Organ System of Human Body:

The human body is a complex machine and its organs work like the parts of a machine. Different ‘organs’ of the human body form a ‘system’, all the systems collectively form the human body.


We take in food every day because it provides us energy. We use this energy for all our activities. Our food basically consists of a few important compounds. These are carbohydrates, proteins, nd fats. All these compounds are in the form of very large molecules and cannot be taken into the cells of the body until they are broken down into smaller molecules. The broken-down food molecules enter the cell where they take part in supplying energy to the cells.


The breakdown of large food molecules into the smaller ones is called “digestion”. Digestion of food is the basic function of the stive system. The digested food is absorbed into the blood vessels and is transported to all parts of the body. Within

the cells, it provides energy. All these activities take place in the digestive tube or alimentary canal.

Alimentary Canal:

The alimentary canal starts from the mouth. Here the food enters the alimentary canal. The mouth opens into the oral cavity where the use and the teeth are present. The teeth break the food into very fine pieces by mastication. The tongue, by its rolling activity, gathers the fine particle of food into a bolus. There are special sensory cells on the tongue which help, to taste the. The oral cavity has salivary glands that produce saliva. Saliva not only helps to digest carbohydrates present in the food but also lubricates it, which makes swallowing easier.


The last part of the cavity is called the lynx, which opens into the esophagus. Oesophagus receives the food from the ynx and carries it the stomach. hat enter the body along with food and causes acidity. The wall of the arch by its muscular movements grinds the food into a semi-fluid paste. The food now leaves the stomach in small quantities and enters in the l intestine. Small intestine:

From the stomach, the food enters the small intestine. Here it receives a secretion known as bile from the liver. Bile changes the medium from acidic to alkaline and also kills germs. In the l intestine, food is also mixed with another digestive juice from the pancreas. This secretion is called pancreatic juice.

Pancreatic juice:

It completely digests carbohydrates, proteins,and fats. This is followed by the absorption of digested food into the blood vessels present on the inner surface of the wall of the stine from where it is distributed throughout the body via the r.

Large intestine:

The part of the food is not digested in the intestine. is called undigested food. This undigested part of food passes into the large intestine. Most of the water and salts are reabsorbed into the blood vessels present in the wall of thee intestine. Undigested food becomes semi-solid and is stored in the rectum in the form of feces. The feces are discharged through the.


The animals cannot prepare their food and are dependent on the food prepared by the green plants. According to the modes of nutrition, animals are placed in five groups:

  1. Herbivores: These are the animals that feed- on grasses, trees, vegetables, fruits,or seeds. For example cow, goat, rabbit, pigeon, sparrow, parrot etc.
  2. Carnivores: The animals which get their food from other animals (flesh eaters). For example: lion, wolf, eagle etc.
  3. Omnivores: The animals which can use both plants and animals as their food.. For example: human, crow, bear etc.
  4. Parasites: These are the animals which get food from other living animals. They

absorb digested food from their host. For example: leech, mosquito, lice etc:

  1. Symbionts: Animals’ which live together in a mutually beneficial relationship. They provide food and protection to each They are so dependent on each other that cannot exist independently. For example, termite eats wood as food but single celled tiny animals live in its intestine and digest the food.


Living things need oxygen for respiration and food for energy. The supply of food, oxygen and other important materials to all the cells and removal of the waste products from the body is called transportation.

Transport in unicellular organisms:

In unicellular organisms, gases and food simply diffuse in from the surroundings, while waste products simply diffuse out. Transport:

In multicellular animals e.g., in human beings, the cells in the middle of their bodies are away from the body surface. It will take long for gases, food or water to reach them by diffusion alone. In order to speed up the transport of substances, God has •made a system which is called the transport system. HUMAN CIRCULATORY SYSTEM

In this system, blood circulates in the body. It consists of heart, arteries, veins and capillaries. When heart pumps, then blood reaches through arteries to the body. From here, it goes in capillaries and comes back to the heart through veins.


The heart is an organ which is enclosed in a very thick membrane. Its size is nearly equal to your fist. It lies under the rdand 7th rib, somewhat to the left from the center of the chest. Heart is four chambered. Two upper chambers of heart are small and thin walled, called atria. The two lower chambers are relatively large and thick walled called ventriclesValves: Valves are present between the atria and ventricles. These valves ensure that blood flows easily from atria into the ventricles and not in the opposite direction.


