Digestive system of human

Digestive system of human consists of the digestive tract (alimentary canal) which forms a continuous passage from the mouth to the anus. The food is taken by the mouth, and sent downwards. As the food moves downwards into the alimentary canal, it comes in contact with a series of juices, called digestive juices, which contain various enzymes. In the digestive tract, the food is broken down so that the carbohydrates, fats, proteins, minerals, vitamins etc. that it contains may be absorbed into the blood stream to fuel the body. The unabsorbed food remnants are passed out from the alimentary canal by a process called egestion.






Digestive system of humans


1) Mouth and Buccal cavity

The mouth is a transverse slit like aperture, bounded by two soft movable lips. Inside the Buccal cavity there is a muscular tongue and teeth.

a) Tongue

It is a thick, musculo-sensory organ present on the floor of the Buccal cavity. The posterior part of tongue is attached with a soft ligamentous fold said to be frenulum. The upper and lateral surface of the tongue remain covered with various types of Papillae.



Filiform Papillae are conical projection distribution in parallel rows over the anterior two-thirds of the tongue. They are whitesh and contain no taste buds.
Fungiform Papillae are mushroom like elevation distributed among the filiform papillae and are more numerous near the tip of the tongue, and most of them contain taste buds.
Ballard Papillae are aranged in the form of an inverted 'V' on the posterior lateral surface of the tongue and the contain taste buds.


b) Teeth

An adult human has 16 teeth on each jaw, embedded in jaw sockets (thecodont) . These teeths ate of four types in their structure and their functions (heterodont) and they appear twice in the life time (diphyodont).

In adult human being the dental formula is 2123/2123, in each half of the jaw, from middle to backwards, these are two incisors, one canine, two premolars and three molars.


The primary function of teeth is to grasp and hold the food in the mouth cavity. They are also modified to serve as a grinding mill for chewing the food. With the help of teeth, tongue and jaw movements, food is chewed and mixed with saliva in the mouth.





c) Structure of tooth

In general, a tooth consists of an upper exposed part, the crown, and one or more roots which are embedded in sockets in the jaw bone. The junction of crown and root is called neck. The greater part of tooth is formed by a bone like material called dentine. In the region of the crown, the dentine is covered by a much harder white material known as enamel. The dentine is covered by a thin layer of cement over the root. The cement is united to the wall of the bony socket in the jaw by a layer of fibrous tissue said to be periodontal ligament. There is a pulp cavity with in the dentine which contains a mass of cells, blood vessels, and nerves. These together constitute the pulp.




2) Pharynx

The pharynx, or throat, is the passageway leading from the mouth and nose to the esophagus and larynx. The pharynx permits the passage of swallowed solids and liquids into the esophagus, or gullet, and conducts air to and from the trachea, or windpipe, during respiration. The pharynx also connects on either side with the cavity of the middle ear by way of the Eustachian tube and provides for equalization of air pressure on the eardrum membrane, which separates the cavity of the middle ear from the external ear canal.

 The pharynx has roughly the form of a flattened funnel. It is attached to the surrounding structures but is loose enough to permit gliding of the pharyngeal wall against them in the movements of swallowing. The principal muscles of the pharynx, involved in the mechanics of swallowing, are the three pharyngeal constrictors, which overlap each other slightly and form the primary musculature of the side and rear pharyngeal walls.


3) Oesophagus

The Oesophagus is a 22-25 cm long, narrow, muscular and tubular structure. It runs downward through the neck behind the trachea, and opens in the stomach in the abdomen. The swallooed food is propelled towards the stomach through the oesophagus by the movement of its muscular wall.

A muscular sphincter (gastro-oesophageal) regulates the opening of Oesophagus into the stomach.





4) Stomach

The stomach is a large muscular and somewhat J-shaped sac. It occupies the left side of the upper part of the abdominal cavity. The upper part of the stomach is called the cardiac (fundus) the middle dome shaped part, the body, and the distal part, the pyloric (antrum). The stomach thus has two ends : the cardiac end where it receives Oesophagus and the pyloric end where it opens into the duodenum. The opening of the stomach into the duodenum is guarded by the pyloric sphincter. The stomach has two curvature : the greater curvature at the left and the lesser curvature at the right side.



