"Digestion and Absorption" Human Nutrition PPT Courseware 2

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"Digestion and Absorption" Human Nutrition PPT Courseware 2

Nutrients in food: protein, sugar, fat

Must be absorbed after digestion

Water, inorganic salts, vitamins

Can be absorbed directly without digestion

cellulose

cannot be digested

The concept of digestion and absorption

Digestion: The process by which food is broken down into absorbable nutrients in the digestive tract.

Absorption: The process in which nutrients, water, inorganic salts, etc. enter the blood circulation through the digestive tract mucosa after digestion.

1. Composition of the digestive system

Digestive tract Oral cavity - pharynx - esophagus - stomach - small intestine - large intestine - anus

Digestive glands: salivary glands, gastric glands, liver, intestinal glands, pancreas, etc.

Changes of steamed buns in the mouth

The mouth is the beginning of the digestive system, with openings ( ), ( ) and ( ).

Question: Is the sweetness of steamed buns related to chewing with teeth and stirring with tongue?

Is the sweetness of steamed buns related to saliva?

hint:

1. Design a set of experiments, some only explore the chewing of teeth and stirring of tongue, some only explore the role of saliva, some explore both chewing of teeth and stirring of tongue, and some explore the role of saliva.

2. Starch is the main ingredient of steamed buns.

3. The oral temperature is about 37℃.

4. Starch has no sweetness, but the maltose formed after starch is decomposed has sweetness.

5. Starch turns blue when exposed to iodine, but maltose does not turn blue when exposed to iodine.

What do you see?

Analyze the results and draw conclusions

Test tube 1: Not turning blue. The starch in the steamed bun crumbs is decomposed into maltose by salivary amylase.

Test tube 2: The steamed buns turn blue. No saliva is added, the starch is not decomposed, and the starch turns blue when it encounters iodine.

Test tube 3: The steamed buns turned blue. The starch in the steamed buns was not completely digested by saliva, and the starch turned blue when exposed to iodine.

discuss

1. What are the differences and connections between the functions of teeth, tongue and saliva?

Chewing by the teeth and stirring by the tongue belong to physical digestion, while the action of saliva belongs to chemical digestion.

2. What substances in the mouth change the properties of starch?

Salivary amylase in saliva

Digestion of food in the mouth

Experimental proof:

Fats and proteins are not digested in the mouth.

Only part of the starch is converted into maltose by the action of salivary amylase.

Maltose also requires further digestion before it can be absorbed.

Conclusion: The oral cavity only plays a preliminary role in digestion

Thinking: Bile is also a digestive juice, but there are no enzymes in bile. What role does bile play in the digestion of food?

Bile emulsifies fat

Emulsification: turning immiscible oil and water into a large number of small oil droplets to increase the contact area between fat and enzymes.

What structural characteristics does the small intestinal wall have that are compatible with its digestive and absorptive functions?

(1) The small intestine has many folds and villi (expanding the internal surface area of ​​the small intestine)

(2) Rich capillaries have only a thin layer of epithelial cells (conducive to absorbing nutrients)

(3) The small intestine is long and contains a variety of digestive juices (food stays for a long time, which is conducive to digestion and absorption of nutrients)

The picture below is the digestion curve of the three major organic compounds in food - protein, fat, and starch in the digestive tract. Please analyze the digestion of the three organic compounds. A represents starch, B represents protein, and C represents fat.

1. Which of the three substances has the most content after digestion?

2. Which section of the digestive tract has no digestive function?

3. At what stage must the three substances reach before they can be broken down into components that can be absorbed?

4. What is the main part of digesting food?

Digestion of food in the stomach

The thick muscle layer of the stomach wall plays a certain role in gastric motility.

Gastric glands secrete gastric juice into the stomach to aid digestion

Gastric juice contains protease and hydrochloric acid, which can initially digest proteins

The stomach can temporarily store food

The small intestine is the main site of digestion

Bile is involved in the digestion of fats

Pancreatic juice is involved in the digestion of proteins, starches and fats

Intestinal juices are involved in the digestion of proteins, starches and fats

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Update Time: 2024-10-17

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