Bio

• Neurotransmitter

  • Released by the presynaptic neuron
  • Binds to receptors on the postsynaptic neuron
  • Transmits a signal across the synapse
• Neurotransmitter


  A chemical substance that is synthesized and packaged by the presynaptic neuron. It is released into the synaptic cleft and binds to receptors on the postsynaptic neuron, transmitting a signal across the synapse
• Synaptic cleft

  The space between the presynaptic and postsynaptic neurons
• Synaptic transmission


  The process by which the impulse in the presynaptic neuron signals the postsynaptic cell
• Presynaptic neuron


  A neuron that releases neurotransmitters into the synaptic cleft
• Postsynaptic neuron

  A neuron that has receptors for neurotransmitters on its surface
• Synaptic vesicles


  Membranous sacs in the synaptic knobs that contain neurotransmitter molecules
• Release of neurotransmitters

  The process by which neurotransmitters are released from synaptic vesicles into the synaptic cleft
• Synaptic knobs


  Rounded structures at the terminals of axons that contain synaptic vesicles
• Components of a synapse


  • Presynaptic neuron
  • Synaptic cleft
  • Postsynaptic neuron
  • Synaptic vesicles
  • Synaptic knobs
• Glands are structures which produce hormones and other useful substances
• Types of glands


  • Exocrine
  • Endocrine
• Exocrine glands


  Release their secretion to the target group through the duct and are called duct glands
• Endocrine glands


  Release their secretion to the blood stream as there are no ducts
• The Endocrine System consists of a number of glands that discharge hormones into the blood circulation
• Hormones


  Organic chemical substances produced in small amounts and move by diffusion into the blood, stimulating or inhibiting the activities of target organs
• Hormones control processes such as

  • Growth
  • Development
  • Metabolism
  • Response to crises
• Glands in the endocrine system

  • Thyroid glands
  • Parathyroid gland
  • Adrenal gland
  • Pituitary glands
  • Pancreas
  • Gonads
• The thyroid gland is located in the neck region and consists of two lobes on each side of the trachea
• Thyroxin is a hormone secreted by the thyroid gland, controlling the rate of body metabolism and regulating growth and development in children
• Too little production of thyroxin

  Leads to slow growth and poor mental development in children, tiredness and lack of energy in adults, and complications in pregnancy
• Too much production of thyroxin


  Leads to a higher metabolic rate, weight loss, sweating, and irritability
• Iodine deficiency can lead to thyroid issues like goiter
• Parathyroid glands are four tiny structures found embedded on the back surface of the thyroid glands in the neck region
• Parathyroid glands secrete a hormone called parathyroid hormone (parathormone) which controls the level of Calcium and Phosphate ions in the blood
• Glands


  • Four tiny structures found embedded on the back surface of the thyroid glands in the neck region
• The parathyroid glands secrete a hormone called parathyroid hormone (parathormone)
• Parathyroid hormone controls


  The level of Calcium and Phosphate ions in the blood
• Calcium is necessary in the body for bone formation & for the proper functioning of the nervous & muscular system
• It is important to maintain the level of Calcium in the blood at a correct and constant level
• When the amount of Calcium falls below the required level


  The hormone is secreted by parathyroid glands
• The hormone promotes


  The release of Calcium from bones, the absorption of Calcium from food in the small intestine, and the reabsorption of Calcium in the tubules or nephrons of the kidneys
• The pancreas is a small pink organ situated below the stomach
• The pancreas


  • Both an exocrine and an endocrine gland
• As an exocrine gland, the pancreas secretes digestive enzymes and releases these enzymes to the duodenum through duct
• As an endocrine gland, the pancreas contains small masses of cells known as islets of Langerhans
• Cells in Pancreatic islets

  • β-cells which produce the hormone insulin
  • α-cells which produce the hormone glucagon
• The main function of the two hormones (insulin and glucagon) is to regulate blood glucose concentration fairly constant
• When the concentration of glucose in the blood stream is low

  An alpha-cells of the islets of Langerhans secretes the hormone glucagon
• When the concentration of glucose in the blood stream is high


  A beta-cells of the islets of Langerhans secretes the hormone insulin