Hypothalamus

Question 1

how does th epituitary and hypothalaamus comunicate?

Answer 1

Both structures use conventional synaptic transmission and soluble humoral factors to exchange afferent and efferent information.

Unlike any other brain structure the hypothalamus both sends and receives information by way of the bloodstream

Question 2

What do these two organs (hypothalamus and pituitary) do?

Answer 2

Serving as a crucial link between the neural and
endocrine systems, pituitary and hypothalamus play a
pivotal role in regulating various physiological
processes.

• The hypothalamus holds a central position as the
  primary regulator of homeostasis, and it’s referred to
  as the “homeostatic head ganglion.”

Question 3

WHta does the hypothalamus maintain and how?

Answer 3

The hypothalamus actively maintains the body’s internal balance by interacting with and exerting
regulatory influences over key systems, participating in:

1.Homeostatic mechanisms
2.Endocrine control, via the pituitary
3.Autonomic control
4.Limbic mechanisms

Question 4

How does the HT maintain homesotasis?

Answer 4

 Regulating thirst and water balance,
 Controlling Adenohypophysis (anterior pituitary) and (posterior pituitary) Neurohypophysis release
of hormones produced in the hypothalamus
 Regulating Hunger
 Sleep–wake cycle
 Autonomic nervous system
 Temperature
 Sexual urges

Question 5

WHat hormones does HT produce and release?

Answer 5

A) The ones released from the hypothalamus into the blood and travel to the anterior pituitary:
1. thyrotropin-releasing hormone (TRH)
2. gonadotropin-releasing hormone (GnRH),
3. growth hormone-releasing hormone (GHRH),
4. corticotropin-releasing hormone (CRH),
5. somatostatin (inhibits hormone release)
6. dopamine (inhibits prolactin, also called prolactin inhibitory factor, PIF)

B) The ones are released from the hypothalamus nerve terminals and travel to the posterior pituitary:
1. oxytocin – Released mostly from the paraventricular nucleus of the Ht
2. vasopressin (also known as antidiuretic hormone or ADH)- released mostly from the supraoptic nucleus of the Ht

Question 6

which part of the pituitary is an extension of the hypothalamus?

Answer 6

th eposterior lobe

Question 7

where is the location of the pituitary?

Answer 7

The pituitary gland is located inferior to the hypothalamus and is connected directly to the hypothalamus by a stalk. This Pituitary stalk has blood vessels and nerve fibers

Question 8

how is hormonal secretion by anterior pituitary controllbed by?

Answer 8

by hypothalamic-releasing hormones that reach their target endocrine cells in the anterior pituitary via the pituitary stalk

Question 9

describe the hypothalamus anatomically

Answer 9

*Part of diencephalon
*Named for its location under the thalamus
*Separated from thalamus by the hypothalamic sulcus (groove on 3rd ventricle)
*Forms walls and floor of inferior portion of 3rd ventricle

Question 10

The Hypothalamus is seen posterior to optic chiasm forming:

Answer 10

*tuber cinereum “gray protuberance”

*mammillary bodies-paired structures forming posterior portion of Ht

*infundibulum- “funnel,” arises from tuber cinereum and continues inferiorly as the pituitary stalk

*median eminence- anterior part of infundibulum, receives Ht input

Question 11

What is the location of the pituitary?

Answer 11

Lies within the pituitary (hypophysial) fossa, which sits in a depression of the sphenoid bone called the sella turcica “the turkish chair” which surrounds inferior, anterior and posterior aspects of the gland.
*
Around the gland: The optic chiasma lies anteriorly, and the mammillary bodies lie posteriorly. Superior to the pituitary gland is the diaphragma sellae, inferior lies the sphenoidal air sinuses, and lateral is the cavernous sinuses.

Question 12

What covers th epituitary?

Answer 12

A fold of dura matter covers the pituitary and has an opening to allow for the infundibulum to pass through, allowing a connection to the hypothalamus

Question 13

What is the clinical relation of the pituitary lying behind and inferior to optic chiasm?

Answer 13

tumors in this region can compress the optic chiasm, causing visual problems, including bitemporal hemianopia [ocular defect that leading to impaired peripheral vision in the outer temporal halves of the visual field of each eye].

bound by clinoid (bony) processes, the pituitary fossa can be accessed through the sphenoid sinus with instruments inserted through the nose by a transsphenoidal surgical approach to remove tumors in the pituitary.

