Biology

• Blood is a liquid connective tissue with two basic components:

  • Blood Plasma (55%):
  • Constitutes about 55% by volume of blood in a normal person
  • Contains 90% water and 10% dissolved substances
  • Includes plasma proteins like fibrinogen, immunoglobulins, and albumin
  • Contains mineral salts in the form of ions like chlorides, bicarbonates, sodium, potassium, and calcium
  • Carries metabolites such as amino acids, glucose, vitamins, lipids, and metabolic wastes like urea and uric acid
  • Transports hormones and dissolved gases like carbon dioxide and oxygen
  • Blood Cells and Cell Like Bodies (45%):
  • Includes Red Blood Cells (erythrocytes), White Blood Cells, and Platelets
  • Red Blood Cells are circular flattened, biconcave disc-shaped cells without a nucleus, containing 95% haemoglobin and formed in bone marrow after birth
• Red Blood Cells (RBCs):

  • Number in human male: 5-5.5 per cubic milliliter
  • Number in human female: 4-4.5 million/cubic milliliter
  • Life span: 120 days
  • Function: carry oxygen and transport a small amount of carbon dioxide
  • When worn-out, they are destroyed in spleen and liver
• White Blood Cells (WBCs):

  • Also known as leukocytes
  • Life span: 3-4 days
  • Each WBC is irregular in shape and contains a nucleus
  • Number: 7000 to 8000 in one cubic millimeter
  • Life span: 5-20 days
• Types of White Blood Cells:

  • Granular leukocytes
  • Agranular leukocytes
• Granular Leukocytes (Granulocytes):

  • Nucleus is variable in shape
  • Cytoplasm contains fine granules
  • Types: neutrophils, eosinophils, and basophils (Remembered As BEN)
• Neutrophils:

  • Engulf pathogens during phagocytosis
• Eosinophils:

  • Involved in the control of allergic reactions
• Basophils:

  • Release histamine in injured tissue and in allergic response
• Agranular Leukocytes (Agranulocytes):

  • Types: monocytes and lymphocytes
• Monocytes:

  • Phagocytic and ingest bacteria and dead cells at the damaged tissue region
• Lymphocytes:

  • Two types: B lymphocytes (produce antibodies) and T lymphocytes (destroy any cell that bears antigens)
• Dead white blood cells accumulate and form pus at infection sites
• In dengue fever, there is a sharp decrease in the number of platelets in blood, leading to bleeding from the nose, gums, and under the skin
• Platelets, also known as thrombocytes, are fragments of bone marrow cells called megakaryocytes
• Platelets are colorless, lack a nucleus, and range from 2 to 4 Lac per cubic milliliter with an average lifespan of 8-9 days
• Platelets produce thrombin which aids in blood clotting and their main function is to clot blood when blood vessels are injured
• Composition of Blood with Functions:

  • Plasma: liquid portion of blood
  • Red Blood Cells (Erythrocytes): transport oxygen and a small amount of CO2
  • White Blood Cells (Leukocytes): play a role in the body's defense by engulfing small particles, releasing anticoagulants, producing antibodies, and being involved in blood clotting
  • Platelets (Thrombocytes): fragments of bone marrow cells, involved in blood clotting
• Functions of Blood:

  • Maintenance of Osmotic Pressure: plasma proteins maintain osmotic pressure, mainly by albumin and globulin
  • Transport of Nutrients and Hormones: blood transports nutrients, water, salts, waste products, and hormones
  • Transport Respiratory Gases: blood transports respiratory gases, oxygen, and carbon dioxide
• The human heart is a hollow pumping organ, somewhat conical in shape, about the size of a man's fist
• External structure of the human heart:

