Digestion and Absorption of Carbohydrates Lipids and Proteins

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Polysaccharides and polypeptides are hydrolyzed into their subunits. These subunits enter the epithelial cells of the intestinal villi and are secreted into blood capillaries. Fat is emulsified by the action of bile salts, hydrolyzed into fatty acids and monoglycerides,and absorbed into the intestinal epithelial cells. Once inside the cells, triglycerides are resynthesized and combined with proteins to form particles that are secreted into the lymphatic fluid.

The caloric (energy) value of food is derived mainly from its content of carbohydrates, lipids, and proteins. In the average American diet, carbohydrates account for approximately 50% of the total calories, protein accounts for 11% to 14%, and lipids make up the balance. These food molecules consist primarily of long combinations of subunits (monomers) that must be digested by hydrolysis reactions into free monomers before absorption can occur. The characteristics of the major digestive enzymes are summarized in table 18.7.

Clinical Investigation Clues

Remember that Alan's pain below his right scapula was triggered by eating peanut butter and bacon, but not by eating fish or skinned chicken.

What component of the food triggered Alan's pain? What physiological mechanism is involved in this process?

Table 18.7 Characteristics of the Major Digestive Enzymes

Enzyme

Site of Action

Source

Substrate

Optimum pH

Product(s)

Salivary amylase

Mouth

Saliva

Starch

6.7

Maltose

Pepsin

Stomach

Gastric glands

Protein

1.6-2.4

Shorter polypeptides

Pancreatic amylase

Duodenum

Pancreatic juice

Starch

6.7-7.0

Maltose, maltriose, and oligosaccharides

Trypsin, chymotrypsin, carboxypeptidase

Small intestine

Pancreatic juice

Polypeptides

8.0

Amino acids, dipeptides, and tripeptides

Pancreatic lipase

Small intestine

Pancreatic juice

Triglycerides

8.0

Fatty acids and monoglycerides

Maltase

Small intestine

Brush border of epithelial cells

Maltose

5.0-7.0

Glucose

Sucrase

Small intestine

Brush border of epithelial cells

Sucrose

5.0-7.0

Glucose + fructose

Lactase

Small intestine

Brush border of epithelial cells

Lactose

5.8-6.2

Glucose + galactose

Aminopeptidase

Small intestine

Brush border of epithelial cells

Polypeptides

8.0

Amino acids, dipeptides, tripeptides

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Responses

  • stephanie sankt
    What is the carbohydrates,protein, and lipids for peanut butter?
    8 years ago
  • juan meier
    What is the meuchanism of carbohydrates, proteins and lipids absorption?
    8 years ago
  • ASMERET LUWAM
    What are the steps involved in absorption of carbs, lipids & proteins?
    7 years ago
  • LOLA HUGHES
    What is digestive system digestion and absorption of carbohydtayes lipids and protein?
    3 years ago
  • semrawit
    What is digestion and describe mechanism and absorption of carbohydrates proteins and lipids?
    2 years ago
  • sara
    How carbohydrates, fats, and proteins are digested and absorbed?
    2 years ago
  • orsola boni
    What is the action of intestinal juice on carbohydrates?
    1 year ago
  • lidia
    Where are carbs lipids and proteins primarily absorbed and digested?
    1 year ago
  • quirico
    What is carbohydrates protiens fats ppt human physiology?
    10 months ago
  • ALEXANDRA
    Where are carbs lipids protein digest and absorb?
    10 months ago
  • YORDA
    What enxymes digest carbohydrates, lipids and proteins?
    10 months ago
  • milly
    How digestion and absorption of carbs, proteins, and lipids is accomplished?
    9 months ago
  • Constance
    How do the absorbtion of carbohydrates and proteins differ in digestion?
    8 months ago
  • manuel
    How do you know what helped digest lipids carbohydrates and protein in the physiology lab?
    2 months ago

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