10: Digestive System - Biology

10: Digestive System - Biology

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This chapter outlines the structure and function of the gastrointestinal tract and accessory organs of digestion. It explains the processes of peristalsis, mechanical and chemical digestion of food, and absorption of nutrients. The chapter also describes several disorders of the gastrointestinal tract.

  • 10.1: Case Study - Food Processing
    Angela and Mariah are college students who met in physics class. They decide to study together for their upcoming midterm, but first they want to grab some lunch. Angela says there is a particular restaurant she would like to go to because they are able to accommodate her dietary restrictions. Mariah agrees and they head to the restaurant.
  • 10.2: Introduction to the Digestive System
    The digestive system consists of organs that break down food, absorb its nutrients, and expel any remaining waste. Organs of the digestive system are shown in the following figure. Most of these organs make up the gastrointestinal (GI) tract. Food actually passes through these organs. The rest of the organs of the digestive system are called accessory organs. These organs secrete enzymes and other substances into the GI tract, but food does not actually pass through them.
  • 10.3: Digestion and Absorption
    Digestion of food is a form of catabolism, in which the food is broken down into small molecules that the body can absorb and use for energy, growth, and repair. Digestion occurs when food is moved through the digestive system. It begins in the mouth and ends in the small intestine. The final products of digestion are absorbed from the digestive tract, primarily in the small intestine. There are two different types of digestion that occur in the digestive system: mechanical digestion and chemica
  • 10.4: Upper Gastrointestinal Tract
    Besides the esophagus, organs of the upper gastrointestinal (GI) tract include the mouth, pharynx, and stomach. These hollow organs are all connected to form a tube through which food passes during digestion. The only role in digestion played by the pharynx and esophagus is to move food through the GI tract. The mouth and stomach, in contrast, are organs where digestion, or the breakdown of food, also occurs. In both of these organs, food is broken into smaller pieces and broken down chemically.
  • 10.5: Lower Gastrointestinal Tract
    Most of the bacteria that normally live in the lower gastrointestinal (GI) tract live in the large intestine. They have important and mutually beneficial relationships with the human organism. We provide them with a great place to live, and they provide us with many benefits, some of which you can read about below. Besides the large intestine and its complement of helpful bacteria, the lower GI tract also includes the small intestine. The latter is arguably the most important organ of the digest
  • 10.6: Accessory Organs of Digestion
    Accessory organs of digestion are organs that secrete substances needed for the chemical digestion of food but through which food does not actually pass as it is digested. Besides the liver, the major accessory organs of digestion are the gallbladder and pancreas. These organs secrete or store substances that are needed for digestion in the first part of the small intestine, the duodenum, where most chemical digestion takes place.
  • 10.7: Disorders of the Gastrointestinal Tract
    Inflammatory bowel disease is a collection of inflammatory conditions primarily affecting the intestines. The two principal inflammatory bowel diseases are Crohn's disease and ulcerative colitis. Unlike Crohn's disease, which may affect any part of the GI tract and the joints as well as the skin, ulcerative colitis mainly affects just the colon and rectum. Both diseases occur when the body's own immune system attacks the digestive system.
  • 10.8: Case Study Celiac Conclusion and Chapter Summary
    The garlic bread stuffed with spaghetti shown above may or may not look appetizing to you, but for people with celiac disease, it is certainly off limits. Bread and pasta are traditionally made with wheat, which contains proteins called gluten. As you learned in the beginning of the chapter, even trace amounts of gluten can damage the digestive system of people with celiac disease. When Angela and Mariah met for lunch, Angela chose a restaurant that she knew could provide her with gluten-free fo

Thumbnail: Scheme of digestive tract, with esophagus marked. ( CC BY-SA 2.5; Olek Remesz).

10 Interesting Facts About Your Digestive System

Robert Burakoff, MD, MPH, is board-certified in gastroentrology. He is the vice chair for ambulatory services for the department of medicine at Weill Cornell Medical College in New York, where he is also a professor. He was the founding editor and co-editor in chief of Inflammatory Bowel Diseases.

Like most things related to our bodies, we only pay attention to our digestive system when it's giving us a problem. Otherwise, we tend to overlook it and put all sorts of things into it without a second thought. Although we learn about the process of digestion in high school, most of us had other things on our minds back then. But knowing how your digestive system is supposed to work can help tremendously in terms of overall digestive health—knowledge which can help you take better care of your digestive system, more quickly identify any possible digestive problems, and help you to communicate more effectively with your doctor.

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As already explained, the nutrients obtained by most green plants are small inorganic molecules that can move with relative ease across cell membranes. Heterotrophic organisms such as bacteria and fungi, which require organic nutrients yet lack adaptations for ingesting bulk food, also rely on direct absorption of small nutrient molecules. Molecules of carbohydrates, proteins, or lipids, however, are too large and complex to move easily across cell membranes. Bacteria and fungi circumvent this by secreting digestive enzymes onto the food material these enzymes catalyze the splitting of the large molecules into smaller units that are then absorbed into the cells. In other words, the bacteria and fungi perform extracellular digestion—digestion outside cells—before ingesting the food. This is often referred to as osmotrophic nutrition.

Like bacteria, protozoans are unicellular organisms, but their method of feeding is quite different. They ingest relatively large particles of food and carry out intracellular digestion (digestion inside cells) through a method of feeding called phagotrophic nutrition. Many protozoans also are osmotrophic to a lesser degree. Some organisms, such as amoebas, have pseudopodia (“false feet”) that flow around the food particle until it is completely enclosed in a membrane-bounded chamber called a food vacuole this process is called phagocytosis. Other protozoans, such as paramecia, pinch off food vacuoles from the end of a prominent oral groove into which food particles are drawn by the beating of numerous small hairlike projections called cilia. In still other cases of phagotrophic nutrition, tiny particles of food adhere to the membranous surface of the cell, which then folds inward and is pinched off as a vacuole this process is called pinocytosis. The food particles contained in vacuoles formed through phagocytosis or pinocytosis have not entered the cell in the fullest sense until they have been digested into molecules able to cross the membrane of the vacuole and become incorporated into the cellular substance. This is accomplished by enzyme-containing organelles called lysosomes, which fuse with the vacuoles and convert food into simpler compounds (see figure ).

Most multicellular animals possess some sort of digestive cavity—a chamber opening to the exterior via a mouth—in which digestion takes place. The higher animals, including the vertebrates, have more elaborate digestive tracts, or alimentary canals, through which food passes. In all of these systems large particles of food are broken down to units of more manageable size within the cavity before being taken into cells and reassembled (or assimilated) as cellular substance.

Chapter Notes: Nutrition and Digestive System, Class 10, Biology Class 10 Notes | EduRev


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

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

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

Function- Water is a carrier, distributing essential nutrients to cells, such as minerals, vitamins

and glucose. Its five top functions are as following:-

2) Chemical and metabolic reactions,

4) Body temperature regulation,


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

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

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


 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

 Appendix - a small sac located on the cecum.

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

 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

 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

 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

 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

 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

 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

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