Digestive System PDF

**DIGESTIVE SYSTEM** ==================== - Also called the [gastrointestinal (GI) tract or alimentary cana]l, - a hollow tube with a lumen of variable diameter and a wall made up of - **Four main layers**: the **[mucosa, submucosa, muscularis, and serosa]** - the inner layer...

**DIGESTIVE SYSTEM** ==================== - Also called the [gastrointestinal (GI) tract or alimentary cana]l, - a hollow tube with a lumen of variable diameter and a wall made up of - **Four main layers**: the **[mucosa, submucosa, muscularis, and serosa]** - the inner layer of the entire digestive tract forms an important protective barrier between the content of the tract's lumen and the internal milieu of the body's connective tissue and vasculature. - oral cavity - esophagus - stomach - small and large intestines - anus - ### ASSOCIATED GLANDS - salivary glands - liver - pancreas **Four main layers/ tunics**: +-----------------------------------+-----------------------------------+ | [Mucosa] | - - | | | | | \- called a mucous membrane. | | +===================================+===================================+ | Submucosa | - | +-----------------------------------+-----------------------------------+ | Thick muscularis (or | - - | | | | | Muscularis externa) | | +-----------------------------------+-----------------------------------+ | Serosa | - - - - - - | +-----------------------------------+-----------------------------------+ Function of the digestive system: 1. Ingestion of food 2. Digestion of food 3. Elimination of wastes 4. Absorption of nutrients  STRUCTURES WITHIN THE DIGESTIVE TRACT **(**IMMSHCAE**)** ======================================================== - Ingestion - Mastication - Motility - Secretion - Hormone release - Chemical Digestion - Absorption - Elimination **[PERITONEUM:]** 1. **[VISCERAL PERITONEUM]** - Serous membrane that covers the organs 2. **[PARIETAL PERITONEUM ]** - Serous membrane that covers the walls of the abdominal cavity **[OMENTUM:]** - Sheets that hold the abdominal cavity organs in place. 1. **[LESSER OMENTUM]** - Connects the lesser curvature of the stomach to the liver and the diaphragm 2. **[GREATER OMENTUM ]** - Connects the greater curvature of the stomach to the transverse colon and the posterior body wall - **Omental bursa** -- a long double fold of mesentery that extends inferiorly from the stomach before looping back to the transverse colon to create a cavity or pocket - **Mesentery proper** -- attaches the small intestine to the posterior abdominal wall. 3. **[RETROPERITONEAL ]** - Abdominal organs that have no mesenteries: duodenum, pancreas, ascending and descending colon, rectum, kidneys, adrenal glands, urinary bladder **ORAL CAVITY** =============== - stratified squamous epithelium, which may be keratinized, partially keratinized, or nonkeratinized depending on the location. - Epithelial differentiation and keratinization are **similar to epidermis and dermis**. - Superficial cells undergo continuous **desquamation**. - **The keratinized cell layers** - resist damage from abrasion - best developed in the **masticatory mucosa** on the gingiva (gum) and hard palate. #### - #### **Lamina propria** - rests directly on the periosteum of underlying bone - #### **Nonkeratinized squamous epithelium** - predominates in the lining mucosa over the soft palate, cheeks, the floor of the mouth. - #### **Pharynx (or throat)** - the posterior region of the oral cavity leading to the esophagus. - #### **Lining mucosa** - overlies a thick submucosa containing many minor salivary glands, - secrete continuously to keep the mucosal surface wet, and diffuse lymphoid tissue  ### **LIPS OR LABIA** - well-developed core of striated muscle - highly mobile for ingestion, speech, and other forms of communication - muscular structure formed by the orbicularis oris muscles - #### **Internal Mucous Surface** - lining mucosa with a thick, nonkeratinized epithelium and many minor labial salivary glands - #### **Red Vermilion Zone** - covered by very thin keratinized stratified squamous epithelium - transitional between the oral mucosa and skin. - lacks salivary or sweat glands and is kept moist with saliva from the tongue. - underlying connective tissue is very rich in both sensory innervation and capillaries, which impart the pink color to this region - #### **Outer Surface** - thin skin - #### keratinized stratified squamous epithelium - #### consisting of epidermal and dermal layers, sweat glands, and many hair follicles with sebaceous glands **TONGUE** ========== - mass of striated muscle covered by mucosa - manipulates ingested material during mastication and swallowing - muscle fibers are oriented in all directions, allowing a high level of mobility - penetrated by the lamina propria - **Lower/ Ventral surface** of the tongue is smooth, with typical lining mucosa. - **Dorsal surface** is irregular, having hundreds of small protruding papillae of various types on its anterior two-thirds and the massed lingual tonsils on the posterior third, or root of the tongue - **Sulcus terminalis** --------------------- - V-shaped groove c - papillary and tonsillar areas of the lingual surface are separated - **Lingual papillae** -------------------- - elevations of the mucous membrane that assume various forms and functions - has four types: +-----------------------------------+-----------------------------------+ | **Filiform papillae** | - - - - | +===================================+===================================+ | **Fungiform papillae** | - - - - | +-----------------------------------+-----------------------------------+ | **Foliate papillae** | - - | +-----------------------------------+-----------------------------------+ | **Vallate (or circumvallate) | - | | papillae** | | +-----------------------------------+-----------------------------------+  - #### **Serous salivary (von Ebner) glands** - empty into the deep, moatlike groove surrounding each vallate papilla - provides a continuous flow of fluid over the taste buds that are abundant on the sides of these papillae, washing away food particles so that the taste buds can receive and process new gustatory stimuli. **TASTE BUDS** ============== - are ovoid structures within the stratified epithelium on the tongue's surface, - has 50-100 cells, about half of which are elongated gustatory (taste) cells - sample the general chemical composition of ingested material - **250 taste buds** are present on the lateral surface of each vallate papilla, with many others present on fungiform and foliate (but not the keratinized filiform) papillae - not restricted to papillae - also widely scattered elsewhere on the dorsal and lateral surfaces of the tongue, where they are also continuously flushed by numerous minor salivary glands. **Salty** **Sodium ions** ------------ ------------------------------------------------- **Sour** **Hydrogen ions from acids** **Sweet** **Sugars and related compounds** **Bitter** **Alkaloids and certain toxins** **Umami** **Amino acids such as glutamate and aspartate** **TEETH** ========= - 32 permanent teeth, arranged in two bilaterally symmetric arches in the maxillary and mandibular bones. - Each quadrant has eight teeth: - two incisors - one canine - two premolars - three permanent molars - **Primary teeth (deciduous or milk teeth)** ------------------------------------------- - 20 of the permanent teeth are preceded - **Each tooth** -------------- - has a crown exposed above the **[gingiva]**, a constricted neck at the gum, and one or more roots that fit firmly into bony sockets in the jaws called **[dental alveol]i**. - **Crown** - covered by enamel, and the roots by cementum **Dentin**- composes the bulk, surrounding the pulp cavity. **Pulp:** a vascular, innervated, loose connective tissue. **Components:** =============== - [**Enamel**:] Hardest body component, mostly hydroxyapatite, covers the dentin of the tooth - **[Dentin]:** 70% hydroxyapatite, secreted by odontoblasts, sensitive to stimuli. - **[Cementum]:** Covers root dentin, resembles bone, avascular. - **[Periodontal Ligament]:** Collagen fibers, supports tooth, permits limited movement. binding the cementum and the alveolar bone - **[Pulp Cavity] -- center of the tooth, contains blood vessels, nerves and pulp (connective tissue)** - **[Gingiva]** − **dense fibrous connective tissue and most stratified squamous epithelium that covers the alveolar processes** - **Pharyngitis** and **Tonsillitis** are caused by *Streptococcus pyogenes.* - **White Excrescences** or **Leukoplakia** can be caused by Epstein-Barr virus. - **Oral Thrush** is caused by a yeast (*Candida albicans) infection.* **PERIODONTIUM** ================ - Maintains teeth in the bones. - Includes cementum, periodontal ligament, alveolar bone, gingiva. - Gingival sulcus and junctional epithelium around the tooth enamel. - **alveolar bone** lacks the typical lamellar pattern of adult bone but has osteoblasts and osteocytes engaging in continuous remodeling of the bony matrix. It is surrounded by the periodontal ligament, which serves as its periosteum.  **PALATE AND TONSILS** ====================== - **[PALATE]** -- roof of the oral cavity, prevents food from passing into the nasal cavity during chewing and swallowing. - **Hard Palate --** anterior part that contains the bone - **Soft Palate --** posterior portion that consists of skeletal muscles and connective tissues **\*\*\*Uvula --** grapelike posterior extension of the soft palate - T**[ONSILS]** -- protects against pathogens from entering the nose and the mouth. **SALIVARY GLANDS** =================== - Produce saliva (serous -- mucous fluid) **SALIVA** ================================ **ESOPHAGUS** ============= - Muscular tube, about 25-cm long in adults, which transports swallowed material from the pharynx to the stomach. - **The four layers of the GI tract f**irst become well-established and clearly seen in the esophagus. - **The esophageal mucosa** has nonkeratinized stratified squamous epithelium, its muscularis is striated at its superior end with smooth muscle at its inferior end, with mixed fiber types in the middle. - Most of the outer layer of the esophagus is adventitia, merging with other tissues of the mediastinum. - At the esophagogastric junction, stratified squamous epithelium changes abruptly to simple columnar epithelium invaginating into the lamina propria as many branched tubular glands. - **Esophageal Sphincter** - Regulate the movement of food from the pharynx to the stomach - **Cardiac Sphincter --** lower ES **ESOPHAGEAL GLANDS** ===================== - Small mucus-secreting glands in the submucosa. - Lubricates and protects the mucosa. **ESOPHAGEAL CARDIAC GLANDS** ============================= - A group of glands that secretes additional mucus. - They secrete neutral mucin that protects the esophagus from acidic gastric juices. **Swallowing** -------------- - begins with voluntary muscle action but finishes with involuntary peristalsis  **STOMACH** =========== - greatly