Anatomy Of The Digestive System PDF

Anatomy of the Digestive System Human Anatomy and Physiology II HUAP220 Objectives List the components of the gastrointestinal tract. Identify the structure of the gastrointestinal tract. Describe the structure of accessory glands. Recognize the micro...

Anatomy of the Digestive System Human Anatomy and Physiology II HUAP220 Objectives List the components of the gastrointestinal tract. Identify the structure of the gastrointestinal tract. Describe the structure of accessory glands. Recognize the microscopic anatomy of the gastrointestinal tract. Human Anatomy and Physiology II HUAP220 Functions of the digestive system Ingestion: taking in food. Propulsion: moving food through the alimentary canal (swallowing & peristalsis). Mechanical breakdown: increasing surface area of ingested food preparing it for digestion (chewing & mixing with saliva). Digestion: breaking down food molecules into their chemical building blocks by the enzymes. Absorption: passage of digested end products from the lumen of the GI Tract through the mucosal layer into the blood or lymph. Defecation: eliminating indigestible substances from the body in the form of feces. Human Anatomy and Physiology II HUAP220 Components of the digestive system The digestive system is formed of: The gastrointestinal tract, or alimentary canal: ▪ A continuous tube (mostly coiled), that extends from the mouth to the anus. ▪ Its length is about 5-7 meters in a living person. It is longer in a cadaver. ▪ It is composed of mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anal canal. The accessory organs: ▪ Include teeth, tongue, salivary glands, liver, gallbladder, and pancreas. Human Anatomy and Physiology II HUAP220 Microscopic anatomy of stomach & Intestines The wall of the GI Tract from the esophagus to the anal canal is arranged in four layers: 1. Mucosa. 2. Submucosa. 3. Muscularis externa. 4. Serosa. Human Anatomy and Physiology II HUAP220 1. Mucosa The innermost mucus layer of the GI Tract (lining). Is composed of: A layer of epithelium which represents the surface of the lumen. (What type of Epithelium?) A layer of connective tissue called the lamina propria surrounding the epithelium. A thin layer of smooth muscle (muscularis mucosa) surrounding the lamina propria. Human Anatomy and Physiology II HUAP220 2. Submucosa Surrounds the mucosa. Consists of areolar connective tissue. Contains many blood vessels, lymphatic vessels, and a network of nerves called the Meissner’s plexus (submucosal plexus). Human Anatomy and Physiology II HUAP220 3. Muscularis Externa Surrounds the submucosa. Consists of smooth muscle arranged in two sheets: ▪ Inner circular layer. ▪ Outer longitudinal layer. Human Anatomy and Physiology II HUAP220 4. Serosa Is the outer visceral peritoneal layer. What type of tissue? Organs not covered with peritoneum have a layer of areolar connective tissue called adventitia. Human Anatomy and Physiology II HUAP220 The oral cavity Divided into the vestibule and the oral cavity. Lined with stratified squamous epithelium. Boundaries of the oral cavity: Anteriorly: lips (labia) and teeth: protect the anterior opening. Posteriorly: continuous with the oropharynx. Laterally: cheeks. Roof: hard palate anteriorly and soft palate posteriorly. Floor: muscles (mylohyoid). Uvula: fleshy finger like projection of the soft palate. Tonsils: *Palatine tonsil * Lingual tonsil. Functions: 1- Mastication (chewing) of food. 2- Mixing masticated food with saliva. 3- Initiation of swallowing by the tongue. 4- Allowing for taste by the papillae located in the tongue. Human Anatomy and Physiology II HUAP220 Pharynx Fibromuscular tube lined by mucous membrane. Serves as passageway for air and food. Food is propelled to the esophagus by the alternating contractions of two muscle layers: Inner longitudinal layer. Outer circular layer. Has 3 parts: Nasopharynx. Oropharynx. Laryngopharynx (Hypopharynx) Human Anatomy and Physiology II HUAP220 Esophagus A Muscular tube extending from the pharynx superiorly to the stomach inferiorly (just below the diaphragm). Conducts food to the stomach by peristalsis (slow rhythmic squeezing). Sphincter: A ring-like muscle that normally maintains constriction of a body passage or orifice. It has 2 sphincters: Upper esophageal sphincter: prevents air from entering the esophagus during breathing & prevents reflux of esophageal contents into the pharynx to prevent airway aspiration. Lower esophageal sphincter: cardiac or lower esophageal sphincter prevents the reflux of acid gastric content into the esophagus. Human Anatomy and Physiology II HUAP220 Stomach C-shaped muscular sac. On the left side of the abdominal cavity, nearly hidden by the liver and diaphragm. Food enters the stomach by passing through the cardiac sphincter and empties into the small intestine through the pyloric sphincter. Has 4 regions: Cardiac region, Fundus, Body, & Pyloric region. Has 2 surfaces: Anterior surface, & Posterior surface. Has 2 borders: Medial border (Lesser Curvature), & Lateral border (Greater Curvature). Human Anatomy and Physiology II HUAP220 Stomach Walls of