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HISTOLOGY OF THE GIT (ONE) Lufukuja. G 1 GIT COMPOSITION Lufukuja. G 2 Oral Cavity • The oral cavity is bound by lips anteriorly and chicks laterally, and it contains the tongue and the teeth supported by periodontium. • The palate forms its roof and posteriorly the mouth communicate with the oropharynx through the oropharyngeal isthmus Lufukuja. G 3 The lips • Each lip is lined by skin on the outside and on the inside is lined by mucous membrane. • The red free margins of the lips do not contain sweat or sebaceous glands or hair follicles. These margins of the lips are covered with a modified skin which represents a transition from skin to mucous membrane. • Its dermis has numerous blood vessels; as a result the blood in the capillaries readily shows through the transparent epidermis to make the lips appear red. Lufukuja. G 4 …the lips • Internally the lips are covered by a mucous membrane consists of stratified squamous non-keratinising epithelium lying upon a connective tissue lamina propria. The connective tissue that contains small mucous glands (labial glands) and nerve endings. Lufukuja. G 5 Lufukuja. G 6 The cheek • Has an outer covering of skin and inner lining of mucous membrane, similar to that of the lips. Superficial cells are constantly being rubbed off the surface and replaced from below. • There are small mucous glands in the lamina propria of the cheek. Lufukuja. G 7 The palate • The palate is described to have hard palate and soft palate. • The hard palate has mucous membranes that covers both surfaces of the bony skeleton and is firmly attached to it by a thin layer of dense connective tissue as a result of which the mucous membrane is not mobile. It is lined by stratified squamous epithelium, which is keratinized to a variable degree. A number of mucous glands are present Lufukuja. G 8 …the palate • The soft palate consists of central skeleton of dense fibrous tissue (palatine aponeurosis). • The soft palate has two surfaces, the oral and nasal. The oral and lower part of the nasal surfaces are lined by stratified squamous non-keratinized epithelium. The lining of the rest of the nasal surface is covered by pseudostratified ciliated columnar epithelium. Lufukuja. G 9 Lufukuja. G 10 Lufukuja. G 11 Teeth • Tooth is hard tissue that fits into the sockets of the alveolar process of the maxilla and mandible. An adult has 32 teeth; 16 each jaw and a child has 20 teeth, 10 on each jaw. Lufukuja. G 12 Lufukuja. G 13 Parts of the tooth Lufukuja. G 14 Tissue component of the tooth • The tooth has both hard and soft tissue; there are three hard tissues, the enamel, dentine and cementum and three soft tissues, the dental pulp, periodontal ligament and gingiva, that is commonly referred to as gums. Lufukuja. G 15 stellate reticulum Lufukuja. G 16 Lufukuja. G 17 The gingiva • Is also known as a gum, it is a dense connective tissue firmly attached to the underlining periosteum of the alveolar bone and is lined by mucous membrane, which is stratified squamous epithelium with patchy keratinization Lufukuja. G 18 The tongue • Is a mobile muscular structure that lies in the oral cavity proper. It consists of intrinsic skeletal muscle covered with mucous membrane. • The tongue is made up of the body and the root; the body forms the anterior two thirds of the tongue while the root forms the posterior one third. The border between the two is indentified by a V-shaped furrow known as the sulcus terminalis. Lufukuja. G 19 …the tongue • The mucous membrane of the ventral surface is stratified keratinized epithelium and appears smooth. • The mucous membrane of the dorsal surface of the anterior two thirds of the tongue is also stratified squamous epithelium that is partially keratinized in some places but contain numerous mucosal projections known as lingual papillae. Because of these mucosal projections the dorsal surface of the tongue appears rough. However it is not associated with lingual tonsils. Lufukuja. G 20 Lufukuja. G 21 The lingual papillae • There are four types of lingual papilla, these are filiform papilla, fungiform papilla, folliate papilla and circumvalate papilla Lufukuja. G 22 Filiform papillae • are the smallest and most numerous papillae. By providing the tongue with a rough surface they aid in the manipulation and processing of foods • The epithelium that forms the filiform papillae is