(a) (i) Describe the following regarding the knee joint : (I) All movements including locking and unlocking with muscles…

Knee joint. The knee is a modified hinge with a small pivot component. Its movements are flexion, produced by hamstrings, gastrocnemius, sartorius and gracilis; extension, produced by quadriceps femoris, while tensor fasciae latae stabilizes the extended knee through the iliotibial tract but is not a primary extensor; in flexion, medial tibial rotation, by popliteus, semimembranosus and gracilis; lateral tibial rotation, by biceps femoris and sartorius; locking (screw-home mechanism), in terminal extension when the tibia externally rotates on the femur (or the femur internally rotates on a fixed tibia) as the ACL tightens and quadriceps, especially vastus medialis oblique, complete extension; and unlocking, initiated by popliteus, which internally rotates the tibia (or externally rotates the femur) to permit flexion. The cruciate ligaments maintain anteroposterior and rotational stability: the ACL prevents anterior tibial translation, resists hyperextension and controls the pivot, while the PCL prevents posterior tibial translation, limits posterior drawer and stabilizes the knee in flexion.

Carpal tunnel syndrome. Carpal tunnel syndrome is compression of the median nerve within the carpal tunnel, a fibro-osseous canal formed by carpal bones and covered by the flexor retinaculum (transverse carpal ligament), overlying flexor digitorum superficialis and profundus tendons and the flexor pollicis longus. Causes include repetitive strain, trauma or carpal fracture, rheumatoid arthritis, hypothyroidism, pregnancy. Clinical features are nocturnal paresthesia and numbness in the thumb, index, middle and radial half of the ring finger, thenar atrophy with weak opposition, and positive Tinel, Phalen and Durkan signs.

PCR. PCR amplifies a defined DNA segment using sequence-specific primers, dNTPs, buffer and thermostable Taq polymerase, with magnesium ions (Mg2+) supplied as MgCl2 as the essential cofactor. The cycle has three steps: denaturation at 94–98°C separates strands; annealing at 50–65°C allows primers to bind; and extension at about 72°C enables Taq polymerase to synthesize complementary strands. After 25–35 cycles, the target is amplified exponentially. Clinical applications include CBNAAT for tuberculosis in India, RT-PCR for SARS-CoV-2, detection of HIV, hepatitis, dengue and malaria, and genetic testing.

Cholestasis markers. Serum biochemical markers of cholestasis include elevated alkaline phosphatase, GGT and 5'-nucleotidase. ALP is nonspecific, so GGT and 5'-nucleotidase help confirm a hepatobiliary source; 5'-nucleotidase is not exclusive to biliary epithelium but is relatively more specific for hepatobiliary disease than ALP. Conjugated hyperbilirubinaemia and raised serum bile acids are characteristic, while AST and ALT are usually less prominent than in hepatocellular injury.

Cardiac output. Intrinsic regulation of cardiac output (CO = HR × SV) is dominated by the Frank-Starling mechanism: increased venous return raises end-diastolic volume, lengthens cardiac sarcomeres and increases stroke volume. The Anrep effect provides a slow, sustained increase in contractility after an acute rise in afterload, independent of end-diastolic volume. The Bowditch effect and treppe allow heart rate to modify intracellular calcium handling and contractility. Autonomic and hormonal influences, especially sympathetic β1 stimulation and catecholamines, modulate these intrinsic properties, but the heart’s intrinsic length-tension, afterload and rate responses match output to venous return.

Erythropoiesis. Erythropoiesis is regulated mainly by oxygen delivery. Tissue hypoxia stabilizes hypoxia-inducible factor in renal peritubular fibroblasts, inducing erythropoietin, which acts on BFU-E and CFU-E progenitors to drive maturation through proerythroblast, erythroblast and reticulocyte stages. Adequate iron, vitamin B12 and folate are required for haemoglobin synthesis and DNA replication. The feedback loop is completed by the resulting increase in red cell mass and oxygen-carrying capacity, which suppresses further EPO release.

Conclusion. Thus, the knee, carpal tunnel, PCR, cholestasis, cardiac and erythropoietic systems are each defined by precise structural, biochemical and regulatory relationships, showing how movement, nerve compression, nucleic-acid amplification, liver excretion, circulation and red-cell production are integrated at the molecular and organ level.