פרק 26 Chapter 26 The Hypothalamus and Neuroendocrine Disorders Flashcards
Table 26-1
ANTERIOR PITUITARY HORMONES
היפותלמוס
Precocious puberty
This term refers to the abnormally early onset of androgen secretion and spermatogenesis in boys and of cyclic estrogen secretion, and sometimes ovulation, in girls. It is associated with the premature development of secondary sexual characteristics. The occurrence of precocious puberty should prompt both neurologic and endocrine investigations.
* A hamartoma of the hypothalamus is a leading cause of precocious puberty in both boys and girls. These lesions can be associated with Neurofibromatosis type 1 (von Recklinghausen disease) or the polyostotic fibrous dysplasia of McCune-Albright syndrome). The clinical presentation of these lesions can include so-called gelastic seizures.
* In the male, one searches for evidence of a teratoma of the pineal gland or mediastinum or an androgenic tumor of the testes or adrenals.
* In the female with early development of secondary sexual characteristics and menstruation, one seeks other evidence of hypothalamic disease or an estrogen-secreting ovarian tumor.
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A particular combination of gelastic seizures and precocious puberty has been traced to a hamartoma of the hypothalamus. If such lesions are acquired early in life, pubertal changes are prevented from occurring; or, hamartomas
of the hypothalamus, as in von Recklinghausen neurofibromatosis and tuberous sclerosis, may cause sexual precocity.
- Pinealomas: raised ICP, Parinaud, ataxia of limbs, chore, spastic weakness (late) Precocious puberty occurs in those with Germinoma. Sleep NOT affected.
מטופל התקבל בתמונה של אירועים פירכוסיים המלווים בצחוק. איפה המקור המוחי
(GELASTIC SEIZURES) ?
א. היפותלמוס hamartoma
ב.פריאטלי ימני
ג.אורביטו פרונטלי
ד.פרהסנטרלי
המרטומה של ההיפותלמוס
(לציין כי יכול להיות גם פרכוס טמפורלי)
Rarely, laughter may be the most striking feature of a seizure (gelastic epilepsy). A particular combination of gelastic seizures and precocious puberty has been traced to a hamartoma of the hypothalamus.
איזו פגיעה היפותלמית עלולה לגרום לאכילת יתר והשמנה ?
א. Anterior nucleus
ב. Pre-optic nucleus
ג. Suprachiasmic nucleus
ד. Ventro-medial nucleus
Ventro-medial nucleus
כשמדיאה נפגעת היא אוכלת כי היא לא מצליחה לשבוע יותר
Hypothalamic Disorders Associated With Alterations in Weight
* appetite center in the ventrolateral nucleus and a satiety center in the ventromedial nucleus of the hypothalamus.
Lesions in the lateral hypothalamus may result in a failure to eat and, in the neonate, failure to thrive; lesions in the medial hypothalamus may result in overeating and obesity.
- A diencephalic syndrome that occurs in infants describes a progressive and ultimately fatal emaciation (failure to thrive), despite normal or near-normal food intake, in an otherwise alert and cheerful infant. The lesion has usually proves to be a low-grade astrocytoma of the anterior hypothalamus or optic nerve
- Extrahypothalamic parts of the brain, if diseased, may also be associated with increased food-seeking behavior, food ingestion, and weight gain. Examples are involvement of limbic structures, as in the Klver-Bucy syndrome, and basal frontal lobe lesions leading to gluttony.
Abnormalities of Growth
* Some instances of growth retardation relate to a deficiency of either GHRH or GH.
Prader-Willi syndrome (obesity, hypogonadism, hypotonia, mental retardation, and short stature), deficiency in GHRH.
* other congenital and developmental diseases, the hypothalamus appears to be incapable of releasing GH. de Morsier septooptic defect of the brain (median facial cleft, cavum septum pellucidum, optic defect), isolated deficiency of GH.
* some dwarfs (Laron dwarf, Seckel bird-headed dwarf ), there are extremely high levels of circulating GH,
The therapeutic use of GH in such children is a controversial matter.
- In gigantism, most reported cases have been caused by pituitary adenomas that secrete an excess of GH. This must occur prior to closure of the epiphyses. Hypersecretion of GH after closure of the epiphyses results in acromegaly.
Ventromedial nucleus (VMN):
Satiety center stimulated by Leptin
Damage leads to Hyperphagia and Obesity
בת 41 , בבירור הדמייתי ממצא היפותלמי אחורי. איזו מבין תלונותיה הבאות יכולה להיות מוסברת ע”י
ממצא זה?
א. דיכאון.
ב. היפותרמיה.
ג. עליה במשקל.
ד. שלשול כרוני
היפותרמיה
Systemic Effects and Other Disorders of Hypothalamic Disease
Disturbances of Temperature Regulation
* Bilateral lesions in the anterior parts of the hypothalamus, specifically of temperature-sensitive neurons in
the preoptic area, may result in hyperthermia. floor of the third ventricle ,after massive rupture of an anterior communicating artery aneurysm.
