DIGESTION IN HUMAN BEINGS

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  • DIGESTION IN HUMANS

  • (BY YASH)


  • Humans are heterotrophic organisms, going deep into that they are omnivores ( feed on both plants and animals).


  • Being Multicellular and having greater complexity They have a complex digestive system.


  •  Their digestive system is made up of an alimentary canal and many digestive glands.


There are five stages in human nutrition; Ingestion, Digestion, Absorption, Assimilation and Egestion.



STRUCTURE AND FUNCTIONS OF ALIMENTRY CANAL AND RELATED DIGESTIVE GLANDS


  • Alimentary canal has a long tube with muscular walls And extends to mouth to anal opening (anus). 

  • It is about 9 Metre long tube in which several digestive glands open to secrete their respective digestive enzymes.



  • The elementary Canal consists of following…


  1. MOUTH

  2. BUCCAL CAVITY

  3. PHARYNX

  4. OESOPHAGUS

  5. STOMACH

  6. SMALL INTESTINE

  7. LARGE INTESTINE



1.MOUTH


It forms the uppermost opening of human digestive system that helps in ingestion of food.

Inside the mouth there is a Chamber of cavity called buccal cavity.

It also has set of teeth inside which help in mastication and chewing of food. 


2. BUCCAL CAVITY


Buccal cavity is also known as oral cavity. 

It is bounded by throat from the lower side and palate from the upper side.

The tongue forms the floor of the cavity and the Jaws also surround the cavity.


So it consists of -

  Tongue

  Palate

  Teeth

  Glands


      TEETH

  

     The jaws bear the team. Both the upper And lower jaws Are provided with teeth.The teeth are made of DENTINE with a upper supficial layer of ENAMEL. 


Each jaw has a total of 16 teeth and an adult human has 32 permanent teeth. There are 4 kinds of teeth- incisor, canine, premolars,molars.


There is a dental formula to learn the differentiation and location for different types of teeth given below… 



Here I - INCISOR   C- CANINES    P- PREMOLAR   M-MOLAR






As Seen in the above diagram that each jow consists of 16 teeth and each side of each job contains 8 teeth that too in the count of

 2 1 2 3 (INCISOR ,CANINE, PRE-MOLARS, MOLARS)


The buccal cavity has three pairs of salivary glands located at different locations.


Note - The bacteria responsible for tooth decay is know as Streptococcus mutans. 

    

  1. Parotid salivary glands - Located at sides of the face

  2. Sublingual salivary glands - under tongue

  3. Submaxillary salivary glands- near lower jaws.


   The salivary glands secrete saliva which in turn contains salivary amylase or it is also called ptyalin.


The enzyme ptyalin splits starch and glycogen into maltose. Thus, carbohydrate digestion begins in the buccal cavity( about 25-30% starch is hydrolysed here). 



   3. PHARYNX          


 It is about 12 cm long tube and provide a passage for the food from buccal cavity to oesophagus .



  1. OESOPHAGUS


It is also a long tube which serves to carry the food from pharynx to stomach. The wall of the oesophagus is very muscular.


So it shows PERSTALTIC MOVEMENTS ( contraction and relaxation of walls of oesphagus) and also add MUCUS to food.

  

   

  1. STOMACH


It is J-shaped muscular structure present on the left side of the abdomen.  It is divided into 3 main parts -

  1. Cardia 

  2. Fundus

  3. Pylori





The inner lining of stomach wall has gastric glands which release some enzymes, hcl, and mucus.



 

Mucus is secreted by gastric glands. 

Mucus protect stomach wall from corroding action of hcl. In its absence, hcl would lead to acidity. 

 


Hcl also helps in activating Pepsinogen to Pepsin ( protein digesting enzymes) 



Note- Apart from 2 enzymes of stomach there's an another enzyme called RENIN that is secreted by Kidneys and works in stomach to digest Milk protein called Caesin protein. 


The stomach has 4 main functions-

  1. STORAGE OF FOOD-  Stomach receive food from oesophagus. Here carbohydrate digesting enzymes called ptyalin or salivary amylase are destroyed by hydrochloric acid.

  2. MECHANICAL CHURNING OF FOOD- it helps in getting the food churned and mixing of gastric juice and food.

  3. PARTIAL DIGESTION- Food is partially digested by the action   gastric enzymes .

  4. PASSAGE OF FOOD TO SMALL INTESTINE- Food goes into duodenum through pyloric sphincter.



 6. SMALL INTESTINE


It is the longest part of the alimentary canal. The length varies from herbivores to carnivores. 

 As the digestion of cellulose takes more time therefore the small intestine is longer in herbivores bcz they feed on grasses which contain cellulose. 

And thus Carnivores have a shorter small intestine as they feed on meat. 



Small intestine is also divided into 3 parts -


  1. Duodenum( connected to stomach) 


  1. Jejunum


  1. Ileum ( to large intestine) 



We know that food coming from the stomach is acidic so it needs to be made alkaline before for the digestion in small intestine. 


Now let us see how digestion takes place in intestine and how it nutrilize acidic envirment of food or of chyme coming from stomach. 


Intestine does not produce enzyme of its own but only the intestinal juice. The enzyme here come from PANCREAS and LIVER as shown in diagram. 


INTESTINAL JUICE IS ALSO CALLED SUCCUS ENTERICUS



Pancreas secrete trypsin, P. Lipase, P amylase. Whereas Liver produces BILE JUICE. 

All these enzymes and juice reach the small intestine which is their site of working. 


This Bile contains Bicarbonate ions that help in creating a basic environment in small intestine. 


About enzymes…(as shown in diagram above)


3 enzymes release by pancreas helps in digestion in small intestine.

  • Trypsin helps in digestion of proteins into amino acid

  • Pancreatic lipase helps in digestion of lipids and fats into glycerol.

  • Pancreatic amylase breaks Complex carbohydrates into simple glucose.

 


PANCREAS


It's is small gland located beneath stomach. We have seen the enzymatic functions of the organ above. These were the exocrine functions of pancreas. 


Pancreas has 2 parts-

1.Exocrine - It include the release of enzymes via ducts. for example. Trypsin, amylase etc. 


2. Endocrine - It includes the release of HORMONES (chemical messenger) without any duct. So it means they are ductless. 

Examples-

  • Glucagon hormone helps in increasing blood sugar level is released by alpha cells of pancreas. 

  • Insulin hormone helps in decreasing the blood sugar level and is released by beta cells of pancreas. 


Whole of digestion as a Chart 




Absorption, Assimilation and Villis in small intestine is explained in the next page (click on the link provided below) 


PROTEINS AND AMINO ACIDS ARE MADE UP OF NITROGEN


7. LONG INTESTINE


  • No significant digestion takes place in large intestine. It's concerned with absorption of water and little solids. 


  • For absorption and assimilation click absorption and assimilation in humans link provided. 



 CLICK HERE >https://yournotesparadise.blogspot.com/2021/08/absorption-in-humans.html
                                          

 

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