Notes

Nutrition:

The process in which food is obtained or prepared, absorbed and converted into body substances for, for growth and energy is called nutrition.

Nutrients:

Nutrients are the elements and compounds that an organism obtains and use as energy source or as components for the synthesis of new materials.

Nutrition is essential for several purposes:

1. It constitutes a source of energy for the organism.
2. It provides building material for growth and development.
3. It regulates various body functions.

We know that autotrophic organisms (some bacteria, all algae, and all plants) obtain water, carbon dioxide, and minerals from their environment and prepare their food which is then used for growth and energy. On the other hand, heterotrophic organisms (most bacteria, and all protozoans, fungi, and animals) obtain their food from other organisms and use it for growth and energy.

Macronutrients:

The elements which are required by plants in larger quantities are called macronutrients. These are nine in number.

Micronutrients:

The minerals elements which are required in lower quantities are called micronutrients. These are eight in number.

Note:

If any one of these is not supplied, plants display abnormalities of growth and do not reproduce normally.

Note: Carbon and oxygen are absorbed from the air, while other elements are absorbed from the soil.

Roles of Nitrogen:

Plants get nitrogen in the form of nitrates. Nitrogen is a major component of proteins, hormones, chlorophyll, vitamins, and enzymes essential for plant life. Nitrogen metabolism is a major factor in stem and leaf growth. Too much nitrogen can delay flowering and fruiting.

Effects of the lack of nitrate ions:

Deficiencies of nitrogen can reduce yields, cause yellowing of the leaves, and stunt growth. Roles of Magnesium: Magnesium is a structural component of the chlorophyll molecule and is necessary for the functioning of plant enzymes to produce carbohydrates, sugars, and fats. It is used for fruit and nut formation and is essential for the germination of seeds. Effects of the lack of magnesium ions: Deficiency of magnesium causes yellowing and wilting of leaves

The distinction between organic and inorganic fertilizers is not always clear-cut. Urea, for example, is an organic compound, but chemically synthesized urea is generally grouped with inorganic fertilizers.

Fertilizers:

Nutrients applied to crops to speed up their growth are called fertilizers.

Classification of Fertilizers:

Fertilizers are broadly classified as organic or inorganic.

1. Importance of inorganic fertilizers:

Naturally occurring inorganic fertilizers include rock phosphate, elemental sulfur, and gypsum that are not chemically modified. If nitrogen is the main element, they are often described as nitrogen fertilizers. Most inorganic fertilizers dissolve readily in water and are immediately available to plants for uptake. These fertilizers efficiently supply the required nutrients for plant growth

1. Importance of organic fertilizers:

Natural organic fertilizer is derived from either plant or animal materials containing one or more essential elements. Organic fertilizers are more complex chemical substances that take time to be broken down into forms usable by plants. They have fewer salts so their larger amounts can be applied without injury to plant roots. However, their excessive amounts can cause environmental degradation due to nitrate leaching or runoff of soluble organic compounds. Manure and compost are used as organic fertilizers. They can also increase soil drainage, aeration, water holding capacity, and the ability of the soil to hold nutrients.

Environmental hazards related to fertilizers' use:

1. The massive quantities of inorganic fertilizers affect the soil nutrient-holding capacity
2. Eutrophication:

High solubilities of fertilizers also degrade ecosystems through eutrophication (which means an increase in chemical nutrients - typically compounds containing nitrogen or phosphorus - in an ecosystem).

1. Storage and application of some nitrogen fertilizers may cause emissions of the greenhouse gas nitrous oxide (N₂O). Ammonia gas (NH₃) may be emitted from the applied inorganic fertilizers. This extra ammonia can also increase soil acidity
2. Excessive nitrogen fertilizers can lead to pest problems by increasing their reproduction rate.

Note:

For these reasons, it is recommended that the nutrient content of the soil and nutrient requirements of the crop are carefully balanced with the application of inorganic fertilizer.

Carnivorous plants have evolved mechanisms for trapping and digesting small animals. The products of this digestion are used to supplement the plant's supply of nitrogen. 

Phases of Nutrition in Animals:

Nutrition in animals occurs in five phases namely ingestion, digestion, absorption, assimilation, and defecation.

Inorganic fertilizer, 

Carbohydrate:

Food belonging to the group consisting of sugars, starch, and glucose is called carbohydrates. Carbohydrates are vital for energy in humans.

Importance of Carbohydrates in Food:

Carbohydrates are the basic source of energy for all animals. Animals get their carbohydrates from their environment (compared with plants, which synthesize carbohydrates during photosynthesis). Carbohydrates require less water for their digestion. About half to 2/3 of the total calories every animal consumes daily is from carbohydrates. Glucose is the carbohydrate most often used as an energy source. It is metabolized during cellular respiration and part of the energy is used to synthesize ATP. Other useful carbohydrates are maltose, lactose, sucrose, and starch.