dilated segment of the digestive tract - **Main functions**: - To continue the digestion of carbohydrates initiated by the amylase of saliva. - To add an acidic fluid to the ingested food and mixing its contents into a viscous mass called chyme by the churning activity of the muscularis. - To begin digestion of triglycerides by a secreted lipase. - To promote the initial digestion of proteins with the enzyme pepsin. **Four major regions make up the stomach** +-----------------------------------+-----------------------------------+ | **CARDIA** | | +===================================+===================================+ | **PYLORUS** | | +-----------------------------------+-----------------------------------+ | **FUNDUS AND BODY** | - - - | +-----------------------------------+-----------------------------------+ **EPITHELIAL CELLS OF THE STOMACH** ===================================  **SECRETIONS OF THE STOMACH** ============================= - **Chyme** **--** semifluid mixture (food + stomach secretions). - **Hydrochloric** **acid** kills microorganisms and activates pepsin. - **Pepsin** breaks covalent bond of proteins to form smaller peptide chains. - **Mucus** lubricates and protects epithelial cells from the damaging effect of acidic chime + pepsin. - **Intrinsic** **factor** binds with vit. B12 (DNA synthesis and RBC prod.) and makes it more readily absorbed in the small intestine. **REGULATION OF STOMACH SECRETIONS** **MOVEMENT IN THE STOMACH** **SMALL INTESTINES** ==================== - site where the digestive processes are completed and where the nutrients (products of digestion) are absorbed by cells of the epithelial lining. - Covered by a thin serosa with mesothelium continuous with that of the mesenteries. - Has three segments (3): +-----------------------------------+-----------------------------------+ | Duodenum | - - | +===================================+===================================+ | Jejunum | - | +-----------------------------------+-----------------------------------+ | | - | +-----------------------------------+-----------------------------------+ **INCREASED SURFACE AREA** ==========================  **SIMPLE COLUMNAR EPITHELIUM** ============================== 5. M (Microfold) cells - are specialized epithelial cells in the mucosa of the ileum overlying the lymphoid follicles of Peyer patches. - Selectively endocytose antigens and transport them to the underlying lymphocytes and dendritic **\*\*\* Absorption of nutrients occurs in the duodenum and the jejunum** - - lining of the small intestine shows a series of permanent circular or semilunar folds (plicae circulares) - - covers the entire mucosa. - it is covered by a simple columnar epithelium. - its core has loose connective tissue that extends from the lamina propria. - Between the villi are the openings of short tubular glands called intestinal glands or crypt - **MUCOSAL LAMINA PROPRIA** -------------------------- - extensive blood and lymph microvasculature, nerve fibers, smooth muscle cells, and diffuse lymphoid tissue. - penetrates the core of each intestinal villus, bringing with it microvasculature, lymphatics, and nerves - **MUSCULARIS MUCOSAE** ---------------------- - produce rhythmic movements of the villi that increase the absorption efficiency. - Its fibers produce local movements of plicae circulares that help propel lymph from the lacteals into submucosal and mesenteric lymphatics. - **SUBMUCOSA** ------------- - larger blood and lymph vessels and the diffuse, interconnected neurons of the submucosal (Meissner) nerve plexus. - **DUODENAL (OR BRUNNER) GLANDS** -------------------------------- - small excretory ducts opening among the intestinal crypts - Mucus from these glands is distinctly alkaline - neutralizes chyme entering the duodenum from the pylorus, protecting the mucous membrane - bringing the intestinal contents to the optimum pH for pancreatic enzyme action **SECRETIONS OF THE SMALL INTESTINE** ===================================== **MOVEMENT IN THE SMALL INTESTINE** ===================================  **LARGE INTESTINES** ==================== - bowel, about 6-7 cm long - absorbs water and electrolytes and forms indigestible material into feces - portion of the digestive tract extending from the ileocecal junction to the anus - functions: - Feces formation - Mass movements - Defecation reflex **FUNCTIONS OF THE SMALL INTESTINE** ==================================== +-----------------------------------+-----------------------------------+ | **CECUM** | - | +===================================+===================================+ | **COLON** | - - - - | | | | | | FOUR PARTS: | | | | | | - Ascending colon | | | | | | - Transverse colon | | | | | | - Descending colon | | | | | | - Sigmoid colon | +-----------------------------------+-----------------------------------+ | **RECTUM** | - - - - | +-----------------------------------+-----------------------------------+ | **ANAL CANAL** | - - - - - | | | | | | | | | | | | - **[Internal Anal | | | Sphincter]** -- | | | smooth muscle layer at | | | superior end | | | | | | - **[External Anal | | | Sphincter] --** | | | skeletal muscle at inferior | | | end | +-----------------------------------+-----------------------------------+ **DIGESTION, ABSORPTION AND TRANSPORT** ============================================================== **PROTEIN** ===========  **CARBOHYDRATES** ========================================= **LIPIDS** ==========  **WATER AND MINERALS** ======================