BIO-249 Lecture Exam 6: Cell Signaling & Endocrine System

Gap Junction Definition

• shortest distance signaling

• Cells have to be RIGHT NEXT to each other

• Chemicals, proteins, & signal molecules simply diffuse across them

Contact Signaling Definition

• using membrane proteins as a receptor AND ligand

• the first membrane protein (ligand) binds to the receptor’s active site to create a response

Autocrine/Paracrine Signaling Definition

• Similarities:

  1. SHORT DISTANCE

  2. BOTH secrete lots of signaling molecules that bind to receptors

  3. BOTH heavily rely on diffusion! which limits the signaling distance to the local level

• Autocrine Signaling: cell sends signal to ITSELF

• Paracrine Signaling: cell releases signal molecules to NEARBY cells

Hormone/Endocrine Signaling

LONG-DISTANCING signaling

1. Endocrine Cell RELEASES chemical signal to the bloodstream

2. Chemical signal in the bloodstream → hormone

3. Hormone binds to the receptors on the target cells

   • Target cells NEED the receptor for the response, if they don’t have it

4. Response is created

Neurotransmitter Signaling

LONG-DISTANCING SIGNALING

1. Electrical signal reaches the axon terminal

2. Axon terminal RELEASES neurotransmitters

3. Neurotransmitters bind to receptors & send commands to the target cell (postsynaptic cell)

4. Response is created

Neurohormone Signaling

• LONG-DISTANCE Signaling

1. Electrical signal travels down the neuron (neuro part)

2. Axon terminal secretes neurotransmitter into the bloodstream (hormone part)

3. Hormone goes down the bloodstream (acts like a hormone)

4. Hormone interacts with the target cells

5. Response is created

Cell Communication Summary

• SHORT DISTANCE

  1. Gap Junction

  2. Contact Signaling

  3. Autocrine

  4. Paracrine

• LONG DISTANCE

  1. Endocrine/Hormone

  2. Nervous system Signaling

     1. Neurotransmitters

     2. Neurohormones

1. What kind of responses can you expect to get from a chemical signal?

2. What kind of cellular processes can chemical signals regulate?

Chemical Signal RESPONSES

1. Enzyme activity: working more efficiently or shutting them off

2. Membrane proteins

   • opening/closing them

3. Gene Activity: creating new proteins

Cellular Processes Regulated

1. Homeostasis

2. Reproduction

3. Growth

4. Development

Describe the generalized signal pathway.

• Given a signal molecule, what events occur from the time the signal binds with the receptor to the target cell’s response?

1. Signal Molecule/Ligand binds to membrane receptor protein

   • signal molecule/ligand = first messenger (outside the cell)

2. Ligand & receptor protein activate intracellular (within the cell) signal molecules

3. Intracellular signal molecules alter target proteins

   • Intracellular signal molecules are the second messenger system

4. Target proteins create a response

What are second messengers?

• Intracellular (within the cell) signal molecules that alter target proteins

• Quickly spread out throughout the cell via diffusion

Where are two places in the cell where can we find receptors for chemical signals?

1. Extracellularly (on the cell membrane)

   • Signal molecules/ligands: proteins because they’re too big

2. Intracellularly (inside the cell membrane)

   • Signal molecules/ligands: lipids because they can diffuse through the cell membrane

What are the two chemically different groups of hormones in the human body? Describe the characteristics of each group. Note: see the table in the lecture slides.

How do hydrophilic hormones trigger a cell response?

• Where are the receptors?

• How do the receptors lead to a response?

1. Peptide hormone (first messenger) binds to the receptor on the cell membrane

2. G protein system activates

3. Second messenger is created

4. Second messenger changes protein activity

How do hydrophobic hormones trigger a cell response?

• Where are the receptors?

• How do the receptors lead to a response?

1. Steroid hormone diffuses straight into the cell & binds to the intracellular receptor

2. Transduction occurs & gene expression starts or is altered

3. Transcription of DNA occurs, creating mRNA

4. Translation of mRNA creates protein, which leads to the alteration of cellular structure & activity

For hormone feedback loops, where is the receptor?

