0709-Homeostasis and Equilibrium

Background reading material by Professor Omar Hasan Kasule Sr. for Year 1 Semester 1 PPSD Session on Wednesday 12th September 2007

Scope of equilibrium: For optimal functioning optimal equilibrium must exist between the internal and external environment. Equilibrium must also exist between opposing actions and phenomena such as blood clotting (coagulation) and clot dissolution (fibrinolysis). Equilibrium must also exist between change and constancy. Maintenance of these various equilibria is due to sophisticated homeostatic mechanisms in the body.


Definition of homeostasis: WB Cannon coined the word homeostasis to refer to the ‘various physiological arrangements which serve to restore the normal state once it has been disturbed. Homeostasis enables the organism to maintain internal stability while responding and adjusting to external change. The stability maintained is dynamic and not static.


Unity and homeostasis: The whole cosmos and what it contains have one deliberate Creator. Thus all the contents must relate to one another in some harmonious way. It is unthinkable that the one Creator could create systems that are contradictory to one another. The harmony must however be looked at in a dynamic way. Because there are constant changes, there must arise from time to time contradictions in the state of flux. There must therefore exist mechanisms for restoring the status quo after the changes have been accomplished. Homeostasis is one of these mechanisms.


Why homeostasis?

It is a miracle of human biology that homeostatic mechanisms exist. They enable the organism to survive in various external circumstances because it can absorb the changes with temporary changes and has mechanisms to return to the original status. If homeostasis did not exist organisms would live in a given external environment and would die if the external environment changes because they would not be able to adjust to the changes.


Concept of the baseline and change: The base-line is not constant. It changes with the environment and time. Muscle hypertrophy is a new level of homeostasis. Variation can be within the range of normality or outside the range of normality. Change may be temporary or permanent. Sleep is a temporary change. Physical fatigue or psychological fatigue are temporary. Lameness and blindness are permanent changes.


Internal and external milieu. The human body is in harmony with its internal and external milieu. The internal and milieu and the external milieu are themselves in harmony. Internal environment: Hormones, fluids etc. External environment: water, air, elements, energy. Hormones are chemical messengers. Main areas of hormone production: pituitary, thyroid, parathyroid, adrenal, pancreas, kidney. Human anatomy and physiology is ground of interaction with both the internal and external environments.


COAGULATION AND FIBRINOLYSIS: Illustration of equilibrium

The processes of coagulation and fibrinolysis are kept in finely tuned balance. Hemostasis refers to control of blood coagulation which stops bleeding from injured blood vessels. It has three components: platelets which plug the injury, the coagulation process, and the contraction of the vascular smooth muscles that cuts off blood supply to the injured area. Coagulation is the process of stopping bleeding; its eventual product is the clot that plugs the injured blood vessel. The change of prothrombin to thrombin is a result of a series of events (a cascade) triggered by contact with a 'foreign' substance; the amplification factor in the cascade could be as much as a million. Thrombin causes the change of fibrinogen to fibrin that is the basis of the clot. The fibrinolytic system acts opposite to the coagulation system. It is triggered at the same time as the coagulation system by damage to tissues. Plasminogen is activated to change to plasmin (fibrinolysin). Anti-plasmin in serum and platelets controls the small amounts of plasmin that are formed spontaneously. Urokinase and similar substances in tears, sweat, milk, and other secretions are plasminogen activators. Once a clot is formed fibrin is covered and plasmin does not reach the inside.

ŠProfessor Omar Hasan Kasule, Sr. September 2007