E155 Homeostasis

set-point

The physiological value around which the normal range fluctuates

What are the components of a negative feedback loop and what is the function of each one?

sensor/receptor, control center, effector

sensor/receptor

monitors a physio value and alerts the control center of changes

control center

compares changes identified by the sensor to the normal values

effector

causes change to revert back to normal values 

What are some examples of physiological variables that are regulated by a negative feedback loop?

homeostasis, body temperature, blood sugar concentration

negative feedback loop

a mechanism that reverses a deviation from the set point… maintains body parameters within their normal range

positive feedback loop

intensifies a change in the body’s physiological condition rather than reversing it.

• Example = childbirth

positive vs negative feedback

Positive feedback increases the response, while negative feedback takes measures to decrease it. 

Draw and describe a simple feedback loop that includes a(n) effector, receptor, response and stimulus.

Example = seeing a speed limit sign 

• Receptor (R): human eye 

• Effector (E): foot to step on the gas 

• Stimulus 1 (S1): going 40 mph 

• Response 1 (R1): slowing down 

• Stimulus 2 (S2): going 20 mph 

• Response 2 (R2): speeding up

Explain why Type I diabetes is an example of a disrupted feedback loop

T1D: when the pancreas is unable to produce insulin, which is responsible for bringing glucose into the cell from the bloodstream

• Without insulin, the negative feedback loop is disrupted, therefore, to ensure proper function, DM1 patients use insulin injections.

homeostasis

regulation of various values

• physio variable: pH, osmosis, ions, glucose, BP, blood gases, body temp

• some deviation along the set point

you have a pt with an elevated body temp. make a diagram that shows how the body temperature will be returned to normal

increase body temp → sensor (central hypothalamus; peripheral skin receptors) → integrating center (hypothalamus) → effector (different sites like sweat glands) → response (blood vessels constriction or dilation, metablism, sweating, muscles

what happens if the blood vessels cannot constrict efficiently

hypothermia

• losing heat because the body cannot retain it via constriction

• stays in a dilated position, losing heat

blood vessels and heat

constriction = retaining heat

dilation = losing heat

simple positive feedback loops

ex - someone yells “pop quiz” → panic level increases → number of people running away increases → also increases panic level

examples of positive feedback loops

blood clotting after a wound

• iniation = a cut that damages blood vessels

• variable sensed = chemicals being released

• variable amplified = platelet count

• receptor = skin receptors

• effector = immune system

ex - immune activation, sepsis, ovulation

why is this false? homeostasis is the same thing as an equilibrium

homeostasis revolves around a set point that moves forward and backward rate of the reaction

• homeostasis is maintaining around the set point, not necessarily equilibrium

why is this false? negative feedback always means that a variable (ex - heart rate) is decreasing

negative feedback always means a variable is maintained with homeostasis (ex - glucose concentration can go up or down)

why is this false? heart rate can change, therefore, it is a regulated variable

HR = no receptor specific to HR (HR is not regulated; it changes due to regulation of something else)

• regulated variable: narrow range (ex = BPM could have a wide range)