The pineal gland is outside the blood-brain barrier, making it unique among parts of the brain. Furthermore, the concentration of blood supply to the pineal gland is second only to that of the kidneys. The blood-brain barrier serves to protect parts of the brain from certain chemicals, including recreational and prescription drugs and alcohol. The barrier bars larger particles and many neurotransmitters in the bloodstream from entering the brain. The pineal gland secretes hormones into the bloodstream, so doesn't need the barrier. However, this also means that the gland can be affected by toxins and other chemicals from which the rest of the brain is protected, influencing the quality and amount of sleep.

sankalpmaya / Getty Images
This site offers information designed for educational purposes only. You should not rely on any information on this site as a substitute for professional medical advice, diagnosis, treatment, or as a substitute for, professional counseling care, advice, diagnosis, or treatment. If you have any concerns or questions about your health, you should always consult with a physician or other healthcare professional.