Question 14

pituitary embryological origin

Answer 14

The anterior pituitary, or adenohypophysis, is formed by a thickened area of ectodermal cells on the roof of the developing pharynx that invaginate, forming Rathke’s pouch. It is important to know that this pouch is of oral ectodermal origin, not neural ectoderm.
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The anterior pituitary contains glandular cells that secrete a variety of hormones into the circulation. Release of hormones from the anterior pituitary is controlled by the hypothalamus through factors carried in a specialized vascular portal system (see Figure 17.5).
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The posterior pituitary, or neurohypophysis, forms from an evagination of the floor of the developing ventricular system and is of neural ectodermal origin.
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IMPORTANT: The posterior pituitary does not contain glandular cells. Instead, it contains axons and terminals of neurons whose cell bodies are located in the hypothalamus.
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The posterior wall of Rathke’s pouch forms a small region called the intermediate part of the anterior lobe (also called the intermediate lobe) of the pituitary (see Figure 17.1D), which has less prominent endocrine functions in humans.

Question 15

describe histological feature of adenohypophysis

Answer 15

The anterior pituitary is composed of 3 different regions:
Anterior Pituitary = Adenohypophysis = Pars distalis (PD) + Pars tuberalis (PT) + Pars intermedia (PI)
*
The adenohypophysis, contains many hormone-producing (7 hormones) and secreting epithelial cells. It contains acidophils, basophils, and chromophobes (such as amphophilic and melanotropes). Melanotropes for ex. secrete melanocyte-stimulating hormone (MSH). The other hormones produced by the adenohypophysis are: growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), beta endorphin, and prolactin

Question 16

describe the neurohypophysis histologically

Answer 16

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The posterior pituitary has one region:
Posterior Pituitary = Neurohypophysis = Pars nervosa (PN)
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The neurohypophysis, is made up of unmyelinated secretory neurons, pituicytes (specialized glial cells in the pituitary gland that help store and release neurohypophysial hormones, oxytocin and vasopressin), and nerve fibers.

Question 17

how does hypothalamus distinguishes from other pathways?

Answer 17

establishes extensive non-neural communication pathways with both other brain regions and the periphery

Question 18

whata re the regions of th e11 nuclei?

Answer 18

*Preoptic Area
* Anterior-Supraoptic region
* Middle- Tuberal region
* Posterior- Mammillary region

Question 19

where is preoptic area derived from?

Answer 19

preoptic area is derived embryologically from the telencephalon, while the hypothalamus is derived from the diencephalon. Nevertheless, the preoptic area is functionally part of the hypothalamus.

Question 20

what are some major hypothalamic nuclei and fucntions

Answer 20

Question 21

Mention the afferent pathways entering hypothalamus

Answer 21

There are 9 different afferent pathways that target the hypothalamus from CNS and PNS. The Ht consolidates their information to modulate its output for its homeostatic, endocrine, autonomic and limbic mechanisms:

1. Tegmental fibers (from red nucleus, the periaqueductal gray, and the substantia nigra)
2. Auditory pathway (unknown afferents)
3. Olfactory fibers
4. Visual pathway to suprachiasmatic nucleus
5. Corticohypothalamic fibers
6. Hippocampohypothalamic fibers
7. Amygdalohypothalamic fibers
8. Thalamohypothalamic fibers
9. Visceral and somatic afferents (from Lemniscus, tractus solitarius and reticular formation)

Question 22

Mnetion the efferent pathways from hypothalamus

Answer 22

There are 4 different efferent pathways from the hypothalamus to the different areas of the brain allowing for the appropriate modulation of homeostatic, endocrine, autonomic and limbic mechanisms:
-Hypothalamohypophyseal tract
-Mammillothalamic tract
-Mamillotegmental tract
-Descending fibers to brainstem and spinal cord

Question 23

Sympathetic and parasympathetic outflow of information are controlled by higher centers, including:

Answer 23

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Hypothalamus,
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brainstem nuclei, such as the nucleus solitarius
*
the amygdala
*
several regions of limbic cortex

Question 24

Autonomic responses are also regulated by:

Answer 24

afferent sensory information, including signals from internal receptors such as chemoreceptors, osmoreceptors, thermoreceptors, and baroreceptors

Question 25

The hypothalamus receives autonomic regulatory inputs from various synaptic and humoral sources such as:

Answer 25

*
amygdala
*
specific areas of the limbic cortex, such as the orbital frontal, insular, anterior cingulate, and temporal cortices

Question 26

when Ht gets inputs, it send what?

Answer 26

sends descending projections affecting sympathetic and parasympathetic divisions of the autonomic nervous system.

these projections originate from:
*paraventricular nucleus
*dorsomedial hypothalamic nucleus
*lateral/posterior hypothalamus

Autonomic fibers traverse the medial forebrain bundle, dorsolateral brainstem, and periaqueductal gray matter.
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Ultimately, they synapse onto preganglionic parasympathetic nuclei in the brainstem and sacral spinal cord (S1-S4), as well as preganglionic sympathetic neurons in the thoracolumbar cell column of the spinal cord (T1 to L2).

