Homeostasis

Question 1

Define Physiology

Answer 1

The study of the normal functioning of living organisms and their component parts

Question 2

What are the Major Organ Systems?

Answer 2

Integumentary, Muscular, Skeletal, Nervous, Endocrine, Circulatory, Lymphatic, Respiratory, Digestive, Urinary, Reproductive systems

Question 3

What main point did Claude Bernard emphasize?

Answer 3

the stability of the internal environment in spite of the variability of the external environment

Question 4

Changes in the External Environment are compensated mostly by what?

Answer 4

the Extracellular Fluid (internal environment of the body)

Question 5

Who coined the term “homeostasis”? What does it mean?

Answer 5

Walter B. Cannon

It means a condition which may vary, but which is relatively constant

Question 6

What are some Homeostatically regulated variables?

Answer 6

Osmolarity, Temperature, pH, Nutrients (e.g. glucose), Water, Inorganic ions (e.g. Na+, Ca++), Oxygen, Hormones, Other chemical messengers

Question 7

What is Homeostasis regulated by?

Answer 7

Physiological control systems

Question 8

Describe the 4 major components of Physiological Control Systems

Answer 8

1. Input Signal : Change in regulated variable; Detected by sensors
2. Controller / Integrating Center : Integrates incoming info; Initiates response
3. Output Signal : Creates response
4. Response : Carried out by effectors

Question 9

Give an example of a Long-distance (reflex) control system

Answer 9

Regulation of Body Temp (35.5-37.2 degrees C)

Question 10

What is a Feedback Loop?

Answer 10

The response to a signal feeds back to influence the signal

Question 11

What are the features of Negative Feedback?

Answer 11

1. Response triggered when variable falls outside of range around setpoint
2. Response decreases/eliminates signal
3. Involves oscillations around a setpoint
4. Homeostatic (maintains stability)

Question 12

Give an example of a Negative Feedback. What are the Signal and Response?

Answer 12

Control of Blood Glucose Levels
Input Signal = rising glucose level
Response = as body cells take up blood glucose, glucose levels in blood decline, and insulin release stops

Question 13

What are the features of Positive Feedback?

Answer 13

1. Response increases the signal, which then increases the response
2. Must be terminated by an even outside the feedback loop
3. Not homeostatic (increases variability)

Question 14

Give an example of a Positive Feedback. What are the Signal and Response?

Answer 14

Oxytocin and Uterine Contractions
Input Signal = baby drops lower in uterus to initiate labor
Response = uterine contractions

Question 15

What are the features of Feedforward Control? Give 2 examples.

Answer 15

1. Involves responses to anticipated changes
2. Doesn’t involve sensing of the regulated variable
3. Homeostatic (maintains stability)
   e. g. food smells elicit salivation & secretions of stomach fluids before food is ingested
   e. g. breathing & HR increase at beginning of exercise before physiological effects occur to stimulate these changes

Question 16

Describe the 3 [simple] types of Cell-Cell Communication.

Answer 16

1. Gap Junctions : form direct cytoplasmic connections btwn adjacent cells
2. Contact-Dependent Signaling : require interactions btwn membrane molecules on two cells
3. Local Chemical Communication : Autocrine signals act on the same cell that secreted them. Paracrine signals are secreted by one cell and diffuse to adjacent cells

Question 17

Describe the two components of Long-Distance Communication

Answer 17

a. Endocrine system:
- uses chemical signals – hormones
- hormones are secreted into blood & act on target cells (cells that contain specialized receptors for the particular hormone)
b. Nervous system:
- uses electrical signals (mostly within cells) – action potentials, receptor potentials
- uses chemical signals (btwn cells) – neurotransmitters, neuromodulators, neurohormones [neurocrines]

Question 18

Describe Lipopillic (Hydrophobic) Signal Molecules. Give an example.

Answer 18

• Diffuse into all cells
• Binds to protein or glycoprotein receptors in cytoplasm or nucleus (usually)
• Activate or repress gene transcription (and increase or decrease protein synthesis)
• Effects develop over hours (fairly slow)
  e. g. steroid hormones

Question 19

Describe Lipophobic (Hydrophilic) Signal Molecules. What are the 4 categories of membrane receptors?

Answer 19

• Cannot diffuse into cells; remain in extracellular fluid
• Bind to protein or glycoprotein receptors in cell membrane
• Rapid response (milliseconds to minutes)
  1. Receptor-channels (ionotropic)
  2. Receptor-enzymes (metabotropic – activate signal-transduction pathways)
  3. G protein-coupled receptors (metabotropic– activate signal-transduction pathways)
  4. Integrin receptors (metabotropic– activate signal-transduction pathways)

Question 20

Describe Receptor-channels (ionotropic receptors)

Answer 20

[Lipophobic/Hydrophillic Signal Molecule)

• Ligand-gated ion channels
• Ligand binds to receptor -> opens or closes ion channel gate -> alters ion flow across cell membrane
• Fastest-acting receptors (sec to mins)
• Most are neurotransmitter receptors in nerves and muscles

Question 21

Describe the mechanism of [Lipophobic] Signal Transduction pathways

Answer 21

signal molecule binds to membrane receptor -> activation of receptor ->
-> activation of protein kinases -> phosphorylation of proteins -> cellular response
or
-> acctivation of amplifier enzymes -> increase 2nd messenger inside cell -> intracellular cascase –> cellular response

Question 22

Describe Receptor-Enzymes (metabotropic receptors)

Answer 22

[Lipophobic/Hydrophillic Signal Pathway]

• Receptor on extracellular side of cell membrane, enzyme on cytoplasmic side (same or different proteins)
• Binding of ligand to receptor activates enzyme

Question 23

Describe G Protein-Coupled Receptors (metabotropic receptors)

Answer 23

[Lipophobic/Hydrophillic Signal Pathway]

• Receptor is linked to a G protein (3 part, membane-bound protein, binds GDP and GTP)
• Binding of ligand to receptor activates G protein (activated G protein can open an ion channel or activate an amplifier enzyme inside the cell)

Question 24

Describe 6 general features of Signal Pathways

Answer 24

1. Diff. ligands may bind to same receptor
2. 1 ligand may bind to diff. receptors (isoforms)
3. Receptor down-regulation/desensitization (decrease receptor # &/or affinity; often in response to increase conc. of ligand)
4. Receptor up-regulation (increase in receptor #; often in response to decrease conc. of ligand)
5. Agonists and Antagonists (activate receptors for another ligand / block action of another ligand’s receptors
6. Termination of Signals (degradation of ligands by extracellular enzymes; transport of ligands into neighboring cells; endocytosis of receptor-ligand complex)