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absorp, transport , digest
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Arif Pandega,MD
© 2010 Pearson Education, Inc.
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
© 2010 Pearson Education, Inc.
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
© 2010 Pearson Education, Inc.
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
© 2010 Pearson Education, Inc.
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
© 2010 Pearson Education, Inc.
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
© 2010 Pearson Education, Inc.
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
© 2010 Pearson Education, Inc.
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
© 2010 Pearson Education, Inc.
Nutrient Absorption Some absorption takes place in the stomach and large
intestine• Water and salt are absorbed in the large intestine
© 2010 Pearson Education, Inc.
• 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
© 2010 Pearson Education, Inc.
• 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