The Digestive System

Process by which organisms obtain and utilize energy from food. There are two parts to Nutrition: 1. Ingestion- process of taking food into the digestive system so that it may be broken down or digested. 2. Digestion- the breakdown of food (either chemically or mechanically) in order to utilize nutrients for cellular processes. Biological molecules must be broken down into their subunit parts to be useful to the cells of the body

 Micronutrients- vitamins, minerals, & water  Macronutrients- proteins, lipids and carbohydrates

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

Organs of the Digestive System Alimentary canal – continuous coiled hollow tube that food travels through Mouth (including teeth) Pharynx Esophagus Stomach Small intestine Large intestine Rectum Anus Salivary glands Pancreas Liver Gall bladder Accessory digestive organs – involved in (help with) digestion, but not part of the tube that food travels through

◦Mechanical digestion  Teeth - breaking up food ◦Chemical digestion  Saliva (from salivary glands – accessory)  Amylase - enzyme digests starch *Bolus (lump) is formed with saliva and the tongue

 Epiglottis ◦flap of cartilage ◦closes trachea (windpipe) when swallowing ◦food travels down esophagus Pharynx – back of the throat

Peristalsis - series of involuntary wave-like muscle contractions which move food along the digestive tract Esophagus The tube that connects your mouth and your stomach no digestion happens here Sphincter – muscle that opens into the stomach and prevents bolus from coming back up.

 Food is temporarily stored here. ◦can stretch to fit ~2L food  Gastric juices (HCl and pepsin) are secreted for digestion.  HCl = pH 2  kills bacteria ◦Mechanical digestion  Peristalsis ◦Chemical digestion  Pepsin - enzyme breaks down proteins into amino acids Food in the bolus is further broken down into a thin liquid called chyme.

 Function ◦ chemical digestion  major organ of digestion & absorption ◦ absorption through lining  over 19 feet (6 meters) long.  Named small intestine based on diameter  Structure ◦ 3 sections  duodenum = most digestion  jejunum = absorption of nutrients and water  ileum = absorption of nutrients and water material passes through by peristalsis

 Most chemical digestion takes place here. ◦Completed digestion of carbohydrates and proteins  Lipids are broken down here ◦Step 1: Emulsification from bile made in liver and stored in gall bladder. ◦Step 2: Breakdown into glycerol and fatty acids by lipases (enzyme) from the pancreas

Absorption in Small Intestine Lined with villi - Microscopic finger-like projections that line the inner wall of the small intestine. Help to increase the surface area for absorption. After food passes from the stomach into the small intestine, nutrients in the food are absorbed into the body through the villi. Every person has millions of villi in his/her intestines. Simple sugars, amino acids, glycerol and fatty acids are absorbed into the inner lining of the villi and enter the bloodstream.

 Related to small intestine ◦Liver ◦Pancreas ◦Gall Bladder

◦Liver produces bile ( bile salts, electrolytes, bilirubin, cholesterol and other fats. Has a yellow- greenish color) which is then stored in gallbladder until needed in the small intestine for digestion  Emulsification - The breakdown of fat globules in the duodenum into tiny droplets.

 An organ which secretes the digestive enzymes lipases.  Lipases – enzyme that breaks down emulsified lipids into glycerol and fatty acids

Biological Molecules Digestion Carbohydrates: Amylase in mouth -completed by enzymes in small intestine Proteins: Pepsin in stomach -completed by enzymes in small intestine Lipids: Emulsification by bile -completed by lipases in small intestine

◦Only 4.9 ft (1.5 meters) long. Named for the diameter ◦Absorb water from the remaining indigestible food matter ◦Pass (by peristalsis) useless waste material from the body as a solid waste material  not enough water absorbed  diarrhea  too much water absorbed or not enough ingested  constipation

Rectum Last section of colon (large intestines) -No digestion happens here -Eliminate undigested materials (feces)  extracellular waste  mainly cellulose from plants (roughage or fiber)  masses of bacteria Anus -The external opening of the rectum -Its opening and closing are controlled by sphincter muscles

 Living in the large intestine is a community of helpful bacteria  produce vitamins  vitamin K; B vitamins  generate gases  by-product of bacterial metabolism  methane, hydrogen sulfide

Vestigal organ - characteristics of organisms that have appeared to have lost all or most of their original function in a species (through evolution) Narrow, dead-end tube about three-to-four inches long that hangs off of the cecum portion of the large intestine. Historically, contained bacteria for digesting cellulose Currently, theorized to support the immune system

The Digestive System

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 ULCERS – erosion of the surface of the alimentary canal Associated with some kind of irritant or bacteria.

 CONSTIPATION – a condition in which the large intestine is emptied with difficulty.  Too much water is absorbed from the large intestine and the solid waste hardens  This can also occur if not enough water is ingested

 DIARRHEA – a gastrointestinal disturbance characterized by decreased water absorption and increased peristaltic activity of the large intestine. ◦Results in increased, multiple, watery feces.  This condition may result in severe dehydration, especially in infants

 APPENDICITIS – an inflammation of the appendix ◦Occurs when the appendix becomes blocked, often by feces or a foreign body (bacteria or virus). Blockage may also occur from infection, since the appendix swells in response to any infection in the body.  Common treatment is removal of the appendix via surgery  Bursting – releasing poisons into the body

 GALLSTONES – cholesterol and bile particles that clump into a solid mass.  Can either be passed by entering the small intestine or surgically removed

 HEART BURN – ACID from the stomach backs up into the esophagus.  Causes: Eating foods that often trigger heartburn, such as acidic foods (tomatoes and citrus fruits) Drinking alcohol Smoking cigarettes Having certain medical conditions, such as diabetes and asthma