3& 4: Nutrition and Digestion System; Digestive Process Notes | Study RAS RPSC Prelims Preparation - Notes, Study Material & Tests - UPSC

UPSC: 3& 4: Nutrition and Digestion System; Digestive Process Notes | Study RAS RPSC Prelims Preparation - Notes, Study Material & Tests - UPSC

The document 3& 4: Nutrition and Digestion System; Digestive Process Notes | Study RAS RPSC Prelims Preparation - Notes, Study Material & Tests - UPSC is a part of the UPSC Course RAS RPSC Prelims Preparation - Notes, Study Material & Tests.
All you need of UPSC at this link: UPSC



Nutrition is the process of acquiring energy and food materials. Nutrition is the provision, to cells and organisms, of the materials necessary (in the form of food) to support life. The human body contains chemical compounds, such as water, carbohydrates (sugar, starch, and fibre), amino acids (in proteins), fatty acids (in lipids), and nucleic acids (DNA and RNA). These compounds in turn consist of elements such as carbon, hydrogen, oxygen, nitrogen, phosphorus, calcium, iron, zinc, magnesium, manganese, and so on. All of these chemical compounds and elements occur in various forms and combinations (e.g. hormones, vitamins, phospholipids, hydroxyapatite), both in the human body and in the plant and animal organisms that humans eat.

What is Nutrient-A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy.

Classification of Nutrient-:  There are six major classes of nutrients- Carbohydrates, protein, vitamins, minerals, fats and water. 



Nature- A Carbohydrate is an organic compound that consists only of Carbon, Hydrogen and Oxygen. It is divided into four chemical groupings: monosaccharide’s, disaccharides, oligosaccharides, and polysaccharides. For example, blood sugar is the monosaccharide glucose, table sugar is the disaccharide sucrose, and milk sugar is the disaccharide lactose.

Function- Carbohydrates perform numerous roles in living organisms. Polysaccharides serve for the storage of energy (e.g., starch and glycogen), and as structural components (e.g., cellulose in plants and chitin in arthropods). The 5-carbon monosaccharide ribose is an important component of coenzymes (e.g., ATP, FAD, and NAD) and the backbone of the genetic molecule known as RNA. The related deoxyribose is a component of DNA. Saccharides and their derivatives include many other important biomolecules that play key roles in the immune system, fertilization, preventing pathogenesis, blood clotting, and development.

Source-Starch (such as cereals, bread, and pasta) or simple carbohydrates, such as sugar (found in candy, jams, and desserts).



Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Fats can be categorized into saturated fats and unsaturated fats.

Function-Fat provides needed energy.  It is difficult to eat the large amounts of food in a very low fat diet to get all the energy you need. 

  • Fat is needed to prevent essential fatty acid deficiency.
  • Fat is needed so your body can absorb the fat soluble vitamins A, S, E, K, and prevent deficiencies of these vitamins.
  • Fat provides flavor and texture to help prevent food from being bland and dry.
  • Fat may help your body produce endorphins (natural substances in the brain that produce pleasurable feelings).

Source- Mutton, Milk, Egg Etc. are rich in fat.



Just like vitamins, minerals help your body grow, develop, and stay healthy. The body uses minerals to perform many different functions — from building strong bones to transmitting nerve impulses. Some minerals are even used to make hormones or maintain a normal heartbeat.

Function-Minerals such as calcium, zinc and potassium are needed by the body for a number of processes such as breaking down, digesting and releasing energy from food, strengthening bones, nails and teeth and regulating fluid and cholesterol in the body. There are 16 essential minerals required by the body, which are divided into macro minerals, or minerals that are needed in fairly large quantities, micro minerals, which are needed in smaller quantities and trace elements, which are needed in minute quantities but which are still vital for the body's well-being.

The benefits of some minerals cannot be seen without the presence of certain minerals and vice versa, for example, vitamin D is required in order to absorb calcium and when foods containing vitamin C are consumed, iron is absorbed more efficiently. A short description of some important minerals has been given:-



Calcium is the top macro mineral when it comes to your bones. This mineral helps build strong bones, so you can do everything from standing up straight to scoring that winning goal. It also helps build strong, healthy teeth, for chomping on tasty food.

Dairy products, such as milk, cheese, and yogurt, canned salmon and sardines with bones, leafy green vegetables, such as broccoli, calcium-fortified foods — from orange juice to cereals and crackers are rich source of Calcium.



