DIGESTION and ABSORPTIONDIGESTION and ABSORPTION

Learning Objectives:Learning Objectives:• Understand the physical and chemical Understand the physical and chemical

processes of digestionprocesses of digestion• Learn the function of each organ in the Learn the function of each organ in the

digestive systemdigestive system• Gain an understanding of common Gain an understanding of common

Gastrointestinal DisordersGastrointestinal Disorders

TASTE and SMELLTASTE and SMELLThe ChemosensesThe Chemosenses

1. Olfactory Cells:1. Olfactory Cells:• Stimulated by odors around usStimulated by odors around us• Found high inside the nose, connect directly to Found high inside the nose, connect directly to

the brainthe brain

2. Gustatory Cells:2. Gustatory Cells:• React to food and beveragesReact to food and beverages• Clustered into taste budsClustered into taste buds• TASTE: salty, sweet, bitter, sour, and umamiTASTE: salty, sweet, bitter, sour, and umami

TASTE and SMELLTASTE and SMELLThe ChemosensesThe Chemosenses

3. Common Chemical Sense3. Common Chemical Sense• Thousands of nerve endings on the moist Thousands of nerve endings on the moist

surfaces of the eyes, nose, mouth, and surfaces of the eyes, nose, mouth, and throat accent our sense of smell and tastethroat accent our sense of smell and taste

• FLAVOR = texture, temperature, common FLAVOR = texture, temperature, common chemical sense, taste, and odorchemical sense, taste, and odor

CEPHALIC (preabsorptive) CEPHALIC (preabsorptive) PHASE RESPONSEPHASE RESPONSE

In response to sensory stimulation, your In response to sensory stimulation, your body primes its resources to better absorb body primes its resources to better absorb and use anticipated nutrientsand use anticipated nutrients

EXAMPLE:EXAMPLE:

Sound (Hearing a description of food) can Sound (Hearing a description of food) can cause the salivary glands to increase the cause the salivary glands to increase the flow of salivaflow of saliva

Important StructuresImportant Structures

ASSISTING ORGANSASSISTING ORGANS

PHYSICAL PROCESSESPHYSICAL PROCESSES ChewingChewing Peristalsis – the wavelike, rhythmic muscular Peristalsis – the wavelike, rhythmic muscular

contractions of the GI tract that move chyme contractions of the GI tract that move chyme down its tractdown its tract

Segmentation – periodic squeezing and Segmentation – periodic squeezing and partitioning of the SI which mixes the chyme partitioning of the SI which mixes the chyme and promotes close contact with digestive and promotes close contact with digestive juices and absorbing cellsjuices and absorbing cells

Sphincters – regulate the flow of food particlesSphincters – regulate the flow of food particles

CHEMICAL PROCESSESCHEMICAL PROCESSES Enzymes: protein compounds that facilitate Enzymes: protein compounds that facilitate

chemical reactions but are not altered in the chemical reactions but are not altered in the process process

CHEMICAL PROCESSESCHEMICAL PROCESSES

Acid in the stomach (hydrochloric acid)Acid in the stomach (hydrochloric acid) Base in the small intestine (bicarbonate)Base in the small intestine (bicarbonate) BileBile MucusMucus

MOUTHMOUTH

• SalivaSaliva• Amylase – breaks down starches into small Amylase – breaks down starches into small

sugar molecules (only about 5%)sugar molecules (only about 5%)• Lingual Lipase – breaks down fats, but only Lingual Lipase – breaks down fats, but only

in a miniscule amountin a miniscule amount• Epiglottis – guards entrance to the tracheaEpiglottis – guards entrance to the trachea

STOMACHSTOMACHGASTRIC JUICE:GASTRIC JUICE:• WaterWater• Hydrochloric Acid (pH = 2) page 77Hydrochloric Acid (pH = 2) page 77• MucusMucus• EnzymesEnzymes• HormonesHormones• Intrinsic FactorIntrinsic Factor

