Body Fluids and Circulation Class 11 Biology Chapter 15 Notes

Body Fluids and Circulation Class 11 Biology Chapter 15 Notes

• Living cells require nutrients, O2, and other essential substances for proper functioning.
• Efficient mechanisms are necessary to transport these substances to and from cells.
• Various animal groups have evolved different transport methods.
• Simple organisms like sponges and coelenterates circulate water through body cavities.
• More complex organisms use special fluids for transport.
• Blood is commonly used for transport in higher organisms, including humans.
• Lymph also aids in transporting certain substances.

Blood

Blood is a unique connective tissue with a fluid matrix (plasma) and formed elements.

1. Plasma

• Makes up about 55% of blood and has a straw-colored, viscous appearance.
• Composed of approximately 90-92% water and 6-8% proteins.
• Major proteins in plasma include fibrinogen (clotting), globulins (defense mechanisms), and albumins (osmotic balance).
• Contains small amounts of minerals like Na+, Ca++, Mg++, HCO3–, Cl–, etc.
• Includes glucose, amino acids, lipids, and other substances in transit within the body.
• Inactive clotting factors are present in plasma.
• When plasma lacks clotting factors, it is referred to as serum.

2. Formed Elements in Blood

• Erythrocytes (Red Blood Cells or RBCs), leucocytes (White Blood Cells or WBCs), and platelets make up the formed elements, accounting for approximately 45% of blood.
• Erythrocytes are the most abundant cells in blood, lacking a nucleus, and having a biconcave shape. They contain hemoglobin, which gives them their red color and plays a vital role in transporting respiratory gases. They have an average lifespan of 120 days and are produced in the red bone marrow.
• Leucocytes, or white blood cells, are nucleated and fewer in number (averaging 6000-8000 mm–3 of blood). They include granulocytes (neutrophils, eosinophils, and basophils) and agranulocytes (lymphocytes and monocytes). Neutrophils and monocytes are phagocytic cells that destroy foreign organisms. Basophils secrete substances involved in inflammatory reactions, while eosinophils resist infections and are linked to allergic reactions. Lymphocytes (B and T forms) are responsible for immune responses.
• Platelets, also known as thrombocytes, are cell fragments produced from megakaryocytes in the bone marrow. Normally, there are 1,500,00-3,500,00 platelets mm–3 of blood. Platelets release various substances involved in blood clotting. A decrease in platelet count can lead to clotting disorders and excessive blood loss.

Blood Groups

• Human blood varies in certain aspects despite its apparent similarity, leading to various blood group classifications.
• Two widely recognized blood group systems are ABO and Rh.

1. ABO Blood Grouping

• ABO blood grouping is based on the presence or absence of two surface antigens, A and B, on red blood cells (RBCs).
• Individuals also have natural antibodies in their plasma in response to the missing antigens.
• The distribution of antigens and antibodies in the four blood groups (A, B, AB, and O) is as follows:
  • Group A: Antigen A, Antibody anti-B
  • Group B: Antigen B, Antibody anti-A
  • Group AB: Antigens A and B, No antibodies
  • Group O: No antigens, Antibodies anti-A and anti-B
• Blood transfusions require careful matching to prevent clumping (destruction of RBCs).
• Donor compatibility:
  • Blood Group A can donate to A and O.
  • Blood Group B can donate to B and O.
  • Blood Group AB can donate to AB, A, B, and O.
  • Blood Group O can donate to all blood groups.
• Group O individuals are called “universal donors” because they can donate to anyone.
• Group AB individuals are called “universal recipients” because they can accept blood from all blood groups.