Energy value of carbohydrates:

Carbohydrates contain 04 kilocalories per gram.

Sources of carbohydrates:

Humans get carbohydrates from foods like bread, pasta, beans, potatoes, bran, rice, and cereals.

Carbohydrates are the most common source of energy. Proteins and lipids are vital building components for the body, but they can also be used for energy.

Good calcium nutrition, along with low salt and high potassium intake, prevents hypertension and kidney stones.

Lipids (fats) in Food:

The lipids present in food are composed of fatty acids bonded to glycerol. The fatty acids of lipids may be saturated or unsaturated. Saturated fatty acids have all of their carbon atoms bonded to hydrogen atoms, whereas unsaturated fatty acids have some of their carbon atoms double-bonded in place of a hydrogen atom.

Saturated fatty acids:

Generally, the lipids containing saturated fatty acids are solid at room temperature.

Unsaturated fatty acids:

The lipids containing unsaturated fatty acids are liquid at room temperature. For example, butter contains nearly 70% saturated and 30% unsaturated fatty acids Sunflower oil, on the other hand, contains nearly 75% unsaturated fatty acids.

Importance of lipids in our diets:

Lipids are used to form membranes, the sheaths surrounding neurons, and certain hormones. Lipids are also extremely useful energy sources.

Energy value of lipids:

One gram of lipids contains 09 kilocalories of energy.

Dietary sources of lipids:

Important sources of lipids include milk, butter, cheese, eggs, mutton, fish, mustard seeds, coconut, dry fruits, etc.

Proteins in Food:

Proteins can be converted into carbohydrates. Proteins are composed of amino acids. The body requires amino acids to produce new body protein and to replace damaged proteins.

Classification of Amino Acids:

Amino acids are classified as essential (which we cannot produce) and nonessential (which we can produce from other nitrogen-containing compounds) amino acids.

Importance of proteins in our diets:

Proteins are essential components of the cytoplasm, membranes, and organelles. They are also the major components of muscles, ligaments, and tendons, and many of them play the role of enzymes. Proteins can also be used for gaining energy.

Energy value of proteins:

One gram of proteins contains 04 kilocalories of energy.

Dietary sources of protein:

Dietary sources of protein are meat, eggs, grains, legumes, and dairy products such as milk and cheese. 

Saturated fatty acids can increase a person's cholesterol level. An increased cholesterol level may eventually result in the clogging of arteries and, ultimately, heart disease. 

Minerals in Food:

Minerals are categorized into major and trace minerals. Major minerals are those that are required in the amounts of 100 mg (milligrams) or more per day, while trace minerals are required in amounts less than 100 mg per day.

Role of Calcium:

Calcium is essential for the development and maintenance of bones and teeth. It is also needed for maintaining cell membranes and connective tissues and for the activation of several enzymes. Calcium also aids in blood clotting.

Foods Containing Calcium:

Humans get calcium from milk, cheese, egg yolk, beans, nuts, cabbage, etc.

Effects of Deficiency of Calcium:

The deficiency of calcium causes the spontaneous discharge of nerve impulses which may result in tetany Bones also becoming soft, blood clots slowly, and wounds healing slowly.

Role of Iron:

Iron plays a major role in oxygen transport and storage and is a component of hemoglobin in red blood cells and myoglobin in muscle cells. Cellular energy production also requires iron which acts as an enzyme cofactor. Iron also supports immune function.

Foods Containing Iron:

Humans get iron from red meat, egg yolk, whole wheat, fish, spinach, mustard, etc.

Effects of Deficiency of Iron:

Iron deficiency causes anemia which affects hundreds of millions of people. Infants, young children, adolescents, and pregnant and lactating women are especially vulnerable due to their high demand for iron.

Sources of Vitamins A:

Humans get vitamin A from leafy vegetables (spinach, carrots), yellow/orange fruits (mango), liver, fish, egg, milk, butter, etc.

Deficiency symptoms of vitamins A:

The deficiency of vitamin A is the leading cause of blindness in children worldwide. One of the symptoms of vitamin-A deficiency is night blindness. It is a temporary condition, but if left untreated it can cause permanent blindness. Vitamin-A deficiency can also cause a condition in which hair follicles become plugged with keratin, giving a bumpy appearance and rough, dry texture to the skin.

Vitamins: Organic substances which are essential in a small amount to regulate the metabolism and maintain the immune system are called vitamins.

Importance of vitamin A/Function of vitamin A:

Vitamin A was the first fat-soluble vitamin identified in 1913). It performs the following functions.

