USMLE Step 1 Physiology Review 52 02 Homeostasis & Control Systems

USMLE Step 1 Physiology Review 52 02 Homeostasis & Control Systems

 

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Play USMLE Audio MP3 52 02 Homeostasis & Control Systems Below

Begin 52 02 Homeostasis & Control Systems Transcription

Physiology is the study of the functions of the organs and the systems of the body.  In the human body, there is a continual exchange between the internal and external environments.

What are the four major organs or sets of organs through which this exchange takes place?  List them alphabetically.

  • First: Gastrointestinal Tract
  • Second: Kidneys
  • Third: Lungs
  • Fourth: Skin

What system communicates between the cells and the roots of exchange?  For example, what system communicates between the cells and the lungs, or between the cells and the gastrointestinal tract?

  •   The Circulatory System. 

Much of the study of physiology concerns the maintenance of the constancy of the body’s internal environment.  What is the state of constancy called?

  • Homeostasis

Student Doctor, please pause the tape and summarize the information on the basics of physiology and homeostasis discussed this far.

  • Physiology is the study of the functions of the organs and the systems of the body.  In the human body, there is a continual exchange between the internal and external environments.
  • The four major organs or sets of organs through which this exchange takes place are the Gastrointestinal Tract, the Kidneys, the Lungs and the Skin.
  • The circulatory system communicates between the cells and the roots of exchange.  Much of the study of physiology concerns the maintenance of the constancy of the body’s internal environment.  This state of constancy is known as Homeostasis.

Now we’ll talk a bit about control systems.

What are the three elements of a formal control system?  List them in terms of cause and effect, and I’ll give you a clue for each one.

  • First, this element of a control system monitors the rate of output or level of product of a system.  The Sensor.
  •  Second, this element receives information from the sensor, compares the rate of output with the set point and directs the necessary adjustment. The Integrator.
  • Third, this element makes the necessary adjustment.  The Effector. 

One kind of control system is called negative feedback and another is called positive feedback; which kind is more common in humans?

  •  Negative feedback.

Imagine a biological system with a given level of output that is currently at a set point, or level of stasis.  Suddenly, there is a deviation in the output from that set point.  Would a negative feedback control system elicit a response that opposes the deviation or reinforces the deviation?

  • The response elicited by negative feedback opposes the deviation.  Therefore, the response could lead to a decrease or an increase in output, as long as the deviation from the set point is opposed.

What is the net effect of negative feedback on the level of operation?

  •  The level of operation of systems controlled by negative feedback remains more or less constant.

What effect does positive feedback have on change in the output of the system?

  • Positive feedback accelerates change.

Student Doctor, please pause the tape and summarize the information discussed thus far about control systems.

 

  •  The three elements of a formal control system are the sensor, the integrator and the effector.
  • The sensor monitors the rate of output or level of product of the system.
  • The integrator receives information from the sensor, compares the rate of output with the set point, and directs the effector to make the necessary adjustment.
  • The effector makes the necessary adjustment. Negative feedback and positive feedback are two kinds of control systems.  Negative feedback is more common in humans.  In the negative feedback system, a deviation in the output from the set point elicits a response that opposes the deviation.  Therefore, the response could lead to a decrease or an increase in output as long as the deviation from the set point is opposed.  The level of operation of systems controlled by negative feedback remains more or less constant.  Positive feedback accelerates change.

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