Homeostasis and Transport

Question 1

Homeostasis

Answer 1

• physical function or variables that fluctuate within a narrow (usually) and predictable range`
• ex: body temp
• can refer to any variable: body temp, blood pressure, blood sugar, different ions, etc.
• just because an organism does not have homeostasis for one variable (ie ectotherms do not for body temp), does not mean that it does not maintain homeostasis for other variables

Question 2

Homeostasis Advantages

Answer 2

• if something is off, your body knows to send out alarms
• buffered from environment, freedom from environment
• you know the infrastructure works well - need less of it
• when it works, it’s efficient
• doesn’t require conscious effort to check itself

Question 3

Homeostasis Disadvantages

Answer 3

• requires energy
• dependent on the infrastructure working - since you have less, you could be in trouble if there are drastic changes
• your body is always checking to make sure its working

Question 4

Feedback Systems

Answer 4

• systems where the output affects the process
• Positive: not used often, generally leads to spiraling out of control - ex labor: you want to get the baby out
  
  • the product signals to create more and more of the product
• Negative: really helpful for homeostasis
  
  • the product signals to make less of the product, the lack of the product allows for more of it to be made

Question 5

Feedforward Systems

Answer 5

• responses to systems before it’s needed

- ex: salivate when you smell food because you know food is coming

Question 6

Homeostatic Control: Reflex Arc

Answer 6

stimulus –> receptor –> integrating center –> effector –> response

• negative feedback: the response turns off the stimulus
• afferent pathway: receptor to integrating center
• efferent pathway: integrating center to effector
• integrating center is usually the brain

Question 7

Reflex Arc Example: body temp

Answer 7

decreased body temp (stimulus) –> temperature sensitive neurons (receptor) - nerves (afferent pathway) -> specific neurons in brain compare to set point and alter rates of firing (integrating center) - smooth muscle in skin, blood vessels increase constriction, decrease blood flow (efferent pathway) -> decrease heat loss (response)

OR (integrating center) - skeletal muscles contract in shivering (efferent pathway) -> increase heat production (response)

Question 8

Everything is connected

Answer 8

one response may fix an off variable (ex: shivering improves body temp) but it takes energy so it may throw off other variables (ex: blood sugar) which requires the use of more controls to maintain

Question 9

Homeostatic Control: Levels of Response

Answer 9

• Hormones
  
  • gland secretes hormone –> hormone travels in blood vessel –> target cells are in distant places in the body
  • can affect any cell that it can bind to on its way to target, send out a lot because they diffuse
• Nerve Cells
  
  • electrical signal causes release of NT from neuron
  • NT travels across synaptic cleft, and only hits cells on other side (they are neurons or effector cells)
• Paracrine Signaling: signal affects cells near the cell that sent it
• Autocrine Signaling: signal affects the cell that sent it

Question 10

Chemical messengers

Answer 10

• Receptor Locations: cytoplasm, nucleus, cell membrane
• First Messenger: chemical released outside of cell
  
  • bind to receptor on cell, initiate cellular response
  • signaling cascade creates secondary messenger
• Secondary Messenger: inside the cell and causes changes in the cell
• complex signaling cascades are common
  
  • harder to get the job done, but really hard to screw up –> easier to maintain homeostasis

Question 11

Shape drives Function

Answer 11

• proteins make up receptors
• tertiary structure is really important because it determines shape
• shape determines what can bind to the receptor
• receptors change shape when something binds to them
• shape change in receptors turns their ability to react with things on and off

Question 12

Fluids

Answer 12

• you are 60% fluids
  
  • 2/3 of fluid is intracellular (ICF)
  • 1/3 of fluid is extracellular (ECF)
    - 80% of ECF is interstitial
    - 20% of ECF is plasma

Question 13

Comparing the fluids

Answer 13

• ICF is very diff from ECF in ion content because it is separated by the membrane
• the two types (interstitial and plasma) of ECF are similar
• proteins and potassium are found more in the cell
• sodium is found more outside the cell

