Blood, Heart | Science & Technology for State PSC Exams - BPSC (Bihar) PDF Download

Blood

Blood is a bright red fluid connective tissue that circulates throughout the body. It comprises a straw-coloured fluid called plasma, which makes up about 60% of total blood volume and contains various cells or corpuscles. Plasma is the non-living, slightly alkaline fluid part of blood, with a pH ranging from 7.2 to 7.4.

The viscosity of blood is nearly five times that of water, and its specific gravity ranges from 1.035 to 1.075. When freshly drawn blood is allowed to stand (after adding an anticoagulant), the erythrocytes (red blood cells) begin to settle. The rate at which these cells settle is known as the erythrocyte sedimentation rate (E.S.R.), measured in mm/hr, with a normal range of 4 to 10 mm/hr.

Blood Glucose

In a healthy individual, blood glucose levels are typically around 80-100 mg per 100 ml of blood 12 hours after eating. This level can increase, but should not exceed 180 mg, shortly after a carbohydrate-rich meal. Consistently high glucose levels above this threshold can lead to diabetes mellitus. If glucose levels persistently exceed 180 mg per 100 ml, it may start to appear in urine, a condition known as glucosuria.

Blood Cholesterol

Cholesterol levels in blood plasma range from about 50-180 mg per 100 ml. Cholesterol is vital for building new cell membranes, producing vitamin D, steroid hormones, and bile salts. It enters blood plasma mainly through:

• Production by the liver and release into the blood.
• Absorption of fats from the intestines.

A high intake of saturated fats, such as ghee and butter, can elevate blood cholesterol levels. Since cholesterol and its esters do not dissolve in water, they can deposit on the walls of arteries and veins, contributing to high blood pressure and various heart disorders.

Composition of Blood

An average adult has about 5-6 litres of blood, constituting 5-8% of their body weight. Blood is composed of corpuscles (blood cells) and plasma.

• Water: 90 to 92%
• Dissolved solids:. to 10%
• Proteins: 7% (e.g., serum albumin, serum globulin, fibrinogen)
• Inorganic constituents: Na ⁺  , Ca ²⁺  , P, Mg ²⁺  , Cl ⁻  , HCO ₃   ⁻ 
• Organic constituents: urea, uric acid, ammonia, amino acids, neutral fats, glucose

Blood Cells

Blood cells play a crucial role in transporting respiratory gases, internal secretions, and maintaining overall bodily functions.

Erythrocytes or RBC

• Shape and Nucleus: In humans, red blood cells (RBCs) are shaped like biconcave discs and do not have a nucleus. In contrast, RBCs in fishes, amphibians, reptiles, and birds are oval and contain a nucleus.
• Average Count: The average number of RBCs is about 5,400,000 per cubic mm in men and around 4,800,000 in women.
• Lifespan: The typical lifespan of an RBC is approximately 110 to 120 days.
• Composition of RBCs:
  • Water: 62%
  • Haemoglobin: 28% (nearly 100 million molecules)
  • Lipids: 7% (fatty acids)
  • Sugars, Salts, Enzymes, and Proteins: 3%
• Function of Haemoglobin: Haemoglobin acts as a respiratory pigment, facilitating the transport of oxygen and carbon dioxide.
• Site of Formation: In embryos, RBCs are produced in the liver and spleen. After birth, RBCs are formed in the bone marrow.
• Process of Formation: The process of RBC formation is called haemopoiesis or erythropoiesis, and the red bone marrow cells involved are known as erythroblasts.
• Haemolysis: This occurs when RBCs are placed in hypotonic solutions, causing them to swell and burst, releasing haemoglobin into the surrounding fluid.
• Anemia: Anemia is characterized by a decrease in the amount of haemoglobin per unit volume of blood, leading to reduced oxygen-carrying capacity.
• Normal Range of Haemoglobin: In adult males, the normal range of haemoglobin is typically 13.5 to 17.5 gm/100 ml. Symptoms of anemia may begin to appear when the level drops below 70%.

