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Introduction The digestive system is used for breaking down food into nutrients, which then pass into the circulatory system and are taken to all the cells in the body. Types of Digestive Organs Alimentary digestive organs (major) Mouth Pharynx Esophagus Stomach Small and large intestine Accessory digestive organs Teeth and tongue Liver Pancreas Salivary glands Gall bladder The Processes of Digestion Ingestion = taking in food Secretion = releasing digestive fluids and enzymes Mechanical digestion = grinding, tearing, and churning food to break it into smaller chunks Propulsion = moving food through the digestive tract The Processes of Digestion Chemical digestion = using digestive fluids/enzymes to break down food to release nutrients Absorption = taking nutrients into the bloodstream to deliver to cells Defecation = release of waste products via the excretory system Mouth, Teeth, and Tongue Begins when food enters the mouth (ingestion). It is physically broken down by the teeth. (mechanical digestion). Mouth, Teeth, and Tongue Food is also being broken down by amylase, an enzyme in saliva that breaks down carbohydrates/starches (chemical digestion). The tongue moves the food around until it forms a ball called a bolus. Pharynx and Esophagus The bolus is passed to the pharynx (throat). The epiglottis is a flap of tissue that covers the trachea to make sure the bolus passes into the esophagus and not into the lungs! Pharynx and Esophagus The bolus passes down the esophagus by peristalsis. Peristalsis is a wave of muscular contractions that push the bolus down towards the stomach. The part of the esophagus right above the bolus pinches in to push it further down Stomach To enter the stomach, the bolus must pass through the lower esophageal sphincter, a tight muscle that pinches inward to keep stomach acid out of the esophagus. Stomach The stomach is a muscular pouch where the majority of chemical digestion happens. As the stomach muscles contract and relax, they toss and churn the food around (mechanical digestion) Folds called rugae make the inside of the stomach rough to help with breaking food down. Stomach As the stomach muscles toss and churn the food it mixes with gastric juice, a mixture of stomach acid, mucus and enzymes (chemical digestion). Stomach The stomach’s strong hydrochloric acid destroys foreign bacteria and viruses. A thick layer of mucus protects the stomach itself from being eaten away by the acid. It is important that stomach acid stays in the stomach! Stomach The stomach does some absorption too. Some medicines (i.e. aspirin), water, and alcohol are all absorbed through the stomach tissue. Once the bolus has been digested, it is now a thick fluid called chyme and it leaves the stomach by passing through the pyloric sphincter. Small Intestine Once it passes through the pyloric sphincter, the chyme is in the small intestine. The majority of absorption occurs here. The small intestine is broken down into three parts: Small Intestine 1. Duodenum Bile = breaks down fat yellowish/greenish fluid produced in the liver stored in and secreted by the gall bladder (through the bile duct) Pancreatic juice = reduces the acidity of chyme produced in the liver stored in and secreted by the pancreas Small Intestine 2. Jejunum Second portion of the small intestine, where the majority of absorption takes place. It is lined with tiny fingerlike projections called villi increase the surface area for absorbing nutrients Small Intestine Each villi has even more tiny fingerlike projections called microvilli, which increase the surface area for absorption even more. Larger surface = more space to absorb nutrients Flat surface = less space to absorb nutrients Small Intestine 3. Ileum The last portion of the small intestine Has fewer villi, so less absorption Main job is compacting the leftovers to pass into the large intestine. Remember DJ ILL! Small intestine = duodendum jejunum ileum Large Intestine (Colon) The large intestine (aka colon) is made of 3 sections too: Ascending colon Right lateral abdominal region, travels superiorly Transverse colon Medial abdominal region, travels across Descending colon Left lateral abdominal region, travels inferiorly Large Intestine (Colon) The large intestine (aka colon) is used to: absorb water from the waste material leftover from the small intestine Causes the waste to shrink and compact into feces Large Intestine (Colon) “Good” bacteria live in the colon Help you by feeding on your food waste and producing vitamin K and some B vitamins Bloodstream All water and nutrients that have been absorbed by the intestines is picked up by the blood, which carries these nutrients to all the cells of the body. Rectum and Anus All unused waste - now called feces - is compacted and stored in a pouch at the end of the large intestine called the rectum. The anal sphincter is a group of muscles that pinch inward to keep the feces from exiting the anus until you want it to. Rectum and Anus When the rectum is full, the anal sphincter loosens and the waste, called feces, passes out of the body through the anus. Some mucles of the anus and anal sphinter are voluntary, and some are involuntary… Digestion and Homeostasis The endocrine, nervous, digestive and circulatory systems all work together to control digestion. Before we eat, smelling food releases saliva in our mouths to prep for food intake. A hormone called gastrin is released in our stomachs to alert the body to prepare for a snack. The Hormone Gastrin Digestion and Homeostasis If a meal is high in fat, digestion is slowed, allowing more time for the fat to be broken down. This is why we feel fuller after eating a “heavy” high fat meal.