2. Rh Grouping

• The Rh grouping is based on the presence or absence of the Rh antigen on the surface of red blood cells (RBCs).
• About 80% of humans have the Rh antigen (Rh+ve), and the remaining individuals lack it (Rh-ve).
• An Rh-ve person exposed to Rh+ve blood will produce specific antibodies against the Rh antigen. Rh group matching is essential for transfusions.
• A special case of Rh incompatibility can occur when an Rh-ve pregnant mother carries an Rh+ve foetus. During the first pregnancy, the placenta separates the two blood types, preventing exposure. However, during delivery, a small amount of the foetus’s Rh+ve blood might mix with the mother’s Rh-ve blood, leading to the formation of Rh antibodies in the mother’s blood.
• In subsequent pregnancies, these Rh antibodies from the mother can enter the Rh+ve foetus’s blood and destroy its RBCs, potentially causing severe complications such as erythroblastosis foetalis (fatal to the foetus or resulting in severe anemia and jaundice in the baby).
• Administering anti-Rh antibodies to the mother immediately after the first child’s delivery can prevent this condition.

Coagulation of Blood

• When you get injured, your blood doesn’t keep flowing endlessly; it stops eventually. This is due to the process of blood coagulation or clotting, which prevents excessive blood loss.
• After an injury, you might notice a dark reddish-brown scab forming at the site. This is a clot, primarily composed of a network of threads called fibrins, which trap dead and damaged blood components.
• Fibrins are formed by the conversion of inactive fibrinogens in the plasma through the action of the enzyme thrombin. Thrombin, in turn, is produced from another inactive substance in the plasma known as prothrombin.
• An enzyme complex called thrombokinase is needed for this reaction, and it is formed through a cascade process involving multiple inactive factors in the plasma.
• Platelets in the blood are stimulated by injury or trauma to release certain factors that activate the coagulation process. Tissues at the injury site can also trigger coagulation.
• Calcium ions play a crucial role in the blood clotting process.

Lymph (Tissue Fluid)

• When blood flows through capillaries in tissues, some water and small water-soluble substances exit into the spaces between tissue cells, leaving behind larger proteins and most of the formed elements in the blood vessels.
• This fluid released into the tissue spaces is known as interstitial fluid or tissue fluid. It has the same mineral composition as plasma.
• Nutrient and gas exchange between blood and cells occurs through this tissue fluid.
• The lymphatic system, consisting of a network of vessels, collects this fluid and returns it to major veins.
• The fluid within the lymphatic system is called lymph. Lymph is colorless and contains specialized lymphocytes responsible for the body’s immune responses. It also acts as a carrier for nutrients, hormones, and fats. Fats are absorbed through lymph in structures called lacteals found in the intestinal villi.

Circulatory Pathways

• Circulatory systems can be categorized as open or closed.
• Open circulatory systems are found in arthropods and mollusks, where blood pumped by the heart flows through large vessels into open spaces or sinuses within the body.
• Annelids and chordates have a closed circulatory system, where blood pumped by the heart circulates through a closed network of blood vessels. This system allows for more precise regulation of fluid flow.
• Vertebrates, including fish, amphibians, reptiles, birds, and mammals, possess muscular, chambered hearts.
• Fish have a 2-chambered heart with an atrium and a ventricle. Blood is pumped out, deoxygenated, and then oxygenated by the gills before being supplied to the body (single circulation).
• Amphibians and reptiles (except crocodiles) have a 3-chambered heart with two atria and a single ventricle. Oxygenated and deoxygenated blood can mix in the ventricle, resulting in incomplete double circulation.
• In birds and mammals, a 4-chambered heart with two atria and two ventricles allows for complete separation of oxygenated and deoxygenated blood. They have double circulation with two separate circulatory pathways.

