HEART : Internally, the human heart is divided into four chambers.

The function of the heart is to pump the pure blood into different parts of the body and the impure blood into the lungs for purification.

SALIVA : Saliva is alkaline in nature. It is secreted by salivary glands situated in the mouth.

Pancreas or Sweet Bread : It is situated in the bend of duodenum, secretes juices which help in food digestion and keep sugar balance in the body.

The inability of pancreas to secrete sufficient insulin to make use of sugar in the food digestion. (It can be cured by insulin injections invented by Banting).

LIVER : It  is the largest gland in the body. It stores extra sugar from the blood and gives it when required by the body. Liver secretes bile that helps digestion and manufacture Urea from the products of protein destruction.

KIDNEY : Kidneys  filter blood. They filter the nitrogenous waste of the body from the blood and throw them out in the form of Urine.

Dialysis is used when kidneys fail to work.

Retina is the inner most layer of the eyeball.

BLOOD : It consists of  :

1. Red Blood Corpuscles (R.B.C.) : They contain haemoglobin (an iron compound). They supply oxygen to the body.
2. White Blood Corpuscles or Leucocytes (W.B.C.) : They are formed are spleen. They protect the body from bacterial attack.
3. Plasma : It contains 90% water and allows the corpuscles to float in it.

Functions of Blood  

(i)  Blood maintains the temperature of the human body . (ii) removes the waste matter.

(iii) supplies food to various organs of the body . (iv) fights against the attack of germs

(v) carries hormones to different organs. Spleen is the grave yard of worn out red blood    corpuscles.

EYES  :

The defects of the Vision are  :

(i)  Myopia ( or short sight ) : In this, the eyeball becomes more Convex ( i.e., elongated ) and the man suffering from it can see nearer objects distinctly but not the distant ones. Remedied by use of concave glasses .

(ii)  Hypermetropia (or long sightedness) : In this, a person can see distant objects clearly but not the nearer ones. Remedied by use of Concave glasses.

(iii)  Astigmatism : The person can see vertical lines clearly but not the horizontal ones or vice-versa. Remedied by the use of Cylindrical glasses.

VITAMINS are natural substances present in various food stuffs. They are soluble in water as well as fat. Their deficiency causes diseases .

Infectious Diseases : These diseases are conveyed from one person to another by Viruses . Viruses are the smallest living organisms. It is almost non-living by itself. It can function and reproduce only within a living organism .