11. Human Body and Organ System

In the last class, we have studied some characters of living organisms. All the vital processes which are essential properties of living beings, are collectively called as life processes.

Different organs in our body are working in group so as to smoothly carry out various life processes. These life processes takes place in various steps. Specific organs carry out the specific steps. Group of organs working together to perform a specific function is called as organ system. Various organ systems like digestive, respiratory, circulatory, nervous, excretory, reproductive, skeletal, muscular, etc. are functioning in our body.

Energy is essential to operate all the life processes in human body. Energy production occurs within the cells. Cells need the supply of soluble nutrients and oxygen for this purpose. This supply takes place with the help of respiratory and circulatory systems. Respiration is carried out through following three steps.

  1. External Respiration:
  2. Inspiration / Inhalation : Air is taken in through nose and sent towards the lungs through trachea (wind pipe).
  3. Expiration / Exhalation : Oxygen from the inspired air goes into blood. Blood carries the CO2 from various parts of body towards lungs. This air is given out by exhalation. Both of these processes occurring with the help of lungs are collectively called as external respiration.
  4. Internal Respiration : Exchange of gases between cells and tissue fluid is called as internal respiration. Oxygen moves from blood into tissue fluid and carbon dioxide moves from tissue fluid into blood.
  5. Cellular Respiration : Dissolved nutrients like glucose are slowly burnt (oxidized) with the help of oxygen and energy is released in the form of ATP. Waste materials like CO2 and water vapours are produced during this process. Cellular respiration can be summarized as follows. C6 H12O6 +6O2 6CO2 +6H2 O+ Energy (38ATP)

Respiratory system : Structure and function

  1. Nose : Respiratory system and respiration begins with nose. Air is filtered with the help of hair and mucus present in the nose.
  2. Pharynx : Food pipe and wind pipe originate in the pharynx. Wind pipe is present in front of the food pipe. There is a lid at the beginning of wind pipe. This lid closes the wind pipe during passing of food into food pipe and thereby normally prevents the entry of food particles into wind pipe. Otherwise, wind pipe remains open. Hence air passes through pharynx into wind pipe.
  3. Wind pipe : Wind pipe is swollen at the beginning due to sound box. Wind pipe bifurcates in the thorax. One branch enters the right lung and the other into left lung.
  4. Lungs : A lung is present on either sides of heart in thoracic cavity. Maximum area of thoracic cavity is occupied by lungs and they cover the maximum part of heart. Each lung has double layered covering. It is called as pleura. Lungs are elastic like a sponge. Lungs are made up of many small compartments, called as alveoli. Rich network of capillaries is present around each alveolus. Walls of alveoli and capillaries are extremely thin. Gaseous exchange can easily take place across these thin walls. As large number of alveoli is present in lungs, larger surface is available for gaseous exchange. Exchange of gases in lungs : Gaseous exchange occurs continuously while blood is circulating around the alveoli. An iron containing protein- hemoglobin is present in the RBCs of blood. Hemoglobin absorbs the oxygen from air within alveoli. Simultaneously, CO2 and water vapours move from blood into the alveoli. Thus, oxygen is taken into the blood and CO2 and water vapours are removed from the blood and given out by exhalation.
  5. Diaphragm : A muscular partition is present at the base of thoracic cage. This partition is called as diaphragm. It is present between the thoracic cavity and abdominal cavity. Simultaneous rising up of ribs and lowering of diaphragm causes the decrease in pressure on lungs. Due to this, air moves into the lungs through nose. When ribs return to their original position and diaphragm rises up, pressure on the lungs increases. Due to this, air moves out from it through nose. Continuous upward and downward movement of diaphragm is necessary to bring about the breathing.

Blood circulatory system

 Circulatory system performs the function of transport of various substances like water, hormones, oxygen, soluble nutrients, and waste materials through different organs. An independent system for blood circulation is present in humans and higher animals. It consists of heart, blood vessels and capillaries.

Heart: Structure and Functions

Heart is present almost at centre in thoracic cage. It is present behind the ribs, between two lungs and slightly inclined on left side. Size of our heart is equal to one’s own fist and its weight is about 360 gram. It is covered by a double layered peritoneal membrane. A fluid is present between two membranes due to which heart is protected from friction and mechanical shocks.

