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ACTH & MSH By: Zachary Lopez
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Production of POMC Corticotropin releasing hormone is sent from the hypothalamus Causes anterior pituitary to synthesize tropic hormone in corticotroph cells Proopiomelanocortin(POMC) is a chain of 241 amino acids, which is the precursor to many biologically active substances
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Cleavage of POMC Depending on the tissue types and available convertases, POMC is enzymatically cleaved into multiple peptides.
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Structure of ACTH Consists of the peptide chain between 138 to 176 of the POMC Human ACTH has a molecular weight of 4,540 Da.
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Function of ACTH Stimulates secretion of glucocorticoids from adrenal cortex cells Facilitates cholesterol delivery to the mitochondria Stimulates lipoprotein uptake into cortical cells increasing the bioavailability of cholesterol in the adrenal cortex
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Regulation Glucocorticoids inhibit further secretion of CRH from the hypothalamus Glucocorticoids may also inhibit rates of POMC transcription Half-life in human blood is approximately ten minutes
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Problems with ACTH ACTH levels are diurnal with normal ranges between 5-50 pg/ml Levels exceeding normal ranges may result in Cushing's syndrome, characterized by puffy appearance and skin redness Low levels of ACTH may lead to Addison's disease, which is a case of severe electrolyte imbalance and dehydration.
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Structure of MSH Different forms of MSH have different amino acid sequences α-MSH: Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val β-MSH: Ala-Glu-Lys-Lys-Asp-Glu-Gly-Pro-Tyr-Arg-Met-Glu-His-Phe- Arg-Trp-Gly-Ser-Pro-Pro-Lys-Asp γ-MSH: Tyr-Val-Met-Gly-His-Phe-Arg-Trp-Asp-Arg-Phe-Gly
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Functions of MSH Acts as an anti-inflammatory and a regulatory peptide hormone Involved with production and release of melanin from melanocytes Also has hypothalamic control of sleep through melatonin, endorphins, and sexual arousal Critical in the regulation of hunger
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MSH and appetite MSH binds to melanocortin receptors to decrease hunger Expression occurs in the arcuate nucleus of the hypothalamus
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MSH and appetite Ghrelin stimulates the hypothalamus to release glutamate Glutamate synapses with AgRP and NPY neurons which induce the feeding response AgRP and NPY neurons inhibit POMC neurons
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Regulation Produced in the intermediate lobe of the pituitary
Melanocortin 1 receptors(MC1R) is primarily involved in melanin production in melanocytes Melanocortin receptors 3 & 4 are involved with hunger, sleep, and sexual arousal The type of MSH affects the expression of the hormone
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Melanin Melanin- an effective absorber of light, protects against UVB radiation which reduces cancer risk Eumelanin- most common, two types(brown and black) Pheomelanin- responsible for red hair, possible expression through agouti signaling peptide Neuromelanin- found exclusively in the brain
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MSH Deficiency Damage to MC4R may result in increased food intake and obesity Hypopituitarism: when the pituitary doesn’t produce enough of one of its hormones. Results in inflammation, pain, reduction in ADH, and frequent thirst/urination Albinism: abnormality in the melanin formation pathway
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The End
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