The study of physiological structure and life processes is very important for understanding the different biological processes that occur inside the human body. So, human body structure and life processes are one of the most important topics, covered in science and technology to help students get more involved in human body structure and life processes occurring in the human body. So, here is complete notes for secondary-level students which will help them understand the human body structure and life processes and perform well in examinations too.

This note is based on the NEB syllabus, and focuses on the topics as per the requirement of the CDC, whereas this can be used as reference study materials for any secondary-level curriculum around the world.

You can get a pdf of the science and technology textbook from here.

Introduction To Physiological Structure & Life Process

Physicological Structure

Physiological structure refers to the arrangement, organization, and composition of various tissues, cells, and organs within a living organism that are involved in its physiological functions. These structures are responsible for carrying out specific tasks and maintaining the overall function and balance of the body.

Life process refers to the various processes that occur in living organisms from birth to death, The most important life processes in human life are reproduction, respiration, digestion, excretion, growth and development, movement, response to stimuli, reproduction, and heredity, All these life processes are interrelated and they work in coordination.

Life Process is possible only when there is balance and coordination among the operating systems. The steady state of the physical, chemical, and internal state of the human body is maintained by various processes which are called homeostasis.


Homeostasis is the collective form of normal body functioning to sustain the life process. It includes the maintenance of various biochemical factors of the body like temperature, fluid balance, pH maintenance, the concentration of different ions, level of biomolecules, etc. There are various indicators that show whether the life process is normal or fluctuating. Such indicators are blood pressure, blood glucose level, uric acid level, cardiac rate, pulse rate, etc. Diseases or infirmities are the consequences of disturbances in normal life processes.

Fundamental Aspects of Life Process

The study of life process is a vast topic, and not every life processes are feasible to study. So, studying the fundamental aspects of life processes is one of the approaching ways to study different life processes.

The Circulatory System is one of the most fundamental aspects of life processes. The circulatory system is related to the internal transportation of the body system. i.e. it transports nutrients, gases, hormones, and other necessary materials in the body. The major function of the Circulatory system is to circulate blood to the body. So, we will study about human blood Circulatory system.

Human Blood Circulatory System

The blood Circulatory system is one of the systems in the body, which is responsible for the transportation of various substances like oxygen, carbon dioxide, and nutrients from one part of the body to another part.

The blood Circulatory System is also known as the transportation system of the body. The major components of the human blood circulatory system are blood, heart, and blood vessels.

Human Heart

Components of the Human Blood Circulatory System

As mentioned earlier, blood, heart, and blood vessels are the major components of the human blood circulatory system. We’ll describe each of the components briefly.


Blood is red-colored, opaque, and complex fluid with connective tissue that constantly circulates in a closed vessel system. The pH range of the blood varies within a narrow range of 7.40 to positive or negative 0.05 (I.e. 7.35 to 7.45). Blood is composed of 55% plasma and 45% blood cells, which are also called blood corpuscles.

Components of Blood

a. Plasma

Plasma is a yellow-colored fluid that constitutes about 55% of the total volume of human blood. It contains 90% water and the remaining 10% is dissolved in salts, proteins, glucose, etc. Plasma contains proteins such as albumin, globulin, fibrinogen, thrombin, and heparin. These different proteins have different functions. For example, globulin functions for immunity, fibrinogen functions for blood clotting, and so on. The liquid part of the blood after coagulation is serum.

The proteins and antibodies in the plasma are used in therapies for rare chronic conditions. The main function of plasma is to transport nutrients, hormones, and proteins to the different parts of the body. Plasma also carries water, salt, and enzymes. It is also necessary to recover the body from injuries, remove wastes and prevent infection.

Functions of Plasma

The functions of Plasma are as follows.

  • Plasma maintains the temperature of the body.
  • It maintains the water contained in the body.
  • It carries nutrients from one part of the body to another and also carries unnecessary waste products from the body.
  • It keeps the chemical composition of the blood as well as pH of the blood balanced.
  • Plasma- Fibrinogen=Serum. The serum is used in diagnosing various diseases.

Blood Corpuscles (Blood Cells)

Blood Cells are another component of the blood, which is 45% of the total blood. There are three types of blood cells present in the blood. They are

  • Red Blood Cells (RBC)
  • White Blood Cells (WBC)
  • Platelets

Red Blood Cells (RBC)

Red Blood Cells are also known as erythrocytes. They are red in color and biconcave disc-shaped blood cells. The nucleus is absent in red blood cells. The red blood cells are formed inside the bone marrow and approximately 1 ml of blood contains 45 to 50 lakhs of RBCs. Red Blood Cells are red in color due to the presence of hemoglobin in them.

Iron plays a crucial role in the formation of hemoglobin, the protein responsible for transporting oxygen in the blood. Without an adequate supply of iron, the body’s ability to produce hemoglobin is compromised, leading to a decrease in the number of red blood cells (RBCs) in a condition known as ‘Anaemia.’ These red blood cells, which have an average lifespan of approximately 120 days, are essential for delivering oxygen to various tissues and organs throughout the body. However, due to the shortage of iron, their production and functionality are impaired, leading to a host of symptoms such as fatigue, weakness, and paleness.