the stomach: 3 layers of smooth muscle: Outer longitudinal. Middle circular. Inner oblique. Mucosa: Rugae: (internal folds of the mucosa) can be seen in the inner surface. Gastric pits: formed by folded mucosa and lead to the gastric glands. Gastric glands: secrete the gastric juice. Human Anatomy and Physiology II HUAP220 Small Intestine The body’s major digestive organ. Muscular tube that extends from the pyloric sphincter to the ileocecal valve. Site of nutrient absorption into the blood. Suspended from the posterior abdominal wall by the fan-shaped mesentery. Types of Movements: Segmentation. Peristalsis. Human Anatomy and Physiology II HUAP220 Subdivisions of small intestine Duodenum: About 25 cm. Attached to the stomach. Curves around the head of the pancreas. Has 4 parts (first, second, third, & fourth). The second part contains the hepatopancreatic ampulla & sphincter. Jejunum: About 2 meters long. Between the duodenum and the ileum. Ileum: About 3 meters long. Extends from the jejunum to the large intestine. Opens into the large intestine through the ileocecal junction (valve). Human Anatomy and Physiology II HUAP220 Mucosa of the small intestine Circular folds (plicae circulares): deep folds of the mucosa and submucosa. Villi: Finger-like structures formed by the mucosa: The function of villi is to increase the surface area of the small intestine Microvilli: tiny projections of the plasma membrane. The submucosa has Peyer’s patches (collections of lymphatic tissue). Human Anatomy and Physiology II HUAP220 Large intestine Larger in diameter, but shorter in length, than the small intestine. Extends from the ileocecal valve to the anus. Subdivisions: Cecum: the appendix is attached to its distal end. Appendix: Contain more lymphoid tissue. Colon: Ascending. Transverse. Descending. S-shaped sigmoidal. Rectum. Anal canal. Human Anatomy and Physiology II HUAP220 Large intestine No villi present in mucosa of large intestine Goblet cells produce mucus which lubricates the passage of feces. Muscularis externa layer is reduced to three bands of muscle called teniae coli. These bands cause the wall to pucker into haustra (pocketlike sacs). Epiploic appendages: are small pouches of peritoneum filled with fat, mostly found on the transverse and sigmoid colon. They are absent in the rectum. Human Anatomy and Physiology II HUAP220 Salivary Glands Parotid gland: the largest of the salivary glands, located anterior to the ear, secretes saliva into the vestibule by the parotid duct. Submandibular gland: on the floor of the cavity and secretes saliva by the submandibular duct to the sides of the tongue. Sublingual gland: below the tongue and secretes saliva into the floor through small sublingual ducts. Structure of salivary glands: Number of lobules made up of small acini lined with secretory cells. Surrounded by fibrous capsule. Human Anatomy and Physiology II HUAP220 Teeth Their role is to masticate (chew) food. Incisors & canines: cutting teeth. Premolars & molars: grinding & chewing. Human Anatomy and Physiology II HUAP220 Tongue Skeletal muscles that are attached to the hyoid bone and styloid process, and by the frenulum to the floor of the mouth. Assists in mastication, deglutition (swallowing), speech and oral cleansing. The papillae: Are little peglike projections in the dorsal surface of tongue that contain the taste buds. Taste buds are specific receptors for the sense of taste and are widely scattered in the oral cavity. Human Anatomy and Physiology II HUAP220 Pancreas Head: in the cavity of duodenum. Uncinate process. Neck: between the head and the body. Body: behind the stomach. Tail: extends to the spleen and lies behind the left kidney. Exocrine pancreas: produces pancreatic juice, consist of a wide spectrum of digestive enzymes that digest carbohydrates, proteins and fats. Enzymes are secreted into the duodenum (second part). The pancreatic duct joins the common bile duct to form the hepatopancreatic ampulla (Ampulla of Vater) that drains into the duodenum. The duodenal opening of the ampulla is controlled by the sphincter of Oddi Alkaline fluid produced with enzymes neutralizes acidic chyme. Endocrine pancreas: Secrete hormones directly into bloodstream to control blood glucose level. Human Anatomy and Physiology II HUAP220 Liver Largest gland in the body. Incompletely covered by peritoneum. Connected to the gall bladder via the common hepatic duct. Location: Rt. Hypochondrium. Epigastric region. Lt. Hypochondrium. 4 Lobes: Left. Quadrate. Caudate. Right. Each lobe has lobules – Contains hepatocytes – Surround sinusoids – Feed into central vein. Human Anatomy and Physiology II HUAP220 Gallbladder & biliary tree Sac found in hollow fossa of the liver. Pear shaped; has fundus, body, neck. Stores bile from the liver, by way of the cystic duct it releases stored bile, in addition to concentration of bile. Bile is secreted into the duodenum in the presence of fatty food. Gallstones can cause blockages (obstructive jaundice) Inflammation of the gallbladder is called cholecystitis and of the biliary tree is cholangitis Human Anatomy and Physiology II HUAP220