Nutrition is defined as the process by which an organism gets food which is utilized for the provision of energy and things for its life sustaining activities. It includes ways an organism gets its food and as well the processes by which the nutrients in the food are converted to simpler molecules for use by the body.

Holozoic Nutrition

Animals exhibit holozoic nutrition because they are not able to manufacture their own food. Holozoic animals are roughly divided into three categories in relation to their mode of feeding. These three categories of animals are Herbivores, Omnivores, and Carnivores.
Herbivores feed on grasses, carnivores feed on animal fresh and omnivore feed on both glasses and flesh.
Digestive System in Cockroach (Invertebrates)
Nutrition in cockroach is holozoic and it is an omnivore, feeding on various types of organic matter. It eats pieces of food and grinds them before digesting them. Thus a cockroach has mouth parts that are modified accordingly for chewing the food.

Structure of the Human Digestive System

The structure of the human digestive system is tailored to the omnivorous diet. The human digestive system is made up of an alimentary canal, which is roughly 8 metres long. The alimentary canal takes care of digestion, absorption and egestion.
Mouth Cavity
The Mouth cavity is the anterior opening of the digestive system through which food is ingested. It has a muscular tongue which bears the taste buds. The human mouth is made up of two rows of teeth – upper and lower.
The Pharynx is the part of the alimentary canal that is located after the mouth. It is a funnel-shaped air and food passage.
The oesophagus opens into the stomach. The stomach is situated on the left side of the abdomen. It is a sac-like organ, which is linked to the oesophagus at the anterior by a cardiac sphincter and to the small intestine at the posterior end by a pyloric sphincter.
The stomach is a flexible organ with a wall made up of folds. These folds unfasten to give room for more food.
It serves as a temporary storage organ for the food for about 4 hours. It is made up of three layers of muscles, not like the other parts of the alimentary canal, which assist in churning the food.
Small Intestine
Duodenum is a short part of the small intestine which is made up of loops and measures about 25 cm.
Large Intestine
The small intestine enlarges a little to form a tubular large intestine which is 5cm wide and 2m long.

Digestive Glands and Their Secretions

It is the largest gland and is found in the upper part of the abdomen on the right side just below the diaphragm. Its secretion is called bile juice. It is alkaline and rich in organic (steroid) salts called the bile salts.
The alkaline nature serves to neutralize the acidic pH of the gastric juice and creates the right environment for the intestinal enzymes to function.
Organ System: Gall Bladdar
This is a minute sac-like elongated organ close to the liver. The surplus bile secretion is stored in the gall bladder. It is linked with the liver by a duct known as the cystic duct. If there is no food in the intestine, the bile juice passes into the gall bladder and is stored there.
It is pumped out by the muscular contraction of the gall bladder wall when the food enters into the small intestine. The cystic duct empties into the widespread bile duct which opens into the small intestine.
Physiology of pancreas
The pancreas is located at the bend of the duodenum. It secretes pancreatic juice which possesses just about neutral pH (6 to 7). This juice is secreted into the common bile duct and subsequently into the duodenum. About 700cc of pancreatic juice is secreted daily.

Mechanism of Digestion

Renin is seen only in young children. The enzyme digests the milk protein, casein. Casein is hydrolysed into paracasein which in turn is precipitated as insoluble calcium paracaseinate. This is known as coagulation.
Renin secreted by the gastric mucosa of the calf is collected to manufacture rennet tablets used commercially to curdle milk.

Digestion Mechanism in Human

The bolus is then transported into the pharynx by an involuntary swallowing action. It is made simpler through the presence of mucus along the walls of the alimentary canal.
Hormonal Control of Digestion
Digestion is in fact carried out by enzymes but the secretion of these enzymes is regulated by the nervous system and the endocrine system.
Digestion is as well regulated by the secretion of organic materials known as hormones by the endocrine glands. Every hormone has a particular target organ. The hormones get to the target organ via the blood stream. The hormones controlling digestion are secreted by the walls of the stomach and duodenum.
After the ingested food has been converted into a soluble form, the intestinal walls of ileum suck up the nutrients as well as water. Due to its larger surface area, skeletal wall lining the cavity and huge number of finger-like projections, known as the villi, the highest absorption occur in this part of the alimentary canal.
The absorbed food passes through the epithelial cells of the villi and then into the blood capillaries in the villi. From the capillaries, the fat-soluble substances move into the lymph. These materials are subsequently transported all through the body by the lymphatic system, which drains them into the blood near the heart.
The food that is digested is absorbed into the blood and lymphatic systems. The lymphatic system transports the digested fats as fatty acids and glycerol into the blood vessel going into the heart. The digested food in the blood stream reaches the liver.
In the liver excess glucose is stored as glycogen to be utilized when needed. The cells obtain the glucose they require from the blood directly for respiration. Cholesterol is produced from a few fatty acids.
The amino acids are utilized to form needed proteins. Excess amino acids are deaminated. During the process of deamination, ammonia is liberated as waste.
This ammonia is broken down into the less unsafe material known as the urea. The urea is subsequently transported through the blood stream to the kidney from where it is given out as urine.

