Homeostasis Flashcards
(45 cards)
What is homeostasis?
Property of a system in which variables are regulated so that the internal conditions remain stable and relatively constant
Refers to physiological mechanisms that maintain relatively constant the variables to the internal milieu of the organism
The steady state internal environment that is required for the maintenance of life
What are the key components of homeostatic circuits?
Controlled variable
Regulated variable
Sensor
Set point
Error detector
Controller
Effector
What is the controlled variable in a homeostatic circuit?
Physiological variable that is manipulated in order to maintain the regulated variable
What is the regulated variable in a homeostatic circuit?
Physiological variable for which sensors are present in the homeostatic circuit and is maintained at a stable level by a negative feedback system
What is a sensor in a homeostatic circuit?
A device that measures the magnitude of a physiological variable by generating an output signal that is proportional to the magnitude of the stimulus
Sensors can be specialised sensory cells or cellular components
What is a set point in a homeostatic circuit?
Range of values of the regulated variable that the homeostatic circuit attempts to maintain
Set points are changeable either physiologically or due to pathological change
What is an error detector in a homeostatic circuit?
Determines the difference between the set point value and the actual value of the regulated variable- error signal
What is a controller in a homeostatic circuit?
Receives information (error signal) from the error detector and sends out output signals to increase or decrease the activity of effectors
Typically endocrine cells and sensory neurons of the automatic nervous system, lower brainstem (medulla), and hypothalamus.
What is an effector in a homeostatic circuit?
Component of the circuit that is activated by the controller to change the value of the regulated variable
Term should only be applied to physical entities such as a cell, tissue or organ
What is external disturbance?
Any chance in the conditions of the external environment that result in a change to the internal environment
What is internal disturbance?
Any chance in the structure or function of the organism that results in a change to the magnitude of the regulated variable
What is the order of the homeostatic circuit?
Sensor
Error detector
Controller
Effector
Controlled variable
Regulated variable
What is negative feedback?
Mechanism that maintains a regulated variable within its set point
Reverses the direction of change
What is positive feedback?
Self-amplifying cycle in which physiological change leads to even greater change in the same direction
What is the positive feedback mechanism of blood clotting?
Damaged cells in the blood vessel wall release chemicals that begin the clotting process
Chemicals start chain reactions where cells, cell fragments, and soluble proteins in the blood begin to form a clot
As clotting continues, each step releases chemicals that further accelerate the process
This escalating process is a playing feedback loop which ends in the formation of a blood clot, which patches the vessel wall and stops the bleeding
What are the ‘sticky points’ of homeostatic circuits?
The same regulated variable can have a different dynamic range in different tissues
A regulated variable can also be a controlled variable under certain circumstances
What are common cell shapes?
Squamous
Spheroid
Columnar
Polygonal
Discoid
Fibrous
Cuboidal
Fusiform
Stellate
What is filtration?
Process in which water and solutes are driven through the cell membrane by hydrostatic pressure. It is a passive mechanism by which water and solutes move from high pressure areas to low pressure areas
What is facilitated diffusion?
The carrier mediated transport of a solute through the cell membrane down its concentration gradient. It is a passive mechanism of transport.
What is active transport?
Carrier mediated transport of a solute through the cell membrane up its concentration gradient using energy provided by ATP
How does the Na+/K+ pump work?
Pumps 3 Na+ ions out of the cell for every 2 K+ ions in
- Na+ binding on the cytoplasmic site induces ATP-mediated phosphorylation of the protein
- Phosphorylation triggers a conformational change in the protein
- The conformational change induces the expulsion of Na+ to the outside and allows extracellular K+ to bind
- K+ binding triggers the release of phosphate
- Loss of phosphate restores original conformation
- The release of K+ restores Na+ site receptivity, allowing the cycle to repeat
What is vesicular transport?
Movement of large particles, droplets of fluids, or numerous molecules at once through the cell membrane, contained in bubble-like vesicles or membrane
Endocytosis- bring material into the cell
Exocytosis- release material from the cell
What are some types of endocytosis?
Phagocytosis
Pinocytosis- process of taking in droplets of ECF containing molecules of some use to the cell
Receptor-mediated endocytosis- phagocytosis or pinocytosis in which specific molecules bind to specific receptors on the cell membrane, and are taken into the cell in clathrin-coated vesicles with a minimal amount of ECF
What are gap junctions?
Proteins between cells, which allow the passage of certain molecules
