digestion

DIGESTION

The process of preparing your food for absorption

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What Happens to the Food We Eat?

Digestion

To break nutrients into smaller moleculesPhysical DigestionMechanical breakdown of food particlesChemical DigestionEnzyme 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 componentsFood 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 swallowingDuring 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 stomachBolus is moved towards the stomach by a contractile movement called peristalsisAllows food to move through thoracic cavity, through diaphragm, to peritoneal cavity and the stomach (peristalsis)

Digestion: Chewing

Digestion: Swallowing

Digestion: Swallowing

DIGESTION:THE STOMACH

Food passes through a sphincter, (esophageal sphincter) a valve Bolus mixes with stomach secretions to become chymeHCl denatures proteins and kills bacteriaMucus protects stomach wall from acidChyme 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 lengthdivided into three segments: – duodenum– jejunum– ileum

95% of digestion occurs in small intestineBile: 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 mineralsSupports growth of bacteria that produce Vitamin KSupports 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 liningPicked 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 smallerSmall 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 activityStomach: very little activitySmall 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

CardiovascularHormonal and NervousStorage– Liver– Muscle– Fat