Homeostasis Flashcards
Define Physiology
The study of the normal functioning of living organisms and their component parts
What are the Major Organ Systems?
Integumentary, Muscular, Skeletal, Nervous, Endocrine, Circulatory, Lymphatic, Respiratory, Digestive, Urinary, Reproductive systems
What main point did Claude Bernard emphasize?
the stability of the internal environment in spite of the variability of the external environment
Changes in the External Environment are compensated mostly by what?
the Extracellular Fluid (internal environment of the body)
Who coined the term “homeostasis”? What does it mean?
Walter B. Cannon
It means a condition which may vary, but which is relatively constant
What are some Homeostatically regulated variables?
Osmolarity, Temperature, pH, Nutrients (e.g. glucose), Water, Inorganic ions (e.g. Na+, Ca++), Oxygen, Hormones, Other chemical messengers
What is Homeostasis regulated by?
Physiological control systems
Describe the 4 major components of Physiological Control Systems
- Input Signal : Change in regulated variable; Detected by sensors
- Controller / Integrating Center : Integrates incoming info; Initiates response
- Output Signal : Creates response
- Response : Carried out by effectors
Give an example of a Long-distance (reflex) control system
Regulation of Body Temp (35.5-37.2 degrees C)
What is a Feedback Loop?
The response to a signal feeds back to influence the signal
What are the features of Negative Feedback?
- Response triggered when variable falls outside of range around setpoint
- Response decreases/eliminates signal
- Involves oscillations around a setpoint
- Homeostatic (maintains stability)
Give an example of a Negative Feedback. What are the Signal and Response?
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
What are the features of Positive Feedback?
- Response increases the signal, which then increases the response
- Must be terminated by an even outside the feedback loop
- Not homeostatic (increases variability)
Give an example of a Positive Feedback. What are the Signal and Response?
Oxytocin and Uterine Contractions
Input Signal = baby drops lower in uterus to initiate labor
Response = uterine contractions
What are the features of Feedforward Control? Give 2 examples.
- Involves responses to anticipated changes
- Doesn’t involve sensing of the regulated variable
- 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
Describe the 3 [simple] types of Cell-Cell Communication.
- Gap Junctions : form direct cytoplasmic connections btwn adjacent cells
- Contact-Dependent Signaling : require interactions btwn membrane molecules on two cells
- 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
Describe the two components of Long-Distance Communication
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]
Describe Lipopillic (Hydrophobic) Signal Molecules. Give an example.
- 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
Describe Lipophobic (Hydrophilic) Signal Molecules. What are the 4 categories of membrane receptors?
- 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)
Describe Receptor-channels (ionotropic receptors)
[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
Describe the mechanism of [Lipophobic] Signal Transduction pathways
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
Describe Receptor-Enzymes (metabotropic receptors)
[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
Describe G Protein-Coupled Receptors (metabotropic receptors)
[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)
Describe 6 general features of Signal Pathways
- Diff. ligands may bind to same receptor
- 1 ligand may bind to diff. receptors (isoforms)
- Receptor down-regulation/desensitization (decrease receptor # &/or affinity; often in response to increase conc. of ligand)
- Receptor up-regulation (increase in receptor #; often in response to decrease conc. of ligand)
- Agonists and Antagonists (activate receptors for another ligand / block action of another ligand’s receptors
- Termination of Signals (degradation of ligands by extracellular enzymes; transport of ligands into neighboring cells; endocytosis of receptor-ligand complex)
