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48544
The hypothalamus and anterior pituitary
Descripción
Endocrinology Mapa Mental sobre The hypothalamus and anterior pituitary, creado por maisie_oj el 17/04/2013.
Sin etiquetas
endocrinology
endocrinology
Mapa Mental por
maisie_oj
, actualizado hace más de 1 año
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maisie_oj
hace más de 11 años
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Resumen del Recurso
The hypothalamus and anterior pituitary
The hypothalamus and anterior pituitary
Recognises external and internal stimuli and stimulates an appropriate bodily response
Stimuli; cold, stress, metabolic demand, dehydration, exercise, time, mestrual cycle, sleep, breastfeeding, puberty, pregnancy/menstrual cycle
Responses; adrenal/thyroid/gonadal function, lactation, growth, osmoregulation, parturition and metabolism
Structure and connections
Hypothalamus
Part of the brain (below the thalamus) - major coordination centre for stimuli
Anterior pituitary
Not part of the brain (embryoinically derived from the oral actoderm)
Lies in the pituitary fossa of the sphenoid bone - if it grows it presses n the optic chiasm (visual disturbances seen in pituitary tumours)
Not neurally connected to the brain
Instead nuclei within the hypothalamus detect a stimulus produce an appropriate releasing hormone (e.g. CRH, TRH, GnRH etc.)
These hormone producing neurnes secrete the releasing hormone into a network of cappillaries (neurocrine) called the portal system
From here the releasing hormones travel in the blood to the hormone producing cells of the anterio pituitary
Releasing hormones stimulate secretion of tropic hormones into a second capillary network which carries the hormones to their target tissues
The posterior pituitary develops from the brain and is connected neurally
Anterior pituitary hormones
Three major families of hormone are produced here
POMC family - ACTH (and MSH)
Produced by corticotrophs (basophil)
Glycoprotein family - TSH, FSH, LH (hCG)
TSH: thyrotrophs (basophil)
FSH and LH: gonadotrophs (basophil)
Somatotropic family - GH and prolactin
GH: somatotroph (acidophil)
PRL: lactotroph (acidophil)
All are regulated by hormones secrted by the hypothalamus into the protal system
= hypothalamic releasing hormones and release-inhibiting factors
Corticotropin releasing hormone (CRH)
Stimulates ACTH release
Thyrotropin releasing hormone (TRH)
Stimulates TSH release
Gonadotropin releasing hormone (GnRH)
Stimulates FSH and LH secretion
Growth hormone releasing hormone (GHRH)
Stimulates GH release
Somatostatin
Inhibits GH secretion
Dopamine (prolactin inhibitory factor, PIF)
Inhibits PRL secretion
Endocrine axes
E.g. Hypothalamo-pituitary-thyroid axis
Metabolic demand detected in hypothalamus -> secretes TRH
TRH acts on thyrotrophs in the ant. pituitary -> TSH secretion
TSH acts on follicular cells in the thyroid -> secrete T4 and active T3
T3 acts on target cells to increase metabolism
-
T4 can be converted to active T3 in the peripheral tissues
+
T3 and T4 negatively feedback on the hypothalamus and ant. pituitary
-
-
Axes; hypothalamo-pituitary-thyrod/ganadal/adrenal axes and; the GH-IGF axis
Prolactin
Acts on mammary tissues to stimulate breast development and increase milk production
There is no end product from this system to feedback and inhibit PRL secretion
Instead PRL is constituitively prodcued by lactotrophs and constantly ready to be secreted
To regulate this pathway dopamine (prolactin inhibitory factor, PIF) is constantly being secreted when there is no requirement for milk production
Regulation
Hypothalamus: Dopamine constantly secreted
Lactotrope: Constitutive PRL secretion
Breast tissue: milk production
+
-
Dopamine agonists (e.g. Bromocriptine - parkinson's drug)
Used in prolactinomas (PRL secreting tumours - the most common pituitary tumour)
-
-
Nipple stimulation (during suckling)
-
Stress
-
Dopamine antagonists (e.g. Chlopromazine - antipsychotic)
+
GH
Secretion of GH is under dual control from the hypothalamus
Stimulatory: GHRH
Inhibitory: Somatostatin (GHIH)
Both secretiong control hormones act together to regulate GH levels
There is also some negative feedback from IGF-1 (secreted by the liver and bone in response to GH) and by an elevation in blood glucose
GH causes an increase in blood glucose
GH-IGF axis
Hypothalamus: GHRH
Ant. Pituitary (somatotroph): GH secretion
Bone: IGF-1 secretion
IGF-1 promotes linear bone growth
Liver: IGF-1 secretion, reduced glucose uptake and gluconeogenesis
Tissue growth (e.g. muscle)
-
IGF-1 and increased blood glucose
+
+
Exercise, sleep, stress, hypoglycaemia
Hypothalamus: somatostatin
-
Actions
Mobilises fat stores
Opposes insulin and increases blood glucose
Stimulates tissue growth (muscle and bone) through IGF-1
IGF-1
Stimulates growth by....
Increasing amino acid uptake
Promoting protein synthesis in muscle and cartilage
GH is responsible for the linear growth during childhood and puberty
Excess
In childhood = gigantism
Excess long bone growth before puberty
In adulthood = acromegaly
Large; hands, feet, jaw, brow, internal organs; cardiovascular problems, joint pains and glucose intolerance
Testing levels
In general
Endocrine disorders can be...
Primary (gland disorder)
Secondary (pituitary disroder)
Or tertiary (hypothalamus disorder)
Testing of an endocrine axis is important to detemine where the defect is
Also to monitor the disorder
GH
When to take the sample?
GH secretion is episodic and daily levels change
Etherefore something called dynamic testing is done
Dynamic testing
The idea: to challenge the axis and see if the appropriate change occurs
Excess GH
Give IV glucose (take GH level before)
After 1hr check GH level again
GH should have decreased (unless it is being overproduced)
Deficiency (dwarfism)
Have patient excercise (after fasting) - take GH measurement first
After 1hr check GH level again
GH should have increased (unless deficient)
Commercial kits available
Effects of hypophysectomy (loss or removal of anterior pituitary)
Atrophy and functional loss of gonads, thyroid and adrenals
Can be treated with hormone replacement therapy (TSH, ACTH, sex steroids and maybe GH, FSH and LH)
Signs and symptoms
Loss of libido and depression
Failure of beard growth
Hypotension
Hypoglycaemia
Testicular atrophy
Muscle weakness
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