#GhrelinandLeptin

#Biology

#EndocrineSystem

Introduction

• Ghrelin and leptin are hormones that regulate appetite and energy balance:

  • Ghrelin - A fast - acting hormone that increases appetite and food intake. Ghrelin is produced in the stomach and signals the brain when you're hungry. Ghrelin levels increase during fasting and decrease after eating.

  • Leptin - A hormone that decreases appetite and feelings of hunger. Leptin is produced in fat cells and signals the brain when you have enough energy stored and feel “full”. Leptin levels increase after eating and return to baseline after 24 hours. 

• Ghrelin and Leptin are hormones that has many functions in the body, including: 

  • Stimulating appetite: Ghrelin is known as the "hunger hormone" because it signals the hypothalamus to increase appetite. 

  • Regulating glucose homeostasis: Ghrelin inhibits insulin secretion and regulates gluconeogenesis and glycogenolysis. 

  • Regulating energy homeostasis: Ghrelin decreases thermogenesis to reduce energy expenditure. 

  
  

Ghrelin

• Ghrelin activates the GHSR-1a receptor in the hypothalamus, which stimulates neurons in the arcuate nucleus. This activates orexigenic activity.

• Orexigenic activity is the process of increasing food intake or appetite in an organism through substances or signals.and inhibits satiating neurons.

• Orexigenic activity begins with orexin binding to receptors OX1-R and OX2-R in specific brain areas, which influences feeding behavior.

• Basic mechanism of appetite stimulation. Appetite stimulants act by inducing neuropeptide Y (NPY) and agouti-related peptide (AGRP) or by blocking melanocortin receptors.

• AGRP increases food intake and decreases metabolic rate. It does this by binding to melanocortin receptors 3 and 4, which antagonizes anorectic melanocortins.

• In general, anorectic actions of melanocortin signalling at MC4R are considered to occur through neurons in the PVN.

• The Paraventricular Nucleus (PVN) in the hypothalamus is crucial for appetite regulation, releasing hormones like TRH and CRH that influence energy metabolism and food intake.

• TRH: Stimulates the release of thyroid-stimulating hormone (TSH) and prolactin.

• CRH: Stimulates the release of adrenocorticotropic hormone (ACTH), which then stimulates the release of cortisol from the adrenal glands.

• MC4R is activated by α- and β-MSH, which signals to decrease energy intake. Blocking MC4R activity increases food intake. Mutations in the MC4R gene are a common cause of obesity in children, and can lead to hyperphagia, increased fat and lean mass, and hyperinsulinemia.

Leptin

• Leptin acts on the ARC nucleus by stimulating POMC-containing neurons and inhibiting AgRP/NPY containing neurons.

• Pro-opiomelanocortin (POMC)-containing neurons are a network of neurons in the hypothalamus and brainstem that regulate energy balance and body weight.

• Agouti-related peptide (AgRP)/neuropeptide Y (NPY) neurons are located in the arcuate nucleus (ARC) of the hypothalamus and are key regulators of energy homeostasis and feeding.

• AgRP - A neuropeptide that increases appetite and decreases metabolism and energy expenditure. AgRP neurons are activated by peripheral signals associated with hunger.

• NPY - An orexigenic neuropeptide that controls feeding and energy balance. NPY neurons also control energy expenditure, thermogenesis, physical activity, food-seeking behavior, and anxiety.