CBSE Class 11 Biology Revision Notes Chapter 16

CBSE Class 11 Biology Revision Notes Chapter 16 – Digestion and Absorption

All living creatures require food to stay alive and grow. Humans have developed systems for turning food into energy and dispersing it throughout the body. The human digestive system is a collection of interrelated organs that extends from the mouth to the anus. Students will get to learn about the entire human digestive system in this chapter.

Students can refer to the revision notes of this chapter prepared by subject matter experts at Extramarks to better comprehend the chapter. These notes summarise all the important topics covered in the NCERT in an easy-to-understand language.

Revision Notes for CBSE Class 11 Biology Chapter 16 – Download 

Access Biology Class 11 Chapter 16 – Digestion and Absorption

The important topics covered in this chapter are listed below:

Digestion in the stomach:

The highly-developed alimentary canal, as well as accompanying glands, make up the human digestive system.

• Alimentary canal: It is a muscular coiled tube that travels from the mouth to the anus and is around 6 to 9 metres long. From the mouth to the anus, glandular epithelium lines the inner walls. The mouth, oral cavity or buccal cavity, pharynx, oesophagus, stomach, small intestine, large intestine, and anus are lined with glandular epithelium. A set of ducts connect the major glands to the alimentary canal. Salivary glands, gastric glands, liver, pancreas, gallbladder, and intestinal glands are among these glands.
• Mouth and Oral cavity: The mouth is a transverse slit-like aperture surrounded by two lips that starts the alimentary canal. The oral cavity makes up the mouth, and the palate serves as the roof. The upper maxilla (upper jaw) and lower mandible (lower jaw) form the oral cavity (lower jaw). The cheeks house the lateral walls of the oral cavity. The uvula is a tiny roof extension fashioned like a finger. The buccal cavity has stratified squamous epithelium that contributes to mucus secretion and canal lubrication.

A muscular tongue resides at the bottom of the oral cavity, joined by the frenulum’s small fold. It conducts many activities, including absorption, swallowing, and chewing food materials. They also include taste buds that aid in the four flavours in food items: sweet, sour, bitter, and salt. When moist food comes into contact with the taste buds, it produces a flavour sensation.

• Teeth: The masticatory apparatus in the skin surrounding the jaw is controlled by specific cells. Dentition is made of the number of teeth present, their arrangement, and their forms. Thecodont, heterodont, and diphyodont are the three forms of dentition present in humans. In the mouth of an adult person, there are 32 teeth, 16 in each jaw.

Incisors, Canines, Premolars, and Molars are the four categories of teeth based on the functions they perform. These are discussed in detail below.

• Incisors: These are the tools used to cut and chop food into tiny bits. They have sharp cutting edges and are chisel-shaped.
• Canines: They are observed to be dagger-shaped and are responsible for shredding food. Premolars and molars are teeth at the back of the jaws that crush and grind food. The remaining four molars in a man’s mouth, two each from the upper and lower jaws, will appear after a person reaches 17 or 18. The wisdom teeth are a set of four molar teeth.

Two types of teeth appear throughout a person’s life: milk teeth and permanent teeth. That is referred to as diphyodont dentition. Milk teeth occur in childhood and are weak and transitory. They lack molars and have 20 premolars, with ten teeth in each jaw. The dental formula describes the placement and quantity of teeth in the jaws.

The enamel on the teeth is a non-living material made up of calcium salts. Enamel is made up of calcium, calcium carbonate, and phosphate and is the complex bone in the body. Mastication of food is aided by the teeth present in the buccal cavity.

• Pharynx: The funnel-shaped muscle channel aids in the processes of respiration and digestion. The buccal cavity extends into the pharynx, while the nasal cavity opens into it from above. It will then enter the oesophagus and trachea from the back. The glottis is the pharyngeal aperture into the trachea and is always open throughout respiration. The epiglottis is a flap-like structure that helps prevent food particles from moving into the windpipe instead of the food pipe while swallowing, and it shuts into the nasal cavity by the uvula.
• Oesophagus: The oesophagus is a 30 cm long muscle tube connecting the pharynx to the stomach. The neck, thorax, and diaphragm are all places where this tube enters the body (it is a muscular wall that partitions the thorax from the abdomen). Peristalsis is the oesophagus’s wave-like contraction and relaxation, which helps food reach the stomach. The gastro-oesophageal sphincter muscles help the oesophagus in the stomach open.
• Stomach: It is a major portion of the alimentary canal, a C-shaped structure in the upper abdominal cavity below the diaphragm. It is divided into three sections: fundus, cardiac, and pylorus.

