Digestive system.pptx by ali hassan from
- 1. THE DIGESTIVE SYSTEM Jahanzaib Tufail
- 2. THE DIGESTIVE SYSTEM • The digestive system consists of a group of organs that break down the food we eat into smaller molecules that can be used by body cells. • The digestive system is composed of two groups of organs: • The gastrointestinal (GI) tract is a continuous tube that extends from the mouth to the anus through the thoracic and abdominopelvic cavities and • The accessory digestive organs includes the teeth, tongue, salivary glands, liver, gallbladder, and pancreas
- 3. GI Tract • Organs of the gastrointestinal tract include the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. • It is about 5–7 meters (16.5–23 ft) in a living person and about 7–9 meters or 23–29.5 ft) because of the loss of muscle tone after death. • The GI tract contains food and its byproducts from the time it is eaten until it is digested and absorbed or eliminated.
- 4. Functions of Digestive system • Overall, the digestive system performs six basic functions: • Ingestion.(eating) • Secretion. • Mixing and propulsion. • Digestion. Chemical and mechanical • Absorption. • Defecation.
- 6. MOUTH • The mouth, also referred to as the oral or buccal cavity is formed by the cheeks, hard and soft palates, and tongue. • The cheeks form the lateral walls of the oral cavity. • The anterior portions of the cheeks end at the lips. • The lips or labia are fleshy folds surrounding the opening of the mouth. • The inner surface of each lip is attached to its corresponding gum by a midline fold of mucous membrane called the labial frenulum. • The cheeks and lips play important roles in procuring food and keeping it in the mouth.
- 7. contd • The oral vestibule of the oral cavity is the space bounded externally by the cheeks and lips and internally by the gums and teeth. • The palate is a wall or septum that separates the oral cavity from the nasal cavity, and forms the roof of the mouth. • The hard palate—the anterior two-thirds of the palate—is formed by the maxillae and palatine bones and is covered by a mucous membrane. • The soft palate, which forms the posterior portion of the roof of the mouth, is an arch-shaped muscular partition between the oropharynx and nasopharynx.
- 8. contd • Hanging from the free border of the soft palate is a finger-like muscular structure called the uvula. • During swallowing, the soft palate and uvula are drawn superiorly, closing off the nasopharynx and preventing swallowed foods liquids from entering the nasal cavity. • At the posterior border of the soft palate, the mouth opens into the oropharynx through the fauces
- 9. Salivary Glands • A salivary gland is a gland that releases a secretion called saliva into the oral cavity. • Most saliva is secreted by the major salivary glands, three pairs of major salivary glands are the parotid, submandibular, and sublingual glands. • The parotid glands are located inferior and anterior to the ears. • The submandibular glands, found in the floor of the oral cavity beneath the base of the tongue, are medial and partly inferior to the mandible. • The sublingual glands are superior to the submandibular glands.
- 11. Saliva • The amount of saliva that is secreted daily ranges from 1000 to 1500ml by a process called salivation • Chemically, saliva is 99.5 percent water and 0.5 percent solutes and has a slightly acidic pH (6.35 to 6.85). • Salivary amylase plays a minor role in the breakdown of starch in the mouth into maltose, maltotriose, and α1-dextrins. • The feel and taste of food also are potent stimulators of salivary gland secretions.
- 12. Tongue • The tongue is an accessory digestive organ composed of skeletal muscle covered with mucous membrane. • Discussed already
- 13. Teeth • The teeth, or dentes are accessory digestive organs located in sockets of the alveolar processes of the mandible. • The alveolar processes are covered by the gingivae or gums, which extend slightly into each socket to form the gingival sulcus. • The sockets are lined by the periodontal ligament or membrane. • A typical tooth consists of three principal regions. • The crown is the visible portion above the level of the gums. • One to three roots are embedded in each socket. • The neck is the constricted junction of the crown and root near the gum line.
