PSYC 273 Lecture Notes - Lecture 9: Thermostat, Blood Vessel, Ectotherm
Chapter 9 Notes
Part I: Principles of Homeostasis
• Homeostasis: the active process of keeping a particular physiological parameter
relatively constant. Maintenance of a stable, balanced, internal environment.
o General Concepts:
▪ Negative Feedback
▪ Redundancy is often built in.
▪ Behavioral Homeostasis
▪ Allostatic Load
• Motivation: the psychological process that induces or sustains a particular behavior.
o Alternations in the internal environment can have an effect on motivation.
• Our ability to regulate our internal resources is complicated by the fact that simply
staying alive requires us to use up some of them.
• Thermoregulation: the active process of maintaining a constant internal temperature
through behavioral and physiological adjustments.
• Homeostatic Systems Share Several Key Factors.
o Endotherms: an animal whose body temperature is regulated chiefly by internal
metabolic processes. Make our own heat using metabolism and muscular
activity.
▪ If our usles are’t making enough we shiver.
▪ Endothermy allows the muscles of mammals to work for longer periods
of time.
▪ Physiological regulation: sweating, shivering, blood vessel constriction.
▪ Also use behavioral regulation.
o Ectotherm: an animal whose body temperature is regulated by, and whose heat
comes mainly from the environment. Cold blooded.
▪ Only use behavioral regulation.
o Internal states are governed through negative feedback.
▪ Negative Feedback: the property by which some of the output of a
system feeds back to reduce the effect of input signals.
• Analogy: a temperature drops below a certain point and activates
the thermostat, which turns on the heating system. The heat that
is produced has a negative feedback effect on the thermostat, so
it stops calling for heat. To keep it from turning on and off too
often, the system has a little bit of tolerance built in (set zone).
• Set Point: the point of reference in a feedback zone.
• Set Zone: the optimal range of a variable that a feedback system
tries to maintain.
o Can be changed under certain circumstances.
▪ Body temperature drops at night to conserve
energy.
find more resources at oneclass.com
find more resources at oneclass.com
▪ Can increase to produce a fever to fight off an
infection.
o Redundancy is a feature of many homeostatic systems.
▪ Loss of function in one system can be compensated for by the remaining
parts.
▪ Hypothalamus: senses and control body temperature, but different
hypothalamic sites control 2 separate thermoregulatory systems. (ex. Of
homeostatic redundancy= 2 systems for regulating the same variable).
• Preoptic area: damage here impaired physiological responses to
cold (shivering and restriction of blood vessels).
• Lateral hypothalamus: damage here abolishes behavioral
regulation of temperature, but did not affect physiological
responses.
▪ Hierarchy of thermoregulatory circuits.
o Behavioral mechanisms are crucial for homeostasis.
▪ 3 types of temperature regulating behavior:
• Behaviors that changes EXPOSURE of the body surface (ex:
huddling, extending limbs).
• Behaviors that change external INSULATION (ex: using clothing or
nests).
• Behaviors that change SURROUNDINGS (ex: moving into the sun,
shade, or into a burrow).
▪ Behavioral mechanisms are especially important to ectotherms because
they generate little heat through metabolism.
▪ Endotherms: receptors in the skin, body core, and hypothalamus detect
temperature and transmit that information to 3 neural regions:
• Spinal cord.
• Brainstem.
• Hypothalamus.
▪ A wide array of sensors continuously monitors the many internal and
external threats to our physiological stability.
• Allostasis: the combined set of behavioral and physiological
adjustments that an individual makes in response to current and
predicted behavioral and environmental stressors.
o Allostatic Load: the wear and tear of daily life. Stress can
put individuals at a risk of pathology.
o Obligatory Losses: our body is continually challenged by
unavoidable losses (because some of our energy is used up
just keeping us alive) which require us to regain the lost
resources from the external environment.
• How can we mess up homeostasis:
o Ecstasy and thermoregulation.
▪ MDMA is a club drug that can result in hyperthermia.
find more resources at oneclass.com
find more resources at oneclass.com
• Hyperthermia: occurs when a person’s body temperature rises
and remains above the normal 98.6.
▪ Hyperthermia factors risk in MDMA users.
• Higher does, higher ambient temperature, prolonged dancing,
reduced thermal awareness.
o Hyponatremia: drinking too much water.
▪ Alcohol on the other hand:
• Increases feeling of warmth but actually cools body temperature.
• Diuretic, so need to drink more water.
▪ Abnormally low sodium levels.
▪ Rare in healthy people, more likely in special populations.
• Certain clinical conditions (congestive heart failure, pneumonia,
etc.)
• Marathon runners.
▪ Due to drinking more water than kidneys can eliminate and is lost to
sweat.
▪ Water enters cells through osmosis and causes cells to swell.
• Symptoms: confusion, disorientation, nausea, and vomiting, but
also changes in mental state and psychotic symptoms.
• Can cause cell damage in brain.
• Can result in death.
▪ Drink when you are thirsty, stop drinking if pushing fluids become
uncomfortable.
Part III: Fluid Regulation
Water Moves Between 2 Major Body Compartments
• Fluid regulation is maintained through hormones (such as atrial natriuretic peptide,
vasopressin, and angiotensin II) and behaviors.
• Intracellular Compartment: the fluid space of the body that is contained within cells.
Most of the water contained within this compartment.
• Extracellular Compartment: the fluid space of the body that exists outside the cells.
o Interstitial Fluid: the fluid between cells.
o Blood Plasma: the protein rich fluid that carries red and white blood cells.
• Forces driving the movement of water.
o Diffusion: the spontaneous spread of solute molecules through a solvent until a
uniform solute concentration is achieved.
▪ Selectively/ Semi Permeable Membrane: A membrane that is permeable
to some molecules, but not others.
o Osmosis: the passive movement of a solvent, usually water, through a
semipermeable membrane until a uniform concentration of solute (often salt) is
achieved on both sides of the membrane.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Part i: principles of homeostasis: homeostasis: the active process of keeping a particular physiological parameter relatively constant. Make our own heat using metabolism and muscular activity. The heat that is produced has a negative feedback effect on the thermostat, so it stops calling for heat. Water moves between 2 major body compartments: fluid regulation is maintained through hormones (such as atrial natriuretic peptide, vasopressin, and angiotensin ii) and behaviors. Intracellular compartment: the fluid space of the body that is contained within cells. Most of the water contained within this compartment: extracellular compartment: the fluid space of the body that exists outside the cells. Force that is moving the water back and forth to balance the concentration of the fluid. 2 internal cues trigger thirst: hypovolemic thirst: a desire to ingest fluids that is stimulated by a reduction in volume of the extracellular fluid.