The fundus is near the cardiac area, where the oesophagus opens. It aids in the intake of air into the stomach when eating. The cardiac area is the middle area of the body that aids in storage.

The pylorus, also known as the antrum, is a narrow, posterior part of the stomach that empties into the small intestine through a pyloric aperture enclosed by the pyloric sphincter, a ring-shaped muscle. The food will be sent to the small intestine as the sphincter relaxes. Different gastric glands aid the release of gastric juices in the stomach wall. The mucous membrane encloses the stomach folds when it is empty, forming rugae, which lead to the stomach lumen.

• Small Intestine: It’s a massive segment of the alimentary canal, narrow, tubular, and located in the abdomen area. The small intestine measures 7 to 9 metres in length and 2.4 centimetres in width. The three sections of the small intestine are the duodenum, jejunum, and ileum.
• Duodenum: It is the first U-shaped section of the small intestine. The common entrance of the liver and pancreas are included.
• Jejunum: It is the region following the duodenum and is much longer than that. The ileum is the small intestine’s final and longest section. It measures roughly 7 metres in length and 2 to 3 centimetres in diameter. This section of the large intestine is strongly coiled and enters into the lower right area of the abdominal cavity. The mesenteric portion of the small intestine is made of the jejunum and ileum. The small intestine is in charge of the majority of digestion and absorption.
• Large intestine: The large intestine follows the small intestine. It is 2m long and is shorter but more massive than the small intestine. Caecum, colon, and rectum are the three areas. In humans, the caecum is a small pouch. However, in horses and asses, it is enormous. The vermiform appendix is a finger-like structure located in the caecum that is non-functional and hence falls under the category of a vestigial organ. The colon is a massive section of the intestine.

Digestive Glands

The digestive glands are those glands that are found in the alimentary canal that aid in the digestion of dietary items. The salivary glands, liver, and pancreas are among these glands.

Salivary Glands

They are digestive glands that result in saliva release and are located in the oral cavity. Salivary glands come in three pairs in humans:

• Parotid glands are large glands located directly behind and below the ears.
• Sublingual glands are found beneath the tongue on the floor of the mouth.
• Submandibular glands, also known as submaxillary glands, are found beneath the lower jaw’s angles.

Saliva is secreted by these glands and travels to the mouth cavity via the salivary ducts. Saliva is a transparent, watery fluid released by humans in amounts of roughly 1.5 litres every day. It is alkaline, with 99.5 percent water and 0.5 per cent additional compounds like digestive enzymes, electrolytes, mucus, and inorganic salts. Starch digesting enzymes called salivary amylase and an antibacterial agent called lysozyme is present in human saliva. Salivary amylase is responsible for digesting starch and glycogen and converting it to maltose. Cows, buffalo, goats, tigers, lions, and other animals do not have it. Saliva contains electrolytes such as Na+, K+, Cl-, HCO3, and others, generated from blood plasma, serous fluid, and mucus.

Saliva serves the following purposes:

• It protects the oral cavity from deterioration-causing activities.
• The harmful bacteria are eliminated.
• Saliva contains thiocyanate ions and proteolytic enzymes, which aid in the destruction of microorganisms in the mouth.
• The proteins in saliva aid in the destruction of germs in the oral cavity that cause dental cavities.

Liver

It is a massive gland in the human body, weighing between 1.2 and 1.5 kg and having a dark chocolate colour in adult men. It can be located in the right upper section of the abdomen, slightly below the diaphragm. The liver is divided into two lobes, one small left lobe and one right lobe. The lobules are the structural and functional elements of the liver. A capsule known as Glisson’s capsule surrounds them. Hepatic cells, Kupffer cells, and blood-filled cavities termed sinusoids make up the lobules. Hepatic cells cause bile to be secreted. Bacteria, injured blood cells, foreign particles, and other substances are digested by Kuppffer’s cells. The liver produces bile juice, which is greenish in colour and alkaline in composition and contains pigments, mucus, cholesterol, phospholipids, water, and bile salts, among other things. Biliverdin and bilirubin are the two forms of bile pigments.

