Serum is essentially identical to plasma except for the absence of

A. Neutrophils: neutrophils are granulocytes (not agranulocytes) and are the most abundant white blood cells overall, but they are not an agranulocyte.
B. Eosinophils: eosinophils are also granulocytes involved in allergy and parasitic responses, not agranulocytes.
C. Monocytes: monocytes are agranulocytes and differentiate into macrophages in tissues, but they are less abundant than lymphocytes in peripheral blood.
D. Macrophages: macrophages are tissue-resident cells derived from monocytes (not usually counted as circulating agranulocytes) and are not the most abundant agranulocyte in blood.
E. Lymphocytes: lymphocytes are agranulocytes and are the most abundant agranulocyte in peripheral blood (higher % than monocytes).

A. Antagonistic regulation: This refers to hormones with opposing effects (e.g., insulin vs glucagon), not pituitary regulation.
B. Down-regulation: Down-regulation occurs when target cells reduce receptor numbers in response to high hormone levels, not a feedback mechanism to the pituitary.
C. Positive feedback inhibition: Positive feedback is rare (e.g., oxytocin in childbirth) - most pituitary regulation occurs via negative feedback.
D. Up-regulation: Up-regulation increases receptor sensitivity but is not the primary mechanism of pituitary control.
E. Negative feedback inhibition: Most endocrine regulation occurs through negative feedback, where hormones from target organs (like thyroid hormone or cortisol) suppress pituitary hormone release.