Simple Feedback Loops and Glands

Simple Feedback Loops and Glands

1. Pancreas

   • Lies at the pyloralduodenum junction.
   • Islet of Langerhans
     • Beta cells (75%): Secretes insulin Alpha cells (20%): Secretes glucagon Delta cells: Secretes somatostatin (growth hormones) also act as inhibitor to insulin, glucagon and the somatostatin. F Cells: unknown physiological action
     • Insulin
       • Works in concert with glucagon to maintain baseline BGL. Came from proinsulin. Processed in the golgi apparatus.  Cleaved in 2 locations to sever the C-chain. Hence insulin is composed of 2 peptide bonds linked by disulphide bridges.
       • Effects: Fuel Storage
         • Stimulus increase and stimulate beta cells, Down regulation by alpha cells. Generates insulin. Overall increase glucose uptakes, increase in amino acid uptake, increase in protein synthesis, decrease in protein breakdown Effects on other organs: Adipocytes: Increase Fatty acid and triglyceride synthesis, Stop breakdown of TAG Overall effect is to reduce plasma glucose and amino acid concentration. and hence complete the feedback loop cycle. Muscles and 
         • Signalling
           • Acts via cell surface receptors, tyrosine kinase type. Receptor self phosphorylate and activated to generate secondary messengers. It promotes translocation of glucose transporters to the cell surface.
     • Glucagon
       • Precursor: Proglucagon, linear peptide acts via G-protein coupled receptors to increase cAMP.
       • Effects: Fuel Mobilization
         • Lower plasma glucose Increase in plasma amino acids Increased sympathetic activity Increased adrenaline Lowered insulin stimulation Increased alpha cells stimulation, produces more glucagon Adipocytes increases in lipolysis, increased in free fatty acids, decreased triglycerides synthesis Liver: Increased glycogen breakdown, gluconeogenesis degrease in glycogen synthesis and protein synthesis Effect is to increase plasma glucose and fatty acid concentration.
   • Diabetes Mellitus
     • Type 1
       • Inherited or some gene deficit insulin secretion is absent or lowered. High BGL Symptoms include polyuria, polydisia, polyphagia, ketoacidosis, hyperlipidemia, muscle wasting, electrolyte depletion
     • Type 2
       • Non-insulin dependent Very very well fed state, can be controlled via regulation of diet. May evolve from type 2 to type 1

2. Kidney

   • Erythropoietin
     • Peptide hormone to stimulate RBC production, popular amongst cyclist. Acts in the bone marrow
   • Calcitriol
     • Active form of Vit D. Works in concert with parathyroid hormones. Increase the plasma concentration of calcium.
   • Renin-Angiotensin System
     • Peptide hormone system. Regulate plasma volume and BP. Activates angiotensinogen which activates angiotensin 1 and 2

3. Heart

   • Atrial Natriuetic Peptide (ANP) secreted in response to distensionActs on kidneys and inhibit secretion of renin and aldosterone.Aim to reduce plasma volume

4. Pineal Gland

   • Secretes melatonin. Maintains circadian rhythm. May also regulate reproductive function.

5. Thymus Gland

   • Supposedly aid in T-cells, immunosystem. It starts up big, but becomes smaller as age progresses