The body needs iron to transport oxygen from your lungs to the rest of your body. Your entire body needs oxygen to stay healthy and alive. Iron helps because it's important in the formation of haemoglobin (say: HEE-muh-glo-bun), which is the part of your red blood cells that carries oxygen throughout the body. Meat, especially red meat, such as beef, tuna and salmon, eggs, beans, baked potato with skins, dried fruits, like raisins, leafy green vegetables, such as broccoli, whole and enriched grains, like wheat or oats are examples of food which are rich in Iron.



Potassium keeps your muscles and nervous system working properly. Potassium helps make sure the amount of water is just right between cells and body fluids.

Bananas, tomatoes, potatoes and sweet potatoes, with skins, green vegetables, such as spinach and broccoli, citrus fruits, like oranges, low-fat milk and yogurt, legumes, such as beans, split peas, and lentils are good source of Potassium.



Zinc helps your immune system, which is your body's system for fighting off illnesses and infections. It also helps with cell growth and helps heal wounds, such as cuts. Beef, pork, and dark meat chicken, nuts, such as cashews, almonds, and peanuts, legumes, such as beans, split peas, and lentils are rich source of Zinc.

When people don't get enough of these important minerals, they can have health problems. For instance, too little calcium — especially when you're a kid — can lead to weaker bones. Some kids may take mineral supplements, but most kids don't need them if they eat a nutritious diet. So eat those minerals and stay healthy!



Protein-Proteins are large biological molecules consisting of one or more chains of amino acids.

Function- Proteins perform a vast array of functions within living organisms, including catalyzing metabolic reactions, replicating DNA, responding to stimuli, and transporting molecules from one location to another.

Source-Meats, milk, fish and eggs, as well as in plant sources such as whole grains, pulses, legumes, soy, fruits, nuts and seeds are good source of protein.



A Vitamin is an organic compound required by an organism as a vital nutrient in limited amounts. An organic chemical compound (or related set of compounds) is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet.

Function: Vitamins have diverse biochemical functions. Some have hormone-like functions as regulators of mineral metabolism (such as vitamin D), or regulators of cell and tissue growth and differentiation (such as some forms of vitamin A). Others function as antioxidants (e.g., vitamin E and sometimes vitamin C). The largest number of vitamins such as B complex vitamins functions as precursors for enzyme cofactors that help enzymes in their work as catalysts in metabolism.



Function- Water is a carrier, distributing essential nutrients to cells, such as minerals, vitamins and glucose.  Its five top functions are as following:-

   1) Cell life,

   2) Chemical and metabolic reactions,

   3) Transport of nutrients 

   4) Body temperature regulation,

   5) Elimination of waste, 




The human digestive system is a complex series of organs and glands that processes food. In order to consume the food we eat, our body has to break the food down into smaller molecules that it can process; it also has to excrete waste.

The digestive system is essentially a long, twisting tube that runs from the mouth to the anus, plus a few other organs (like the liver and pancreas) that produce or store digestive chemicals.




The digestive process begins in the mouth. Food is partly broken down by the process of chewing and by the chemical action of salivary enzymes (these enzymes are produced by the salivary glands and break down starches into smaller molecules).



After being chewed and swallowed, the food enters the oesophagus. The oesophagus is a long tube that runs from the mouth to the stomach. It uses rhythmic, wave-like muscle movements (called peristalsis) to force food from the throat into the stomach.



The stomach is a large, sack-like organ that releases the gastric acid to digest the food. Food in the stomach that is digested in the stomach and mixed with stomach acids is called chime.



After being in the stomach, food enters the duodenum, the first part of the small intestine. It then enters the jejunum and then the ileum (the final part of the small intestine). In the small intestine, bile (produced in the liver and stored in the gall bladder), pancreatic enzymes, and other digestive enzymes produced by the inner wall of the small intestine help in the breakdown of food.



After passing through the small intestine, food passes into the large intestine. In the large intestine, some of the water and electrolytes (chemicals like sodium) are removed from the food. Many microbes (bacteria like Bactericides, Lactobacillus acidophilus, Escherichia coli, and Klebsiella) in the large intestine help in the digestion process. The first part of the large intestine is called the cecum (the appendix is connected to the cecum). Food then travels upward in the ascending colon. The food travels across the abdomen in the transverse colon, goes back down the other side of the body in the descending colon, and then through the sigmoid colon. Solid waste is then stored in the rectum until it is excreted via the anus.



In general, enzymes are large protein-based molecules that help chemical reactions take place faster than they otherwise would, explain Reginald Garrett and Charles Grisham in their book "Biochemistry." Your body cells run a wide array of chemical reactions, nearly all of which are enzyme-dependent. Specifically, digestive enzymes help you break down large nutrient molecules in your food into smaller nutrient molecules that you can absorb.




