Unit 10 Review Gastrointestinal Tract Overview

Unit 10 Review: Gastrointestinal Tract Overview ● Identify the organs of the gastrointestinal (GI) tract and the accessory organs of digestion. ○ Organs of the digestive tract: ■ Oral cavity (mouth) ■ Pharynx ■ Esophagus ■ Stomach ■ Small intestine ■ Large intestine ○ Accessory organs: ■ Teeth ■ Tongue ■ Salivary glands ■ Liver ■ Gallbladder ■ Pancreas ● Describe the general histology of the four layers of the gastrointestinal tract. ○ Mucosa ■ Innermost mucous membrane ■ Lamina propria: layer of areolar tissue with blood vessels, nerves, lymphatic vessels ○ Submucosa ■ Layer of dense irregular connective tissue that binds the mucosa to the muscular layer ■ Contains submucosal nerve plexus ○ Muscularis externa (muscular layer) ■ Smooth muscles of mechanical digestion ■ Contains myenteric nerve plexus ○ Serosa ■ The serous membrane lining the digestive tract, wherever the serous membrane does not cover there is a layer of adventitia (sheath of connective tissue) ● Describe the peritoneum and its folds. ○ The peritoneal cavity is lined with two layers of serous membranes: the visceral and parietal peritoneum ○ Visceral peritoneum: lines the internal organs ○ Parietal peritoneum: lines the peritoneal cavity and the body wall Oral Cavity ● Describe the structure of the tongue. ○ The frenulum attaches the tongue to the underlying palate ○ ○ ● Lingual papillae projections are on the tongue for surface area and taste buds Function of the tongue: mechanical digestion, manipulation of food, sensory analysis, secretions of mucins and lingual lipase Identify the location and histology of the salivary glands. ○ Parotid glands ■ Gland just under ear, secretes salivary amylase by the back molars ○ Sublingual glands ■ Gland on floor of mouth, secretes mucus for a buffer and lubricant ○ Submandibular glands ■ Found in submandibular groove, secretes most of saliva (mixtures of mucins, buffers, and salivary amylase) Gastrointestinal Structures ● Describe the oral cavity, including the structure of the tongue, location and histology of the salivary glands, and dentition (deciduous vs permanent teeth) ○ The oral cavity is lined with oral mucosa with keratinized cells for extra protection. Salivary amylase is secreted which starts the breakdown of carbohydrates. The mouth also uses the tongue to aid in mechanical digestion and form a bolus as it moves down the esophagus ○ The salivary glands are listed above ○ Dentition refers to the teeth and they aid in mechanical digestion by breaking down food into smaller parts. Each tooth is made of dentin, with an enamel cap, and cement layer over the roots, as well as an inner pulp cavity where the blood vessels and nerves ■ There are 20 deciduous (baby) teeth, and 32 permanent teeth ● Describe the anatomy and histology of the esophagus; describe the structure and functions of the pharynx and esophagus. ○ The esophagus is found just below the pharynx and larynx and it is the passageway for food entering the stomach. ○ The swallowing reflex is initiated when the palatal arch and uvula become stimulated and the sensory info is sent to the medulla ○ Primary peristaltic waves move the bolus towards the stomach through the esophageal sphincter. Secondary waves may be needed if the bolus is too dry or poorly lubricated ○ 3 phases of swallowing ■ Buccal phase ■ Pharyngeal phase ■ Esophageal phase ● Describe the anatomy (including major regions) and histology of the stomach. ○ Cardia: fist portion of stomach, lots of mucous to protect esophagus ○ Fundus: side region, where the stomach is in contact with the diaphragm ○ Body: the main portion of the stomach where gastric acid and swirling motions act as a mixing tank for the bulk of chemical digestion ○ Pylorus: the end part of the stomach by the entrance to the duodenum ○ ● ● ● ● ● The stomach is an expandable tube-like organ with rugae that expand when the stomach is full. The stomach temporarily stores food and uses both mechanical and chemical digestion. The stomach forms chyme which is the substance that enters the small intestine of absorption of digested nutrients. Describe the anatomy of the small intestine and how it is modified for digestion and absorption ○ Duodenum: the first portion of the small intestine that receives chyme through the pyloric sphincter. The main function of this