- Certain areas of the brain have a reduced blood-brain barrier and retain a direct connection with the systemic circulation in order to
- Detect alterations in composition of the blood
- Allow secretion of hormones
- Areas that are outside the BBB are known as ‘circumventricular organs’:
Hypothalamus
- Hypothalamic osmoreceptors monitor the osmolarity of systemic blood
Area postrema
- Contains a chemoreceptor trigger zone
- In the presence of noxious substances, sends afferent signals to the vomiting centre triggering vomiting
Anterior & posterior pituitary gland
- Secretes eight pituitary hormones directly into the systemic circulation
Choroid plexus
- Uses plasma from systemic blood to produce CSF
Pineal gland
- Secretes melatonin directly into the systemic circulation.
Subfornical organ
- Contains a chemoreceptor area
- Monitors blood angiotension II leveI as part of the regulation of body fluids