Anterior versus posterior pituitary: Rathke's pouch and neuroectoderm
The anterior pituitary grows up from the mouth as Rathke's pouch, while the posterior pituitary grows down from the brain.
Remember
The anterior pituitary makes its own hormones; the posterior pituitary only stores and releases hormones made in the hypothalamus.
Memory aid
the anterior lobe comes up from the mouth and is a true gland; the posterior lobe comes down from the brain and is a hormone store
Use it to pair each lobe with its source and its job.
The pituitary gland has two lobes, a front lobe and a back lobe, with different origins, and their origins explain how they work. The anterior pituitary, the front lobe, starts as Rathke's pouch, an upgrowth of oral ectoderm from the mouth. Ectoderm is the embryonic layer that forms the skin and the lining of the mouth. Because the pouch begins as epithelium rather than nervous tissue, it becomes a true gland that makes and secretes its own hormones into the bloodstream.
The posterior pituitary, the back lobe, has a different origin. It is brain tissue that grows down from the forebrain as the infundibulum, a downgrowth of neuroectoderm (the part of the ectoderm that forms the brain and nervous system), so it is functionally an extension of the hypothalamus and makes no hormones itself. Nerve cells in the hypothalamus make antidiuretic hormone (which regulates water balance) and oxytocin (which acts on the uterus in labour and also acts in milk ejection). These hormones travel down the axons (long nerve fibres) of those cells to the posterior pituitary, which stores and releases them. That is why it is called neuroendocrine: nerve cells acting as an endocrine organ.
If Rathke's pouch fails to form, all the anterior hormones are lost, yet the posterior pituitary can be normal because it develops separately. Part of the pouch can also persist as a cyst-like remnant (part of the pouch left behind) between the two lobes, and when it enlarges and fills with mucoid (mucus-like) material it is a Rathke's cleft cyst.
Key facts
- Anterior pituitary
- grows up from oral ectoderm as Rathke's pouch and is a true gland that makes its own hormones.
- Posterior pituitary
- grows down from the forebrain as the infundibulum and makes no hormones itself.
- Posterior hormones
- antidiuretic hormone and oxytocin are made in the hypothalamus and are stored and released by the posterior pituitary.
- Name trap
- pharyngeal pouches are pockets of endoderm (the inner embryonic layer that lines the gut) in the pharynx, but Rathke's pouch is a pocket of ectoderm.
- Pouch failure
- if Rathke's pouch fails to form, all the anterior hormones are lost, but the posterior pituitary can be normal.
- Rathke's cleft cyst
- a persistent remnant of Rathke's pouch that has enlarged and filled with mucoid (mucus-like) material, lying in the midline between the anterior and posterior lobes.
Exam traps
- The posterior pituitary does not come from oral ectoderm and does not make hormones within the gland, because it grows down from the forebrain and only stores and releases antidiuretic hormone and oxytocin made by nerve cells in the hypothalamus.
- A rich blood supply does not show that the anterior pituitary comes from mesoderm (the middle embryonic layer that forms muscle, bone and connective tissue), because its hormone-making cells come from ectoderm.
- The two lobes of the pituitary do not both come from neuroectoderm, because only the posterior lobe does; the anterior lobe comes from oral ectoderm.
Read the full notes
Tested in 6 SimpleMed+ questions
Practice it in Head and Neck, with the answer and a full explanation after every question.
Practice these questions