CBSE Class 11 Biology Revision Notes Chapter 18

CBSE Class 11 Biology Revision Notes Chapter 18 – Body Fluids and Circulation 

Class 11 Biology Chapter 18 is about Body fluids and Blood circulation. The chapter introduces the core concepts and theories associated with the human body to the 11th-standard students. In order to help students with their preparation for this chapter, Extramarks offers Class 11 Biology Chapter 18 Revision Notes. These notes summarise all the important concepts covered in the chapter in a clear and concise manner for students’ reference. These notes can be accessed from the Extramarks website at any time.

Biology Notes for Class 11 Chapter 18- Body Fluids and Circulation 

Chapter 18 covers many important concepts of the human body, blood fluids and circulation. This chapter talks about blood, plasma, groups of blood, blood groups and antigens on Red Blood Cells, coagulation of blood, lymph nodes, pathways of circulation, the circulatory system of the human body, the cycle, sound of the heart and so on.

Blood

Blood is one kind of fluid connective tissue that contains plasma and other cellular elements. These cellular components are red blood corpuscles, white blood corpuscles and platelets. Plasma plays the role of matrix in blood.

Plasma

The primary component of blood is a plasma-based fluid. It is an adhering, straw-coloured fluid which fills 55% of the total volume of the blood. It contains several protein elements, including albumins, globulins and fibrinogens. Albumins control and balance the body’s osmotic equilibrium. On the other hand, globulins are anti-inflammatory proteins. Last but not least, fibrinogens help in blood clotting. 

Plasma carries sodium, calcium, magnesium and bicarbonate ions to maintain equilibrium and supply nutrients to the body. In addition, it also has amino acids and glucose. CBSE Class 11 Biology Chapter 18 notes help students in understanding the topics with summarised details and explanations. 

Formed Elements

Examples of formed elements include erythrocytes, leukocytes and blood platelets. Different blood cells play various roles in the human body. Red Blood Corpuscles (RBC) are one kind of erythrocyte. They play a vital role in forming blood cells.

The blood cells are formed in the bone marrow. The RBCs are present are biconcave but lack a nucleus. Spleen has been known to be RBC’s graveyard. 

On the other hand, White Blood Corpuscles (WBCs) are leukocytes. As they lack haemoglobin, these cells appear colourless. WBCs carry a lifespan of three to four days.

Another two categories include Granulocytes and Agranulocytes. Granulocytes are basophils, neutrophils and eosinophils. The latter category comprises lymphocytes and monocytes. 

Neutrophils and polymorphonuclear leukocytes are the same. Neutrophils are present in the most numbers among the three granulocytes. These are also known as phagocytic cells as they eat other cells. Compared to the other granulocytes, basophils are the smallest. Basophil secretes histamine and serotonin. Therefore, it has an integral function in inflammatory reactions. On the other side, eosinophils are associated with allergic reactions.

Platelets are commonly known as thrombocytes. Megakaryocytes produce the blood platelets in the bone marrow. Platelets aid in blood coagulation. A fall in the platelet count can result in blood loss in the body. 

Groups of Blood

Blood Groups have been classified into two types: ABO and Rh. Let us look into the functionalities of both in the following sections.

The ABO Blood Grouping System

The presence and absence of antigens on RBCs surface determine the ABO blood groups. Two primary surface antigens present in the red blood corpuscles are A and B—the blood groups are found, including A, B, AB and O. 

Diagram of Blood Groups and Antigens on Red Blood Cells

Blood Groups and individuals need to be compatible to donate or receive blood. The O blood group does not carry surface antigens, so the O+ blood group people are known as universal donors. Individuals with this blood group can donate blood to others, irrespective of the receivers’ blood groups. In contrast, the AB blood group is known to be the universal recipients as they carry both surface antigens. It is always safe to transfuse blood, depending on the donor’s blood group and the receivers.

Rhomboid Classification

Rhomboid is scientifically known as Rh. Rh is an antigen compared to the ones found in the blood of the Rhesus monkeys. Individuals with Rh antigen in their RBCs are known to be Rh+, and those who do not have Rh antigen are Rh-. If an Rh-positive person receives blood from an Rh-Negative one, the person will begin producing antibodies against the Rh-Positive blood. 

For this reason, before blood transfusion, individuals need to evaluate the Rh group. A critical mismatch case has been detected when an Rh-negative pregnant woman carries an Rh-Positive embryo. Due to a barrier termed as placenta, the embryo’s Rh antigens are not exposed to the mother’s Rh-negative blood during the first pregnancy.