Question 14

Polarity

Answer 14

• like dissolves like, like things clump together
• polar things can’t get through the plasma membrane because the membrane is nonpolar
• polar molecules have an uneven sharing of charge among atoms
• nonpolar has an equally shared charge and the molecule will be more even looking
• nonpolar can get through the plasma membrane

Question 15

Polarity of Chemical Messengers

Answer 15

• first messengers are polar, they bind to receptors outside of membrane, don’t go through it
• non polar substances don’t need to worry about messengers because they go through membrane and not channels

Question 16

Transport Across the Membrane

Answer 16

• Diffusion
• Mediated Transport
  
  • Facilitated Diffusion
  • Active Transport
• Osmosis

Question 17

Diffusion

Answer 17

• through pores in the membrane (aka channels)
  
  • open = leak channels, let whatever can fit through
  • gated: can open and close
    
    • ligand gated: ligands are like keys, bind to and open channel
    • voltage: open when specific voltage is on the other side
    • mechanical: responds to physical deformation, ex stretching the membrane
• or not through pores - lipid soluble things and really small things

Question 18

Specificity of channels

Answer 18

• channels can be very specific, only let molecule with specific shape through
• some let only one molecule type in, some let a family of molecules in

Question 19

Mediated Transport

Answer 19

• Two Types: Facilitated Diffusion and Active Transport
• lots of specificity
• become saturated - only so many molecules can go through at once because there are only so many channels
  
  • the rate of transport levels off, it does not for diffusion
• channell closed until molecule binds, then change shape and molecule moves to other side

Question 20

Rate of Transport Determined by

Answer 20

• Number: theres only so many transporters so only that much stuff can be transported
• Rate of Conformational Change: transporters can only open and close so quickly
• Becomes Saturated - the rate of transport levels off (unlike diffusion

Question 21

Facilitated Diffusion

Answer 21

• Energetics: no energy required, still a type of diffusion
• Directionality: down concentration gradient, high to low
• Types of Molecules: polar (nonpolar doesn’t need channel), and bigger things (smaller use open channel)
• Used for glucose - glucose follows glucose gradient, but there are enzymes right next to the membrane that convert it to glucose-6-phosphate to keep the glucose gradient favorable, no energy required to transport glucose

Question 22

Active Transport

Answer 22

• against a diffusion gradient
• Primary: direct use of ATP
• Secondary: use of electrochemical gradient to drive the process
• see notebook for picture

Question 23

Secondary Active Transport

Answer 23

• use of an electrochemical gradient to drive the process
• usually uses sodium to bring a solute into the cell
  
  • Na+ follows its concentration gradient from high to low into the cell
  • it is also attracted to neg charge inside cell
• cotransport: solute moves in the same direction as Na+
• countertransport: solute moves opposite direction as Na+
• solute is always going against its gradient - otherwise it wouldn’t be active

Question 24

Osmosis

Answer 24

• aquaporins: channels for water specifically, leak channels
• osmolarity - molarity of water, concentration of water
  - high solute = low osmolarity
  - milli Osmols, mOsm
  - land mammals are 300 mOsm
• nonpenetrating solutes do not move, water does

Question 25

Comparing Cells Osmolarity for Nonpenetrating Solutes

Answer 25

• hypertonic: environment has higher solute conc
• isotonic: env. has same solute conc.
• hypotonic: env. has less solute conc.
• nonpenetrating: solutes cannot go through membrane, water is going to move to balance conc
• see notebook

Question 26

Endocytosis and Exocytosis

Answer 26

• Endo: grab a bunch of stuff, put it in a vesicle, and bring it into cell
• Exo: bring a vesicle of waste or whatever to plasma membrane and release its contents out of cell
• use these for big changes - either big molecules or lots of little ones
• nonpolar go in/out on their own, don’t need these
  - use chaperones to control nonpolar