The Hypothalamus

By: Alicia Brosnan

and Alessandra

Coronel

Physical Description of the

•  • The hypothalamus is classified

as part of the diencephalon of the brain.– It is located anteriorly to the

pituitary gland, mainly because the two work hand in hand.

– It is divided into 4 sections:• Preoptic• Anterior• Tuberal• Mammilary

Hypothalamus Structure and Function

• There are 3 different layers of the hypothalamus, each having its own specific function:– The first layer provides a direct link to many systems

within the PNS, including olfactory, pituitary, and autonomic centers.

– The second, has neurons which send and receive projections from the limbic systems from multiple areas.

– The third and final layer is the most lateral layer, made up of pre-optic nuclei.

•  

Chemical Description• The hypothalamus’ main function is to control the secretions

of the pituitary gland.• The levels of the hormones in the blood and sensory

information that enters the CNS controls the activities of the hypothalamus.

• Neurosecretory cells allow the hypothalamus to control the posterior pituitary gland and it automatically sets the rest of the hypothalamus’ activities within the body.

• The hypothalamus produces small amounts of releasing hormones which are secreted directly into the capillaries and veins where the hormones enter the anterior pituitary, where they affect the production of anterior pituitary hormones.

• e.g. “nerve signals from the brain pass sensory information to the hypothalamus about the seasonal changes and the availability of a mate. The hypothalamus in turn, regulates the release of reproductive hormones required for breeding.”

Job Description• The hypothalamus is responsible for

– thirst, hunger, and temperature control.– Controlling the pituitary gland. This is important

because the pituitary gland has control over important glands such as the adrenal gland, the thyroid, testis, and ovaries.

– Limbic (emotional) control

The hypothalamus is friendly!

• The hypothalamus interacts with many of the organs in the body, as it sends hormones to them. It uses blood as its pathway to send these hormones, and will receive stimuli back from organs as well. It monitors everything going on with these organs and makes sure no organ strays from homeostasis. If one should, the hypothalamus will send hormones to it through the blood so that it will stimulate a response and correct the problem.

WHAT ORGANS DOES IT AFFECT?

• A rise in plasma osmolality (the amount of substance in plasma) is detected by the hypothalamus, which then sends signals to the posterior pituitary gland which in turn secretes anti-diuretic hormone (ADH), resulting in water re-absorption by the kidney and an increase in urine concentration.

THE KIDNEYS

THE GONADS• The hypothalamus sends

hormones to the anterior pituitary gland which then releases either FSH or LH to the gonads in order to make either sex hormones or gametes.

e.g. when FSH is at high levels the uterine lining becomes thick and ready for a possible fertilized egg, but when they FSH levels reach a certain level and there is no fertilized egg LH comes into play with a negative feedback reaction and FSH decreases causing the uterine lining to disintegrate causing the menstrual cycle

THE SKIN• High heat stimulates our hypothalamus’ body

temperature “thermometer”, and the hypothalamus thus makes us secrete sweat, in turn cooling us off and opening the hair follicles making arm hair flat against the skin.

• Cold temperatures stimulates our hypothalamus’ “thermometer”, and in order to maintain a balanced body temperature we shiver in order for our bodies to produce heat and closing hair follicles making arm hair stand up.

Fröhlich’s syndrome

• Aka: Adiposogenital Dystrophy, 

• Rare childhood metabolic disorder that is usually associated with tumors (mass or growth..NOT CANCER) of the hypothalamus, causing increased appetite and depressed secretion of gonadotropin.

• Mostly seen in boys

• Is sometimes also seen as a pituitary problem because of the hypothalamus’ close contact with the pituitary gland.

• Fröhlich’s syndrome is treated by removing the tumor and restricting diet until normal weight is achieved.

 

Fröhlich’s Syndrome (con’t…)Symptoms of Froehlich syndrome

• Headache • Growth retardation • Retarded sexual development • Mental retardation • Vision problems • Excessive urination • Excessive thirst • Large hips • Fatty breast growth before puberty • Fatty stomach deposits before puberty • Fatty thigh deposits before puberty • Delayed secondary sexual characteristics • Delicate skin • Hypopituitarism • Delayed skeletal ossification

You can die laughing!• Pathological laughter is a disease of the hypothalamus

that manifests itself through a tumor on the hypothalamus, aneurysm nearby, or hemorrhage in the third ventricle. The disease is characterized by uncontrollable laughter, especially in inappropriate situations, followed by death, caused by the burst of the aneurysm.

Glastic EpilepsyWhat is it?• Gelastic Epilepsy a rare type of epilepsy that involves gelastic siezures or

sudden laughing seizures• This laughter usually sounds “hollow” and “unpleasent”

Causes• The cause is a benign growth (tumor) of abnormally formed tissue called a

hamartoma in the hypothalamus (Hypothalamic Hamartoma)• Usually present at birth, but does not cause problems until early childhood

Symptoms:• abnormally early puberty • partial seizures with laughing as a frequent feature • increased irritability and aggression between the seizures.

Gelastic EpilepsyHow can it be found?• MRI is necessary to identify the hamartoma. CT scans

are usually normal.

How is it treated?

• If the hamartoma is big enough that it extends beyond the hypothalamus to the lower part of the brain than surgery is definitely an option. Seizure and hormonal medicines help as well.

Websites Used:• http://www.toxpath.org/membersonly/forum/WYD/002.jpg• http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0004-282X2002000600021• http://courses.cvcc.vccs.edu/WisemanD/functions_of_the_hypothalamus.htm• http://www.cliffsnotes.com/study_guide/The-Hypothalamus-and-Pituitary-Glands.topicArticleId-22032,articleId-

21959.html• http://brainmind.com/LimbicOverview.html•  http://www.britannica.com/EBchecked/topic/220674/Frohlichs-syndrome• http://www.riversideonline.com/source/images/slideshow/bn22_innerbrain.jpg• http://www.britannica.com/EBchecked/topic/220674/Frohlichs-syndrome• http://www.wrongdiagnosis.com/f/froehlich_syndrome/symptoms.htm#symptom_list• http://www.epilepsy.com/epilepsy/epilepsy_hypothalamichamartoma

http://biology.clc.uc.edu/courses/bio105/endocrin.htm • http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/hypopit/overview.html • http://www.montgomerycollege.edu/~wolexik/Labeled%20Photomicrographs/205/Endocrine/Pituitary%20w

%20Hypothalamus-Dissecting-All%20Labels-11173449%20copy.jpg• http://www.epilepsy.org.uk/info/syndromes/gelastic-epilepsy

Books Used:• Pediatric Endocrinology: Mechanisms, Manifestations, and Management. Pescovitz, Ora. 2004.• Williams Textbook of Endocrinology. Low, Malcolm J. 2008. • Biology. Miller, Kenneth R & Levine, Joseph. 1993• AP Edition Biology. Campbell, Neil A., et al. 8th Edition. 2009