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The process of food assimilation
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“I will give thanks to you because I have been so amazingly and miraculously made.” Psalm 139:14
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“This department offers to the student the means of acquiring a practical knowledge of the workings of the wonderful mechanism of the human body, and furnishes an opportunity of becoming acquainted with the most approved methods in the rational treatment of disease. The study of anatomy, the form and structure of the body; of physiology, the use and functions of the various organs; and of hygiene, the laws that underlie their healthful activities, is pursued from a Biblical and scientific point of view.” RH, October 11, 1898 par. 12
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The process whereby the food we eat is broken down into its basic units so it can be absorbed and assimilated.
Proteins, fats and carbohydrates are broken down to absorbable units.
Absorption is the passage of nutrients across the intestinal wall.
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Where does digestion begin?
When does digestion begin?
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MOUTH: teeth, tongue, salivary glands
ESOPHAGUS: involuntary muscles, mucous
STOMACH: 3 muscle layers, fundus, pyloris
SMALL INTESTINE: duodenum, jejunum, illeum
LARGE INTESTINE: cecum, asscending, transverse, decending, sigmoid, rectum
ANNUS:
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Chewing: breaking down large pieces of food to much smaller ones.
Forms a bolus that is then swallowed.
Food is mixed with salivary enzymes: amylase lingual lipase.
Release of enzymes stimulated by presence of food.
Food should not be washed down.
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Muscular tube to carry the bolus from the mouth to the stomach.
Glottis provides marvelous control to keep food from going to the lungs.
Moved by peristaltic contractions
Humans can swallow standing on their heads!
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Muscular holding tank that can further pulverize poorly chewed food.
Two major sections: fundus, pyloris
Mucosal lining contains 35 million mucus glands.
Gastric glands secrete about 2 liters of gastric juices per day.
Amazing that it does not digest itself! Mucin lubricates and coats stomach wall.
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Stomach is primary site of protein digestion.
HCl: helps pepsin and destroys microorganisms
Enzymes:
Renin: milk protein converted to casein
Gastric lipase: begins break down of fats
Pepsin: pepsinogen is activated by HCl and breaks down the long protein chains
Note: digestive system makes its own enzymes, and does not use those in foods.
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Takes 3-5 hours to digest a meal in the stomach.
Pyloric sphincter controls stomach emptying.
Meal content regulates emptying to a large degree: fat slows the process, CHO speeds it.
Stress can slow or speed this process.
Between meal eating will slow emptying.
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21 feet long and the main site for CHO and FAT digestion.
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21 feet long and the main site for CHO and FAT digestion.
Duodenum (8”) pancreatic juices and bile drain into this part
NaHCO3 neutralizes the HCl from the stomach
Enzymes: Amylase works on CHO, lipase on FAT and trypsin on PRO
Bile: emulsifies and homogenizes FAT molecules.
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21 feet long and the main site for CHO and FAT digestion.
Duodenum (8”) pancreatic juices and bile drain into this part
NaHCO3 neutralizes the HCl from the stomach
Enzymes: Amylase works on CHO, lipase on FAT and trypsin on PRO
Bile: emulsifies and homogenizes FAT molecules.
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Jejunum (upper 40%): secretes digestive juices containing more enzymes for the breakdown of FAT, CHO, and PRO.
Ileum (lower 60%): mixes the food mass further, moves it downward and accomplishes the final breakdown of food.
Majority of assimilation occurs here in the villi and brush border of the walls into the thoracic duct.

Jejunum (upper 40%): secretes digestive juices containing more enzymes for the breakdown of FAT, CHO, and PRO.
Ileum (lower 60%): mixes the food mass further, moves it downward and accomplishes the final breakdown of food.
Majority of assimilation occurs here in the villi and brush border of the walls into the thoracic duct.
Vitamins and minerals require no chemical changes to be absorbed.
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Jejunum (upper 40%): secretes digestive juices containing more enzymes for the breakdown of FAT, CHO, and PRO.
Ileum (lower 60%): mixes the food mass further, moves it downward and accomplishes the final breakdown of food.
Majority of assimilation occurs here in the villi and brush border of the walls into the thoracic duct.
Vitamins and minerals require no chemical changes to be absorbed.
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Concentration of waste through absorbtion of water.
Storage and elimination of waste.
Vit K synthesized by bacteria and absorbed.
Vit B12 synthesized in same way, but not absorbed in significant quantities.
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Healthy individuals can digest almost any kind of food.
Digestion can be improved by adequate chewing, exercise, stress control, etc.
Avoid stimulants and irritants: tea, coffee, spices, condiments, vinegar, pickles, concentrated sweets.
Certain food combinations may cause problems for a limited number of people.
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The larger the meal, the longer the digestion.
Snacks lengthen stomach emptying time.
Digestion slows markedly when sleeping.
Irregular meal times can delay digestion.
Extremes of hot or cold can delay digestion.
Excess liquids can delay digestion.
The orderly process of digestion requires the integrated function of multiple actions many of which are enzyme dependant
Enzymes function in a strictly controlled environment and they will only perform their function if the pH and appropriate cofactors are present
Salivary Glands, Salivary Amylase works on Starch producing maltose, dextrins, maltotriose
Lingual Glands, Lingual lipase works on triglycerides producing fatty acids + 1,2-diacylglycerols
Peptidases of several varieties