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Important sytems of Human body

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(A) Skeleton system

The skeleton system (also known as the Bony system) consists of bones and cartilage. The skeleton is the framework of bones which are organized to form distinct parts such as skull, vertebral column, thoracic cage, hands and legs. The joints give the movements to the bones. Bones have great tensile strength, almost as high as that of cast iron.

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There are different types of bones in our body:
Long, short, flat and irregular bones.
The skeleton system consists of 206 bones in human.


The skeleton system performs following functions:
1. It gives framework to the body.
2. It gives shape and posture to the body.
3. The primary purpose of skeleton is to support the body.
4. It protects the soft and delicate organs like heart, lungs, brain etc.
5. It also permits necessary movements and locomotion.

(B) The Muscular system

There are a large number of muscles (about 500) that help in movement of our body. The muscles bring about movement and locomotion of various organs and parts of the body.

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The main functions of muscles are:
1. They help in movement and locomotion of various organs and parts of the body.
2. They give shape to the body.
3. They provide protection to the internal organs of the body, for example- muscles of the abdomen form a strong muscular anterior wall of the abdominal cavity.
4. Muscles help in various important internal processes of the body like respiration, urination, circulation, changing facial expression etc.
5. Muscles store glycogen, which is used as energy during movements of the muscles.


Fill in the blanks:
a) The skeleton system consists of ............. and...............
b) There are............... bones in our body.
c) Muscles help in.............. and............. .
d) Muscles store.............. .

C) The Digestive system

To do any kind of work, our body needs energy. This energy comes from the food that we eat. The process of digestion can be defined as the breakdown of big and complex food particles into smaller and simpler form so that it is suitable for absorption. The food that we eat, has to be converted into simpler form through a series of changes which release its constituent nutrients i.e. proteins are converted into amino acids, carbohydrates into starch and fats into fatty acid. These changes occur with the help of enzymes, which are secreted into the alimentary canal by special glands.
Enzymes are chemical substances that causes, or speeds up a chemical change in other substances without itself being changed.

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Organs of the digestive system:

Digestive system mainly consists of alimentary canal, which is a long tube like structure through which food passes. It begins at the mouth and terminates at the anus. Various organs of digestive system are:

  • Mouth (food is taken in by mouth)
  • Oesophagus (or food pipe)
  • Stomach(Digestion of food takes place with the help of gastric juice which is Secreted from the stomach)
  • Small intestine(Further breakdown or digestion of food takes place with the help of bile and some enzymes)
  • Large intestine(The digested food particles are absorbed in the blood and some of the water and electrolytes are removed from the food)
  • Rectum(The solid waste material is temporarily stored here)
  • Anus(It is an opening from where waste materials are excreted out as faeces)

D) The Respiratory System

The respiratory system provides the route through which ‘oxygen’ – which is present in the atmosphere, enters inside the body and carbon dioxide isexcreted out from the body. The exchange of gases between the blood and the lungs is called external respiration and that between the blood and the cells is known as internal respiration.

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The organs of the respiratory system are:

It is the first of the respiratory organs and consists of a large irregular nasal cavity, divided into two equal parts (i.e. right and left nostril) by a septum.


It is a tube like structure that lies behind the nose and mouth. Larynx: It is a small chamber situated in the region of neck. It is also known as ‘voice box’, since it helps in the production of sound.


It is also known as windpipe and is a continuation of the larynx. It extends downward and divides or bifurcates into the right and left bronchi, one bronchus going to each lung.

Two bronchi:

The two bronchi enter into right and left lungs of either side. Inside the lungs, they are further divided into many smaller bronchioles and finally into alveoli.

Two Lungs:

There are two lungs, one lying on each side of the midline in the thoracic cavity. They are cone-shaped. Each lung is covered by a layer called ‘pleura’ which contains a fluid called pleural fluid. Muscles of respiration i.e. the intercostals muscles and the diaphragm.

(E) The Circulatory System

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The circulatory or the blood circulatory system consists of the heart, which acts as a pump and the blood vessels through which the blood circulates. The main blood vessels are Arteries, veins and capillaries. Arteries are the blood vessels that carry blood away from the heart. Veins are the blood vessels that transport blood to the heart. The smallest arterioles break up into a number of minute vessels called capillaries. Heart The heart is a cone-shaped hollow muscular organ. It is situated in the thoracic cavity in between the lungs, a little more to the left than the right. Interior of the heart is divided into a right and left side by the septum, so that blood cannot cross the septum from one side to the other. Each side is further divided by an atrioventricular valve into an upper chamber, the atrium and a lower chamber, the ventricle. Hence the human heart has four chambers viz. right atrium, right ventricle, left atrium and left ventricle.