Bilirubin is a reddish yellow pigment, while biliverdin is a green pigment.

Sodium taurocholate and sodium glycocholate are two bile salts that aid in fat digestion and absorption of fat-soluble vitamins A, D, E, and K.

There are no bile enzymes. The material entered the hepatic ducts after that. The gallbladder causes cystic development. The hepatic and cystic ducts form the common bile duct, which joins the pancreatic duct to form the common hepatopancreatic duct. The Sphincter of Oddi protects the common duct.

Pancreas

They are the elongated parts of the digestive gland situated in the bend of the duodenal loop. It is the second-largest gland in the human body after the liver, measuring 12-15 cm in length and being reddish-yellow in hue. They aid in pancreatic juice, a clear, watery, alkaline fluid that contains several enzymes that aid in the digestion of carbohydrates, proteins, lipids, and nucleic acids. The pancreatic juice is transferred into the Duct of Wirsung, which joins the common bile duct to form the hepatopancreatic duct. It then opens into the duodenum loop. The pancreas is divided into two sections: endocrine and exocrine. The exocrine portion is glandular chambers known as acini or alveoli, which aid in the alkaline pancreatic juice-containing enzymes.

The endocrine system is made of Islets of Langerhans, which are small clusters of cells that secrete insulin and glucagon hormones.

It is made up of three different types of cells:

• Alpha cells-secrete glucagon 
• Beta cells secrete insulin 
• Delta cells secrete somatostatin.

Food absorption

Digestion is divided into two stages: mechanical and chemical digestion.

Digestive mechanical action

It breaks down food into simpler compounds through mastication, insalivation, and peristaltic movement of the alimentary canal’s wall.

Digestion by chemicals

Digestion is aided by substances generated by the mouth region, most notably saliva, which mixes with food particles and aids partial digestion. Saliva contains compounds, including mucin, thiocyanate, lysozyme, and ptyalin, which aid in digestion.

Mucin is a glycoprotein that helps lubricate food particles and aids in swallowing.

Lysozyme is bactericidal, meaning it destroys bacteria. Ptyalin, found in saliva, aids in the digestion of starch and transforms it into maltose. Only 30 per cent of starch is processed in the mouth.

Ptyalin is found in the saliva since the food they eat is made up of starch. Ptyalin is a starch digesting enzyme that can only digest ripe and cooked starch. It cannot digest raw starch.

After mixing with saliva, the teeth and tongue are responsible for mastication, lubrication, and adherence of food into the bolus, which is then conveyed into the throat by swallowing or deglutition. Swallowing is a reflex motion in conjunction with the peristaltic wave and results in food being pushed into various regions of the alimentary canal.

Bolus travels to the oesophagus, where it is assisted by peristaltic movement before entering the stomach through the gastro-oesophageal sphincter.

Digestion in the stomach

Gastric digestion refers to breaking down food particles in the stomach. After entering the stomach, the bolus causes rugae or the straightening of the stomach walls. The food particles are crushed, kneaded, and churned by these walls. They mix them with gastric secretions secreted by the stomach glands.

The secretion of the gastric glands is produced by four different types of cells that are found throughout the stomach’s inner region:

• Mucous neck cells, also known as Goblet cells: Help secrete alkaline mucus that protects the epithelium from hydrochloric acid. The fundic, cardiac, and pyloric areas of the stomach are where these cells are found.
• Parietal or oxyntic cells: They cause the gastric glands to secrete hydrochloric acid, which activates the pepsin enzyme, which aids in protein digestion. Their job is to kill any microorganisms that get into the meal with it.
• Chief cells (Zymogenic cells or peptic cells): They aid in secretion, an enzyme located in the fundic area.
• G cells: They are located in the fundic, pyloric, and gastric areas of the stomach and are responsible for the secretion of the gastric enzyme and hydrochloric acid.