1. Vitamin A combines with a protein called opsin to form rhodopsin in the rod cells of the retina of the eye. When vitamin A is inadequate, the lack of rhodopsin makes it difficult to see in dim light.
2. It is involved in normal cell differentiation, a process through which embryonic cells transform into mature cells with highly specific functions.
3. Vitamin A supports male and female reproductive processes and bone growth. iv. It is essential for immune function and vitamin-A deficiency causes decreased resistance to infections.
4. It is essential for immune function and vitamin-A deficiency causes decreased resistance to infections.

Importance of vitamin C/Function of vitamin C (Ascorbic Acid):

1. Vitamin C participates in many reactions by donating electrons, essential to the activity of many enzymes. Collagen: Vitamin C is needed to form collagen (a fibrous protein) that gives strength to connective tissues. Collagen is also needed for the healing of wounds.
2. Vitamin C in white blood cells enables the immune system to function properly.

Importance of vitamin D/Function of vitamin D:

1. The best-known function of vitamin D is to help regulate blood levels of calcium and phosphorous
2. Vitamin D increases absorption of these minerals from the intestine and their deposition in bones.

Proteins. 

Minute quantities of vitamin C are present in muscles. Since meat consists of muscles so it is not a good source of vitamin C

Sources of Vitamins C:

We get vitamin C from citrus fruits (e.g., oranges, lemons, and grapefruit), leafy green vegetables, beef liver, etc.

Deficiency symptoms of vitamins C:

The deficiency of vitamin C causes connective tissue changes throughout the body.

Scurvy:

The disease known as Scurvy results from a lack of vitamin C in this condition the synthesized collagen is too unstable. Symptoms of scurvy include tiredness, nausea, muscle and joint pain, swollen and bleeding gums, slow wounds healing, and dry skin and hair.

Sources of Vitamins D:

Vitamin D is mainly found in fish liver oil, milk, ghee, butter, etc. It is also synthesized by the skin when ultraviolet (UV) radiation from the sun is used to convert a cholesterol derivative into vitamin D.

Deficiency symptoms of vitamins D:

Long-term deficiency of vitamin D affects the bones.

Rickets:

In children, vitamin D deficiency leads to rickets, a condition in which bones weaken and bow under pressure.

Osteomalacia, or "soft bones,":

In adults, vitamin D deficiency causes Osteomalacia, or "soft bones," increasing the risk for fractures in bones.

Effects of water and dietary fibre:

Water and dietary fibre are not considered nutrients, but they do play important role in life.

Importance of water in our diets:

1. Approximately 60% of the adult human body is composed of water. Nearly all life-sustaining chemical reactions require an aqueous (watery) environment.
2. Water also functions as the environment in which water-soluble foodstuff is absorbed in the intestines and the waste products are eliminated in urine.
3. Another essential role of water is to maintain body temperature through evaporation, as in sweating.
4. Severe dehydration may result in cardiovascular problems.
5. Water toxicity (too much water) is also possible, resulting in dilution of important electrolytes (mineral salts) that may lead to irregular heart rhythm.
6. The estimated water requirement of an average adult is two litres per day.

Important sources of daily water intake are natural water, milk, juicy fruits and vegetables.

Importance of Dietary fibre "roughage" in our diets:

Dietary fibre (also known as "roughage") is the part of human food that is indigestible. It is found only in plant foods and it moves undigested through the stomach and small intestine and into the colon.

Types of dietary fibre:

There are two types of dietary fibre; insoluble and soluble.

Insoluble fibre:

Insoluble fibre travels through the small intestines quickly. Wheat bran, whole-grain bread and cereals, as well as the skins of many fruits and vegetables consist of insoluble fibres.

Soluble fibre:

Soluble fibre breaks down as it passes through the digestive tract, forming a gel. This gel traps some substances, and it helps in lowering the blood levels of cholesterol and sugars. Examples of soluble fibres are oats, beans, barley, and many fruits and vegetables.

The recommended dose of fibre per day:

Physicians recommend consuming 20 to 35 grams of fibre per day.

Functions of fibre:

1. Fibre prevents and relieves constipation by stimulating the movement of the intestinal muscles, increasing stool bulk and making stools softer and easier to pass.
2. It also controls weight by creating a feeling of fullness without adding too many calories to the diet.

Reduction of risks by dietary fibre:

Dietary fibre can also reduce the risk of many other health conditions for example:

1. Avoiding constipation reduces the risk of developing haemorrhoids (swollen anal tissues).
2. Soluble fibre takes some acids away in the stool and in response, the liver draws cholesterol from the blood to make more acids, thus lowering blood cholesterol.
3. Soluble fibre slows the absorption of blood sugar from the small intestine, lowering blood sugar levels.
4. Insoluble fibre minimizes exposure to carcinogens (cancer-causing agents) that may be in the stool by diluting them and speeding their movement through the bowel.

