Cellular action of hormone action II

• What is the nature/chemical composition of insulin

  peptide hormone
• what is insulin in reference to solubility

  hydrophilic
• where is the receptor location for insulin

  cell surface receptor, binds to insulin receptors on the plasma membrane
• receptor basis

  kinase receptors
• insulin binds to a tyrosine kinase receptor, leading to signal transduction via phosphorylation
• where is insulin produced?

  pancreas
• main functions on insulin?


  allow the entry of glucose from the blood into certain tissues

  reducing blood glucose levels
• which diabetes is irreversible?


  type 2 diabetes
• The pancreas is composed of exocrine & endocrine cells
• endocrine cells

  Islets of Langerhans – secrete insulin & glucagon
• what are the 5 types of endocrine cells in the Islet of Langerhans

  beta cells

  alpha cells

  delta cells

  F cells

  epsilon cells
• 1. Beta cells release insulin

  2. Alpha cells release glucagon

  3. Delta Cells release somatostatin

  4. F cells release pancreatic polypeptide

  5. Epsilon Cells release ghrelin
• alpha cells produce glucagon, glucagon stimulates beta cells to release insulin
• beta cells produce insulin, insulin acts on alpha cells to inhibit glucagon release
• delta cells produce somatostatin, somatostatin inhibits both insulin and glucagon release
• insulin synthesis steps

  pre - proinsulin

  proinsulin

  maturation

  insulin formation
• insulin synthesis begins in the Endoplasmic reticulum
• single peptide is removed converting pre -proinsulin into proinsulin
• in the golgi apparatus, proinsulin is folded and forms disulfide bonds then packed into secretory granules
• high blood glucose levels trigger the secretion of insulin
• type 1 diabetes 


  loss of beta cells disrupts insulin production

  leading to unchecked glucagon release and hyperglycemia
• type 2 diabetes

  Beta cells dysfunctions & insulin release causes pancrine imbalance
• insulin receptors are linked by disulfide bonds
• alpha subunit = extracellular

  beta subunit penetrates through plasma membrane
• when insulin binds, it activates tyrosine kinase activity on both subunits
• effect of insulin

  Glucose Uptake: Insulin binding to its receptor on liver cells triggers glucose uptake.
• effect of insulin

  •Glycogenesis: Insulin promotes glycogen production and storage by upregulating enzymes involved in glycogenesis.
• effect of insulin

  •Glycolysis: Insulin increases glycolysis, breaking down glucose for energy.
• effect of insulin

  •Lipogenesis: Insulin stimulates the synthesis of fats (lipogenesis) for energy storage.
• effect of insulin

  Protein Synthesis: Insulin also promotes protein synthesis
• modulation of insulin release

  nutrients = blood glucose concentration

  paracrine hormones = glucagon, somatostatin
• glucagon = stimulation

  somatostatin = inhibition
• Hyperglycemia: Failure to regulate glucose leads to elevated blood glucose
• Polyuria: Excess glucose spills into urine, increasing urination frequency.
• Polydipsia: Leads to dehydration, leading to excessive thirst.
• type 2 diabetes is diagnosed by blood glucose sample

  glucose tolerance test = test
• role of insulin = regulates glucose homeostasis