NUTRIENT ABSORPTION in NUTRIENT ABSORPTION in the STOMACHthe STOMACH

Only:Only:• Some lipid-soluble compoundsSome lipid-soluble compounds• Weak acids, such as alcohol and Weak acids, such as alcohol and

aspirinaspirin

SMALL INTESTINESMALL INTESTINE

Almost all digestion of protein, fat, and Almost all digestion of protein, fat, and carbohydrate is performed in the SIcarbohydrate is performed in the SI

Divided into three parts:Divided into three parts:• Duodenum (the first 10-12 inches)Duodenum (the first 10-12 inches)• Jejunum (~ 4 feet)Jejunum (~ 4 feet)• Ileum (~ 5 feet)Ileum (~ 5 feet)

NUTRIENT DIGESTION in the NUTRIENT DIGESTION in the SMALL INTESTINESMALL INTESTINE

SECRETIN is released upon the SECRETIN is released upon the appearance of chyme in the SI appearance of chyme in the SI SECRETIN stimulates the release of SECRETIN stimulates the release of BICARBONATE from the pancreas BICARBONATE from the pancreas BICARBONATE neutralizes the BICARBONATE neutralizes the chymechyme

NUTRIENT DIGESTION in the NUTRIENT DIGESTION in the SMALL INTESTINESMALL INTESTINE

The neutralization is important because The neutralization is important because the enzymes in the SI need a neutral the enzymes in the SI need a neutral environmentenvironment

Pancreatic juice and secretions from Pancreatic juice and secretions from the intestinal wall cells contain a the intestinal wall cells contain a variety of digestive enzymes that help variety of digestive enzymes that help to digest fats, carbohydrates, and to digest fats, carbohydrates, and proteinsproteins

NUTRIENT DIGESTION in the NUTRIENT DIGESTION in the SMALL INTESTINESMALL INTESTINE

BILE is released from the gall bladder BILE is released from the gall bladder upon the appearance of fat in the SIupon the appearance of fat in the SI

BILE acts as an emulsifier, and without BILE acts as an emulsifier, and without it, lipids might not come into contact it, lipids might not come into contact with pancreatic lipase, and would not with pancreatic lipase, and would not be properly digestedbe properly digested

NUTRIENT DIGESTION in the NUTRIENT DIGESTION in the SMALL INTESTINESMALL INTESTINE

• With pancreatic and intestinal enzymes With pancreatic and intestinal enzymes working together, digestion creates working together, digestion creates smaller compounds of protein, fat, and smaller compounds of protein, fat, and carbohydrate which can then be easily carbohydrate which can then be easily absorbedabsorbed

• Minerals, vitamins, and cholesterol are Minerals, vitamins, and cholesterol are not broken down and are generally not broken down and are generally absorbedabsorbed unchangedunchanged

NUTRIENT ABSORPTION in NUTRIENT ABSORPTION in the SMALL INTESTINEthe SMALL INTESTINE

• Most absorption occurs in the SI – 90%Most absorption occurs in the SI – 90%• Provides the surface area equivalent to a Provides the surface area equivalent to a

tennis court!tennis court!• Nutrients are trapped in folds of the Nutrients are trapped in folds of the

intestinal wall and absorbed through the intestinal wall and absorbed through the microvillimicrovilli

• Each villus contains blood vessels and a Each villus contains blood vessels and a lymph vessel which transport nutrients lymph vessel which transport nutrients

NUTRIENT ABSORPTION in NUTRIENT ABSORPTION in the SMALL INTESTINEthe SMALL INTESTINE

• Water-soluble nutrients are absorbed Water-soluble nutrients are absorbed directly into the bloodstreamdirectly into the bloodstream

• Fat-soluble lipid compounds are Fat-soluble lipid compounds are absorbed into the lymph rather than the absorbed into the lymph rather than the bloodblood

NUTRIENT ABSORPTION in NUTRIENT ABSORPTION in the SMALL INTESTINEthe SMALL INTESTINE

• Duodenum and Upper Jejunum: most Duodenum and Upper Jejunum: most minerals (except sodium, chloride, and minerals (except sodium, chloride, and potassium)potassium)

