Chapter: 04. Human Digestive System
4 Human Digestive System
All living forms require energy to stay alive and healthy, which they obtain from food. Nutrition is the process of acquiring and utilizing food substances.
Why We Need Food
Food is essential for several vital functions in our body:
Energy: It provides energy for various life processes, such as movement, growth, and maintaining body temperature. Growth and Repair: Food helps in the growth of the body and the repair of worn-out or injured cells and tissues. Maintenance of Chemical Composition: It maintains the correct chemical balance within our cells. Raw Materials: Food provides raw materials for the synthesis of important substances like enzymes and hormones. Protection: It helps protect the body from diseases.
Nutrients and Food
Nutrients are all the chemical compounds that nourish our body. Food is any substance that contains these nutrients.
The main nutrients found in food are:
1. Carbohydrates (Energy Food)
Carbohydrates are nutrients that provide energy. They are produced in green plants through the process of photosynthesis. Sources: Sugars, Cereals, Apple, Banana, Potato, Pea, Beans, Green vegetables, and Dry fruits. Many processed foods like bread, sweets, pizza, burger, jams, noodles, and jellies are also rich in carbohydrates. 2. Fats (Energy-rich Food)
Fats provide more energy than carbohydrates. One mole of fats releases 9.45 kcal of energy, while one mole of carbohydrates produces 4.2 kcal energy. Examples: Butter, Ghee, Vegetable oils, Fish liver oil, and Animal fats. 3. Proteins (Body-building Food)
Proteins are organic molecules that help in body building. Nitrogen is a crucial element found in proteins. During digestion, proteins are broken down into amino acids, which are considered the building blocks of proteins. Sources: Milk, Curd, Paneer, Meat, Fish, Eggs, Nuts, and Pulses. 4. Vitamins (Protective Food)
Vitamins are needed in very small quantities by our body. Essential for body growth and maintenance. Help the body properly use carbohydrates, fats, and proteins. Play an active role in many chemical reactions within the body. Our body needs vitamins A, B (B-complex), C, D, E, and K. B-complex is a group of several vitamins, including B1, B2, B6, B9, and B12. Note: Our body can produce only two vitamins: Vitamin D and K. All other vitamins must be obtained from food. 5. Minerals (Balancing Food)
Minerals like calcium, iron, iodine, phosphorus, sodium, and fluorine are required by our body in small quantities. Essential for proper body growth. Help maintain good health. Calcium and phosphorus are crucial for bone formation. Iron is necessary for haemoglobin formation. Sodium and potassium help maintain water balance in the body. Something More on Nutrients
Macronutrients: Carbohydrates, fats, and proteins are needed by our body in large quantities. Micronutrients: Vitamins and minerals are needed in minute quantities. Dietary Fibres (Roughage): These are cellulose fibres obtained from vegetables, salads, fresh fruits, and whole grains. Roughage is essential for proper bowel movement. It prevents constipation. It reduces acidity in the stomach.
Nutrition and Steps in Nutrition
Nutrition Definition
Nutrition is the process by which living organisms obtain or synthesize their food and convert it into simple substances that can be absorbed and utilized by body cells.
Steps in Nutrition
The food we eat contains complex macromolecules like carbohydrates, fats, and proteins. These need to be broken down into simpler, soluble molecules to be absorbed by the intestinal wall.
The process of nutrition involves the following five steps:
Ingestion: This is the process of taking food into the body, typically through the mouth. Digestion: This is the breaking down of complex, insoluble organic compounds into simple, soluble molecules through the action of digestive enzymes. Absorption: This is the process by which the molecules of digested food are taken into the blood through the intestinal wall. Assimilation: This refers to the utilization of absorbed nutrients by the body cells for energy production and the synthesis of new protoplasm for growth and repair. Egestion (or Defecation): This is the removal of undigested solid parts of the food from the body as faeces.
Human Digestive System
The human digestive system is responsible for breaking down the food we eat into simple molecules. It consists of two main sets of organs:
Alimentary Canal: A long, coiled food tube, approximately 9 metres long, open at both ends. It starts at the mouth and ends at the anus. Digestive Glands: Glands that produce and store digestive juices or enzymes, which aid in digestion.
1. Mouth and Buccal Cavity
The first chamber of the alimentary canal is the buccal cavity, which opens via the mouth. The mouth is bordered by upper and lower lips, which assist in sipping, sucking liquids, and closing the mouth during swallowing.
Inside the buccal cavity, you will find:
Openings of salivary glands Teeth
Humans typically have 32 teeth in total. They are the hardest non-bony structures in the body. Teeth are categorized into four types based on their shape and function:
Each jaw (upper and lower) has the following arrangement: 4 Incisors (front teeth with cutting margins) 2 Canines (one on either side, pointed, long in flesh-eating animals) 4 Premolars (2 on either side, broad and flat surface) 6 Molars (3 on either side, broad and flat surface) Dentition in Humans (Something More)
Dentition refers to the arrangement of different types and number of teeth in the buccal cavity. Humans have two sets of teeth during their lifetime: Milk Teeth (Deciduous Teeth): The first set of 20 teeth. Appears from 6 months onwards. They do not have premolars. They fall off and are replaced by permanent teeth. Replaces milk teeth between 6 to 8 years of age. Total 32 teeth in adults. Comprises two pairs of incisors, one pair of canines, two pairs of premolars, and two pairs of molars in each jaw (total 14 in each jaw initially). This set persists throughout life or falls off in old age. Until age 18, there are typically 28 permanent teeth (8 molars). Four additional molars that appear one on either side in the upper and lower jaw, after the age of 18 years. 
Self Study