Fiber supplements (such as ispaghol husk) should be used only with a physician's recommendations. Taken properly, these supplement constipation and in lowering cholesterol levels.

Balanced Diet:

A balanced diet may be defined as one which contains all the essential nutrients like carbohydrates, fats, proteins, minerals, and vitamins in the correct proportion for the normal growth and development of the body.

Relation of a balanced diet with age, gender, and activity:

A balanced diet is related to the state of one's age, sex, and activity Balance Diet during growth period: During the growth period of the body there is a higher metabolic rate in body cells and so the body needs a balanced diet that contains more energy.

Balance Diet during the adult period:

Adults need fewer proteins per kg body weight, but a growing boy or girl needs more proteins per kg weight. Similarly, children need more calcium and iron for their growing bones and red blood cells respectively.

Impact of gender on Balance Diet:

Gender has an impact on the requirements of a balanced diet. Women have comparatively less metabolic rates than men of the same age and weight. So, men need a balanced diet that provides comparatively more energy than women require.

Different people have different lifestyles and varied nature of work. A man with sedentary habits does not require as much energy as a man who is on his feet for most of the day.

Dietary fibre.

Problems Related to Nutrition (Malnutrition)

Problems related to nutrition are grouped as malnutrition. Malnutrition is a term for the condition caused by an improper or insufficient diet. It most often refers to undernutrition resulting from inadequate consumption, poor absorption, or excessive loss of nutrients, Malnutrition also includes overnutrition, resulting from overheating or excessive intake of specific nutrients.

Major Forms of Malnutrition:

Common forms of malnutrition include protein-energy malnutrition (PEM), mineral deficiency disease (MDD), and over-intake of nutrients (OIN).

Protein-Energy Malnutrition (PEM):

Protein-energy malnutrition refers to inadequate availability or absorption of energy and proteins in the body. It is the leading cause of death in children in developing countries.

Primary PEM:

Primary PEM results from a diet that lacks sufficient sources of protein and/or energy.

Secondary PEM:

Secondary PEM occurs as a complication of other diseases (AIDS, cancer, kidney failure, etc) that impair the body's ability to absorb or use nutrients.

Diseases caused by PEM:

PEM may lead to diseases such as Kwashiorkor and marasmus

1. Kwashiorkor:

   Kwashiorkor is due to protein deficiency at the age of about 12 months when breastfeeding is discontinued, but it can also develop at any time during a child's growing years. Children may grow to normal height but are abnormally thin.

2. Marasmus:

   Marasmus usually develops between the ages of six months and one year in children. Patients lose all their body fat and muscle strength and acquire a skeletal appearance. Children with marasmus show poor growth and look small for their age.

Mineral Deficiency Diseases (MDD):

Diseases resulting from the deficiency of a mineral are relatively rare among humans. Some examples are given below:

1. Goiter:

   Goiter is a condition caused by an insufficient amount of iodine in the diet. Iodine is used by the thyroid gland to produce hormones that control the body's normal functioning and growth. If sufficient iodine is not available in a person's diet, the thyroid gland becomes enlarged and results in swelling in the neck and the condition is known as goiter.

2. Anemia:

   Anemia is the most common of all mineral deficiency diseases. The term anemia means "a lack of blood." The condition is caused when the number of red blood cells is reduced to a level lower than normal. We know that the hemoglobin molecule contains a single atom of iron at its center. If the body fails to receive sufficient amounts of iron, an adequate number of hemoglobin molecules will not be formed. In that case, there are not enough functioning red blood cells. A person becomes weak and listless.

Over-Intake of Nutrients (OIN):

Over-intake of nutrients (OIN) is a form of malnutrition in which more nutrients are taken than the amounts required for normal growth, development, and metabolism. The effects of the over-intake of nutrients are usually intensified when there is a reduction in daily physical activity (decline in energy expenditure).

Over-intake of nutrients causes several health problems. For example, a high intake of carbohydrates and fats leads to obesity, diabetes, and cardiovascular problems. Similarly, a high dose of vitamin A causes loss of appetite and liver problems, and an excess dose of vitamin D can lead to the deposition of calcium in various tissues, etc.

Effects of Malnutrition:

An extended period of malnutrition can lead to problems like starvation, heart diseases, constipation, and obesity.

Starvation:

Starvation is a severe reduction in nutrient and energy intake and is the most horrible effect of malnutrition. In humans, prolonged starvation causes permanent organ damage and eventually results in death.