Human Circulatory System

• The human circulatory system, also known as the blood vascular system, comprises a muscular chambered heart, a network of closed branching blood vessels, and blood, the circulating fluid.
• The heart, a mesodermally derived organ, is located in the thoracic cavity between the two lungs, slightly tilted to the left and about the size of a clenched fist. It is protected by a double-walled membranous sac called the pericardium, which encloses pericardial fluid.
• The human heart consists of four chambers: two relatively small upper chambers called atria and two larger lower chambers called ventricles. The right and left atria are separated by a thin, muscular wall called the interatrial septum, while the left and right ventricles are separated by a thick-walled interventricular septum. Each septum has an opening connecting the two chambers on the same side. The right atrium and right ventricle are separated by the tricuspid valve, while the left atrium and left ventricle are separated by the bicuspid or mitral valve. The openings of the ventricles into the pulmonary artery and aorta are equipped with semilunar valves to allow one-directional blood flow and prevent backward flow.
• The entire heart is composed of cardiac muscles, with thicker walls in the ventricles. Nodal tissue, specialized cardiac musculature, is distributed throughout the heart. The sino-atrial node (SAN) is located in the right upper corner of the right atrium, and the atrio-ventricular node (AVN) is found in the lower left corner of the right atrium near the atrio-ventricular septum. An atrio-ventricular bundle (AV bundle) extends from the AVN through the atrio-ventricular septa and divides into right and left bundles on top of the interventricular septum. These branches give rise to purkinje fibers throughout the ventricular musculature. The nodal tissue can generate action potentials without external stimuli and is autoexcitable. The SAN, known as the pacemaker, is responsible for initiating and maintaining the rhythmic contractile activity of the heart.
• On average, the human heart beats 72 times per minute, with the SAN generating the maximum number of action potentials (70-75 per minute).

Cardiac Cycle

• The cardiac cycle is a sequence of events that describes how the heart functions. It includes systole (contraction) and diastole (relaxation) of both the atria and ventricles.
• At the beginning of the cycle, all four heart chambers are in a relaxed state, known as joint diastole. The tricuspid and bicuspid valves are open, allowing blood from the pulmonary veins and vena cava to flow into the left and right ventricles through the left and right atria. The semilunar valves are closed.
• The sino-atrial node (SAN) generates an action potential, triggering simultaneous contractions of both atria (atrial systole). This increases blood flow into the ventricles by about 30%.
• The action potential is conducted to the ventricles through the atrio-ventricular node (AVN) and atrio-ventricular bundle (AV bundle). The bundle of His transmits it through the entire ventricular musculature, causing ventricular contraction (ventricular systole).
• Ventricular systole increases ventricular pressure, leading to the closure of the tricuspid and bicuspid valves to prevent backflow into the atria. As ventricular pressure rises further, it forces open the semilunar valves guarding the pulmonary artery and aorta, allowing blood to flow into the circulatory pathways.
• The ventricles then relax (ventricular diastole), and the ventricular pressure falls, closing the semilunar valves to prevent backflow into the ventricles.
• As ventricular pressure decreases further, the tricuspid and bicuspid valves open, allowing blood to flow into the ventricles once more. The ventricles and atria are now in a relaxed (joint diastole) state, as at the beginning of the cycle.
• The SAN generates a new action potential, and these events are repeated in sequence, continuing the process.
• The cardiac cycle is cyclically repeated and consists of systole and diastole for both the atria and ventricles.
• The human heart typically beats 72 times per minute, with each cardiac cycle lasting 0.8 seconds.
• During a cardiac cycle, each ventricle pumps out approximately 70 mL of blood (stroke volume). The cardiac output is the product of the stroke volume and heart rate (number of beats per minute) and averages 5000 mL or 5 liters per minute in a healthy individual.
• The body can adjust the stroke volume, heart rate, and cardiac output as needed. For example, an athlete’s cardiac output is typically higher than that of an ordinary individual.
• Two prominent sounds, the first heart sound (lub) and the second heart sound (dub), are produced during each cardiac cycle. These sounds have clinical diagnostic significance and can be heard through a stethoscope. The first heart sound is associated with the closure of the tricuspid and bicuspid valves, while the second heart sound is associated with the closure of the semilunar valves.

