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 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: 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 tripeptides – 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