human phys 1

The nervous and endocrine systems are the body's two major control systems, one using rapid electrical signals and the other slower chemical (hormonal) ones.

Most cells are bathed directly in extracellular (interstitial) fluid, their immediate internal environment.

The adrenal gland is a solid, ductless organ with no opening to the body surface, so it never contacts the external environment.

Both processes drive fluid loss in the same direction, compounding the disturbance rather than correcting it, so this is not homeostatic.

Childbirth is the classic positive feedback loop; contractions trigger oxytocin release, which drives even stronger contractions.

Clot formation is a positive feedback loop; each activated platelet recruits and activates more, amplifying the response until the clot is complete.

The integrating center receives input, compares it against the set point, and determines the response.

Local control operates at the tissue or cell level through paracrine and autocrine signals, without a distant integrating center.

The nervous and endocrine systems carry out long-distance communication using electrical and chemical signals.