The human body consist of various cells,tissues,organs and organ system. Cell is the structural and functional unit of life on earth. Cell is mainly composed of various macro-nutrients such as lipid, amino acid, carbohydrate,protein etc. A group of similar cells that perform a specific function constitute a tissue. A group of tissues form an organ and further the group of organs constitute the organ system. The basic processes of human body such as respiration, digestion, excretion and reproduction are carried out by specific organs systems catalyzed by various enzymes and hormones. Every organ system is co-ordinated by the nervous system and integrated by the chemical system of hormones. The different types of organ system in our body are described below.

Respiratory System

The respiratory system consists of a pair of lungs, trachea and the glottis (wind pipe). Our nasal chamber opens up into the pharynx which is proceeded by the larynx i.e. our voice box. The air we breathe in passes through the trachea to the bronchia and then the minute air filled sacs called alveoli. Trachea is made up of stratified squamous and columnar epithelium tissue. The actual diffusion of oxygen and carbon dioxide takes place through the membrane of alveoli via blood. The diffusion membrane is made up of the combined membrane of the alveoli and the blood vessel. The diffused gas is transported to each and every cell of the body. In the cell , oxidation takes place which releases energy in the form of ATP ( Adenosine Triphosphate) and residual carbon dioxide. Energy is required in every process of the body. This Carbon dioxide is transported back to the alveoli and then to the outer atmosphere. The diffusion of gases is a complex process so, partial pressure of the gas is maintained at each level of exchange. The gases are transported in the blood with the help of a binding pigment called Hemoglobin. Hemoglobin has more binding affinity to carbon monoxide than oxygen and so it is said that one should not sleep closer to a place where fuels burn. This may lead to carbon monoxide poisoning. Lungs are a very delicate organ. It is advised to avoid smoking as it may lead to liver cirrhosis. Some of the diseases of respiratory system are asthma, bronchitis, lungs cancer, emphysema, tracheal cancer etc.

Circulatory System

The circulatory system consists of the heart, veins, arteries, blood vessels and blood. Blood is a fluid connective tissue which consists of Red Blood Cells, White Blood Cells, platelets and protein. Heart is the first organ which is formed in an embryo. Human heart is a closed fist sized, myogenic organ. Human heart is four chambered consisting of a pair of auricles and a pair of ventricles. Pumping heart is necessary for the transport of blood to each and every part of our body. Veins carries the deoxygenated blood from the various organs to the heart except the pulmonary vein which carries oxygenated blood from the heart to the lungs. Arteries generally carry purified oxygenated blood from the heart to the organs except the pulmonary artery which carry carbon laided blood from the lungs to the heart. The heart beats 72 times per minute approximately. The blood pressure is calculated on the basis of heart beat. Blood pressure of a normal adult is 120/80. Consumption of too much of fats cause accumulation in the artery of heart which may lead to cardiac arrest.

Digestive System

Our digestive system comprises of mouth, oesophagus ( food pipe), stomach, liver, small and large intestines. The food we eat is made up of various macro molecules such as protein, carbohydrate, fats, nucleic acid, various minerals and so it has to be digested separately. The first step of carbohydrate digestion begins in the mouth itself. Our saliva contains ptylin i.e. an enzyme which digests simple carbohydrate. The churned food from our mouth then descends down to the stomach where it is acted upon by the HCl of the stomach and various enzymes secreted by the stomach. The combined enzymes of the liver, gall bladder and pancreas are secreted in the duodenum of the small intestine. Maximum digestion of food takes place in the small intestine. Digestion of food is very important for the liberation of energy and attainment of essential vitamins and minerals. A person should take proper diet in order to fulfill the demands of the body.

Excretory System

Excretory System

A pair of kidneys, ureter, urinary bladder and urethra make up the excretory system. The food we consume is digested and then the nitrogenous waste produced is excreted out of the body. The elimination of wastes make take place in the form of urine, feces or even sweat. The nitrogen laded blood is transported from the liver to the kidneys. Excretion in kidney is carried out by three processes namely filteration, tubular secretion and re-absorption. Nephrons are the structural unit of kidney which carries out excretion. Extra water and minerals are reabsorbed in the tubules of kidney and the nitrogenous waste is excreted out. Aldosterone and ADH are the two hormones which facilitate the function of kidneys. Even if one kidney gets damaged the other one does the work of both kidneys. But if both the kidneys fail then the patients are treated through the dialysis machine which purifies the blood. Kidneys are also easily transplanted if there is a willing donor.

Reproductive System

Male Reproductive System

The human body has two different reproductive system – male and the female reproductive system. Male reproductive system consists of a pair if testes, vasa efferentia, epididymis, vas deferens and the reproductive glands. Testes produces the sperm which gets matured in the epididymis and gets transported through vas deferens.

The female reproductive system consists of a pair of ovaries, fallopian tube, uterus, cervix and vagina. Ovaries produce ova alternately every month. The production of ova is facilitated by a series of changes called the Menstrual cycle. The ova produced in ovary is transported to the fallopian tube where fertilization takes place. The fertilized zygote divides and gets implanted in the uterus. The embryo remains there till it attains full maturity. The gestation period of a human is of 9 months or 280 days. The period may vary by few days according to the development of the baby.

Nervous System

The nervous system consists of the brain, spinal chord and the nerves. Brain has a layered covering around it called the meninges which acts as a protective cushion. Brain is divided into cerebrum, cerebellum and medulla oblongata. Cerebrum is the store house of intelligence and memory. Cerebellum carries out the involuntary activities of the body whereas medulla facilitates the activities of the vital organs. Brain is made up of neurons. Brain also contains hypothalamus, thalamus, pineal body and amygdela. Hypothalamus is responsible for the temoerature regulation of the body. Pineal body guards the maturity process of the human body. Brain is held upon by the spinal chord which consists of numerous nerve fibres. There are two types of nerves in our body i.e. sensory and motor nerve. Sensory nerve carry impulse from sense organs to the brain and motor nerves carry impulse from brain to the organs. There are 12 pairs of cranial nerves and 31 pairs of spinal nerves in our body. We can feel the sensation of touch of various things only because of the nerves.