Which of the following is not an endocrine organ?

A. Kidneys: ADH (vasopressin) increases water reabsorption in the kidney’s collecting ducts, reducing urine volume and conserving body water.
B. Pancreas: The pancreas regulates blood sugar via insulin and glucagon; it is not the target of ADH.
C. Hypothalamus: ADH is synthesized in the hypothalamus (supraoptic & paraventricular nuclei), but the hypothalamus is not its main target organ.
D. Anterior pituitary: The anterior pituitary is regulated by hypothalamic releasing hormones, not ADH.
E. Adrenal gland: The adrenal gland produces corticosteroids and catecholamines, but ADH does not act directly on it.

A. initiate blood clotting: Platelets and coagulation factors initiate clotting; erythrocytes do not initiate clot formation.
B. transport nutrients: Plasma carries most nutrients (glucose, amino acids, lipids), not erythrocytes.
C. defend the body against pathogens: White blood cells (leukocytes) are the main defenders; erythrocytes do not have immune functions.
D. transport some carbon dioxide: Erythrocytes carry a portion of CO₂ (dissolved as bicarbonate via carbonic anhydrase inside RBCs and also some carbaminohemoglobin).
E. regulate erythropoiesis: Erythropoiesis is regulated mainly by erythropoietin (from kidneys) and iron/nutritional signals, not by erythrocytes themselves.