• Jejunum and Upper Ileum: carbohydrates, Jejunum and Upper Ileum: carbohydrates, amino acids, water-soluble vitaminsamino acids, water-soluble vitamins

• Jejunum: lipids and fat-soluble vitaminsJejunum: lipids and fat-soluble vitamins• Terminal Ileum: Vitamin B12Terminal Ileum: Vitamin B12

LARGE INTESTINELARGE INTESTINE

• Is ~ 5 feet long and includes the Is ~ 5 feet long and includes the cecum, colon, rectum, and anal canalcecum, colon, rectum, and anal canal

NUTRIENT DIGESTION in the NUTRIENT DIGESTION in the LARGE INTESTINELARGE INTESTINE

• Little digestion occurs in the large Little digestion occurs in the large intestineintestine

• The large population of bacteria digests The large population of bacteria digests small amounts of fibersmall amounts of fiber

• This bacterial activity forms: Vitamin This bacterial activity forms: Vitamin K, Vitamin B12, Thiamin, Riboflavin, K, Vitamin B12, Thiamin, Riboflavin, Biotin, and gasesBiotin, and gases

NUTRIENT ABSORPTION in NUTRIENT ABSORPTION in the LARGE INTESTINEthe LARGE INTESTINE

• Little absorption occurs in the large Little absorption occurs in the large intestineintestine

• However, it does absorb: water, However, it does absorb: water, sodium, potassium, chloride, and some sodium, potassium, chloride, and some of the Vitamin K produced by bacteriaof the Vitamin K produced by bacteria

• It does not absorb Vitamin B12It does not absorb Vitamin B12

Healthy BacteriaHealthy Bacteria ProbioticsProbiotics are live microorganisms (in most are live microorganisms (in most

cases, bacteria) that are similar to beneficial cases, bacteria) that are similar to beneficial microorganisms found in the human gut.microorganisms found in the human gut.

Probiotics are available to consumers mainly Probiotics are available to consumers mainly in the form of dietary supplements and foods. in the form of dietary supplements and foods.

Look for “live and active cultures”. The good Look for “live and active cultures”. The good bacteria most often comes from two groups: bacteria most often comes from two groups: LactobacillusLactobacillus or or BifobacteriumBifobacterium. .

Prebiotics Prebiotics are not digested in the SI, and are not digested in the SI, and are used as food by bacteriaare used as food by bacteria

NUTRITION and GI DISORDERSNUTRITION and GI DISORDERSCONSTIPATIONCONSTIPATION• Occurs when the colon absorbs too much water, or Occurs when the colon absorbs too much water, or

if the colon’s muscle contractions are slow and if the colon’s muscle contractions are slow and sluggishsluggish

• CAUSES:CAUSES:• Not enough liquids in the dietNot enough liquids in the diet• Not enough fiber in the dietNot enough fiber in the diet• Sedentary lifestyleSedentary lifestyle• Some medicationsSome medications• Abuse of laxativesAbuse of laxatives

• TREATMENT?TREATMENT?

NUTRITION and GI DISORDERSNUTRITION and GI DISORDERSDIARRHEADIARRHEA• Occurs when the colon absorbs too little waterOccurs when the colon absorbs too little water

• CAUSES:CAUSES:• Most common: infection from bacteria, viruses, or Most common: infection from bacteria, viruses, or

parasitesparasites• AntibioticsAntibiotics• Chronic diarrhea may signal a more serious medical Chronic diarrhea may signal a more serious medical

problem (Inflammatory Bowel Disease)problem (Inflammatory Bowel Disease)

• TREATMENTTREATMENT• BRAT diet (bananas, rice, applesauce, toast)BRAT diet (bananas, rice, applesauce, toast)• Rehydrate and replace electrolytesRehydrate and replace electrolytes