State True or False:

1. Diaphragm is a respiratory muscle. ( )
2. Pharynx is also known as ‘voice box’. ( )
3. In a minute we respire for about 72 times. ( )
4. The interchange of gases takes place in heart. ( )
5. Arteries carry blood away from the heart. ( )

Please tick the correct answer:

1. After digestion proteins are converted into:
a) Fatty acids ( )
b) Amino acids ( )
c) Starch ( )
d) Remain unchanged ( )
2. Stomach secretes:
a) Bile ( )
b) Saliva ( )
c) Enzymes ( )
d) Gastric juice ( )
3. Total number of chambers present in human heart is:
a) 1 ( )
b) 2 ( )
c) 3 ( )
d) 4 ( )
4. Arteries and veins are:
a) Muscles ( )
b) Glands ( )
c) Blood vessels ( )
d) Chamber ( )

(f) The Excretory System (or the urinary system)

All plants and animals produce harmful substances due to a number of metabolic activities occurring in their body. The waste material formed by the body must be removed. Hence, the process of excretion can be defined as the elimination of wastes from the body which otherwise are toxic if retained One urinary bladder – it is an elastic distensible bag where urine collects and is temporarily stored. One urethra – it is an opening through which urine is discharged from the urinary bladder to the exterior. Functions of the excretory system Functions of the excretory system are as follows: 1. It excretes waste products from the body for example, ammonia, urea and uric acid. 2. It helps in the maintenance of fluid and electrolyte balance. 3. It helps to maintain the normal pH of blood and other fluids. 4. It also helps to maintain the optimum concentration of certain constituents of blood like calcium. 5. It maintains the osmotic pressure in blood and tissues.


The endocrine system consists of various glands that are widely separated from each other. These glands are commonly known as the ‘ductless glands’ because the hormones they secrete pass directly from the cells into the blood. The ductless glands secrete many hormones which play a vital role in the normal functioning of the body.

A hormone is a chemical substance which, having been formed in one gland or, is carried in the blood to another organ or the target organ where organ influences activity. Our body cannot work and grow normally without hormones. Glands which release chemicals directly into blood stream. The endocrine system consists of the following glands: Pituitary gland – This gland is located on the ventral side of the brain. It is known as the master gland of the body because it secretes maximum number of hormones and also it controls the secretion of hormones secreted by other glands. Thyroid gland – It is found in the neck region, at the base of larynx. It secretes thyroxin which helps in normal development of the body. Parathyroid glands – They are 4 small oval shaped bodies, two on each side of thyroid glands. Adrenal glands – One situated on the top of each kidney. Pancreas (Islets of Langerhans)- It secretes ‘insulin’ hormone that helps in maintaining normal blood sugar level.

Pineal gland – This gland is situated in the brain near pituitary. 2 Ovaries in female They secrete two important female sex hormones - estrogen and progesterone. 2 Testes in male They secrete male sex hormone - Testosterone.

(h) The Nervous System

The system that receives the stimulus, transmits it to other parts of the body and the corresponding effects shown is known as the nervous system.

The nervous system consists of a large number of units called ‘neurons’. Neurons are simply referred as nerves. Nervous system is concerned with the following main functions: 1. It controls and regulates various activities of the organs and the organism as a whole. For example, muscular contraction, rate of respiration, heartbeat, sense of vision, hearing, pain etc. 2. It coordinates the working of various glands and tissues of the body; thus regulating the internal environment of the body. 3. It helps the organism to react to the external environmental fluctuations. Nervous system mainly consists of three parts: 1. CENTRAL NERVOUS SYSTEM (CNS) 2. PHERIPHERAL NERVOUS SYSTEM (PNS) 3. AUTONOMIC NERVOUS SYSTEM (ANS) Central Nervous System It consists of the brain and the spinal cord. Entire CNS is protected and surrounded by membranes called ‘meninges’. These cavities or

the space between the membranes and the brain or spinal cord are filled with a clear fluid called ‘cerebrospinal fluid’ or ‘CSF’. Peripheral Nervous System It consists of the nerves that arise from brain and spinal cord. Nerves are solid, white and thread like structure. There are mainly there types of nerves: sensory, motor and mixed nerves. The peripheral nervous system consists of- 31 pairs of spinal nerves (arising from the spinal cord) 12 pairs of cranial nerves (arising from the brain) Autonomic Nervous System The ANS controls the functions of the body carried out automatically, which are initiated in the brain. For example, maintenance of blood pressure, secretion of glands.

(I) The Reproductive System

The ability to reproduce is one of the properties that distinguish living beings from non-living matter. The reproductive system is a system of organs within an organism which work together for the purpose of reproduction. Human reproduction is a sexual reproduction that takes place as internal fertilization. In human beings the reproductive organs of the male and the female differ anatomically and physiologically. Both males and females produce specialized reproductive cells known as gametes, containing genetic material-genes and chromosomes.

Female reproductive system

The human female reproductive system consists of a series of organs primarily located inside the body and around the pelvic region of a female that contribute towards the reproductive process. The internal organs of the female reproductive system lie in the pelvic cavity and consist of: Vagina, which acts as the receptacle for the male’s sperm Uterus, which holds the developing foetus Two fallopian or uterine tubes which extend from the sides of the uterus and Two ovaries (female sex glands) which produce the female’s ova. Breasts are located in the chest region. They play an important role in reproductive functioning such as breast feeding. Important sexual hormones of females include ‘ estrogen’ and ‘progesterone’.

Male reproductive system

The primary direct function of the male reproductive system is to produce spermatozoa for fertilization of the ovum. The major reproductive organs of the male are: Penis- It is the male sex organ for sexual intercourse. Scrotum- It contains the testes. Testes- Production of sperm and sexual hormone takes place in testes. Epididymis- Development and storage of sperms takes place in epididymis. Prostrate- Nourishment of sperm takes place with the help of prostate fluid. Urethra - It is the tube that carries urine from the bladder to outside the body. In addition it ejects semen. An important sexual hormone of males is ‘testosterone’.


In this lesson, you have gained the knowledge of the structure and function of human body, the contribution of each system and a general description of interrelationships between all body systems. You can now understand how our body performs its functions. The sum of these activities enables the human being to live in and utilize his environment in a useful way.

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