Human heart is a muscular organ. It is made up of involuntary cardiac muscles. They contract and relax with a definite rhythm. This is called as beating of heart. Internally, heart is divided into left and right compartments by a vertical partition. Each of those compartments is again divided into two chambers. Thus, in all, heart consists of four chambers. Upper chambers are called as atria (singular – atrium) and lower chambers as ventricles

Blood vessels – Structure and functions : Heart is beating continuously. Due to this, blood continuously circulates through blood vessels. There are two main types of blood vessels.

Arteries : Blood vessels which carry the blood away from heart are called as arteries. Except the one carrying blood towards lungs, all carry oxygenated blood. These are deeply located in the body and their walls are thick. These vessels do not have valves.

Veins : Vessels carrying the blood towards the heart from various parts of body are called as veins. All veins except the one carrying blood from lungs transport deoxygenated blood. Most of the veins are superficially located in the body. Their walls are thin and these are provided with valves.

Capillaries : Arteries gradually branch out with decrease in their diameter as they spread in the body and finally form fine hairlike vessels called as capillaries. Walls of capillaries are extremely thin and made up of single layer of cells. Due to this, exchange of materials between capillaries and cells becomes easy. During the exchange, the oxygen, nutrients, hormones, vitamins, etc. are sent towards the cells and waste materials of the cells move into blood. Capillaries unite together to form the vessels of more diameter, called as veins. Capillary network is present in each organ.

Blood circulation through heart / Functioning of Heart

Process of pumping the blood towards various parts of the body and bringing it back towards the heart is called as blood circulation. So as to maintain the continuity in circulation, heart alternately contracts and relaxes. Consecutive single contraction and relaxation of heart constitutes a single heart beat.

Material : Two feet long rubber tube with small aperture, stop watch, funnel.
1. Fit a funnel at one end of rubber tube.
2. Keep the wide mouth of funnel on left side of thorax.
3. Bring the other end of tube near the ear to hear the sound.
4. Record the number of beats per minute using stop watch.

Pulse : Find correlation between heart beats & pulses felt at wrist.


Blood is a red colored fluid material. It is fluid connective tissue. The oxygenated blood is deep red colored, salty in taste and its pH is 7.4. Blood is composed of mainly two components.

Human Blood Groups

 Depending upon the proteins like antigens and antibodies, different blood groups are formed. There are four main groups of human blood as A, B, AB and O. Besides, there are two types as ‘Rh’ negative and ‘Rh’ positive of each of those four groups. Thus, in all eight blood groups are formed. (Eg. A Rh +ve & A Rh -ve).

 Blood Donation : If a person meets an accident, bleeding occurs through wounds. Many times, blood transfusion is necessary during the surgical operation. Similarly, blood is transfused in case of patients of anemia, thalassaemia, cancer too. Blood transfusion is carried out to compensate the blood shortage in body. This is called as blood transfusion.

From where the blood is supplied for blood transfusion?

 Blood banks : Blood is collected in blood banks by specific method from the healthy persons and supplied to the needful persons. If the collected blood is not to be used immediately, it can be stored for some days in refrigerator.

Blood donor : Person who donates the blood is referred as blood donor.

Blood recipient : Person who receives the blood is referred as recipient. Person of the blood group ‘O’ can donate the blood to the person having any other blood group where as the person with ‘AB’ blood group can receive the blood from the person with any other blood group. Hence, person of blood group ‘O’ is called as universal donor and the person with blood group ‘AB’ is called as universal recipient.

Blood Pressure : Blood is continuously kept flowing through blood vessels due to contractionrelaxation of the heart. Due to contraction of the heart, pressure is exerted on the wall of arteries and it is called as blood pressure. Proper blood pressure is necessary to supply the blood in all parts of the body. Pressure recorded during the contraction of heart is called as ‘systolic pressure’ and that one recorded during relaxation is called as ‘diastolic pressure’. Blood pressure of a healthy person is about 120/80 mm to 139/89 mm of Hg. It is measured with the help of sphygmomanometer’.

Hypertension (High Blood Pressure) : High blood pressure than the normal is referred as hypertension. In arteries of the person with hypertension, unnecessary tension develops. Heart needs to perform more function than the normal condition in case of hypertension. Both, systolic and diastolic pressures are high in hypertension.