Heart acts as double pump. It can be divided into two parts i.e., right side and left side. Left side consists of left auricle and left ventricle and right side has right auricle and right ventricle. In the right auricle, blood from the whole body comes back through two large veins, venacava. It has less amount of oxygen. When right auricle contracts, blood is pushed into right ventricle. From this chamber, the blood is pumped out through pulmonary artery to the lungs. In the lungs, the blood collects oxygen from the inhaled air and gives up its carbon dioxide. This oxygenated (rich in oxygen) blood from the lungs then returns to the left auricle through pulmonary veins. When left auricle contracts, it is pushed into the left ventricle. From this chamber of the heart, the blood through a large artery, aorta, is carried to the upper parts and to the lower side that is liver, digestive system, kidneys and legs etc. In this way, it circulates in the whole body.

Heart-beat: One contraction and relaxation of heart is one heartbeat.

Pulse: The pressure produced as a result of heartbeat is called pulse.


Arteries: The blood vessels which carry blood from heart, to the body are called arteries. Their walls are thick and elastic. Due to this reason, these vessels can bear the high pressure of blood. All the arteries have the oxygenated blood except pulmonary arteries.

Pulmonary arteries carry deoxygenated blood from heart to the lungs. Arteries divide into many small vessels and supply blood to different parts of the body.

Capillaries: At the end, these branches divide into microscopic vessels called capillaries. Their walls are very thin. So exchange of materials from blood and tissues takes place. Oxygen and food from the blood of capillaries diffuse into the cells. Carbon dioxide and nitrogenous wastes from cells diffuse into blood of the capillaries.

Veins: These capillaries gradually unite to froin large blood vessels. These are called veins. Veins are the vessels, which take blood back to the heart. This blood contains less oxygen except pulmonary veins which contain oxygenated blood. Veins are wide and thin walled vessels.


Blood is a red fluid in which red cells, white blood cells and platelets are present in a yellowish-white liquid called plasma. Blood plasma consists of water, digested food materialS, carbon dioxide, hormones and waste substances. Red blood cells contain haemoglobin which transport oxygen. Function of white blood cells is to defend the body. They engulf the bacteria which enter in the body and destroy them. The function of platelets is to clot the blood in case of injury. Red blood cells do not have nucleus while white blood cells have nucleus of different shapes.


Respiration is the reverse process of photosynthesis. It is the process in which energy is produced by the oxidation of food. HUMAN RESPIRATORY SYSTEM

Human respiratory system consists of (1) Nose, (2) Pharynx, (3) Larynx, (4) Trachea, (5) Bronchi, and (6) Lungs. Respiratory system takes in oxygen and takes out carbon dioxide of the body.


Air enters into the nasal cavities through nostrils. Mucous present in the nostrils traps the bacteria and dust particles. Mucous maintains the temperature of the air


according to the temperature of the body and moistens it also.


From the nasal cavities, air enters into the pharynx.


It passes through glottis in order to enter in the larynx.


Below the larynx is air tube i.e., trachea. This tube is located in front of the food pipe in the chest. Trachea consists of incomplete • “C” shaped cartilaginous rings regularly placed in its walls. These rings prevent the collapsing of the tube.


Trachea divides into two smaller tubes. Both of these are called bronchi (single bronchus).


Right bronchus enters into right lung while left bronchus enters into left lung. Each bronchus on entering into the lungs divides into more small branches which ends into bunch of grapes-like air sacs called alveoli. There is network of capillaries in the walls of air sacs where the exchange of gases takes place. Lungs are reddish sac-like organs which are spongy in structure. These are protected in the chest box.


Breathing is a part of respiration in which air is inhaled and exhaled from the lungs. This process is completed in two steps: Inspiration: When air enters into the lungs, it is called inspiration. In this step, the ribs and diaphragm play an important role. Ribs move forward and upward. While dome-shaped diaphragm contracts and deflates downwards. As a result of increase in the volume of chest cavity, the pressure of air in the. lungs decreases and the air from outside due to increased pressure enters in the lungs.

Expiration: Removal of air from lungs is called expiration. In this step, ribs move inward and downward. Diaphragm (floor of chest cavity) expands upward and pressure on lungs is increased. So, air from lungs is expelled out.


An animal gets energy by the breakdown of food in the presence of Oxygen. In this procesS, energy and other excess and waste products are produced. e.g., carbon dioxide, excessive water, nitrogenous waste materials (ammonia, urea, uric acid). In order to keep the body healthy, removal of these materials is very necessary. The process through which excessive and waste materials from animals are removed is called excretion.


In human body, lungs, kidneys and skin are the organs which help in excretion. So these are called excretory organs. We have studied that lungs help in the excretion of carbon dioxide from blood. Let us see how kidneys help in excretion.


Kidneys excrete excess water, salts and nitrogen waste materials (urea) in the form of urine from the blood. There are two kidneys in our abdominal cavity. One is located on each side of the backbone. Right kidney is little bit below the left. Each kidney is bean-shaped. A tube called ureter arises from the kidney. Both ureters open in the urinary bladder. Urine is carried from the kidneys into the urinary bladder by ureters. When bladder is full, we have a feeling to excrete urine from bladder. Urine is excreted or passed out through the urethra.