Classification of foods

Carbohydrates are the main energy providers of the organism. They are composed of carbon, hydrogen and oxygen.
Classification and Function of Proteins
Proteins are the main body builders of the body. They are compound molecules made up of carbon, hydrogen, oxygen and nitrogen and occasionally sulphur and phosphorus.
Proteins are used in the synthesis of enzymes (like pepsin, trypsin), hormones (like insulin, adrenaline), carrier proteins (like Haemoglobin), contractile proteins (like myosin, actin), structural proteins (like collagen) and defensive proteins or antibodies.
They as well produce skin pigments such as melanin and nucleic acids of the genetic material, DNA and RNA – purines and pyrimidines.
Fats are the major energy storers of the body. When fat is oxidized, they produce about two and a half times the energy of glucose or glycogen. This is why it majorly appropriate for energy storage.
Fat on the other hands makes use of more oxygen molecules for the oxidation process in comparison with carbohydrates which uses up less oxygen.
Fats are stored in adipose tissue in definite parts of the body like under the skin and between internal organs. As well as serving as an organ for storage, fats are also utilized to manufacture structural lipids like those of membranes.
Vitamins are a multifaceted group of organic compounds that are needed in small quantities for the control of different activities of the body. Although they are required in minute quantities, they are necessary for our well being.
The fact that the majority of them cannot be synthesized in the body, they ought to form a part of our diet. Deficiencies of these vitamins in the diet lead to deficiency disorders.
Minerals of Human Body
Minerals are inorganic nutrients which can be metallic and non-metallic elements that absorbed by the body in the form of salts. There are 24 elements that are utilized in our body. They possess many functions like tissue formation eg., the bone, conduction of nervous impulses, formation of RBCs, and so on.
There are eight key elements needed by man and the others are required in traces. The major elements are sodium, chlorine, potassium, calcium, phosphorus, sulphur and magnesium.
Some of the trace elements or microelements are fluorine, zinc, copper, iodine, iron, manganese, chromium, cobalt, and so on. Nevertheless all of them are crucial for the well-being of the human body. All the minerals are primarily obtained from the plants which absorb them from the soil.

Adult Balanced Nutrition

The human body needs different types of nutrients in order to keep the body healthy and fit. These nutrients ought to be taken properly in our diet. The diet that we follow ought to be balanced. Balanced diet is a diet, which contains all the nutrients required by the body in the right proportions.
Nutritional Deficiency Disorders
Nutritional disorders take place due to malnutrition. Malnutrition refers to bad nutrition and can as a result be applied to both undernourishment and overeating.
Undernourishment is a grave issue especially in the developing countries which occasionally have a large population percentage being deprived of a balanced diet or even a day of full meal. The majority of those affected are children who are below the age of five.
Undernourishment may as a result of proteins, vitamins or minerals deficiency. Deficiency of these nutrients results to diseases, time and again grave and lethal.
Vitamin Deficiency Diseases
The vitamin deficiency disease is caused by the deficiency of vitamin A, which affects the rod cells of the retina. This results to poor adaptation of eyes to dim or night light- a condition known as night blindness.
The cornea and the conjunctiva as well turn dry. This condition is known as xerophthalmia or dry eyes. Serious deficiency results in keratomalacia. In this case, ulcers develop on cornea, giving rise to eventual blindness.
Mineral Salt Deficiency Diseases
Mineral salt deficiency diseases are caused by deficiency of iron. Iron is essential for the production of haemoglobin, a protein that is an oxygen carrier in the blood.
When the level of haemoglobin in the blood drops, it results in the person feeling tired easily, loss of appetite, loss of weight and pale appearance as a result of oxygen lost in the blood.
This condition is referred to as anaemia. This condition can be averted and cured by eating food that are rich in iron like spinach, liver, milk, apple, guava, etc.
Digestive Systems
Animals make use of the organs of their digestive systems to extract crucial nutrients from food they consume, which can later be assimilated.
Digestive Systems of Invertebrate
Invertebrate digestive systems are composed of a gastrovascular cavity with a single opening or an alimentary canal with a true mouth and anus.

Vertebrate Digestive Systems

Vertebrates may have one stomach, complex stomach chambers, or complementary organs that assist to break down ingested food.
Digestive System: Mouth and Stomach
Animal digestion starts in the mouth and subsequently transferred to the pharynx, into the esophagus, and after that into the stomach and small intestine.
Digestive System: Small and Large Intestines
Nutrients are absorbed in the small intestine and waste is geared up for elimination in the large intestine.
Nutrition and Energy Production
Food Requirements
Essential nutrients are nutrients that cannot be manufactured by an animal’s metabolism and need to be obtained from the diet.
Food Energy and ATP