The

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secrete(s)

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which promotes Na" and water retention

A. It is a cause of anemia: Sickle cells are fragile and hemolyze prematurely, producing a chronic hemolytic anemia.
B. It is cause of malaria: Malaria is caused by Plasmodium parasites; sickle-cell disease does not cause malaria (in fact, sickle-cell trait provides some protection against severe malaria).
C. It is due to a hereditary hemoglobin defect: Sickle-cell disease is inherited and results from a mutation in the β-globin (HBB) gene producing hemoglobin S.
D. It is advantageous in that it can protect carriers against malaria: Heterozygous carriers (sickle-cell trait) have relative resistance to severe forms of Plasmodium falciparum malaria.
E. It is caused by excessive allele that modifies the structure of hemoglobin: The disease is caused by a point mutation (a single nucleotide change) in the β-globin allele that alters hemoglobin structure (Glu→Val at position 6). Saying “excessive allele” is misleading -the cause is a specific mutant allele, not an “excessive” one.

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.