Chapter 3: Digestion

Digestive SystemEssentially a hollow tube extending from mouth

to anus Epithelium lines the lumen

Barrier to invaders Submucosal layer Muscularis 4 sphincters (valves) located in certain locations

to prevent food/fecal matter from backing up Under autonomic (automatic) control

Fig. 3.2

GI Tract

Food Mouth Bolus Esophagus

Stomach Chyme Duodenum

JejunumIleum

“Waste” CecumAscending colonTransverse colonDescending colon

Sigmoid colon

Movement Along the Intestine Peristalsis

A ring of contraction propelling material along the GI tract

Segmentation A back-and-forth action that breaks apart food

Mass movement Peristaltic wave that contracts over a large area of

the large intestine to help eliminate waste

Movement Peristalsis

Segmentation

4 Sphincters Cardiac or lower esophageal sphincter

Prevents reflux of stomach content to cause heartburn and ulcers

Pyloric sphincter Controls the amount of stomach content into the small

intestine Sphincter of Oddi

Controls the amount of bile into the small intestine Ileocecal sphincter

Prevents large intestine content (bacteria) back up into the small intestine

An Example of a Sphincter Muscle

Esophagus muscles contract,squeezing on the inside.

Esophagus muscles relax,opening the passageway.

Diaphragm muscles relax,opening the passageway.

Longitudinal muscle

Esophagus

Diaphragm muscles contract,squeezing on the outside.

When the circular muscles of a sphincter contract, thepassage closes; when they relax, the passage opens.

Circular muscle

Stomach

Mouth to Stomach Cooking actually starts the digestion Chewing Saliva (3 functions)

Contains enzymes to help breakdown carbohydrates Provides mucus to lubricate the food for easier

swallowing Contains lysozymes to kill bacteria

Tongue Taste receptors

Esophagus Food propels down by rhythmic muscle contractions

strong enough that even food swallowed while standing on your head will reach your stomach

Epiglottis functions to cover the passage to the airway and prevent food from entering the lungs bacteria naturally present in food can cause pneumonia

Ends at cardiac or lower esophageal sphincter prevents reflux of stomach content that cause heartburn

and ulcers

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The Stomach

Capacity of ~4 cups Secretion of hydrochloric acid and enzymes

begins digestion of proteins Mucus layer prevents autodigestion from acid/enzymes Holds food for 2-6 hours

Passage into small intestine regulated by pyloric sphincter Distension of small intestine inhibits empyting Large meal takes longer to leave the stomach Solid meal takes longer than liquid More complex meal takes longer Higher fat meal takes longer

Secretion of the intrinsic factor

Physiology of the Stomach

How does the stomach know to produce acid?Stimulated by Stomach distention Histamine Thoughts of food (nerve input) Food itself Hormone: Gastrin

Additional Function Assists in calcium absorption

The pH Scale

Basic

Acidic

pH neutral

pH’s of common substances:

Oven cleaner

BilePancreatic juice

Concentrated lye

Battery acid

Gastric juiceLemon juice

Vinegar

Orange juice

Urine

BloodWater

Baking soda

Household ammonia

Saliva

Coffee

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

The Small Intestine Duodenum

~10 inches in length Primary site of digestion

Jejunum ~4 feet in length Some digestion

Ileum ~5 feet in length Little digestion

Activity In the Small Intestine: Accessory Organs Bile acid from the liver via the gallbladder Bicarbonate ions and enzymes from the

pancreas Muscle contractions to mix the food with

digestive juices Food remains 3-10 hours in the small intestine ~95% of digestion takes place here

The Small Intestine

Anatomy of the Small Intestine The wall is folded Villi projections are located on the folds Microvilli is located on the villi Glycocalyx is located on the microvilli Increases intestinal surface area 600 x Absorptive cells (enterocytes) are located on

the villi

Intestinal Mucosa

Absorptive cells Produced in crypts Migration and maturation from the crypts to the

tips of the villi Degradation of cells at the tips of the villi by

digestive enzymes Newly formed cells constantly migrate to replace

dying ones (3-6 days) High turnover causes the cells to deteriorate during

nutrient deficiency

Gastrointestinal Hormones

Gastrin Originated from the pyloric region of the

stomach and upper duodenum Stimulated by food, thoughts of food Stimulates flow of stomach enzymes and HCl Stimulates contraction of cardiac sphincter Slows gastric emptying