The mucous membrane of the stomach is thick. It is thrown into numerous longitudinal folds, called rugae, when stomach is empty. In distended stomach these folds are not seen. There are numerous glands in the stomach which are called gastric glands. 

The muscles on the stomach walls churn and mix the food with the gastric juice. They also help in propelling the food to the small intestine through the pyloric end.



5) Small Intestine

It is the longest part of the alimentary canal, about 6 metre in length. It is narrow and tubular and occupies the central and lower parts of the abdominal cavity. It is divided into the following three regions.


a) Duodenum

The first part of the small intestine is called duodenum. It looks somewhat like the alphabet 'c' . The ducts conveying pancreatic juice as well as the duct carrying bile open in the duodenum.

b) Jejunum

The duodenum opens into jejunum, which is about 2.5 meters long.

c) Ileum

The Ileum is the longest part of the small intestine and it opens in the caecum in the lower part of the abdominal cavity. Both ileum and Jejunum are highly coiled structures. Inner mucosa of small intestine is raised into millions of minute finger like projections called villi.

All the three parts of the small intestine have tube like gland in there walls. These glands secrete intestine juice into the intestinal lumen. The muscles on the intestinal wall churn, knead and crush the food mix it with intestinal juice and propel it towards the large intestine by contractions. The digested products are absorbed mostly by the small intestine.





6) Large Intestine

The Ileum opens into the large intestine. It is much shorter and wider then the small intestine. It does not posses villi or brush bordered cells. It is distinguished into the following three regions.


a) Caecum

It is a small, pouch like structure which ends into a tubular part called vermiform appendix. Both, caecum and vermiform appendix are vestigial in function and are not involved in cellulose digestion.

b) Colon

It is a long sacculated structure which is differentiated into ascending colon extending up to liver on the right side transverse Colon which crosses the abdominal cavity below the pancreas, descending colon running downwards on the left side and pelvic Colon which is S-shaped continues into the rectum.

c) Rectum

It is slightly dilated and about 13 cm long. It opens outside by anus and is guarded by two anal sphincter muscles.

The large intestine does not secrete enzymes and plays only a minor role in the absorption of nutrients. It stores unabsorbed food remnants temporarily and also concentrates the contents of absorbing water to form faeces. The movement of coloncolonChelp to void faeces through anus.


OrganMovement
MouthChewing
EsophagusPeristalsis
StomachUpper muscle in stomach relaxes to let food enter, and lower muscle mixes food with digestive juice
Small intestinePeristalsis
PancreasNone
LiverNone
Large intestinePeristalsis




Hydrogen

Hydrogen is the most abundant element in the universe. It was first discovered by Paracelsus during the reaction of sulphuric acid on iron in sixteenth century. Later on in 1766, Henry Cavendish prepared it in the Pur form and studied many of its properties. The name hydrogen, meaning the substance capable of forming water was given by Lavoisier in 1783.



Hydrogen is the lightest element and is the first memeber of the periodic table.The Chemistry of hydrogen is quite interesting as it show unique properties due to its unique electo configuration 1s.

As we all know that hydrogen never exist in single atomic form, but it used to eaxist in diatomic form. So here we are going to study its diatomic form.


1)  Dihydrogen

Hydrogen atoms cannot exist in free state thus it combine together to form a diatomic molecules, Hշ. Thus, molecular hydrogen is diatomic and is covalent in nature. In order to distinguish Hշ from H, the diatomic molecules of hydrogen is termed as dihydrogen.

1.1)  Occurrence of Hydrogen

As mentioned earlier, hydrogen is the most abundant element in the universe. In free state, hydrogen is not much abundant on earth. In air, it is found to an extent of one part in 15,00,000 parts. The gases coming out from volcanoes, coal mines and oil wells also contain free hydrogen. on earth crust it presents in water, coal, petroleum, clay and in all animals and vegetables matter. It constitute about 0.9% by weight of the earth crust. It is the ninth element in the order of abundance in earths crust.

