Gastrointestinal Tract Histology Lecture 1 PDF

GASTROINTESTINAL TRACT HISTOLOGY LECTURE 1  CONTENTS Histological structure of foregut: oral cavity and its components, pharynx, esophagus  DIGESTIVE SYSTEM The digestive system consists of the digestive tract and its associate d glands.  FUNCTIONS 1 Its function is to obtain th...

GASTROINTESTINAL TRACT HISTOLOGY LECTURE 1  CONTENTS Histological structure of foregut: oral cavity and its components, pharynx, esophagus  DIGESTIVE SYSTEM The digestive system consists of the digestive tract and its associate d glands.  FUNCTIONS 1 Its function is to obtain the molecules necessary for the maintenance, growth, and energy needs of the body from ingested food. 2. Large molecules such as proteins, fats, complex carbohydrates, and nucleic acids are broken down into small molecules that are easily absorbed through the lining of the digestive tract, mostly in the small intestine. 3. Water, vitamins, and minerals are also absorbed from ingested food. 4. In addition, the inner layer of the digestive tract is a protective barrier between the content pf the tract's lumen and the internal mileu of the body.  MUCOSA 1. The mucosa comprises an epithelial lining. 2. lamina propria : Loose connective tissue rich in blood and lymph vessel and smooth- muscle cells, sometimes also containing glan ds and lymphoid tissue. 3.The muscularis mucosae, usually consisting of a thin inner circular layer and an outer longitudinal layer of smooth muscle cells separating the mucosa from the submucosa. The mucosa is frequently called a mu cous membrane.  SUBMUCOSA The submucosa is composed of dense connective tissue with many blood and lymph vessels and a submucos al (Meissner's) nerve plexus. It may also contain glands and lymphoid tissue. The muscularis contains smooth muscle cells that are spirally oriented and divided into two sublayers according to the main direction the muscle cells follow. In the internal sublayer (close to the lumen), the orientation is generall y circular; in the external sublayer, it is mostly longitudinal. The muscularis also contains the myenteric (or Auerbach's) nerve plexus, which lies between the two muscle sublayers , and blood and lymph vessels in the connective tissue between the muscle sublayers  SEROSA 1. The serosa is a thin layer of loose connective tissue, rich in blood and lymph vessels and adipose tissue, and a simple squamous covering epithelium (mesothelium). 2. In the abdominal cavity, the serosa is continuous with the mesenteries (thin membranes covered b y mesothelium on both sides), which support the intestines, and with the peritoneum, a serous membrane that lines the cavity wall. 3. In places where the digestive organ is bound to other organs or structures, however, the serosa is replaced by a thick adventitia, consisting of connective tissue containing vessels and nerves, without the mesothelium.  HIRSCHSPRUNG DISEASE CHAGAS DISEASE( trypanosomiasis) 1. Hirschsprung disease Plexus in the digestive tract’s enteric nervous system are absent or severely injured Digestive tract motility is disturbed Dilations are produced in some areas 2. Chagas disease- caused by Trypanosoma Cruzi. Infection causes GIT complications.  MAIN FUNCTIONS OF EPITHELIAL LINING OF DIGESTIVE TRACT 1.To provide a selectively permeable barrier between the contents of the tract and the tissues of the body, 2.To facilitate the transport and digestion of food, 3.To promote the absorption of the products of this digestion, and to produce hormones that affect the activity of the digestive system. Cells in this layer produce mucus for lubrication and protection. 4. The abundant lymphoid nodules in the lamina propria and the submucosal layer protect the organism (in association with the epithelium) from bacterial invasion. 5. The lamina propria, located just below the epithelium, is a zone rich in macrophages and lymphoid cells, some of which a ctively produce antibodies. These antibodies are mainly immun oglobulin A (IgA). This complex protects against viral and bacterial invasion. 6. The muscularis mucosae promotes the movement of the mucosa independent of other movements of the digestive tract, increasing its contact with the food.  ORAL CAVITY The oral cavity consists of the mouth, lips, tongue teeth, salivary glands(major & minor), tonsils. Lined with stratified squamous epithelium Keratinised cell layers - masticatory mucosa of gingiva and hard palate. Nonkeratinized squamous epithelium - the lining mucosa over the soft palate, cheeks, the floor of the mouth, and the pharynx (or throat), the posterior region of the oral cavity leading to the esophagus.  LIPS The skin of the lips is stratified squamous epithelium  TONGUE 1. A mass of striated muscle covered by mucosa 2. Two surfaces The lower surface of the tongue is smooth, with typical lining mucosa. The dorsal surface is irregular- has protruding papillae (anterior two- thirds) and the massed lingual tonsils on the (posterior third) 3. Sulcus terminalis V shaped groove which separates papillary and tonsillar areas of lingual surface.  LINGUAL PAPILLAE 1. Elevation of mucous membrane 2. Four types: A. Filiform papillae B. Fungiform Papillae C. Foliate Papillae D. Vallate/Circumvallate Papillae  PHARYNX 1.It is a transitional space between the oral cavity and the respiratory and digestive systems, & forms an area of communication between the nasal region and the larynx. 2. The pharynx is lined by stratified nonkeratinized squamous epithelium in the region continuous with the esophagus and by ciliated pseudostratified columnar epithelium containing goblet cells in the regions close to the nasal cavity. 3. The pharynx contains the tonsils. 4.The mucosa of the pharynx also has many small mucous salivary glands in its lamina propria, composed of dense connective tissue. 5.The constrictor and longitudinal muscles of the pharynx are locat ed outside this layer.  REFERENCES CHAPTER 5 Junquiera’s histology