The life cycle of red blood cells comes to an end when they become old and damaged. The spleen and liver play critical roles in the process of breaking down and recycling these worn-out red blood cells. Red Blood Cells are destroyed in the liver. Iron produced while destroying of the Red Blood Cells is reused for the further cycle. RBC helps to transport oxygen from the lungs to other parts of the body.

White Blood Cells (WBC)

Those blood cells that are irregular in shape but have a nucleus provided are known as white blood cells. They are colorless and do not contain hemoglobin. White Blood Cells are also known as leukocytes.


There are two types of white blood cells. They are:

  • Granular Leukocytes – Those white blood cells which have granules inside their cytoplasm are called granular cytoplasm. Examples – Neutrophil, Basophil, Eosinophil, etc.
  • Non-Granular Leukocytes – Those white blood cells which do not have granules inside their cytoplasm are called nongranular leukocytes. Examples – Lymphocyte, Monocyte, etc.

The average lifetime of the white blood cells is about two weeks. There are 4000 to 11000 leukocytes present in 1 cubic ml of blood. They are formed in the bone marrow and destroyed in the spleen.

If the number of white blood cells excessively increases in the blood, it will destroy other blood cells and leads to blood cancer also known as leukemia. White Blood Cells helps to fight the diseases by killing the germs and it also helps to heal the wounds. The deficiency of white blood cells also causes leukopenia.


Platelets are the smallest blood cells. They also don’t have a nucleus. Platelets are also called thrombocytes. One cubic ml of blood contains 2 to 4 lakhs of platelets. The average lifespan of the platelets is about 2-3 days and they are also formed inside the bone marrow.

Platelets are destroyed in the spleen. During the wound in the body, they prevent the clotting of the blood by mixing with the fibrinogen. The lack of platelets in the body prevents the clotting of the blood even in small injuries. This condition is known as haemophilia. If the number of platelets in the body increases unconditionally. it causes thrombocytosis, which can lead to heart and brain attacks.


Platelets also prevent excessive bleeding.

Functions of Blood

There are various functions of blood. The major function of blood is TRP. They are:

  • Transportation – Blood transports oxygen and carbon dioxide in different parts of the body. It also transports various nutrients, enzymes, and hormones to the different parts of the body.
  • Regulation – Blood regulates and maintains the temperature of the body. It also regulates the amount of water containing other fluids and chemicals inside the body.
  • Protection – Blood protects the body from diseases by fighting germs and viruses. They also produce antibody and improves the immunity of the body. They also prevent excessive bleeding by clotting the blood during the injuries.

Human Heart

Activity – Observe the heart of any animal and sketch a well-labeled diagram of the heart.

The heart is the central part of the human blood circulatory system. The heart helps to pump blood to different parts of the body. The heart is a strong, cone-shaped muscle located inside the chest, below the lungs. It has the special ability to squeeze and relax. The heart is protected by a covering called the pericardium, which is like a shield. This covering has a special fluid called pericardial fluid that acts like a cushion, protecting the heart from any sudden bumps or shocks from the outside. The average weight of a human heart is 300 grams.

The heart pumps blood to every cell and tissue of the body with the help of the blood vessels. About two third of the heart lies to the left of thoracic cavity. A hair-like, very fine network of capillaries surrounds the heart. The coronary artery supplies oxygenated blood to the heart, while the coronary sinus vein transports deoxygenated blood to the right auricle of the heart.

Internal Structure of the Heart and Blood Circulation

The human heart is four-chambered. The upper two chambers are called auricles or atria while the lower two are called ventricles. There is a thick muscular septum in the middle of the heart that divides the heart into left and right parts and also prevents the mixing of oxygenated and deoxygenated blood in the heart. The four chambers in the heart are named right auricle, right ventricle, left auricle, and left ventricle. Blood Vessels are connected to these chambers through which the heart supplies and receives blood. Auricles receive blood from different parts of the body, but ventricles send blood to various parts of the body.

The heart pumps blood to different parts of the body with great pressure. To withstand such pressure, the walls of the ventricles are thicker than those of the auricles. The right ventricle pumps blood only up to lungs, but the left ventricle pumps the blood to various organs with great pressure. Therefore, the wall of the left ventricle is thicker than the wall of the right ventricle.

The blood vessels that bring deoxygenated or impure blood to the right auricle of the heart are the superior vena cava and inferior vena cava. The superior vena cava brings impure blood from the upper parts of the body, while the inferior vena cava brings impure blood from the lower parts of the body. When the auricle contracts, impure blood from the right auricle is passed to the right ventricle, and pure blood from the left auricle to the left ventricle. The pulmonary artery transports deoxygenated blood to the lungs for oxygenation, while the pulmonary vein transports oxygenated blood to the left auricle of the heart. The only artery that transports oxygenated blood in the human body is the pulmonary artery and the vein that transports the oxygenated blood in the human body is the pulmonary vein. After the pure blood is passed from the left auricle to the left ventricle, blood from the left ventricle is pumped to various parts of the body through the aorta.

