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Renin Angiotensin Mechanism.

Homeostasis and its control

 Introduction to the Human Body: Homeostasis & its Control. 

Introduction:

  • Human beings are the most complex of all the living organisms.

  • Human body contains many organs which work in an organized manner for an efficient working of the human body.

  • The study of human body is divided broadly in two divisions,

    • Anatomy

    • Physiology.

  • Human Anatomy is the branch of science that deals with the study of structures of different body parts.

  • Human Physiology is the branch of science that deals with the study of functions of different body parts.

Human Anatomy: Study of Structure.

Human Physiology: Study Of Functions.

Homeostasis:

  • Homeostasis literally means keeping everything normal.

  • It can be defined as the ability of the body to respond to the changes in the environment and keeping its internal environment at an equilibrium.

  • It's a dynamic process.

  • Various body parameters like body fluids pH, body temperature are maintained at a constant level called Set Points, keeping these values NORMAL is crucial for the body to function properly.

Body Fluids.

  • One of the important aspects of homeostasis is to maintain volume and composition of the body fluids.

  • Body fluids are watery solutions containing dissolved chemicals present inside and outside of the cells.

    • Intracellular Fluid (ICF): Present inside the cell.

    • Extracellular fluid (ECF): Present outside the cell.

  • Extracellular Fluid:

    • It is called by many names as per its location,

      • Plasma: Inside blood vessels.

      • Lymph: Inside lymph vessels.

      • Cerebrospinal fluid: In brain and spinal cord.

      • Synovial fluid: In joints.

      • Interstitial Fluid: In the tissues surrounding th cells.

    • Interstitial fluid is also called the body's internal environment.

    • The composition of ICF and ECF changes when the components move inside and outside of the cell, this causes physiological changes.

Control of Homeostasis:

  • Body responds to many outside and inside triggers like change in the external environment, psychological stress etc which results in a shift in equilibrium maintained by homeostasis.

  • Most of the time this shift is mild and temporary and the balance is maintained quickly.

  • Sometimes the change in the balance is prolonged to set normal as in major surgeries, infections or in poisoning.

  • Nervous system along with the endocrine system plays a crucial role in maintenance of the homeostasis through FEEDBACK SYSTEMS.

FEEDBACK SYSTEMS:

  • It is a cycle of events through which a body condition is maintained in homeostasis.

  • These events monitor, evaluate and alter the condition, it's an ongoing process.

  • The condition which is thus monitored is called a “Controlled Condition”.

  • Anything that brings about change in the controlled condition is called a “Stimulus”.

  • A feedback system is composed of three basic components,

    • A Receptor.

    • A control center.

    • An effector.

  • Receptor:

    • It is a body structure that monitors change in the controlled condition and sends information of change to the control center.

    • The input is received in the form of nerve impulses or chemicals.

  • Control Center:

    • The brain acts as a control center in the body, it maintains the controlled conditions in a set value.

    • It monitors the responses received from the receptors and sends outputs in the form nerve impulses or chemicals to the effectors.

  • Effectors:

    • It is a body structure that receives output from the brain and produces a response that changes or alters the controlled condition.

    • Evry organ or tissue in the body have capacity to act as an effector however muscles and glands are effectors in prominent conditions.

  • Feedback systems that control the body conditions are of two types,

    • Negative Feedback Mechanism

    • Positive Feedback Mechanism.

Negative Feedback Mechanism:

  • In this type of feedback system the response from the effector decreases or negates a change in the controlled condition.

  • eg. Blood Pressure Control in the body.

  1. Some stimuli increase heart rate causing the rise in blood pressure.

  2. The Baroreceptors present in the blood vessels detect the change in blood pressure and send impulses to the Brain.

  3. Brain analyses the impulses received from Baroreceptors and send impulses to the blood vessels and Heart.

  4. Heart rate get reduced and blood vessels get dilated causing fall in blood pressure. 

  5. As this case is an example of the negative feedback mechanism the effector that is heart and blood vessels action “Decreases” the change in controlled condition.

Positive Feedback Mechanism:

  • In this type of feedback system the response from the effector increases as long as stimulus is there.

  • In positive feedback mechanisms, the stimulus progressively increases the response, so that as long as the stimulus is continued the response is progressively being amplified. 

  • Examples include blood clotting and uterine contractions during labour.

  1. In Childbirth the release of the Oxytocin causes an increase in uterine contraction.

  2. The uterine contraction pushes the part of the foetus in the cervix which opens in vagina.

  3. The stretch receptors in cervix detect stretching and send impulses to the brain.

  4. Brain detects and analyses the impulses from stretch receptors and sends impulses to the pituitary for more release of oxytocin.

  5. More oxytocin levels causes more contractions of the uterus moving further the foetus forwards.

  6. The cycle continues till the baby comes out and stretching becomes nil.

  7. As this case is an example of the positive feedback mechanism the effector response that is uterine contractions  “Increases” till there is stimulus.

Commonly Asked Questions:

  1. Define homeostasis.

  2. Comment of Positive and Negative feedback mechanisms.

  3. Write a note on Homeostasis and its control.
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