keratinized and do not contain the taste buds Lufukuja. G 23 Fillform Papilla Lufukuja. G 24 Fungiform papillae • They occur singly and are fairly evenly spaced between the filiform papillae. Their connective tissue core is richly vascularized. The epithelium is slightly thinner than on the remaining surface of the tongue • The epithelium at the tip of the papilla contain smaller number of taste buds and hence play an important role in appreciation of taste Lufukuja. G 25 Foliate papilla • These are not well developed in humans and may be absent in aged individuals. • If present, they form lamellae along the posterior and lateral border of the tongue. Lufukuja. G 26 Circumvallate papillae • These are the largest and least numerous papillae • They are located along the V-shaped depression, the sulcus terminalis. Taste buds are particularly numerous on the lateral surfaces of these papillae. • They are associated with serous glands (von Ebner glands) whose ducts open into the trenches surrounding the papillae and the furrow of the sulcus terminalis. Lufukuja. G 27 Lufukuja. G 28 Taste Buds • Taste buds are end organs for taste sensations. They are barrel shaped and extend throughout the whole thickness of the epithelium to open to the surface through a minute gustatory pore. They are composed of three types of cells; the gustatory cells, sustentacular cells and basal cells. Lufukuja. G 29 Lufukuja. G 30 Pharynx • The pharynx is divided into three parts; the Nasopharyx, Oropharynx, Laryngopharynx). The pharynx has three coats, an outer fibrous, middle muscular and inner mucous membrane. The epitheliums is stratified squamous nonkeratinized type Lufukuja. G 31 Tonsils • In the oropharynx two types of tonsils: the lingual tonsil is located in the lamina propria in the posterior third or pharyngeal part of the tongue. The palatine tonsils are pair of tonsils on the lateral wall of the oropharynx between to arches, the palatoglossal and palatopharyngeal muscles respectively. Lufukuja. G 32 Lufukuja. G 33 Waldeyer’s ring Lufukuja. G 34 Salivary Glands Lufukuja. G 35 Salivary Glands • There are three pairs of large salivary glands they include: The parotid, Submandibular, and sublingual glands. The function of these glands is to secrete saliva which enters the oral cavity via the ducts. Lufukuja. G 36 The parotid glands • The gland is a compound tubuloalveolar of serous type. • A dense fibroelastic capsule encloses the gland, which is part of the investing layer of the deep cervical fascia. Lufukuja. G 37 The parotid glands • The parenchyma of the glands consists of secretory end pieces (the acini) and a branching duct system arranged in lobes & lobules, separated by septae of connective tissue originating from the capsule Lufukuja. G 38 Lufukuja. G 39 … parotid (histological features) • The duct system is divided into intralobular and extralobular ducts. • The intercalated ducts represent the first duct system and they originate from the acini. They are lined by simple cuboidal epithelium. Striated ducts are large ducts in diameter and are lined by columnar cells that has microvilli on their apical surface. • The extralobular ducts are large and include the excretory ducts and the main duct, the Stensen’s duct which is lined by stratified columnar cells. Lufukuja. G 40 Lufukuja. G 41 Lufukuja. G 42 The submandibular gland • This is located below the body of the body of the mandible, its main ducts are known as Wharton’s duct and opens into floor of the mouth underneath the tip of the tongue. • It is a compound tubuloalveolar gland with mixed but mainly serous and few mucous acini. Lufukuja. G 43 Lufukuja. G 44 …submandibular gland • The duct system differs from the parotid gland in that it has short intercalated ducts this makes them less prominent. • The epithelium of the interlobular ducts is lined by pseudostratified epithelium with few goblet cells, which modify the saliva by addition of mucous. Lufukuja. G 45 Sublingual gland • This is not a single gland but a collection of small groups of mixed glands, which are predominantly mucous in nature. It lies in the floor of the mouth over the mylohyoid muscle. • The main ducts from sublingual glands may open together with the main duct of the submandibular gland. The duct system is less prominent because they are short and not well demonstrated in histological sections. Lufukuja. G 46 Sublingual gland Lufukuja. G 47