gingiva of the lower jaw by frenulum of the lower lip. – Lip consists of a central core of striated muscle (orbicularis oris) that makes it highly mobile for ingestion and speech. – Both lips have three differently covered surfaces: 1. An outer cutaneous portion 2. A transitional zone/free margin = vermilion region 3. Internal mucous portion 1. Cutaneous Portion (External surface of lip) – has thin skin, consisting of epidermal and dermal layers, – The epidermis is composed of KSSE with desquamating surface cells – the dermis consists of hair follicles, a r r e c t o r p i l i mu s c l e , sebaceous and sweat glands. – irregular in outline due to hair follicles and ducts of sweat glands which open onto the surface. 2. Mucous Portion (Internal surface) – This is the oral mucous membrane portion (lining mucosa) – The mucosa of lip consists of – Thick epithelium: non-keratinized stratified squamous – Compact Lamina propria: – houses minor salivary glands of mucous type known as labial glands, blood vessels and adipocytes. – Has smooth outline when compared to the outer cutaneous portion  3. Red (Vermilion) zone or Transition Zone – bright red portion of the lip between outer skin surface and inner mucosal surface of the lip. – covered by very thin KSSE which is transparent to blood in the rich microvasculature of the underlying connective tissue. – The underlying connective tissue is: – very rich in both sensory innervation and capillaries, which impart the pink color to this region. – devoid of hair follicles, salivary, sebaceous and sweat glands, as a result it is prone to excessive dryness and chapping in cold, dry weather. – is kept moist with saliva from the tongue. Histology of Lip G= Salivary glands OM= Oral mucosa M= Orbicularis oris muscle F= Hair follicle S= Skin (Cutaneous part) V= Vermilion border  TONGUE(L. lingua; G. glossa) – is a mobile muscular organ covered with mucous membrane. – Parts: root, body and apex – Surfaces: rough upper (dorsal) surface and smooth lower (ventral) surface which attached to floor of mouth by lingual frenulum. – Functions: mastication, swallowing, speech, oral cleansing and taste 24 – Muscles of the forms the bulk of the tongue. Tongue (Lingual Muscles) – Tongue muscles are both extrinsic and intrinsic Extrinsic muscles: change the position of the tongue Intrinsic Muscles: change the shape of the tongue – arranged in bundles that generally run in three planes, Longitudinal, Transverse and Vertical fibers mucous and serous minor salivary glands (lingual glands) are interspersed between the bundles of muscles. – This form of muscle organization is found only in the tongue, which allows easy identification of this tissue as lingual muscle. A, transverse fibers in x plane; B, vertical fibers on y plane; C, longitudinal fibers on z plane Tongue coronal section Tongue skeletal muscle in three planes: A, transverse fibers in x plane; B, vertical fibers in y plane; C, longitudinal fibers in z plane direction Tongue: papilla and lingual glands  Surfaces of the Tongue Tongue has 2 surfaces: inferior/ventral and superior/dorsal surfaces inferior/ventral surface of the tongue is smooth, with typical lining mucosa superior/dorsal surfaces of the tongue Irregular and roughened by a great number of small surface projections or eminences. is divided into anterior two third & posterior third by a V-shaped groove, the Sulcus terminalis (terminal sulcus). Posterior one-third of dorsum of tongue: – lies behind the sulcus terminalis – constitutes the root or base of the tongue – roughened by masses of lymphoid nodules (lingual tonsils) Anterior two-third of dorsum of tongue: – lies in front of the sulcus terminalis. – constitutes the body and apex or tip of the tongue – roughened by mucosal projections called lingual papillae.  Lingual papillae – are elevations of the mucous membrane over dorsal surface of anterior 2/3rd of tongue. – Four types of papillae: filiform, fungiform, foliate & circumvallate (Vallate) papillae – all contain connective tissue core (lamina propria) covered by stratified squamous epithelium (keratinized in filiform, in the others all, non-keratinized) on the taste free zones. Lingual papillae 1. Filiform papillae: are very numerous and cover the entire anterior dorsal surface of the tongue have an elongated conical shape, are heavily keratinized, which gives their surface a gray or whitish appearance. lacks taste buds. They provide a rough surface that facilitates movement of food during chewing. 2. Fungiform papillae: Are less numerous but larger, broader, and taller than the filiform papillae These papillae exhibit a mushroom-like shape and are more prevalent in the anterior region of the tongue. irregularly interspersed among the filiform papillae. covered by a thin non-keratinized stratified squamous epithelium scattered taste buds on their upper surfaces. Fungiform papillae: 3. Foliate papillae: located on the postero- lateral margins of the tongue consist of several parallel ridges separated by deep mucosal clefts, which are aligned at right angles to the long axis of the tongue. are rudimentary or poorly developed in adult humans. contain several taste buds in the epithelium of the facing walls of neighboring papillae Small serous glands empty into the clefts. TASTE BUDS on foliate papillae  4. Vallate (or Circumvallate) papillae – are the least numerous(Not more than 12 (8-12) in number) and largest lingual papillae – Arranged as a single row in front of sulcus terminalis – Are round, knob-like papillae – Each is surrounded by a moat-like deep circular groove, called trench. – The bottom trench surrounding each papilla receives the openings of the ducts of Von Ebner's glands (minor salivary glands of serous type). – Each contains numerous taste buds (TB) that are located in the epithelium of the lateral surfaces of the circumvallate papilla – CT- connective tissue(LP), GL-Gland, TB- Taste bud, SS-stratified squamous epi.  Von Ebner’s glands minor salivary glands of serous type that are associated with foliate and vallate papillae Von Ebner’s glands Von Ebner’s glands  Lingual Glands (mucous type) – The mucous secretory cells have basally located nuclei & apical cytoplasm with ‘soap bubble’ or honey comb appearance.  TASTE BUDS – oval, pale-staining structures that are found in the epithelium of lingual papillae except in the filiform papillae. – Occasional taste buds are also located on the soft palate, pharynx, and epiglottis – Human adults have 2000 to 8,000 taste buds, and children have a few more. They have basal and apical (free) surfaces A small opening onto the epithelial surface at the apex of the taste bud is called the taste pore. TASTE BUDS TASTE BUDS  Types of Cells in Taste Buds – Each taste bud has three types of cells: taste cells, supporting & basal cells. – Cells of taste buds have average life-span of 10 days. 1. Taste (Gustatory/Neuroepithelial/sensory) cells – are the most numerous cells in the taste bud. – Exhibit a lighter cytoplasm and a more oval, lighter nucleus. – are elongated cells that extend from the base of the taste bud to the taste pore. – The apices of each taste cell exhibit numerous microvilli (taste hairs ) that protrude through the taste pore. – Their taste hairs (microvilli) provide the receptor surface for taste. – At their base they form a synapse with the processes of afferent sensory neurons of the facial (cranial nerve VII), glossopharyngeal (cranial nerve IX), or vagus (cranial nerve X) nerves. – Molecules (tastants) dissolved in saliva contact the microvilli through the pore and interact with cell surface taste receptors – Receptor binding produces depolarization of the gustatory cells, stimulating the sensory nerve fibers that send information to the brain for processing. 2. Supporting/sustentacular cells are less numerous exhibit a darker cytoplasm and a slender, dark nucleus. They are also elongated cells that extend from the basal lamina to the taste pore. they do not synapse with the nerve cells Their function is not well-understood yet 3. Basal cells are small cells located in the basal portion of the taste bud, near the basal lamina. Undifferentiated stem cells that give rise to all cells of the buds by division Types of Cells in Taste Buds NSC-Gustatory/Neuroepithelial/sensory) cells, SC-Supporting cells, BC-basal cells, NF-nerve fibers, TP-Taste pore Types of Cells in Taste Buds  PRIMARY TASTE MODALITIES – A person can perceive hundreds of different tastes. – They are all supposed to be combinations of five primary taste sensations, – Taste buds detect at least five broad categories of tastants: – sodium ions (salty); – hydrogen ions from acids (sour); – sugars and related organic compounds (sweet); – alkaloids and certain toxins (bitter); and – certain amino acids such as L-glutamate (umami; Jap. umami, savory). Some areas of the tongue are more responsive to certain tastes than others. In general, taste buds:  at the tip of the tongue detect sweet stimuli,  those immediately posterolateral to the tip detect salty stimuli,  those more posterolateral detect sour-tasting stimuli.  Those on the circumvallate papillae detect bitter and umami stimuli. Regional specificity of taste buds  DIGESTIVE SYSTEM II: H ISTOLOG Y OF ESOPHAGUS AND GASTRO-INTESTINAL TRACT (GIT) OVERVIEW OF THE ESOPHAGUS AND GASTROINTESTINAL TRACT – The portion of the alimentary canal that extends from the proximal part of the esophagus to the distal part of the anal canal is a hollow tube of varying diameter. – This tube has the same basic structural organization throughout its length. – Its wall is formed by four distinctive layers. – from inside to outside these basic layers are: 1. Mucosa, 2. Submucosa, 3. Muscularis propria/externa, and 4. Outer coat (Serosa or adventitia). 