Body Fluids & Circulation Chapter Notes | Biology Class 11 - NEET PDF Download

Introduction

• Body fluids are a type of fluid within an organism that helps the cells to transport substances via body cavities. They can be blood, lymph, urine, tissue fluid, etc. 
• Two types of fluid circulation can be observed – intracellular circulation and extracellular circulation.
• Single-celled organisms like amoeba perform intracellular circulation inside their cell via cyclosis.
• In the extracellular circulation process, body fluids circulate across the cells.
• Through the circulatory system, body fluids distribute different substances like hormones, gasses, nutrients, etc. throughout the body and eliminate waste materials like urine from the body. 
• The circulatory system has two types – open and closed.

Blood

• Blood is a connective tissue that consists of plasma, formed elements, and fluid matrix.
• PlasmaConstituting 55% of the entire blood volume, this viscous fluid contains 90%-92% of water and 6%-8% proteins, glucose, amino acids, and electrolytes.

• The major protein elements are albumins, fibrinogens, and globulins.
• The electrolytes like  Na+,Ca++,Cl− etc. are found in small amounts.

Formed Elements

These formed elements are composed of thrombocytes, erythrocytes, and leukocytes.

Thrombocytes

• Thrombocytes or blood platelets help in the process of blood clotting.
• A specific cell in the bone marrow called megakaryocyte produces blood platelets.
• Count – 1.5-3.5 lakh per mm-3 blood.

Erythrocytes

• They are commonly known as red blood cells or RBC.
• Colour – Red due to hemoglobin.
• Count – 50-55 lakh per mm-3 blood in adult humans.
• Created in - Bone marrow.Shape – Biconcave.Nucleus – mostly absent.
• Lifespan - 120 days on average.
• Wrecked in – the spleen that is known as the RBC graveyard.
• The primary function of RBC, the most abundantly available cell in blood, is to transport the respiratory gasses in cells.

Leucocytes

• Commonly known as white blood cells.
• Colour – Colourless.
• Count – 6-8 thousand per mm-3 blood in adult humans.
• Nucleus – Present.
• Lifespan – 3-4 days on average. 
• Majorly two types – agranulocytes and granulocytes.

• Both neutrophils and monocytes have the phagocytic ability.
• Basophils secrete serotonin, histamine, etc., and thus, present in inflammatory reactions.
• Eosinophils help in resisting infections and are also, present in allergic reactions. Lymphocytes help to build up the immune response of organisms.

Body Fluids

• Human body consists of various fluids which are essential for the smooth functioning of tissues that carry  an important function by providing nutrition to living cells and eliminating the harmful substances that are produced in our bodies.
• Blood is a connective tissue that comprises a plasma fluid matrix and formed elements
• Fluid matrix is also known as Plasma. These cells cater to a special function and consist of highly specialized cells.
• Plasma is a viscous fluid that consists of almost 50 to 55% of the blood volume. It is 90 to 92 % of water.
• Plasma also contains small amounts of minerals like Na+,Ca++,Mg++,HCO3−,Cl−
• Formed elements constitute about 45% of blood and comprise enterocytes, leukocytes, thrombocytes.
• Enterocytes are also known as RBCs are formed in the red bone marrow. It is Biconcave and devoid of any nucleus.
• Leukocytes are also known as WBC which are much less in number and are nucleated.
• Thrombocytes are also known as platelets that release substances that help in the coagulation and circulation of blood.

ABO Grouping

There are four types of blood groups A, B, AB and O. Given below are the detail about blood groups:-

Blood Groups

Rh Group

RH antigen is present in 80% of human beings and forms an important part of Fluids and circulation. Those with RH antigen are RH positive and those without RH antigens are RH negative.

Coagulation of Blood

Blood clotting prevents excess loss of blood from an injury. The clot is made up of a network of fibrins, which traps dead formed elements.

• Inactive fibrinogen → Fibrin by the enzyme Thrombin
• Inactive prothrombin → Thrombin by the enzyme Thrombokinase
• An injury stimulates platelets to release certain factors, which initiate the blood coagulation process.
• Ca++ plays an important role in the process of coagulation.

Lymph

• Lymphs are released as the blood passes through the capillaries in tissues. 
• It is also a fluid connective tissue. In this liquid, the mineral distribution is the same as in plasma. 
• The exchange of nutrients and gases  between the blood and cells is facilitated by this fluid connective tissue.

Circulatory System

• The circulatory system supplies the body with oxygen and nutrients while removing waste and carbon dioxide. 
• It is a network of blood vessels and can either be open or closed which depends on the free movement of blood in a cavity or the containment of the same in vessel. 

Differences between Open and Closed Circulatory Systems:

Human Circulatory System

Heart- Four chambered, derived from mesoderm. It is present between the two lungs in the thoracic cavity and protected by the pericardium.