- 15. contd • Internally, dentin forms the majority of the tooth. • Dentin consists of a calcified connective tissue that gives the tooth its basic shape and rigidity. • The dentin of the crown is covered by enamel, which consists primarily of calcium phosphate and calcium carbonate. • Periodontics is a branch of dentistry concerned with the treatment of abnormal conditions of the tissues immediately surrounding the teeth.
- 16. Name of teeth • Humans have two sets of teeth, or dentitions: Deciduous also called primary teeth, milk teeth, or baby teeth. Permanent • Number of teeth • The incisors, which are closest to the midline 2 • The canines, which have a pointed surface called a cusp. 1 • First and second premolars (bicuspid) 2 • Molars ( the 1st 2nd and 3rd 3 • 3rd molar is called wisdom teeth after age 17 or not at all.
- 18. PHARYNX • Through chewing, or mastication the tongue manipulates food, the teeth grind it, and the food is mixed with saliva. • As a result, the food is reduced to a soft, flexible mass called a bolus that is easily swallowed. • When food is first swallowed, it passes from the mouth into the pharynx. • The pharynx or throat is a funnel shaped tube that extends from the internal nares to the esophagus posteriorly and the larynx anteriorly • (Discussed already)
- 19. ESOPHAGUS • The esophagus long collapsible muscular tube that lies posterior to the trachea. • It begins at the inferior end of the laryngopharynx, passes through the inferior aspect of the neck, enters the mediastinum and descends anterior to the vertebral column, pierces the diaphragm through an opening called the esophageal hiatus • It ends in the superior portion of the stomach. • Food is pushed through the esophagus by a progression of involuntary coordinated contractions and relaxations of the circular and longitudinal layers of the muscularis called peristalsis
- 20. Esophageal Sphincters • The passage of food from the laryngopharynx into the esophagus is regulated at the entrance to the esophagus by a sphincter (a circular band or ring of muscle that is normally contracted) called the upper esophageal sphincter • Just superior to the level of the diaphragm, the esophagus narrows slightly. • This narrowing is a physiological sphincter in the inferior part of the esophagus composed of smooth muscle, known as the lower esophageal sphincter (LES) or gastroesophageal sphincter. • It is also called the cardiac sphincter
- 22. Stomach • The medical specialty that deals with the structure, function, diagnosis, and treatment of diseases of the stomach and intestines is called gastroenterology. • The stomach is typically a J-shaped enlargement of the GI tract directly inferior to the diaphragm in the epigastric, umbilical, and left hypochondriac regions of the abdomen. • The stomach connects the esophagus to the duodenum, the first part of the small intestine.
- 23. contd •The stomach is the most distensible portion of the GI tract and can accommodate a large quantity of food, up to 6.4 liters (6 qt.). •In the stomach, the digestion of starch and triglycerides that began in the mouth continues, digestion of proteins begins, the semisolid bolus is converted to a liquid, and certain substances are absorbed.
- 24. Anatomy of the Stomach
- 25. Gastric Glands • The gastric glands contain three types of exocrine gland cells • Mucous neck cells. Secrete mucous • Chief cells (zymogenic). secrete pepsinogen and gastric lipase. • Parietal cells. produce intrinsic factor (needed for absorption of vitamin B12) and hydrochloric acid. • The secretions of the mucous, parietal, and chief cells form gastric juice, about 2000–3000 mL. • Gastrin stimulates growth of the gastric glands and secretion of large amounts of gastric juice.