1. Mucosa: (frequently called a mucous membrane) innermost layer lining the lumen most variable layer across the regions both structurally and functionally composed of: a. Lining epithelium: b. Lamina propria: loose connective tissue rich in blood & lymph vessels, mast cells, macrophages, plasma cells, lymphocytes, mucosal glands, and rarely smooth myocytes. c. Muscularis mucosa or muscularis interna: Is a thin layer of smooth muscle tissue separating mucosa from submucosa and allowing local movements of the mucosa. – There are four basic mucosal forms in the digestive tract, based on their structure and functions: a. Protective mucosa – found in the oral cavity, oro- and laryngopharynx, esophagus and lower half of the anal canal – the surface epithelium is non-keratinized stratified squamous and may be keratinized in animals which have a coarse diet. e.g. rodents, herbivores b. Glandular (Secretory) mucosa – occurs in the stomach – consists of long closely packed tubular glands which are simple or branched dependingon its region. c. Absorptive mucosa – is typical of the entire small intestine – the mucosa is arranged into leaf or finger-like projections called villi (to increase surface area) with intervening ducts of short mucosal glands called Crypts. d. Both absorptive and protective mucosa – this is the feature of the entire large intestine, except the lower half of the anal canal. – the mucosa is smooth & arranged into closely packed straight tubular glands consisting of cells specialized for water absorption and mucus-secreting goblet cells which lubricate the passage of feces for protection.  2. Submucosa separated from the mucosa by muscularis mucosa It consists of dense irregular connective tissue which houses: Large lymphatic vessels Meissner’s nerve plexus (submucosal nerve plexus), which supply the mucosa and control mucosal motility/agitation. Heller’s plexus (are submucosal vascular plexuses of arteries and veins) Submucosal glands (mucous type) in some regions: esophagus, duodenum & anal canal very large lymphoid masses in some regions  Medical Eponym Meissner’s: 1. corpuscles – tactile nerve endings in skin; 2. plexus – the submucosal autonomic plexus of the intestine. – George Meissner (1829–1905), Professor of Anatomy and Physiology, Basle, Switzerland; Zoology and Physiology, Freiburg, Germany; and Physiology, Göttingen, Germany 3. Muscularis Externa/propria – It is the thick muscular wall of tract – Chiefly composed of smooth muscle except in the proximal ⅔ of esophagus and distal half of anal canal where striated muscles are found. – The muscles are mostly arranged into inner circular & outer longitudinal sublayers but in the stomach consists of three sublayers (inner oblique, middle circular and outer longitudinal) separated by loose CT partition – In the connective tissue between the muscle sublayers are blood and lymph vessels, as well as another autonomic nerve plexus called myenteric plexus (also called Auerbach’s plexus). – This myenteric nerve plexus triggers the entire gut motility (peristalsis).  Medical Eponym Auerbach’s plexus was named for the sake of Leopold Auerbach (1828–1897), Professor of Neuropathology, Breslau,Poland. 4. External coat (serosa / adventitia) – can be adventitia or serosa depending on the region. – If the organ is found in the abdomen, it acquires a partial or complete covering of the serous membrane derived from peritoneum. Serosa: –is a serous membrane consisting of a layer of simple squamous epithelium, called the mesothelium, and a small amount of underlying loose connective tissue layer rich in blood & lymph vessels, nerves, and adipose tissue. It is equivalent to the peritoneum Adventitia: only loose CT rich in blood & lymph vessels, nerves, and adipose tissue without a covering mesothelium.  ESOPHAGUS – Long(25cm) muscular tube extending between the pharynx and stomach – its function is to transport food from pharynx to stomach – has all the four principal histological layers : 1. Mucosa 2. Submucosa 3. Muscularis externa 4. Adventitia/serosa four principal histological layers of esophagus  ESOPHAGUS 1. MUCOSA – thrown into longitudinal folds when empty, permits distension with food during swallowing – It consists of three parts: – an inner lining of nonkeratinized stratified squamous epithelium – an underlying thin layer of loose connective tissue, the lamina propria – a layer of smooth muscle fibers, the muscularis mucosae – Lamina propria houses: – small blood vessels – diffuse & nodular lymphatic tissues scattered throughout its length – mucus secreting glands called esophageal cardiac glands, near the cardia of stomach E-surface epithelium LP-Lamina propria MM-muscularis mucosae 2. Submucosa is a wide layer of moderately dense irregular connective tissue Houses: larger blood and lymphatic vessels, nerve fibers and ganglion cells(submucosal plexus (Meissner’s plexus)), Adipocytes esophageal glands proper (mucous glands) Mucoa&Submucosa at high magnification power Histological Layers of Esophagus (Mucosa & Submucosa) 3. Muscularis Externa – consists of thick, clear outer longitudinal and inner circular muscle layers which are separated by thin CT layer – Within the CT between the muscle layers are myenteric (Auerbach’s) plexus – its proximal third: consists of striated muscle only – its middle third: consists of both (mixed) striated and non- striated (smooth) muscles – its distal third: only smooth muscles St-striated muscle Sm-smooth muscle Esophagus muscularis, middle 1/3rd with striatedand smooth Ms  4. External coat a. Adventitia: loose CT covers the outer surface of extra-abdominal part of esophagus and binds it to the surrounding structures like trachea b. Serosa: below the diaphragm (abdominal part), esophagus is covered with a serosa  Esophageal glands – Are of two types: A. Esophageal cardiac glands - are mucosal glands, found only in the Lamina propria - mucous secreting, in the distal esophagus only B. Esophageal glands proper - are submucosal glands, only in the submucosa - throughout the length of esophagus  Functions of mucus:  Lubrication&protection of esophageal mucosa Histological Layers of Esophagus  Esophago-Gastric Junction – the tract undergoes abrupt transition from stratified squamous epithelium to simple columnar epithelium. The surface of the stomach also exhibits numerous gastric pits into which open the gastric gland – lamina propria becomes highly crowded by numerous glands. – the muscularis mucosae, submucosa and muscularis externa continues uninterrupted beneath the mucosal junction; the thickness of muscularis externa also increase in the stomach Esophago-Gastric Junction Esophago-Gastric Junction, LS Esophago-gastric Junction, LS Esophagus-Stomach junction Oesophagus-Stomach junction Oesophagus-Stomach junction  MEDICAL APPLICATION 1. Gastroesophageal reflux: is associated with incompetent barriers at the gastroesophageal junction, caused by a decrease in the lower esophageal sphincter tone or hiatus hernia. 2. Reflux esophagitis (from mild to erosive) develops when the mucosal defenses are not sufficient to protect the esophageal mucosa from the acid, pepsin, and bile, causing symptoms such as heartburn or atypical chest pain. – Excessive gastric distention, fatty meals, smoking, and beverages such as tea and coffee (with high xanthine content) also cause relaxation of the lower esophageal sphincter, facilitating the reflux of gastric contents to the esophagus.  THE STOMACH – is a large muscular sac located in the upper left quadrant of the abdominal cavity. – Gross inspection of stomach reveals four regions: cardia, fundus, body, and pylorus – Because the fundus and body are identical histologically, only three histological regions are recognized: Cardia, Fundic and body, and Pyloric. The Stomach – The wall in all regions of the stomach is made up of all four major layers: 1. Mucosa 2. Submucosa 3. Muscularis externa/propr ia and 4. Serosa – In undistended stomach, the mucosa and submucosaare thrown into temporary longitudinal folds known as gastric rugae. – When the stomach is filled with food and fluid, these folds flatten out and disappear. 1. The Gastric mucosa – As usual for the entire GIT, gastric mucosa consists of surface lining epithelium, lamina propria and muscularis mucosae. Surface Lining Epithelium of Stomach – simple columnar epithelium lines the stomach. – invaginates into the lamina propria, forming gastric pits/foveolae. – Emptying into the gastric pits are branched, tubular glands characteristic of the stomach region (cardiac, gastric, and pyloric). The stomach- Gastric pits (P) P P  The epithelium that lines the surface and the gastric pits of the stomach consists of the columnar cells called surface mucous (foveolar) cells. surface mucous (foveolar) cells. Have large mucinogen granules in their apical cytoplasm In routine H&E stained sections exhibits basal oval nuclei and a lightly stained cytoplasm owing to the presence of mucinogen droplets/granules. They secretes a thick, adherent, and highly viscous mucous that is rich in bicarbonate ions  It forms a thick, gel-like coat that adheres to the epithelial surface that protects the mucosa from both abrasive effects of intraluminal food and the corrosive effects of stomach acid. surface mucous (foveolar) cells. Stomach, surface lining epithelial cells (mucous surface (foveolar cells) are columnar cells with basal oval nuclei and apical mucinogen granules under high power Stomach, free surface and pit lining foveolar cells  The lamina propria: – is relatively scant and restricted to the limited spaces surrounding the gastric pits and Glands – Consists of fibroblasts, plasma cells, mast cells, lymphocytes with interspersed smooth muscle fibers. – Also consists of diffuse lymphatic tissues and occasional lymphoid nodules (GALT) The muscularis mucosae – Thin smooth muscle layer which separates the mucosa from submucosa – supports the bases of gastric glands 2. Submucosa 4. Serosa (outer coat) Composed of dense irregular connective – Loose Areolar CT tissue Occupy the core of gastric rugae with mesothelium houses large blood and lymph vessels, and Meissner’s /submucosal nerve plexus 3. Muscularis Externa it is well developed & consists of three sublayers: – an innermost oblique, – a middle circular, and – a thin outer longitudinal layers of smooth muscle. The circular layer is especially thickened at the pylorus, to form pyloric sphincter. Wall of the fundic stomach  Regional Differences in the Stomach Mucosa 1. The cardia: Lamina propria is filled with cardiac glands depth of pit = length of the cardiac gland cardiac glands are simple, occasionally branched branched tubular glands with coiled secretory portions They are composed of mucus-secreting columnar cells that are similar in appearance to the cells of the esophageal cardiac glands. They have a flattened basal nucleus, and the apical cytoplasm is typically filled with mucin granules. Gastric pit & cardiac glands Gastric pit & cardiac glands 2. fundus and body: the lamina propria is filled with long branched, tubular gastric/fundic or oxyntic glands The body of each gland is approximately 3x longer than the pit into which it opens (3:1 gland to pit depth ratio) Fundic /Oxyntic or Gastric Glands make the greatest contribution to the gastric juice (2L/day). contain- Chief or Zymogenic cells, parietal or oxyntic cells, mucous neck cells, enteroendocrine cells and niche of stem cells. Fundic stomach, mucosa & fundic glands  each gland has three distinct regions: the isthmus, neck, and base, with different cell type distribution. 