  • Consists of 3 layers: epicardium (outer layer), myocardium (middle layer), endocardium (inner layer)
  • The heart is enclosed in a thin tough transparent sac called the pericardium, with lubricating pericardial fluid between the heart and the pericardium to reduce friction
• Each half of the heart is divided into an upper thin-walled atrium and a lower thick-walled ventricle
• The major portion of the heart is called myocardium, consisting largely of cardiac muscle tissues that aid in pumping
• Internal structure of the human heart:

  • Divided by a vertical partition into two halves, the right and left, with the partition called septum
• Chambers of the heart:

  • Consist of four chambers: right and left atria (thin-walled chambers) and right and left ventricles (thick-walled chambers)
• Blood Circulation in Human:

  • Atria receive blood and ventricles distribute it
  • Deoxygenated blood from head, neck, and arms returns to the right atrium via the superior vena cava
  • Deoxygenated blood from lower body parts returns to the right atrium via the inferior vena cava
  • Right atrium receives deoxygenated blood from both vena cava
• Valves of Heart:

  • Tricuspid Valve:
  • When right atrium contracts, blood flows into right ventricle through tricuspid valve
  • When right ventricle contracts, tricuspid valve closes to prevent backflow into atrium
  • Semilunar Valve:
  • Prevents return of blood into ventricle in the pulmonary trunk
  • Bicuspid Valve:
  • When left atrium contracts, blood enters left ventricle through bicuspid valve
• Muscle of Left Ventricle is Thicker than the Muscle of Right Ventricle:

  • When left ventricle contracts, blood leaves by aorta to be distributed to all body parts except lungs
  • Aorta has semilunar valves to prevent backflow into left ventricle
• The cardiac cycle is the alternating contraction and relaxation of the atria and ventricles
• Phases of the Cardiac Cycle:

  • Relaxation Phase (Diastole):
  • Deoxygenated blood enters the right atrium through the vena cava, while oxygenated blood enters the left atrium through pulmonary veins
  • Atria and ventricles are relaxed, heart is relaxed, AV valves are open
  • Atria become distended and have more pressure than ventricles, known as diastole
  • Atria Contract (Atrial Systole):
  • Atria contract when filled and distended with blood
  • Blood passes through tricuspid and bicuspid valves into the relaxed ventricles
  • Ventricles Contract (Ventricular Systole):
  • Ventricles contract simultaneously when receiving blood from the atria
  • Blood is pumped to pulmonary arteries (to lungs) and aorta (to all parts of the body)
  • Tricuspid and bicuspid valves close, producing the 'lubb' sound due to the cluster of valves
• During diastole, the heart chambers are relaxed, while during systole, the atria and ventricles contract
• Cardiovascular disorders are the leading cause of untimely death in man
• Atherosclerosis is the deposition of materials in the arteries
• The deposits of cholesterol in arteries are called plaques which increase in size and begin to block arteries
• Atherosclerosis is the build-up of waxy plaque inside the blood vessels
• Cardiovascular Disorders are the disorders of the heart and blood vessels
• Atherosclerosis

  Derived from two Greek words: 'athere' means gruel and 'skleros' means hard
• Causes and Consequences of Atherosclerosis

  1. Atherosclerosis affects the inner lining of arteries by forming plaque which blocks the blood flow

  2. The plaque is made of fatty substances, waste products of some cells, calcium, and substances that form blood clots

  3. Blockage of blood vessels can cause death

  4. It can begin in late teens and usually takes decades to cause symptoms

  5. The blood clots within the arteries are called thrombus

  6. If a clot breaks and becomes free-floating, it is called an embolus
• Symptoms of Atherosclerosis include chest pain, heart attack, sudden death in coronary arteries; dizziness, weakness, loss of speech, blindness in carotid arteries; cramping, fatigue in the calves when walking in femoral arteries; and high blood pressure in renal arteries
• Arteriosclerosis

  Hardening of the arteries characterized by the loss of elasticity of the walls of arteries
• Causes and Consequences of Arteriosclerosis

  1. Due to calcification and thickening of blood arteries

  2. Results in decreased blood supply to peripheral organs