1 DNT 200 NUTRITION FOR HEALTH SCIENCES DIGESTION AND ABSORPTION.

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DNT 200NUTRITION FOR HEALTH

SCIENCES

DIGESTION AND ABSORPTION

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“I have finally cum to the konklusion that a good reliable set ov bowels iz worth more to a man than enny quantity of brains.”

Josh Billings, 19th century American writer

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• Digestion is the process by which food is broken down into absorbable units

• The digestive system includes all the organs and glands associated with the ingestion and digestion of food; it is a flexible muscular tube about 26 feet long from the mouth to the anus

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DIGESTION AND ABSORPTIONThe Digestive Organs

The Mouth– Fiber is crushed and torn– Food is moistened with

saliva for swallowing– Amylase in saliva begins the

digestion of starch to smaller polysaccharides and maltose

– Some hard fats begin to melt as they reach body temperature

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The Epiglottis– Cartilage in the throat that

guards the entrance to the trachea and prevents fluid or food from entering it when a person swallows

The Esophagus– The food pipe; the conduit from

the mouth to the stomach– Digestion of starch continues as

swallowed food moves down the esophagus

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The Digestive Organs

Cardiac Sphincter– The sphincter muscle

at the junction between the esophagus and the stomach

– Closes behind the bolus so that it cannot slip back up the esophagus

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The Stomach– A muscular elastic portion of

the digestive tract that grinds and churns swallowed food mixing it with acid and enzymes to form chyme

– Starch digestion stops in stomach as stomach acid and enzymes digest the salivary enzymes

– Sucrose and maltose begin to be hydrolyzed by stomach acid

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The Stomach (continued)– Triglycerides are split into

diglycerides and fatty acids (a slight action for most fats except milk)

– Protein, through the action of pepsin and stomach acid is split into smaller polypeptides

– Intrinsic factor attaches to Vitamin B-12 (Intrinsic factor is a substance made in the stomach and aids in the absorption of Vitamin B-12)

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The Stomach (continued)– Stomach acid acts on iron

to make it more absorbable

– A watery fluid is secreted turning a moist chewed mass of solid food into chyme (a semi-liquid mass of partially digested food), which is then expelled into the duodenum

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Pyloric Sphincter– The sphincter muscle

separating the stomach from the small intestine

– Is the “gate keeper” keeping chyme from going back into the stomach

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The Digestive Organs The Small Intestine

– Composed of three segments

• Duodenum (upper-most portion)

• Jejunum (middle-most portion)

• Ileum (last-most portion)

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The Digestive Organs The Small Intestine (con’t)

– Pancreas produces carbohydrases and releases them into the small intestine

• Polysaccharides are broken down into maltose (glucose + glucose) by pancreatic amylase

• Maltose is broken down by maltase to glucose

• Sucrose is broken down by sucrase to glucose and fructose

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The Digestive Organs The Small Intestine (con’t)– Bile flows in from the liver

and emulsifies fat– Pancreatic lipase flows in from

the pancreas and breaks the emulsified fat into monoglycerides, glycerol and fatty acids, which are absorbed

– Pancreatic and small intestine enzymes split polypeptides into dipeptides, tripeptides and amino acids, which are absorbed

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The Digestive Organs The Small Intestine (con’t)

– Bile emulsifies fat soluble vitamins and aids in their absorption with other fats

– Water soluble vitamins are absorbed

– Many minerals are absorbed

– Water is secreted from the small intestine, pancreas, and liver

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Ileocecal Valve– The sphincter

muscle separating the small and large intestine

– Keeps chyme from going back to the small intestine

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The Digestive Organs The Large Intestine

– Most fiber has passed so far intact -- bacterial enzymes break down some fiber into glucose, which is absorbed

– Some fat and cholesterol, trapped in the fiber, is excreted

– Bacteria produce Vitamin K, which is absorbed

– More minerals and most of the water are absorbed

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Rectum– The muscular terminal

part of the intestine to the anus

Anus– The terminal sphincter

muscle of the GI tract

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Involuntary Muscles and Glands• Except for swallowing and defecating, the muscles

and glands of the digestive tract work with no conscious effort

• Salivary glands secrete just enough saliva to moisten each mouthful of food

• Muscles of the GI tract help liquefy the bolus into chyme (i.e. chewing, in addition to saliva and the action of the tongue, reduces food into a coarse mash suitable for swallowing)

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DIGESTION AND ABSORPTIONInvoluntary Muscles and Glands

