Digestive System 4 fuctions Ingestion intake of food Digestion Chemical breakdown Mechanical breakdown Absorption Uptake of nutrients Defecation elimination Digestive tract rectum anus Alimentary canal digests and absorbs mouth esophagus stomach small intestine large intestine Accessory organs teeth tongue salivary glands gallbladder liver pancreas Four layers of digestive tract outer to inner Esophagus stomach and intestines motility secretion and blood flow Serosa adventitia Muscularis Externa Myenteric nerve plexus longitudinal outer circular inner Myenteric nerve plexus GI tract motility Submucosa blood lymph vessels submucosal plexus Submucosal plexus secretory activity Mucosa stratified squamous epithelium lamina propria muscularis mucosae Parietal Peritoneum serous membrane that lines the wall of the abdominal cavity Mesenteries connective tissue sheets that hold the abdominal viscera Other functions would be routes for nerves lymphatic blood vessels and store fat Dorsal mesentery two layered membrane to the digestive tract layers separate around an organ and meet on other side forming the serosa Sometimes come together again and form another sheet of tissue ventral Ventral mesentery hang freely in the abdominal cavity or attach to anterior abdominal wall or other organs covers small intestine Greater omentum from greater curvature of stomach loosely Lesser omentum from the liver to lesser curvature of stomach Digestive tract regulation Neural short and long autonomic reflexes Short myenteric reflexes response to stretching or chemical stimulation of the digestive tract stimulates myenteric nerve plexus to stimulate contractions in nearby regions of muscularis externa Ex peristaltic contractions of swallowing Long vasovagal reflexes Autonomic nervous system sensory signals from digestive tract to the brain stem and motor commands back to digestive tract Parasympathetic fibers of vagus nerve stimulate motility and secretion Hormonal digestive tract produces hormones such as Gastrin and Secretin that stimulate digestive function Hormones secrete into blood and stimulate relatively distant parts of digestive tract Paracrine paracrine secretions such as Histamine and Prostaglandins stimulate digestive function Paracrine secretions diffuse through tissue fluids and stimulate nearby target cells Oral Cavity Saliva Electrolytes Structures cheeks lips tongue palate teeth Functions Ingestion Mastication Chemical Digestion Swallowing contents Salivary amylase Lingual lipase Mucus Lysozyme Immunglobin A Intrinsic glands small glands constant secretion saliva made of lysozyme and lingual lipase Lingual in tongue Labial inside of lips Buccal inside of cheeks Extrinsic glands 3 pairs of larger glands Parotid over massester submandibular along mandible sublingual floor of mouth Salvation extrinsic secretes 1 0 1 5L per day food in the mouth stimulates tactile pressure and taste receptors sends signal to Salivary nuclei in the medulla and pons Even aroma sight or thought of food stimulates salivation Parasympathetic stimulates saliva abundant and thin rich in enzymes Sympathetic inhibits saliva less abundant and thicker w more mucus Pharynx deep skeletal muscle superficial smooth muscle pharyngeal constrictors upper esophageal sphincter physiological sphincter remains contracted to exclude air Esophagus long muscular tube pharynx to stomach has all GI tract layers has esophageal glands in submucosa that secrete mucus for lubrication Cardiac orfice cardiac sphincter Deglutition swallowing center pair of nuclei in medulla oblongata Buccal phase voluntary control tongue collects food by pushing against hard palate and push to oropharynx and waits there until bolus becomes certain size Pharyneal esphageal phase involuntary Root of tongue blocks food from coming back up soft palate rises and blocks the nasopharynx Peristalsis food being pushed down by constrictions Stomach mechanical and chemical digestion liquefy food into chyme regions cardiac fundic body pyloric circulation gastric artery hepatic portal vein system Micro Anatomy of Stomach Similar to GI tract exception muscularis externa 1 Serosa Muscularis externa longitudinal circular oblique 1 Submucosa blood vessels Mucosa gastric pits tubular glands based on locations Mucosal Barrier protects mucosa from own secretions Three factors contribute Mucous coat bicarbonate rich mucus Epithelial cell replacement every 3 6 days Tight junctions prevents gastric juice leaking Gastric Pits Mucous cells secrete mucous in cardiac and pyloric regions Regenerative cells divide rapidly continual supply of cells Parietal cells secretion of Hydrochloric acid HCL mainly intrinsic factor and found in gastric region Chief cells most numerous gastric lipase and pepsinogen only in gastric Enteroendocrine secrete hormones and paracrine to regulate digestion HCL activates enzymes liquefies food converts iron and nonspecific resistance bicarbonate reaction carbonic anhydrase alkaline tide high blood pH during digestion Pepsinogen Zymogens inactive digestive enzymes Activated by Hcl forms pepsin for protein digestion Other Gastric Secretions Digestive enzymes gastric lipase chymosin Intrinsic factor absorption of Vitamin B12 Chemical messengers hormones paracrine secretions gut brain peptides VIP GIP NPY secretin CCK Substance P Gastric Motility Swallowing center of medulla signals stomach to react Receptive relaxation response smooth muscle relaxes to accommodate food Peristaltic contractions pacemaker cells in longitudinal layer Plyoric sphincter controls chyme into small intestine Vomiting Forceful ejection of stomach and intestinal contents Multiple muscular actions integrated by Emetic center in medulla Cause overstretching chemical irritants trauma or pain psychological stimuli Physiology retching thoracic expansion and abdominal contraction create pressure difference resulting in reverse peristalsis throwing up Projectile vomiting no prior nausea or retching Regulation of Gastric Function Nervous and Endocrine systems collaborate 3 phases Cephalic controlled by brain responds to sight smell taste thought hypothalamus medulla oblongata Vagus nerve fibers parasympathetic stimulate enteric system of stomach stimulates gastric secretion Gastric controlled by stomach bolus enters stomacah stomach expands Short and long reflexes stimulated and Hcl pepsinogen acetylcholine histamine and gastrin is released Intestinal controlled by small intestine SI chyme goes