The skin forms a continuous protective covering over the surface of our body, beside this it acts as an excretory organ. It removes salts and water in the form of perspiration (sweat) and plays an important role in regulating the body temperature.


All the movements of human body are possible with the help of bones and muscles.


Specific shape and formation of human body is due to the presence of bones in it. Without bones, our body will be nothing


than a heap of flesh. Our body has a specific bony framework which is called skeleton. A human skeleton consists of 206 bones. These are of different shapes and sizes. Some bones are long, small and flat while some others are irregular in shape.Our skin and muscles cover this skeleton. Skull is joined with the anterior of the vertebral column. Vertebral column provides support to the ribs. Ribs are joined with vertebral column at the back and with breast bone at the front. Vertebral column provides support to the skull at its upper end.

The bones of arms are joined with the help of shoulder bone to the vertebral column below the neck region. Similarly, hip bone and bones of legs are attached to the posterior part of vertebral column.

Muscles: Muscles of the skeleton are attached to the bones firmly. They play an important role in providing support and beautify the shape. Muscles can contract. Due to contraction and relaxation of muscles, bones move and as a result the whole body can move.

Joints: Different bones are attached with the help of joints. These joints are moveable or immoveable. Joints of elbow, hip-bone, knee and ankle are called moveable joints. Bones of skull are firmly attached with each other and form immovable joints.

FUNCTIONS OF SKELETON Support and Shape: Skeleton provides support to different organs of the body and maintains their specific shape.

Movement: It helps in the movement of our different organs.

Protection: It protects most delicate part of our body such as brain, heart, liver, lungs and spinal cord etc.


Reproductive system of any organism, including man is meant for the continuity of race. It ensures the survival of the species. The transmission of characteristics generation after generation are carried through this system.


In man, reproductive system consists of two testes, where male gametes or sperms are produced. Testes, are enclosed in a loose bag of skin. During adulthood, testes form sperms. These are the male reproductive fluid.


Two ovaries are Oresent in the female body. These produce eggs or ova called female gametes. These are present in lower part of the abdomen. These are small structures of almond shape. Egg is released from ovary and it enters into a long tube and fuses with sperms to form a zygote. Zygote travels to another special structure called uterus where offspring develops.

Gamete: In organisms, two types of reproductive cells are produced, called gametes. They are of two types, male gametes or sperms and female gametes or eggs.

Fertilization: Union between egg and sperm takes place within the female body and this is called fertilization. This results in the formation of a zygote. This zygote divides rapidly and passes through developmental changes giving rise to a new offspring in nearly nine months.


Nervous system of man consists of brain, spinal cord and nerves. Brain and spinal cord together form central nervous


system. Brain and spinal cord are connected to all parts of the body by network of nerves. The function of nervous system is to transmit messages rapidly from one part of the body to another and to coordinate the body’s action.


Brain is large and specialized organ enclosed and protected within the skull. It contains millions of nerve cells.

  • Forebrain mainly consists of cerebrum, which is the largest part of the Cerebrum controls sight, speech, hearing, movement of body parts and other functions.
  • Midbrain is small and present under the cerebrum. Some of its functions are to control the eye movements and hearing
  • Hindbrain has two main parts cerebellum and The cerebellum lies under the back part of cerebrum. Cerebellum controls our sense of balance and allows us to make precise and accurate movements. The medulla forms the base of the brain where it connects with spinal cord. This region controls heart beat and breathing.


Spinalcord is continuous anteriorly with medulla of hindbrain and is protected inside the backbone. Like other parts of nervous system, spinal cord consists of thousands of nerve cells. It is concerned with

conducting messages from the skin and muscles to brain and from brain to muscles of the limbs and trunk. It controls many reflexes (involuntary actions) of the body.


Nerves are white, tough, and string-like structures. There are two types of nerves: (i) sensory nerves, (ii) motor nerves.

Sensory nerves carry messages from sense organs i.e., eyes, ear, nose, etc. to central nervous system while motor nerves carry messages from central nervous system to muscles and glands.

Neuron is a basic unit of structure and function of nervous system. Brain, spinal cord and nerves are made up of neurons. Coordination of Nervous System:

Nervous system works together with other parts of body. The neurons in the receptors (sense organs) are the first to receive stimuli (any change inside or outside the body which produces a change in behaviour). These messages are then transmitted through the sensory nerves to. the central nervous system.

nervous central neoUs system then interprets the messages and sends to the effectors (muscles &glands) through the motor nerves. The result is that muscles and glands respond (muscles contract and glands secrete).