There is still a chance that the mother’s blood might get mixed with the kids during the first child’s delivery. Consequently, the mother starts to produce antibodies against the Rh antigens. The Rh antibodies from the Rh-Negative mother can leak into the blood of the foetus who carries the +Rh antigen, and the leakage can damage the foetal RBCs when the mother conceives for the second time. Agglutination of Red Blood Corpuscles (RBC) happens due to this. The condition has been termed Erythroblastosis foetal.

In this case, the foetus is prone to be anaemic and suffers from jaundice. The mother needs to be injected with anti-Rh antibodies shortly after giving birth to her first kid to avoid the issue. 

Coagulation of Blood

Blood coagulation is the condition when the blood clots. It is another term used for blood clotting. Any type of accident or injury can cause bloodshed leading to coagulation. The system helps the body prevent unnecessary blood loss. When an individual gets physical wounds, a reddish-brown scum is seen at the injured site after a specific time. A clot is a medical term used to describe a condition. A network of threads called fibrils aids the clot. The grid shows the accumulation of dead or damaged blood. 

When inactive fibrinogen transforms in the presence of the enzyme thrombin, fibrils are produced. Platelets let out specific substances, which result in blood coagulation. Calcium ions play a crucial function in clotting the blood.

Lymph

Lymph is another fluid substance that is present in our bodies, in addition to blood. Blood circulates through the blood capillaries in tissues. A few water and water-soluble compounds leak into the interstitial spaces. It is known as interstitial fluid or tissue fluid found in the human body. 

The lymphatic system comprises a series of tubes that accumulate the interstitial fluid and supply it to the central veins. Lymph is a vital fluid present in the lymphatic system. The fluid contains lymphocytes which are an essential kind of immune cell. 

Pathways of Circulation

Two circulatory systems are referred to as the open and closed circulatory systems found in bodies. When blood flows in sinuses and cavities, the process is known as the open circulatory system. It is located in molluscs, arthropods, etc. 

The heart is a pumping, muscular organ located in invertebrates. Fishes’ hearts have two chambers. All amphibian animals have a three-chambered heart. The only exception is the crocodile. Reptiles, humans and birds have four-chambered hearts.

The Circulatory System of the Human Body

The human circulatory system comprises blood, the heart, and blood arteries. The heart is a mesodermal organ. It is situated between the two lungs in the thoracic cavity. A double membrane called pericardium encircles the heart. The pericardium is a tissue ring covering the pericardial fluid and protecting it. The human heart comprises four chambers: two atria and two ventricles. A small wall divides the left and right atria. It has been termed the intra-atrial septum. On the other side, a strong, muscular interventricular septum separates the left and right ventricles. 

The tricuspid valve shields the entrance between the right ventricle and the right atrium. The bicuspid, also known as the mitral valve, protects the access between the left atrium and left ventricle. Semilunar valves can be noticed in the entrances of the left and right ventricles towards the pulmonary artery and aorta. 

The human heart is a musculoskeletal organ. Cardiac muscles form the core. The organ comprises a particular cardiac muscle known as nodal tissue. SA node or Sinoatrial notes are situated at the top of the corner of the right atrium. On the other hand, the AV node or Atrioventricular node can be found in the upper left corner of the right atrium. 

The AV or AtrioVentricular bundle expands from AVN and bifurcates into the left and right bundle after passing through the septa. The Purkinje fibres are tiny ones that originate from the branches. The Sinoatrial node has been termed the heart’s pacemaker as it possesses the ability to be excited and take potential actions.

Cycle of the Heart

The cardiac cycle is a sequence of mechanical and electrical events which happen with each heartbeat. Diastole and systole are the two subsequent stages of the heartbeat. The heart’s ventricles relax during diastole and allow blood to flow into them. On the other side, the ventricles contract during systole to pump and circulate blood into the arteries. The electrical stimulation follows the shrinkage of the right and left atria in the atrial systole—the blood pressure in both left and right atria increases as a result of this. The AV valves remain open while the blood is pushed into the ventricles, and the semilunar valves are closed. The process takes roughly around 0.1 seconds.

The core features of ventricular systole include the right and left ventricles’ contraction and electrical stimulation. The AB valves remain closed during the ventricular systole, and the semilunar valves open. This process takes roughly around 0.3 seconds to complete. 

