1/18: Homeostasis Flashcards
What is homeostasis?
Process of maintaining a relatively constant/stable internal environment (set point) in spite of changing external environments
What is homeostasis important for?
Cell functions
What is the external environment?
Outside the body
What is extracellular fluid?
Internal environment; inside body, outside cells
What are the two compartments of the ECF?
- Plasma
- Interstitial fluid
Where is plasma?
In blood vessels, fluid portion of blood
Where is interstitial fluid?
Outside blood vessels and cells
What is intracellular fluid?
Intracellular environment = inside cells
Where is the intracellular fluid?
Cytoplasm
What are examples of the body maintaining homeostasis?
BP, [Na+], [Glu], [K+], pH, body H2O, BT
When do homeostatic processes restore balance to the ECF?
Following a disturbance
ex: blood glucose levels increase after eating, return to their set point via homeostasis
What kind of process is homeostasis?
A dynamic, not a static process
Steady state (requires energy input) vs equilibrium
What is dynamic constancy?
Levels change over short periods of time, but remain relatively constant over long periods of time
What happens to the system when physiological variables change dramaticall over a 24-hr period?
The system is still in overall balance
What do we refer to when homeostasis is maintained?
Physiology
What do we refer to when homeostasis is not maintained?
Pathophysiology
What are the two levels that homeostasis can occur in?
Cellular homeostasis
Extracellular fluid
What are components of cellular homeostasis?
Function of each cell
Cytoplasm of single cell
Necessary for normal cell function
Relies on components of extracellular fluid
What are components of extracellular fluid?
Environment outside of the cell
Necessary for normal cell function
What are the two types of extracellular fluid?
Local
Systemic
What is local homeostasis restricted to?
One tissue space
What does local homeostasis utilize?
Paracrines and autocrines
What does local homeostasis maintain?
Function of tissue
What does systemic homeostasis involve?
Entire body
What does systemic homeostasis utilize?
Nervous system and endocrine system
What does systemic homeostasis maintain?
Function of heart and brain
What is typically referred to when talking about homeostasis?
Extracellular fluid levels
What do paracrines target?
Cells close by
What do autocrines target?
Same cell that secreted the substance
What does the endocrine system target?
Cells in one or more distant places in the body
What does the nervous system target?
Neuron or effector cell in close proximity to site of neuro-transmitter release
Describe the flow of simple systemic homeostatic process
What are examples of stimulus that initiate the flow of systemic homeostatic process?
Changes in ECF composition, body temperature, BP
Ex: changes in [substances]
- Na, K, Ca
-H (pH)
- glucose, O2, CO2
- endocrine (hormones) and neural (neurotransmitters)
What does a reflex receptor detect?
Changes in [substance]
Where is a threshold stimulus sensed in?
Reflex receptor stage of a simple systemic homeostatic process
What does a threshold stimulus determine?
Amplitude of the normal range
What is an example of a reflex receptor?
Cluster of cells, individual cells, cell parts of molecules in membrane or cytoplasm of cell
What does the afferent pathway carry information from?
Reflex receptors to integrating center
What kind of reflexes does the afferent pathway have?
NS reflexes only
What kind of neurons are in the afferent pathway?
Sensory
What does the integrating center do?
Receives stimulus, analyzes information and generates appropriate response
What is the integrating center of the endocrine system?
Endocrine gland
What is the integrating center of the nervous system?
Brain/spinal cord
What does the efferent pathway carry?
Commands from integrating center to effectors
What does the endocrine system in the efferent pathway target?
Hormones (travel via blod)
What does the nervous system in the efferent pathway target?
Motor neurons
What is impacted by the effector portion of the simple systemic homeostatic process?
Any cell affected by efferent pathway (Change in function)
What are the two levels of the effector response?
- Local effector response
- Systemic effector response
What is the local effector response?
How cell (effector) function is changed by the efferent pathway
What is the systemic effector response?
How ECF (whole body) changed by local effector response
Different efferent pathways can create ___________ systemic effector response while having _________ local effector responses
The same; different
What is the feedback regulation pathway?
How systemic effector response changes the function of the reflex receptor
What are the two types of feedback regulation pathway?
- Negative feedback
- Positive feedback
What is the function of a negative feedback loop?
Decreases activity shutting off pathway
Keeps variable fluctuating around the setpoint
Is a negative feedback loop homeostatic or non-homeostatic?
Homeostatic; most common
What is the function of the positive feedback loop?
Increases activity further activating pathway
Is a positive feedback loop homeostatic or non-homeostatic?
Non-homeostatic
What does it mean to have a tonic level of activity?
At rest, a homeostatic pathway is neither completely shut off or fully active
- regulates parameters in an up and down fashion
What is antagonistic control?
In many instances a
single systemic effector
response is controlled by
two different efferent
pathways but in opposite
directions.
Ex. [Glucose]ECF,
[Ca++]ECF, Blood Pressure
What is a mechanistic explanation?
Describes how something happens
What is a teleological explanation?
Describes why something happens
How does a mechanistic explanation work in regards to blood flow?
Due to pressure gradient generated by heart contractions
Why does teleological explanation work in regards to blood flow?
To deliver O2 and nutrients to cells of body and to carry CO2 and other wastes generated by cells to excretory organs
Check all the following that are examples of a homeostatic process.
a. The lowering of blood sugar levels following a meal.
b. The elevation of heart rate during exercise.
c. The elimination of metabolic waste by the kidney.
d. Sweating in response to increased ambient temperature.
All of the above
The changes in the body during intense exercise is an example of local homeostasis. Neurotransmitters and paracrines mediate local homeostasis.
a. Both statements true
b. Both statements false
c. First statement true and second statement false
d. First statement is false and second statement is true
b. Both statements false
Which of the following determines the normal range for body temperature?
a. Negative feedback
b. Ambient temperature
c. Threshold stimulus of reflex receptor
d. Positive feedback
C. Threshold stimulus of reflex receptor
Which of the following statements about the homeostatic process is true?
a. The afferent pathway is found in reflexes mediated by both the nervous system and endocrine system.
b. It is the local effector response that alters the activity of the reflex receptor via negative feedback.
c. The efferent pathway alters the functions of the effector cells.
d. Negative feedback increases the activity of the reflex receptor.
c. The efferent pathway alters the functions of the effector cells.
