Hypothalamus-Pituitary Axis

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Disorders of pituitary function
Melanocyte-stimulating hormones (MSH)
The nuclei of the hypothalamus

The hypothalamus is a division of the diencephalon that is principally involved in homeostasis.

Anatomically it is located in close proximity to the hypothalamus with which it is closely related. The hypothalamus secretes a number of releasing hormones which trigger the release of hormones from the anterior pituitary. The hormones of the posterior pituitary (ADH and oxytocin) are actually synthesised in the hypothalamus then transported to the posterior pituitary and stored pending release.

Pituitary gland and relation to hypothalamus and optic chiasm. click on image to enlarge

Hypothalamus-Pituitary axis. *note the posterior pituitary hormones are synthesised in the hypothalamus itself so do not require releasing hormone stimulation. Click on image to enlarge

Disorders of pituitary function

Pituitary disorders may be broadly categorised into deficiency disorders related to underproduction of pituitary hormones or excess production of pituitary hormones. Pituitary tumours may cause over or underproduction of pituitary hormones. Head injuries, autoimmune conditions, vascular disease and infection are other causes of pituitary dysfunction.

Hormone	Deficiency	Excess
ADH	Central (cranial) diabetes insipidus	SIADH
Oxytocin	Depression symptoms	Emotional lability
FSH and LH	Hypogonadism Infertility Failure of secondary sexual characteristic development Low testosterone causing low muscle mass and bone density	Infertility Ovarian hyperstimulation Oligomenorrhea Cystic ovaries
TSH	Secondary hypothyroidism	Secondary hyperthyroidism
Prolactin	Insufficient lactation Subfertility Delayed puberty Menstrual disorders	Anovulatory infertility, Amenorrhea or oligomenorrhea Galactorrhea (lactation not associated with pregnancy)
Growth hormone	Pituitary dwarfism in children Decreased muscle mass Decreased bone density Increased central adipose tissue Increased LDL to HDL cholesterol ratio Tiredness and depression	Acromegaly in adults or gigantism in children
Cortisol	Adrenal insufficiency	Cushing syndrome

Dopamine
Dopamine is a hormone released by several areas of the brain, most notably the substantia nigra, ventral tegmental area and the hypothalamus.

Dopamine has many roles including pain modulation, neuronal functioning, arousal and sexual gratification. It is also an inhibitor of prolactin.

Melanocyte-stimulating hormones (MSH)

MSH is produced by the anterior pituitary. MSH and ACTH share the same precursor molecule (proopiomelanocortin or POMC) which is cleaved into ACTH and MSH. Conditions where ACTH is raised, such as pregnancy, Cushing disease and primary adrenal insufficiency, typically feature hyperpigmentation as a result of ACTH binding to melanocytes and raised MSH.

The nuclei of the hypothalamus

The hypothalamus is made up of groups of nuclei. There are 3 main nuclei areas:

Anterior (Supraoptic) nuclei
Middle (Tuberal) Nuclei
Posterior (Mammillary) Nuclei

These nuclei may be further subdivided on their anatomical position including their anatomical relationship to the optic nerve. The layout of the nuclei and an overview of their function is shown below to help understanding. A detailed knowledge is not required for the exam.

Nuclei of the hypothalamus. Click on image to enlarge

The table below shows the major nuclei of the hypothalamus:

Region	Area	Nucleus	Functions
Anterior (supraoptic)	Preoptic	Preoptic nucleus	Thermoregulation
Anterior (supraoptic)	Medial	Medial preoptic nucleus	Regulates the release of gonadotropic hormones from the adenohypophysis Contains the sexually dimorphic nucleus, which releases GnRH, differential development between sexes is based upon in utero testosterone levels Thermoregulation
Anterior (supraoptic)	Medial	Supraoptic nucleus	Vasopressin release Oxytocin release
Anterior (supraoptic)	Medial	Paraventricular nucleus	thyrotropin-releasing hormone release corticotropin-releasing hormone release oxytocin release vasopressin release somatostatin round
Anterior (supraoptic)	Medial	Anterior hypothalamic nucleus	thermoregulation panting sweating thyrotropin inhibition
Anterior (supraoptic)	Medial	Suprachiasmatic nucleus	Circadian rhythms
Anterior (supraoptic	Lateral	Lateral nucleus	Lateral hypothalamus functions: feeding behaviour sleep arousal thermoregulation regulating gastrointestinal motility reducing pain and nociception regulating energy homeostasis and neuroendocrine functions regulating visceral functions (e.g., respiration, blood pressure, and urination)
Middle (tuberal)	Medial	Dorsomedial hypothalamic nucleus	blood pressure heart rate GI stimulation
Middle (tuberal)	Medial	Ventromedial nucleus	satiety neuroendocrine control
Middle (tuberal)	Medial	Arcuate nucleus	Growth hormone-releasing hormone (GHRH) feeding Dopamine-mediated prolactin inhibition
Middle (tuberal)	Lateral	Lateral nucleus	Lateral hypothalamus functions: feeding behaviour sleep arousal thermoregulation regulating gastrointestinal motility reducing pain and nociception regulating energy homeostasis and neuroendocrine functions regulating visceral functions (e.g., respiration, blood pressure, and urination)
Middle (tuberal)	Lateral	Lateral tuberal nuclei
Posterior (mammillary)	medial	Mammillary nuclei (part of mammillary bodies)	memory
Posterior (mammillary)	medial	Posterior nucleus	Increase blood pressure pupillary dilation shivering ADH release
Posterior (mammillary)	lateral	Lateral nucleus	Lateral hypothalamus functions: feeding behaviour sleep arousal thermoregulation regulating gastrointestinal motility reducing pain and nociception regulating energy homeostasis and neuroendocrine functions regulating visceral functions (e.g., respiration, blood pressure, and urination)
Posterior (mammillary)	lateral	Tuberomammillary nucleus	arousal (wakefulness and attention) feeding and energy balance learning memory sleep