The Digestive System Chapter 23 PDF

The Digestive System Chapter 23 23.1 – Overview of the Digestive System Break down food to release and absorb nutrients Alimentary canal or gastrointestinal (GI) tract is about 25 ft. long from mouth to anus, has 4 layers Pharynx, esophagus, stomach, small and large intestines Accessory digestive or...

The Digestive System Chapter 23 23.1 – Overview of the Digestive System Break down food to release and absorb nutrients Alimentary canal or gastrointestinal (GI) tract is about 25 ft. long from mouth to anus, has 4 layers Pharynx, esophagus, stomach, small and large intestines Accessory digestive organs – teeth, tongue, salivary glands, liver, gallbladder, pancreas 23.1 – GI Tract Layers Mucosa – mucous membrane epithelium in contact with food Epithelium – non-keratinized, stratified squamous in mouth, esophagus and anal canal. Columnar in stomach and intestines. Interspersed with goblet (secret mucous) and enteroendocrine cells. Lamina propria – loose connective tissue with blood and lymphatic vessels to transport absorbed nutrients, contain MALT Muscularis mucosa – smooth muscle always in a state of tension 23.1 - Layers Submucosa – dense connective tissue between mucosa and muscularis, has blood and lymphatic vessels, and has a collection of nerves called the submucosal plexus Muscularis – inner circular layer and outer longitudinal layer in the small intestine, mechanical digestion, exposes food to more chemicals, and peristalsis (moving food along the canal). Skeletal muscle at both ends (swallowing and defecation). Stomach adds a third layer of oblique muscle Serosa – most superficial, only in the region inside the abdominal cavity, loose connective tissue holding the canal in place 23.1 – Nerve Supply Gives food taste, lets you feel food, avoid biting yourself as you chew Enteric nervous system runs from esophagus to anus and is separated into 2 plexuses. Myenteric for motility and submucosal for regulating digestive secretions Autonomic nervous system extrinsically innervates the alimentary canal. Sympathetic nerves restrict enteric neurons. Parasympathetic nerves increase GI secretion and motility. 23.1 – Blood Supply Transport protein and carbohydrate to the liver, hepatic portal system Deliver nutrients and oxygen to organs of alimentary canal While resting and digesting 25% of blood pumped enters arteries serving the intestines 23.1 – The Peritoneum Holds digestive organs in place, 2 different regions Parietal peritoneum – lines the abdominal wall Visceral peritoneum – envelopes the abdominal organs Peritoneal cavity – space between parietal and visceral 23.2 – Digestive System Processes and Regulation Mouth – ingest, chew, and mix food. Begin chemical breakdown of carbs and lipids (activates in stomach). Move food to pharynx. Moistens and tastes food, cleans and lubricates teeth, and antimicrobial activity. Pharynx – Propel food to the esophagus. Lubricates food and passage Esophagus – Propel food to stomach. Lubricates food and passage Stomach – mix food with gastric juices to form chyme. Begin chemical breakdown of proteins. Release food to duodenum. Absorb some fat soluble substances (alcohol, aspirin). Antimicrobial functions. Stimulates protein digesting enzymes and secretes intrinsic factor for vitamin B12 absorption in small intestine. 23.2 Small Intestine – Mix chyme and digestive juices. Propels food slowly. Absorb macro and micro nutrients. Segmentation. Optimal medium for enzymatic activity. Large Intestines – further breakdown of food residue. Absorb residual water, electrolyte, and vitamins produced by enteric bacteria. Propel and eliminate feces. Food residue is concentrated and temporarily stored. Mucus eases passage of feces through colon. 23.2 – Accessory Organs Liver – Produce bile salts to emulsify lipids for digestion and absorption Gallbladder – stores, concentrates, and releases bile Pancreas – produce digestive enzymes and bicarbonate. Bicarbonate helps to neutralize acidic chyme and provide optimal environment for enzymatic activity 23.2 Ingestion – entry of food into alimentary canal through the mouth Swallowing – last voluntary act until defecation, propulsion Peristalsis – sequential smooth muscle contraction and relaxation to propel food 23.2 Mechanical digestion – physical process that does not change chemical nature of food (mastication, churning, segmentation). Exposes a larger surface area to digestive juices. Chemical digestion – breaking down complex food molecules into their building blocks (water, acid, enzymes, and salts) Absorption – primarily in the small intestine, taking nutrients into the bloodstream or lipids into lymphatic system Defecation – undigested materials are removed from the body 23.2 – Regulatory Mechanisms Neural control – sensors for expansion of stomach, if food particles are broken down enough, amount of liquid present, and type of nutrient. Can activate glands and muscle. 