1
Q
Homeostasis definition
A
- Maintenance of a relatively constant internal environment in the presence of an ever- changing external environment
2
Q
Homeostasis characteristics
A
- Dynamic (not an unchanging) condition
- Achieved by physiological processes (homeostatic mechanisms)
3
Q
Homeostatic mechanisms
A
- Detect changes in the body and act to counter the changes
- Balance concept is inherent
4
Q
Homeostasis refers to
A
- The dynamic mechanisms that detect deviations in physiological variables from their “ideal” values
5
Q
Homeostasis initiates
A
- Effector responses that restore these variables to the optimal physiological range
6
Q
Control systems provide
A
- Communication between cells, tissues, and organs
7
Q
Types of control systems
A
- Nerves only
- Endocrines only
- Dual systems
8
Q
Dual systems
A
- Provide backup systems
- Greater plasticity of function or control
- Some faster, some slower
9
Q
Chemically addressed systems
A
- Most control is mediated via chemical messengers
- Nervous system (via neurotransmitter)
- Endocrines
- Local chemicals
10
Q
Types of chemically addressed systems
A
- Local chemicals
- Local hormones
- Neurotransmitters
- True hormones
11
Q
Local chemicals
A
- Oxygen, carbon dioxide, other metabolites
- Act on adjacent cells, geared to metabolism
- Probably play no regulatory function
12
Q
Local hormones
A
- Gastrin, secretin, other GI hormones, prostaglandins
- Paracrines
- Autocrines
13
Q
Autocrines
A
- Hormone or neuronal secretion that may, after being secreted from a cell, act back onto cell of origin
14
Q
Neurotransmitters
A
- Released into interstitial fluids (synapse)
- Affect only cells in synaptic contact
15
Q
True hormones
A
- Released into circulating body fluids, reaching all cells of the body
- Endocrines
- Neurocrines (neurosecretions)
16
Q
Characteristics of a true hormone
A
- Chemical substance
- Secreted directly into the blood by discrete specialized cells
- In response to a specific stimulus (neural or blood-borne)
- Amounts vary with the strength of stimulus
17
Q
True hormones are found
A
- Only in minute (physiological) concentrations in blood
18
Q
When carried to their target cells, true hormones
A
- Exert specific effects that frequently involve the regulation of preexisting cellular reactions
19
Q
Six components of control systems
A
- Sensor
- Afferent pathway
- Error signal generator
- Integrator
- Efferent pathway
- Effector
20
Q
Sensor
A
- Monitors environment
21
Q
Afferent pathways
A
- Signals to integrator
22
Q
Integrator
A
- CPU; center
23
Q
Efferent pathway
A
- Signals from integrator
24
Q
Effector
A
- Changes environment
25
Set point
- Ideal value of a control system's parameter
26
Error signal
- Difference between set point and actual value
27
Gain
- Ratio of correction to error
28
Negative feedback
- Tries to restore homeostasis
| - Reduces error signal
29
Positive feedback
- Disturbs homeostasis
- Increases error signal
- Often employed to generate the rising phase of a cyclic event (e.g. blood clot, action potential, birth)
- Self-limiting normally
30
Feedforward
- Disturbs homeostasis
- Regulatory mechanism for meeting future needs
- Works with negative feedback controls
31
Components of electrical communication involve
- Nerves alone
32
Components of chemical communication involve
- Endocrines alone
33
Components of electrical and chemical communication combined
- Neuroendocrine
34
Balance depends on
- Rate of gain vs. loss of some property
35
Positive balance
- Net gain
| - Rate of gain > rate of loss
36
Negative balance
- Net loss
| - Rate of gain < rate of loss
37
Stable balance
- No net change
| - Rate of gain = rate of loss
38
Balance incorporates the concepts of
- Steady state
- Equilibrium
- Both are states of stable balance
39
Steady state
- Requires energy to maintain it
40
Equilibrium
- Does not require energy to maintain it
41
Nervous system control
- Extrinsic control system
- Relatively fast system
- Controls many of one’s quick/immediate responses
42
Endocrine system (extrinsic)
- Controls responses that need to continue for long times or occur more slowly
- Works with/alongside the nervous system
- Keeping systems essentially in balance and allowing cells, tissue, organs and the entire body to adjust to changes in the environment
43
Fever involves
- Up-regulation and down-regulation
| - Thermostatic resetting
44
Effects of a fever on homeostasis
- Set point for body temp is elevated
- Release of pyrogen(s) by microorganisms (such as certain bacteria)
- Pyrogen changes the set point
- Increased heat production by shivering
- Heat conservation by cutaneous vasoconstriction
Physiology I: Cellular Neuro
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