Cell Injury Homeostasis - B. pharma 2nd year Pathophysiology notes pdf

Cell Injury Homeostasis

Content

•       Components involved in homeostasis

•       Mechanism involved in the Homeostasis

•       Positive feedback mechanism

•       Negative feedback mechanism

Objectives

At the end of this lecture student will be able to –

•       Describe the components of homeostasis system

•       Explain mechanism involved in the internal environment maintenance

•       Describe feedback loop

HOMEOSTATIC CONTROL MECHANISMS

HOW HOMEOSTATIC CONTROL MECHANISMS WORK?

•       Homeostatic control mechanisms work through ‘Feedback Mechanisms’.

•       Status of a body condition is continually monitored, evaluated, changed, re-monitored & reevaluated.

FEEDBACK MECHANISM

•       A feedback mechanism is a cycle in which the output of a system “feeds back” to either modify or reinforce the action taken by the system.

•       A feedback mechanism may operate at:

–      Tissue level

–      Organ level

–      Organ system level

–      Body level, integrating with other organ systems.

–      Feedback mechanism can be:

–      Negative feedback (more common)

–      Positive feedback

A FEEDBACK SYSTEM CONSISTS OF THREE COMPONENTS

1. SENSOR (RECEPTOR): detects specific changes (stimuli) in the environment.
2. INTEGRATOR: act to direct impulses to the place where a response can be made.
3. EFFECTOR: performs the appropriate response.

A FEEDBACK LOOP

NEGATIVE FEEDBACK

•       Mechanisms that maintain the factor at some mean value.

•       Reverse a change

•       Restore abnormal values to normal

 

EXAMPLE: NEGATIVE FEEDBACK BLOOD PRESSURE REGULATION

POSITIVE FEEDBACK

•       Strengthens or reinforces a change.

•       Makes abnormal values more abnormal.

•       Produces ‘Vicious Cycle’.

•       But in body a mild degree of positive feedback can be overcome by the negative feedback control mechanisms of the body, and the vicious cycle fails to develop.

POSITIVE FEEDBACK LOOP

EXAMPLE: POSITIVE FEEDBACK MEMBRANE DEPOLARISATION

POSITIVE FEEDBACKS IN BODY

•       Action potential

•       Clotting of blood

•       Parturition

•       Release of calcium from SR

•       Sexual arousal

•       LH surge

Summary

•       Homeostasis is involved in continuous monitoring of body’s internal environment with respect to altering external environment

•       Components of homeostasis are ESI (Effector, Sensor, Integrator)

•       Internal environment is maintained by positive and negative feedback mechanisms

•       Most of the homeostasis mechanisms involve negative feedback