Digest,Absorp,Transport

Arif Pandega,MD

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What Are…?

Digestion: The process of breaking down food into individual molecules small enough to be absorbed through the intestinal wall

Absorption: The process of moving nutrients from the gastrointestinal (GI) tract into the bloodstream

Transport: The process of moving absorbed nutrients throughout the body through the circulatory and lymph systems

Elimination: The excretion of undigested and unabsorbed food through the feces

Figure 3.1

Figure 3.4

The stomach usually empties completely within3-4 hours after a meal. The rate of gastric emptying depends on the contents of the stomach as well as duodenal factors

Concentration of hydrogen ions in a solution

The more hydrogen ions (H–) the more acidic

The more hydroxide ions (OH–) the more basic

Villi require proper nutrients or will deteriorate and flatten causing malabsorption

Figure 3.5

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Small Intestine Most digestion occurs in the small intestines Extends from the pyloric sphincter to the ileocecal valve Contains three sections

• Duodenum• Jejunum• Ileum

Takes 3 to 10 hours for food to traverse the small intestine

Figure 3.6

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Large Intestine Site of water, sodium, potassium, and chloride absorption Bacteria produces vitamin K, thiamin, riboflavin, biotin,

and vitamin B12

• Only biotin and vitamin K can be absorbed In the large intestine, 1 liter of fluid material is gradually

reduced to 200 grams of brown fecal material• Brown color is due to unabsorbed iron mixed with

yellowish-orange substance called bilirubin• Greater the iron content, the darker the feces

Figure 3.1

Final stage of defecation is influenced by age, diet, prescription medications, health, and abdominal muscle tone

Figure 3.7

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The Accessory Organs Liver

• Is the first organ to receive absorbed nutrients from the portal vein

• Is essential in carbohydrate metabolism• Produces proteins• Manufactures bile salts that are used to digest fats• Is the site of alcohol metabolism• Removes and degrades toxins and excess hormones

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The Accessory Organs Gallbladder

• Receives bile from the liver via common hepatic duct• Releases bile into small intestine via common bile duct

Pancreas• Endocrine function – releases hormones to maintain

blood glucose levels• Exocrine function – secretes digestive enzymes into the

small intestine

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Propelling Food through the GI Tract Food is propelled through the GI tract by synchronized

contractions of the diagonal, circular, and longitudinal muscles

Two primary contractions are• Peristalsis – Squeezes food through the GI tract• Segmentation – Shifts food back and forth along the GI

tract- Allows contact with surface of small and large

intestine and increase absorption• Dependent on coordination between muscles, nerves, and

hormones

Figure 3.8

Figure 3.10

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Nutrient Absorption Majority of absorption takes place in the small intestine

• Nutrients are absorbed via- Passive diffusion – nutrients move from high

concentration to low concentration; no energy is required

- Facilitated diffusion – nutrients move from high concentration to low concentration with the help of a carrier protein; no energy is required

- Active transport – nutrients move from low concentration to high concentration with the help of a carrier protein, energy is required

- Endocytosis – cell forms a vesicle to surround and engulf a nutrient

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Nutrient Absorption Some absorption takes place in the stomach and large

intestine• Water and salt are absorbed in the large intestine

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• Water-soluble nutrients

GI tract Capillaries

• Water-soluble nutrients

Hepatic Portal Vein • Water-

soluble nutrients

Liver

Transportation of Nutrients Throughout the Body Nutrients are absorbed into the circulatory or lymphatic

system• Water-soluble nutrients are absorbed into the circulatory

system- Carbohydrates, amino acids, and water-soluble

vitamins

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• Fat-soluble nutrients

Lymph Capillaries

• Fat-soluble nutrients

Lymphatic vessels • Fat-

soluble nutrients

Thoracic Duct

Transportation of Nutrients Throughout the Body

• Fat-soluble nutrients are absorbed into the lymphatic system- Fat-soluble vitamins, long-chain fatty acids, and

proteins too large to be transported via the capillaries