There are four valves in the heart. The valve situated between the right auricle and the right ventricle of the heart is called the tricuspid valve. By opening this valve, blood passes from the right auricle to the right ventricle. The valve situated between the left auricle and left ventricle of the heart is called the bicuspid valve or mitral valve. Pure blood from the left auricle flows to the left ventricle by opening this valve. Both valves open simultaneously when the auricles contract together, and the contraction of the auricles is followed by the contraction of both ventricles. When the right ventricle contracts, the tricuspid valve is closed and the pulmonic valve between the right ventricle and pulmonary artery opens, and deoxygenated blood is pumped to the lungs through the pulmonary artery for oxygenation.

Likewise, when the left ventricle contracts, the bicuspid valve is closed and the aortic valve between the aorta and left ventricle opens, and the deoxygenated blood is pumped to the various organs of the body through the aorta.

Blood Vessels

Blood Vessels are the flexible, muscular tubes that transport the blood to various cells and tissues of the body. Arteries, veins, and capillaries are the three types of blood vessels.


The blood vessel that transports blood from the heart to the various parts of the body is called an artery. Arteries are highly muscular blood vessels. Such walls help to withstand the pressure of the blood. There are no valves in arteries. The aorta is the largest artery in the human body, and it divides to give off numerous small arteries. Arteries, in turn, divide to give off arterioles. Each arteriole, again, divides to form a fine network of blood capillaries.


Arterioles divide to form a network of fine thread-like or hair-like blood vessels called capillaries. Blood capillaries supply nutrients like oxygen, hormones, enzymes, etc dissolved in the blood to the cells and receive the wastes like carbon dioxide, urea, and other unnecessary substances produced in the cells to transport them up to excretory organs. After receiving wastes from the cell, capillaries unite to form venules and veins.


The blood vessel which transports blood from various organs of the body to the heart is called a vein. Their wall is composed of three layers as found in an artery but they have a thinner layer of smooth muscles. So, veins are thin-walled blood vessels. Veins carry carbon dioxide and waste-rich blood collected by venules to the heart, so there is less speed and pressure of blood in veins and also the probability of blood flow in the reverse direction. To prevent the blood flow in the reverse direction, veins have valves at frequent intervals. Venules, veins, and vena cava have the same function, but their size and numbers vary from each other.

Blood Circulation

Blood Circulation is the process by which blood is transported from the heart to various body parts and vice versa. The healthy heart pumps about 5-6 liters of blood per minute in an adult human. Blood circulation in the human body can be classified in two ways.

  • Systematic Blood Circulation
  • Pulmonary Blood Circulation

Systematic Blood Circulation

The process of blood circulation in which deoxygenated blood from the left ventricle flows through an aorta and its branches (arteries) to various parts of the body, and deoxygenated blood from these organs returns to the heart through veins is called systematic blood circulation.

When the left ventricle contracts, pure blood flows from the heart into the aorta. From the aorta to the small arteries and arterioles, blood reaches the cells through capillaries. In this way, nutrients, oxygen, and other essential substances are supplied to each cell of the body. When these substances are utilized in the cells, carbon dioxide gas and other wastes are produced, which are then transported by blood through veins. These veins, in turn, combine to form the vena cava, and hence impure blood (blood rich in carbon dioxide) is transported to the right auricle through the vena cava. In this way, the process in which blood from the left ventricle goes to various parts through arteries and then returns to the right auricle through veins is called systematic blood circulation.

Left Ventricle ————artery———>different parts of body————–vein—————>right auricle

Pulmonary Blood Circulation

The circulation of blood between the heart and lungs through the pulmonary artery and pulmonary veins is called pulmonary blood circulation. When the right ventricle contracts, the pulmonic valve opens, and deoxygenated blood (impure blood) flows through the pulmonary artery and finally through the capillaries network surrounding the millions of alveoli of the lungs. Then the carbon dioxide is left in the alveoli where oxygen is picked up by the blood which becomes pure or oxygenated. The pure blood is then carried to the left auricle through the pulmonary veins. Therefore, the process in which impure blood flows from the right ventricle to the lungs and pure blood flows from the right ventricle to the lungs, and pure blood flows from the lungs to the left auricle of the heart is called pulmonary blood circulation.

right ventricle——–pulmonary artery———->lungs———–pulmonary vein——–>left auricle


In conclusion, it’s important for students to understand how our body works to do well in biology exams. The human body has different parts like tissues, cells, and organs that work together to keep us healthy. Life processes, such as breathing, digestion, and blood circulation, are all connected and need to be balanced for our body to function properly.

The circulatory system is a vital part of our body that moves nutrients and gases through our blood. It includes the heart, blood vessels, and blood.

In summary, this study material is a helpful resource for secondary-level students to learn about how our body functions and stay successful in their biology studies. It explains these complex topics in simple words, making it easier to understand the physiological structure of our body and life processes.

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