Human Digestion -Ch 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 1.Ingestion: taking in food 2.Digestion: mechanical and chemical breakdown of food so that it can be absorbed by the cells 3.Absorption: cells lining the digestive tract take up (absorb) small nutrient molecules 4.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)

Mouth Functions – mechanical digestion 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!

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  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 hydrochloric acid = pH 2 – kills bacteria – food storage can stretch to fit ~2L food – digests protein pepsin enzyme But the stomach is made out of protein! What stops the stomach from digesting itself? mucus secreted by stomach cells protects stomach lining

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

Ulcers 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 Colonized by H. pylori Free of H. pylori white blood cells cytokines inflammatory proteins (CagA) cell damaging proteins (VacA) helper T cells neutrophil cells H. pylori 

Small intestine Functions – digestion 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!

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

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

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

stomach  kills germs  break up food  digest proteins  store food mouth  break up food  digest starch  kill germs  moisten 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 bile contains colors from old red blood cells collected in liver = iron in RBC rusts & makes feces brown

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

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!

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