Nutrition in human beings
Nutrition in human beings-
Human beings are heterotrophic omnivorous organisms. They obtain their food from plants, animals and their products by holozoic mode of nutrition. The essential components of human diet are water, carbohydrates, fats, proteins, minerals and vitamins.
Human Digestive system-
The human digestive system consists of an alimentary canal and many digestive glands. So human digestive system is divided into two main parts the first one is the alimentary canal and the other one is different digestive glands associated with alimentary canal.
(1) Alimentary canal
(2) Digestive glands associated with alimentary canal
(1) Alimentary canal-
The alimentary canal is a long tube with muscular walls, glandular epithelial lining and varying diameter. It extends from the mouth to the anal opening (anus). When uncoiled, the alimentary canal measures nearly 9 metre long tube in which the ducts of several digestive glands open to secrete their respective digestive secretions. The alimentary canal consists of several organs. These organs are given below in the order in which they are involved in digesting food.
(A) Mouth
(B) Buccal (or oral) cavity
(C) Pharynx
(D) Oesophagus
(E) Stomach
(F) Small intestine
(G) Large intestine
(A) Mouth-
Mouth is the uppermost opening of human digestive system which gives passage for ingestion of food. It is guarded by two soft movable lips and opens into a chamber or cavity called buccal cavity.
(B) Buccal (or oral) cavity-
It is a large space bounded above by the palate, below by the throat and on the sides by the jaws. The throat supports the muscular tongue which forms the floor of this cavity and helps in injestion of food.
Teeth-
The jaws bear teeth. Both upper and lower jaws are provided with teeth. Each jaw has two pairs of incisors, one pair of canines, two pairs of premolars and three pairs of molars. Thus, each jaw possesses total 16 teeth and human adults has 32 permanent teeth. The incisors are sharp and have cutting edges. The canines are pointed and occur next to the incisors The premolars and molars are called the grinding teeth. Teeth cut the food into small pieces and chew them to make it soft for easy swallowing. The full dental formula (arrangement of teeth) of humans is represented as-
I2/2,C1/1,Pm2/2,M3/3
Salivary glands-
The buccal cavity has three pairs of salivary glands located at at different locations the parotid glands lie on the sides of the face sublingual glands lie under the front part of the tongue and submaxillary gland lie at the angles of the lower job these celebrity glands secrete saliva through their ducks saliva contains these salz new seen and an enzyme ptyalin. the enzyme ptyalin is celebrity mileage which splits starch and glycogen into maltose carbohydrate digestion begins in the buccal cavity itself which is responsible for hydrolysis of about 30% starch present in the food.
(C) Pharynx-
The pharynx is about 12 centimetre long funnel shaped vertical canal which serves as a passage way for the food from the buccal cavity to the oesophagus.
(D) Oesophagus-
The oesophagus is a long and tubular structure which serves to carry the food from pharynx to the stomach. The wall of oesophagus is highly muscular. The oesophagus is not concerned with the digestion of the food. It exhibits peristaltic movement, i.e., contraction and expansion movement of walls, so that the partially digested food is pushed forward in the track. In fact, this movement occurs throughout the alimentary canal.
(E) Stomach-
The stomach is a wide C-shaped or j- shaped muscular sac present on the left side of the abdomen. Partially digested food reaches into the stomach from the buccal cavity through pharynx and oesophagus. Now further digestion of food takes place in the stomach. The stomach serves 4 main functions:
(a) storage of food - The food is Stored in the stomach variable duration. Carbohydrates continue to get digested till the salivary enzyme ptyalin is destroyed by the hydrochloric acid secreted in the stomach. The carbohydrates remain in the stomach for about one or two hours proteins up to 3 hours and fats for 3 to 6 hours. Storage of food in the stomach enables us to take food at intervals.
(b) Mechanical churning of food- Wall of the stomach undergoes periodic muscular contraction so that the food gets churned and mixes thoroughly with the gastric juice .