Heart diseases:

Heart diseases are also increasing on the global level and one of the causes of these is malnutrition. People who take an unbalanced diet (high in fats) are more exposed to heart problems. We know that fatty foods increase 'blood cholesterol levels, which obstructs the blood vessels leading to heart diseases.

Constipation:

Malnutrition often leads to situations where people cannot schedule their meals. This irregularity results in several health problems including constipation.

Obesity:

Obesity means becoming overweight and it may also be due to malnutrition. People who take food that contains energy more than their requirement and do very little physical work can become obese. Obesity is known as the mother's disease and may lead to heart problems, hypertension, diabetes, etc.

The World Health Organization (WHO) estimates that, within the next few years, diseases due to malnutrition will become the principal global cause of mortality.

According to the Food and Agriculture Organization of the United Nations, more than 25,000 people die of starvation every day. On average, every five seconds a child dies from starvation.

Famine-the major Cause of Malnutrition:

Famine is the lack of enough food to feed all the people living in an area. It is a social and economic crisis that results in malnutrition and increased mortality Historically, famines have occurred because of drought, crop failure, and because of man-made causes such as war or misguided economic policies. The most terrible famines of the twentieth century include the disaster in Bengal (1942-1945), famines in China (1928 and 1942), and famine in Ukraine (1932-33). The last great famines of this century were the disaster in Cambodia Ethiopian famine (1983-85) and the North Korean famine (the 1990s). Famine may be due to unequal distribution of flood, drought, flooding, or increasing population.

Unequal distribution of food:

The achievements in science have enabled human beings to produce better food in terms of quality and quantity. Today the agricultural practices produce more than enough food that can be supplied to everyone on earth. But due to political and administrative problems, the food is not equally distributed to the different regions of the world. The result is that there is always surplus food in countries like America, the UK, Canada, etc, and at the same time people have nothing to eat in countries like Ethiopia, Somalia, etc.

Drought:

A drought is a period when there is not enough water to support agricultural and human needs. Drought is usually due to an extended period of below-normal rainfall. Droughts decrease or even stop the crop yields resulting in famine.

Flooding:

It occurs due to more than normal rainfall or due to a weak water distribution system. Rivers and canals overflow their banks and destroy the soil quality of agricultural lands, it becomes impossible to grow crops immediately after flooding. In this way, flooding may be a reason for short-term famine in a country.

Increasing population:

Despite the global increase in food production, millions of human beings are undernourished. In the over-populated regions of the world, large populations overuse natural resources to grow maximum food to meet the problems of food shortage. It leads to dry and infertile lands and depletion of resources. In such situations, crops can no longer be grown and famines result.

Importance of the process of digestion in humans:

Our cells require oxygen, water, salts, amino acids, simple sugars, fatty acids, and vitamins. These can cross cell membranes to enter the cells. Amino acids, simple sugars, and fatty acids are rare in our environment. Such substances are usually parts of larger molecules like proteins, polysaccharides, and lipids, which cannot cross the membranes. There is a need of converting such large and non-diffusible molecules into smaller and diffusible molecules that can cross the membranes. This is achieved through the process of digestion.

Difference between mechanical and chemical digestion:

Mechanical digestion: Mechanical digestion involves mastication, the use of teeth to tear and crush food, and churning in the stomach.

Chemical digestion:

Chemical digestion involves the action of enzymes to break down complex molecules into simple structures. Proteins are digested into their constituent amino acids, polysaccharides are digested into simple sugars (e.g., glucose), and lipids are digested into fatty acids and glycerol.

Responsibilities of the digestive system:

Our digestive system is responsible for the ingestion of food, its digestion into diffusible molecules, absorption of digested food, and the elimination of indigestible material.

Alimentary canal:

The digestive system of a human consists of a long tube that extends from the mouth to the anus. This tube is called the alimentary canal. Structure of human alimentary canal: Main sections of the alimentary canal are:

1. Oral cavity 2. Pharynx 3. Oesophagus,                 
2. Stomach 5. Small intestines               6. Large intestine.

Glands associated with the alimentary canal:

In addition, there are many glands associated with the alimentary canal. These are the three pairs of salivary glands, the pancreas, and the liver.

Oral cavity - (Selection, grinding, partial digestion):

Functions of the oral cavity:

1. Food Selection:

The oral cavity is the space behind the mouth and has many important functions in the whole process. Food selection is one of them. When food enters the oral cavity, it is tasted and felt. If the taste of mutton suggests that it is old, we reject it. If the teeth or tongue detect some hard object, such as dirt, we also reject that bite. The senses of smell and vision also help the oral cavity in the selection of food.