1. Isthmus: near the gastric pit: is a site of stem cells location (stem cell niche) in which stem cells replicate and differentiate. 2. neck: consists of: – Most numerous parietal cells, – mucous neck cells 3. Base/fundus: primarily consists of – Chief (Zymogenic) cells, – Occasional parietal cells, and – dispersed Enteroendocrine cells such as enterochromaffin cells (EC cells) which secrete principally serotonin (5- hydroxytryptamine) and substance P. The body of each gland is approximately 3x longer than the pit into which it opens (3:1 gland to pit depth ratio) Fundic /Oxyntic or Gastric Glands  cells of the fundic/gastric glands 1. Mucous neck cells: – are present in clusters or as single cell between parietal cells in the necks of gastric glands. – The mucous neck cell is much shorter than the surface mucous cell and contains considerably less mucinogen in the apical cytoplasm. – Also, the nucleus tends to be spherical compared with the more prominent, elongated nucleus of the surface mucous cell. – The mucous neck cells secrete a acidic, soluble mucus compared with the alkaline insoluble or cloudy mucus produced by the surface mucous cell. – Release of mucinogen granules is induced by vagal stimulation; thus, secretion from these cells does not occur in the resting stomach. Mucous neck cells  2. Parietal cells/Oxyntic Cells- – are present mainly in the upper half of gastric glands, with fewer in the base. – they are large rounded or pyramidal cells, each with one or two central spherical nucleus and cytoplasm that is intensely eosinophilic due to the high density of mitochondria – secrete both hydrochloric acid (HCl) and intrinsic factor Normal parietal cells in the stomach  3. Chief cells/zymogenic cells or peptic cells – predominate in the lower region of the tubular glands (the basal half of the gastric glands in body & funds) – Ultrastructurally chief cells show abundant RER in the basal cytolplasm and numerous apical secretory granules (zymogen granules). – The granules contain inactive enzyme pepsinogens and gastric lipase – On contact with the acid gastric juice, pepsinogen is converted to pepsin, a proteolytic enzyme. – Have basophilic basal cytoplasm due to extensive RER Chief cells/zymogenic cells or peptic cells Chief cells/zymogenic cells or peptic cells Cells of Gastric glands Normal Chief cells in the stomach Stomach, Parietal cells & Chief cells Gastric glands Gastric glands  4. Enteroendocrine cells – scattered in the base of the gastric glands – In general, two types of enteroendocrine cells can be distinguished throughout the gastrointestinal tract. – “closed” type, in which the cellular apex is covered by neighboring epithelial cells, and do not always reach the glandular lumen; – An “open” type, in which the constricted apical end of the cell contacts the glandular lumen – difficult to identify them in routine preparations – Electron micrographs reveal small membrane-bound secretory vesicles throughout their basal cytoplasm which contain hormones – Upon stimulation, they release their secretions (hormones) towards the basal lamina and then to the blood stream in the lamina propria that then exert paracrine (local) or endocrine (systemic) effects via the vasculature. – Effects of the hormones include regulation of peristalsis and tract motility; secretion of digestive enzymes, water, and electrolytes; and the sense of being satiated after eating. Enteroendocrine cells Closed $ open type Enteroendocrine cells  Electron micrograph of an Enteroendocrine cell nucleus secretory granules in basal cytoplasm  5. Stem cells stem cells are undifferentiated cells only in restricted niches of isthmus and/or neck region of the gastric glands. They give rise to all epithelial cells of gastric mucosa  3.Pyloric region have deep pits and short tubular pyloric glands Pyloric Glands They are branched, coiled, simple tubular glands They are composed mainly of mucus-secreting cells, with occasional interspersed enteroendocrine cells such as G (Gastrin-secreting) cells, D (somatostatin-secreting) cells. The transition from fundic to pyloric glands is gradual and marked by disappearance of chief and parietal cells. Gastric pit $ Pyloric Glands Gastric pit $ Pyloric Glands Difference between cardia, fundus & body, & pylorus Cardia Fundus & body Pylorus Contain cardiac Contain gastric Contain pyloric glands glands glands Gastric pit less Gastric pit less Gastric pit more deeper than deeper than deeper than pyloric gland pyloric gland gastric or cardiac glands Parietal cells Parietal cells Parietal cells few, absent or very most numerous numerous few mucous cells  Gastritis – is inflammation of the lining of all or part of the gastric mucosa – may be classified as acute or chronic. – Acute gastritis maybe characterized as erosive (damaged areas where mucosal cells are disrupted or missing) and nonerosive. – Chronic gastritis is determined by histopathology (appearance of the gastric mucosa).  Gastritis – has many causes including: ingested substances such as aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), or ethanol; the hyperosmolality of meals; and some infectious microorganisms such as Helicobacter pylori (H. pylori). – In cases of atrophic (chronic) gastritis, both parietal and chief cells are much less numerous, and the gastric juice has little or no acid or pepsin activity. – In humans, parietal cells are the site of production of intrinsic factor, a glycoprotein that binds avidly to vitamin B12. ILLUSTRATED INTESTINES  THE SMALL INTESTINE (SI) – about 5m long tube, thrown into several coils and twists, extending between the stomach & large intestine (LI). – site of most digestion and absorption – Subdivided into: duodenum, Jejunum, and Ileum – The three segments of SI have many characteristics in common and will be discussed together. – The wall in all regions of the small intestine is made up of all four major layers: – Mucosa – Submucosa – Muscularis externa/propria and – Serosa and /or adventitia four major layers of SI  Mucosa The small intestine exhibits specialized structural modifications that increase the cellular surface areas for absorption of nutrients and fluids. These modifications include the plicae circulares, villi, and microvilli. Plicae Circulares (Valves of Kerckring): – a series of permanent circular folds consisting of mucosa and submucosa. – begin in the upper duodenum, reach their maximum development in the proximal jejunum, and thereafter diminish in size and disappear in the distal half of the ileum – increase surface area of small intestine by three fold – are most developed in, and consequently a characteristic of the jejunum. Plicae Circulares (Valves of Kerckring):  Plicae Circulares Mucosa lining the duodenum (1st part of small intestine) Plicae circulares (circular folds) of the jejunum: mucosa & submucosa (SM) of the small intestine form distinct projecting folds called plicae (P), which encircle or spiral around the inner circumference and are best developed in the jejunum. Plicae circulares (circular folds) of the jejunum:  Medical Eponym Plicae Circulares (Valves of Kerckring): – a series of permanent, transverse folds lining the SI. – described in 1670 by a Dutch anatomist, Theodor Kerckring (1640-1693) – can be viewed with the naked eye.  VILLI: – outgrowths of the mucosa (Epithelium plus LP) projecting into the lumen of the small intestine – Each villus consists of a core of lamina propria covered by simple columnar epithelium with goblet cells. – Lamina propria houses mast cells, plasma cells, smooth muscle fibers, lymphatic tissues, blood & vertically oriented lymph capillaries known as Lacteals. – Best developed in the duodenum and Jejunum – Ducts of intestinal glands open between each villus – Villi increase surface area for absorption and digestion by 10-fold. VILLI: VILLI: VILLI: VILLI: VILLI: Jejunum  Microvilli: – cylindrical extensions of the apical cytoplasm of the intestinal absorptive cells that enclosed by the cell membrane. – They are visible under a light microscope as a striated (brush) border. – The microvilli are coated by a glycoprotein coat glycocalyx, which contains such brush border enzymes as lactase, peptidases, sucrase, lipase, and others that are important for digestion – Each absorptive cell is estimated to have an average of 3000 microvilli – 1 mm2 area of mucosa contains about 200 million microvilli – increase intestinal surface area by 20-30 fold Microvilli: Microvilli of enterocytes forming brush /striated border TEM, microvilli that make up the brush border of human jejunum epithelial cell embedded in glycocalyx sugar coat  Glands of small intestine(mucosal & submucosal) 1. Crypts of Lieberkühn, Crypts=intestinal glands – are simple tubular glands, found in the intestinal mucosa – extend from the level of muscularis mucosa and open into the intestinal lumen between the villi. – muscularis mucosa supports the base of the glands Intestinal villi and intestinal crypts of Lieberkuhn Intestinal villi and intestinal crypts of Lieberkuhn  2. Duodenal (Brunner’s) glands – are compound branched tubular mucous glands, – are submucosal glands th at a re concentrated mainly in the upper duodenum – Their excretory ducts open into the lumen of the mucosal glands/intestinal crypts of duodenum –their product is distinctly alkaline (PH 8.1– 9.3), which neutralizes chyme entering the duodenum from the pylorus: –protecting the mucous membrane and –bringing the intestinal contents to the optimum pH for pancreatic enzyme action. Duodenal (Brunner’s) glands  Duodenal (Brunner’s) glands Photomicrograph of Brunner’s glands in the duodenum. This photomicrograph shows part of the duodenal wall in an H&E preparation. A distinctive feature of the duodenum is the presence of Brunner’s glands. The dashed line marks the boundary between the villi and the typical intestinal glands (crypts of Lieberkühn). The latter extend to the muscularis mucosae. Under the mucosa is the submucosa, which contains Brunner’s glands. These are branched tubular glands whose secretory component consists of columnar cells. The duct of the Brunner’s gland opens into the lumen of the intestinal gland (arrow). 