Electrocardiograph (ECG)

• An electrocardiograph (ECG) is a machine used to obtain an electrocardiogram, a graphical representation of the heart’s electrical activity during a cardiac cycle.
• To obtain a standard ECG, a patient is connected to the machine using three electrical leads (one to each wrist and the left ankle) to continuously monitor heart activity. For a detailed evaluation, multiple leads can be attached to the chest.
• The ECG records electrical events in the heart using letters from P to T to correspond to specific activities:
  • The P-wave represents the electrical excitation (depolarization) of the atria, leading to atrial contraction.
  • The QRS complex represents the depolarization of the ventricles, initiating ventricular contraction (systole).
  • The T-wave represents the repolarization of the ventricles, indicating the return to their normal state and marking the end of systole.
• By counting the number of QRS complexes in a given time period, one can determine an individual’s heart rate.
• ECGs from different individuals have similar shapes for a given lead configuration. Any deviation from this shape can indicate an abnormality or disease, making ECG a clinically significant diagnostic tool.

Double Circulation

• Blood flows through a fixed route in the blood vessels, which include arteries and veins. Each artery and vein has three layers: the inner tunica intima (endothelium), the middle tunica media (smooth muscle and elastic fibers), and the external tunica externa (fibrous connective tissue).
• The right ventricle pumps deoxygenated blood into the pulmonary artery, while the left ventricle pumps oxygenated blood into the aorta.
• The deoxygenated blood in the pulmonary artery is sent to the lungs, where it becomes oxygenated. It is then carried back to the heart by the pulmonary veins, entering the left atrium. This constitutes the pulmonary circulation.
• The oxygenated blood from the aorta is distributed through a network of arteries, arterioles, and capillaries to the body’s tissues. Deoxygenated blood is collected by venules, veins, and the vena cava and returned to the right atrium. This is the systemic circulation, which provides nutrients, oxygen, and other essential substances to the tissues and removes carbon dioxide and other waste products.
• The hepatic portal system is a unique vascular connection between the digestive tract and the liver. It carries blood from the intestine to the liver before it enters the systemic circulation.
• The heart has a specialized coronary system of blood vessels dedicated to the circulation of blood to and from the cardiac musculature.

Regulation of Cardiac Activity

• The normal activities of the heart are intrinsically regulated by specialized muscles, specifically the nodal tissue. This intrinsic regulation makes the heart myogenic.
• The cardiac function can also be influenced by a special neural center located in the medulla oblongata, which operates through the autonomic nervous system (ANS).
• Neural signals through the sympathetic nerves (part of the ANS) can increase the heart rate, strengthen ventricular contractions, and raise the cardiac output.
• In contrast, parasympathetic neural signals (another component of the ANS) can decrease the heart rate and slow down the conduction of action potentials, thus reducing the cardiac output.
• Adrenal medullary hormones can also increase the cardiac output.

Disorders of the Circulatory System

1. High Blood Pressure (Hypertension):
   • Hypertension is characterized by blood pressure levels higher than the normal range, which is typically around 120/80 mm Hg (systolic/diastolic).
   • A blood pressure reading of 140/90 mm Hg or higher on multiple checks indicates hypertension.
   • High blood pressure can lead to various cardiovascular diseases and can also affect vital organs like the brain and kidneys.
2. Coronary Artery Disease (CAD):
   • Coronary Artery Disease, often referred to as atherosclerosis, affects the arteries that supply blood to the heart muscle.
   • It is caused by the buildup of deposits containing calcium, fat, cholesterol, and fibrous tissues, narrowing the lumen of the arteries.
3. Angina:
   • Angina, also known as “angina pectoris,” is a symptom characterized by acute chest pain that occurs when the heart muscle doesn’t receive sufficient oxygen.
   • Angina can affect both men and women of various age groups but is more common among middle-aged and elderly individuals.
   • It arises due to conditions that impact blood flow to the heart.
4. Heart Failure:
   • Heart failure refers to the state in which the heart is unable to effectively pump blood to meet the body’s needs.
   • It is sometimes called “congestive heart failure” because one of the main symptoms is the congestion of the lungs.
   • Heart failure is distinct from cardiac arrest (when the heart stops beating) and a heart attack (when the heart muscle is suddenly damaged due to inadequate blood supply).