2. Grinding of food:

The second function of the oral cavity is the grinding of food by teeth. It is known as chewing or mastication. This is useful first because the esophagus can pass only small pieces and secondly because enzymes cannot act on large pieces of food. They require small pieces with large surface areas to attack.

3. Lubrication and chemical digestion of food:

The third and fourth functions of the oral cavity are the lubrication and chemical digestion of food. The chewing process stimulates the three pairs of salivary glands (under the tongue, behind the jaws, and in front of the ears) to release a juice called saliva in the oral cavity.

Functions of Saliva:

Saliva has two main functions. First, it adds water and mucous to the food which acts as lubricants to ease the passage of food through the esophagus. Second, saliva contains the enzyme salivary amylase, which aids in the partial digestion of starch.

Bolus:

After the processes of chewing, lubrication, and partial digestion the pieces of bread and mutton are rolled up by the tongue into a small, slippery, spherical mass called a bolus. We swallow the bolus and push it into the esophagus through the pharynx.

Pharynx and Oesophagus- (Swallowing and Peristalsis):

The bolus is swallowed and then pushed down by the movement called peristalsis.

Steps in swallowing:

During swallowing the bolus is pushed to the back of the mouth by the tongue. The soft palate moves upward and to the rear to close the opening of the nasal cavity.

When swallowed, the bolus goes to the pharynx, which makes special adaptations to prevent choking or aspiration when food is swallowed. When the larynx (the top of the trachea) moves upward, it forces the. epiglottis (a flap of cartilage) into a more or less horizontal position thus closing the glottis i.e., opening of the windpipe (trachea) The beginning of the swallowing action is voluntary, but once the food reaches the back of the mouth, swallowing becomes automatic.

After being swallowed, the food enters the tube called the esophagus, which connects the pharynx to the stomach. Neither the pharynx nor the esophagus contributes to digestion and the previous digestive actions of saliva continue.

Steps in Peristalsis:

Peristalsis moves the food from the oral cavity to the rectum. It is defined as the rhythmic sequence of waves of contraction in the smooth muscles of the walls of the alimentary canal, thus squeezing the food down along the alimentary canal.

Note:

If due for any reason, the direction of peristalsis reverses, what would be the result? It results would be vomiting.

Stomach - (Digestion, churning, and melting):

The stomach is a dilated part of the alimentary canal. It is J-shaped, located on the left of the abdomen, just beneath the diaphragm.

Portions of Stomach:

The stomach has two main portions.

1. Cardiac portion:

The cardiac portion is present immediately after the esophagus.

1. Pyloric portion:

 The pyloric portion is located beneath the cardiac portion. The stomach has two sphincters (openings that are guarded by muscles).

Cardiac sphincter and pyloric sphincter:

The cardiac sphincter is between the stomach and esophagus while the pyloric sphincter is between the stomach and the small intestine. The bolus enters the stomach from the esophagus through the cardiac sphincter.

Entrance of Food In the stomach:

When food enters the stomach, the gastric glands found in the stomach wall are stimulated to secrete gastric juice. It is composed chiefly of mucous, hydrochloric acid, and a protein-digesting enzyme pepsinogen.

Functions of Hydrochloric acid:

Hydrochloric acid converts the inactive enzyme pepsinogen into its active form called pepsin, HCI also kills microorganisms present in food. Pepsin partially digests the protein portion of the food (the bulk of mutton) into polypeptide and shorter peptide chains.

Churning action:

In the stomach, food is further broken apart through a process of churning. The walls of the stomach contract and relax and these movements help in the thorough mixing of the gastric juice and food. The churning action also produces heat which helps to melt the lipid content of the food.

Note:

The starch in our bite of bread and the protein in mutton have been partially digested and the food has been converted to a soup-like mixture called chyme. After it, the pyloric sphincter allows a little mass of chyme to enter the duodenum.

Small Intestine - (Complete digestion and absorption):

The function of Small Intestine:

Duodenum comprises the first 10 inches (25 cm) of the small intestine and it is the part of the alimentary canal where most of the digestive process occurs. Here the food is further mixed with 3 different secretions.

1. Bile from the liver helps in fat digestion through emulsification.
2. Pancreatic juice from the pancreas contains enzymes trypsin, pancreatic amylase, and lipase which digest proteins, carbohydrates, and lipids respectively
3. Intestinal juice from the intestine walls contains many enzymes for the complete digestion of all kinds of food.

Jejunum:

Next to the duodenum is 2.4 meters long jejunum. It is concerned with the rest of the digestion of the proteins, starch, and lipids of our bite.

The function of Ileum:

Last 3.5 meters long part of the small intestine is the ileum. It is concerned with the absorption of digested food.