Note: The information provided is based on general observations and may vary among individuals.

Leucocytes or WBC

• Size and Nucleus: White blood cells (WBCs) are larger than red blood cells, measuring between 8 to 15 micrometers in diameter. They have a nucleus and are non-pigmented. WBCs are capable of amoeboid movement, allowing them to move through tissues.
• Average Count: The average count of WBCs in the blood is about 10,000 per cubic millimeter.
• Role in Defense: WBCs play a crucial role in defending the body against bacterial infections. They act as phagocytes, engulfing and destroying bacteria through a process called phagocytosis.
• Classification of WBCs: WBCs are classified into three main types based on their size, presence of granules, staining reaction, and the appearance of their nuclei:
• Granulocytes: These WBCs have lobated nuclei and fine granules in their cytoplasm. They are formed in the red bone marrow.
  • Neutrophils: Comprising about 65% of WBCs, neutrophils are phagocytic and play a key role in fighting infections.
  • Eosinophils: Making up about 2.8% of WBCs, eosinophils are non-phagocytic and are involved in combating parasitic infections and allergic reactions.
  • Basophils: Constituting about 0.2% of WBCs, basophils are non-phagocytic and play a role in inflammatory responses.
• Lymphocytes: Lymphocytes have larger nuclei without granules and are formed in lymph nodes. They make up about 26% of WBCs and are involved in immune responses and wound healing.
• Monocytes: Monocytes are the largest WBCs, with deeply indented nuclei. They are formed in the tonsils, spleen, thymus, and intestinal mucosa. Monocytes account for about 6% of WBCs and play a role in phagocytosis and immune responses.

Functions of WBC

The life span of granulocytes is less than 10 days, while lymphocytes live for less than 15 hours. Leukemia is a type of cancer that leads to the excessive production of abnormal white blood cells.

Main Functions of WBC:

• Transport substances.
• Remove dead cells and decaying tissues.
• Fight bacteria.
• Act as guardians of the circulatory system.

Some phagocytic WBC may be destroyed. The fragments of tissue and other materials form pus.

Defensive Actions of WBC:

• Engulfing attacking bacteria or antigens directly.
• Producing antibodies.

Antibodies are special proteins in the plasma that kill or neutralise invading bacteria. Antigens are substances like foreign proteins and microorganisms that trigger the formation of antibodies.

The interaction between antigens and antibodies is the basis for all types of vaccines. For example, introducing a small dose of the pox virus into the blood stimulates the body to produce pox-antibodies for several years. Antibodies are very specific; each type works only against the microorganism that caused its production or closely related organisms. An antibody created from a mumps virus infection will not affect the organisms that cause diphtheria or typhoid.

Thrombocytes or Blood Platelets

Thrombocytes are round or oval bodies, generally non-nucleated, measuring between 2 to 4 µm in diameter. The platelet count is about 250,000 per cubic mm of human blood. They are formed in the red bone marrow and play a crucial role in initiating blood clot formation.

Mechanism of Blood Clotting:

• Blood clotting is a function of the plasma.
• The basic reaction for blood clotting involves converting the soluble plasma protein fibrinogen into the insoluble protein fibrin.
• Fibrinogen is produced in the liver.
• In the presence of calcium and thrombin, fibrinogen clots into fibrin through a series of reactions:

Thromboplastin

• Prothrombin + Ca(ions) → Thrombin (in plasma)
• Thrombin (from platelets) → Fibrinogen → Fibrin monomer + peptides
• Fibrin monomer → Fibrin polymer → Fibrin
• Fibrin polymer → Insoluble fibrin clot stabilising factor

Anticoagulants:

Normally, blood does not clot inside blood vessels, but coagulation begins when blood is drawn outside. Certain substances or processes can prevent blood coagulation, including:

• Heparin. the best and most powerful anticoagulant.
• Antithromboplastin.
• Antithrombotic activity.
• Oxalates and Citrates.
• Defibrination.