1.2)  Isotopes of Hydrogen

The mass spectrographic studies of hydrogen reveal that it has three isotopes with the mass number 1,2 and 3. These are -


a) Protium : 

This is the ordinary hydrogen and it has atomic number 1 and mass number also 1. Naturally occurring hydrogen contain 99.985% of this isotopes.

b) Deuterium :

It is also referred as heavy water. It has atomic number 1 and the mass  2. It is present to an extent of 0.016% in the naturally occurring hydrogen.

c) Tritium :

It has atomic number 1 and mass number 3. It is  radioactiv in nature and is an extremely rare isotope.




1.3)  Preparation of Dihydrogen


i) General method


a) From water

2Na + 2HշO  ----->  2NaOH + Hշ

Mg + HշO  ------->  MgO + Hշ

b) From acids

Zn + HշSO --------> ZnSO + 

Fe + 2HCl ---------> FeClշ + 


ii) Laboratory preparation

In the laboratory dihydrogen can be prepared very conveniently by the action of dilute sulphuric acid on granulated zinc even at room temperature.



The apparatus used for this purpose is shown in image. Granulated zinc is taken in a Woulf's bottle fitted with a thistle funnel in one mouth and a delivery tube in the other. Dilute sulphuric acid is poured through the funnel. The reaction takes place at room temperature and no heating is required. The evolved Hydrogen gas is collected by the downward displacement of water.


1.4)  Properties of Dihydrogen

  • Is colourless, orderless and tasteless gas.
  • Ithas very low solubility in water.
  • It is highly inflammable and should be handled with care.
  • It is the lightest element among all the substance.
  • Its melting and boiling points are 13.957 K and 20.39 K respectively.



1.5). Usese of Hydrogen


    • The largest industrial use of Dihydrogen is in the manufacture of ammonia by Haber's process.
    • Large quantities of hydrogen are used in the hydrogenation of oils for the manufacture of vanaspati ghee. 
    • Liquid hydrogen mixed with liquid oxygen is used as a fuel for rockets in space programmes
    •  It used in the manufacture of synthetic petrol.
    • It is used in oxy-hydrogen torch for welding.
    • It is used in atomic hydrogen torch which produces temperature of the order of 4000°C and is used for welding.
    • It is used as a reducing agent in the laboratory and in various industries.


        Free video lecture of Motion in a Straight Line class 11 Physics


        Class 11 : Motion in a straight line : Physics : chapter-4




        Note - All the information has been taken by an Youtube channel Physics wallah and all the credits goes to Mr. Alakh panday the owner of this YouTube channel.

        NEET 2019 Syllabus || NEET ofiical Syllabus

        NEET Syllabus 2019 – National Testing Agency (NTA) has released the NEET 2019 syllabus on the basis of which the question paper of NEET 2019 will be prepared. It has been made clear by NTA, the syllabus of NEET 2019 will remain same as that of the previous year. NEET 2019 will be held in offline mode or pen and paper mode. The duration of the exam will be three hours with multiple choice questions derived from the NEET syllabus 2019. NEET UG will be conducted in one shift on May 5, 2019.



        Free video lecture of Unit and measurement class 11 physics

        Class 11 Physics : Chapter 1- Unit and Measurement : Error Analysis : Dimensional Analysis



        Note - All the information has been taken by an Youtube channel Physics wallah and all the credits goes to Mr. Alakh panday the owner of this YouTube channel.

        NEET 2019 registration form || available on @nta.ac.in

        NEET Application Form 2019 – The National Testing Agency (NTA) has released the NEET 2019 application form on November 1, 2018, at 11.30 AM on its new website -ntaneet.nic.in. The mode of release of the application form of NEET 2019 is only online and there is no change in the application fees this year. NEET 2019 registration facility will be available till November 30, 2018. Candidates will be allowed to submit the fee of NEET 2019 application form till December 1 up to 11.50 PM in case of online payment and till the banking hours in case payment is through Echallan.