NUTRITION and GI DISORDERSNUTRITION and GI DISORDERS

Gastroesophageal Reflux Disease Gastroesophageal Reflux Disease • Basically, chronic “heartburn”Basically, chronic “heartburn”CAUSES:CAUSES:• Hiatal HerniasHiatal Hernias• Foods that relax the lower esophageal sphincter Foods that relax the lower esophageal sphincter

(LES)(LES)• Frequently occurs in people with asthma, Frequently occurs in people with asthma,

irritable bowel syndrome, and developmental irritable bowel syndrome, and developmental disabilitiesdisabilities

• Concern because of increased risk of Concern because of increased risk of esophageal canceresophageal cancer

TREATMENTTREATMENT• Avoid foods that relax the LESAvoid foods that relax the LES• Don’t lie down or exercise too soon after Don’t lie down or exercise too soon after

eating, raise the head of the bedeating, raise the head of the bed• Wear loose fitting clothingWear loose fitting clothing• MedicationsMedications

NUTRITION and GI DISORDERSNUTRITION and GI DISORDERS

DIVERTICULOSIS DIVERTICULOSIS • Result of rising pressure in the colon, believed to Result of rising pressure in the colon, believed to

be caused by low-fiber diet and constipationbe caused by low-fiber diet and constipationDIVERTICULITISDIVERTICULITIS• Infected or inflamed diverticulum (fecal matter or Infected or inflamed diverticulum (fecal matter or

bacteria gets trapped)bacteria gets trapped)• May experience abdominal pain, indigestion, feverMay experience abdominal pain, indigestion, fever• Diverticulum may rupture causing infection, or Diverticulum may rupture causing infection, or

can form scar tissue and create an obstructioncan form scar tissue and create an obstruction

Diverticulosis/itisDiverticulosis/itis

• TREATMENTTREATMENT• Diverticulosis – high fiber dietDiverticulosis – high fiber diet• Diverticulitis – low fiber dietDiverticulitis – low fiber diet

NUTRITION and GI DISORDERSNUTRITION and GI DISORDERSIRRITABLE BOWEL SYNDROMEIRRITABLE BOWEL SYNDROME• Disorder that interferes with normal functions of the Disorder that interferes with normal functions of the

colon. Symptoms are abdominal pain, bloating, colon. Symptoms are abdominal pain, bloating, constipation, and diarrheaconstipation, and diarrhea

• People with IBS have more sensitive colons and react People with IBS have more sensitive colons and react more strongly to: stress, large meals, certain foods, more strongly to: stress, large meals, certain foods, caffeine, or alcoholcaffeine, or alcohol

• Diagnosed by symptoms and the absence of other Diagnosed by symptoms and the absence of other diseasesdiseases

• TREATMENTTREATMENT• Reduce stressReduce stress• Change dietChange diet• MedicationsMedications

NUTRITION and GI DISORDERSNUTRITION and GI DISORDERS

ULCERSULCERSCAUSES:CAUSES:• Helicobacter pylori infection (most common), Helicobacter pylori infection (most common),

chronic use of anti-inflammatory drugs, and chronic use of anti-inflammatory drugs, and disorders that cause excessive gastric acid disorders that cause excessive gastric acid secretionsecretion

• Not caused by spicy foods or stressNot caused by spicy foods or stress

TREATMENTTREATMENT• AntibioticsAntibiotics• Medications (acid suppressors)Medications (acid suppressors)

NUTRITION and GI DISORDERSNUTRITION and GI DISORDERS

LACTOSE INTOLERANCELACTOSE INTOLERANCECAUSES:CAUSES:• Inability to digest lactose, caused by a shortage of Inability to digest lactose, caused by a shortage of

lactaselactase• Symptoms: nausea, cramps, bloating, gas, and Symptoms: nausea, cramps, bloating, gas, and

diarrheadiarrhea

• TREATMENTTREATMENT• Don’t eat dairy products! Or eat less, and more Don’t eat dairy products! Or eat less, and more

processed types (ex. Yogurt vs. milk )processed types (ex. Yogurt vs. milk )