120. Concentrated in the upper duodenum are large masses of compound branched mucous glands, the duodenal glands (DG), with many lobules that occupy much of the submucosa and may extend above the muscularis mucosae (MM) into the mucosa. Many small excretory ducts (D) extend from these lobules through the lamina propria and empty into the lumen among the small intestinal crypts. Alkaline mucus from duodenal glands neutralizes the pH of material entering the duodenum and supplements the mucus from goblet cells in lubricating and protecting the lining of the small intestine. X100. H&E.  Medical Eponym – Duodenal (Brunner’s) glands are named for Johann Conrad Brunner (16 January 1653 – 2 October 1727), a Swiss anatomist, especially cited for his work on the pancreas and duodenum. – Johann Brunner (1653–1727): – had observed in 1673 that a dog experienced polyuria and thirst after experimental removal of both its pancreas and spleen.  Epithelial cells of the Intestinal mucosa – Heterogeneous population of cells line the villi and intestinal glands, which include: – Absorptive cells/Enterocytes – Goblet cells – Paneth cells – M (microfold) cells – Enteroendocrine Cells and – Undifferentiated pluripotential cells (Stem cells that give rise to all these cell types)  1. Absorptive cells(Enterocytes): are tall columnar cells with a basally positioned Nucleus The apical end of each enterocyte displays abundant prominent microvilli that are covered by glycocalyx densely packed mitochondria absorb the nutrient molecules produced by digestion disaccharidases and peptidases secreted by these cells and bound to the microvilli hydrolyze the disaccharides and dipeptides into monosaccharides and amino acids that are easily absorbed through active transport. E-Enterocytes G-Goblet cell TE micrograph of enterocytes Enterocytes= Absorptive cells  2. Goblet cells are interspersed between the absorptive cells fewer in the duodenum and their number increase distally to the ileum and then also in large intestine and maximum number is found the rectum. produce mucus, whose main function is to protect and lubricate the lining of the intestine. Examination with the TEM reveals a large accumulation of mucinogen granules in the apical cytoplasm that distends the apex of the cell The basal portion is narrow and intensely basophilic in histologic preparations because it is occupied by a nucleus, extensive rER, and free ribosomes. as in other epithelia, because mucinogen is lost during preparation of routine H&E sections, the part of the cell that normally contains mucinogen granules appears empty Small intestine, jejunum, cell membranes are distinct by H&E Goblet cells Brush border TE of Goblet cells  The characteristic shape, with the apical accumulation of granules and the narrow basal stem, is responsible for the name of the cell, as in a glass “goblet.”  3. Paneth cells – are found in the bases of the intestinal glands (a few Paneth cells may also found sporadically in the cecum and appendix). – They have a basophilic basal cytoplasm and large, intensely eosinophilic secretory granules in their apical cytoplasm. – Paneth cell granules release lysozyme, phospholipase A2, and hydrophobic peptides called defensins, all of which bind and break down membranes of microorganisms and bacterial cell walls. – Paneth cells have an important role in innate immunity and in regulating the microenvironment of the intestinal crypts. Photomicrograph of intestinal glands showing Paneth cells. This photomicrograph shows the base of intestinal (jejunal) glands in an H&E preparation. The gland on the right is sectioned longitudinally; the circular cross- sectional profile of another gland is seen on the left. Paneth cells are typically located in the base of the intestinal glands and are readily seen in the light microscope because of the intensive eosin staining of their vesicles. The lamina propria contains an abundance of plasma cells, lymphocytes, and other connective tissue cells. Note several lymphocytes in the epithelium of the gland (arrows). Inset. This high magnification of the area indicated by the rectangle shows the characteristic basophilic cytoplasm in the basal portion of the cell and large accumulations of intensely staining, eosinophilic, refractile secretory vesicles in the apical portion of the cell. An arginine-rich protein found in the vesicles is probably responsible for the intense eosinophilic reaction.  Paneth cell (P) C G P PP G - are microscopically identified by their large eosinophilic refractive granules which occupy most of their cytoplasm. - these granules consist of several antimicrobial compounds that are known to be important immunity and host defense. Paneth cells (arrows) in the base of intestinal crypts Secretory Paneth cells lie deep at the base of each intestinal crypt, below the level of the stem cells from which they and cells covering the villi all arise. Paneth cell granules are shown immunohistochemically to contain lysozyme (arrowheads), which is also present in macrophages (M). M M M Electron micrograph of a Paneth's cell: Note the basal nucleus with prominent nucleolus, abundant rough endoplasmic reticulum, and large secretory granules with a dense protein core surrounded by a halo of polysaccharide-rich material. These granules contain lysozyme, a lytic enzyme involved in the regulation of intestinal bacteria. Medical Eponym –Paneth cells are named after Joseph Paneth (1857-1890), an Austrian physiologist.  4. Enteroendocrine Cells scattered within the epithelium of the villi and glands, contain secretory granules containing hormones at their basal cytoplasm secrete peptide hormones that influence gastric and intestinal secretion and motility, gall bladder contraction difficult to identify them in routine preparations Transmission Electron micrograph of an enteroendocrine cell (open type) of the human duodenum. Note the microvilli in its apex. Nucleus Secretory granules in the basal cytoplasm 5. Stem cells – Lining cells of stomach and intestine are renewed rapidly by continuous mitotic activity of their stem cells. – the intestinal epithelium is replaced every week, derived completely from stem cells found in the basal third of the simple tubular glands/crypts. Stem cells and their differentiating progeny known by mitotic activity  Lymphatic nodules of SI They are particularly numerous and well developed in the ileum, and often extend full length of the mucosa and into submucosa May be solitary or grouped together in aggregates called Payer’s patches Instead of absorptive cells, its covering epithelium mainly consists of M (microfold) cells. 5. M (microfold) cells M cells are highly specialized epithelial cells that found in the epithelium that cover the Peyer’s patches and large lymphatic nodules have microfolds rather than microvilli on their apical surface On the basal side M cells have large intracellular pockets that contain transient populations of lymphocytes and dendritic cells and open to the underlying lymphoid tissue through a highly porous basement membrane Antigens in the intestinal lumen are continuously sampled at the apical surface of these cells and transferred to the immune cells in the pockets Dendritic cells then take up the antigen, process it, and present it to helper T lymphocytes and helper T lymphocytes stimulates B lymphocytes to differentiate into IgA-secreting plasma cells. Then the produced IgA is transported by enterocytes into the intestinal lumen to bind and neutralize potentially harmful antigens. M (microfold) cells Submucosa – has larger blood and lymph vessels and the diffuse, interconnected neurons of the submucosal (Meissner) nerve plexus. – In the Duodenum-consists of duodenal (Brunner’s glands)- compound branched tubular glands of mucous type. – In the ileum both the lamina propria and submucosa contain the lymphoid nodule aggregates known as Peyer’s patches, an important component of the MALT. Duodenal glands  Muscularis Externa: – inner circular, outer longitudinal- between them is myenteric plexus of nerves Serosa: – loose CT invested by a layer of mesothelial cells Adventitia – on posterior surface of fixed part of duodenum Muscularis Externa: inner circular (IM) and outer longitudinal (EM)- b/n them is myenteric (Auerbach) plexus of nerves (MP)  The Large Intestine (L= 1.5m, Φ= 7.5cm) Consists of – Cecum – Appendix – Colon – Rectum and – Anal canal Four regions of the colon – Ascending – Transverse – Descending – Sigmoid colon  The Common Histology of Large Intestine The wall of the large intestine has the same basic layers as the small intestine. Mucosa: has smooth interior surface, except in the distal portion (rectum and anal canal, where the mucous membrane forms a series of folds) No plicae circularis and villi are present in this portion of the intestine If undistended, the mucosa and submucosa exhibit temporary folds Epithelium: simple columnar epithelium (absorptive cells / colonocytes) with goblet cells that continues with glandular epithelium  goblet cells increase towards the rectum  Lamina Propria:  Rich in diffuse and nodular lymphoid tissues that frequently extend into the submucosa  This richness in lymphoid tissue (GALT) is related to the abundant bacterial population of the large intestine  Intestinal glands of the colon are larger and more closely packed than those in the small intestine.  