Cardiac diastole occurs when the heart relaxes to fill up the blood vessels. Complete cardiac diastole happens when the ventricles and atria relax together. The pressure in the ventricles becomes less than the left atrial pressure during ventricular diastole. The mitral valve opens and fills the left ventricle with blood.

When the pressure in the right ventricle falls under that in the right atrium, the tricuspid valve opens and allows the blood to flow into the right ventricle. During the diastole process, the pressure inside the left ventricle is less than in the aorta. It enables the blood to spread within the heart via the coronary arteries. When the pressure in the right ventricle falls under the right atrium, the tricuspid valve becomes open and allows blood to flow into the right ventricle. In the course of the diastole, the pressure inside the left ventricle is less than in the aorta and allows blood to pump within the heart via the coronary arteries. 

The Sound of the Heart

The sound of the heartbeat is commonly termed “lubb-dubb”. When the tricuspid and mitral valves collapse at the beginning of the ventricular systole, the first sound, ‘lubb,’ is resonated. And, when the pulmonary and aortic valves close at the end of the ventricular systole, the second sound, ‘dubb’, is originated. 

ECG

ECG refers to an Electrocardiograph, which is a graphical representation of the heart’s electrical activities during the cardiac cycle. The letter P implies various peaks through T in any typical ECG. 

• P Wave: P-wave shows the atrioventricular electrical stimulation. The atrial depolarisation is vivid.
• QRS Complex: The ventricular depolarisation is displayed by the QRS complex. Ventricular contraction starts as a result of this. Shortly after Q, the shrinkage begins. 
• T-Wave: The T-Wave shows the repolarisation of the ventricles. It represents the restoration of ventricles to their natural state after the excitation—the conclusion of the T-Wave signals to the end of the ventricular systole.

Double Circulation: It is a circulation system where blood circulates two times through the heart in a single cycle. The cycle is bifurcated into two segments: systematic and pulmonary circulation.

Blood Circulation: Pulmonary circulation between the heart and the lungs is blood circulation. The deoxygenated blood enters the lungs to take oxygen, and then the oxygenated blood returns to the core. A circulation system where the blood passes twice through the heart in one cycle is termed double circulation. The circulation has two sections: pulmonary circulation and systemic circulation. Pulmonary circulation refers to blood exchange between the heart and the lungs. The deoxygenated blood of the heart gets oxygenated in the lungs before it returns to the core.

The ANS (Autonomous Nervous System) stimulates heart activities through the neural centre located in the medulla oblongata. The sympathetic nervous system increases the heart rate and ventricular contraction power, enhancing the cardiac input. Specific adrenal medullary hormones can influence cardiac output. 

Circulatory System Disorders:

Coronary Heart Disease: CHD is also known as atherosclerosis. The artery lumen becomes narrow in this disease due to fat, cholesterol, calcium, and fibre tissue disposition. It affects the blood supply of heart muscles. 

Hypertension: Hypertension is another term used for high blood pressure. It is a physical condition where an individual’s blood pressure remains higher than the standard rate. The blood pressure of a healthy adult should be 120/80. 120 mm HG is the systolic pressure in the pressure chart, and 80 mm HG is the diastolic pressure.

Angina: Angina is also known as angina pectoris. It creates a kind of chest pain caused by the lack of oxygen inside the heart muscles. 

Heart Failure: Heart failure is caused due to the inefficient pumping of blood by human hearts. The primary reason for the disease includes heart congestion. The attack is also known as congestive heart failure.

Biology Notes for Class 11 Chapter 18 – Body Fluids and Circulation

Notes of Class 11 Biology chapter 18 cover each vital concept of the chapter body fluids and circulation. The core objective of the revision notes is to help the students internalise the basic concepts of blood, which is the primary fluid in our body. Blood contains plasma and cellular elements like WBC, RBC and platelets.

The chapter includes the description of different blood group classifications, which shows the blood group and their uniqueness. Rh is a concept that students need to prepare thoroughly. Rh is an antigen which is similar to that present in Rhesus Monkey. The functionalities of the antigens in the body of a pregnant woman and her embryo have been explained in the notes in minute detail. Blood coagulation is another critical topic incorporated in the chapter. 

Another primary body fluid is lymph, which flows through the lymphatic system. The blood circulatory system in the human body comprises the heart, blood vessels and blood. Class 11 students can refer to the revision notes to understand the function and role of each component mentioned in the chapter.