Digestion And Absorption: Overview, Topics, Books, Tips, Diagrams

Digestion and absorption help break down the food we eat into simple nutrients that the body uses for energy, growth, and repair. The digestive system is about 9 meters long and includes the stomach, small intestine, and large intestine. Most nutrients are absorbed in the small intestine, which has tiny finger-like projections called villi and microvilli to increase surface area. Enzymes like amylase, pepsin, and lipase help break down carbohydrates, proteins, and fats, with support from organs like the liver, pancreas, and salivary glands.

This Story also Contains

1. What is the Human Digestive System?
2. Stages of Digestion
3. Role of Enzymes and Digestive Juices
4. Recommended Video for Digestion and Absorption

Digestion starts in the mouth with chewing and saliva, then continues through the oesophagus, stomach, and intestines. At each stage, food is mixed with different enzymes and acids. In the end, nutrients are absorbed into the blood to fuel the body’s needs. Digestion and Absorption is an important chapter in Biology.

Important Topics of Digestion and Absorption

The chapter discusses high-scoring topics that include the human digestive system, digestive enzymes, and nutrient absorption. Studying topics helps in answering conceptual and fact-based questions correctly. Below is a list of the most important areas that you must give priority to when studying.

• Human Digestive System
• Alimentary Canal
• Digestive Glands
• Absorption of Food
• Disorder of the Digestive System

What is the Human Digestive System?

Imagine that you're having a great dinner, enjoying your food bits. But have you ever thought about exactly what happened to your food after it left your plate and passed on to your body? How food is digested within the human system is a rather interesting journey for survival. Each piece of your food intake undergoes chemical and physical changes, breaking it down into nutrients that help energise your body with all its vital functions.

Attention to the human digestive system enables one to make much better food choices and makes us appreciate the inner complexity of what goes on within us. In this article, we will look into the structure and function of the digestive system, the steps of digestion, and discuss practical applications and relevance in our daily lives.

Diagram of the Digestive System

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• Difference Between Oesophagus and Trachea

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Major Organs in Digestion

Mouth: The mouth is the anterior opening of the digestive system. It receives food, and the types of teeth in the mouth break it down mechanically and chemically into simpler substances. Digestion in the mouth starts right from the act of chewing and partial digestion by food mixed with saliva, which is aided by the tongue, to break the carbohydrates down with salivary amylase into simpler subunits.

Oesophagus: This is a muscular tube that transports food from the mouth down to the stomach. The rhythmic muscle contraction, known as peristalsis in the oesophagus, moves the bolus to the stomach.

Stomach: A sac-like organ that churns up food and mixes it with digestive juices. The cellular lining of the stomach secretes gastric juices for the hydrolysis of proteins to chyme.

Small Intestine: This is a long tube and is the site for most digestion and absorption of nutrients. The principal area of nutrient absorption is aided by villi and microvilli in the small intestine. They are finger-like outgrowths still increasing the absorptive area.

Large Intestine: This absorbs water and produces waste products in the form of faeces. This is where the absorption of water and electrolytes occurs. It is also the site where the faeces are collected and expelled.

Rectum and Anus: These store and expel faeces.

Given below is the diagram of the various organs of the digestive system and their function.

Accessory Organs

The accessory organs are also the digestive glands that help in digestion.

Liver: The liver manufactures bile for fat digestion.

Pancreas: Secretes digestive enzymes and bicarbonate.

Salivary glands: The salivary glands help in the secretion of saliva, which has the enzymes required for the initial digestion of carbohydrates.

Gallbladder: The gallbladder stores and concentrates the bile.

Stages of Digestion

The stages of digestion are:

Ingestion

The digestion process starts in the mouth, where food is chewed and mixed with saliva to form a bolus.

Mixing And Movement

• Muscle contractions in the oesophagus pass the bolus into the stomach, a wave of contractions that propel food down the digestive tract in wave-like peristalsis motions.
• Additional mixing with digestive juices in the stomach breaks down the food into a semi-fluid substance called chyme.