They increase in length distally to reach their maximum length in rectum.  They are characterized by a great abundance of goblet and absorptive cells and a small number of enteroendocrine cells  Epithelial stem cells are located in the bottom third of each gland Muscularis mucosae: separates mucosa from submucosa Submucosa: – Distensible tissue with large blood vessels, adipose tissue and submucosal nerve plexus – In the anal canal contains very few submucosal glands of mucous type (around recto-anal junction) The mucosa of large Intestine (colon) This photomicrograph of an H&E preparation shows the mucosa and part of the submucosa. The surface epithelium is continuous with the straight, unbranched, tubular intestinal glands (crypts of Lieberkühn). The openings of the glands at the intestinal surface are identified (arrows). The epithelial cells consist principally of absorptive and goblet cells. As the absorptive cells are followed into the glands, they become fewer in number, whereas the goblet cells increase in number. The highly cellular lamina propria contains numerous lymphocytes and other cells of the immune system. Large intestine GI-intestinal glands LP-lamina propria Muc-mucosa MM-muscularis mucosae SubM-submucosa GC-Goblet cell M-mitotic figures of stem cells AC-Absorptive cell Muscularis mucosa  The Large Intestine Muscularis Externa: – Inner circular & outer longitudinal – In ceacum and colon outer longitudinal muscle layer is thrown into three longitudinal bands - taenia coli – Haustra coli are outwardly bulging pockets between Taenia coli.  they are absent in the rectum, anal canal, and vermiform appendix. The Large Intestine, taenia coli Serosa : – complete in Transverse colon, sigmoid colon, cecum and appendix. – incomplete in the upper part of rectum, ascending and descending colons because they are retroperitoneal – Absent in anal canal and lower part of rectum  where a serosa is present it contains large pendulous lobules of fat called Omental appendices/ appendices epiploicae.  Appendix. a blind ended evagination of the cecum Its morphology is similar to that of the colon, except for certain modifications. has a very small lumen, shorter and fewer glands in its mucosa, and no taeniae coli & haustra. The lamina propria and submucosa are generally filled with lymphocytes and lymphoid follicles, making the appendix a significant part of the MALT. The outermost layer of the appendix is the serosa Appendix. Photomicrograph of a cross section through the vermiform appendix. The vermiform appendix displays the same four layers as those of the large intestine except that its diameter is smaller. Typically, lymphatic nodules are seen within the entire mucosa and usually extend into the submucosa. Note the distinct germinal centers within the lymphatic nodules. The muscularis externa is composed of a relatively thick circular layer and a much thinner outer longitudinal layer. The appendix is covered by a serosa that is continuous with the mesentery of the appendix (lower right). 10. Transverse section of human vermiform process  MEDICAL APPLICATION – Because the appendix is a closed sac and its contents are relatively static, it can easily become a site of inflammation (appendicitis). – With the small lumen and relatively thin wall of the appendix, inflammation and the growth of lymphoid follicles in the wall can produce swelling that can lead to bursting of the appendix. – Severe appendicitis is a medical emergency since a burst appendix will produce infection of the peritoneal cavity. – Appendectomy- a surgical procedure involving complete removal of appendix.  RECTUM – Rectum is the dilated distal portion of the alimentary canal. – Its upper part is distinguished from the rest of the large intestine by the presence of folds called transverse rectal folds. – The mucosa of the rectum is similar to that of the rest of the distal colon, having straight, tubular intestinal glands with many goblet cells. – No characteristic taenia coli and haustrations – Partially covered by serosa RECTUM RECTUM RECTUM Rectum  Anal Canal  Is the short (4cm) most distal portion of the alimentary canal extends from the upper aspect of the pelvic diaphragm to the anus. The anal canal is divided into three zones according to the character of the epithelial lining: 1. Colorectal zone, 2. Anal transitional zone and 3. Cutaneous zone. Anal Canal 1. Colorectal zone (Zona columinaris): – found in the upper part of the anal canal – Histologically similar to rectum containing simple columnar epithelium – Distally limited by the anorectal/pectinate/dentate line – Its mucosa and submucosa are thrown into a series of longitudinal folds known as Anal columns (of Morgagni); which are united inferiorly by crescentic folds termed anal valves. – Anal sinuses: small longitudinal luminal spaces between adjacent anal columns and above the anal valves.  Giovanni Battista Morgagni (25 February 1682 – 6 December 1771) 2. Anal transitional zone (Anal pecten) lies between the pectinate line above & the anocutaneous line (white line of Hilton) below. lined by nonkeratinized stratified squamous epithelium and contains mucus-secreting tubular glands (anal glands) in its lamina propria&submucosa It represents a transition between the simple columnar epithelium of the rectal mucosa and the stratified squamous epithelium of the perianal skin  3. Cutaneous zone Lies distal to the anocutenous line, lined by thin skin with hair follicles and sebaceous glands.  recto-anal junction. The change from the rectal mucosa (simple columnar )to the anal mucosa (stratified squamous epithelium ) occurs at the anorectal junction. The muscularis mucosae and the intestinal glands of the digestive tract terminate in the vicinity of the anorectal junction circular layer of the muscularis externa thickens to form the internal anal sphincter. The external anal sphincter is formed by striated muscle of the pelvic floor. Recto-anal Junction SSE Lamina propria Recto-Anal Junction Enteroendocrine Cell Hormone Produced Major Action Types and Location X/A-like—stomach Ghrelin Increase sense of hunger G—pylorus Gastrin Stimulation of HCl secretion S—small intestine Secretin Pancreatic and biliary bicarbonate and water secretion K—small intestine Gastric inhibitory Inhibition of gastric acid polypeptide secretion L—small intestine Glucagon-like peptide 1 Decrease sense of hunger (GLP-1) I—small intestine Cholecystokinin (CCK) Pancreatic enzyme secretion, gallbladder contraction D—pylorus, duodenum Somatostatin Local inhibition of other endocrine cells Mo—small intestine Motilin Increased gut motility EC—digestive tract Serotonin, substance P Increased gut motility D1—digestive tract Vasoactive intestinal Ion and water secretion, polypeptide (VIP) increased gut motility  MEDICAL APPLICATION Cancer of the Digestive Tract – Approximately 90–95% of malignant tumors of the digestive system are derived from intestinal or gastric epithelial lining cells. – Malignant tumors of the large bowel (colon cancers) are derived almost exclusively from its glandular epithelium (adenocarcinomas) and are the second most common cause of cancer deaths in the United States. – It is number one common cause of cancer deaths in males worldwide followed by prostatic cancer. – Some proteins such as the carcinoembryonic antigen produced exclusively by malignant cells are very important for the diagnosis of cancer. Thank you! DEVELOPMENT OF DIGESTIVE SYSTEM.  Introduction  The primordial gut formed during the fourth week as the head, tail, and lateral folds incorporate the dorsal part(endodermal lined) of the umbilical vesicle (yolk sac) into the embryo.  The primordial gut at the beginning of the fourth week is closed at its cranial end by the oropharyngeal membrane and at its caudal end by the cloacal membrane  Endoderm forms the most of the epithelial lining of the digestive tract and gives rise to the parenchyma of glands, such as the liver and pancreas.  Epithelium at the cranial end- is derived from ectoderm of the stomodeum.  Epithelium at the caudal end-is derived from ectoderm of the proctodeum  Muscle, connective tissue, and peritoneal components of the wall of the gut are derived from splanchnic mesoderm.  Neural crest cells migrate into gut wall and give rise to autonomic (Meissner’s&myenteric) nerve plexuses  Cont…  For descriptive purposes, the primordial gut is divided into three parts: foregut, midgut, and hindgut  A part of the gut communicates with the yolk sac temporarily, this part is called as midgut.  The part above it within the head fold is foregut  The part below it within the tail fold is hindgut  Mesenteries Portions of the gut tube and its derivatives are suspended from the dorsal and ventral body wall by mesenteries (double-layered peritoneum) Two types of mesenteries: dorsal and ventral dorsal mesentery Derived from splanchnic mesoderm extends from the lower end of the esophagus to the cloacal región of the hindgut. Suspends the caudal part of the foregut, the midgut, and a major part of the hindgut from the post. abdominal wall Its parts are named according to the organ connected to it:  Mesogastrium – of the stomach  Mesoduodenum – of the duodenum  Mesentery proper– of the jejunum and ileum  Mesocolon – of the colon Ventral mesentery  Its derived from septum transversum  Exists only in the region of the terminal part of the esophagus, the stomach, and the upper part of the duodenum and connects them to the anterior abdominal wall  Growth of the liver into the mesenchyme of the septum transversum divides the ventral mesentery into: 1. Lesser omentum Extending from the lower portion of the esophagus, the stomach, and the upper portion of the duodenum to the liver 2. Falciform ligament, Extending from the liver to the ventral body wall Dorsal and ventral Mesenteries  The mesenteries contain blood vessels, lymphatic and nerves of the respective organs Three arteries derived from the dorsal aorta, pass between the two layers of the dorsal mesentery to supply the gut. These are:  Celiac artery → supplies the fore-gut  Superior mesenteric artery → supplies the mid-gut  Inferior mesenteric artery → supplies the hind-gut Development of Foregut Development of respiratory/laryngotracheal diverticulum from the floor of foregut, divides the foregut into two parts: 1. Primitive pharynx: cranial to the diverticulum 2. Foregut proper: caudal to the diverticulum  The Foregut derivatives  Derivatives of the foregut are:  The primordial pharynx and its derivatives  The lower respiratory system  Derivatives of foregut proper:  esophagus  stomach  duodenum, distal to the opening of the bile duct  liver, biliary apparatus (hepatic ducts, gallbladder, NB# These foregut derivatives, other than the and bile duct), and pharynx, lower respiratory tract, and most of  pancreas the esophagus, are supplied by the celiac trunk, the artery of the foregut  Development of the Esophagus  The esophagus develops from the foregut immediately caudal to the pharynx.  