- 26. PANCREAS • The pancreas a retroperitoneal gland that is about 12–15 cm (5–6 in.) long and 2.5 cm (1 in.) thick, lies posterior to the greater curvature of the stomach. • The pancreas consists of a head, a body, and a tail and is usually connected to the duodenum by two ducts. • The secretions of pancreas called pancreatic juice that goes into duodenum though pancreatic duct contains enzymes for digestion
- 27. Pancreatic juice • Each day the pancreas produces 1200–1500 mL (about 1.2–1.5 qt) of pancreatic juice, a clear, colorless liquid consisting mostly of water, some salts, sodium bicarbonate, and several enzymes. • The sodium bicarbonate gives pancreatic juice a slightly alkaline pH (7.1–8.2) that buffers acidic gastric juice in chyme, stops the action of pepsin from the stomach, and creates the proper pH for the action of digestive enzymes in the small intestine. • Pancreatic lipase • Trypsin • Pancreatic lipase • RNAs and DNAs
- 28. LIVER AND GALLBLADDER • The liver is divided into two principal lobes—a large right lobe and a smaller left lobe—by the falciform ligament • The free border of the falciform ligament is the ligamentum teres. • The parts of the gallbladder are the broad fundus, which projects downward beyond the inferior border of the liver; the central portion, called the body; and a tapered portion called the neck.
- 30. Anatomy of liver and gall bladder
- 31. Bile Duct and Bile Juice • Bile pass form liver hepatocytes passes into bile ductules and then bile ducts. • The bile ducts merge and eventually form the larger right and left hepatic ducts, which unite and exit the liver as the common hepatic duct • The common hepatic duct joins the cystic duct from the gallbladder to form the common bile duct. • From here, bile enters the duodenum of the small intestine to participate in digestion.
- 33. SMALL INTESTINE • Most digestion and absorption of nutrients occur in a long tube called the small intestine. • The small intestine begins at the pyloric sphincter of the stomach, coils through the central and inferior part of the abdominal cavity, and eventually opens into the large intestine. • It averages 2.5 cm (1 in.) in diameter; its length is about 3 m (10 ft) in a living person and about 6.5 m (21 ft) in a cadaver due to the loss of smooth muscle tone after death.
- 34. Duodenum • It starts at the pyloric sphincter of the stomach and is in the form of a C-shaped tube that extends about 25 cm (10 in.) until it merges with the next section, jejunum • It receives the openings of the bile and pancreatic ducts and is divided into four parts. • At the site where the bile duct and the main pancreatic duct pierce the medial wall of the second part is a small, rounded elevation called the major duodenal papilla
- 36. Jejunum and Ileum • The jejunum and ileum measure about 20 ft (6 m) long; the upper two fifths of this length make up the jejunum. • The jejunum begins at the duodenojejunal flexure, and the ileum ends at the ileocecal junction • The ileum is mostly in the right lower quadrant. • Function. • The completion of the digestion of carbohydrates, proteins, and lipids is the result of the collective action of pancreatic juice, bile, and intestinal juice in the small intestine.
- 37. VILLI • These are fingerlike projections of the mucosa that are 0.5–1 mm long. • The large number of villi (20–40 per square millimeter) vastly increases the surface area of the epithelium available for absorption and digestion and gives the intestinal mucosa a velvety appearance. • Each villus (singular form) is covered by epithelium and has a core of lamina propria; embedded in the connective tissue of the lamina propria are an arteriole, a venule, a blood capillary network, and a lacteal
- 38. Microvilli • Besides circular folds and villi, the small intestine also has microvilli which are projections of the apical (free) membrane of the absorptive cells. • Each microvillus is a 1-μm-long projection of the cell membrane that contains a bundle of 20–30 actin filaments. • There are an estimated 200 million microvilli per square millimeter of small intestine. • Because the microvilli greatly increase the surface area of the plasma membrane, larger amounts of digested nutrients can diffuse into absorptive cells in a given period.
- 40. LARGE INTESTINE • The large intestine is the terminal portion of the GI tract and is divided into four principal regions. As chyme moves through the large intestine, bacteria act on it and water, ions, and vitamins are absorbed. • As a result, feces are formed and then eliminated from the body. • The large intestine, which is about 1.5 m (5 ft) long and 6.5 cm (2.5 in.) in diameter in living humans and cadavers, extends from the ileum to the anus