General Histology By Sahar M. Ahmed Assistant lecture at Al-Rafidain University college Department of Dentist 1 DIGESTIVE SYSTEM (part -1-) 2 groups of organs compose the digestive system Gastrointenstinal (GI) tract or alimentary canal – mouth, most of pharynx, esophagus, stomach, small intestine, and large intestine Accessory digestive organs – teeth, tongue, salivary glands, liver, gallbladder, and pancreas Or can classify to 3 parts, these are: 1. Oral cavity: consist of (lips, cheek, teeth, tongue, & salivary glands). 2. Digestive tract: include (most of pharynx, esophagus, stomach, small intestine, and large intestine). 3. Digestive glands: these include (liver, gallbladder, & pancreas). The digestive system is a group of organs working together to convert food into energy and basic nutrients to feed the entire body. Food passes through a long tube inside the body known as the alimentary canal or the gastrointestinal tract (GI tract). The alimentary canal is made up of the oral cavity, pharynx, esophagus, stomach, small intestines, and large intestines. In addition to the alimentary canal, there are several important accessory organs that help the body to digest food, but do not have food pass through them. Accessory organs of the digestive system include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. 2 Functions of digestive system . Ingestion: Taking in food through the mouth . Propulsion (movement of food) Swallowing Peristalsis – propulsion by alternate contraction &relaxation . Mechanical digestion Chewing Churning in stomach Mixing by segmentation . Chemical digestion: By secreted enzymes: see later . Absorption: Transport of digested end products into blood and lymph in wall of canal . Defecation: Elimination of indigestible substances from body as feces Chemical digestion: Complex food molecules (carbohydrates, proteins and lipids) broken down into chemical building blocks (simple sugars, amino acids, and fatty acids and glycerol) Carried out by enzymes secreted by digestive glands into lumen of the alimentary canal 3 ORAL CAVITY . The oral cavity is lined with a keratinized or nonkeratinized stratified squamous epithelium depending on what region you’re in. 1. This epithelium is often called the mucous epithelium. 2. The transition between the stratified keratinized squamous epithelium of the skin and the stratified non-keratinized squamous epithelium of much of the oral cavity occurs at the lips. 3. Below the stratified squamous epithelium is a layer of loose connective tissue, called lamina propria. This lamina propria shows some interdigitation with the stratified squamous epithelium of the oral region as the dermis of the skin does with the epidermis. It contains blood and lymph vessels, small glands, nerves and aggregations of lymphocytes. 4. Together, the stratified squamous epithelium and the lamina propria form the oral mucosa - No muscularis mucosae Lips When we think of lips we usually only think of a small part, the vermilion border (or prolabium), of the "anatomical" lips, which comprise the entire fleshy fold surrounding the oral orifice. The outside and inside of the lips are lined by skin and oral mucosa respectively. Between the two, we find labial vessels, nerves, the orbicularis oris muscle (striated), which shapes the lips, and labial salivary glands. The vermilion border is the area of transition from the skin to the oral mucosa. The epithelium is somewhat thicker than in other parts of the facial skin. Connective tissue papilla extend deep into the epithelium and are heavily vascularized. It is the proximity of these vessels to the surface of the epithelium which gives the prolabium it's red appearance. 4 The roof of the mouth consists of soft and hard palates. 1. The hard palate has an intramembranous bone backing which is covered by a keratinized mucous epithelium. 2. The soft palate has a core of skeletal muscle and is covered by a non-keratinized mucous epithelium & Uvula. Tongue The tongue consists of a mass of striated muscle covered by a mucosa consisting of a non-keratinized, stratified, squamous epithelium and lamina propria in most places. The mucous epithelium is strongly adherent to the muscle below. This is because the C.T. of the lamina propria penetrates into spaces between the muscle bundles. Tongue muscle is striated and composed of bundles that are oriented in 3 planes. This sort of structure increases both the potential stiffness and the mobility of the tongue. 