The function of Villi:

There are circular folds in the inner wall of the ileum. These folds have numerous fingerlike projections called villi (singular: Villus). The villi increase the surface of the inner walls and it helps a lot in the absorption of digested food. Each villus is richly supplied with blood capillaries and a vessel of the lymphatic system called a lacteal. The walls of the villus are only single-cell thick. The digested molecules i.e., simple sugars and amino acids are absorbed from the intestine into the blood capillaries present in villi. The blood carries them away from the small intestine via the hepatic portal vein and goes to the liver for filtering, removal of toxins, and nutrient processing. Fatty acids and glycerol are absorbed into the lymphatic vessel (lacteal) present in villi, which carries them to the main lymphatic duct, from where they enter the bloodstream.

Large intestine- (Absorption of water and defecation)

After the digested products of our bite have been absorbed in the blood, the remaining mass enters the large intestine.

Parts of Large intestine:

It has 3 parts:

1. The caecum (or pouch that forms the T-junction with the small intestine).
2. The colon
3. The rectum.

From the colon, water is absorbed into the blood. As the water is absorbed, the solid remains of the food are called feces. The feces contain the undigested material A large number of bacteria, sloughed-off cells of the alimentary canal, bile pigments, and water are also part of the feces. Feces are temporarily stored in the rectum, which opens out through the anus. Under normal conditions when the rectum is filled up with feces, it gives rise to a reflex, and the anus is opened for defecation.

Appendix:

From the blind end of the caecum, there arises a non-functional finger-like process called the appendix. Inflammation of the appendix due to infection causes severe pain. The infected appendix must be removed surgically otherwise it may burst and the inflammation may spread to the abdomen.

Many bacteria live in the colon. They produce vitamin K, which is necessary for the coagulation of blood.

Pharynx and Oesophagus - (Swallowing and Peristalsis):

The bolus is swallowed and then pushed down by the movement called peristalsis.

Steps in swallowing:

During swallowing the bolus is pushed to the back of the mouth by the tongue. The soft palate moves upward and to the rear to close the opening of the nasal cavity. When swallowed, the bolus goes to the pharynx, which makes special adaptations to prevent choking or aspiration when food is swallowed. When the larynx (the top of the trachea) moves upward, it forces the epiglottis (a flap of cartilage) into a more or less horizontal position thus closing the glottis i.e., opening of the windpipe (trachea) The beginning of the swallowing action is voluntary, but once the food reaches the back of the mouth, swallowing becomes automatic.

After being swallowed, the food enters the tube called the oesophagus, which connects the pharynx to the stomach. Neither the pharynx nor the oesophagus contributes to digestion and the previous digestive actions of saliva continue.

Steps in Peristalsis:

Peristalsis moves the food from the oral cavity to the rectum. It is defined as the rhythmic sequence of waves of contraction in the smooth muscles of the walls of the alimentary canal, thus squeezing the food down along the alimentary canal.

We saw that pepsin is not released in its active form. Rather it is secreted as inactive pepsinogen, which requires HCI for activation. The mucous of gastric juice form a thick coating over the inner walls of the stomach and neutralizes the HCI there. It makes pepsinogen difficult to be activated and to attack stomach walls.

When we bite off a piece of roti and mutton, chew it and then swallow it, there is some gastric juice already present in the stomach. Sometimes even the sight of food causes the release of gastric juice. When the bite is in the oral cavity, the message is conveyed to the brain in the form of nerve impulses. From the brain, the message is passed to the walls of the stomach for the secretion of some gastric juice. When food touches the walls of the stomach, more gastric juice is secreted. If we eat only a bite of bread, which has little protein in it, the stomach does not secrete more gastric juice.

When we eat mutton, it results in the release of abundant gastric juice. The reason is that when food reaches the stomach the already present gastric juice begins the digestion of any proteins present in it. The huge protein molecules are broken down into peptides. These peptides stimulate some cells of the stomach walls to release a hormone called gastrin. This hormone enters the blood and is distributed to all parts of the body, including the stomach. Here it has a specific effect and stimulates the cells of gastric glands to secrete more gastric juice.

Absorption of water and salts. 

Liver:

A dark reddish organ, the liver is the largest gland of the body. In an adult human, it weighs about 1.5 kg and is the size of a football. The liver lies beneath the diaphragm on the right side of the abdomen. It consists of a larger right lobe and a smaller left lobe.

Gallbladder:

A pear-shaped greenish-yellow sac, the gallbladder lies along the right lobe of the liver on the ventral side.

Secretion of Liver (Bile):

The liver secretes bile, which is stored in the gallbladder. When the gallbladder contracts the bile is released into the duodenum through the common bile duct. Bile has bile salts that keep lipid droplets separate from one another, a process called emulsification. It helps the lipid-digesting enzymes to attack lipids.