(c) Partial digestion- Stomach possess branched and tubular glands present on the inner surface of its wall. There are three types of glands which secrete hydrochloric acid, protein digesting enzyme and mucus. All these secretions are collectively called gastric juice. The hydrochloric acid makes the medium is acidic. Protein digesting enzyme pepsin acts in acidic medium which breaks down proteins into peptones. Gastric juice also contains some gastric lipase which partially breaks down lipids. The gastric juices can also be secreted in the stomach by the sight, smell or thought of appetising food.
(d) regulation of the flow of food into the small intestine- The stomach regulate the flow of partially digested food into the small intestine.
(F) Small intestine-
The small intestine is the longest part of the alimentary canal. It is a narrow tube of about 6 metres which lies coiled in the abdomen. The length of small intestine vary in different animals depending on the type of food they eat. It is comparatively longer in herbivores animals which eat grass and shorter in carnivorous which eat meat. Long intestine of herbivores is helpful in digestion of cellulose. Meat is digested easily, therefore carnivores have a shorter small intestine. Partially digested and churned food from the stomach enters into the small intestine. The exit of food from the stomach is regulated by the sphincter muscles located at the pyloric end. This food is acidic which has to the made alkaline before further digestion.
(G) Large intestine-
The small intestine is followed by large intestine which is shorter but wider than a small intestine. It is arranged around the mass of small intestine in the form of a question mark (?). It lacks villi but secretes mucus. The greater part of large intestine is colon which gives sacculated appearance due to a series of constrictions. The colon is followed by about 15 to 20 cm long vertical column called rectum. It has longitudinal folds and large blood vessels. The undigested food is collected as faeces in the rectum. The rectum leads through 2 to 5 cm long anal canal to the exterior at the anus. The rectal wall mainly absorbs water from the undigested food. It also secrets mucus for lubrication . The faecal matter is egested out through an opening by the activity of anal sphincter.
(2) Digestive glands associated with alimentary canal-
Human digestive system having different types of digestive glands which is helpful in the digestion of the food. Some important digestive glands which is helpful in the process of digestion are given below-
(A) Salavary glands
(B) Gastric glands
(C) Liver
(D) Pancreas
(E) Intestinal glands
Human beings are heterotrophic omnivorous organisms. They obtain their food from plants, animals and their products by holozoic mode of nutrition. The essential components of human diet are water, carbohydrates, fats, proteins, minerals and vitamins.
Human Digestive system-
The human digestive system consists of an alimentary canal and many digestive glands. So human digestive system is divided into two main parts the first one is the alimentary canal and the other one is different digestive glands associated with alimentary canal.
(1) Alimentary canal
(2) Digestive glands associated with alimentary canal
(1) Alimentary canal-
The alimentary canal is a long tube with muscular walls, glandular epithelial lining and varying diameter. It extends from the mouth to the anal opening (anus). When uncoiled, the alimentary canal measures nearly 9 metre long tube in which the ducts of several digestive glands open to secrete their respective digestive secretions. The alimentary canal consists of several organs. These organs are given below in the order in which they are involved in digesting food.
(A) Mouth
(B) Buccal (or oral) cavity
(C) Pharynx
(D) Oesophagus
(E) Stomach
(F) Small intestine
(G) Large intestine
(A) Mouth-
Mouth is the uppermost opening of human digestive system which gives passage for ingestion of food. It is guarded by two soft movable lips and opens into a chamber or cavity called buccal cavity.
(B) Buccal (or oral) cavity-
It is a large space bounded above by the palate, below by the throat and on the sides by the jaws. The throat supports the muscular tongue which forms the floor of this cavity and helps in injestion of food.
Teeth-
The jaws bear teeth. Both upper and lower jaws are provided with teeth. Each jaw has two pairs of incisors, one pair of canines, two pairs of premolars and three pairs of molars. Thus, each jaw possesses total 16 teeth and human adults has 32 permanent teeth. The incisors are sharp and have cutting edges. The canines are pointed and occur next to the incisors The premolars and molars are called the grinding teeth. Teeth cut the food into small pieces and chew them to make it soft for easy swallowing. The full dental formula (arrangement of teeth) of humans is represented as-
I2/2,C1/1,Pm2/2,M3/3
Salivary glands-
The buccal cavity has three pairs of salivary glands located at at different locations the parotid glands lie on the sides of the face sublingual glands lie under the front part of the tongue and submaxillary gland lie at the angles of the lower job these celebrity glands secrete saliva through their ducks saliva contains these salz new seen and an enzyme ptyalin. the enzyme ptyalin is celebrity mileage which splits starch and glycogen into maltose carbohydrate digestion begins in the buccal cavity itself which is responsible for hydrolysis of about 30% starch present in the food.