5 The dorsal surface of the tongue can be divided into two areas by a V-shaped boundary found in the posterior dorsal tongue surface. The dorsal surface of the anterior 2/3 of the tongue is covered by various types of papillae. Beneath the surface are serous and mucous glands. But the posterior 1/3, behind the V, is composed of small bulges that contain lymphatic nodules. * These include the lingual tonsils that consist of lymph nodules surrounding a single crypt. The type of papillae found depends on what part of tongue you look at. 1. Filiform papillae: Have an elongated conical shape. These papillae have a keratinized surface, are the most numerous and are found over the entire dorsal surface. There are no taste buds in the epithelium covering filiform papillae. 2. Fungiform papillae: These are mushroom shaped. There are far fewer fungiform than filiform papillae.They are found interspersed between the filiform papillae over the entire anterior dorsal surface of the tongue. A few taste buds may be found in the epithelium covering these papillae. 6 3. Circumvallate papillae: These are extremely large circular papillae which have a flattened surface that extends above the other tongue papillae. About 8- 12 in number. these papillae are distributed in the V region of the posterior dorsal surface of the tongue. Many taste buds can be found in the epithelium covering their lateral surfaces. the excretory ducts of serous glands open into the trenches surrounding the papillae ("rinsing glands" or glands of von Ebner). 4. Foliate papilla: these are arranged as closely packed folds along the posterior lateral margins of the tongue and are only common in young children. There are numerous taste buds in the epithelium covering foliate papillae. Serous glands drain through openings at their bases. Taste Buds Oval multicellular structures, Cells surround a cavity that communicates with the oral cavity via a small pore between the apexes of the cells. 7 Teeth In adult humans there are 32 permanent teeth. These are preceded during childhood by 20 deciduous teeth. The tooth lies in a bony socket, the alveolus, that is covered my an oral mucosa called the gingiva (gums) that consists of, keratinized stratified squamous epithelium & lamina propria of loose connective tissue that lies directly adjacent to the bone of the alveolus. The tooth consists of two major parts a. the crown - the portion that protrudes above the gum line. b. the root - the portion that extends into the alveolus. Internally, the tooth consists of a layer of dentin that surrounds a pulp consisting of loose connective tissue, nerves and blood vessels. In the dentin, directly adjacent to the pulp is a layer of specialized cells called odontoblasts - secrete organic matrix that calcifies and forms the dentin. 8 Crown region Dentin is covered by a layer of calcified organic matrix - the enamel, hardest substance in body, Formed by ameloblasts before tooth “erupts” from socket Root region Dentin (mineralized organic matrix) surrounds the pulp. In the root region, the dentin is covered by calcified organic matrix - the cementum - similar to bone, but no haversian system, Between the cementum and the bone of the socket lies the periodontal ligament. Where the gingiva meets the tooth - specialized epithelium - junctional epithelium - binds epithelium to enamel. • Junctional epithelium is non-keratinized stratified squamous without “dermal” papillae • Bound to enamel by cuticle (looks like extra thick basal lamina - called epithelial attachment of Gottlieb) • Cells of junctional epithelium tightly attached to cuticle by hemidesmosomes • Between this attachment and the gumline is the gingival sulcus. Lined by sulcular epithelium. This is a non-keratinized stratified squamous epithelium. • When dentist probes around your teeth - checking depth of sulcus. • If too deep, indicates breakdown between enamel and junctional epithelium - periodontal disease 9 Salivary Glands Saliva is a mixed secretion, which is derived from numerous large and small salivary glands that all open into the oral cavity. Small salivary glands are situated in the connective tissue beneath the epithelia lining the oral cavity, and, in the case of the tongue, they may also be found between the muscular tissues. Depending on the localisation they are grouped into lingual, labial, buccal, molar and palatine glands. The large salivary glands form three paired groups: 1. the sublingual glands, which are positioned beneath the tongue and embedded deeply in the connective tissue of the oral cavity, 2. the submandibular glands and 3. The parotid glands, which lie outside the oral cavity. All of these glands are tubuloacinar glands, they have secretory acini but the first part of the duct system originating from the acini also participates in the secretory process. The salivary glands are divided by connective tissue septa into lobes, which are further subdivided into lobules. Functionally the secretory acini can be divided into two groups: those that secrete a rather liquid