Secretin Originated from the duodenum, jejunum Stimulated by the presence of acidic chyme

and the presence of peptones in the duodenum Stimulates the secretion of bicarbonate

Neutralizes stomach acid Slows gastric emptying

Cholecystokinin (CCK) Originated from the duodenum, jejunum Stimulated by food, presence of fat and

protein in the duodenum Stimulates contraction of gallbladder and flow

of bile Stimulates the release of enzyme rich

pancreatic fluids Slows gastric emptying

Gastric Inhibitory Peptide (GIP) Originated from the duodenum, jejunum Stimulated by fats and protein Inhibits the secretion of stomach acid and

enzymes Slows gastric emptying

Site of Absorption

Types of Absorption Passive

Intestinal wall is permeable to the nutrient Going from higher to lower concentration No energy expended

Facilitated A carrier shuttles substances into the absorptive cells Going from higher to lower concentration No energy expended

Active Uses a carrier and ATP

Endocytosis Phagocytosis and pinocytosis

Types of Absorption

After Absorption: Circulation Intestinal villi drains into

1. Portal circulation Water-soluble vitamins and minerals Monosaccharides and amino acids Portal vein

2. Lymphatic circulation Fat-soluble Large particles Thoracic duct Left subclavian vein

The Large Intestine Little digestion occurs Indigestible food stuff (ie fiber) Absorption of 85-90% of the water,

some minerals, vitamins Formation of feces for elimination

Colon Health Colon contains both good and bad bacteria (called

microflora) Usually exist in balance

Imbalances can cause problems Good bacteria have beneficial effects on the colon

Protect against invading pathogenic bacteria Synthesize vitamin K produce short chain fatty acids

Probiotics Consumption of beneficial bacteria in foods

or supplements Yogurt with “live and active cultures”

L. acidolphilus and Bifidus Other claims:

prevents diarrhea boosts the immune system supresses some cancers Lowers cholesterol and blood pressure

Prebiotics Consumption of foods that promote growth of

good bacteria (and not the bad bacteria) Consist of non-digestable food ingredients

Examples: banana, beans Active ingredients are fructo-oligosachhrides

(FOS) Available in supplemental form

A Summary ORGAN FUNCTIONS

Mouth Chewing, digestion of starch

Esophagus Passage way

Stomach Food Storage, acid kills bacteria

Some protein digestion

Small Intestine (duodenum, jejunum

and ileum)

Final digestion

Absorption of most of the nutrients

Large Intestine Absorption of water, some minerals, fatty acids

Rectum Elimination

Liver Production of bile

Gallbladder Store and release bile

Pancreas Enzymes and bicarbonate

Gastrointestinal Tract-Recap

GI Problems

Dysphagia Difficulty swallowing

Causes: usually a stroke with subsequent paralysis

Can be temporary or permanent Risk for aspiration

Food entering the lungs Swallow study will determine if at risk Diet therapy may involve liquid, thickened

liquid or pureed foods.

Normal Swallowing and Choking

Larynx rises

Food

Tongue

Esophagus (to stomach)

Trachea (to lungs)Epiglottis closesover larynx

.

Heartburn (GERD) Acid from the stomach to the esophagus due to relaxing of

esophageal sphincter Symptoms: Gnawing pain in the upper chest Causes: obesity, pregnancy Diet Treatment

Smaller, less fatty meals, chew thoroughly, eat slowly Do not lie down after eating, don’t exercise for 2 hours Save drinking fluids for between meals Avoid general list of offending foods

Chocolate, caffeine, peppermint, spearmint, onions garlic, peppers,spicy and greasy foods, acidic foods

Gastroesophageal Reflux (GERD)

Weakened loweresophageal

sphincter

Stomach

Acidic stomachcontents

Diaphragm

Reflux

Esophagus

GERD/Esophageal stricture

Barrett’s esophagus develop as a result of long term exposure to

stomach acid Normal cells that line the esophagus are replaced

by different types of cells Can develop into esophageal cancer

.