It separates from laryngotracheal tube (trachea) by tracheoesophageal septum  Initially, the esophagus is short, But elongates rapidly, mainly because of the growth and relocation of the heart and lungs.  Its final relative length is attained by the seventh week Formation of the esophagus 1. Respiratory diverticulum 2. Foregut 3. Esophagotracheal septum 1. Pharynx 2. Trachea 3. Esophagus 4. Lung buds  The epithelium and glands of esophagus are derived from endoderm.  Other layers splanchnic mesenchyme  The epithelium proliferates and partly or completely obliterates the lumen and recanalization occurs by the end of the eighth week  Development of the Stomach appears as a fusiform dilation of the foregut in the 4th week of development is initially oriented in the median plane and it has:  2 ends: cranial&caudal or (cardiac & pyloric ends) which lie in the midline.  2 borders: dorsal & ventral borders which are equal in length.  2 surfaces: Right & left related related to right and left vagus nerves respectively.  2 peritoneal folds: dorsal & ventral mesogastrium.  ventral mesogastrium= connecting the ventral border to the anterior abdominal wall  dorsal mesogastrium =connecting the dorsal border to the posterior abdominal wall. LATER ON:- The dorsal border grows faster than the ventral border forming the greater curvature. Development of the Stomach  Rotation of Stomach As the stomach enlarges and acquires its final shape, it slowly rotates 90 degrees in a clockwise direction around its longitudinal axis Enlargement of the mesentery and adjacent organs, as well as growth of the stomach walls (dorsal border of the stomach grows faster than its ventral border;), contribute to the rotation of the stomach. The effects of rotation on the stomach are: The ventral border (lesser curvature) moves to the right The dorsal border(greater curvature) moves to the left The original left side becomes the ventral surface The original right side becomes the dorsal surface. Its cranial region moves to the left and slightly inferiorly Its caudal region moves to the right and superiorly The rotation and growth of the stomach explain why the left vagus nerve supplies the anterior wall of the adult stomach and the right vagus nerve innervates its posterior wall. After rotation, the stomach assumes its final position with its long axis almost transverse to the long axis of the body Results of rotation…  Mesenteries of the Stomach Dorsal mesogastrium (mesentery)  The stomach is suspended from the dorsal wall of the abdominal cavity by a dorsal mesentery.  This mesentery is originally in the median plane, but it is carried to the left during rotation of the stomach and formation of the omental bursa or lesser sac of peritoneum  spleen develops within the dorsal mesogstrium and divide it into 2 parts:  gastrosplenic ligament: is the part between stomach and spleen  lienorenal ligament: Between spleen and postr abdominal wall.  Rest of the dorsal mesogastrium forms the greater omentum. ventral mesogastrium Suspend the stomach from the anterior abdominal wall. In the ventral mesogastrium (mesentery) liver develops.  Part of ventral Mesogastrium between Stomach and liver is called lesser omentum  Part of ventral Mesogastrium between liver and anterior Abdominal wall is falciform ligament  greater omentum overhangs the developing intestines inferior recess disappears as the layers of the greater omentum fuse 8/18/2024 265  omental foramen 8/18/2024 266  Changes after rotation and descent of the stomach  Sagittal section showing the relation of the 270 organs due to the peritoneal change Development of the Duodenum The terminal part of the foregut and the cephalic part of the midgut form the duodenum. The junction of the two parts is directly distal to the origin of the liver bud. 8/18/2024 271  As the stomach rotates, the duodenum takes on the form of a C-shaped loop and rotates to the right. This rotation, together with rapid growth of the head of the pancreas, swings the duodenum from its initial midline position to the left side of the abdominal cavity. The duodenum and head of the pancreas press against the dorsal body wall, and the right surface of the dorsal mesoduodenum fuses with the adjacent peritoneum. 8/18/2024 272  Both layers subsequently disappear, and the duodenum and head of the pancreas become fixed in a retroperitoneal position. The dorsal mesoduodenum disappears entirely except in the region of the pylorus of the stomach, where a small portion of the duodenum (duodenal cap) 8/18/2024 273 8/18/2024 274 8/18/2024 275  During the fifth and sixth weeks, the lumen of the duodenum becomes progressively smaller and is temporarily obliterated because of the proliferation of its epithelial cells. Normally vacuolation occurs as the epithelial cells degenerate; as a result, the duodenum normally becomes recanalized by the end of the embryonic period. 8/18/2024 276  Dev’t of the Liver and Biliary Apparatus Early in the fourth week hepatic diverticulum- arise as a ventral outgrowth, from the caudal or distal part of the foregut The hepatic diverticulum enlarges rapidly and divides into two parts as it grows between the layers of the ventral mesogastrium. PARS HEPATICA: The larger cranial part of the hepatic diverticulum is the primordium of the liver. PARS CYSTICA: The smaller caudal part of the hepatic diverticulum becomes the gallbladder, and the stalk of the diverticulum forms the cystic duct Development 1. Liver bud of the liver 2. Stomach 3. Gallbladder 4. Ventral pancreatic bud 5. Dorsal pancreatic bud 1. Esophagus 2. Hindgut 3. Stomach 4. Tracheobronchial diverticulum 5. Duodenum 6. Midgut loop 7. Septum transversum 8. Cloaca 9. Gallbladder 10. Liver 11. Cloacal membrane 12. Pancreas 278 13. Heart 14. Ventral mesogastrium 15. Dorsal mesogastrium  The liver grows rapidly and, from the 5th to 10th weeks, fills a large part of the upper abdominal cavity.  By the 9th week, the liver accounts for approximately 10% of the total weight of the fetus.  Initially, the right and left lobes are approximately the same size, but the right lobe soon becomes larger. Cont…  Hematopoiesis begins during the 6th week, giving the liver a bright reddish appearance.  Bile formation by hepatic cells begins during the 12th week.  Formation of biliary apparatus  The stalk connecting gall bladder to hepatic diverticulum forms cystic duct  The two branches of pars hepatica forms hepatic duct  The part connecting hepatic duct with cystic duct forms common hepatic duct  The stalk connecting the hepatic and cystic ducts to the duodenum becomes the common bile duct. Initially, this duct attaches to the ventral aspect of the duodenal loop, later with the rotation of the duodenal it will shift to the dorsomedial aspect.  The lumen of extrahepatic biliary apparatus is occluded with epithelial cells, later canalized because of degeneration of cells.  The bile entering the duodenum through the bile duct after the 13th week gives the meconium (intestinal contents) a dark green color.  Histogenesis of liver  The proliferating endodermal cells of hepatic diverticulum give rise to interlacing cords of hepatocytes and to the epithelial lining of the intrahepatic part of the biliary apparatus.  The fibrous and hematopoietic tissue and Kupffer cells are derived from mesenchyme in the septum transversum (ventral mesentery).  Ventral Mesentery  This thin, double-layered membrane gives rise to:  The lesser omentum, passing from the liver to the lesser curvature of the stomach (hepatogastric ligament) and from the liver to the duodenum (hepatoduodenal ligament)  The falciform ligament, extending from the liver to the ventral abdominal wall  The ventral mesentery, derived from septum transversum, also forms the visceral peritoneum of the liver.  The liver is covered by peritoneum except for the bare area that is in direct contact with the diaphragm Ventral Mesentery  Development of the pancreas  The pancreas develops between the layers of the mesentery from dorsal and ventral pancreatic buds of endodermal cells.  Most of the pancreas is derived from the dorsal pancreatic bud. The larger dorsal pancreatic bud appears first and grows rapidly in the dorsal mesentery.  The ventral pancreatic bud develops near the entry of the bile duct into the duodenum and grows between the layers of the ventral mesentery.  As the duodenum rotates to the right and becomes C shaped, the ventral pancreatic bud is carried dorsally with the bile duct  It soon lies posterior to the dorsal pancreatic bud and later fuses with it.  dorsal and ventral pancreatic buds of endodermal cells, which arise from the caudal or dorsal part of the foregut 8/18/2024 288  duodenum rotates to the right and becomes C shaped, the ventral pancreatic bud is carried dorsally with the bile duct 8/18/2024 289 Pancreas during the rotation of the duodenum 290  Duct system of pancreas  Initially dorsal and ventral pancreatic ducts open seperately.  Connections appear between dorsal and ventral duct.  Main pancreatic duct develops from dorsal duct distal to communication of two ducts, Anastomosis between two ducts and ventral duct proximal to communication.  