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
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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