Chapter 6 - Communication, Integration, and Homeostasis

Question 1

Describe three forms of local communication and two forms of long-distance communication.

Answer 1

Local:
1) Gap junctions –> form direct cytoplasmic connections between adjacent cells
2) Contact-dependent signals –> require interaction between membrane molecules on two cells
3) Diffusing chemicals
- autocrine –> act on the same cell that
secreted them
- paracrine –> secreted
by one cell and diffuse to adjacent cells

Long-Distance:
1) blood transport (hormones) –> hormones secreted by endocrine glands/cells into blood; only target cells w/ receptors for the hormone respond to the signaling
2) neurochemicals
- neurotransmitters –> chemicals secreted by neurons that diffuse across a small gap to the target cell
- neuromodulators
- neurohormones –> chemicals released by neurons into the blood for action at distant targets

Question 2

Explain the general sequence of events that follow lipophilic ligand binding to intracellular receptors.

Answer 2

lipophilic signal molecules diffuse thru the cell membrane –> signal binds to receptor in cytosol –> receptor goes to nucleus –> transcription + translation –> binding to cytosolic/nuclear receptors triggers slower responses related to changes in gene activity

Question 3

Describe the general sequence of events that follow lipophobic ligand binding to a cell surface receptor.

Answer 3

extra cellular signal molecule binds to a cell membrane –> binding triggers rapid cellular responses

Question 4

Name and describe four major groups of cell surface receptors.

Answer 4

1) Chemically gated (ligand-gated) ion channels = receptor-channels –> Ligand binding opens or closes the channel

2) G protein-coupled –> Ligand binding to a G
protein–coupled receptor opens an ion channel or alters enzyme activity

3) Receptor-enzymes –> Ligand binding to a
receptor-enzyme activates an intracellular enzyme

4) Integrin receptors –> Ligand binding to integrin receptors alters enzymes or the cytoskeleton

Question 5

Explain how cascades and signal amplification play a role in signal transduction.

Answer 5

Cascade:
- signal activates an inactive “A” –> which activates inactive B…etc.

Amplification:
- each A can activate multiple B’s

Question 6

What signals do cytokines act as?

Answer 6

both local and long-distance signals

Question 7

What is the most rapid signal pathway to change ion flow?

Answer 7

channels

Question 8

When G proteins are activated, what do they do?

Answer 8

• open ion channels in the membrane
• alter enzyme activity on the cytoplasmic side of the membrane

Question 9

Outside of the cell, what do integrins bind to?

Answer 9

extracellular matrix proteins or to ligands

Question 10

Inside of the cell, what do integrins attach to?

Answer 10

the cytoskeleton via anchor proteins

Question 11

what are novel signal molecules?

Answer 11

• calcium
• gases
• lipids

Question 12

List five ways calcium acts as an intracellular messenger.

Answer 12

1) Ca++ binds to calmodulin and alters enzyme or transporter activity or gating of ion channels.

2) Ca++ binds to other regulatory proteins (such as troponin in striated muscle) and alters movement of contractile or cytoskeletal proteins such as microtubules.

3) Ca++ binds to regulatory proteins to trigger exocytosis of secretory vesicles.

4) Ca++ binds directly to ion channels to alter gating state.

5) Ca++ entry into a fertilized egg initiates development of the embryo.

Question 13

Describe the advantages and disadvantages of gaseous second messenger molecules.

Answer 13

Advantages:
- fast-acting

Disadvantages:
- gone quickly
- can only act on nearby cells

Question 14

what can carbon monoxide (CO) activate?

Answer 14

guanylyl cyclase and cGMP

Question 15

what can nitric oxide (NO) activate?

Answer 15

guanylyl cyclase –> cGMP

Question 16

Apply the concepts of specificity, competition, affinity, and saturation to receptors and their ligands.

Answer 16

1) can have multiple ligands that can bind to one receptor
- must have certain specificity (similar enough in structure)
2) one ligand can also have multiple receptors
- and therefore can have different effects (constriction vs dilation)

Question 17

Explain the role of up-regulation, down-regulation, and pathway termination in modulating cell responses to receptors and their ligands.

Answer 17

• up regulation –> Inserts more receptors in cell membrane
  *don’t release saturation as quickly –> makes the cell more responsive to the signal molecule –> won’t reach saturation as quickly
• down regulation –> Decrease in receptor number
  *take time
• use energy
• desensitization –> By binding a chemical modulator to receptor
• Phosphorylating a b-adrenergic receptor will desensitize it
• pathway termination –> cells have to be able to stop pathway
  *remove free or bound ligand (terminates signal pathway)

Question 18

List Cannon’s four postulates of homeostatic control and give an example of each.

Answer 18

1) Nervous system helps regulate internal environment
ex:

2) Some systems are under tonic control (usually sympathetic control)
ex: The signal is always present but changes in intensity –> one system used and either increased or decreased (depends on how many neurotransmitters are released –> depends on APs)

3) Some systems are under antagonistic control (2 systems have opposite effects when attached to the same system)
ex: antagonistic neurons control heart rate: some speed it up, while others slow it down

4) One chemical signal can have different effects in different tissues
ex:

Question 19

Compare the speed, specificity, types of signals, and duration of action in neural and endocrine reflexes. How is stimulus intensity coded in each type of reflex?

Answer 19

Neural Reflexes:
- speed –> faster
- specificity –> more specific (will only effect cells where neuron ends)
- types of signals –>
- duration –> does not last as long

Endocrine reflexes:
- speed –> slower
- specificity –> less specific (will effect cells that respond to whatever is released)
- types of signals –>
- duration –> lasts longer