Receptor in endocrine eclls

1. Membrane protein receptors

2. Intracellular receptors

What is an efferent pathway, and what is it typically in a hormone feedback loop?

• Efferent Pathway: how the control center relays info to the effectors using hormones

• Hormone Feedback Loop Process

  1. Stimulus:

     1. humoral (blood)

     2. neural (nervous system)

     3. Hormonal (endocrine)

  2. Receptor (on/in the endocrine cells)

     1. Membrane Protein Receptors ON the cell membrane

     2. Intracellular Receptors IN the cell

  3. Control Center: endocrine cells

  4. Efferent Pathway: hormones TRAVELING via the bloodstream

  5. Effector: other cells and/or organs

  6. Response: Long-term changes in cells

Describe how blood sugar (e.g., glucose plasma concentration) is regulated with insulin

1. Stimulus: Humoral- increase in blood sugar

2. Receptor: receptor in beta cells of pancreas

3. Control Center: Beta cells

   • signal pathway response: secrete insulin

4. Efferent Pathway: Insulin (secreted into the bloodstream)

5. Effectors

   • Liver

   • Other Cells

6. Response

   1. Liver: Glycogenesis, creating glycogen from glucose

   2. Other cells: intake of glucose

   3. Overall: decrease in blood sugar

Describe how blood sugar (e.g., glucose plasma concentration) is regulated with the glucagon hormone

1. Stimulus: Humoral: decrease in blood sugar

2. Receptor: receptor in the alpha cells of the pancreas

3. Control Center: alpha cells

   • singal pathway response: secrete glucagon hormone

4. Efferent Pathway: Glucagon (travels via bloodstream)

5. Effector: Liver

6. Response

   • Liver: glycogenolysis, INCREASE in blood sugar

Insulin Issues

• What will happen to plasma glucose levels if beta cells can’t make insulin?

• What will happen to plasma glucose levels if other cells don’t respond to insulin?

Blood sugar remains high for both questions

What is the vital function of Thyroxine?

1. Affects most cells in the body

2. Support development

3. Increase metabolic rate

Describe how the hypothalamus and anterior pituitary gland regulate thyroid hormone (a.k.a. Thyroxine). Make sure you include the following hormones: thyrotropin-releasing hormone (TRH), Thyroid-stimulating hormone (TSH).

1. Hypothalamus secretes thyrotropin-releasing hormone (TRH)

   • flows through the portal system until it reaches the Anterior pituitary gland

2. TRH will interact with the cells in the anterior pituitary gland → anterior pituitary gland secretes thyroid-stimulating hormone (TSH)

3. TSH flows OUT into the bloodstream & reaches the thyroid gland

4. The thyroid gland makes thyroxine (thyroid hormone- TH)

How does iodine deficiency creat Goiters (an enlarged thyroid)?

See pic!!

Be comfortable with the Thyroxine feedback loop to describe the effects of changing various feedback loop components.

1. Thyroid hormone (thyroxine) goes BACK to the hypothalamus & anterior pitutiary gland

2. TOO MUCH thyroxine inhibits the secretion of TRH at the hypothalamus & TSH at the anterior pituitary gland

3. TRH and TSH production decrease

4. Thyroxine production decreases

What happens when you add “exogeneous” testosterone?

Decrease body production of testosterone (see pic!)

Antagonistic Hormone Interaction

• Antagonistic: hormone responses are OPPOSITE of one another

• increase insulin concentration, decrease glucagon concentration

Permissive Hormone Interaction

• Hormone A (thyroid hormone) gives “permission” to hormone B (sex hormone) to function

• Sex hormones work by themselves, but work BETTER in the presence of thyroid hormone

Syngeristic Hormone Interaction

• When multiple hormones come together, they can amplify their effect

• These common hormones have a common RESPONSE/EFFEt, they all do the same thing (they don’t give each other permission)

What are the 3 hormone interactions?

1. Antagonistic

2. Permissive

3. Synergistic