The proximal part of dorsal duct persists as accessory pancreatic duct  Duct system of pancreas… Initially dorsal and ventral pancreatic ducts open seperately. Connections appear between dorsal and ventral duct. Main pancreatic duct develops from dorsal duct distal to communication of two ducts, Anastomosis between two ducts and ventral duct proximal to communication. The proximal part of dorsal duct persists as accessory pancreatic duct  Histogenesis of the Pancreas The parenchyma (basic cellular tissue) of the pancreas is derived from the endoderm of the pancreatic buds, which forms a network of tubules. Early in the fetal period, pancreatic acini begin to develop from cell clusters around the ends of these tubules (primordial pancreatic ducts). The pancreatic islets develop from groups of cells that separate from the tubules and lie between the acini. The glucagon- and somatostatin-containing cells develop before differentiation of the insulin- secreting beta-cells. Insulin secretion begins at 10th weeks. connective tissue sheath and interlobular septa  from the surrounding splanchnic mesenchyme.  Development of spleen  The mesenchymal cells in the dorsal mesogastrium forms the spleen.  Development begins around 5th week of gestation.  It is lobulated in the early fetal life but lobules disappear before birth.  The notches in the superior border of the adult spleen are remnants of the grooves that separated the fetal lobules.  With the rotation of the stomach the spleen comes to lie on the left side of the stomach. Development of spleen Adult spleen Histogenesis of the spleen  The mesenchymal cells in the splenic primordium differentiate to form the capsule, connective tissue framework, and parenchyma of the spleen.  The spleen functions as a hematopoietic center until late fetal life. Dev’t of Midgut Dev’t of Midgut the midgut is suspended from the dorsal abdominal wall by a short mesentery and communicates with the yolk sac by way of the vitelline duct or yolk stalk 1. Foregut 2. dorsal mesentry 3. postr. Abdominal wall 4. Midgut loop 6. Umbilical ring  Dev’t of Midgut… In the adult, the midgut begins immediately distal to the entrance of the bile duct into the duodenum and terminates at the junction of the proximal two-thirds of the transverse colon with the distal third. Over its entire length, the midgut is supplied by the superior mesenteric artery  Early in the 4th wk of development it grows in length and forms a ventral U-shaped loopprimary intestinal loop (midgut loop); which is suspended from the dorsal body wall by dorsal mesentery Artery of the midgut (Superior mesenteric artery) runs in the dorsal mesentery from aorta towards the loop. It divides the loop into:  CEPHALIC (PROXIMAL) LIMB (PRE ARTERIAL SEGMENT) – Superior to axis artery  CAUDAL (DISTAL) LIMB (POST ARTERIAL SEGMENT) – Inferior to axis artery. The loop communicates with the umbilical vesicle through the narrow omphaloenteric duct (yolk stalk) until the 10th week. The omphaloenteric duct is attached to the apex of the midgut loop where the two limbs join.  Herniation of midgut loop Because of rapid elongation of midgut loop and rapid growth of liver and the developing mesonephric kidney, the abdominal cavity becomes too small to contain the elongated loops. So they project into the extraembryonic cavity in the umbilical cord during the sixth week of development This herniation of intestinal loop is called physiologic umbilical herniation.  the cranial limb grows rapidly and forms small intestinal loops, but the caudal limb undergoes very little change except for caecal swelling (diverticulum), the primordium of the cecum, and appendix.  Rotation of the Midgut Loop  Coincident with growth in length, the midgut loop rotates around the axis of superior mesenteric artery.  When viewed from the front, this rotation is counterclockwise, and it amounts to approximately 270° when it is complete.  A 90° rotation occurs during the herniation and the remaining 180° during the return of intestinal loop into the abdominal cavity  During rotation:  the cranial limb elongates and forms intestinal loops (e.g., primordia of jejunum and ileum).  caudal limb (primordia of Large intestine) also shows elongation but without coiling. Gut Rotation 305 Gut Rotation  First 900 anticlockwise rotation.  While it is in the umbilical cord, the midgut loop rotates 90 degrees counterclockwise around the axis of the superior mesenteric artery.  This brings the:  cranial limb of the midgut loop to the right  caudal limb to the left Rotation of Midgut 90 dgrs  Retraction of Intestinal Loops and 2nd 1800 rotation:  During the 10th week, the intestines return to the abdomen (reduction of the midgut hernia).  It is not known what causes the intestine to return; however, the enlargement of the abdominal cavity and the relative decrease in the size of the liver and kidneys are important factors.  The cranial limb returns first, passing posterior to the SMA and occupies the left and central part of the abdomen.  As a result, The third part of the duodenum lies posterior to the SMA  The caudal limb reduced last, passing anterior to SMA. It occupies right side of the abdomen after undergoing further 1800 counterclockwise rotation.  As a result, the transverse colon lies anterior to the SMA. Descent of cecal bud (primordia of caecum and appendix)  The cecal bud, which appears at about the sixth week as a small conical dilation of the antimesenteric border of caudal limb of the midgut loop, is the last part of the gut to reenter the abdominal cavity.  At first, it lies in the right upper quadrant directly below the liver  From here, it descends into the right iliac fossa, placing the ascending colon and hepatic flexure on the right side of the abdominal cavity  Derivatives of the midgut Small intestine: The duodenum distal to the opening of the bile duct, jejunum and most of the ileum are derived from the prearterial segment of the midgut loop. The terminal portion of the ileum is derived from the postarterial segment proximal to the cecal bud Large intestine Ascending and right 2/3rd of transverse Colon: develops from the postarterial segment of the midgut loop distal to the cecal bud.  Cecum and Appendix formed by enlargement of cecal bud from postarterial segment of the midgut loop. The proximal part of the bud grows rapidly to form the cecum. Its distal part remains narrow and elongate to form the appendix During greater part of fetal life, the appendix arises from the distal end (apex) of the cecum After birth, the lateral (or right) wall of the cecum grows much more rapidly than the medial (or left) wall with the result the point of attachment of the appendix comes to lie on the medial side Positions of the appendix The appendix is subject to considerable variation in position. As the ascending colon elongates, the appendix may pass posterior to the cecum (retrocecal appendix) or colon (retrocolic appendix). It may also descend over the brim of the pelvis (pelvic appendix). In approximately 64% of people, the appendix is located retrocecally  Fates of dorsal mesentery of mid gut  The dorsal mesentery of midgut loop undergoes profound changes during rotation.  the dorsal mesentery of jejunum & ileum is retained – mesentery proper.  the mesentery of transverse colon is also retained – transverse meso colon.  The mesentery of cecum and appendix is also retained – meso-appendix  So, jejunum, ileum, transverse colon, ceacum and appendix are intraperitonal derivatives of midgut  The mesentery of lower portion of duadenum and ascending colon regress, making them retroperitoneal Fates of dorsal mesentery of mid gut… Illustrations showing the mesenteries and fixation of the intestines. A, Ventral view of the intestines before their fixation. B, Transverse section at the level shown in A. The arrows indicate areas of subsequent fusion, C, Sagittal section at the plane shown in A, illustrating the greater omentum overhanging the transverse colon. The arrows indicate areas of subsequent fusion. D, Ventral view of the intestines after their fixation. E, Transverse section at the level shown in D after disappearance of the mesentery of the ascending and descending colon. F, Sagittal section at the plane shown in D, illustrating fusion of the greater omentum with the mesentery of the transverse colon and fusion of the layers of the greater omentum. Dev’t of Hindgut  Dev’t of Hindgut  Derivatives of the hindgut  The left one third of the transverse colon  The descending colon  Sigmoid colon, rectum  The superior part of the anal canal  The epithelium of the urinary bladder and most of the urethra  All hindgut derivatives are supplied by the inferior mesenteric artery, artery of the hindgut The junction between the segment of transverse colon derived from the midgut and that originating from the hindgut is indicated by the change in blood supply from a branch of the superior mesenteric artery to a branch of the inferior mesenteric artery.  Cloaca  The expanded terminal part of the hindgut, the cloaca, is an endoderm-lined chamber that is in contact with the surface ectoderm at the cloacal membrane  It is separated from proctodeum (anal pit) by cloacal membrane (composed of endoderm of the cloaca and ectoderm of the proctodeum or anal pit)  The cloaca receives the allantois ventrally which is a fingerlike diverticulum  Partitioning of the Cloaca The cloaca is divided into dorsal and ventral parts by a wedge of mesenchyme the urorectal septum-that develops in the angle between the allantois and hindgut. As the septum grows toward the cloacal membrane, it develops forklike extensions that produce infoldings of the lateral walls of the cloaca These folds grow toward each other and fuse, forming a partition that divides the cloaca into two parts.  Rectum and cranial part of anal canal dorsally  The urogenital sinus ventrally Successive stages in the partitioning of the cloaca into the rectum and urogenital sinus by the urorectal septum. A, C, and E, Views from the left side at 4, 6, and 7 weeks, respectively. B, D, and F, Enlargements of the cloacal region. B1 and D1, Transverse sections of the cloaca at the levels shown in B and D. Note that the postanal portion (shown in B) degenerates and disappears as the rectum forms. Partitioning of the Cloacal membrane  By the seventh week, the urorectal septum has fused with the cloacal membrane, dividing it into a dorsal anal membrane and a larger ventral urogenital membrane.  