Human Circulatory and Immune System Biology

Chordae tendinae are fibrous cords located in the ventricles of the heart, connecting the atrioventricular valves (tricuspid and mitral) to the papillary muscles. They prevent valve inversion during ventricular contraction. Options A, B, and C are incorrect - chordae tendinae are specific to heart ventricles, not joints, atria, or brain.

Immunoglobulins are produced by lymphocytes.

Thrombocytopenic purpura is characterized by excessive bleeding due to insufficient platelets. The term 'thrombocytopenic' literally means low platelet count, which prevents proper blood clotting and leads to spontaneous bruising and bleeding.

Haemoglobin consists of two components: heme (iron-containing porphyrin) and globin (protein). When iron is removed from haemoglobin, the remaining protein portion is called globin. This is distinct from bilirubin (a breakdown product) or haematin (an oxidized, iron-containing form).

Megakaryocytes are large, specialized cells in the bone marrow that produce platelets (thrombocytes) through fragmentation of their cytoplasm. They do not produce erythrocytes (from erythroblasts), granulocytes (from myeloblasts), or agranulocytes (from lymphoblasts).

The heart's natural pacemaker is the sinoatrial (SA) node, located in the wall of the right atrium near the opening of the superior vena cava and close to the eustachian valve (valve of the inferior vena cava). It initiates each heartbeat by sending electrical signals.

Haemocyanin is a copper-based respiratory pigment found primarily in molluscs (such as snails, octopus, and clams) and some arthropods. Unlike haemoglobin (iron-based in vertebrates), haemocyanin is blue when oxygenated and colorless when deoxygenated.

RBCs are primarily destroyed in the spleen and liver by macrophages, while WBCs (particularly lymphocytes) are destroyed in various tissues throughout the body. The spleen is a major site for lymphocyte destruction during immune regulation, though other lymphoid tissues also participate.

Histamine is primarily stored and released by mast cells (found in connective tissue) and basophils (a type of granulocyte). Macrophages and Kupffer cells are phagocytic cells involved in antigen presentation and debris clearance, not histamine secretion.

In mammals, deoxygenated blood from the right atrium (auricle) enters the right ventricle, then is pumped to the lungs via the pulmonary artery (pulmonary aorta). This is part of pulmonary circulation. The systemic aorta carries oxygenated blood from the left ventricle.

Platelets (thrombocytes) are not true cells but small, anucleate cell fragments derived from megakaryocytes. Monocytes, neutrophils, and basophils are all complete, nucleated white blood cells (leukocytes).

Iron in haemoglobin is in the ferrous state (Fe2+), which allows oxygen binding. The Fe3+ (ferric) state found in methemoglobin cannot bind oxygen. The ionic/unionic terminology is not standard; Fe2+ is the correct notation.

Blood group A has A antigens on red blood cells and anti-B antibodies in plasma. The ABO system is based on the presence or absence of A and B antigens on RBC surfaces. Blood type A has only A antigens, type B has only B antigens, type AB has both, and type O has neither.

The sino-auricular (sinuatrial) valve is located between the sinus venosus and the right atrium in non-mammalian vertebrates. It prevents backflow of blood from the atrium into the sinus venosus. In mammals, the sinus venosus is incorporated into the right atrium.

Tricuspid valves are a characteristic feature of the mammalian heart, specifically located between the right atrium and right ventricle. While prototherians (egg-laying mammals) are indeed mammals, they still possess this valve structure as it is fundamental to mammalian circulatory anatomy.

Human erythrocytes have a lifespan of approximately 120 days (about 4 months) before being removed by the spleen and liver. This relatively short lifespan is due to their lack of nucleus and organelles, which limits their ability to repair damage.

Lymph glands primarily filter lymph, produce lymphocytes and antibodies, and help fight infections by trapping pathogens. The destruction of red blood cells occurs mainly in the spleen and liver, making this the correct choice as it is NOT a primary function of lymph nodes.

Unlike most mammals where mature erythrocytes lack nuclei, camelids (camels, llamas, alpacas) retain nucleated red blood cells throughout their lifespan. This unique feature is an adaptation to their high-altitude environments and oxygen transport needs.

Haemoconia refers to small, granular particles occasionally observed in blood plasma, distinct from platelets which are cellular components involved in clotting. Chylomicrons are lipoprotein particles transporting dietary lipids, and chyluria indicates a milky appearance of urine due to lymph presence.

The liver synthesizes major plasma proteins including albumin (maintains oncotic pressure), fibrinogen (essential for clotting), and prothrombin (a clotting factor). This protein synthesis function is exclusive to hepatocytes, distinguishing the liver from other organs listed.

Agranulocytes are white blood cells lacking visible cytoplasmic granules, primarily lymphocytes and monocytes. In contrast, eosinophils, basophils, and neutrophils are granulocytes, each containing distinctive granules that give them their staining properties and functional characteristics.

A picometer is a unit of length equal to 10⁻¹² meters, not a measuring instrument. The other options, barometer (atmospheric pressure), thermometer (temperature), and hygrometer (humidity), are all actual devices used to measure physical properties.

Heparin, produced by mast cells and basophils, acts as a natural anticoagulant by enhancing antithrombin III activity, which inhibits thrombin and factor Xa. This prevents inappropriate clotting in intact blood vessels during normal circulation.