Head kidney
The anterior region of a fish’s kidney, rich in blood-forming and immune cells and endocrine tissue involved in stress responses.
Fish kidney: A vertebrate organ in fish that filters blood, regulates water and ion balance, and supports blood-cell production. The head kidney is the anterior region of this organ, with functions that differ from its posterior region.
Hypothalamic–pituitary–interrenal axis: An endocrine pathway in fishes that coordinates stress responses through hypothalamic, pituitary, and interrenal signals. Its interrenal output includes cortisol produced by tissue in the head kidney.
Fish immunology: The study of immune defenses and immune organs in fishes. The head kidney is a central organ for investigating fish innate and adaptive immunity.
Trunk kidney: The posterior region of a fish kidney, commonly specialized for filtration and excretion. It contrasts with the head kidney’s prominent hematopoietic, immune, and endocrine roles.
Hematopoiesis: The production and development of blood cells from precursor cells. The head kidney is a major hematopoietic site in many fish.
Cortisol: A steroid hormone that regulates metabolism and helps coordinate physiological responses to stress. Head-kidney interrenal tissue releases cortisol during activation of the stress axis.
Fish hematology: The study of blood cells, blood-forming tissues, and blood disorders in fishes. Head-kidney samples reveal blood-cell precursors and support studies of fish blood formation.
Mammalian adrenal gland: An endocrine organ above each mammalian kidney, composed of cortex and medulla. Fish interrenal and chromaffin tissues are associated with the head kidney rather than forming this separate organ.
Leukocyte: A white blood cell that participates in immune defense. Head-kidney tissue contains diverse leukocytes, including lymphocytes and phagocytes.
Catecholamine: A class of signaling molecules that includes adrenaline, noradrenaline, and dopamine. Head-kidney chromaffin cells release catecholamines during acute stress.