BIO-249: Lecture Exam 1: Homeostatsis & Feedback Loops

1. What is homeostasis?

2. What parameters/variables of the body are held “in balance” through homeostasis?

1. Homeostasis

   • State of balance in nearly everything

   • Physiological conditions stay close to a set point

2. Parameters

   1. Blood Pressure

   2. Heart Rate

   3. “Energy Levels”

   4. Calcium

   5. Most chemicals

1. What is a set point?

2. How does a set point relate to homeostasis?

• Set point: physiological value around which the normal range fluctuates

  • Normal range: restricted set of values that’s optimally healthy & stable

• Deviations from the set point, which are detected by receptors, initiate a negative feedback loop for homeostasis

1. Stimulus Definition

2. Control Center Definition

3. Effector Definition

4. Response Definition

1. Stimulus: disrupts homeostasis/deviates from set point

2. Receptor: sensor that detects the stimulus & relays info to the control center

3. Control Center: the thinking structure; compares the value to the normal range

   • receives info from receptor → deciphers it → issues a command

4. Effector: action structure (organs & tissues) that creates an effect to reverse the stimulus

5. Response: opposite of the stimulus

Homeostatic control example (increase in blood sugar)

1. Stimulus: an increase in blood sugar

2. Receptor: receptors on pancreatic beta cells

   • detect an increase in blood sugar

3. Control Center: pancreatic beta cells

   • receive information from their receptors & communicate with the other cells in the body using insulin

4. Effector: pancreatic beta cells

   • respond to insulin by taking in sugar from the bloodstream

5. Response: decrease in blood sugar levels

1. What is a negative feedback mechanism?

2. Describe the negative feedback loop of body temperature regulation

   1. Identify the stimulus, receptors, control center, effectors, & response

• Negative Feedback Loop

  • mechanism that reverses the deviation from the set point

  • response is the opposite of the stimulus

  • maintains body parameters within their normal range

• Body Temperature Regulation

  1. Stimulus: changes in body temp

  2. Receptor: thermoreceptors & sensory nerves

  3. Control Center: hypothalamus

  4. Effector:

     1. Sweat glands: secrete sweat to cool down body temp

     2. Skeletal muscles: break down ATP to generate heat/energy

  5. Response: lower body temp/increase body temp

What is a positive feedback mechanism?

A mechanism that is used to rapidly accelerate an action, helps drive processes to completion

Compare & contrast positive & negative feedback

• Negative Feedback

  • Response is the OPPOSITE of the stimulus

  • Response is fed BACK to the receptor to maintain homeostasis

• Positive Feedback

  • Response rapidly amplifies the stimulus

  • Needs an external stimulus to end the loop

Which feedback mechanism is best used for homeostatic control?

• Negative Feedback

  • Counterattacks deviations from the set point & maintains body stability

1. Does a positive feedback loop ever stop on its own?

2. How does a positive feedback loop stop?

NO it cannot stop on its own, needs an external stimulus

• Blood clotting & childbirth

Describe how positive feedback works in delivering a baby

• Pressure of the baby’s head against stretch sensors stimulate the uterus to contract, which increases the pressure against the cervix and increases the strength of the contractions until the baby is delivered

  

Positive Feedback Lactation Example