Homeostasis Flashcards
Define homeostasis
Maintenance of a nearly constant internal environment, referred to as a steady state
Steady state
STEADY STATE is the maintenance of nearly constant conditions over time
Equilibrium
Steady state is not the same as EQUILIBRIUM.
A system is said to be at equilibrium when its solute concentrations and other parameters are constant in time without requiring the input of energy from metabolism or other sources.
Basal metabolic rate
Basal metabolic rate (BMR) is the amount of energy expended daily by humans and other animals at rest. Units of kcal/hr/sq-meter body surface area. About 60% of all metabolic rate.
Resting metabolic rate
A more common and closely related measurement to BMR, used under less strict conditions, is resting metabolic rate (RMR). Note that the BMR is less than the RMR due to various forms of daily activity.
Factors that influence metabolic rate
is increased by several hormones (*thyroid hormone, growth hormone, testosterone,
epi/norepi), arctic weather, fever, higher in males and younger ppl due to increased muscle mass.
Decreased in tropical weather, older folks, women (compared to men), sleep, and malnutrition.
Describe the roles of negative feedback control & set points in maintaining homeostasis
Negative feedback is the major process used to maintain a stable internal environment (Homeostasis). It is the initiation of responses that counter deviations of a controlled variable from a normal range (the result of a process influences the operation of the process itself in such a way as to reduce changes). The loop includes an integrator, effector, & receptor. It is more stable than positive feedback & negative feedback improves the reliability of control.
Sensor
Usually a receptor, it detects changes in the controlled variable
Receptor
A specialized cell or group of nerve endings that responds to sensory stimuli.
Comparator/ Integrator
The integration center of the of the negative feedback response, it analyzes the data from the sensor, compares it to the set-point and if the two are incongruent, the comparator sends a signal
Effector
Receive the signal from the comparator. Appearing in the form of nerve pathways, cells or tissues, they carry out the response, with the goal of returning the control variable back to normal value/set point.
1) Why does positive feedback lead to instability?
2) What are some beneficial roles of positive feedback?
Positive feedback accelerates a process and thus can be unstable; it is less common in nature than negative feedback, but important in many cases.
There are also many useful positive feedback systems, such as blood clotting after vessel rupture, uterine contractions during childbirth, estrogen effects on the pituitary-hypothalamus before ovulation, the generation of an all-or-none action potential via Na+ channel activation*, and calcium-induced calcium release in heart.
ORGANS
ORGANS are composed of 2 or more kinds of tissues (muscle, nervous, epithelia, connective) arranged in various proportions & patterns
Mass balance
In the steady state, when a substance is said to be “in balance,” intake and excretion + amount removed by metabolism are nearly equal
Gain of negative feedback system =
Correction/ Remaining Error
- The capacity of the system to restore a controlled variable to its set point after a perturbation is called the gain. In response to a perturbation, the negative feedback control system makes a correction. If the correction is not 100% effective in preventing the change, there is an error.
- The higher the gain of the system, the better able it is to restore a controlled variable (e.g., mean arterial pressure) to its set point (e.g., 100 mm Hg) in response to a perturbation (e.g., rapid blood loss).