Sense organs are the receptors of the body. They receive information about conditions both inside the body and the world around it. This information is stimulus, which produces a response in body structures. Receptors in man are eye, ear, nose, tongue and skin.

Eye: The eye is the organ of sight.


The human eye consists of an eyeball which is a hollow spherical body placed in a bony cavity of the skull. The wall of the eyeball consists of three layers. The front of the eyeball is transparent called the cornea. Beneath the cornea, the free edge of the middle layer forms iris, which is coloured part of the eye which has ability to contract and relax. In the center of the iris, is an opening called pupil. Just behind the pupil is the lens, which helps to focus light. The inner layer of the eyeball is called the retina. It receives images of objects focused by the lens which we see. The eye is connected to the brain by the optic nerve.

Defects of the Eye: The common defects of the eye are short-sightedness, long­sightedness, and cataract. They are mainly caused by excessive eye strain, defect in lens and old age.

Short sightedness is also known as Myopia. In this defect, short-sighted person can see near objects, distant object look blur. This defect can be corrected by using suitable concave spectacle lens.

Ih Long-sightedness, a person can see distant objects clearly, but near objects look blur. This condition can be remedial by the use of a suitable convex spectacle lens/contact lens.

Cataract is the disease of old age. It is due to the opaqueness of lens. It is corrected by removing the lens by simple surgery and then replaced by an artificial lens. Ear: Ear is an organ of hearing.

Structure: Human ear consists of three parts, external ear, middle and inner ear.

The outer ear is connected to middle ear by a membrane called the eardrum. On the other side of the eardrum is chamber called the middle ear. This contains three little bones. The inner ear consists of a cavity which contains fluid. This part consists of a series of chambers and canals which help to keep our balance and enable us to hear. This part is connected to the brain by the auditory nerve.

The voice sets up vibrations or sound waves, which quickly reach your ears. The outer ear catches the sound waves and directs them to the eardrum. When they hit the eardrum, they make it vibrate three bones present in middle ear. The vibrations then transfer from the middle ear to inner ear. This stimulates the receptor cells, which sends off messages via the auditory nerve to the brain. Only then you actually hear. Ears can hear the sound having the frequencies between 20 to 20,000 hertz (Hz) – SI unit for frequency. Defects: There are different kinds of deafness depending upon which part of the ear is affected:

Serious type of deafness occurs due to growth of three little bones in ear chamber or rupture of eardrum. The person’s hearing may be improved by a hearing aid, which amplifies the sound waves.

  • Deafness may also be caused by
    damage of canals in inner ear. This can happen if a person is continuously hearing a very loud sound. The vibrations are so great that the receptor cells get damaged making the person deaf. There is no cure for this kind of deafness. For this reason, people who work with noisy machinery should always wear ear plugs.

Effects of Noise Pollution:

Chaotic and irregular sound is called noise. It is unwanted or unpleasant sound that is often very loud. When noise becomes unbearable, then it is called noise pollution.

It is very difficult for people to relax and think properly in noise. Noise makes them often irritable or bad tempered. Constant noise can also cause fatigue and headache. Noise can cause high blood pressure and may disturb our digestive system. Excessive noise can make people work less safely, suffer from stress, lose their hearing and eventually become deaf. Loud noise of a long duration also damages hearing permanently. Listening to personal stereos, which are too loud and for too long can also cause hearing loss. Excessive noise is a serious aspect of pollution. For this reason, it is important that the amount of noise in the environment should be cdntrolled.

Tongue: The organ of taste is tongue. Numerous swellings/projections in the form of groups of sensory cells are present on the upper surface of tongue. Each group forms a “taste bud or taste receptor”. These sensory cells have sensory process on their upper surfaces and are associated with nerve endings.

There are four types of taste receptors/taste buds for tasting bitter, sour, salty and sweet foods.

Nose : Nose is the sense organ of smell. Sensory cells in the roof of the nasal cavity are sensitive to chemicals. These cells detect chemicals in the air given off by objects.Smells are chemicals in the air. The chemical dissolves in moisture on the lining of your nose. This stimulates nerve endings in your nose to send message to the brain through olfactory nerve. The brain interprets the message and thus we recognize the smell pleasant or unpleasant.

Skin: Skin is the organ of touch. The skin forms a continuous layer over the entire body. Our skin is formed of three layers, an outer, middle and an inner layer. The outer layer is made up of dead cells and has no sensation at all. Its function is to protect the other layers. The middle layer is thick and consists of tissues, muscles, blood vessels, glands and nerves. This layer is the sensitive part of the skin. The sensory cells of this layer transmit message from skin to brain. The inner layer consists of cells which store fats.