The stomach glands’ secretions combine to form gastric juices, which are acidic in response and include dilute HCl. About 99 per cent of gastric juice is water, consisting of pepsinogen, gastric lipase, prorenin, mucus, bicarbonates, HCl, and other substances.

The stomach stores food for roughly 4 to 6 hours. After gastric digestion, the meal becomes acidic, developing chyme, a semi-digested and paste-like substance. The chyme is subsequently gradually transported into the duodenum of the small intestine through the pyloric sphincter of the stomach.

Mucus and bicarbonates in the stomach juice protect and lubricate the mucosal epithelium. They shield the mucosal epithelium from the very concentrated HCl.

Digestion in the intestine

The produced chyme travels via the small intestine to the duodenum. The distension occurs in the duodenum, resulting in a rise in osmotic pressure. The acidic chyme is neutralised thanks to the bile generated by the liver. The Brunner’s gland then releases the mucus after passing through the alkaline part of the pancreatic juice. Food is mixed with bile, snot, pancreatic juice, and intestinal juice called succus entericus in the jejunum and ileum regions of the small intestine.

Due to the chemical action of several digestive enzymes in the intestinal juice and the peristaltic and pendulous movement of the gut, complete digestion occurs. There are two types of intestinal glands.

• Lieberkuhn’s Crypts: They are mucosal invaginations in the small intestine that occur between the villi and open at the base of the villi. They are made up of three different kinds of secreting cells:
• Cells in goblet: It is in charge of secreting mucus.
• Cells of Paneth: It is in charge of secreting a vast number of digesting enzymes.
• Enterocytes: It’s in charge of secreted water and electrolyte
• Brunner’s gland: They are tubular glands located in the duodenum’s submucosa. They cause the production of mucoid fluid, a viscous, alkaline, enzyme-free, and watery fluid that aids the duodenum in withstanding the acidic chyme that enters through the stomach and is later neutralised by the alkaline pancreatic juice and bile.

The secretions of the intestine and Brunner’s glands are combined into enterics, a somewhat straw-coloured alkaline fluid containing enzymes, inorganic salts, and mucus. After the food has been digested, it will become a semifluid called chyle. The digested meal is absorbed through the chyle.

The macromolecules are broken down in the duodenum while absorbed in the jejunum and ileum of the small intestine. The ileocaecal valve allows undigested food particles to pass into the big intestine.

Large Intestine:

The large intestine is the location where liquids are absorbed. It involves the absorption of water and minerals and the secretion of mucus to aid adhesion and lubrication. Food that is not digested results in the development of solid wastes called faeces, which are temporarily deposited in another organ called the rectum before being expelled from the body through defecation.

• Food digestion and absorption: Absorption is a process in which the canal assists in taking up digested food products and other nutrients and transporting them into cells or tissues of the body. Glucose, fatty acids, amino acids, glycerol, pyrimidines, purines, mineral salts, water, vitamins, and other substances are generated. The small intestine is the primary location for food digestion. The ileum of the small intestine is where absorption takes place. The digested products are absorbed in the small intestine by the microvilli of the absorptive cells, while water is taken in the large intestine.

The digested food is absorbed through passive or active absorption and enhanced transport pathways.

• Diffusion is simple: It facilitates the absorption of amino acids, glucose, and electrolytes, such as chloride ions. Facilitated diffusion occurs when carrier ions such as Na+ aid in the absorption of fructose and certain amino acids. Water transfer occurs as a result of the osmotic gradient.

Active transport occurs when the transfer occurs against a concentration gradient. This process requires energy in the form of ATP, which results in amino acids, electrolytes such as Na+, and monosaccharides (glucose). The insoluble nature of fatty acids and glycerol means the circulation cannot absorb them. As a result, they must first be broken down into droplets known as micelles, which then travel into the intestinal mucosa, are turned into small protein-coated fat globules (Chylomicrons), and transported to the lymph vessels in the villi. After that, it enters the bloodstream.

Food is absorbed in the mouth, stomach, small intestine, and large intestine occurring primarily in the small intestine. Assimilation is transporting ingested food into various tissues via the bloodstream. Undigested food is stored as solid waste (faeces) in the rectum and released via defecation’s neural reflex.

