MCDB 111 -Midterm 1

• Homeostasis


  Life in balance
• Equilibrium


  a system that is stable over time without the input of external energy
• Steady state


  a system that can only be maintained with the input of external energy
• What parameters does the body need to regulate?

  gases (O2 and CO2),

  nutrient availability,

  waste removal,

  temperature,

  water (ion balance),

  volume/pressure,

  pH
• What are the components of a biological regulatory system?

  receptors, integrating center, effectors, negative feedback
• Receptors


  to monitor homeostatic parameter (example: heat loss and body temperature via nerves)
• Integrating center


  to analyze the information from the receptors and bring about the proper response
• Effectors


  a way to bring about the desired change
• Negative feedback


  A way to turn the effectors off when homeostasis is restored
• Afferent pathway


  Receptor to integrating center ("approaching" integrating center)
• Efferent pathway


  Integrating center to effector ("escaping" integrating center)
• Why does homeostasis not maintain an exact set point?

  The system always fluctuates because the system shuts off when you reach the set point rather than gradually decreasing activity. The system is reactionary, so it only responds to abnormal state and won't keep it in the one desired range
• Integrating centers examples


  Brain and pancreas
• Components of negative feedback systems

  Sensor (receptor), set point, integrator, effector
• Speed of response for endocrine system

  slow (minutes to days)
• Duration of action for endocrine system

  Long-term changes
• Travel (how does message reach target) for endocrine system

  Hormones travel through the blood and cells with specific receptors respond
• Target for endocrine system

  Far reaching (many target cells throughout the body that contain appropriate receptors)
• Speed of response for nervous system

  Very fast (fractions of seconds)
• Duration of action for nervous system

  Short-lived
• Travel (how does message reach target) for nervous system


  Nerve cells release neurotransmitters that travel to target organs such as muscles and glands
• Target for nervous system


  Local neurons or effector cells, very small target
• neurosecretory neurons


  neurons that release hormones into the bloodstream
• When do the nervous and endocrine systems overlap?

  Seen in neurosecretory neurons which can be seen in the adrenal medulla and the hypothalamus.
• Do autocrine/paracrine agents travel through the blood?

  No, they do NOT travel through blood. They provide local control within tissues/organs
• Paracrine agent


  Produced by one cell and acts on surrounding cells
• Autocrine agent


  Produced by same cell that is targeted
• How is short term modulation/amplitude of responses controlled in endocrine system?

  Concentration of the circulating (and available) hormone is key to determining the short-term strength of the response
• How is short term modulation/amplitude of responses controlled in nervous system?

  Frequency of impulses (action potentials) of nerve cells in key to determining the short-term strength of the response
• Acclimatization


  Enables organisms to survive rapid environmental chances by alteration of existing homeostatic mechanisms
• Lipid bilayer


  Serves as a barrier to the movement of mostpolarmolecules in or out of cell (lipid soluble pass directly through while other molecules require transmembrane proteins)
• Examples of transmembrane proteins


  Ion channels and transporter proteins
• Diffusion


  random thermal motion will cause molecules to move from high to low concentrations
• Flux


  rate of solute flow per unit area
• Net flux


  difference between two one-way fluxes. Always occurs in direction from high to low concentrations
• Diffusion equilibrium


  When concentrations of intercellular and extracellular are the same
• What is the main determinant that influences the net flux of a molecule across a membrane?

  Mass of the diffusing molecules (smaller molecule moves faster)
• Fick's first law of diff

  J = D(Co - Ci)

  J is flux units (mol s-1 m-2), D is diffusion coefficient, Co is outside concentration, Ci is inside concentration
• Do nonpolar molecules diffuse across plasma membranes slow or fast?

  Diffuse rapidly because they can dissolve in the nonpolar regions of the membrane occupied by fatty acid chains of the membrane phospholipids
• Do polar molecules diffuse across plasma membranes slow or fast?

  Diffuse very slowly or not at all