NEET Important Chapter - Digestion and Absorption

This article includes important topics from the chapter Digestion and Absorption as per the NEET 2022 syllabus for biology. This article will make concepts easy for students for those who are preparing for NEET 2022 as it contains the essential topics and concepts for last-minute revision. 

This article gives information on all of the important areas that need to be covered from Digestion and Absorption and provides an insight into the exam pattern. By going through this document, students can recall all the answers to the important questions related to the chapter such as what does the digestive system in humans consists of and its functions, what are alimentary canal and digestive glands, what is the process of digestion of food, how does the absorption of digested food takes place, what are the disorders of the digestive system, etc.

Important Topics of Digestion and Absorption

• Digestive system

• Alimentary canal

• Digestive glands

• Digestion of food

• Absorption of digested food

• Disorders of digestive system

Important Concepts

Digestive System

One of the essential parts of the human body is the digestive system which plays an important role in assimilation and absorption of many types of nutrients in our body. The body assimilates the nutrients when the food is broken down and this function is performed perfectly by the digestive system. This continuous process will keep us healthy and give optimal growth. Our body health and gut health are maintained by a healthy digestive system. Many people suffer from varying digestive disorders that can make normal functioning of the body a difficult task.

Alimentary Canal

The alimentary canal is a major part of the digestive system. It is a continuous muscular tube which runs through the body and is around 8 to 10 metres long. It is open at two ends, with the mouth at the anterior end and the anus at the posterior end.

The alimentary canal performs the function of digesting food. It breaks it down into smaller pieces and aids in the absorption of the digested food.

The Alimentary Canal Consists of:

• The mouth

• Salivary glands

• Teeth

• Tongue

• Pharynx

• Oesophagus

• Stomach 

• Small intestine

• Large intestine

Stomach is Further Divided Into

• The cardiac stomach

• The fundus stomach

• The body

• The antrum stomach and

• The pyloric stomach

Digestive Glands

The digestive glands are those having ducts that pour secretions into the digestive system. An alimentary canal and digestive glands are parts of the human respiratory system.

The digestive glands associated with the alimentary canal include the salivary glands, the liver, pancreas, gastric glands, and intestinal glands. Out of these, the major glands are salivary glands, pancreas, and liver.

Functions:

• Salivary Gland – It secretes salivary amylase enzyme which breaks starch into sugar molecules.

• Gastric Glands – They secrete hydrochloric acid (HCl), pepsin enzyme, and mucus. Pepsin helps in the digestion of proteins while mucus helps in the protection of the inner lining of the stomach from acid.

• Intestinal Glands – They secrete intestinal juices to break fat molecules and bile salts into simpler substances.

• Liver – It is an organ that secretes bile juice to break fat molecules.

• Pancreas – An organ that secretes insulin hormone along with pancreatic juices that break proteins, and fats molecules in the small intestine.

Digestion of Food

As the food enters the mouth, it undergoes mechanical digestion by the action of mastication (chewing) and it also becomes when it is in touch with saliva. Saliva contains salivary amylase which starts the digestion of starch in the food.

After the food undergoes mastication and starch digestion, it will be in the form of a small, round slurry mass called a bolus. It travels down the oesophagus and into the stomach by the action of peristalsis. 

In the stomach, gastric juices initiate protein digestion. These juices mainly contain pepsin and hydrochloric acid. As the HCl may damage the stomach wall, mucus is secreted by the stomach which provides a slimy layer that acts as a shield against the damaging effects of the acid. 

Protein digestion takes place at the same time via mechanical mixing by peristalsis allowing the mass of food to mix with the digestive enzymes.

After some time, a thick liquid called chyme is produced which enters the duodenum where it mixes with digestive enzymes from the pancreas and bile juice from the liver and then passes through the small intestine. After the chyme is completely digested, it is absorbed into the blood.

Absorption of Digested Products

The absorption of nutrients takes place by diffusion through the wall of the small intestine which is a part of the gastrointestinal tract between the stomach and the large intestine.

The main function of the small intestine is the absorption of minerals and nutrients found in food. Digested nutrients pass across the blood vessels in the wall of the intestine through a process of diffusion.

