GK (Biology)

The atrioventricular (AV) node is located at the base of the interatrial (inter-auricular) septum, between the right atrium's lower part and the fibrous ring. It's not near the bicuspid valve (A), between atria generally (B), or in the interventricular septum (D).

Normal blood pH is 7.35-7.45. A drop from 7.4 to 7.0 indicates increased acidity (acidosis). Alkalemia (B) refers to alkaline pH. Leukemia (C) is blood cancer, and anemia (D) is low hemoglobin - neither relates to pH changes.

Heart rate increases through multiple mechanisms: increased sympathetic nervous activity (A), decreased parasympathetic activity (B), and elevated circulating adrenaline (C). Since all three mechanisms increase heart rate, option D is correct.

Blood pressure slightly below 120/80 mmHg generally indicates good cardiovascular health and physical fitness. Hypertension (B) is BP above 140/90. Options C and D are incorrect - slightly lower BP is not a respiratory problem or disease.

Leucopenia is a condition characterized by decreased white blood cell (WBC) count/production. It's not uncontrolled WBC (A), uncontrolled RBC (B), or excess platelets (C). The term literally means 'white blood cell deficiency'.

Blood platelets (thrombocytes) have a lifespan of approximately 5-7 days in mammals. Option B at 5 days is the closest. Platelets are much shorter-lived than RBCs (120 days) and don't last 10-20 days.

Vitamin K is essential for the synthesis of prothrombin (factor II) and other clotting factors in the liver. It doesn't convert prothrombin to thrombin (A - thrombin does that), convert fibrinogen to fibrin (B - thrombin does that), or form thromboplastin (C - this comes from damaged tissues/platelets).

Fish have a closed circulatory system where blood flows through vessels throughout the body. Cockroaches, scorpions, and Limulus (horseshoe crabs) are arthropods with open circulatory systems where hemolymph bathes tissues directly in sinuses.

The pulmonary vein uniquely carries oxygenated blood from the lungs to the left atrium. All other options carry deoxygenated blood: renal vein (A) from kidneys, hepatic portal vein (B) from GI tract to liver, and pulmonary artery (C) from heart to lungs.

Agglutinogens (A and B antigens) are glycoproteins on the surface of red blood cells (RBCs). They determine blood type. Serum (A) contains antibodies, plasma (C) is serum plus clotting factors, and hemoglobin (D) is inside RBCs - none carry agglutinogens.

A thrombus is a blood clot that forms in a blood vessel and remains attached to its place of origin. It can block blood flow by physically obstructing the vessel lumen. A bolus refers to a rounded mass of food or liquid, pus is an accumulation of dead cells and bacteria from infection, and an ulcer is an open sore on tissue surface.

Heart murmurs are abnormal heart sounds produced when blood flows turbulently through the heart, often due to leaking or narrowing of heart valves. Normal valve closure produces the characteristic 'lub-dub' sounds (S1 and S2). Murmurs indicate turbulent flow caused by valve incompetence, stenosis, or other structural abnormalities.

Heart attacks (myocardial infarction) occur when coronary arteries supplying the heart muscle are blocked, typically by atherosclerotic plaque or thrombus. The carotid artery supplies the brain, the aorta is the main artery from the heart, and pulmonary veins carry oxygenated blood from lungs to the left atrium.

Chronic inflammatory reactions involve persistent immune activation where antigen-antibody complexes can become trapped in tissues, leading to suppression of further immune reactions. Liver dysfunction primarily affects metabolism and detoxification, ACTH stimulates cortisol production, and vitamin K is essential for blood clotting.

Lymphatic vessels collect interstitial fluid (fluid that leaks out of blood capillaries into tissue spaces) and return it to the bloodstream via the thoracic duct and right lymphatic duct. Lymph does not transport CO2 or O2 - those functions are performed by blood. Lymph nodes contain lymphocytes, not RBCs.

Cardiac output is the volume of blood pumped by one ventricle (usually the left ventricle) per minute, calculated as stroke volume × heart rate. It represents the heart's pumping effectiveness. Option A is wrong because blood passes through, it's not 'received' by the heart. Cardiac output is measured per minute, not per second or hour.

The three-chambered frog heart has one ventricle where oxygenated blood from the lungs and deoxygenated blood from the body partially mix, reducing oxygen delivery efficiency. The mixing occurs because there's no complete septum separating the ventricle. This is the key disadvantage compared to the four-chambered human heart which keeps oxygenated and deoxygenated blood completely separate.

Lymph is derived from interstitial fluid and contains water, ions, nutrients, WBCs (especially lymphocytes), but lacks RBCs and large plasma proteins like albumin which cannot easily leave capillaries. It's essentially blood plasma without RBCs and some proteins. Lymph is not a secretion of RBCs, nor does it contain RBCs.

Blood pressure is the force exerted by circulating blood against the walls of blood vessels, primarily arteries. It's measured in mmHg and expressed as systolic/diastolic pressures. Option B is wrong (not just legs), C is wrong (not from atrium), D is wrong (ventricles generate pressure, but blood pressure is defined against vessel walls throughout circulation).

Mammals have a double circulatory system: pulmonary circulation (heart to lungs and back) carries deoxygenated blood, while systemic circulation (heart to body tissues and back) carries oxygenated blood. The two circuits are separate and don't mix. Option A is incomplete, C is wrong (circuits connect at the heart chambers).

The three types of blood corpuscles (formed elements) are erythrocytes (RBCs), leucocytes (WBCs), and thrombocytes (blood platelets). Hemoglobin is a protein within RBCs, not a separate cell type. Plasma is the liquid portion containing water, proteins, etc., not a corpuscle. This is fundamental blood cell classification.

Antibodies are glycoprotein molecules (immunoglobulins) produced by plasma cells (differentiated B lymphocytes) that bind specifically to antigens and neutralize them. They are not a blood component in themselves, not a WBC type (though they're produced by WBC derivatives), and not secreted by RBCs. Antibodies circulate in blood and lymph as part of humoral immunity.

The spleen serves as a haemopoietic (blood-forming) organ, particularly during fetal development and in some adult mammals where it produces red and white blood cells. While its major functions include filtering blood and supporting immune responses, blood cell formation remains one of its important biological roles.

The mitral (bicuspid) valve is located between the left atrium (auricle) and left ventricle of the heart. It prevents backflow of blood from the left ventricle to the left atrium when the ventricle contracts, ensuring one-way flow toward the aorta.

Sodium citrate is the most commonly used anticoagulant in blood banks because it binds calcium ions, which are essential for the coagulation cascade. It effectively prevents clotting while being safe for transfusion. EDTA is used primarily in diagnostic blood samples, not for storage.