Digestion, digestive system, Absorption, Assimilation, defecation, Salivary glands, disorder of digestive system.
What is digestion?
Biomacromolecules like Carbohydrate and proteins in food cannot be utilized by our body in their original form they have to broken down and converted into simple substances in the digestive system This to simple absorbable forms process of conversion of complex food substances to simple absorb able forms is called digestion and it is carried out by our digestive systems by mechanical and biochemical methods.
Digestive System:
The digestive system consists of gastrointestinal tract(alimentary canal) and its glands .The function of gastrointestinal tract are ingestion, digestion and absorption of food and excretion of waste products.
Parts of digestive system:
1.Mouth
2.pharynx
3.Oesophagous
4.Stomach
5.small intestine
6.Large intestine
7.Rectum
8.Anus
1.Mouth(buccal cavity):
It is upper expanded portion which forms the beginning of alimentary canal. It can be divided into two parts.
-Vestibule
-cavity of mouth
Palate forms the roof of mouth cavity. It consists of hard palate which is in front and soft palate which is behind Uvula is a conical process which hangs from the middle of soft palate.
The important structures of mouth are:
1.Tounge
2.Teeth
3.Salivary glands
Tounge:
Tounge lies in the floor of mouth and it is attached to hyoid bone.
Teeth:
Teeth are concerned with mastication.
depending on the ageat which they arise teeth can be classified into two types:
Permanent teeth:
They are 32 in number and 16 are present in each jaw. Each half of the upper and lower jaw contains 8 teeth. they are two incisor, one canine, two premolars, and three molars.
Temporary Teeth:
They are also known as Milk teeth and present in childhood.
They are 20 in number and each jaw has 10 teeth. Each half of jaw has 2 incisors 1canine and 2 molars.
Dental formula in human adult: 2123/2123
Hard chewing surface of teeth,made up of enamel,helps in the mastication of food.
Salivary glands:
Saliva is mainly produced by three pairs of salivary glands:
1.parotid(cheek)
2.sub-maxillary or sub-mandibular(lower jaw)
3.sub-linguals(below the tounge) glands.
These glands situated just outside the buccal cavity secrete salivary juice into the buccal cavity.
Gastric glands:
The mucosa of stomach has gastric glands.gastric glands have three major types of cells namely:-
1.mucous neck cells which secrete mucous.
2.Peptic or chief which secrete the proenzyme pepsinogen.
3.Parietal or oxyntic cells which secrete HCL and intinsic factor like vitamin B12.
Gastric juice:
The mucous and bicarbonates present in gastric juice play an important role in lubrication and protection of mucosal epithelium from excoriation by the highly concentrated hydrochloric acid(HCL) provides the acidic PH(pH 1.8) optimal for pepsins.Rennin is a proteolytic enzyme found in jastic juice of infants which helps in the digestion of milk proteins.Small amounts of lipases are also secreted by gastric glands.
Pancreatic juice:
The pancreatic juice contains inactive enzymes-trypsinogen,chymotrypsinogen,procarboxypeptidases,amylases,lipases,and nucleases.
Trypsinogen is activated by an enzyme enterokinase,secreted by the intestinal mucosa into active trypsin,which turn activates the other enzymes in the pancreatic juice.
Bile:
The bile released into the duodenum contains bile pigments(like bilirubin and bili-verdin),bile salts,cholesterol and phospholipids but no enzyme.Bile helps in emulsification of fats that is breaking down of fats into very small micelles.Bile also activates lipases.
Stomach:
The stomach stores the food for 4-5 hours.
The food mixes throughly with the acidic gastric juice of stomach by the churning movements of its muscular wall and is called Chyme.The proenzyme pepsinogen on exposure to hydrochloric acid gets converted
into active enzyme Pepsin,the proteolytic enzyme of the stomach. Pepsin converts proteins into proteases and peptones.
Function of Stomach:
Absorptuon of water ,simple sugars,and alcohals etc. takes place.
Small intestine:
Small intestine is distuinguishable into three
reigons,a 'C' shaped duodenum,a long coiled middle portion jejunum and highly coiled ileum.
The opening of the stomach into the duodenum is guarded by the pyloric sphincter.Ileum opens into the large intestine.
Functions of small intestine:
Principal organ for absorption of nutrients.
The digestion is completed here and the final
products of digestion such as glucose,fructos
Fatty acids,glycerol,and amino acids are absorbed through the mucosa into the blood
stream and lymph.
Large intestine:
The undigested and unabsorbed substances
are passed on the large intestine.It consists of caecum,colon,rectum.Caecum is a blind sac which hosts some symbiotic micro-organisms.
No significant digestive activity occurs in the large intestine.
The undigested,unabsorbed substances called faeces enters into the caecum of the large intestine through ileo-caecal valve,which prevents the back flow of matter.It is temporarily stored in the rectum till defaecation.
Functions of large intestine:
1.Absorption of some water,minerals and certain drugs.
2.Secretion io mucous which helps in adhering the waste particles together and lubricating it for an easy passage.
Disorder of digestive system:
The inflammation of the intestinal tract is the most common ailment due to the bacterial or viral infection.The infections are
caused by the parasites of the intestine like
Tapeworm,roundworm,threadworm,hookworm, and pinworm etc.
Some disease of digestive system are given
below:-
Vomiting:-
It is ejection of stomach contents through the mouth.This reflex action is controlled by the vomit centre in medulla.A feeling of nausea precedes vomiting.
Jaundice:
The liver is affected skin and eyes turn yellow due to the deposits of the pigments.
Diarrhoea:-
The abnormal frequency of bowel movement and increased liquidity of the faecal discharge is known as diarrhoea.It reduces the absorption of food.
Constipation:
In constipation,the faeces are retained within the colon as the bowl movements occur irregularly.
No comments:
Post a Comment