The human digestive system consists of the associated glands and the alimentary canals.

Alimentary Canals

The Alimentary Canals begins with the mouth- an anterior start point that opens the posteriorly via the anus. The mouth then leads to the oral cavity, which has several teeth and a muscular tongue.

Thecodont: It is a type of attachment where each tooth is fixed in a socket of a jaw bone.

Diphyodont: Many mammals, including human beings, have two different sets of teeth during their lifetime, i.e. temporary milk teeth and permanent or adult teeth. Diphyodont is a dentition where permanent teeth replace milk teeth.

An adult has 32 teeth which are four different types namely: incisors(I), Premolars(PM), Canine(C), and Molars(M). Dental Formula is that each half of the upper and lower jaw has no. of teeth -  2123/2123

• Pharynx: The oral cavity leads into the pharynx that serves as a passage that is common for air and food. Epiglottis, which is a cartilaginous flap, prevents the food from entering the windpipe during swallowing.
• Stomach: The oesophagus leads to the stomach. Gastro-oesophageal (muscular sphincter) regulates the opening of the oesophagus into the stomach. The stomach has three divisions: Cardiac, Fundus, and Pyloric.
• Small Intestine: It is the longest part of the alimentary canal that is divided into three regions: duodenum, jejunum, and ileum. The pyloric sphincter is present between the stomach and duodenum
• Large Intestine: The large intestine is divided into three regions: caecum, colon, and rectum. The caecum is a blind sac that hosts microbes. Vermiform appendix arises from the caecum. The rectum opens through the anus.

Digestive Glands

Digestive Glands include The Salivary Glands, Liver, and Pancreas.

Salivary Glands: saliva is produced by the salivary glands that have three pairs, i.e. cheeks (the parotids), lower jaw (the submaxillary), and below the tongue (the sublingual).

Liver: It is the biggest gland in the human body that is situated just below the diaphragm in the abdominal cavity. It has two lobes: Hepatic are functional and structural units of the liver that contain hepatic cells. The thin connective tissue sheath, Glisson's capsule covers each lobule. The secretion is concentrated and stored in the gallbladder. The pancreatic duct and bile duct together open into the duodenum, which is guarded by a sphincter, also known as the Sphincter of Oddi.

The Pancreas: The pancreas is a long compound organ present between the Limbs of the Duodenum. Its exocrine portion discharges an alkaline juice that contains enzymes, while the endocrine discharges insulin, hormones, and glucagon.

 

• Mechanical and chemical processes accomplish the process of digestion in the body.
• Two major functions performed by the buccal cavity are Rumination and the helping in swallowing.
• With the help of saliva, the teeth and the tongue ruminate and mix the food to form bolus that is passed into the pharynx and then the oesophagus by swallowing.
• The bolus is further passed down the oesophagus by peristalsis. The gastro-oesophageal sphincter handles the passage of the food-intake into the stomach.
• The oral cavity releases the saliva that contains enzymes and electrolytes, lysozyme, and salivary amylase that act as antibacterial agents in the mouth to prevent infection.
• Gastric glands have three major types of cells: mascus neck cells, peptic or chief cells, and oxyntic cells.
• The churning moment mixes food thoroughly with the gastric juice in the stomach to form chyme.
• The mucus and bicarbonates present in the gastric juice play an important role in the lubrication and protection of the mucosal epithelium from the HCl.
• The small intestine discharges bile, pancreatic juice, and intestinal juice. The pancreatic juice contains Trypsinogen, an inactive enzyme activated by enterokinase, which in turn activates other enzymes in the pancreatic juices.
• Bile contains bile pigments, cholesterol, bile salt, and phospholipids that help in the emulsification of fats.
• Mucosa and goblet cells contain the enzyme succus entericus that is released by brush border cells containing various enzymes to complete the process of Digestion.

Absorption is the process by which the digested products pass through the intestinal mucosa into the lymph or blood. Then, it is carried out by passive, facilitated, and active transport mechanisms. Glucose, fructose, fatty acids, glycerol, amino acids, and other nutrients are absorbed into the bloodstream and rest of the left water, and other minerals are absorbed in the large intestine.

• Amino acids, fatty acids, salts, vitamins, glycerol, water, and monosaccharide are absorbed. About 90% of absorption occurs in the small intestine while the rest in the stomach, mouth, and large intestine.
• Assimilation is the process in which the absorbed substances finally reach the tissue that utilizes them for their activities.
• The digestive waste is further solidified into coherent faeces in the rectum, which initiates neural reflex, causing a desire for its removal, a voluntary process carried out by a mass peristaltic movement.

TABLE 16.1 The Summary of Absorption in Different Part of Digestive System

Mouth	Stomach	Small Intestine	Large Intestine
Certain drugs coming in contact with the mucosa of mouth and lower side of the tongue are absorbed into the blood capillaries lining them.	Absorption of water, simple sugars, and alcohol etc. take place.	Principal organ for absorption of nutrients. The digestion is completed here and the final products of digestion such as glucose, fructose, fatty acids, glycerol and amino acids are absorbed through the mucosa into the blood stream and lymph.	Absorption of water, some minerals and drugs takes place.

The inflammation due to bacterial or viral infection that is caused by intestine like tapeworm, roundworm, threadworm, etc

• Jaundice: In Jaundice the liver is affected, and the eyes and skin turn yellow due to the deposit of bile pigments.
• Vomiting: It is an ejection of stomach content through the mouth, which is a reflex action controlled by the vomiting centre in the medulla.
• Diarrhoea: The abnormal frequency of bowel movement and increased fluidity of the faecal discharge is called diarrhoea. It reduces the absorption of food.
• Constipation: In this situation, the faeces are retained within the colon due to irregular bowel movement.
• Indigestion: In indigestion, you feel fullness which was due to improper digestion of food. It is caused by inadequate enzyme discharge, food poisoning, spicy food, anxiety, and overeating.

 
Here are the class 11 Biology NCERT Solution Digestion And Absorption. 

Source - NCERT Solutions For Class 11 Biology Digestion and Absorption (learncbse.in)

1. Explain the process of digestion of protein in the stomach.

The digestion of protein starts from the stomach and finishes in the small intestine. When food enters the stomach, it gets mixed with the gastric juice, which is discharged through the gastric glands on the walls of the stomach and becomes acidic. Hydrochloric present in the gastric juice dissolves a bit of food to create an acidic medium which assists the pepsinogen to convert into pepsin, an oesophagus digestive enzyme. When it is discharged it is inactive, and it is activated by hydrochloric acid. The pepsin after activation then transfers the proteins into peptides and proteases.

Rennin has a vital role in the milk’s coagulation and is released in an inactive form called prorenin.

2. Describe the functions of the liver. 

The function of the liver is to discharge digestive juices and bile that plays a major role in the emulsification of fats.

3. What is the digestion of food?

Digestion of food is a mechanical and chemical process that accomplishes the process of digestion in the body. Digestion turns the food you eat into nutrients that the body utilizes for energy, growth, and cell repair needed to survive. It also involves the elimination of digestive waste.