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Fat as an endocrine organ (Hypothalamus (Suprachiasmatic nucleus (Receives…
Fat as an endocrine organ
White adipose tissue
Insulation and energy storage
Produce hormone adipokines
Role in inflammation
Adipose cells swollen up lipid droplet and nucleus pushed to one side
Cells larger than brown adipose tissue
Not many organelles
Originate from connective tissue
Brown adipose tissue
Bathed rich network capillaries
Smaller than white adipose tissue
Thermogenesis: Conversion food to heat
Lipid utulisation
Not much lipid, nucleus more central
Multioccular: many compartments (mainly tiny lipid droplets)
Originate from muscle
Fat as endocrine tissue
Adipokines different hormones produced by white adipose tissue
Include leptin and adiponectin
Leptin
: satiety hormone: helps regulate energy balance b inhibiting feeling of hunger: WHITE AT
Adiponcetin
: boosts metabolism, increase fat breakdown, improve vascular function anti-inflammation and insulin sensitising
Higher % body fat, more adipokines produced
Both leptin and adiponectin: protein hormones and leptin can cross blood brain barrier
Leptin
Mutation
Leptin binds receptors hypothalamus
mutation in gene codes for these receptors results in defective receptors being produced
Leptin unable to bind/nothing happens
Obesity, hyperphagia and early onset diabetes
Function
Acts on Ob/Rb receptors hypothalamus
Acts on arcuate nucleus, stop it producing neurotransmitter Nueropeptide Y, does opposite of leptin: orexigenic
Leptin counteracts fatty acid neurotransmitter: anandamide and agouti related peptide (protein hormone) : both are orexigenic
Leptin promotes synthesis of alpha MSH (cleaved from POMC): hunger suppressant (anorexigenic)
Hypothalamic nuclei appetite regulation
Hypothalamus divided into nuclei
Arcuate nucleus
main place
neuropeptide Y and agouti related peptide
is produced
Paraventricular nuclues
mainly r
egulating energy balance
: site where many neuronal pathways cross
Dorsomedial and ventromedial nuclei rich in ObRb
receptors and when ventromediall nucleus is stimulated,
brown adipose tissue theromgeneisis is increased
Hypothalamus
Suprachiasmatic nucleus
Receives input from retina
Controls circadian rhythm
Arcuate nucleus
Produces hypothalamic releasing factors
Contains DOPA-ergic neurons inhibit prolactin release
Preoptic area
Sexually dimorphic nucleus
Regulates release GnRH
Ventromedial nucleus
Satiety center
Destruction results obsesity and savage behaviour
Anterior nucleus
Thermal regulation (dissipation heat)
Stimulates parasympatheitc NS
Destruction results hyperthermia
Mamillary body
Receives input hippocampal formation via fornix
Projects anterior nucleus of thalamus
Contains hemorrhagic lesions in Wernickes's encephalopathy
Paraventricular and supraoptic nuclei
Regulate water balance
Produce ADH and oxytocin
Destruction causes diabetes insipidus
Paranventricular nucleus projects to autonomic nuclei of brainstem and spinal cord
Lateral nucleus
Stimulates induces eating
Destruction = starvation
Posterior nucleus
Thermal regulation (conservation heat)
Destruction results inability to thermoregulate
Stimulates symphathetic NS
Dorsomedial nucleus
Stimulation results in obesity and savage behaviour
Ghrelin
Orexigenic hormone complete opposite effect of leptin and stimulates hunger
Production stimulated by neuropeptide Y
Secreted from GI tract
Insulin
Anorexigenic hormone
Reduce glucose level blood
Reduce food intake when lots of glucose blood
Further assisted by adiponectin: increases insulin sensitivity