Lec 36 - Pineal gland and endocrine pancreas

• Majority of the pancreatic islets are in the tail of the pancreas
• Each pancreatic islet receives blood through an insuloacinar portal system forming a network of fenestrated capillaries
• The exocrine pancreas receives blood

  • from the islet capillaries
  • from an independent acinar vascular system
• Pancreatic islets do not have a true capsule. They contain cords of cells and fenestrated capillaries
• The pancreatic islet portal system goes from an artery -> fenestrated capillaries within the islets -> dumps products into sinusoids -> form another capillary bed -> feed pancreatic acini
• Islets have an endocrine function to regulate the exocrine pancreas
• Cell types in the pancreatic islets

  • alpha
  • beta
  • delta
  • F cell
• Pancreatic islet alpha cells make up 15 - 20% of the cells. They release glucagon that functions to increase blood glucose
• Pancreatic islet beta cells make up 60 - 70% of the cells. They release insulin that functions to decrease blood glucose
• Pancreatic islet delta cells make up 5 - 10% of the cells. They release somatostatin that functions to inhibits release of insulin and glucagon. Paracrine signaling - effects the cells near them
• Pancreatic islet F cells make up 2% of the cells. They release pancreatic polypeptide that functions to inhibit pancreatic enzyme secretion. They tell the acini to secrete digestive enzymes or not
• What is this an image of - pancreatic islet

  
• In EM alpha cells, they contain glucagon vesicles that have a halo around them whereas delta cells have small uniform vesicles with somatostatin

  
• beta cells have glucose transporters on its plasma membrane. When blood glucose goes up, glucose will enter the cells through sinusoids. premade insulin in secretory vesicles are signalled to exocytose. Insulin will be released and help signal to other cells via the insulin receptors to take up some of the blood glucose. If glucose levels do not fall or remain high, there is going to be an upregulation of new synthesis of insulin
• Clinically, the C peptide from insulin is used in glucose test, because the insulin gets used really quickly
• The pineal gland is under the control of the hypothalamus and secretes melatonin
• Cells of the pineal gland are called pinealocytes. They are arranged in cords alongside
• Pinealocytes are neurons of the pineal gland. These cells produce melatonin. Their nucleus contains both euchromatin and heterochromatin. They have a predominant nucleolus. They also contain an eosinophilic cytoplasm
• Pineal gland cells

  • pinealocytes
  • interstitial cells
• Interstitial cells of the pineal gland are glial cells that contain a very basophilic nucleus
• The pineal gland contains brain sand which is calcified concretions of carrier proteins. Overtime they collect within the pineal gland; will have more as you age. Key that you are in the pineal gland
• What is this a slide of and label it

  • Pineal gland

  A) brain sand

  B) pinealocytes

  C) interstitial cells

  
• Pinealocytes synthesize melatonin from tryptophan. Melatonin is transported along cytoplasmic processes which terminate along capillaries (modified axons that synapse onto blood vessels). Axons from the sympathetic nerve fibers originating in the superior cervical ganglia innervate pinealocytes and regulate melatonin production
• The pineal gland is under sympathetic control '
• How does the Pineal gland see light

  • light signals are transmitted from the optic nerve -> optic chiasm -> suprachiasmatic nucleus via the retinohypothalamic tract
  • signals are sent to the thoracic spinal cord (sympathetic ns) by the hypothalamospinal tract
  • signals are sent to the superior cervical ganglia
  • postganglionic sympathetic fibers alongside the carotid artery convey signals to the pineal gland
• Darkness stimulates melatonin production and light suppresses it