section is to receive and neutralize the acidic chyme with bile and buffers. ○ Jejunum: the middle portion of the small intestine where the bulk of chemical digestion and absorption occur. There are circular folds with villi and microvilli to increase the surface area ○ Ileum: the last section of the small intestine where the intestine has already absorbed most of the nutrients from the chyme and prepares to enter the large intestine through the ileocecal valve. It contains peyer's patches which are clumps of lymphoid nodules Describe the anatomy and histology of the large intestine. ○ The large intestine lacks villi, but contains goblet cells for mucous secretion as the chyme substance slowly turns into feces ○ Cecum: pouch-like portion of the small-intestine that stores materials from the ileum and has appendix attached at the bottom ○ Colon: smooth muscles support the colon and use peristaltic waves to move the digested lump through the ascending colon, transverse colon, descending colon and then the sigmoid colon ○ Rectum: the very end of the large intestine that temporarily stores feces that are ready for excretion. There are two anal sphincters, the internal sphincter is involuntary, and the external sphincter is voluntary Describe the four basic digestive processes. ○ List the cell types of the gastric mucosa and their secretions and explain how gastric secretion is regulated during the cephalic, gastric and intestinal phase. ○ Gastric pits: shallow depression that actively divide to replace cells killed by gastric acid and also secretes products of the gastric glands ○ Chief cells: secretes pepsinogen that is turned into active pepsin in contact with stomach acid to digest proteins (works best in acidic environment) ○ Parietal cells: secrete intrinsic factor (for vitamin B12 absorption) and indirectly secretes HCl as H+ and Cl○ G-cells: secrete gastrin that stimulates parietal and chief cells and contractions of gastric wall as well as gastric secretions. Histamine is released to stimulate HCl secretion ○ D-cells: secrete somatostatin that inhibits gastrin and HCl secretion ○ p/d1 cells: secretes ghrelin (hungry) and leptin (full) ○ goblet cells: secretes watery mucus and bicarbonate Describe the roles of digestive hormones on gastrointestinal functions. ● ● ● ● ○ Listed above Differentiate between mechanical digestion, chemical digestion, and absorption. ○ Mechanical digestion: crushing, shearing, squashing, moving food ○ Chemical digestion: via enzymes and digestive juices ○ Absorption: the movement of ions, organic material, water, or vitamins across the digestive epithelium Describe the location and functions of the brush border enzymes of the small intestine. ○ Brush border enzymes are found on the tips of the microvilli in the circular fold of the small intestine and the digest food that are exposed to them with the enzyme enteropeptidase Describe the anatomy and function of the liver, pancreas, and gallbladder ○ Liver ■ The largest visceral organ, covered by visceral peritoneum. Two lobes separated by falciform ligament from fetal development ■ Within each lobule of the liver there are sinusoid capillaries, kupfer cells, and bile canaliculi. The sinusoids empty into a central vein ■ Liver functions ● Metabolic regulation: extracts toxins and nutrients, carbohydrate, lipid and amino acid metabolism ● Hematological regulation: plasma protein synthesis, removal of circulating hormones, antibodies and toxins ● Bile production: made from water, ions, bilirubin, cholesterol and bile salts ○ Pancreas ■ Endocrine pancreas: insulin and glucagon ■ Exocrine pancreas: acinar cells make pancreatic secretions/juices ■ Pancreatic juices are made of an alkaline mix of digestive enzymes, water, and ions. The enzymes break down ingested material while the water and ions dilute and neutralize chyme ■ Pancreatic duct delivers pancreatic secretions to the duodenum at the duodenal ampulla ○ Gallbladder ■ Stores and concentrates bile by removing water before secretion ■ Bile released into the duodenum at the hepatopancreatic sphincter when stimulated by CCK ■ 3 regions of gallbladder: fundus, body, neck ■ Gallstones are overly concentrated bile that leads to solid bits that increase in size until they are too big to be secreted Differentiate between the exocrine and endocrine functions of the pancreas ○ Stated above