Role of Liver indigestion/Functions of Liver:

Besides digestion, the liver carries out several other functions, some of which are summarized here:

1. Removes amino groups from amino acids (de-amination)
2. Converts ammonia to a less toxic form the urea
3. Manufactures most blood plasma proteins e.g., prothrombin and albumin
4. Forms red blood cells in the fetus
5. Destroys the old red blood cells
6. Manufactures blood clotting proteins called fibrinogen
7. Synthesizes non-essential amino acids
8. Converts galactose and fructose to glucose
9. Converts glucose into glycogen and, when required, breaks glycogen into glucose
10. Converts carbohydrates and proteins into fats
11. Carries out the oxidation of fatty acids
12. Forms lipoproteins, cholesterol, and phospholipids
13. Synthesizes vitamin A from carotene, and activates vitamin D
14. Produces heat to maintain body temperature
15. Stores fat-soluble vitamins (A, D, E, and K) and mineral ions, such as iron.
16. Produces antiviral proteins e.g., Interferon

There is a growing concern about the harmful effects of carbonated soft drinks. They are very acidic and make our bodies poor in oxygen. They contain phosphoric acid which dissolves calcium from the bones. This results in bones weakening. The caffeine present in colas increases the heart rate and raises blood pressure.

Small intestine

Stomach, small intestine, oral cavity. 

Disorders of the gut:

Diarrhea, constipation, and ulcer are the most common disorders of the gut that affect several people.

Diarrhea:

Diarrhea is a condition in which the sufferer has frequent watery, loose bowel movements.

Signs and symptoms of Diarrhea:

This condition may be accompanied by abdominal pain, nausea, and vomiting.

Causes of Diarrhea:

It occurs when required water is not absorbed in blood from the colon. If the colon is damaged or inflamed, absorption is inhibited, and watery stools result. The main causes of diarrhea include a lack of adequate safe water. Diarrhea is also caused by viral or bacterial infections.

Recovery of diarrhea:

If sufficient food and water are available a patient recovers from diarrhea in a few days. However, for malnourished individuals’ diarrhea can lead to severe dehydration and can become life-threatening.

Treatment of diarrhea:

The treatment for diarrhea involves consuming adequate amounts of water to replace the loss, preferably mixed with electrolytes to provide essential salts and some amount of nutrients. Antibiotics may be required if diarrhea is due to bacterial infection.

Preventions for diarrhea:

Preventions for diarrhea include taking proper water and electrolytes, eating regularly, and taking hygienic measures.

Constipation:

Constipation is a condition where a person experiences hard feces that are difficult to eliminate.

Signs and Symptoms of constipation:

In severe cases, it may lead to symptoms of bowel obstruction.

Causes of Constipation:

The main causes of constipation include hardening of the feces due to excessive absorption of water through the colon, insufficient intake of dietary fiber, dehydration, use of medicines (e.g., those containing iron, calcium, and aluminum), injured anal sphincter, and tumors in the rectum or anus.

Treatment of constipation:

Treatment of constipation is with a change in dietary and exercise habits. Enemas can be used to provide a form of mechanical stimulation. Laxatives (e.g., paraffin) may be necessary in some cases.

Prevention of constipation:

Constipation is usually easier to prevent than to treat. One should take the required quantities of water and dietary fibers.

Ulcers:

An ulcer (peptic ulcer) is a sore in the gut lining caused by a gradual breakdown of the tissue by the acidic gastric juice. An ulcer of the stomach is called a gastric ulcer of the duodenum, a duodenal ulcer, and of the esophagus, an esophageal ulcer.

Causes of Ulcer:

The causes of ulcers include excess acid, infection, long-term use of anti-inflammatory medicines (including aspirin), smoking, drinking coffee, and colas, and eating spicy foods.

Signs and Symptoms of Ulcer:

The signs and symptoms of an ulcer include abdominal burning after meals or at midnight. Severe ulcers may cause abdominal pain, the rush of saliva after an episode of regurgitation, nausea, loss of appetite, and weight loss.

Treatment of Ulcer:

An ulcer is treated with medicines containing alkaline composition.

Prevention of Ulcers:

Preventive measures should be adopted for such complications. Spicy foods and those containing more acidity should be avoided. As smoking is a major factor in ulcers, it should be avoided.

We should avoid the routine non-medical use of laxatives as this makes us habitual and bowel action becomes dependent upon their use. 

Elimination of Pigments: Bile also contains pigments that are byproducts of red blood cell destruction in the liver, these bile pigments are eliminated from the body with the feces.