A less-dramatic example -postoperative damage in the suprachiasmatic area and suprachiasmatic metastasis associated with other disorders of intrinsic rhythmicity, including sleep and behavior.
Hyperthermia is also part of the malignant hyperthermia syndrome, in which extreme hyperthermia and muscle rigidity occurs in response to inhalation anesthetics and skeletal muscle relaxants.
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Lesions in the posterior part of the hypothalamus have had a different effect; that is, they often produce hypothermia (a persistent temperature of 35°C [95°F] or less) or poikilothermia (equilibration of body and environmental temperatures). The latter may pass unnoticed unless the patient’s temperature is taken after lowering and raising the room temperature. Somnolence, confusion, and hypotension may be associated.
Spontaneous periodic hypothermia, found in association with a cholesteatoma of the third ventricle (and with agenesis of the corpus callosum.
Episodically, there are symptoms of autonomic disturbance—salivation, nausea and vomiting, vasodilatation, sweating, lacrimation, and bradycardia; the rectal temperature may fall to 30°C (86°F), and seizures may occur. Between attacks, which last a few minutes to an hour or two, neurologic abnormalities are usually not discernible and temperature regulation is normal.
Chronic hypothermia is a more familiar state than hyperthermia, being recorded in cases of severe hypothyroidism, hypoglycemia, and uremia; after prolonged immersion or exposure to cold; and in cases of intoxication with barbiturates, phenothiazines, or alcohol. It tends to be more frequent among elderly patients, who are often found to have an inadequate thermoregulatory mechanism.
—- - Gastric Complications of Hypothalamic Dysfunction- In experimental animals, lesions placed in or near the tuberal nuclei induce superficial erosions or ulcerations of the gastric mucosa in the absence of hyperacidity
- Among the cases of acquired changes in personality and sleep patterns from ventral hypothalamic disease
Posterior hypothalamus:
Heating center which senses decreased body temperature and mediates the conservation of heat via sympathetic input.
Damage leads to Poikilothermia (inability to regulate temperature).
functions and lesions of different nucleis of the hypothalamus
- Lateral nucleus: Hunger center inhibited by Leptin. Damage leads to Anorexia and Aphagia. - כשלטיציה נפגעת היא לא מסכימה לאכול.
- Ventromedial nucleus (VMN): Satiety center stimulated by Leptin. Damage leads to Hyperphagia and Obesity. כשמדיאה נפגעת היא אוכלת בלי סוף
- Anterior hypothalamus: Cooling center which senses elevated body temperature and mediates response to dissipate heat via parasympathetic input. Damage leads to Hyperthermia. המזגן יושב מקדימה, אם שוברים אותו אי אפשר להתקרר
- Posterior hypothalamus: Heating center which senses decreased body temperature and mediates the conservation of heat via sympathetic input. Damage leads to Poikilothermia (inability to regulate temperature). התנור נמצא מאחורה, אם שוברים אותו אי אפשר להתחמם.
- Mammillary bodies: Part of papez circuit involved in memory. Damaged in Korsakoff syndrome (thiamine deficiency in chronic alcoholism) leading to both anterograde and retrograde amnesia with confabulations. מאמי זוכרת הכל, אם היא נפגעת פתאום היא לא זוכרת כלום.
-
Arcuate nucleus: Produce releasing hormones and inhibitory factors, which pass through hypophyseal-portal veins to reach anterior pituitary gland.
Dopaminergic projections from arcuate nuclei inhibit prolactin secretion from anterior pituitary.
Damage leads to galactorrhea (milk discharge) and amenorrhea.ארקו היא עובדת במחלבה.. כשהיא נפגעת החלב זורם בלי שליטה. -
Preoptic nucleus: GnRH release which stimulates release of LH and FSH. Damage before puberty leads to arrest of sexual development.
Damage after puberty leads to amenorrhea and impotence. ילד שמשחק כל הזמן בפרה-אופ בסוף יפגע ולא יתבגר מינית.. מבוגר שמשחק בפרה אופ- כנראה יהיה אימפוטנטי ולא יוכל לעשות מין.. -
Paraventricular and Supraoptic nuclei:
Synthesizes neuropeptides ADH and oxytocin which are transported via supraopticohypophyseal tract to Posterior pituitary and stored there.
Damage leads to Diabetes insipidus characterized by polydipsia and polyuria. -
Suprachiasmatic nucleus:
Some of the periodic activities of mammals controlled by the Suprachiasmatic Nucleus are length and time of sleep, hormone levels, activity, body temperature, digestive functions etc.
Damage leads to damage to the periodicity of these activities.
Figure 26-1. Diagram of the hypothalamic–pituitary axis. Indicated on the left is the hypothalamic–neurohypophyseal system, consisting of supraoptic and paraventricular neurons, axons of which terminate on blood vessels in the posterior pituitary (neurohypophysis). The hypothalamic–adenohypophyseal system is illustrated on the right. Tuberoinfundibular neurons, the source of the hypothalamic regulatory hormones, terminate on the capillary plexus in the median eminence. (Courtesy of Dr. J.B. Martin.)
