What is Nutrition
It is a process by which an organism obtains nutrients from food and utilizes them to obtain energy and for building and repairing their tissues.
Nutrients are defined as the substances required for proper growth and maintenance of a living body, i.e. the materials which provide energy to an organism.
All living organisms do not obtain food by the same process, e.g. plants and some bacteria have the green pigment chlorophyll to help synthesize food by the process called photosynthesis. Likewise animals, fungi and other bacteria depend on plants and other organisms for food. Based on this, there are two main modes of nutrition, i.e. autotrophic and heterotrophic.
Nutrition in Human Beings
In human beings, the process of intake of essential nutrients in the form of food takes place through an entire system known as the digestive system.
Human Digestive System
Digestion is a catabolic process, in which complex and large components of food are broken down into their respective simpler and smaller forms with the help of various hydrolytic enzymes.
These simpler forms are finally absorbed and are further taken up by different parts of the body. The human digestive system constitutes a long tubular structure called alimentary canal and various digestive glands associated with it. These glands secrete different digestive enzymes.
The Human digestive system consists of:
- Alimentary canal and
- Digestive glands
The Alimentary Canal
- Alimentary Canal is a muscular tube which starts with the mouth and ends at the anus. It is about 9 meters long and is highly coiled in certain regions especially in the small intestine. Its various regions are different both in structure and function.
- Digestive glands located in the lining of the various regions of the digestive tube.
- Two large digestive glands, the liver and pancreas, are also associated with it, and three different salivary glands are associated with the oral cavity.
The major Organs of alimentary canal are as follows
It is the first part of the digestive system from where the food enters into the alimentary canal. It is mainly comprised of two major parts
- It is a highly muscular sensory organ present at the floor of the buccal cavity.
- It bears several taste buds and helps in mixing food with saliva.
- It is also helpful in producing speech.
- These are hard structures present on the bones of both lower and upper jaw.
- Teeth are basically used for the purpose of grinding, cutting and chewing food.
- It is a small funnel-shaped chamber located behind the oral cavity.
- It communicates with both esophagus and trachea (windpipe).
- It is a thin and long muscular tube that leads into the stomach.
- It is the most dilated J-shaped part of the alimentary canal.
- It is situated between the esophagus and the small intestine, below the diaphragm.
- It serves as a storehouse of food where partial digestion takes place through the secretion of gastric glands.
- The muscular walls of the stomach help in mixing the food properly with digestive juices.
- The exist of food from the stomach is regulated by a sphincter muscle, which releases it in small amounts into the small intestine.
- It is the longest part of the alimentary canal. It is fitted in a compact space because of Fib extensive coiling.
- The length of the small intestine differs in all organisms depending upon their food habits, e.g. herbivores have a longer small intestine to facilitate cellulose digestion. Carnivores have a shorter small intestine as meat fat is easily digestible.
- The small intestine is the site of the complete digestion of food into different components. Secretions from liver and pancreas enter the intestine to help the digestion process.
- The inner lining of the small intestine has numerous finger-like projections called villi, which increase the surface area for absorption.
- It is shorter in length and wider in diameter than the small intestine.
- Appendix is the part of the large intestine.
- The large intestine secretes no enzyme. It absorbs much water but very little digested foodfrom the contents which mainly consist of undigested material.
- After the water is absorbed, the contents become semi-solid feces which pass into the rectum and are expelled at intervals.
- The expulsion of the undigested remains of the food from the alimentary canal is called defecation.
It is the last and broad chamber-like structure that serves to store fecal matter temporarily.
It is the end point of the alimentary canal, which helps in exit of waste materials.
This process is regulated by anal sphincter
Various glands are associated with the alimentary canal for the process of digestion of food.
Digestive glands in human beings are as follows
These glands are of three types
- Porotial glands
- Sub-mandibular glands
- Sub-maxillary glands
Functions of Salivary glands
The main function of salivary glands are as follows
- It secrete saliva containing an enzyme called salivary amylase (ptyalin).
- It converts starch into sugars at an optimum pH of about 7.
- It is due to these salivary glands that our mouth waters when we eat or smell something we like.
These are found in the wall of the stomach.
Functions of gastric Glands
- These glands release digestive juice containing HCl, pepsin, mucus, etc.
- Hydrochloric Acid (HCI) kills the bacteria ingested with food.
- It creates an acidic medium of pH about 2 which facilitates the action of pepsin enzymes.
- It acts on proteins present in the food.
- Due to this highly acidic nature of HCl, the digestion of starch in the stomach is prevented.
- It also prepares the ingested food for further processing in the small intestine.
- The mucus protects the lining of the stomach from the action of the hydrochloric acid produced under normal conditions.
It is known as the largest gland of the body, which secretes bile juice.
Functions Of Liver
- This juice acts on large fat molecules to form smaller globules, increasing the efficiency of enzyme action, i.e. emulsification.
- Gallbladder stores bile juices for further use.
The walls of the small intestine contain numerous glands that secrete intestinal juice containing amylolytic, proteolytic and lipolytic enzymes.
It is connected to the small intestine through its main duct called pancreatic duct.
Functions of Pancreas
It secretes pancreatic juice, which contains enzymes like amylase, trypsin and lipase.