Disorders of the Digestive System:

Certain bacteria or viruses can infect the digestive tracts, causing inflammation. Infections can also be caused by gut parasites such as roundworms, tapeworms, threadworms, pinworms, and hookworms.

Vomiting, jaundice, diarrhoea, indigestion, constipation, and other digestive system issues are prevalent.

• Jaundice: It is caused by a buildup of bile pigments in the blood, which causes skin, eye, and mucous membrane yellowing.
• Vomiting: It occurs when the stomach contents are ejected out the mouth due to an obstruction in the intestines or reverse peristalsis. It is a reflex activity controlled by the vomiting centre located in the medulla oblongata of the brain. Following the sensation of nausea, vomiting happens.
• Diarrhoea: The frequent occurrences of watery stools are indications of diarrhoea caused by insufficient water absorption. That causes irregular bowel movements, as well as increased faecal output fluidity and decreased meal absorption.
• Constipation: When the amount of water absorbed in the large intestine is considerable, it causes the development of dry and hard faeces, which causes the dry muscles of the colon of the large intestine to become incapable of regular peristaltic motions and remain tight. That causes stools to be stored in the rectum and defecation at irregular intervals. Constipation is the name for this condition. The meal consumed should be high in cellulose fibres. Constipation and diarrhoea are two different types of irregular defecation to avoid constipation.
• Indigestion: The syndrome is caused by poor digestion, which causes a feeling of fullness. Indigestion can be caused by many things, including a lack of enzymes, nervousness, secretion, food poisoning, spicy foods, and overeating.

Fast Track Revision:

Food is a nutritive substance required for an organism’s growth, development, maintenance, and activities.

Digestion is the breakdown of complicated foods into more absorbable and soluble forms. The human digestive system is a well-developed alimentary canal and its accompanying glands. The alimentary canal, which comprises the mouth, oral cavity, buccal cavity, pharynx, oesophagus, stomach, small intestine, large intestine, and anus, is surrounded by the glandular epithelium.

Human dentition is divided into three categories: thecodont, heterodont, and diphyodont. The Pharynx is a muscular, funnel-shaped tube found in both the respiratory and digestive systems.

The food enters the stomach via the peristaltic action in the oesophagal walls.

Gastric glands line the inside of the stomach wall, assisting in gastric juice.

The duodenum of the small intestine receives a duct from the pancreatic and liver.

Succus entericus, an intestinal juice, aids in the digestion of meals.

The large intestine is responsible for water absorption, which results in the rectum storing undigested food in solid form, which is evacuated out of the anus.

The glands in charge of digestion are the salivary glands, liver, and pancreas.

Revision Notes for CBSE Class 11 Biology Chapter 16 – Download

Class 11 Biology revision notes on digestion and absorption make the chapter more fascinating and enjoyable to learn. The notes of Class 11 Biology Chapter 16 make test preparation simple. The revision notes also assist in solving difficult questions. The notes are available to download from Extramarks website.

Class 11th Biology Chapter 16 Notes

The two most critical physiological processes in human life are digestion and absorption. Locomotion, movement, chemical and gas exchange, and neurological and chemical coordination are all part of digestion and absorption. We fuel our bodies with food and nutritious supplements every day. Our bodies require nourishment to grow and perform a variety of jobs. Nutrition is the physiological process by which our body’s organs consume food. Many vital fibres, proteins, carbs, and healthy fatty acids are found in the diet, which our bodies require in everyday life. Digestion breaks down food in our stomach and absorbs all essential nutrients. Some of our body organs assist us in the digestion and absorption process. All these concepts are thoroughly discussed in the revision notes. These Class 11 Biology Chapter 16 notes will help to understand these topics better.

Class 11 Chapter 16 Biology Revision Notes

Class 11 notes on Digestion and Absorption contain a detailed discussion of all of the human digestive system including the organs involved, their roles, and their capabilities. The notes for CBSE Class 11 Biology Chapter 16 notes summarise all the important concepts covered in the chapter in a clear and concise manner for the students’ ready reference.