Receptors, Feedback, and Effectors

 I like that my Anatomy prof is constantly phrasing her questions as critical thinking questions. For example, what does oxygen do for the body? Someone answered that it helps keep us alive. Yes, but how? I thought for a sec and recalled that it is an integral part in respiration (creates ATP) and deals with the exchange of electrons and protons to help maintain homeostasis.

Feedback is interesting - negative feedback vs positive feedback. It's part of maintaining homeostasis. There is the receptor, the control center, and the effector. The control center determines the set point or range for a set point of a variable (such as temperature.) The receptor monitors the environment and responds to stimuli by sending signals for needed changes. The control center receives the input from the receptor and sends output to the effector on what to do.

Negative vs positive feedback cannot be thought of as good vs bad. It is simply the type of process the body uses to keep itself in balance. Negative feedback goes in the opposite direction as stimulus and is more common, like shivering to warm up or sweating to cool down. Positive feedback responds in the same direction as the stimulus, like platelets coming to plug a cut.

Here's something cool - do you know what platelets are? They're the things sent by blood that clot a cut. Platelets have receptors that activate when they attach and send signals for more platelets to come and attach. 

Q: do they also send signals for the healing chemicals?

A: platelets send signals for the growth signals / hormones - growth factor. Once the wound is healed, then signals are sent that break down the platelets.

Other positive feedback: labor contractions get stronger and stronger. If it was a negative feedback, the body would try to stop that process.

Temperature signals are sent to the hypothalamus section of the brain.

We're talking about positive feedback and thinking about birth when the following quesion occurred to me: if gestation is typically 40 weeks, why are babies that have gone through the same duration of gestation different sizes? If cell division is cell division, then why wouldn't a smaller baby be born just at an earlier date? Shouldn't all babies go through the same growth within the same time frame?