May 14, 2018 Journal: What organs make up the digestive system?

Digestive Tract

Parts of the Digestive Tract Oral Cavity  Pharynx  Esophagus  Stomach  Small Intestines  Large Intestines  Anus

Oral Cavity Tongue – muscular organ that moves food in the mouth Teeth – used for mastication Children have 20 deciduous teeth Adults have 32 primary teeth Salivary Glands – produce saliva that aids in chemical breakdown of food by producing amylase which breaks down starch Largest is the Parotid gland located in the cheeks right in front of the ear

Pharynx Transmits food from the oral cavity into the esophagus Epiglottis moves when swallowing to block the food from entering the larynx

Esophagus Muscular tube lined with moist stratified squamous epithelium that connects the pharynx to the stomach The openings of the esophagus contain sphincters that regulate how much food can move through the tube at a time Top – Upper Esophageal Sphincter Bottom – Lower Esophageal Sphincter

Swallowing Phases: Voluntary Phase – bolus in the mouth is pushed into the oropharynx by the tongue and hard palate Pharyngeal Phase – reflex that pushes food through the pharynx and into the esophagus past the epiglottis Esophageal Phase – food is moved from the pharynx to the stomach using peristalsis

Stomach Broken up into sections: Fundus – Superior part near the heart Body – Largest part that curves Pyloric Part – Inferior part that connects to the small intestines Connection between stomach and small intestines is the pyloric sphincter

Tissues of the Stomach Stomach itself is made up of three layers of smooth muscle that churn to help break down food Inner layers of the stomach are arranged in large folds called rugae which can stretch out as the stomach becomes full

Epithelial Cells Lining the Stomach Mucous Cells – produce mucus to coat and protect the stomach Parietal Cells Hydrochloric acid that converts pepsinogen to pepsin, kills pathogens, breaks down connective tissues in meat Intrinsic factor which binds to B12 to make it digestible Chief cells – produce pepsinogen used in protein digestion Endocrine cells – produce gastrin to stimulate gastric glands to secrete gastric juices (HCl, pepsinogen, and mucus)

Phases of Gastric Secretion Cephalic Phase – Smell or sight of food causes stomach to prepare for food by increasing gastric juice production Gastric Phase – As food enters the stomach more gastric juice is produced and both chemical and mechanical digestion occur as chyme is formed Intestinal Phase – Chyme moves into the first part of the small intestines, the duodenum, and gastric juice production decreases

Small Intestines Primary site of digestion and where nutrients are absorbed into the blood stream Sections: Duodenum – first section about 25 cm long connected to stomach Jejunum – middle section about 8 ft long Ileum – last section about 7 feet long that connects to the large intestines through the ileocecal valve

Digestion in the Duodenum Liver and gallbladder secrete bile into the duodenum which emulsifies fats Pancreas secretes pancreatic juice into the duodenum which neutralizes the acidic chyme and breaks down most foods Exocrine cells produce additional digestive enzymes and mucus that help break down food Lactase, maltase, and sucrose break down disaccharides in starch Peptidase breaks down peptides in proteins

Pancreatic Juice Contains enzymes that are secreted into the small intestines to help break down food Trypsin break down protein into amino acids Lipases break down emulsified fats to glycerol and fatty acids Amylase breaks down starch

Structure of the Small Intestines Modifications to allow for increased surface area Has circular folds Each circular fold has villi, finger- like projections that extend out into the intestines Each villi has an outer layer of columnar epithelial cells with microscopic extensions called microvilli

Absorption Each villi contains a network of blood and lymph capillaries called a lacteal which aids in absorption Amino acids from proteins Sugars from carbohydrates Glycerol and fatty acids from fats called chyle that get absorbed right into the lymphatic system

Large Intestine Connects from the small intestine to the anus Functions: Reabsorbing water Absorbing vitamins Compacting waste for elimination Three Sections: Cecum + Appendix Colon Rectum

Colon Where the majority of water and electrolyte reabsorption occur Contains bacteria that help us break down indigestible materials and produce vitamins B and K Further divided into four sections: Ascending: up right side towards the liver Transverse: across the abdomen Descending: down the left side Sigmoid: extends to the rectum

Rectum and Anus Sigmoid colon connects to the rectum, which is where solid waste will condense until it is ready to be excreted out of the body through the anal sphincter