General Biology 2 (Zoo)

• Animal hormones


  Chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body
• Animal hormones


  • Reach all parts of the body, but only target cells have receptors for that hormone
  • Controlled by the Endocrine System
  • The nervous and endocrine systems often overlap in function
• Intercellular communication in animals

  • Endocrine Signaling
  • Paracrine and Autocrine Signaling
  • Synaptic and Neuroendocrine Signaling
• Endocrine Signaling


  Hormones secreted into extracellular fluids by endocrine cells and reach their targets via the bloodstream
• Endocrine Signaling


  • Maintains homeostasis, mediates responses to stimuli, regulates growth and development
• Paracrine Signaling


  Local regulators that act on nearby cells
• Autocrine Signaling


  Local regulators that act on the same cell that secretes them
• Paracrine and Autocrine Signaling


  • Play roles in processes such as blood pressure regulation, nervous system function, and reproduction
• Local regulators


  • Prostaglandins
• Synaptic Signaling


  Neurons form specialized junctions with target cells, called synapses
• Neurotransmitters


  Molecules secreted by neurons at synapses that diffuse short distances and bind to receptors on target cells
• Neuroendocrine Signaling


  Specialized neurosecretory cells secrete molecules called neurohormones that travel to target cells via the bloodstream
• Pheromones


  Chemicals that are released into the environment used by members of an animal species to communicate
• Pheromones


  • Serve many functions, including marking trails leading to food, defining territories, warning of predators, and attracting potential mates
• Local regulators


  Signaling molecules that act on nearby cells (paracrine signaling) or on the same cell that secretes them (autocrine signaling)
• Local regulators


  • Elicit rapid responses that are usually short-lived
• Hormones


  Signaling molecules secreted by endocrine glands into the bloodstream, which carry them to distant target organs
• Hormones


  • The response time is generally slower compared to local regulators, but the effects are often longer-lasting
• Classes of local regulators

  • Prostaglandins
  • Polypeptides
  • Gases (e.g. nitric oxide)
• Classes of hormones


  • Polypeptides
  • Steroids
  • Amines
• Water-soluble hormones


  Secreted by exocytosis, travel freely in the bloodstream, bind to cell-surface receptors
• Lipid-soluble hormones


  Diffuse across cell membranes, travel in the bloodstream bound to transport proteins, diffuse through the membrane of target cells, bind to receptors in the cytoplasm or nucleus of the target cells
• Hormones


  • The same hormone may have different effects on target cells that have different receptors for the hormone or different signal transduction pathways
• Endocrine tissues and organs

  • Endocrine glands (ductless organs)
  • Exocrine glands (have ducts to carry secreted substances)
• Simple hormone pathways


  Hormones are released from an endocrine cell, travel through the bloodstream, and interact with specific receptors within a target cell to cause a physiological response
• Simple neuroendocrine pathways


  Stimulus is received by a sensory neuron, which stimulates a neurosecretory cell, Neurosecretory cell secretes a neurohormone, which enters the bloodstream and travels to target cells
• Negative feedback loop


  Results in the inhibition or slowing down of a process
• Positive feedback


  Reinforces a stimulus to produce an even greater response
• Vertebrate endocrine system


  • The hypothalamus receives information from the nervous system and initiates responses through the endocrine system
  • The posterior pituitary stores and secretes hormones that are made in the hypothalamus
  • The anterior pituitary makes and releases hormones under regulation of the hypothalamus
• Posterior pituitary hormones


  Antidiuretic hormone (ADH) and Oxytocin
• Anterior pituitary hormones


  Regulated by releasing hormones and inhibiting hormones from the hypothalamus