2 types of reflexes Short reflex – local stimulus and result. Expanding stomach causes increase in digestive juices. Long reflex – ANS and CNS reacting to stimuli outside the digestive tract. Smell, sight, and taste of food cause digestive juice secretion Hormonal control – gastrin to stimulate release of gastric acid. Secretin stimulates bicarbonate release from pancreas. CCK stimulates pancreatic secretion of enzymes and bile from liver and gallbladder. Gastric inhibitory peptide inhibits gastric secretion and slows gastric emptying and motility. 23.3 – Mouth, Pharynx, and Esophagus Mouth – oral cavity lined by cheeks, tongue, lips, and palate. Can handle digestion and respiration at the same time. Hard palate is anterior and soft palate is posterior on roof. Uvula drops down from the soft palate to stop food from entering the nasal cavity Tongue – ingestion, mechanical and chemical digestion (lingual lipase), swallowing, and vocalization. Attached to mandible, styloid processes, and hyoid bone. It has 2 symmetrical halves. Intrinsic and extrinsic muscles for dynamic movement. Taste buds. Lingual frenulum – connects tongue to floor of mouth. Too short is tongue tied. Severed is like Gene Simmons. 23.3 – Salivary Glands Secrete 1–1.5 L per day of saliva, even while we sleep, produce more while eating Saliva – 95.5% water, 4.5% ions, glycoproteins, enzymes, growth factors, and waste. pH of 6.35-6.85. Contains IgA. Regulated by ANS Salivary amylase – initiates the breakdown of carbohydrate, stops as it reaches the stomach Sympathetic stimulation and dehydration cause a decrease in saliva production Saliva is also produced after eating to cleanse the mouth 23.3 - Teeth 2 sets of teeth – 20 deciduous (baby) teeth and 32 permanent teeth 8 incisors – sharp front teeth 4 cuspids (canines) – pointy to tear up food, beware of vampires 8 premolars – flatter shape to mash food 12 molars – largest to crush food ready for swallowing, 3rd molars top and bottom are called wisdom teeth and they erupt toward early adulthood, they may need to be removed 23.3 – Tooth Anatomy Gingivae (gums) and the periodontal ligament hold teeth in socket Crown – part above gum line, covered by enamel over dentin Root – embedded in maxilla and mandible, covered by cementum over dentin Pulp cavity – nerves and blood vessels, surrounded by dentin Cavity – colony of bacteria feeding on sugar degrade the enamel 23.3 – The Pharynx (Throat) Handles food and air by involuntary muscle contraction Nasopharynx – most superior, only handles air Oropharynx – middle portion of pharynx Laryngopharynx – inferior, connects to esophagus and larynx Epiglottis is pulled over the larynx due to muscle contractions while swallowing Food into the trachea causes coughing to force food back up into the pharynx 23.3 – The Esophagus Muscular tube connecting the pharynx to the stomach, 10 in. long, posterior to trachea Upper esophageal sphincter – controls food into esophagus Lower esophageal sphincter – controls food entering stomach and acid leaving the stomach (GERD) Deglutition (Swallowing) – movement of food to stomach, 4-8 seconds for solid food and 1 second for very soft food and liquid, 3 phases Voluntary – skeletal muscle you control Pharyngeal phase – moves food into esophagus Esophageal phase – initiation of peristalsis to push food into stomach 23.4 – The Stomach Links the esophagus to the small intestine, lots of digestion, contractions and constantly changing position and size Empty it is about half the size of your fist, can stretch to hold 4 liters Body weight does not correlate to stomach size Holds and stores food, released as chyme into small intestine Has an additional oblique muscle to churn food 23.4 - Structure Cardia – where esophagus enters Fundus – domed area, stores undigested food and gases Body – main part of stomach Pylorus – connects to duodenum Pyloric sphincter – controls emptying Without food it deflates inward and the fold is called a ruga