Which of the following does not cause the release of a hormone from an endocrine organ?
*somatic motor neuron stimulation
*levels of circulating ions
*another hormone
*neural reflex arc

Somatic motor neuron stimulation doesnot cause the release of a hormone from an endocrine organ.

Somatic motor neurons innervate skeletal muscles not endocrine organs. They originate in the central nervous system (CNS) and project their axons to the muscles involved in locomotion (limbs, abdominal). These neurons are called efferent because they transport information from the CNS to the periphery.

Hormone release from an endocrine organ can be caused by:

•Levels of circulating ions-e.g. Ca ions control the release of parathyroid hormones from parathyroid glands

•Another hormone- e.g Thyrotropin-releasing hormone (TRH) from hypothalamus affect the release of Thyroid-stimulating hormone (TSH) from the pituitary gland which then affect the release of thyroid hormones T4, T3 from thyroid gland

•Neural reflex arc-e.g. Parasympathetic neurons increase insulin secretion.

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.