Pepsin is secreted by the gastric glands and is responsible for breaking down proteins into smaller pieces, called polypeptides. Pepsin is secreted in its inactive form, known as pepsinogen, and is converted into its active form in the acidic environment of the stomach. The acidic environment of the stomach also alters the shape of proteins, allowing pepsin access to break the peptide bonds holding them together. Pepsin's role in breaking protein down into polypeptides allows enzymes in the small intestines to further break down these polypeptides into amino acids for use by the body, according to the University of Cincinnati Clermont College.

Protein digestion is initiated by pepsin in the stomach but is finished by proteases in the small intestines. Proteases are secreted by the pancreas and function to break down polypeptides, or broken down proteins, into amino acids -- the building blocks critical to life. Trypsin and chymotrypsin are the two primary proteases secreted by the pancreas, according to Colorado State University.



Bile is a digestive fluid primarily involved in the digestion of fats. Secreted by the liver and stored in the gallbladder, bile is a complex mixture of bile acids, potassium and sodium, cholesterol and bilirubin -- a byproduct from the breakdown of red blood cells. In the small intestine, the bile acids break down dietary fat and fat-soluble vitamins into fatty acid components, which can then be absorbed by the body. Bile acids are synthesized from cholesterol and thus play a large role in the breakdown and elimination of cholesterol from the body.



 Abdomen - the part of the body that contains the digestive organs. In human beings, this is between the diaphragm

 Pelvis alimentary canal - the passage through which food passes, including the mouth, esophagus, stomach, intestines, and anus.

 Anus - the opening at the end of the digestive system from which feces (waste) exits the body.

 Appendix - a small sac located on the cecum.

 Ascending colon - the part of the large intestine that run upwards; it is located after the cecum.

 Bile - a digestive chemical that is produced in the liver, stored in the gall bladder, and secreted into the small intestine.

 Cecum - the first part of the large intestine; the appendix is connected to the cecum.

 Chyme - food in the stomach that is partly digested and mixed with stomach acids. Chyme goes on to the small intestine for further digestion.

 Descending colon - the part of the large intestine that run downwards after the transverse colon and before the sigmoid colon.

 Digestive system - (also called the gastrointestinal tract or gi tract) the system of the body that processes food and gets rid of waste.

 Duodenum - the first part of the small intestine; it is c-shaped and runs from the stomach to the jejunum.

 Epiglottis - the flap at the back of the tongue that keeps chewed food from going down the windpipe to the lungs. When you swallow, the epiglottis automatically closes. When you breathe, the epiglottis opens so that air can go in and out of the windpipe.

 Esophagus - the long tube between the mouth and the stomach. It uses rhythmic muscle movements (called peristalsis) to force food from the throat into the stomach.

 Gall bladder - a small, sac-like organ located by the duodenum. It stores and releases bile (a digestive chemical which is produced in the liver) into the small intestine.

 Gastrointestinal tract - (also called the GI tract or digestive system) the system of the body that processes food and gets rid of waste.

 Ileum - the last part of the small intestine before the large intestine begins.

 Intestines - the part of the alimentary canal located between the stomach and the anus.

 Jejunum - the long, coiled mid-section of the small intestine; it is between the duodenum and the ileum.

 Liver - a large organ located above and in front of the stomach. It filters toxins from the blood, and makes bile (which breaks down fats) and some blood proteins.

 Mouth - the first part of the digestive system, where food enters the body. Chewing and salivary enzymes in the mouth are the beginning of the digestive process (breaking down the food).

 Pancreas - an enzyme-producing gland located below the stomach and above the intestines. Enzymes from the pancreas help in the digestion of carbohydrates, fats and proteins in the small intestine.

 Peristalsis - rhythmic muscle movements that force food in the oesophagus from the throat into the stomach. Peristalsis is involuntary - you cannot control it. It is also what allows you to eat and drink while upside-down.

 Rectum - the lower part of the large intestine, where faces are stored before they are excreted.

 Salivary glands - glands located in the mouth that produce saliva. Saliva contains enzymes that break down carbohydrates (starch) into smaller molecules.

 Sigmoid colon - the part of the large intestine between the descending colon and the rectum.

 Stomach - a sack-like, muscular organ that is attached to the oesophagus. Both chemical and mechanical digestion takes place in the stomach. When food enters the stomach, it is churned in a bath of acids and enzymes.

 Transverse colon - the part of the large intestine that runs horizontally across the abdomen.

The document 3& 4: Nutrition and Digestion System; Digestive Process Notes | Study RAS RPSC Prelims Preparation - Notes, Study Material & Tests - UPSC is a part of the UPSC Course RAS RPSC Prelims Preparation - Notes, Study Material & Tests.
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