Genbio 2: CHAPTER 41, 42, and 45

• Hormone


  Secreted molecule that circulates through the body and stimulates specific cells

  
• Hormones can reach all parts of the body but only target cells have receptors for that hormone
• Nervous system

  Network of specialized cells - neurons - that transmit signals along dedicated pathways
• Criteria to classify intercellular information flow

  • Type of secreting cell
  • The route taken by the signal in reaching its target
• Endocrine signaling


  Uses blood vessel stream, and through the vessels, it reaches target cells

  
• Endocrine signaling

  • Maintains homeostasis
  • Mediates responses to stimuli
  • Triggers changes underlying sexual maturity and reproduction
• Paracrine signaling


  There is a carrier that can communicate directly to the target cell
• Autocrine signaling


  Target cell is also the secreting cell
• Local regulators

  Molecules that act over short distances, reaching target by diffusion
• Local regulators have roles in blood pressure regulation, nervous system function, and reproduction
• Prostaglandins


  Local regulators that mediate signaling
• Prostaglandins also function in the immune system and blood clotting
• Some local regulators such as Nitric Oxide (NO) are gasses
• O2 level falls

  Blood vessel walls release NO
• NO diffuses to smooth muscle cells

  It activates an enzyme to relax the cell
• Synaptic signaling

  From the synapse direct to the target cell
• Neuroendocrine signaling


  From the synapse, it diffuses neurohormones into the bloodstream

  
• Neurotransmitters

  Secreted molecules that diffuse short distances and bind receptors on target cells
• Pheromones


  Chemicals released into the environment that can be used to mark trails to food, define territories, warn predators, and attract potential mates
• Chemical classes of hormones

  • Polypeptides - water soluble
  • Amines - water soluble
  • Steroids - lipid soluble
• Water soluble hormones

  Secreted by exocytosis, travel freely in the bloodstream and bind to cell-surface receptors
• Water soluble hormone pathway

  1. Vesicle fuses to plasma membrane to release water soluble hormones

  2. Water soluble hormones enter the blood vessel

  3. Blood vessel interacts with the surface of the cell with receptor protein

  4. Leads to gene regulation or cytoplasmic response

  
• Response pathway for water soluble hormones

  1. Binding of a hormone to a receptor initiates a cellular response

  2. Signal transduction = chain of events that convert chemical signal to intracellular response

  
• Epinephrine


  Received by G protein-coupled receptors, enacts changes that allow the G-protein to move using GTP, delivers the message towards adenylyl cyclase, adenylyl cyclase with ATP (converted to cyclic AMP) will enable the changes to be delivered to cAMP (second messenger), enzyme protein kinase A is activated and it can result to inhibition of glycogen synthesis, or promote glycogen breakdown

  
• Lipid soluble hormones

  Diffuse through the cell membrane, travel in the bloodstream bound to transport proteins, and diffuse to cell membrane of target cells
• Lipid soluble hormone pathway

  1. Lipid soluble hormone can directly leave the cell as long as there is a transport protein in the blood vessel

  2. Transport protein makes sure the hormones reach target cell

  3. Hormones enter target cell and binds with receptor protein

  4. Leads to gene regulation or cytoplasmic response
• Response pathway for lipid-soluble hormone

  1. Thyroxine, vitamin D, and other lipid soluble hormones that are not steroids typically have receptors in the nucleus

  2. Steroid hormone passes through the cell membrane and binds with the receptor protein

  3. Hormone receptor complex enters the nucleus to specific regulatory sites on the target cell's DNA

  4. Hormone acts as a transcription factor, a DNA activator

  5. Messenger RNA is transcribed which is then translated into a protein, e.g. enzyme

  6. The new protein created would alter the function of the target cell

  
• The same hormone may have different effects on target cells that have different receptors for the hormone, different signal transduction pathways
• Endocrine glands


  Endocrine cells grouped in ductless organs like thyroid, parathyroid, testes or ovaries

  
• Exocrine glands


  Have ducts to carry secreted substances onto body surfaces or into body cavities
• Feedback regulations

  • Simple endocrine pathways - uses the bloodstream to reach the target cells
  • Negative feedback - signals that stops a response to a stimulus (Reduces)
  • Simple neuroendocrine pathways - stimulus is received by a sensory neuron, which stimulates a neurosecretory cell
  • Positive feedback - signals that encourages to stimulus (Increases)

  
• Feedback regulation in invertebrates

  1. Brain will release PTTH(Prothoracicotropic Hormone)

  2. Prothoracic Gland Activated

  3. Molting is promoted

  4. Ecdysteroid will turn caterpillar into a larva

  5. Corpora cardiaca releases Juvenile Hormone

  6. When JH drops, the pupa matures and becomes an adult

  
• Metamorphosis will not be triggered until JH drops
• Hypothalamus

  Coordinates endocrine signaling

  
• Pituitary gland

  Composed of the posterior and anterior pituitary, where signals from the hypothalamus travel to

  
• Anterior pituitary


  Different from the hypothalamus
• Posterior pituitary


  Extension of the hypothalamus
• Posterior pituitary hormones


  Responsible for antidiuretic hormone which regulates physiology and behavior, neurosecretory cells of the hypothalamus synthesize the two posterior pituitary hormones, oxytocin regulates milk secretion

  
• Anterior pituitary hormones


  Responsible for metabolism, osmoregulation, reproduction, hormones secreted by the hypothalamus control release of all anterior pituitary hormones, unlike the posterior, anterior hormones require regulation via passing through portal vessels, sets of hormones from the hypothalamus, anterior pituitary, and a target endocrine gland are often organized into a hormone cascade

  
• Thyroid regulation


  When thyroid hormone drops, the hypothalamus releases thyrotropin-releasing hormone (TRH), causing the anterior pituitary to secrete thyroid-stimulating hormone (TSH), TSH stimulates the release of thyroid hormone by the thyroid glands