CAS BI 315 Lecture Notes - Lecture 2: Surface Tension, Covalent Bond, Pineal Gland
1 Jun 2018
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I. Homeostasis
A. Core concept
B. Homeostasis - a stable internal condition
C. Dynamic stability
D. Because our environment is always changing, our homeostatic mechanisms are always
compensating
E. Homeostatic mechanisms can be physiological, behavioral, or both
1. Cold - huddled, shivering
2. Hot - spread out, sweaty, red face (blood flowing closer to face to release heat)
3. Muscle contraction = more cellular respiration = generate heat (reason for
shivering)
a) C6H12O6 + O2 → ATP + H2O + heat
II. Negative Feedback Systems
A. One way to maintaining homeostasis is to monitor output
B. A negative feedback loop is where the product of the pathway (in this case, HEAT) turns
the pathway off
1. Heater set to 68 degrees
a) Falls to 66 → heater turns on → 68 → heater turns off (cycles)
2. Same with testosterone - good is 680 ng/dL (anything lower will turn testosterone
production on)
III. Anatomy of a Negative Feedback Loop
A. Stimulus (change to internal environment) → Sensor (change is detected by
receptor/sensor) → Control Center (change is compared to set point - ex: brain) →
Effector (muscles or glands) → Change is corrected
IV. Biochemistry of Negative Feedback
A. Negative feedback systems are often used to control production, secretion, or activation
of a chemical product (Ex: testosterone)
V. Positive Feedback Sys
A. A positive feedback loop is where the product of the pathways makes the pathway
continue, or accelerates the pathway
1. Mosquito bite → itch → scratch → scratching spreads the toxin and increases
inflammation → so if you become more itchy and needs to scratch more → return
to scratching step and recycle
2. Childbirth
a) Baby’s head puts pressure on cervix → pressure of the fetus’s head
against the cervix triggers release of hormone oxytocin → oxytocin
causes uterine contractions, squeezing fetal head onto cervix → returns
to step of triggering more oxytocin → continues until baby out and then
loop resolves
3. Negative loop tends to be more hallmark ex of feedback loop bc its regulated but
positive can continue going dependent of the stimulus
VI. Feedback System Control Center
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Document Summary
Anatomy of a negative feedback loop production on: stimulus (change to internal environment) sensor (change is detected by receptor/sensor) control center (change is compared to set point - ex: brain) . Effector (muscles or glands) change is corrected. Biochemistry of negative feedback: negative feedback systems are often used to control production, secretion, or activation of a chemical product (ex: testosterone) Feedback system control center: all homeostatic mechanisms involve coordination and communication, nervous system or via secreted chemicals. Andes mountain natives: control s sleep-wake cycle, body temp, hormone concentrations in blood, excretion of ions in urine, and others, 24 hour clock, anatomy involved: hypothalamus, pineal gland (secretes melatonin) targets of. Influenced by: light, external temp, meal timing, social cues. Saving accounts melatonin: an important component of being ready to maintain homeostasis in an ever-changing environment, storage, don"t need to put in all the time but if you continue to take out, won"t have a savings account anymore.