Secretion

• Digestive enzymes, bile, and other juices are secreted by the stomach, pancreas, liver, and small intestine, which help in digestion.

Digestion

• Enzymes break down carbohydrates, proteins, and fats in the small intestine into smaller molecules.

Absorption

• Nutrients are absorbed through the walls of the small intestine into the bloodstream.

Excretion

• Absorption of water and the formation of waste products in the large intestine, followed by proper excretion of waste through the rectum and anus.

These are the steps of digestion, each of which is highly important in making food into energy and valuable nutrients. In this regard, the digestive system has become very basic not just for nutrition but also related to health and disease. Knowing about digestion makes it possible to maintain better health and prevent diseases.

Mechanism of Digestion

Food absorption generally refers to the act or process of absorption or assimilation. Absorption in biology refers to the process of absorbing or assimilating substances into the cell or across tissues and organs. Absorption of food takes place in the small intestine. The small intestine is responsible for the absorption of minerals and vitamins from food.

Some important events of Digestion are discussed below:

Biochemical Processes Of Digestion

Digestion is the process by which macromolecules are broken down into smaller molecules that will be free for absorption and utilisation within the body.

Digestion of Carbohydrates

• Digestion of carbohydrates is initiated inside the mouth, facilitated by means of salivary amylase.
• The majority of carbohydrate digestion takes place inside the small intestine.
• The important enzyme is pancreatic amylase, which yields disaccharides from starch via the means of digesting the alpha 1-four glycosidic bonds.
• The disaccharides produced (maltose, maltotriose, and α-dextrins) are all transformed to glucose via the means of brush border enzymes.
• Disaccharides don't require amylase to break them down. The enzymes (lactase, sucrase, trehalase) hydrolyse those compounds into molecules of glucose, galactose, and fructose.

Absorption of Glucose

• Glucose and galactose are absorbed throughout the apical membrane via means of secondary energetic transport (alongside Na+) via the Sodium-Glucose cotransporter (SGLT1).
• Both glucose and galactose go out of the cell through GLUT2 receptors throughout the basolateral membrane into the blood.
• Fructose enters the cell via means of facilitated diffusion through GLUT5 and is transported into the blood through GLUT2 receptors.

Digestion and Absorption of Proteins and Fats

Digestion of protein and fats takes place throughout the digestive system at different sites. Some of the major sites are discussed below:

Role of Enzymes and Digestive Juices

• Carbohydrates: Ptyalin in the saliva and amylopsin secreted by the pancreas react with the small intestines to degrade complex starches into monosaccharides, where monosaccharides are monomeric small sugars.

• Proteins: In the stomach, the principal work of protein digestion is done by the gastric juice, namely the pepsin; then, in the small intestine, the pancreatic juice, trypsin and chymotrypsin continue protein digestion.

• Fats: Fats emulsified from the bile salts are further broken down with pancreatic lipase into fatty acids and glycerol, the resultant products that can be absorbed.

Villi and Microvilli

The increased surface area of the small intestine increases the absorption of nutrients Glucose, Amino acids, and fatty acids, into the blood and lymph.

Diagram: Intestinal Wall

Practical Implications and Applications

These are the practical implications and applications of the digestion process:

Dietary Choices

Knowing about digestion helps in choosing a diet. For example, food that is high in fibre would promote the movement of the bowels and avoid constipation.

Prevention Of Disease

Healthy digestion is known to relate to a variety of diseases, from acid reflux to IBS and Crohn's. A good diet coupled with the concept of digestion can help in their management and even in preventing them.

Medical Applications

Medical fields: In-depth knowledge of the digestion process will help to formulate treatment options against digestive disorders. For instance, supplements comprising enzymes can help individuals with insufficient functioning of the pancreas.

Nutritional Science

Nutritionists apply their digestive-system-related expertise in designing diets that are balanced and will yield maximum absorption for optimum health benefits.

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