(C) Pharynx-
The pharynx is about 12 centimetre long funnel shaped vertical canal which serves as a passage way for the food from the buccal cavity to the oesophagus.
(D) Oesophagus-
The oesophagus is a long and tubular structure which serves to carry the food from pharynx to the stomach. The wall of oesophagus is highly muscular. The oesophagus is not concerned with the digestion of the food. It exhibits peristaltic movement, i.e., contraction and expansion movement of walls, so that the partially digested food is pushed forward in the track. In fact, this movement occurs throughout the alimentary canal.
(E) Stomach-
The stomach is a wide C-shaped or j- shaped muscular sac present on the left side of the abdomen. Partially digested food reaches into the stomach from the buccal cavity through pharynx and oesophagus. Now further digestion of food takes place in the stomach. The stomach serves 4 main functions:
(a) storage of food - The food is Stored in the stomach variable duration. Carbohydrates continue to get digested till the salivary enzyme ptyalin is destroyed by the hydrochloric acid secreted in the stomach. The carbohydrates remain in the stomach for about one or two hours proteins up to 3 hours and fats for 3 to 6 hours. Storage of food in the stomach enables us to take food at intervals.
(b) Mechanical churning of food- Wall of the stomach undergoes periodic muscular contraction so that the food gets churned and mixes thoroughly with the gastric juice .
(c) Partial digestion- Stomach possess branched and tubular glands present on the inner surface of its wall. There are three types of glands which secrete hydrochloric acid, protein digesting enzyme and mucus. All these secretions are collectively called gastric juice. The hydrochloric acid makes the medium is acidic. Protein digesting enzyme pepsin acts in acidic medium which breaks down proteins into peptones. Gastric juice also contains some gastric lipase which partially breaks down lipids. The gastric juices can also be secreted in the stomach by the sight, smell or thought of appetising food.
(d) regulation of the flow of food into the small intestine- The stomach regulate the flow of partially digested food into the small intestine.
(F) Small intestine-
The small intestine is the longest part of the alimentary canal. It is a narrow tube of about 6 metres which lies coiled in the abdomen. The length of small intestine vary in different animals depending on the type of food they eat. It is comparatively longer in herbivores animals which eat grass and shorter in carnivorous which eat meat. Long intestine of herbivores is helpful in digestion of cellulose. Meat is digested easily, therefore carnivores have a shorter small intestine. Partially digested and churned food from the stomach enters into the small intestine. The exit of food from the stomach is regulated by the sphincter muscles located at the pyloric end. This food is acidic which has to the made alkaline before further digestion.
(G) Large intestine-
The small intestine is followed by large intestine which is shorter but wider than a small intestine. It is arranged around the mass of small intestine in the form of a question mark (?). It lacks villi but secretes mucus. The greater part of large intestine is colon which gives sacculated appearance due to a series of constrictions. The colon is followed by about 15 to 20 cm long vertical column called rectum. It has longitudinal folds and large blood vessels. The undigested food is collected as faeces in the rectum. The rectum leads through 2 to 5 cm long anal canal to the exterior at the anus. The rectal wall mainly absorbs water from the undigested food. It also secrets mucus for lubrication . The faecal matter is egested out through an opening by the activity of anal sphincter.
(2) Digestive glands associated with alimentary canal-
Human digestive system having different types of digestive glands which is helpful in the digestion of the food. Some important digestive glands which is helpful in the process of digestion are given below-
(A) Salavary glands
(B) Gastric glands
(C) Liver
(D) Pancreas
(E) Intestinal glands
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