Information about HH

The Endocrine System

What is a
Hypothalamic
Hamartoma?

An Expert Speaks Out About HH
by Dr Kore Liow, of Kansas University

The Role of the Hypothalamus
An informative tutorial about the vital role of the hypothalamus in maintaining the body's status quo

MRI Scans of
"The Real Deal"
Actual MRI film of HH

Medical Articles
Check out our list of references on HH & Gelastic Seizures, Precocious Puberty and articles on HH and surgery

See a full description of
Seizure Types

Back to
HHUGS Home Page

What is a hormone?

Definition: Any organic chemical that is secreted by a gland into the circulatory system and is transported to some target organ. The target may be either peripheral tissue (such as muscle or other gland) or brain.

To affect behavior, hormone must eventually interact with brain. This interaction may be either direct (ie hormone binds with receptor on neuron) or indirect (hormone causes release of a second - or more - hormone which binds with brain receptors).

There are four classes of hormones:
1)   Protein and polypeptide hormones
2)   Steroids
3)   Monoamines
4)   Lipid-based hormones

Note: generally only 1 class of hormone produced by gland (exception: placenta and adrenal medulla).

General characteristics of hormones
1)   long latency of action - hours to days (epinephrine is one exception)
2)   promote homeostasis - such as maintaining glucose or calcium levels in blood
3)   control metabolic processes - by regulating enzymes
4)   low concentration (high potency) - 10-12M to 10-8M blood concentrations are effective due to high affinity of hormone-receptor interaction
5)   high specificity - due to differential binding of receptors
6)   closely regulated - negative (most hormones) or positive (steroids) feedback

Some features of hormones
1)   receptor proteins bind to hormones with high affinity and specificity
2)   besides a hormone binding site, receptor proteins also have an active site. The active site mediates the observed biological response of the hormone
3)   biological response is directly coupled to the amount of receptor binding (largely steroids), or partial occupancy may result in full biological response (mostly peptide)
4)   decrease in receptor concentration may result in an endocrine deficiency state despite normal or supra-normal concentrations of hormones
5)   an increase in receptor concentration may result in an excess endocrine state despite normal concentration of hormone
6)   hormones may modulate their homologous receptor concentration (eg high levels of insulin down regulate insulin receptor concentrations)
7)   hormones may modulate their heterologous receptors (eg estrogen induces progesterone receptors in uterus)
8)   genetic or acquired disease states related to receptors have been characterized.

Mechanism of hormone action
1)   2nd messengers
        a)  cAMP - most monoamine and peptide hormones
        b)  non cAMP - some peptide hormones
2)   binding with cytosolic receptors and translation of mRNA to produce biological response

Detail of cAMP mechanism

Non cAMP mechanism is not well understood. Sometimes uses cGMP.

Detail of mRNA mechanism

Hormones vs Neurotransmitters

Similarities:
Both H and NT are packaged in vesicles
Both are expelled from cell through process of exocytosis
Both bind with specific receptors
Both depolarize target membrane

Differences:

Hormones
1)   secreted by neurons and endocrine cells
2)   secreted into bloodstream
3)   travel nanometers to meters
4)   long latency of action
5)   no voluntary control

Neurotransmitters
1)   secreted by neurons
2)   secreted into synaptic cleft
3)   travel 20-30 nanometers
4)   action is generally immediate
5)   some voluntary control

Hypothalamus - a group of nuclei located below the thalamus - function of all the nuclei is not known but generally the hypothalamus is said to control eating/drinking, temperature and emotion.

Hypothalamo-hypophysial system

Blood from superior hypophysial arteries which arise from internal carotids flow through a capillary plexus (loop) in median eminence to enter a sinusoidal network in infundibulum.

From the sinusoids, blood passes into a second capillary plex in the anterior pituitary (adenohypophysis). This vascular network is called the hypothalamo-hypophysial portal system.

Hypothalamic hormones are released into capillary network of median eminence and then transported to anterior pituitary where they control anterior pituitary hormone release.

Several hypothalamic hormones have been isolated and they are called releasing or inhibiting hormones because of their interactions with anterior pituitary hormones:
1)   thyrotrophin-releasing hormone (TRH) stimulates the release of thyrotrophin from the anterior pituitary
2)   gonadotrophin-releasing hormone (GnRH) stimulates lutenizing hormone (LH) and follicle stimulating hormone (FSH) release
3)   somatostatin inhibits somatotrophin (growth hormone, abbreviated GH)
4)   dopamine inhibits prolactin

Other neurosecretions exist but have not been isolated and are therefore called hypothalamic releasing factors:
1)   corticotrophin-releasing factor
2)   somatotrophin-releasing factor (SRF also called GHRH)
3)   prolactin-releasing factor

Generally, there is one type of cell for each hormone produced. Classification is based on hw they stain:
1)   acidophils produce GH and prolactin
2)   basophils produce LH, FSH, TSH
3)   chromophobes produce ACTH, MSH

Neurohypophysial system (posterior pituitary)

Consists of supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus and the posterior pituitary.

Axons of SON and PVN project through median eminence and terminate on capillaries of posterior pituitary.

SON produces vasopressin (also referred to as Antidiuretic hormone - ADH - because of its water etention role).

PVN produces oxytocin.

Hypophysis (Pituitary gland)

Referred to as master gland but it is apparent that it is highly regulated by the hypothalamus.

Located in bony cavity called sella turcica.

Anterior pituitary (adenohypophysis) is outgrowth of roof of mouth. Has few if any neural connections. But blood vessels in 2nd plexus are innervated by neurons so anterior pituitary release is under control of CNS.

Posterior pituitary (neurohypophysis) is outgrowth of hypothalamus.

What is a Hypothalamic Hamartoma?

An Expert Speaks Out About HH

The Role of the Hypothalamus

MRI Scans of "The Real Deal"

Medical Articles

Full Description of Seizure Types

Back to HHUGS Home Page