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Digestion. Digestion. Digestion is the process of breaking down foods into nutrients to prepare for absorption while overcoming 7 challenges. Digestion.

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  • Digestion is the process of breaking down foods into nutrients to prepare for absorption while overcoming 7 challenges.
  • Anatomy of the Digestive Tract – The gastrointestinal (GI) tract is the flexible muscular tube from mouth to anus. The lumen is the inner space of the tract.
the start of the process the mouth
The start of the process – the mouth:
  • The digestive process begins in the mouth. Food is partly broken down by the process of chewing (mastication) and by the chemical action of salivary enzymes (amylase) These enzymes are produces by the salivary glands and break down starches into smaller molecules.
on the way to the stomach the esophagus
On the way to the stomach: the esophagus
  • After being chewed and swallowed, the food enters the esophagus. The esophagus is a long tube that runs from the mouth to the stomach. It uses rhythmic, wave-like muscle movements (called peristalsis) to force food from the throat into the stomach. This muscle movement gives us the ability to eat or drink even when we're upside-down.
in the stomach
In the stomach -
  • The stomach is a large, sack-like organ that churns the food and bathes it in a very strong acid (gastric acid).
  • Food in the stomach that is partly digested and mixed with stomach acids is called chyme
in the small intestine
In the small intestine
  • After being in the stomach, food enters the duodenum, the first part of the small intestine.
  • It then enters the jejunum and then the ileum (the final part of the small intestine).
  • In the small intestine, bile (produced in the liver and stored in the gall bladder), pancreatic enzymes, and other digestive enzymes produced by the inner wall of the small intestine help in the breakdown of food.
in the large intestine
In the large intestine
  • After passing through the small intestine, food passes into the large intestine. In the large intestine, some of the water and electrolytes (chemicals like sodium) are removed from the food.
  • Many microbes (bacteria like Bacteroides, Lactobacillus acidophilus, Escherichia coli, and Klebsiella) in the large intestine help in the digestion process.
in the large intestine15
In the large intestine
  • The first part of the large intestine is called the cecum (the appendix is connected to the cecum).
  • Food then travels upward in the ascending colon. The food travels across the abdomen in the transverse colon, goes back down the other side of the body in the descending colon, and then through the sigmoid colon.
the end of the process
The end of the process
  • Solid waste is then stored in the rectum until it is excreted via the anus.
  • The Secretions of Digestion
    • Includes digestive enzymes that act as catalysts in hydrolysis reactions
    • Saliva from the salivary glands moistens foods
    • Gastric juice from the gastric glands includes hydrochloric acid. The goblet cells of the stomach wall secrete mucus to protect the walls of the stomach from the high acidity levels that are measured by pH units.
  • The Secretions of Digestion
    • Pancreatic juice contains intestinal enzymes (carbohydrase, lipase, protease) and bicarbonate.
    • Bile is produced by the liver, stored in the gall bladder, and acts as an emulsifier to suspend fat.
  • The Final Stage
    • Energy-yielding nutrients are disassembled for absorption.
    • Vitamins, minerals and water can be absorbed.
    • Undigested residues, including some fibers, continue through the digestive tract and form stool.
    • Recycling of usable materials
  • The enormous surface area of the small intestine facilitates nutrient absorption.
  • Nutrients can be absorbed through simple diffusion, facilitated diffusion, or active transport.





Some nutrients (such as water and small lipids) are absorbed by simple diffusion. They cross into intestinal cells freely.

Some nutrients (such as the water-soluble vitamins) are absorbed by facilitated diffusion. They need a specific carrier to transport them from one side of the cell membrane to the other. (Alternatively, facilitated diffusion may occur when the carrier changes the cell membrane in such a way that the nutrients can pass through.)

Some nutrients (such as glucose and amino acids) must be absorbed actively. These nutrients move against a concentration gradient, which requires energy.

Carrier loads nutrient on outside of cell . . .

Outside cell

Carrier loads nutrient on outside of cell . . .

Cell membrane

Inside cell

. . . and then releases it on inside of cell.

. . . and then releases it on inside of cell.

Stepped Art

Fig. 3-9, p. 81

  • Anatomy of the Absorptive System
    • Villi are the fingerlike projections within the folds of the small intestine that move in a wave-like pattern to trap nutrients.
    • Microvilli are the microscopic hairlike projections on each villi.
    • Crypts are the tubular glands that lie between the intestinal villi.
    • Goblet cells are located between the villi and secrete a protective thick mucus.
  • A Closer Look at the Intestinal Cells
    • Specialization of the cells to absorb different nutrients
    • “Food combining” which emphasizes separating food for digestive purposes is a myth.
    • Preparing Nutrients for Transport
      • Water-soluble nutrients and small products of fat digestion are released to the bloodstream.
      • Fat-soluble vitamins and larger fats form chylomicrons and are released to the lymphatic system.
  • Food becomes lodged in the trachea.
  • The larnyx cannot make sounds.
  • The Heimlich maneuver may need to be used.
  • Strategies
    • Small bites
    • Chew thoroughly.
    • Don’t talk or laugh with food in the mouth.
    • Don’t eat when breathing hard.
  • Body’s adaptive mechanism
  • Dehydration is a concern.
  • May be self-induced as in eating disorders
  • Frequent, loose, watery stools
  • Irritable bowel syndrome or colitis is one of the common GI disorders.
  • Strategies
    • Rest
    • Drink fluids
    • Medical help is needed if it persists.
thought of the day
Thought of the day

Never, under any circumstances, take a sleeping pill and a laxative onthe same night

  • Defecation habits are different among people.
  • Many causes are possible.
  • Hemorrhoids may be a problem.
  • Diverticulosis is a condition in which the intestinal walls weaken and bulge. The bulging pockets are called diverticula. Diverticulitis is a worsened condition and requires intervention.
  • Use of laxatives, enemas and mineral oil may not be necessary with lifestyle changes.
  • Colonic irrigation is the internal washing of the large intestine and can be hazardous.
  • Strategies
    • High-fiber diet
    • Increased fluids
    • Exercise regularly.
    • Respond quickly to the urge to defecate.
belching and gas
Belching and Gas
  • Strategies
    • Eat slowly.
    • Chew thoroughly.
    • Relax while eating.
    • Watch bothersome foods.
  • Hiccups are triggered by eating or drinking too fast.
heartburn and acid indigestion
Heartburn and “Acid Indigestion”
  • Gastroesophageal reflux is the backward flow of stomach contents into the esophagus.
  • Antacids and acid controllers may help indigestion.
heartburn and acid indigestion41
Heartburn and “Acid Indigestion”
  • Strategies
    • Small meals
    • Liquids between meals
    • Sit up while eating.
    • Wait 1 hour after eating before lying down.
    • Wait 2 hours after eating before exercising.
    • Refrain from tight-fitting clothing.
    • Avoid bothersome foods.
    • Refrain from tobacco use.
    • Lose weight if overweight.
  • Peptic ulcers can be gastric or duodenal.
  • Strategies
    • Take prescribed medicine.
    • Avoid caffeine- and alcohol-containing foods.
    • Minimize aspirin and ibuprofen use.
    • No smoking.