Human Digestion -Ch. 21.1 Section Objectives: Interpret the different functions of the digestive system organs. Outline the pathway food follows through the digestive tract. Identify the role of enzymes in chemical digestion.

Human Digestion This part of the life process of NUTRITION-> process by which an organism obtains and utilizes food

Overview: Food processing occurs in four stages Ingestion: taking in food Digestion: mechanical and chemical breakdown of food so that it can be absorbed by the cells Absorption: cells lining the digestive tract take up (absorb) small nutrient molecules Elimination: undigested material passes out of the digestive tract

Human Digestion~ a 2 part process that changes food into a form useable by the body cells 1. Mechanical digestion – physical breakdown of large pieces of food into smaller ones 2. Chemical digestion – hydrolysis – the splitting of large insoluble molecules in small, soluble molecules with the use of water and enzymes ( in other words; breaking complex molecules into simple ones) The process of chemical digestion ( hydrolysis) is regulated by enzymes

Examples of chemical Digestion: 1. Carbohydrates+ water -> simple sugars (glucose for instance) 2. Proteins+ water -> amino acids 3. Lipids+ water -> 3 fatty acids +gylcerol

HUMAN DIGESTIVE SYSTEM Human digestive tract = GI (gastrointestinal) Consists of a continuous one way food tube (mouth to anus)

HUMAN DIGESTIVE SYSTEM 1. Mouth: (oral cavity) ingests food 2. Teeth: function in mechanical breakdown of food, increases surface area of food for enzyme action 3.Tongue: acts as a plunger to push food back into the throat (pharynx) taste buds are located on the surface of the tongue

Mouth Functions mechanical digestion chemical digestion (saliva) teeth break up food chemical digestion (saliva) amylase enzyme digests starch mucus protects soft lining of digestive system lubricates food for easier swallowing buffers neutralizes acid to prevent tooth decay anti-bacterial chemicals kill bacteria that enter mouth with food All that in spit!

Yeast Infection of the Mouth!!

mouth break up food digest starch kill germs moisten food

HUMAN DIGESTIVE SYSTEM 4. Pharynx: food is pushed by tongue to back of throat, initiates swallowing – food is now in the form of a bolus Epiglottis: flap that prevents choking 5. Esophagus: muscular tube that moves food from mouth to the stomach by process of peristalsis: wave of muscular contractions that moves chewed food to stomach

Swallowing (& not choking) Epiglottis flap of cartilage closes trachea (windpipe) when swallowing food travels down esophagus Peristalsis involuntary muscle contractions to move food along

Stomach Functions disinfect food food storage digests protein hydrochloric acid = pH 2 kills bacteria food storage can stretch to fit ~2L food digests protein pepsin enzyme Still, the epithelium is continually eroded, and the epithelium is completely replaced by mitosis every three days. Gastric ulcers, lesions in the stomach lining, are caused by the acid-tolerant bacterium Heliobacter pylori. Ulcers are often treated with antibiotics. Pepsin is secreted in an inactive form, called pepsinogen by specialized chief cells in gastric pits. Parietal cells, also in the pits, secrete hydrochloric acid which converts pepsinogen to the active pepsin only when both reach the lumen of the stomach, minimizing self-digestion. Also, in a positive-feedback system, activated pepsin can activate more pepsinogen molecules. But the stomach is made out of protein! What stops the stomach from digesting itself? mucus secreted by stomach cells protects stomach lining

mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food sphincter sphincter

Small intestine Functions digestion absorption digest carbohydrates amylase from pancreas digest proteins trypsin & chymotrypsin from pancreas digest lipids (fats) bile from liver & lipase from pancreas absorption nutrients move into body cells by: diffusion active transport This is where all the work is done! About every 20 seconds, the stomach contents are mixed by the churning action of smooth muscles. As a result of mixing and enzyme action, what begins in the stomach as a recently swallowed meal becomes a nutrient-rich broth known as acid chyme. At the opening from the stomach to the small intestine is the pyloric sphincter, which helps regulate the passage of chyme into the intestine. A squirt at a time, it takes about 2 to 6 hours after a meal for the stomach to empty.

Absorption in Small Intestines Absorption through villi & microvilli finger-like projections increases surface area for absorption SMALL INTESTINES 6 meters long, but can stretch to cover a tennis court

mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food liver produces bile - stored in gall bladder break up fats small intestines breakdown food - proteins - starch - fats absorb nutrients pancreas produces enzymes to digest proteins & starch

Pancreas ~ accessory organ Produces digestive enzymes digest proteins trypsin, chymotrypsin digest starch amylase digest lipids lipase Buffers neutralizes acid from stomach small intestine pancreas

mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food pancreas produces enzymes to digest all foods

Liver & Gall Bladder ~accessory organs Produces bile breaks up fats gallbladder only stores bile that’s why you can have your gall bladder removed bile contains colors from old red blood cells collected in liver = iron in RBC rusts & makes feces brown

mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food liver produces bile - stored in gall bladder break up fats pancreas produces enzymes to digest proteins & starch

Large intestines (colon) Function re-absorbs water use ~9 liters of water every day in digestive juices if don’t reabsorb water would die of dehydration > 90% of water re-absorbed not enough water re-absorbed diarrhea can be fatal! too much water re-absorbed constipation reabsorb by diffusion

You’ve got company! Living in the large intestine is a community of helpful bacteria Escherichia coli: E. coli digest cellulose digests fruits & vegetables produce vitamins vitamin K & B vitamins BUT generate gases by-product of bacterial metabolism methane, hydrogen sulfide STINKY! PEE-YOO!

mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food liver produces bile - stored in gall bladder break up fats small intestines breakdown food - proteins - starch - fats absorb nutrients pancreas produces enzymes to digest proteins & carbs large intestines absorb water

Rectum Last section of large intestines eliminate feces through anus what’s left over? undigested materials mainly cellulose from plants called roughage or fiber keeps everything moving & cleans out intestines masses of bacteria So don’t forget to wash your hands!

Appendix Vestigial organ

Some Digestive Homeostasis Disorders 1.Constipation– person has uncomfortable or infrequent bowel movements results from sluggish peristalsis that allows excess water to be removed from feces (fecal matter hardens)- may result from insufficient fiber in diet 2. Diarrhea– opposite of constipation– associated with intestinal disturbances caused by infections or stress– prolonged diarrhea may result in severe dehydration 3. Gall stones– small hard particles made of cholesterol which form & collect in gall bladder- may block the bile duct and cause pain 4. acid reflux -backflow of stomach contents upward into esophagus 5. appendicitis- inflammation of appendix

  Ulcers Used to think ulcers were caused by stress Free of H. pylori Colonized by H. pylori Used to think ulcers were caused by stress tried to control with antacids Now know ulcers caused by bacterial infection of stomach H. pylori bacteria now cure with antibiotics inflammation of stomach inflammation of esophagus H. pylori cell damaging proteins (VacA) inflammatory proteins (CagA)   cytokines helper T cells neutrophil cells white blood cells