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 function
What is the external environment?
Outside body
What is extracellular fluid? (ECF)
Internal environment; inside body, outside cells
What are the two components of ECF?
Plasma and interstitial fluid
What is plasma?
in blood vessels, but outside cells, fluid portion of blood
What is interstitial fluid?
outside blood vessels and cells
What is intracellular fluid?
intracellular Environment = inside cells; cytoplasm
Is homeostasis dynamic?
Yes, not static
What is dynamic constancy?
levels change over short periods of time, but remain relatively constant over long periods of time
How often do physiological variables change?
Physiological variables can change dramatically over a 24-hr. period, but the system is still in overall balance
What do we call it when homeostasis is maintained?
Physiology
What do we call it when homeostasis is NOT maintained?
Pathophysiology
What are examples of cellular homeostasis?
Function of each cell
Cytoplasm of single cell
Necessary for normal cell function
Relies on components of extracellular fluid
What are the two types of extracellular fluid?
Local and systemic
What is local extracellular fluid?
Restricted to one tissue space
Utilizes Paracrines and Autocrines
Maintain Function of Tissue
What is systemic extracellular fluid?
Involves entire body
Utilizes Nervous System and Endocrine system
Maintain Function of Heart and Brain
What is set point?
The level the body tries to maintain (for example 98.6 degrees)
What is considered external environment?
GI Tract, lungs, urinary tract (post vascular system, once filtered into kidney)
What do homeostatic processes do following a disturbance?
Restore balance
What does steady state require?
Energy input; ex. Na gradient across cell membrane
Is equilibrium equivalent with homeostasis?
NO
What are the levels of homeostasis?
Cellular homeostasis and extracellular fluid
What is does the level of extracellular fluid consist of?
Environment outside of the cell
Necessary for normal cell function
Two types: Local vs. Systemic
What does local homeostasis utilize?
Paracrines and autocrines
What does systemic homeostasis utilize?
Nervous system and endocrine system
What do autocrines do?
Autocrine substance acts on same cell that secreted the substance
What do paracrines do?
Target cells in close proximity to site of release of paracrine substance
What do nerve cells do?
Neuron of effector cell in close proximity to site of neurotransmitter release
What do endocrines (hormones) do?
Target cells in one of more distant places in the body
What is a stimulus?
First domino, could be a change in ECF Composition, Body Temperature, BP, etc.
What is the stimulus flow for a systemic process?
Stimulus to Reflex Receptor to Afferent Pathway to Integrating Center to Efferent Pathway to Effector to Effector Response (Possible feedback regulation)
What is the reflex receptor?
Detects changes in [substance]
Has threshold stimulus
What is threshold stimulus?
(Sensitivity) - Determines amplitude of the normal range
What happens if the threshold stimulus is high?
Takes more stimulus to signal the reflex receptor
What can be a reflex receptor?
Cluster of cells, individual cells, cell parts or molecules in membrane or cytoplasm of cell
What does reflex receptor determine?
Normal range (more sensitive= narrow range; less sensitive= wider range)
What is the afferent pathway?
Carries information from Reflex Receptors to Integrating Center
NS reflexes ONLY
Sensory neurons
Where do we not have an afferent pathway?
Endocrine system
What is the integrating center?
Receives stimulus, analyzes information and generates appropriate response
ES = Endocrine Gland
NS = Brain/Spinal Cord
What is the integrating center in the endocrine system?
Endocrine gland
What is the integrating center in the nervous system?
Brain/spinal cord
What is the efferent pathway?
Carries commands from integrating center to effectors
ES = Hormones (travel via blood)
NS = Motor neurons
What is the efferent pathway in the endocrine system?
Hormones; travel via blood
What is the efferent pathway in the nervous system?
Motor neurons
What is the effector?
Any cell affected by Efferent Pathway (change in function)
What are the two levels of the effector response?
Local and systemic effector response
What is the local effector response?
how cell (effector) function is changed by the Efferent Pathway (ex. GLUT4 receptors to surface of cells)
What is the systemic effector response?
how ECF (whole body) changed by local effector response (ex. fall of blood glucose levels)
T/F: Different Efferent Pathways can create the same systemic effector response while having different local effector responses
T
What is feedback regulation?
How Systemic Effector Response changes the function of the Reflex Receptor
What are the two types of feedback regulation?
Negative and positive
What is a negative feedback response?
Decreases activity shutting off pathway (homeostatic; most common)
Keeps variable fluctuating around the setpoint
What is positive feedback response?
Increases activity further activating pathway (non-homeostatic)
Which feedback response is homeostatic?
Negative; NOT positive
What is the tonic level of activity?
At rest, a homeostatic pathway is neither completely shut off or fully active
What does tonic control regulate?
Physiological parameters in an up-down fashion
Are homeostatic pathways either on or off?
No, usually always some level of activity
What is antagonistic control?
a single systemic effector response is controlled by two different efferent pathways but in opposite directions.
What is a mechanistic explanation?
Describes how something happens
What is a telological explanation?
Describes why something happens