• Stomach muscles work to force the chyme downward toward the pyloric sphincter

• Peristalsis begins when the bolus enters the esophagus– Entire GI tract is ringed with muscles that can squeeze tightly– During peristalsis, successive waves of involuntary muscle

contraction passes along the walls of the intestine

• Intestines segment their contents– Segmentation -- a periodic squeezing or partitioning of the

intestine by its circular muscles– Allows the digestive juices and absorbing cells of the

intestinal wall to make better contact

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The Process of Digestion• Body renders food into the basic units that make

up carbohydrate, protein and fat, absorbs these units, and builds its tissues from them

• Five different organs secrete digestive juices– Salivary glands– Stomach– Small intestine– Liver– Pancreas

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The Process of Digestion

Digestion in the Mouth• Digestion of carbohydrate begins in the mouth

– Saliva (water, salts, and enzymes -- including salivary amylase) break the bonds in the chains of starch

• Enzymes in the mouth have no effect on– Fats– Proteins– Vitamins– Minerals– Fiber

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DIGESTION AND ABSORPTIONThe Process of Digestion

Digestion in the Stomach• Major event -- initial breakdown of protein• Gastric juice is composed of water, enzymes, and hydrochloric acid

– Acidity prevents bacteria growth– Acidity kills bacteria that enter the body with food

• Acid helps uncoil proteins tangled strands so that the stomach enzymes can attack the bonds

• Minor stomach events– Digestion of some fat by gastric lipase– Digestion of sucrose (to a small extent) by stomach acid– Attachment of a protein carrier to vitamin B-12

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DIGESTION AND ABSORPTIONThe Process of Digestion

Digestion in the Small and Large Intestine• Pancreas and liver contribute digestive juices through ducts leading into the

duodenum• Pancreatic juice

– Contains enzymes which act on fats, proteins, and carbohydrates (glands in the intestinal wall also secrete digestive enzymes)

– Also contains sodium bicarbonate (a base) which neutralizes the acid chyme as it enters the small intestine

• Bile– Secreted by the liver continuously– Stored in the gall bladder– Emulsifies fats and brings them into suspension with water enabling enzymes to

work on them and subsequent absorption

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The Process of DigestionDigestion in the Small and Large Intestine (continued)

• All three energy-yielding nutrients are digested in the small intestine

• Rate of digestion depends on the contents of the meal– High in simple sugars -- digestion proceeds rapidly– High in fat -- digestion is slower (fat increases a meal’s satiety

value)

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The Process of DigestionDigestion in the Small and Large Intestine (continued)

• Bacteria in the intestine produce a variety of vitamins (bacterial alone cannot meet the need for these vitamins)– Biotin– Vitamin K

• GI bacteria protect from infection– If normal intestinal flora is thriving, infections have a hard time

getting established– Several types of defending cells are present and confer specific

immunity against intestinal diseases

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The Absorptive System The Small Intestine– Provides a surface

whose extent is comparable to a quarter of a football field in area

– Nutrient molecules make contact with this surface and are absorbed

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The Absorptive System

The Small Intestine (con’t)

– A rush of blood

circulation continuously

bathes the underside of

this surface

• Removes these

molecules rapidly

• Makes room for more to

be absorbed

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DIGESTION AND ABSORPTIONThe Absorptive System The Small Intestine (con’t)

– Is a tube about 20 feet long and an inch across

– Inner surface, through a microscope, is wrinkled into hundreds of folds

– Each fold is covered with with thousands of finger-like projections (villi) which are in constant motion

– Any nutrient molecule small enough to be absorbed is trapped in the microvilli (projections from the cells of the villi), drawn in and absorbed

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DIGESTION AND ABSORPTIONThe Absorptive System

Release of Absorbed Nutrients• Once inside the intestinal cells, the products of digestion must be released

for transport to the rest of the body• Water soluble nutrients are released directly into the bloodstream via the

capillaries• Larger fats and fat soluble vitamins

– Are insoluble in blood (water)– Fats are assembled into triglycerides– These triglycerides, with fat soluble vitamins and other lipids (phospholipids,

cholesterol) form with proteins into lipoproteins called chylomicrons– They are then released into the lymphatic system– Then go from the lymphatic system to the blood stream near the heart

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Transport of Nutrients The Vascular System

• Also known as the blood circulatory system

• Is a closed system of vessels through which blood flows continuously in a figure eight

• Heart is the pump at the crossover point

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Transport of Nutrients

The Vascular System (con’t)