Structure of Human Heart

• A bicuspid (mitral) valve is present between the left, atrium and ventricle
• A tricuspid valve is present between the right, atrium and ventricle
• The right ventricle opens into the pulmonary artery and the left ventricle opens into the aorta. Both the openings are guarded by semilunar valves
• The heart is made up of cardiac muscles. There are nodal tissues also present in the heart.
• The sinoatrial node (SAN) is present on the upper right corner of the right atrium and the atrioventricular node (AVN) is present at the lower-left corner of the right atrium
• The AVN divides into right and left bundle at the interventricular septum and branches into minute fibres, that are present throughout the ventricle and are called Purkinje fibres
• The nodal musculature is auto-excitable, i.e. it can generate action potential without any external stimuli
• Bundle of His- Purkinje fibres along with the AV bundles form the bundle of His. It regulates the heartbeat and conducts the electrical impulses
• The SAN is called ‘pacemaker’, it initiates and maintains the heart’s rhythmic activity. It can generate 70-75 action potentials per minute
• Arteries and veins are together called blood vessels, which transport blood to various parts of the body and bring back to the heart
• Arteries and veins are made up of three layers:
  1. Inner tunica intima – squamous endothelium
  2. Middle tunica media – elastic fibres and smooth muscles (thin in the veins)
  3. Outer tunica externa – fibrous connective tissue having collagen fibres. 

Cardiac Cycle

• Towards the end, the SAN generates a new action potential and the full process repeats
• As the heart beats ~72 times per minute, so there are ~72 cardiac cycles in a minute
• Stroke Volume is the amount of blood each ventricle pumps in a cardiac cycle, i.e. 70 ml
• Cardiac Output is the total output of blood from each ventricle in a minute, i.e. stroke volume multiplied by the no. of heartbeats per minute, which is ~5 L in a healthy individual. The cardiac output varies from person to person. An athlete will have much more cardiac output compared to an ordinary person
• In each cardiac cycle, two distinct sounds are produced, ie. ‘lub’ and ‘dub’, which can be heard using a stethoscope
• The first sound ‘lub’ is produced when bicuspid and tricuspid valves close at the time of ventricular systole
• The second sound ‘dub’ is produced when semilunar valves close at the time of ventricular diastole

ECG (Electrocardiogram)

• The electrical activity of the cardiac cycle can be recorded in a graphical form by electrocardiogram or ECG.
  
• Various phases of each cardiac cycle are represented by a letter from P to T.
  P wave → excitation or depolarisation of atria
  QRS complex → depolarisation of ventricles
  T → repolarisation of ventricles (excited to normal)

The no. of QRS complex recorded in a time period tells the heart rate of the patient. Any abnormality or disease can be diagnosed by ECG if the graph shows any deviation from a regular pattern.

Double Circulation

Double circulation is a process during which blood passes twice through the heart during one complete cycle.

This type of circulation is found in amphibians, reptiles, birds, and mammals. However, it is more prominent in birds and mammals as in them the heart is completely divided into four chambers – the right atrium, the right ventricle, the left atrium, and the left ventricle.

The movement of blood in an organism is divided into two parts:

(i) Systemic circulation

(ii) Pulmonary circulation

• Systemic circulation involves the movement of oxygenated blood from the left ventricle of the heart to the aorta. It is then carried by blood through a network of arteries, arterioles, and capillaries to the tissues. From the tissues, the deoxygenated blood is collected by the venules, veins, and vena cava, and is emptied into the left auricle.
• Pulmonary circulation involves the movement of deoxygenated blood from the right ventricle to the pulmonary artery, which then carries blood to the lungs for oxygenation. From the lungs, the oxygenated blood is carried by the pulmonary veins into the left atrium.
• In double circulation, blood has to pass alternately through the lungs and the tissues.

Significance of double circulation

The separation of oxygenated and deoxygenated blood allows a more efficient supply of oxygen to the body cells. Blood is circulated to the body tissues through systemic circulation and to the lungs through the pulmonary circulation.

Regulation of Cardiac Activity 

• Normal activities of the heart are regulated intrinsically, i.e., auto regulated by specialised muscles (nodal tissue), hence the heart is called myogenic.
• A special neural centre in the medulla oblangata can moderate the cardiac function through autonomic nervous system (ANS).
• Neural signals through the sympathetic nerves (part of ANS) can increase the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output.
• On the other hand, parasympathetic neural signals (another component of ANS) decrease the rate of heart beat, speed of conduction of action potential and thereby the cardiac output.
• Adrenal medullary hormones can also increase the cardiac output.

Disorders of Circulatory System 

1. High Blood Pressure (Hypertension)

• Hypertension is the term for blood pressure that is higher than normal (120/80). 
• In this measurement 120 mm Hg (millimetres of mercury pressure) is the systolic, or pumping, pressure and 80 mm Hg is the diastolic, or resting, pressure.
• If repeated checks of blood pressure of an individual is 140/90 (140 over 90) or higher, it shows hypertension.
• High blood pressure leads to heart diseases and also affects vital organs like brain and kidney.

2. Coronary Artery Disease (CAD) 

• Coronary Artery Disease, often referred to as atherosclerosis, affects the vessels that supply blood to the heart muscle.
• It is caused by deposits of calcium, fat, cholesterol and fibrous tissues, which makes the lumen of arteries narrower.

3. Angina 

• It is also called ‘angina pectoris’.
• A symptom of acute chest pain appears when no enough oxygen is reaching the heart muscle.
• Angina can occur in men and women of any age but it is more common among the middle-aged and elderly.
• It occurs due to conditions that affect the blood flow.

4. Heart Failure 

• Heart failure means the state of heart when it is not pumping blood effectively enough to meet the needs of the body.
• It is sometimes called congestive heart failure because congestion of the lungs is one of the main symptoms of this disease.
• Heart failure is not the same as cardiac arrest (when the heart stops beating) or a heart attack (when the heart muscle is suddenly damaged by an inadequate blood supply).