The area of fusion of the urorectal septum with the cloacal membrane is represented in the adult by the perineal body, the tendinous center of the perineum.  This fibromuscular node is the landmark of the perineum where several muscles converge and attach  Anal Canal  Anal canal developed from 2sources:  The superior 2/3 of the adult anal canal is derived from the hindgut  The inferior 1/3 develops from the proctodeum (anal pit)  The two parts are separated by anal membrane initially  The anal membrane usually ruptures at the end of the 8th week; establishing continuity between the endodermal and ectodermal parts of the anal canal  The site of attachment of anal membrane is represented by pectinate line in the adult.  The remnants of the anal membrane form the anal valves Anal canal of adult  Cont…  The rectum & anal canal up to pectinate line is derived from endoderm of primitive anorectal canal of cloaca.  It is therefore lined by simple columnar epithelium.  The portion of anal canal below the level of pectinate line is derived from ectoderm of proctodeum.  It is therefore lined by stratified squamous epithelium Ø Because of their different embryologic origins, the superior and inferior parts of the anal canal are supplied by different arteries and nerves and have different venous and lymphatic drainages. Fates of dorsal mesentery of hindgut  The mesentery of the left 1/3 of transverse colon and sigmoid colon are retainedtransverse mesocolon and sigmoid mesocolon respectively  The mesentery of the descending colon, rectum and anal canal is disappeared  The descending colon becomes retroperitoneal as its mesentery fuses with the peritoneum on the left posterior abdominal wall and then disappears. The mesentery of the sigmoid colon is retained, but it is shorter than in the embryo. 12/2/2020 33 1 ANOMALIES OF DIGESTIVE SYSTEM  Anomalies of Foregut Esophageal atresia: Esophageal atresia and/or tracheoesophageal fistula results either from spontaneous posterior deviation of the tracheoesophageal septum (or ) from some mechanical factor pushing the dorsal wall of the foregut anteriorly. 8/18/2024 333 Esophageal atresia 8/18/2024 334  Atresia of the esophagus prevents normal passage of amniotic fluid into the intestinal tract, resulting in accumulation of excess fluid in the amnioticsac (polyhydramnios). esophageal stenosis: the lumen of the esophagus may narrow, producing esophageal stenosis, usually in the lower third. Stenosis may be caused by incomplete recanalization, vascular abnormalities (or)accidents that compromise blood flow. 8/18/2024 335  congenital hiatal hernia: Occasionally the esophagus fails to lengthen sufficiently and the stomach is, pulled up into the esophageal hiatus through the diaphragm. 8/18/2024 336 Anomalies of stomach Hypertrophic Pyloric stenosis: This anomaly affects one in every 150 males and one in every 750 females. there is a marked muscular thickening(hyper trophy) of the pylorus, the distal sphincteric region of the stomach. 8/18/2024 337  The circular and, to a lesser degree, the longitudinal muscles in the pyloric region are hypertrophied. This results in severe stenosis of the pyloric canal and obstruction of the passage of food. Surgical relief of the pyloric obstruction (pyloromyotomy) is the usual treatment. 8/18/2024 338 ANOMALIES OF STOMACH CONGENITAL HYPERTROPHIC PYLORIC STENOSIS  Anomalies of the Duodenum Duodenal Stenosis: Partial occlusion of the duodenal lumen- duodenal stenosis. usually results from incomplete recanalization of the duodenum resulting from defective vacuolization. Most stenoses involve the horizontal (third) and/or ascending (fourth) parts of the duodenum. Because of the stenosis, the stomach's contents (usually containing bile) are often vomited. 8/18/2024 340  Duodenal Atresia: Complete occlusion of the lumen of the duodenum-duodenal atresia is not common. the lumen is completely occluded by epithelial cells. If recanalization of the lumen fails to occur a short segment of the duodenum is occluded. The blockage occurs nearly always at the junction of the bile and pancreatic ducts (hepatopancreatic ampulla) but occasionally involves the horizontal (third) part of the duodenum. 8/18/2024 341  ANOMALIES OF DUODENUM Duodenal stenosis. Duodenalatresia. Anomalies of liver Riedel’s lobe Polycystic liver disease Caroli’s disease Intrahepatic biliary atresia Accessory lobes 8/18/2024 344 Polycystic liver disease PCLD is a rare condition that causes cysts -- fluid-filled sacs -- to grow throughout the liver 8/18/2024 345 Caroli disease Caroli disease is a rare inherited disorder characterized by dilation of the intrahepatic bile ducts. This complex form is also linked with portal hypertension and congenital hepatic fibrosis. 8/18/2024 346  Anomalies of the Liver Variations of the hepatic ducts, bile duct, and cystic duct are common and clinically significant. Accessory hepatic ducts may be present, and awareness of their possible presence is of surgical importance. These accessory ducts are narrow channels running from the right lobe of the liver into the anterior surface of the body of the gallbladder. In some cases, the cystic duct opens into an accessory hepatic duct rather than into the common hepatic duct. 8/18/2024 347 Variations of Gall bladder Agenesis of gall bladder Septate gall bladder Double gall bladder Extrahepatic bile duct anomalies Atresia of bile duct Accessory bile duct Choledochal cyst Anomalies of spleen Accessory Spleens (Polysplenia): One or more small splenic masses of fully functional splenic tissue may exist in one of the peritoneal folds, commonly near the hilum of the spleen, in the tail of the pancreas, or within the gastrosplenic ligament. 8/18/2024 350 Anomalies of the Midgut Congenital abnormalities of the intestine are common; most of them are anomalies of gut rotation-non rotation or malrotation of the gut-that result from incomplete rotation and/or fixation of the intestines. Nonrotation occurs when the intestine does not rotate as it reenters the abdomen. 12/2/2020 35 1  As a result, the caudal limb of the midgut loop returns to the abdomen first and the small intestines lie on the right side of the abdomen and the entire large intestine is on the left. The usual 270-degree counterclockwise rotation is not completed, and the cecum lies just inferior to the pylorus of the stomach. 12/2/2020 35 2  The cecum is fixed to the posterolateral abdominal wall by peritoneal bands that pass over the duodenum. These bands and the volvulus (twisting) of the intestines cause duodenal obstruction. This type of malrotation results from failure of the midgut loop to complete the final 90 degrees of rotation. Only two parts of the intestine are attached to the posterior abdominal wall: the duodenum and proximal colon. 12/2/2020 35 3  This improperly positioned and incompletely fixed intestine may lead to a catastrophic twisting of the midgut-midgut volvulus. When midgut volvulus occurs, the superior mesenteric artery may be obstructed, resulting in infarction and gangrene of the intestine supplied by it Infants with intestinal malrotation are prone to volvulus and present with bilious emesis (vomiting bile). 12/2/2020 35 4  Anomalies of midgut rotation Nonrotation Mixed rotation and Reversed rotation volvulus 12/2/2020 35 5  Subhepatic cecum and Internal hernia. Midgut volvulus appendix 12/2/2020 35 6 Ileal Diverticulum and Other Omphaloenteric Remnants This outpouching of the ileum is one of the most common anomalies of the digestive tract. A congenital ileal diverticulum (Meckel diverticulum) occurs in 2% to 4% of people and is three to five times more prevalent in males than females. 12/2/2020 35 7  A large ileal diverticulum, commonly referred to clinically as a Meckel diverticulum 12/2/2020 35 8  The wall of the diverticulum contains all layers of the ileum and may contain small patches of gastric and pancreatic tissues. This ectopic gastric mucosa often secretes acid, producing ulceration and bleeding. An ileal diverticulum is the remnant of the proximal part of the omphaloenteric duct (yolk stalk). It typically appears as a fingerlike pouch approximately 3 to 6 cm long that arises from the antimesenteric border of the ileum 12/2/2020 35 9  An ileal diverticulum may be connected to the umbilicus by a fibrous cord (which may predispose to intestinal obstruction as the intestine can wrap around this cord) or an omphaloenteric fistula (omphalomesenteric duct). Newborn male infant with a patent omphaloenteric duct (omphalomesenteric duct). 12/2/2020 36 0 Ileal diverticula and other remnants of the omphaloenteric duct. Omphaloenteric fistula Section of the ileum and a A diverticulum connected resulting from diverticulum with an ulcer to the umbilicus by a persistence of the fibrous cord entire intra-abdominal portion of the 12/2/2020 omphaloenteric duc5t0 Omphaloenteric cysts at Umbilical sinus The omphaloenteric duct the umbilicus and in a resulting from the has persisted as a fibrous remnant of the persistence of the fibrous cord connecting omphaloenteric duct omphaloenteric duct the ileum with the near the umbilicus umbilicus. 12/2/2020 36 2 Duplication of the Intestine Most intestinal duplications are cystic or tubular duplications. Cystic duplications are more common. Tubular duplications usually communicate with the intestinal lumen. Almost all duplications are caused by failure of normal recanalization of the intestines; as a result, two lumina form. 12/2/2020 36 3 CONGENTAL OMPHALOCELE (Exomphalos) Persistence of the herniation of intestines into the umbilical cord. Occurs in 1 in 5000 live births Can also contain liver in complete variety. Occurs in 1 in 5000 live births. Associated defective development of abdominal wall also is present.  Drawing of the infant with an omphalocele resulting from a median defect of the abdominal An infant with a muscles, fascia, and skin near the umbilicus. large omphalocele This defect resulted in the herniation of