Nutrition in Humans

Nutrition in Humans

Nutrition (also called nourishment or aliment) is the provision, to cells and organisms, of the materials necessary (in the form of food) to support life.

All animals including humans need certain nutrients to stay alive and grow .These nutrients are obtained from food.
These nutrients are:

1. Carbohydrates
2. Fats
3. Proteins
4. Vitamins
5. Minerals

(we also require water and roughage)

• The food that we eat (feeding) is not in the form that can instantly provide you with nutrients.First it has to be broken down into small particles.
• These particles must be changed into simple,soluble,forms which our body cells can absorb.

Only then can food provide nutrients.

The various processes required for digestion of food are as follows:

1. Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in the substance through the mouth.
2. Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream.
3. Absorption is the process by which the food in its soluble form passes through body fluids such as blood.
4. Egestion is the process of elimination of undigested solid parts of the food.

The Human Digestive System

The body performs the steps of nutrition inside a long tube ,coiled in some places called the gut or the alimentary canal.

It's main parts are :

1. The mouth or the Buccal cavity
2. food pipe or oesophagus
3. stomach
4. small intestine
5. large intestine
6. rectum
7. anus

DIGESTIVE JUICES

Salivary glands,liverlgall bladder and pancreas are organs that secrete digestive juices that convert complex substances in food into simpler ones.

digestive juices are also secreted by inner walls of the small intestine and the stomach.

Digestion in the Mouth

Food is taken in or ingested through the mouth.

When food enters the mouth, its digestion starts by the action of mastication, a form of mechanical digestion, and the contact of saliva. Saliva(watery substance located in the mouths of organisms), which is secreted by the salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food. After undergoing mastication and starch digestion, the food will now be in the form of a small, round mass, called a bolus.

Saliva breaks down starch into sugars.

Mastication: Chewing food to break it into small pieces.

Tongue

The tongue is skeletal muscle on the floor of the mouth that manipulates food for chewing (mastication) and swallowing(deglutition). It is sensitive and kept moist by saliva. The underside of the tongue is covered with a smooth mucous membrane. The tongue also has a touch sense for locating and positioning food particles that require further chewing. The tongue is utilized to roll food particles into a bolus before being transported down the oesophagus through peristalsis.

The sublingual region underneath the front of the tongue is a location where the oral mucosa is very thin, and underlain by a plexus of veins. This is an ideal location for introducing certain medications to the body. The sublingual route takes advantage of the highly vascular quality of the oral cavity, and allows for the speedy application of medication into the cardiovascular system, bypassing the gastrointestinal tract.

Teeth

Teeth of humans are small, calcified, hard, whitish structures found in the mouth. They function in mechanically breaking downitems of food by cutting and crushing them in preparation for swallowing and digestion. The roots of teeth are embedded in themaxilla (upper jaw) or the mandible (lower jaw) and are covered by gums. Teeth are made of multiple tissues of varying density and hardness.

The first set of teeth (also called the "baby", "milk", "primary", and "deciduous" set) normally starts to appear at about six months of age.

Humans usually have 20 primary (deciduous or "baby") teeth and 32 permanent (adult) teeth. Teeth are classified as incisors, canines,premolars, and molars. Incisors are primarily used for biting pieces from foods such as raw carrots or apples and peeled but uncutbananas, while molars are used primarily for grinding foods after they are already in bite size pieces inside the mouth.

Journey through the food pipe or Oesophagus

 The oesophagus leads from our mouth to the stomach.It is made up of muscles.These muscles gently push food down to your stomach in a wave like action called peristalsis.This movement takes place throughout the alimentary canal to push the food forward.

Digestion in the stomach

Our stomach is a J shaped bag. Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. As these two chemicals may damage the stomach wall, mucus is secreted by the stomach, providing a slimy layer that acts as a shield against the damaging effects of the chemicals. At the same time protein digestion is occurring, mechanical mixing occurs by peristalsis, which are waves of muscular contractions that move along the stomach wall. This allows the mass of food to further mix with the digestive enzymes. After some time (typically an hour or two in humans, 4–6 hours in dogs, somewhat shorter duration in house cats), the resulting thick liquid is called chyme. When the pyloric sphincter valve opens, chyme enters theduodenum where it mixes with digestive enzymes from the pancreas, and then passes through the small intestine, in which digestion continues.

Digestion in the small intestine

The small intestine is a 7.5 metre long tube through  which most of the digestion occurs.The muscles in the small intestine mix food with more digestive juices.some juices are secreted by the cells of the small intestine itself.others come from the liver,which is the largest gland in the body and produces bile juice which is stored in the gall bladder a. The bile breaks down fats into tiny droplets that can be digested and absorbed more easily. The digestive juices then act on these tiny droplets to form simpler compounds known as fatty acids or glycerol.The pancreas secrete the pancreatic juice that changes starch into simple sugars and proteins into simpler compounds called amino acids.

Absorption in the Small intestine

The digested food is then absorbed through tiny finger like projections called villi (singular=villus).Villi increase the surface area of absorption of digested food. Each villus has a network of fine blood capillaries close to the surface.The food absorbed on the surface of the villus passes into the blood in the capillaries. 

Assimilation

The food absorbed in the blood is transported to different parts of the body.It is used to provide energy and materials for growth and repair of body tissues.

Glucose is broken down in the cells with the help of oxygen into carbon dioxide and water,to provide energy.Amino acids are used for buildings and repairing of body parts.Fatty acids and glycerol are stored under the skin and act as energy reserves.

Egestion

Not all the food you eat is digested and absorbed.The food cannot be digested moves from the small intestine into a wide tube called the large intestine.

Here,most of the water present in the waste is absorbed. The waste food which is now almost solid is stored in the last part of the small intestine called the rectum.It is the passed out through the anus.

Some questions asked by the smart students of the class:

Q.When there is a gall bladder stone and the gall bladder has to be removed, where does the bile go?

A.The bile directly goes to the small intestine and is not stored between meals.

Q.Sweet,salty, sour and bitter are all tastes recognized by the taste buds...then what about spicy?

A.Spicy taste is recognized by the pain sensors in our tongue.