• Except for the digestive system, blood goes from the heart to arteries to capillaries to veins back to the heart

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DIGESTION AND ABSORPTIONTransport of Nutrients

The Vascular System (con’t)• Digestive system

– Blood gets to the digestive system (intestines) by way of arteries to capillaries

– When leaving the digestive system the blood goes not back to the heart but by vein to the liver

• Liver has the first chance at nutrients absorbed form the GI tract

• Liver is the body’s major metabolic organ– Must prepare nutrients for use by the body– Performs many other jobs in this process

– There capillaries give the liver access to the blood– From the liver the blood goes via vein back to the

heart

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Transport of Nutrients The Lymphatic System

• Is a one-way route for fluid from the tissue spaces to enter the blood

• Has no pump– Like water in a sponge, lymph is

squeezed from one portion of the body to another as muscles contract and create pressure here and there

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Transport of Nutrients The Lymphatic System

(continued)– Ultimately collects in a large

duct behind the heart

– Duct terminates in a vein that conducts the lymph into the heart and thereby into the bloodstream

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Review Secretion

ORGAN OR GLAND TARGET ACTION

? AmylaseSalivary Glands Mouth Starch ?

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Review Secretion


Saliva AmylaseSalivary Glands Mouth Starch Maltose

Gastric Juice Pepsin, HClGastric Glands ? ? Smaller

Polypeptides

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Review Secretion



Gastric Juice Pepsin, HClGastric Glands Stomach Protein Smaller

Polypeptides

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Review Secretion



Gastric Juice Pepsin, HClGastric Glands Stomach Protein Smaller

Polypeptides

Intestinal Juice ?Intestinal Glands Small Intestine Carbohydrate

Monosaccharides

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DIGESTION AND ABSORPTIONReview

SecretionORGAN OR GLAND TARGET ACTION


Gastric Juice Pepsin, HClGastric Glands Stomach Protein Smaller Polypeptides

Intestinal Juice CarbohydraseIntestinal Glands Small Intestine Carbohydrate Monosaccharides

? Juice ProteasePancreas Small Intestine Protein dipeptides, tripeptides

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Pancreatic Juice ProteasePancreas Small Intestine Protein dipeptides, tripeptides

and amino acids

Bile Bile Bile ?Liver ? Small Intestine Fats (Emulsified fat)

monoglycerides, ?, & fatty acids

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Pancreatic Juice ProteasePancreas Small Intestine Protein dipeptides, tripeptides

and amino acids

Bile Bile Bile LipaseLiver Gall Small Intestine Fats (Emulsified fat)

Bladder monoglycerides, glycerol, & fatty acids

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DIGESTION IN THE MOUTH

AmylaseCarbohydrate Starch Maltose

Fat, Protein, Vitamins No chemical action Minerals, Fiber

Water Added

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ReviewDIGESTION IN THE STOMACH

Pepsin-AcidProtein Smaller Polypeptides

Carbohydrate, Fat, Vitamins Minor action

Minerals, Fiber No chemical action

Water Added

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DIGESTION IN THE SMALL INTESTINECarbohydrases

Carbohydrate All Carbohydrates Monosaccharides Bile

Fat All Fats Emulsified fats

LipasesEmulsified fats Monoglycerides or

Glycerol and Fatty Acids

ProteasesProtein All Proteins Dipeptides, Tripeptides

and Amino Acids

Vitamins, Minerals, No Chemical Action & Fiber

Water Added

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TRANSPORT OF NUTRIENTS INTO BLOODThe following are transported directly into the blood

– Water Soluble Nutrients• Carbohydrates

– Monosaccharides

• Lipids– Glycerol– Short Chain Fatty Acids– Medium Chain Fatty Acids

• Proteins– Amino Acids

• Vitamins– B Vitamins and Vitamin C

• Minerals

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TRANSPORT OF NUTRIENTS INTO BLOOD (Con’t)

The following are made into triglycerides– Lipids

• Long Chain Fatty Acids• Monoglycerides

These, along with• Cholesterol• Phospholipids

Are assembled into lipoproteins and transported through the lymphatic system to the blood

Vitamins A, D, E, and K are transported through the lymphatic system to the blood

1 DNT 200 NUTRITION FOR HEALTH SCIENCES DIGESTION AND ABSORPTION.

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Transcript of 1 DNT 200 NUTRITION FOR HEALTH SCIENCES DIGESTION AND ABSORPTION.