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Ulcers (stomach or small intestine) Open sore in lining of stomach or small intestine Symptoms: pain 2 hours after eating, weakness,

anemia, black or bloody stools Cause: Helicobacter pylori, heavy use of aspirin,

excessive acid production in the stomach Diet Treatment: nothing specific, avoid offending

foods, limit caffeine, avoid alcohol, smaller meals

Fig. 3.14

Gallstones Precipitation of cholesterol, bile and calcium

into stones in the gall bladder Symptoms: pain after eating Cause: stones caught in bile ducts Diet Treatment: avoid greasy foods

many can even tolerate greasy foods

Celiac Sprue (gluten intolerance) genetic disorder where eating certain types of

protein, called gluten, sets off an autoimmune response that causes damage to the small intestinal villi. This, in turn, causes the small intestine to lose its ability to absorb the nutrients.

Symptoms: chronic diarrhea, abdominal pain, malnutrition

Cause: genetic, but usually requires a trigger Diet treatment: complete avoidance of barley,

wheat and rye

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Normal vs. Celiac

Constipation Slow movement of fecal matter which increases

fluid reabsorption causing hardening of the feces Symptoms: abdominal distention, pain, discomfort Causes:

Results from ignoring normal urge Antacids, calcium and iron supplements Lack of fiber in diet, sedentary lifestyle

Diet Treatment Plenty of dietary fiber and fluids Foods with laxative type effect: prune juice

Diarrhea Medical definition: For people in the Western

World, the usual amount of water in stool each day is generally no more than 200 ml or 7 oz. (8 oz. = 1 cup). When it is consistently more than this, it is called diarrhea.

Causes: stress, bacteria, certain foods, prescription drugs

Diet Treatment: no specific, focus on rehydration

Hemorrhoids Swollen veins of the rectum and anus Symptoms: pain, bleeding, itching and irritation Cause: added stress and pressure to the vessels due

to poor bowel habits, constipation, diarrhea, pregnancy, obesity, and especially frequent straining when having a bowel movement.

Diet Treatment Adequate fiber and fluid

.

Irritable Bowel Syndrome (IBS)IBS = Crohn’s disease and/or Ulcerative Colitis

3 factors: 1. Altered intestinal motility

2. Increased intestinal sensitivity (abdominal pain)

3. likely due to communication issues between digestive tract and the brain

Majority of cases women in 20’s and 30’s, may have a genetic factor, but 2nd insult or injury must occur

Various severities: 25% severe/ 5% very severe

IBS (Irritable Bowel Syndrome).

Ulcerative Colitis chronic, recurring disease of the large intestine Symptoms: abdominal pain, diarrhea, bleeding Cause: unknown, however may be a defect in the

immune system in which the body's antibodies actually injure the colon. Also could be an unidentified microorganism or germ is responsible for the disease. Likely a combination with genetics.

Diet Treatment: nothing specific, avoid foods that seem to cause more cramping and diarrhea

Limit or avoid caffeine

Crohn’s Disease Chronic, recurrent inflammatory disease of the intestinal tract

Can occur in both small and large intestine Symptoms: abdominal cramps, diarrhea

Long term: anemia and weight loss Other characteristics

Begins in teens and twenties Cause: unknown, however genetics and an immune response

are possible factors Diet Treatment: nothing specific, avoid foods that seem to

cause more cramping and diarrhea Limit or avoid caffeine

Crohn’s.

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Diverticulosis Pouches or bubbles that protrude out from the colon

wall due to extra pressure Symptoms: severe abdominal pain which can

eventually cause total obstruction, bleeding Causes: low fiber diets Diet Treatment:

Short-term: low fiber diet Long-term: follow a high fiber diet, avoid foods with little

seeds and husks Strawberries, corn, popcorn, nuts

Diverticula in the Colon

Diverticulum (singular)

Diverticula (plural)

Diverticula may develop anywhere along the GI tract,but are most common in the colon.

Diverticulosis/Diverticulitis

Colorectal Cancer Uncontrolled cell division that evolve into abnormal

cells Symptoms: blood in stool, change in stool,

abdominal pain, fatigue Causes: genetics, high fat, low fiber diet, excessive

red meat Diet Treatment: Diet high in fruits and vegetables

and avoid excessive amounts of red meat diet has more of a preventative affect