Inheritance of Blood Groups

• Blood groups are important for blood transfusions and determining the parentage of children.
• Antigens. and B are the most well-known, but there are also other antigens, M and N, which lead to three blood types: M type, N type, and MN type.
• When these types are mixed during a blood transfusion, there is no clumping, which makes it safe.
• M type blood is very common among American Indians, while N type blood is prevalent in Australian Aborigines.
• It is genetically possible for a man with M type blood to be the father of a child with N type blood under specific circumstances.

Blood Circulation

Closed Circulatory System

In a closed circulatory system, blood is contained within blood vessels as it circulates from the heart. This type of system is found in higher animals, including humans.

Open Circulatory System

In an open circulatory system, such as that found in insects, blood does not remain confined to vessels but flows freely through body cavities and channels known as lacunae and sinuses. The body cavity in this system is called hemocoel, and the blood is referred to as hemolymph. In insects, tissues are in direct contact with the blood.

For instance, in cockroaches, there is a dorsal tubular heart consisting of 13 segments. Blood, or hemolymph, circulates throughout the body due to the contractions of the heart, assisted by fan-shaped alary muscles. Unlike in closed systems, there is no respiratory pigment present in the blood of insects.

Points To Be Remembered

• Wintrobe's hematocrit measures the volume of cells in 100 ml of blood using centrifugation.
• Hemoglobinemia refers to the abnormal destruction of RBCs in the blood, leading to the release of hemoglobin.
• The specific gravity of human RBCs is 1.097, of plasma is 1.02, and of blood is 1.035-1.075 as measured by a pyknometer.
• Plasma proteins create an osmotic pressure ranging from 25 to 30 mm Hg.
• Diapedesis is the term used to describe the movement of WBCs.
• The release of hemoglobin from RBCs or their dissolution is known as hemolysis.
• Both muscle fibers and cardiac muscles contain a protein called myohaemoglobin, which is similar to hemoglobin.
• Haemopoiesis refers to the process of forming blood cells.
• Erythropoiesis specifically denotes the formation of RBCs.
• Leukopoiesis is the term for the formation of WBCs.
• A function of leukocytes is phagocytosis, which involves engulfing and digesting cellular debris and pathogens.
• Thrombocytopenia refers to a decrease in the count of platelets in the blood.
• The normal coagulation time for whole human blood is between 2 to 10 minutes at a temperature of 37°C.
• Leukocytosis indicates an abnormally high count of WBCs in the blood.
• An uncontrolled and rapid increase in the number of WBCs can lead to a condition called leukaemia, which is a type of cancer affecting the bone marrow.

A mammalian heart is made up of four chambers: two auricles and two ventricles. The auricles open into the ventricles, and the openings are protected by the right tricuspid valve and the left bicuspid valve.

Overview of the Heartbeat

The heartbeat is the rhythmic contraction and relaxation of the heart muscles. This process is crucial for pumping blood throughout the body. Let's break down the key components:

• Systole is the phase when the heart muscles contract, and diastole is when they relax. Together, one systole and one diastole make up the cardiac cycle. In a healthy adult at rest, this cycle lasts about eight-tenths of a second.
• On average, a person's heart beats around 72 times per minute, pumping out 60-110 ml of blood with each beat.

Beginning of the Heartbeat

Sinoatrial Node (S-A Node). The heartbeat begins at the sinoatrial node, located in the right auricle of the heart. This area is often called the pacemaker because it initiates the heartbeat. The S-A node sends out an electrical signal that spreads over the two auricles, causing them to contract.

Atrioventricular Node (A-V Node). After the auricles contract, the signal from the S-A node reaches the atrioventricular node, located in the right auricle near the interauricular septum. The A-V node plays a crucial role in coordinating the heartbeat.

Bundle of His and Purkinje Fibre System. From the A-V node, the signal continues through the bundle of His, which splits into two branches and forms the Purkinje fibre system. This system extends over the ventricles and is responsible for conducting the electrical impulse quickly.

