Hypothalamic-pituitary-thyroid axis dynamics:

• Statement (I) is correct: Hypothyroidism is by definition the clinical and biochemical state resulting from insufficient production and secretion of thyroid hormones ($T_4$ and $T_3$) by the thyroid gland.
• Statement (II) is incorrect: In primary hypothyroidism (which constitutes $\gt 95\%$ of clinical cases in animals), circulating levels of free $T_4$ and $T_3$ are low, which relieves negative feedback inhibition on the anterior pituitary gland; consequently, the pituitary secretes markedly elevated (above normal) concentrations of Thyroid-Stimulating Hormone (TSH) in an attempt to stimulate the failing thyroid gland.

Pioneering contributions to humoral immunity:

• Emil von Behring won the first Nobel Prize in 1901 for serum therapy against diphtheria.
• Paul Ehrlich was awarded the 1908 Nobel Prize in Physiology or Medicine (shared with Ilya Metchnikov) for his work on immunity, specifically his revolutionary "Side-Chain Theory" (Seitenkettentheorie) of antibody formation, which correctly postulated that cells display pre-existing side-chain receptors that bind toxins and are subsequently shed as free antibodies into circulation.
• Louis Pasteur pioneered anthrax and rabies vaccines in the 19th century.
• Karl Landsteiner won the Nobel Prize in 1930 for the discovery of human ABO blood groups.

Cardiac diagnostic enzyme biomarkers:

• Creatine kinase-MM (CK-MM) is the predominant skeletal muscle isoenzyme ($\gt 98\%$) elevated in myositis, rhabdomyolysis, and physical trauma.
• Creatine kinase-MB (CK-MB) is specifically enriched in cardiac muscle myocardium ($15\text{--}20\%$ of total cardiac CK). Following acute myocardial infarction, necrotic cardiomyocytes rapidly leak CK-MB into circulation within 3–6 hours, making it a classic diagnostic biomarker for early detection.
• Alkaline phosphatase (ALP) is a hepatobiliary and bone isoenzyme biomarker.
• Gamma-glutamyl transferase (GGT) is a liver cholestatic injury biomarker.