It is now understood that hormones, can be produced by single cells as well. Hormones pass through gap junctions of adjacent cells without entering extracellular fluid.
Hormones pass through synaptic clefts between neurons as do neurotransmitters.
Anterior Pituitary Anterior pituitary lies forward from the posterior pituitary and is composed of three parts. In most mammals the thyroid gland is located on the trachea, just caudal to the larynx. Thyroid Hormones Belong to the amine classification of hormones. They are derived from the amino acid tyrosine. Thyroglobulin is a large glycoprotein molecule secreted into the thyroid follicles by the cells lining the follicles.