Conduction of Heartbeat

• Impulse Transmission: The impulse from the A-V node travels along the bundle of His and the Purkinje fibres, exciting the muscles of the ventricles.
• Ventricular Contraction: This excitation leads to the simultaneous contraction of the ventricles, pumping blood out of the heart.
• Role of Bundle of His and Purkinje System: The bundle of His, its branches, and the Purkinje system act like telephone wires, transmitting the impulse rapidly.
• Conduction Speed: The rate of impulse conduction through the bundle of His is approximately 5 mm/sec, ensuring quick transmission.

Heart Transplant in India

• First Successful Heart Transplant: The first successful heart transplant in India took place on August 3, 1994, led by Dr. P. Venugopal at the All India Institute of Medical Sciences (AIIMS).
• Donor and Recipient Criteria: For a heart donation to be viable, certain criteria must be met, including matching blood groups and weights between the donor and recipient. Additionally, there are age restrictions for donors: male donors should be under 45 years old, and female donors should be under 50 years old.
• Historical Context: The first human heart transplant was performed by Dr. Christian Barnard, a South African surgeon, in 1967.

Blood Vessels

Overview of Blood Vessels

Blood pressure is the force exerted by blood against the walls of blood vessels. Several factors influence blood pressure, including:

• Blood volume
• Blood vessel space
• Force of the heartbeat
• Blood viscosity

There are three main types of blood vessels in the body:

• Arteries: These vessels carry blood away from the heart to various tissues in the body. Blood in arteries flows under high pressure due to the muscle contractions in the artery walls. As arteries branch out, they divide into thinner vessels called arterioles.
• Veins: Veins are responsible for bringing blood back from the tissues to the heart. They collect blood from the capillaries, which are the smallest blood vessels where the exchange of substances occurs.
• Capillaries: Capillaries are the smallest and thinnest blood vessels, forming a delicate network that connects arteries and veins. Their thin walls allow for the exchange of oxygen, nutrients, and waste products between the blood and surrounding tissues.

Lymphatic System

The lymphatic system is evaluated based on its ability to elevate a column of mercury. Blood pressure varies at different locations within the circulatory system. During ventricular contraction, blood pressure in the vessels peaks, known as systolic pressure, typically around 120 mm Hg. When the ventricles relax, the pressure drops to diastolic pressure, averaging about 80 mm Hg in a healthy young male.

Composition and Role of Lymph

• Red blood cells stay within the blood vessels, while plasma and white blood cells (leucocytes) can exit the blood capillaries and enter the tissues.
• This clear fluid, devoid of erythrocytes and large proteins, is referred to as lymph.
• Lymph is responsible for delivering food and oxygen to body cells and returning substances from the tissues back into the bloodstream through lymphatic vessels. Some lymph also enters venous capillaries via osmosis.
• Lymph capillaries merge to form lymph vessels or lymphatics, which have thick walls and feature paired valves.
• These valves, more abundant than those in veins, facilitate the movement of lymph away from the tissues while preventing backflow.
• The high permeability of lymph capillaries allows for the removal of colloids, tissue debris, and foreign bacteria along with the lymph.

Function of Lacteals and Lymph Nodes

• The small lymph capillaries located in the intestinal villi are called lacteals, responsible for absorbing digested fats.
• These absorbed fats give the lymph a milky-white appearance, and this fluid is known as chyle.
• Along the lymph vessels, there are numerous lymph nodes, commonly mistakenly referred to as lymph glands.
• Although mammals do not have distinct lymph hearts, the slowly moving lymph is propelled through the lymph vessels and nodes by muscular activity, pressure in smaller vessels, osmosis, and the absorption of tissue fluids.

Comparison with the Blood Vascular System

• The lymphatic system differs from the blood vascular system as it operates as an open system with lymph spaces located between tissue cells.
• Lymph flows unidirectionally, from the tissues towards the heart.
• Consequently, its capillaries and lymph vessels resemble veins; they do not form a complete circuit like the blood vascular system since lymph moves from tissue cells to the veins of the blood system.