Question 27

What are circumventricular organs?

Answer 27

The circumventricular organs (CVO) are structures that permit polypeptide hypothalamic hormones to leave the brain without disrupting the blood-brain barrier (BBB) and permit substances that do not cross the BBB to trigger changes in brain function.
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There are several sensory circumventricular organs providing information to other brain regions: Median eminence, subfornical organ, postrema, organum vasculosum of the lamina terminalis (OVLT).
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The anterior pituitary is connected to the hypothalamus by a vascular connection through the hypophyseal portal system. A portal system is a vascular connection with two sets of capillary beds.

Question 28

What are some examples of circumventricular organs?

Answer 28

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The organum vasculosum of the lamina terminalis OVLT is a circumventricular organ present in the hypothalamic area. OVLT capillaries (sinusoidal type- leaky) do not have a blood–brain barrier, so neurons in this region can respond to circulating factors present in the systemic circulation.
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OVLT neurons serve as osmoreceptors, detecting sodium content and osmotic pressure in the blood. Lamina terminalis neurons project to the supraoptic and paraventricular nuclei, influencing vasopressin-secreting neurons. Additionally, these neurons connect to the median preoptic nucleus, a key player in thirst regulation.
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Area postrema (AP)- located in the dorsal surface of medulla oblongata at the caudal end of the 4th ventricle, has been implicated as a chemoreceptor trigger zone for vomiting (emetics).

Question 29

explain the limbic inputs to hypithalamus

Answer 29

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The subiculum of the hippocampus, projects to the mammillary bodies of the hypothalamus via the fornix.
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Mammillary bodies project via the mammillothalamic tract to the anterior thalamic nucleus, which in turn projects to limbic cortex in the cingulate gyrus. This is called the Papez Circuit.
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The amygdala, an important limbic nucleus, has reciprocal connections with the hypothalamus via two pathways: the stria terminalis and the ventral amygdalofugal pathway.

Question 30

Why are limbic pathways relveant?

Answer 30

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These Limbic- Hypothalamic connections are involved with emotional influences on:
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Autonomic pathways: explaining why your palms get sweaty and your stomach churns when you are anxious
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Homeostatic pathways such as the immune system can help us explain why depressed individuals may be more susceptible to infection.
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Complex motivational and emotional programs to be activated in the service of homeostatic and reproductive functions.
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Because the hypothalamus provides the integrating mechanism for different forms of emotional behaviors as well as for other visceral and autonomic responses, the limbic system serves as a key modulating region of these processes by virtue of its inputs to the hypothalamus.

Question 31

learn

Answer 31

inputs outputs

Question 32

explain lesions of the hypothalamus

Answer 32

1. Suprachiasmatic nucleus- regulator of circadian rhythms
   Lesion: changes to sleep structure, disrupted patterns of body temperature and behavioral function.
2. Medial preoptic area- regulator of reproductive and sexual behaviors
   Lesion: can disrupt maternal behavior and male sexual behavior in rats
3. Anterior hypothalamus- temperature regulation
   Lesion in anterior Ht: causes hyperthermia
   *
4. Lateral and medial hypothalamus- important in appetite control.
   -Lesions in lateral Ht: causes a decrease in body weight, also decrease water intake.
   -Lesions in medial Ht (ventromedial nucleus): inhibits appetite and causes obesity

Question 33

Neurons in the hypothalamus regulate the release of anterior
pituitary hormones via the

Answer 33

hypophysial portal system

Question 34

explain the pathway of anterior pituitary controlled hormone release

Answer 34

1-Arterial blood from the inferior and superior hypophysial arteries, reaches the pituitary.
2-The 1ry capillary plexus of the portal system is located in the median eminence.
3-Hypothalamic nuclei, including the arcuate, periventricular, medial preoptic, and medial parvocellular portions of the paraventricular nucleus, project to the median eminence, secreting inhibitory and releasing factors.
4,5-From the median eminence, these regulating factors are carried by Hyphophysial portal veins to the anterior pituitary.
6,7-Hormones in anterior pituitary are picked by the 2ry capillary plexus of the portal system and carried by draining veins to the cavernous sinus, to reach the internal jugular vein.

Question 35

hormones released by pituitary

Answer 35

Question 36

memorize

Question 37

explain the hormones released at the posterior pituitary

Answer 37

*The posterior pituitary also has a capillary plexus, which picks up oxytocin and vasopressin and carries these hormones into the systemic circulation.

