homeostasis Flashcards
what is homeostasis?
maintenance of nearly constant conditions in the internal environment
what is steady state?
the condition that homeostasis aims to achieve
how are steady state and equilibrium different?
equilibrium is when solute concentrations are constant in time without requiring the input of energy
how do organ systems collectively create a stable environment for the cells?
by buffering the external environment
what constitutes an organ?
it is made up of two or more kinds of tissues (muscle, nervous, epithelia and connective)
what is an organ system?
collection of organs that perform a general function
what is mass balance?
any substance taken in by the body is nearly equal to the amount leaving the body plus what is removed by metabolism
what is the central compartment of mass balance?
extracellular fluid, including blood plasma
what is the basal metabolic rate? how much of our daily usage does it account for?
energy expenditure at rest. accounts for about 60% of expenditure in sedentary people
when is metabolism lowest?
during sleep
what does metabolism encompass?
all chemical processes involved in energy production, release and growth
how many calories does an individual need per day to sustain resting metabolism ?
abour 30 kcal/kg body weight
what is the difference between BMR and RMR?
RMR includes daily activity while BMR does not
why does RMR decrease during aging?
reduced muscle mass
what are some factors that increase RMR?
more muscle mass, increased body size, some hormones, and cold temperature
what does malnutrition do to RMR?
decreases it
what is net fluid balance and when is it positive?
fluid input needs to match fluid output. it is positive when intake exceeds output. (pee it out)
what is the primary ECF cation and what is the primary ICF cation? How is this established?
ECF- Na
ICF- K
established by Na/K ATPases that transport 3 NA out of the cell in exchange for two K molecules into the cell
T or F. All nutrients are controlled within extremely narrow ranges in homeostasis.
False. some, like plasma glucose, fluctuate over broader ranges.
what is the pattern of plasma glucose throughout the day?
after meals, it spikes to varying degrees depending on the amount of carbohydrates digested. Hormones decrease the high levels without overshooting to a significant degree.
what are the three components of negative feedback systems?
receptor, integrator (compares to a set point) and effector
what does negative feedback do?
initiation of responses that counter deviations of a controlled variable from a normal range
what is feed forward control?
regulates body systems with a desirable change like changing heart rate in anticipation of exercise
(may work with negative feedback)`
what is positive feedback and why is it not widely used in the body?
it accelerates a process. uncommon because it is more likely to be unstable
what is an example of negative feedback control at the molecular level? What is this called?
an active product that inhibits a step in the production of itself. Called end product inhibition
what is an example of negative feedback control at a system level?
secretion of thyroxin activated by TSH hormone secreted by the pituitary. thyroxin then inhibits the pituitary from secreting TSH
what is the “gain” of negative feedback? What is its error?
capacity of the system to restore a controlled variable to its set point after a perturbation. error occurs when the correction does not return the value to normal
what does higher gain mean? what is the formula for gain?
when the system is better able to restore a variable to its set point
gain=correction/remaining error
when is blood loss countered by negative feedback and when by positive feedback?
negative- one liter of blood is lost
positive- two liters of blood are lost
what is the positive feedback mechanism related to blood loss?
decrease in blood pressure leads to a decrease in blood flow to the heart. this weakens the heart further and further diminishes blood flow
what are some physiological examples of positive feedback?
blood clotting, child birth contractions, estrogen effects before ovulation, action potentials and calcium release in the heart
T or F. The set point regulated by homeostatic mechanisms can be changed.
True
what is a hierarchy of importance as it pertains to homeostasis?
certain homeostatic controls are more important to maintain and they will be maintained even if it throws other aspects of homeostasis further out of whack
