The hypothalamus and anterior pituitary

Mind Map by , created over 6 years ago

Endocrinology Mind Map on The hypothalamus and anterior pituitary, created by maisie_oj on 04/17/2013.

Created by maisie_oj over 6 years ago
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The hypothalamus and anterior pituitary
1 The hypothalamus and anterior pituitary
1.1 Recognises external and internal stimuli and stimulates an appropriate bodily response
1.1.1 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
1.2 Structure and connections
1.2.1 Hypothalamus Part of the brain (below the thalamus) - major coordination centre for stimuli
1.2.2 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
2 Anterior pituitary hormones
2.1 Three major families of hormone are produced here
2.1.1 POMC family - ACTH (and MSH) Produced by corticotrophs (basophil)
2.1.2 Glycoprotein family - TSH, FSH, LH (hCG) TSH: thyrotrophs (basophil) FSH and LH: gonadotrophs (basophil)
2.1.3 Somatotropic family - GH and prolactin GH: somatotroph (acidophil) PRL: lactotroph (acidophil)
2.2 All are regulated by hormones secrted by the hypothalamus into the protal system
2.2.1 = 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
3 Endocrine axes
3.1 E.g. Hypothalamo-pituitary-thyroid axis
3.1.1 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 - -
3.2 Axes; hypothalamo-pituitary-thyrod/ganadal/adrenal axes and; the GH-IGF axis
4 Prolactin
4.1 Acts on mammary tissues to stimulate breast development and increase milk production
4.1.1 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
4.2 Regulation
4.2.1 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) +
5 GH
5.1 Secretion of GH is under dual control from the hypothalamus
5.1.1 Stimulatory: GHRH
5.1.2 Inhibitory: Somatostatin (GHIH)
5.1.3 Both secretiong control hormones act together to regulate GH levels
5.1.4 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
5.2 GH-IGF axis
5.2.1 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
5.2.2 Hypothalamus: somatostatin -
5.3 Actions
5.3.1 Mobilises fat stores
5.3.2 Opposes insulin and increases blood glucose
5.3.3 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
5.4 Excess
5.4.1 In childhood = gigantism Excess long bone growth before puberty
5.4.2 In adulthood = acromegaly Large; hands, feet, jaw, brow, internal organs; cardiovascular problems, joint pains and glucose intolerance
5.4.3 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
6 Effects of hypophysectomy (loss or removal of anterior pituitary)
6.1 Atrophy and functional loss of gonads, thyroid and adrenals
6.1.1 Can be treated with hormone replacement therapy (TSH, ACTH, sex steroids and maybe GH, FSH and LH)
6.2 Signs and symptoms
6.2.1 Loss of libido and depression
6.2.2 Failure of beard growth
6.2.3 Hypotension
6.2.4 Hypoglycaemia
6.2.5 Testicular atrophy
6.2.6 Muscle weakness

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