*These hormones are secreted in the posterior pituitary by terminals of neurons whose cell
bodies lie in the supraoptic and paraventricular nuclei.

*Vasopressin is produced predominantly
by supraoptic nucleus

*Oxytocin is produced mainly in paraventricular nucleus

*Hypothalamic nerve terminals reach the posterior
pituitary, unlike the anterior pituitary, where
there is a hypophysial portal system and no nerve
terminals

Question 38

learn

Question 39

Explain the feedback control of CRH nad ACTH production in hypihtlaamic - pituitary aixs

Answer 39

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In the Hypothalamic Pituitary Axis, release of corticotropin-releasing hormone (CRH) by the hypothalamus and release of ACTH by the anterior pituitary both receive feedback inhibition from circulating cortisol in the bloodstream.
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Chronic administration of exogenous steroids can suppress ACTH production to the point that the adrenals atrophy and are unable to provide sufficient cortisol to support life if the exogenous steroids are
abruptly discontinued.

Question 40

What are some clinical associated disorders with hypothalamic lesions?

Answer 40

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Body weight regulation -Severe obesity or cachexia (wasting)
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Reproductive disorders- Impotence or amenorrhea after puberty, sexual retardation, sexual precocity (rare)
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Hyper/Hypothermia-Body temperature
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Diabetes insipidus-Lesion on the supraoptic nucleus or to connection to the posterior lobe of the hypophysis. Feature: extreme thirst
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Sleep disturbances-Sleep patterns
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Emotional disorders with seizures-Attacks of unexplained weeping or laughter, uncontrollable rage, depressive reactions, maniacal outbursts [ when they get seizures its called Hypothalamic Hamartoma]

Question 41

Disorders of the Hypothalamus and Pituitary

Answer 41

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Can arise from any endocrine cell type in the anterior pituitary, and 85% secrete excessively one or more pituitary hormones, the most common one is prolactin.
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-Treatment: Treatment options include medication, surgery, and radiotherapy.
o
Prolactin-secreting tumors (prolactinomas): show good response to treatment with dopaminergic agonists such as bromocriptine or cabergoline, which inhibit prolactin release and shrink tumors.
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Nonhormone-secreting adenomas grow larger and can compress the optic chiasm and cause visual disturbances, including a characteristic bitemporal hemianopia.
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If left untreated, large pituitary adenomas can eventually cause hydrocephalus and brainstem compression.
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Other secretory adenomas include: GH, TSH, ACTH, LH or FSH.

Question 42

explain prader willy syndrome

Answer 42

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Mostly occurs when part of the father’s chromosome 15 is deleted.
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Constant insatiable appetite, often resulting in morbid obesity. It is the most common genetic cause of morbid obesity in children. Must limit food access in patients.
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Currently, no consensus exists as to the cause for this symptom, although genetic abnormalities in chromosome 15 disrupt the normal functioning of the hypothalamus.
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Given that the hypothalamic arcuate nucleus regulates many basic processes, including appetite, a link may well exist.
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In the hypothalamus, nerve cells that produce oxytocin, a hormone contributing to satiety, are believed to be abnormal in people with PWS.
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PWS patients have high ghrelin levels (appetite hormone), are thought to contribute directly to the increased appetite, hyperphagia and obesity seen in this syndrome.
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Medication: Growth hormone.
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Treatment: Feeding therapy, physical therapy, occupational therapy, strict food supervision, exercise program, counseling

Question 43

Explain Kallman syndrome

Answer 43

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Genetic disorder that prevents a person from starting or fully completing puberty.
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Kallmann syndrome is a form of a group of conditions termed hypogonadotropic hypogonadism.
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Additional symptom of a total lack of sense of smell (anosmia) or a reduced sense of smell (hyposmia).
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Failure in the correct production or activity of gonadotropin-releasing hormone by the hypothalamus-> low levels of the sex hormones testosterone in males or oestrogen and progesterone in females.
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Diagnosis normally occurs during teenage years when puberty fails to start.
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If untreated, people will have poorly defined secondary sexual characteristics, show signs of hypogonadism, are infertile and are at increased risk of developing osteoporosis.
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Physical symptoms affecting the face, hands and skeletal system can also occur.
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Lifelong treatment: Hormone replacement therapy (HRT) is the major form of treatment with the aim to replace the missing testosterone or oestrogen and progesterone. Gonadotropin treatment (FSH, LH) is another strategy.

Question 44

in conclusion:

Answer 44

PNS and CNS input and Hormonal input affect hypothalamus and in exchange, this Homeostatic Head Ganglion responds to the information with endocrine control and autonomic control.