Digestion and absorption of nutrients (Carbohydrates, proteins etc.) in the stomach and intestines.

WEEK : 2

 

SUBJECT: FOOD AND NUTRITION

 

CLASS: SS 1

 

TOPIC:  The Digestive system

 

PREVIOUS KNOWLEDGE :

The Digestive system: (i) Meaning of Digestion (ii) Definition of simple metabolic terms e.g. Enzymes absorption. (iii)Digestion and absorption of nutrients (Carbohydrates, proteins etc.) in the mouth and esophagus.

 

BEHAVIOURAL OBJECTIVES : At the end of the lesson , learners will be able to

  • explain the process of the digestion of food in the body
  • state the Function of enzymes in the body 
  • highlight the role of water in digestion and absorption of food

 

 

CONTENT:   (iv) Digestion and absorption of nutrients (Carbohydrates, proteins etc.) in the stomach and intestines.

(v) Functions of enzymes e.g. ptyalin, amylase, trypsin, maltase etc.

(vi) The role of water in digestion and absorption.

Sub-topic 1:

DIGESTION AND ABSORPTION OF NUTRIENTS (CARBOHYDRATES, PROTEINS ETC.)IN THE STOMACH AND INTESTINES.

  1. THE DUODINUM

From the stomach the products of digestion are passed into the duodenum. The pancreatic juice from the pancreas is secreted into the duodenum and the bile from the liver are emptied into the duodenum through the bile duct. The bile does not contain any enzyme rather it emulsifies the fats or oil present in the chyme. The pancreatic juice on the other hand contains carbohydrate, protein and fat splitting enzymes. These enzymes are:

Amylase – converts starch to maltose

Trypsin – converts protein to peptide and peptones.

Lipase – converts fats to fatty acid and glycerol

Digestion in the Small Intestine

The ileum or small intestine is a highly effective digestive organ. By the time food leaves the stomach digestion of protein and carbohydrates has begun and the action gain momentum in the small intestine, the pancreas contributes digestive juice by way of ducts leading into duodenum. The pancreatic juice contains enzymes that act all on the three energy nutrients.

 

Sub-topic 2: ABSORPTION OF DIGESTED NUTRIENTS IN SMALL INTESTINES:

Definition of Absorption:

The process by which the end products of digestion pass through the lining of the digestion tract is called absorption. These end products are now absorbed into the body’s circulatory system where they are utilized.

Function of enzymes:

  • Ptyalin: this enzyme breaks down the starch of the carbohydrate foods in the mouth to different disaccharides.
  • Amylases: also known as carbohydrates – splitting enzymes. They breakdown the various disaccharides (maltose, lactose and sucrose) into their respective monosaccharide units.
  • Maltase’s: these acts on maltose and converts them to glucose units.
  • Lactases: they act on lactose and convert them to a unit of glucose and a unit of galactoses.
  • Sucrose’s: they act on sucrose and convert them to a unit of glucose and a unit of fructose
  • Rennin: these converts soluble protein in milk known as caseinogens into insoluble form called casein.
  • Pepsins: they convert the other protein into smaller peptides and pepsinogen.
  • Trypsin: this breakdown the protein completely into amino acids. Chymotrypsin – it supplement the action of trypsin in breaking down.
  • Lipases: these are also known as fat splitting enzymes. The breakdown emulsifies fats into glycerol and fatty acids.

The bile is not digestive enzymes; it emulsifies fats so that enzymes can break it. This process of digestion ends in small intestines. The simple sugar and amino acid enter the blood system indirectly through the lymphatic system. Absorption takes place through the inner lining of the small intestine called villi.

 

Sub-topic 3: THE ROLE OF WATER IN DIGESTION AND ABSORPTION.

Water is very essential to all living things. It is present in animals and plants cells. Water serves various functions e.g.

  • It helps in the digestion of foods.
  • It serves as medium for the movement of nutrients from one part of the body to another.
  • Water helps in the process of excretion of waste matter from the body.

General Evaluation:

  1. The semi-liquid, partially digested food that travels through the intestinal tracts is called _____. (a) bile (b) lymph (c) chyme (d) secret
  2. The muscular contraction that moves food through the digestive system is called ____. (a)hydrolysis (b) sphincter (c) peristalsis (d) bowl movement
  3. The main function of bile is to _____. (a) emulsifying fat (b) catalyze hydrolysis (c) slow protein digestion (d) neutralize stomach activity
  4. The pancreas neutralizes stomach acid in the small intestine by secreting ______. (a) bile (b)mucus (c) enzymes (d) bicarbonates
  5. The end point of digestion is at the (a) mouth (b) stomach (c) small intestine (d) large intestine

Essay:

  1. Name the enzymes found in the small intestine and specify their respective functions.
  2. Explain briefly the absorption of materials in the small intestine.
  3. State the functions of the following enzymes:
    • Pepsin
    • Rennin
    • Ptyalin
    • Trypsin
  1. Describe digestion process of carbohydrates and protein in small intestines.
  2. What are the functions of the enzymes on digestion process in the small intestine?

(i) Anylase (ii) Trypsin

 

REFERENCE BOOKS:

Food and Nutrition for Senior Secondary Schools Book 1 by F. A. Bakare, N. M. Eze, H. B. Bala

Exam focus, food and nutrition for Senior Secondary Schools, WASSCE and SSCE

 

 

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