        While filling the NEET 2019 application form, candidates will have to choose four exam centres. NEET aspirants must fulfil the minimum requirements laid down by the conducting body in order to be deemed eligible to fill the application form of NEET 2019. Candidates can check the article below for all the information related to NEET 2019 registration process such as eligibility criteria, how to fill the application form, application fee, FAQs, etc.

        Registration form of neet 2019


        NTA has replaced CBSE as the conducting body of NEET UG. NEET 2019 will be conducted on May 5 in a single shift. The shift timing of NEET 2019 is 2.00 AM to 5.00 AM. NEET 2019 will be held only once a year. The mode of conduct of the exam will be offline only i.e. candidates will be provided OMR sheet wherein they will be asked to submit responses. Only those candidates who will fill successfully submit the NEET application form 2019 will be eligible to take the exam on the said date.




        To register 2019 NEET Application- Click here

        To login 2019 NEET 2019 Application- Click here



        NEET eligibility criteria 2019

        • Nationality- Indian citizens, NRIs, PIOs, OCIs and foreign nationals are eligible to appear for NEET 2019. Candidates who wish to study medicine abroad are also required to qualify for NEET.


        • Age Requirement- Candidates must not be less than 17 years of age at the time of admission, and not more than 25 years of age as on May 5 to fill the NEET application form 2019.  For reserved and PwD category candidates, the minimum age limit is the same whereas the upper age limit is 30 years to be eligible to register for NEET 2019. It must be noted that candidates filling the application form of NEET 2019 will be required to upload a photo-identity proof which will mention the 'date of birth' of the candidates. Therefore, the date of birth submitted by the candidates must be in accordance with the one mentioned on the ID proof failing which the candidature will be cancelled.


        • Academic Qualification- Aspirants of NEET 2019 must have English, Physics, Biology and Chemistry in Class 12 or equivalent examination. Candidates must score qualifying score in each of these subjects individually and unreserved category candidates should also score a minimum of 50% marks in Physics, Chemistry and Biology in aggregate. Reserved category candidates are required to score at least 40% while PwD candidates must score a minimum of 45% for NEET registrations 2019.





        Mendeleev's Periodic table and it's defects

        A) Mendeleev's Periodic Law and Significance




        The first meaningful and remarkable contribution in the field of classification of elements was made by a Russian chemist, Dmitri I. Mendeleev in 1869. Mendeleev used a broader range of physical and chemical properties of elements as compared to those used by Lother Meyer and studied the formulae and properties of several compounds of an element. On the basis of these studies, he developed a law known as Mendeleev's Periodic Law. This law can be stated as follows :-


        The physical and chemical properties of the elements (as well as the formulae and properties of their compounds) are the periodic function of their atomic weight (atomic masses).

        Following two inferences can be drawn from this periodic law.


        • The physical and chemical properties of the elements depend upon their atomic masses.



        • The dependence of physical and chemical properties of elements upon their atomic masses is periodic.






        B) Mendeleev's Periodic Table


        On the basis of this periodic law, Mendeleev arranged all the elements known at that time in the form of a table which is now known as Mendeleev's Periodic Table. In this table, the elements were arranged horizontally in ten series in the order of their increasing atomic weights. These series were divided into seven horizontal and eight vertical columns. The horizontal columns were called periods while the vertical columns were named as groups. Mendeleev tried to place the elements having similar properties in the same group. At several places he ignored the order of atomic masses in order to group together the elements having similar properties.

        The important features of the modified form of periodic table are as follows :- 

        i) Series : All the known elements have been arranged in ten horizontal columns called series.

        ii) Groups : There are nine vertical columns in the periodic table, these are called groups.

        iii) Periods : The ten horizontal series have been arranged in seven horizontal columns called periods.


        Original view of Mendeleev's Periodic Table





        C) Defects Of Mendeleev's Periodic Table

        In spite of the remarkable contributions made to chemistry, Mendeleev's periodic table had certain defects. These defects are as follows :-

        • Position of Hydrogen
        • Position of Isotopes
        • Position of lanthanoids and actinoids
        • Variable valency of elements
        • Anomalous pair of elements
        • Similar elements placed in different groups
        • Dissimilar elements placed in same group
        • Eight group



        Also read :-