Counted as the hypothalamus of the midbrain. Secretes hormones (vasopressin and oxytocin) that are produced in neurons inside the hypothalamus and then transported inside the axon of these neurons down through the pituitary stalk to the hind lobe where they are secreted into the bloodstream.
The posterior lobe of the pituitary gland lacks a blood-brain barrier and is counted among the circumventricular organs.