Functional Organization of Human Body (CONT.)

Dr Sadia Amer

Learning ObjectivesControl systems of the body and its examples.

Characteristics of control system.

Automaticity of the body.

Control systems of the bodyHuman body has about thousands of control systems.

Most intricate are genetic control systems that operate in all cells to help control intracellular function as well as extracellular function.

Other control systems operate within the organs to control the interrelations between the organs.

Examples:- Respiratory system operating in association with nervous system for maintaining conc. of CO2 in the ECF

EXAMPLES OF CONTROL MECHANISMSRegulation of O2 and CO2 concentration in ECF

Regulation of Arterial Blood Pressure

Regulation of body temperature and constituents of ECF

Regulation of oxygenIt depends on the chemical characteristics of Hemoglobin.

Oxygen is released at tissues where there is low oxygen concentration.

Not released where too much oxygen is present.

This is Oxygen buffering function of Hb.

Regulation of carbon dioxideIt is regulated by respiratory system.

Excess CO2 excites respiratory centre causing a person to breath rapidly and deeply.This removes excess carbon dioxide.

Regulation of Arterial Blood PressureBaroreceptor system:-Location: 1-Bifurcation of Carotid arteries

2-Arch of Aorta

Mechanism of action:- - Rise in blood pressure causes stretch of arterial wall which in turn stimulates baroreceptors.

- Nerve signals are transmitted to medulla of brain.

- It causes inhibition of vasomotor center

Then inhibitory signals are transmitted through sympathetic nervous system to heart and blood vessels.

It causes decrease pumping activity by heart and dilation of peripheral blood vessels.

It in turn decreases arterial pressure back to normal.

Characteristics of Control SystemsNegative feedback Positive feedbackAdaptive control

Negative feedback controlIf some factor becomes excessive or deficient, a control system initiates negative feedback, which consists of a series of changes that return the factor towards a certain mean value, thus maintaining homeostasis.

ExamplesA high concentration of CO2 initiates events that decrease the concentration towards normal, which is negative to the initiating stimulus and vice versa

Similarly in case of high blood pressure, series of reactions that decreases B.P are negative feedback.

“Gain” of control systemThe degree of effectiveness with which a control system maintains constant conditions is determined by gain of negative feedback.

Formula: Gain=Correction/Error

ExampleIf large amount of blood is transfused to a person whose Baroreceptors are not functioning=B.P rises from 100mm Hg to 175mm Hg

If same amount is transfused if Baroreceptors are normal=B.P rises only to 125mm Hg

So feedback control system has caused a “correction” of -50mm Hg i.e 175-125

There remains an increase in pressure of +25mm Hg i.e 125-100, called the “error” which means control system is not 100% effective in preventing change.

Putting these values in formula result is -2.

The temperature control system is much more effective than Baroreceptor system.

When person is exposed to moderately cold weather, the gain of system controlling internal body temperature is only -33.

Positive Feedback systemWhen initiating stimulus causes more of the same, it is positive feedback.

It usually does not leads to stability but to instability and often death.

Example: If a person bled 2 liters,blood volume decreases,arterial pressure falls,flow of blood to heart decreases.It results in weakening of heart, the cycle repeats itself again and again until death occurs.

Positive feedback is also known as “vicious cycle”.

A mild degree of positive feedback can be overcome by negative feedback and vicious cycle fails to develop.

Example : If person bled 1 liter, the person would recover because negative feedback overcome positive feedback.

Advantages of Positive feedbackBlood clotting ChildbirthGeneration of nerve impulse

Blood clottingWhen blood vessel is ruptured, clotting factors are activated.Some of these enzymes act on other unactivated enzymes of adjacent blood , causing more clotting.

This process stops when hole in the vessel is plugged and bleeding no longer occurs. This process sometimes gets out of hand and causes formation of unwanted clots

This initiates acute heart attacks.

It results when there is clot formation on the inside surface of an atherosclerotic plaque on coronary artry.

Child BirthWhen uterine contractions become strong enough for the baby head to begin pushing through the cervix.

Stretch of cervix sends signals through the uterine muscle back to body of uterus, causing more powerful contractions.

This process goes on and on.If this process is powerful enough, baby is born.

If not , contractions die out.

Generation of nerve signalWhen membrane of nerve fiber is

stimulated, this causes slight leakage of Na ions through Na channels.

Influx of Na causes change in membrane potential, which causes more opening of channels and so on …..

This process continues untill nerve signals goes to the end of the fiber.

Adaptive controlPresent in nervous system.It is delayed negative feed back.

Some movements of the body occurs so rapidly that there is no time for the nerve signals to travel from the periphery to brain and then back again.

Brain uses a principle called feed-forward control to cause required muscle contractions. Sensory nerve signals from moving parts tells the brain whether the movement is performed correctly.

If not, brain corrects the feed-forward signals that it sends to the muscles the next time the movement is required.

If still further correction is needed, this will be done again next time.

This is adaptive control

Automaticity of the bodyEach cell benefits from homeostasis , each cell contributes its share towards the maintenance of homeostasis.This reciprocal interplay provides continuous automaticity of the body.

Thank You