Homeostasis Flashcards
Homeostasis
Physiological variables in a state of dynamic constancy
Ex: blood glucose levels, body temperature, fluid levels, etc.
Homeostasis control mechanisms
-Monitor situation
Receptors (Sensors)—detects Variables
Sends information to Integrator (Control Center)
-Make decisions
Integrator (Control Center) receives input from Receptors (Sensors)
Determines appropriate response
-Make necessary adjustments
Effector receives output from Integrator (Control Center)
Response acts to reduce or enhance the stimulus (feedback)
Variable/Stimulus to
Sensor/Receptor travels to
(afferent pathway) to
Integrator/Control Center travels to
(efferent pathway) to
Effector to
Response
In negative feedback:
Response brings situation BACK TOWARD NORMAL
Example: Regulation of body temperature, blood glucose, etc.
In positive feedback:
In Positive Feedback the response
ENHANCES THE ORIGINAL
STIMULUS
Moves situation further and
further away from normal.
Example: Labor and delivery, clotting blood
Feed-Forward Regulation
Changes in regulated variables are anticipated and prepared for before they actually occur.
Ex: Sight, smell, taste of food-
secretion of saliva, stomach acid
production
Local Homeostatic Responses
Response to a particular stimulus on a local level
Examples -
Active hyperemia:
Exercise
Metabolic wastes build up
Induce vasodilation of nearby blood
vessels
Increased blood flow
Wastes washed away
Negative feedback
What are the four categories of chemical messengers?
1) Hormones- travel through the blood vessels and target cells in one or more distant places in the body.
2) Neurotransmitter- Neurons release neurotransmitters when they communicate with each other. Ex: serotonin, dopamine, etc.
3) Paracrine substance- Targets cells in close proximity
4) Autocrine substance- Acts on same cell that secreted the substance.
Two types of chemical communication without secretion of a chemical messenger?
Gap junctions
* Proteins connect two cell membranes
* Passageway that connects the cytosol
* Ions and small molecules can pass
Juxtracrine signaling
* Extracellular proteins link
* Helps cells “recognize” each other
* Important in growth & immunity
Acclimatization
Improved functioning of an already existing homeostatic system
* Usually reversible
* E.g. Adjustment of the human body to high-altitude environments
Adaptation
A characteristic that favors survival in specific environments
* E.g. the ability of certain individuals to digest lactose in milk
Biological Rhythms
Many body functions are associated with rhythmical changes
Circadian rhythm is most common - cycles approximately once every 24 hours
The Hypothalamus (The suprachiasmatic nucleus) Pacemaker signals the pineal gland.
Pineal gland – secretes melatonin during darkness
General Principles of Physiology
1) Homeostasis is essential for health and survival
2) The functions of organ systems are
coordinated with each other
3) Most physiological functions are controlled by multiple regulatory systems, often working in opposition
4) Information flow between cells, tissues, and organs is an essential feature of homeostasis and allows for the integration of physiological processes
5) Physiological processes are dictated by the laws of chemistry and physics
6) Physiological processes require the
transfer and balance of matter and
energy
7) Structure is a determinant of
function
8) Controlled exchange of materials
occurs between compartments and
across cellular membranes
