The Digestive System Digestion Breakdown of ingested food Absorption of nutrients into the blood Metabolism Production of cellular energy (ATP)

Organs of the Digestive System Two main groups Alimentary canal a/k/a gastrointestinal (GI) tract continuous coiled hollow muscular tube open at both ends Accessory digestive organs

Organs of the Alimentary Canal Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus

Mouth Anatomy Lips (labia) – protect the anterior opening Cheeks – form the lateral walls Hard palate – forms the anterior (front) roof Soft palate – forms the posterior (back) roof Uvula – fleshy projection of the soft palate Vestibule – space between lips externally and teeth and gums internally Figure 14.2a

Mouth Anatomy Oral cavity – area contained by the teeth Tongue – attached at hyoid and styloid processes of the skull, and by the lingual frenulum Tonsils Palatine tonsils Back of the throat Lingual tonsil Base of the tongue Figure 14.2a

Salivary Glands Saliva-producing glands Parotid glands Submandibular glands Sublingual glands Saliva (spit) Contains salivary amylase to begin starch digestion

Processes of the Mouth Mastication (chewing) of food Tongue mixes chewed up food with saliva Saliva contains digestive enzymes, so digestion starts in the mouth. Tongue helps us swallow the food Tongue has papillae (bumps) that contain taste buds allow for our sense of taste

Functions of the Pharynx Serves as a passageway for air and food Food is propelled to the esophagus by two muscle layers Longitudinal inner layer Circular outer layer Food movement by peristalsis Wavelike contractions of the muscle layers

Esophagus Runs from pharynx to stomach through the diaphragm Propels food by peristalsis Passageway for food only (respiratory system branches off after the pharynx)

Layers of Alimentary Canal Organs 1. Mucosa Innermost layer Mucous membrane made of columnar epithelium Goblet cells secrete mucous 2. Submucosa a thin layer of loose connective tissue just beneath the columnar epithelium 3. Muscularis – smooth muscle layer inner circular layer outer longitudinal layer 4. Serosa outermost layer smooth membrane consisting of a thin layer of cells that secrete serous fluid which reduces friction from muscle movement

Layers of Stomach

Stomach Located on the left side of the abdominal cavity Sort of hidden by liver and diaphragm Food enters at the esophageal sphincter sometimes called cardioesophageal sphincter

Stomach Anatomy Regions of the stomach Cardia region – near the heart Fundus Body Pylorus – funnel-shaped terminal end Food empties into the small intestine at the pyloric sphincter Rugae – internal folds of the mucosa

Stomach Anatomy External regions Lesser curvature Greater curvature Layers of peritoneum attached to the stomach Lesser omentum – attaches the liver to the lesser curvature Greater omentum – attaches the greater curvature to the posterior body wall

Functions of the Stomach Acts as a storage tank for food Site of food breakdown Chemical breakdown of protein begins Delivers chyme (processed food that looks like thick cream) to the small intestine

Structure of the Stomach Mucosa Gastric pits formed by folded mucosa turn into the gastric glands Gastric glands are made up of specialized cells that perform specific functions

Specialized Cells of the Stomach Simple columnar epithelium Mucous neck cells – produce a sticky alkaline mucus Gastric glands – secrete gastric juice Chief cells – produce pepsinogens (protein-digesting enzymes) Parietal cells – produce hydrochloric acid Endocrine cells – produce gastrin (hormone)

Ulcers An ulcer is a sore, which means it's an open, painful wound. Peptic ulcers are ulcers that form in the stomach or the upper part of the small intestine.

What causes ulcers? Most peptic ulcers are caused by a particular bacteria (Helicobacter pylori) that lives in the stomach and upper intestine Ulcers are also caused by the overuse of non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin or ibuprofen (Motrin & Advil) Other factors that may put you at risk for developing an ulcer: Smoking Drinking alcohol Uncontrolled Stress

Symptoms of ulcers loss of appetite sudden, sharp stomach pains nausea frequent burping or hiccuping weight loss vomiting (if blood is in the vomit or the vomit looks like coffee grounds, which only happens with severe ulcers, call a doctor right away) bloody or blackish bowel movements (this could indicate a serious problem, so call a doctor right away if you see this)

Small Intestine MAJOR SITE OF NUTRIENT ABSORPTION Extends from the pyloric sphincter to the ileocecal valve 8-18 feet long 3 sections: duodenum jejunum ileum

Special Structures of the Small Intestine villi Fingerlike structures formed by the mucosa Give the small intestine more surface area microvilli Small projections of the plasma membrane plicae circulares Deep circular folds of the mucosa and submucosa Do not disappear when filled with food Peyer’s patches collections of lymphatic tissue in ileum Immune surveillance

Large Intestine Larger in diameter, but shorter than the small intestine Frames the internal abdomen Cecum – saclike first part of the large intestine Appendix Hangs from the cecum Colon ascending transverse descending sigmoid Rectum Anus – external body opening

Functions of the Large Intestine Absorption of water Does not participate in digestion of food Goblet cells produce mucus to act as a lubricant Eliminates indigestible food from the body as feces

Accessory Organs of the Digestive System

Pancreas Produces digestive enzymes pancreatic amylase → starch digestion trypsin → protein digestion lipases → fat digestion nucleases → nucleic acid digestion Enzymes are secreted into the duodenum Produces hormones insulin glucagon

Insulin Insulin is secreted by the pancreas in response to high blood sugar (glucose). After you eat, blood glucose levels rise and in response to this, insulin is secreted into the blood In response to insulin, cells (muscle, red blood cells, and fat cells) take glucose in from the blood to use to generate energy (ATP) This lowers the blood glucose levels back to the normal range As blood glucose falls, insulin secretion by the pancreas decreases.

Diabetes A person with diabetes does not produce enough insulin or produces no insulin at all. Without insulin, body cells can’t take the glucose out of the blood Blood glucose levels become high which leads to other health problems. So, even though the blood has plenty of glucose, the cells are not getting it for their essential energy and growth requirements. Diabetes Type 1 - You produce no insulin at all. Diabetes Type 2 - You don't produce enough insulin, or your insulin is not working properly. Gestational Diabetes - You develop diabetes just during your pregnancy.

Glucagon Glucagon is secreted when blood glucose is low like between meals and during exercise.  Glucagon's function is to cause the liver to release stored glucose from its cells into the blood.  When blood glucose is high, no glucagon is secreted

Liver Largest gland in the body Manufactures bile Bile breaks fat into smaller globs for lipases (fat-digesting enzymes)to work on The liver consists of four lobes suspended from the diaphragm and abdominal wall by the falciform ligament It’s connected to the gall bladder via the cystic duct

Gall Bladder Small sac under the liver Connected to the liver by the cystic duct Stores bile When you eat fatty foods, bile is released from the gallbladder into the duodenum through the common bile duct

What are gallstones? Made from cholesterol and other things found in the bile They can be smaller than a grain of sand or as large as a golf ball. People who are overweight or who are trying to lose weight quickly are more likely to get gallstones. You can live without your gallbladder The liver just dumps bile directly into the duodenum through the common bile duct Body can no longer store bile between meals, but this has little effect on digestion