CONTROL SYSTEM (BODY MECHANICS)
Physiology and philosophy can be considered as a single unit. It means ‘study of different functions and mechanism of various body organs and systems in a normal body.’ Furthermore, it gives the answer of ‘How, when, why and what?’ in a normal body. Its range also reaches to onset of a disease and its treatment, since a ‘disease’ is nothing but an ‘altered or impaired function.’ By reading this subject we are actually opening the lock of ‘suspense’ and realising the fact that, human body is finest creation of God.
CONTROL OF BODY FUNCTIONS
Negative Feedback System
Let us consider following examples
- A high concentration of CO2 in extracellular fluid causes increased pulmonary ventilation which eliminates excess CO2 out of the body.
- When blood pressure of a person becomes high, the baroreceptors are stimulated which lowers the raised blood pressure.
- During normal menstrual cycle, when oestrogen level reaches at its peak then almost on 14th day, the controlling hormone. FSH from adenohypophysis is inhibited so level of oestrogen becomes zero or lowest.
So in nutshell it is clear that, “if some factors become excessive, or too little, a control system initiate negative feedback which consists of series of changes that return the factor towards mean/normal/average values/level.
Positive Feedback System
Let us consider following examples:
- During delivery of a child, the head of foetus irritates the wall of uterus which responds by contraction; and, each contraction will push the baby downwards: Thus the uterine contractions stretch the cervix which causes more contractions (Mechanical irritation theory of delivery).
- When membrane of a nerve is stimulated, it leads to slight leakage of sodium ions through sodium channel in the interior of nerve fibre. This influx of sodium ion will change the membrane potential which will open more sodium channel. So with smallest beginning of sodium ion there occurred bombardment of these ions.
This is positive feedback or ‘vicious cycle.’ This mechanism creates instability; not at all stability.
SERVO MECHANISM
- Stretch reflex which regulates muscle length is its example. In different positions of the limb, the resting muscle length of a given skeletal muscle changes. So set point at which length is regulated varies according to position of limb.
- Explanation
- On simultaneous stimulation of alpha and gamma motor neurones; the degree of stimulation of muscle spindle will be considered unchanged (mean neither increase nor decrease); if extra- and intrafusal fibres contract in equal amounts.
- If muscle is contracting against a load; then extrafusal muscle fibres contract less as compared with intrafusal fibres; then receptor portion of spindle will be contracted; which will terminate into elicitation of stretch reflex, and, because of this, there will be extra excitation of extrafusal fibres.
- Advantages
- Muscle can contract against a load. Less expenditure of nervous energy by brain.
- Compensation for fatigue/other muscular abnormalities occur.
Control by Coupling
During hypoxia, the respiration is stimulated. Since respiration and vasomotor centres are lying very close to each other in brain, so blood pressure also rises, along with respiration. This coupling (respiration + B. P.) is essential because it increases blood flow through these organs.
ANTICIPATORY CONTROL SYSTEM
Hypothalamus controls the body temperature but it is in close touch with environmental temperature via cutaneous thermoreceptors. So by this it manages body temperature before environmental temperature disturbs it.
So by having this much knowledge we can appreciate that how enumerable body cells are working in a harmonious way in normal body to maintain homeostasis and when this hormony is lost, disease process starts.
ELECTROPHYSIOLOGY STUDY (EPS) AND RFA PROCEDURE
Electrophysiology is a sub-speciality of cardiology and deals with electrical properties of the heart. Improved understanding of the mechanism of arrhythmia and radio-frequency ablation (RFA) has revolutionised the management of tachycardia.
EPS is the study of the electrical properties of the heart and helps to diagnose the mechanism of arrhythmias. The procedure is performed after all arrhythmic drugs are withdrawn for at least five half-lives in a cardiac catheterisation laboratory under local anaesthesia and mild sedation. Through the femoral veins, electrode catheters are advanced into cardiac chambers, i.e. right atrium, right ventricle, his bundle region and the coronary sinus. X-ray guidance is used to manipulate the catheters within the cardiac chambers. These electrode catheters help to record electrogram from within the cardiac chambers and electrical stimulation through them helps to initiate and terminate tachycardias. This helps to identify the mechanism of arrhythmia and to locate the abnormal focus or connection responsible for the tachycardia. A special electrode catheter called the radiofrequency or ablation (RFA) catheter is then introduced at that spot and the external end of the catheter is connected to RF generator. Delivery of RF energy creates sufficient heat at the local site to charge the abnormal tissue. The energy is delivered through a 4 mm tip electrode and this results in a 2 mm × 4 mm × 6 mm lesion, not damaging the surrounding cardiac structures. The EPS procedure takes one and a half to two hours. However, the RF energy delivered to destroy the abnormal tissue is given only for 45 to 60 seconds. After the procedure, electrical stimulating is performed for nearly 30 minutes to be sure that the tachycardia is no longer inducible and there are no other mechanisms of tachycardia. The electrode catheters are then removed and the groin manually compressed to achieve haemostasis. Immediately after the procedure, the patient is asked to take oral liquids and after 4–6 hours rest period, patient is mobilised and is ready for discharge the next morning. All drugs are withdrawn at discharge and only low dosage of aspirin is prescribed for three months to promote endocardial healing.
GLOSSARY
- Morphology: Study of external form, structure and relative position of various organs of living beings. It is required in accurate description of organism for identification.
- Molecular biology: Branch of biology concerned with study of nature, physico-chemical-organisation, synthesis. Working and interaction of bio-molecules which bring about and control various activities of protoplasm.
- Biogeography: Distribution of organism in various parts of the earth.
- Exobiology: The branch of scientific enquiry dealing with possibility of life in outer space.
- Eugenics: Science dealing with factors related to improvement/impairment of races, specially of human beings.
- Genetic engineering: It deals with production of organism with combination of new heritable characters at will (gene manipulation).
- Anthropology: Study of physical, cultural, mental and social nature of primitive and modern man.
- DNA finger printing: By this technique, a person can be identified on the basis of his genes, as no two persons have identical sub-genetic make up.
- Euthenics: Study of environment and its influence on mankind.
- Electron microscope: Magnification 1,00,000 times. Used for ultra structure of nucleus and cell organelles. Stream of high speed electrons.
BIBLIOGRAPHY
- Adolph EF. Physiologist. Physiological integration in action, 1982, 25 (supp.): I.
- Gann DS, et al. Neural interaction in control of adenocorticotrophin. Fed Proc. 1985; 44:161.
- Rusak B, et al. Neural regulation of circadian rhythms. Phy Rev 1979;59:449.
- Stein JF. Role of cerebellum in visual guidance of movement. Nature 1986;323:217.
- Thompson RF. The neuro biology of learning and memory, Science 1986;233:941.