Disorders of Digestive System

The following are some commonly found disorders of the digestive system.

• Jaundice

• Vomiting

• Diarrhoea

• Constipation

• Indigestion

• PEM (Protein-energy malnutrition)

Solved Examples From Chapter

1. Gastric juice contains

a) pepsin, lipase and rennin 

b) trypsin, lipase and rennin 

c) trypsin, pepsin and lipase 

d) trypsin, pepsin and renin 

Ans: pepsin, lipase and rennin

The stomach is a J shaped muscular organ present in the abdominal cavity, in between the oesophagus and first part of the small intestine i.e. duodenum. The lining of the stomach contains gastric glands which are made of three main types of cells –

Neck cells: Secrete mucus protects the mucosa of the stomach from an acidic environment.

Peptic of chief cells: Secrete proenzyme pepsinogen which when activated by hydrochloric acid, gets converted to active enzyme pepsin. It is a proteolytic enzyme that breaks down proteins into smaller molecules.

Oxyntic or parietal cells: Secrete hydrochloric acid which activates the pepsin enzyme. It is also essential for the absorption of vitamin B12.

The Key Point to Remember: Gastric juice is a type of body fluid which is helpful in the digestion of food. The gastric juice contains PLR(pepsin, lipase and renin)

2. Match column I with column II

Ans:

Solved Problems of Previous Year Questions

1. Which cells of 'Crypts of Lieberkuhn' secrete antibacterial lysozyme? 

a) Argentaffin cells 

b) Paneth cells 

c) Zymogen cells 

d) Kupffer cells 

Ans: Paneth cells 

Paneth cells are located in the intestine next to the stem cells. The cells form dense granules where an abundance of antimicrobial peptides and immunomodulating proteins function to control the composition of the intestinal region.

Key Points to Remember: Paneth cells are present in small intestinal crypts of Lieberkuhn and they are highly specialised secretory cells which are epithelial cells. 

2. Which of the following guards the opening of the hepatopancreatic duct into the duodenum? 

a) Ileocaecal valve 

b) Pyloric sphincter 

c) Sphincter of Oddi 

d) Semilunar valve 

Ans: Sphincter of Oddi 

The Sphincter of Oddi (SO) is a muscular valve that allows pancreatic juice and bile juice to flow between the small intestine and pancreas through a hepatopancreatic duct.

Key Points to Remember: The end portion of the common bile duct and pancreatic duct is surrounded by a smooth muscle which is the Sphincter of Oddi.

3. In the stomach, gastric acid is secreted by the

a) Parietal cells 

b) Peptic cells 

c) Acidic cells 

d) Gastrin secreting cells 

Ans: Parietal cells 

The parietal cells or oxyntic cells are the epithelial cells present in glands found in the fundus and body of the stomach. Gastric acid is the secretory product of parietal or oxyntic cells. The gastric acid secretion is induced by gastrin.

Key Points to Remember: The gastric acid secreted by parietal cells not only helps in food digestion, and mineral absorption they are also helpful to control harmful bacteria

Practice Questions

1. The enzyme enterokinase helps in the conversion of 

a) Pepsinogen into pepsin 

b) Trypsinogen into trypsin 

c) Caseinogen to casein 

d) Proteins into polypeptides 

Ans: Trypsinogen into trypsin 

Enterokinase catalyses the hydrolysis of peptide bonds in proteins, it does not catalyse the transfer of phosphate groups like other kinases. It has trypsin-like activity, it cleaves proteins following a lysine residue at a specific cleavage site.

2. The stool of a person contains a whitish-grey colour due to the malfunctioning of which type of organ? 

a) Pancreas 

b) Spleen 

c) Kidney 

d) Liver 

Ans: Liver 

If there is decreased bile output, the stool is much lighter in colour. Thus, whitish-grey colour stool occurs due to the malfunctioning of the liver.

Conclusion

These NEET 2022 notes cover all the important concepts required for NEET 2022 aspirants. So it can help NEET 2022 aspirants with effective and quick revision during exams. It includes interesting facts and topics of the chapter and also contains questions from the previous year's NEET 2022 question papers. Try to solve some questions by yourself to get to know how much you have learnt from this chapter.