DIGESTION The process of preparing your food for absorption bin/netquiz_get.pl?qfooter=/usr/web/home/mhhe/biosci/genbio/animation_quizz es/animate_30fq.htm&afooter=/usr/web/home/mhhe/biosci/genbio/animation_qu izzes/animate_30fa.htm&test=/usr/web/home/mhhe/biosci/genbio/animation_qui zzes/animate_

What Happens to the Food We Eat?

Digestion To break nutrients into smaller molecules Physical Digestion Mechanical breakdown of food particles Chemical Digestion Enzyme catalyzed breakdown of nutrient molecules

Absorption Movement of digested nutrients through intestinal wall into: Blood (water soluble nutrients) Lymphatic system - > blood (fat soluble nutrients

Digestion: The Mouth Chewing: physically breaks down food into smaller components Food stimulates salivary glands to release saliva –Saliva contains amylase-breaks down starch –Saliva moistens food for easy swallow Bolus: ball of chewed food mixed with saliva

DIGESTION: THE PHARYNX Area responsible for swallowing During swallowing, air passage is blocked by epiglottis –Blocks the food from entering the trachea and the lungs –Bolus is directed down the esophagus

DIGESTION: THE ESOPHAGUS Connects the pharynx and the stomach Bolus is moved towards the stomach by a contractile movement called peristalsis Allows food to move through thoracic cavity, through diaphragm, to peritoneal cavity and the stomach (peristalsis)

Digestion: Chewing

Digestion: Swallowing

DIGESTION: THE STOMACH Food passes through a sphincter, (esophageal sphincter) a valve Bolus mixes with stomach secretions to become chyme HCl denatures proteins and kills bacteria Mucus protects stomach wall from acid Chyme released into small intestine through pyloric sphincter

DIGESTION: STOMACH Stops salivary amylase and and slows lingual lipase activity (acid denatures enzyme) Starts protein digestion: pepsin activated and starts protein digestion Two Australians win Nobel Prize in medicine - More Health News - MSNBC.com

Digestion: The Stomach

DIGESTION: SMALL INTESTINE 20 feet in length divided into three segments: –duodenum –jejunum –ileum 95% of digestion occurs in small intestine Bile: made in liver, stored in gall bladder –Emulsifies fats

Digestion: Accessory Organs

Absorption

DIGESTION: SMALL INTESTINES Pancreas: –Secretes bicarbonate into duodenum to neutralize stomach acid in the chyme –Secretes enzymes that act on protein (proteases) carbohydrate (carbohydrases) lipids (lipases)

DIGESTION: LARGE INTESTINES Absorbs water and some minerals Supports growth of bacteria that produce Vitamin K Supports growth of other bacteria that partially breaks down fiber –We are then able to absorb some of the breakdown products

Absorption and Transportation All nutrients must pass through intestinal lining Picked up by capillaries or lymphatic vessels

DIGESTION: CARBOHYDRATES Begins in the mouth: salivary amylase –Amylase denatured in stomach Small intestine: pancreatic enzymes breakdown large CHO’s(starch) to smaller Small intestines: brush border cells produce disaccharidases (sucrase, maltase, lactase) –Breakdown sucrose, maltose, lactose Absorption occurs in duodenum & jejunum

DIGESTION: PROTEIN Protein digestion begins in the stomach –Denaturation by HCl –Pepsin breaks large proteins into smaller peptides Pancreatic enzymes introduced into the duodenum –Break down peptides into amino acids, di- and tri- peptides –Intestine enzymes breakdown to amino acids

DIGESTION: LIPIDS Mouth: Lingual Lipase, very little activity Stomach: very little activity Small Intestines: Major activity –Bile from gall bladder emulsifies –Enzymes from pancreas digest and makes the products ready for digestion monoglycerides, glycerol, fatty acids absorbed into cells of microvilli

Other Systems Cardiovascular Hormonal and Nervous Storage –Liver –Muscle –Fat