REGULATION OF BODY FLUIDS AND CHEMICAL AND NERVOUS CONTROL

• Homeostasis


  The relatively stable state inside the body of an animal. Animal organs and organ systems constantly adjust to internal and external changes in order to maintain this steady state.
• Osmoregulation


  The active regulation of osmotic pressure to maintain the balance of water and electrolytes in an organism. Control of osmotic pressure is needed to perform biochemical reactions and preserve homeostasis.
• How Osmoregulation Works


  1. Osmosis: the movement of solvent molecules through a semipermeable membrane into an area that has a higher solute concentration

  2. Organisms excrete excess water, solute molecules, and wastes to maintain water and electrolyte balance
• Two major types of osmoregulation

  • Osmoconformers: use active or passive processes to match their internal osmolarity to that of the environment
  • Osmoregulators: control internal osmotic pressure so that conditions are maintained within a tightly-regulated range
• Osmoregulation Strategies of Different Organisms

  • Bacteria: use transport mechanisms to absorb electrolytes or small organic molecules, synthesize osmoprotectant molecules
  • Protozoa: use contractile vacuoles to transport ammonia and other excretory wastes, control flow of water and electrolytes
  • Plants: use stomata, vacuoles, cuticles, structural modifications to regulate water intake/loss and salt effects
  • Animals: use excretory system to control water loss and maintain osmotic pressure, kidneys are primary regulator in humans
• In human, the primary organ that regulates water is the kidney. Water, glucose, and amino acids may be reabsorbed from the glomerular filtrate in the kidneys or it may continue through the ureters to the bladder for excretion in urine. In this way, the kidneys maintain the electrolyte balance of the blood and also regulate blood pressure.
• Osmoreceptors in the hypothalamus of the brain monitor changes in water potential, controlling thirst and secreting ADH. ADH is stored in the pituitary gland. When it is released, it targets the endothelial cells in the nephrons of the kidneys, opening aquaporins to allow water flow.
• The nervous system uses electrical impulses to collect, process and respond to information about the environment.
• Nervous system cells


  • Neurons: cell body, dendrites, axon
  • Glial cells: surround, protect, insulate neurons
• Types of neurons


  • Sensory neurons: carry impulses from sense organs
  • Motor neurons: carry impulses to muscles and glands
  • Interneurons: transfer signals between sensory and motor neurons, and between other interneurons
• Action potential


  Electrical impulse produced when resting potential of a neuron changes
• Parts of the nervous system

  • Central nervous system (CNS): brain and spinal cord
  • Peripheral nervous system (PNS): Somatic nervous system (voluntary activities, reflexes)
  • Autonomic nervous system (involuntary activities)
• The central nervous system (CNS) is made of the brain and the spinal cord. Commands to the body originate in the brain and the spinal cord connects the brain with the rest of the nerves in the body.
• Resting neuron


  There is a separation of ions in the cell regulated by sodium-potassium pumps
• Action potential


  1. If a neuron receives a large enough signal, the resting potential changes, producing an electrical impulse

  2. The impulse moves down the axon until it reaches the axon terminal
• Central nervous system (CNS)


  • Made of the brain and the spinal cord
  • Commands to the body originate in the brain
  • The spinal cord connects the brain with the rest of the nerves in the body
• Peripheral nervous system (PNS)


  Can be broken down into the somatic nervous system and the autonomic nervous system
• Somatic nervous system (SNS)


  • Regulates voluntary activities such as muscular movement
  • Controls reflexes
• Autonomic nervous system (ANS)


  • Regulates activities that are not under conscious control
  • Has two divisions: the sympathetic and parasympathetic nervous systems
  • The sympathetic nervous system prepares the body for "fight-or-flight" responses
  • The parasympathetic nervous system is active during restful periods
• Endocrine system


  A regulatory system that uses chemical signals called hormones to control the actions of cells and organs
• Regulation of the endocrine system

  1. Negative feedback mechanisms work to maintain homeostasis

  2. The concentration of hormones and how they affect other body systems is controlled in this manner

  3. Blood glucose regulation is controlled by insulin and glucagon
• Plant hormones


  • Chemical messengers that affect all aspects of plant life
  • Hormones travel throughout the plant body via the vascular tissue and cell-to-cell
  • Potentially every cell in a plant can produce plant hormones
• Auxins


  • The main hormones responsible for cell elongation in phototropism and gravitropism
  • Trigger apical dominance, flowering, fruit ripening, and inhibition of abscission
• Cytokinins


  • Promote cytokinesis (cell division)
  • Most abundant in growing tissues where cell division is occurring
  • Delay senescence, promote mitosis, and stimulate differentiation of the meristem
• Gibberellins (GAs)


  Stimulate shoot elongation, seed germination, and fruit and flower maturation
• Abscisic Acid (ABA)


  • Causes the abscission (dropping) of leaves
  • Accumulates in response to stressful environmental conditions
• Ethylene


  • Promotes fruit ripening, flower wilting, and leaf fall
  • Produced by aging tissues and nodes of stems
• Systemin


  • Activates plant responses to wounds from herbivores
  • Initiates production of compounds that deter herbivores
• Methyl Salicylate (MeSa)


  • Helps regulate responses to infection by parasites or pathogens
  • Induces the systemic acquired response (SAR) in response to the hypersensitive response (HR)
• Plant photoreceptors


  • Comprised of a protein covalently bonded to a light-absorbing pigment called a chromophore
• Plant responses to light

  1. Phototropism (movement toward light)

  2. Stem elongation (growth)

  3. Germination (seed sprouting)

  4. Photoperiodism (flowering in response to length of day)
• Other plant growth responses

  1. Apical dominance

  2. Leaf abscission

  3. Fruit growth

  4. Fruit ripening
• Plant responses to water or water stress

  1. Germination

  2. Stomatal closing

  3. Local cell death
• Thigmotropism


  • Movement in response to touch
  • Slow thigmotropism (affects direction of growth)
  • Fast thigmotropism (rapid response like Venus flytrap)