The pituitary gland is the master endocrine gland.
It lies in the sella turcica at the base of the brain and is connected to the hypothalamus by the pituitary stalk (infundibulum).
It is divided into two functionally distinct parts:
- Anterior pituitary (adenohypophysis)
- Posterior pituitary (neurohypophysis)
Key point:
- The anterior pituitary synthesises hormones.
- The posterior pituitary stores and releases hormones made in the hypothalamus.
Relationship to the Hypothalamus
The hypothalamus controls the pituitary by two different mechanisms.
Anterior pituitary:
- Hypothalamic releasing and inhibiting hormones travel through the hypothalamo-hypophyseal portal circulation.
Posterior pituitary:
- ADH and oxytocin are synthesised in the hypothalamus and transported down axons to the posterior pituitary.
Exam rule:
- Anterior pituitary = portal blood supply.
- Posterior pituitary = direct neural connection.
The Anterior Pituitary
The anterior pituitary synthesises and secretes six major hormones:
- ACTH
- TSH
- FSH
- LH
- Growth hormone (GH)
- Prolactin
These hormones are released in response to hypothalamic signals.
The Posterior Pituitary
The posterior pituitary stores and releases:
- ADH (vasopressin)
- Oxytocin
Neither hormone is synthesised in the posterior pituitary.
Anterior Pituitary Hormones
ACTH:
- ACTH is secreted by corticotrophs.
- It is stimulated by CRH.
- Its main action is to stimulate cortisol secretion from the adrenal cortex.
TSH:
- TSH is secreted by thyrotrophs.
- It is stimulated by TRH and inhibited by somatostatin.
- It stimulates synthesis and release of T3 and T4.
FSH and LH:
- FSH and LH are secreted by gonadotrophs.
- They are stimulated by GnRH.
- They regulate gonadal hormone production and gametogenesis.
Growth hormone (GH):
- GH is secreted by somatotrophs.
- It is stimulated by GHRH and inhibited by somatostatin.
- It promotes growth and stimulates IGF-1 production by the liver.
Prolactin:
- Prolactin is secreted by lactotrophs.
- Its main role is milk production.
- Dopamine tonically inhibits prolactin secretion.
Exam rule: Prolactin is under tonic inhibition by dopamine.
Summary Table
|
Pituitary Hormone
|
Hypothalamic Control |
Main Target |
| ACTH |
CRH |
Adrenal cortex |
| TSH |
TRH |
Thyroid gland |
| FSH |
GnRH |
Gonads |
| LH |
GnRH |
Gonads |
| GH |
GHRH (+), somatostatin (−) |
Liver and tissues |
| Prolactin |
Dopamine (−) |
Breast |
Posterior Pituitary Hormones
|
Hormone
|
Site of Synthesis |
Main Action |
| ADH |
Hypothalamus |
Water reabsorption in kidney |
| Oxytocin |
Hypothalamus |
Uterine contraction and milk ejection |
Feedback Regulation
Most pituitary hormones are regulated by negative feedback.
Examples:
- Cortisol inhibits CRH and ACTH.
- Thyroid hormones inhibit TRH and TSH.
- Sex steroids inhibit GnRH, LH, and FSH.
- IGF-1 inhibits GH release.
Clinical Relevance
Pituitary adenomas:
- May cause excess secretion of prolactin, GH and ACTH
Pituitary failure:
- Can lead to deficiency of multiple pituitary hormones.
Diabetes insipidus:
- May result from deficient ADH secretion.
Key Exam Tips
Questions on the pituitary gland commonly test which hormones are secreted from each lobe and how they are regulated.
In every question, focus on:
- Anterior pituitary synthesising six major hormones
- Posterior pituitary storing ADH and oxytocin
- Dopamine inhibiting prolactin
- GH being controlled by GHRH and somatostatin
- Negative feedback from target gland hormones
Common traps to avoid:
- Thinking ADH and oxytocin are synthesised in the posterior pituitary
- Forgetting that prolactin is mainly under inhibitory control
- Confusing pituitary hormones with hypothalamic hormones
- Forgetting that the anterior pituitary is connected by portal circulation