Homeostasis (Physiology Lecture)

Homeostasis, according to Dr Vivek is, “why things happen in a certain manner”. He begins with reminding us that the function of any organ, be it the kidney, liver or the lung, is at the CELL level. The fluid inside these cells are called “Intracellular Fluid (ICF).


As shown in the above diagram, all cells are surrounded by these Extra-Cellular Fluids. They are bathed by ECF, they survive, live in this fluid. Hence these fluids are its environment!

Milieu Interior: (Milieu- Etymology- Mi = Middle (medius-Latin), Lieu = place) Its outside the cell but inside the body, hence it’s the internal environment for these cell, hence it’s called Milieu Interior. The properties of these fluids needs to be constant/stable, The Na level, K+ level, pH level, temperature, the acid-base balance, these are all the constituents of the ECF. The cell survives to its fullest only if all these parameters or constituents of the ECF is kept constant. Maintaining the consistency of the internal environment is called Homeostasis. (Etymology- Gk. stasis "a standing still," related to statos "placed," verbal adj. of histemi "cause to stand," from PIE base *sta- "to stand". sis-suffix in Gk. nouns denoting action, process, state, condition, from Gk. -sis, which is identical in meaning with L. -entia, Eng. -ing.)

Dr Vivek then went on to describe various systems, its function and importance. Interesting things that I now remember is that among systems like skeletal, reproductive, digestive etc., the regulatory systems are Nervous system and Endocrine system. Nervous systems have instantaneous messengers while endocrine system is slower. He gave the example of the thyroid hormones which starts secretion 24-48 hours after receiving the go ahead! He added that hormones are mainly created in ductless organs and secretion of such glands come directly into the blood stream.

Other tidbits that I remember from the class are, Digestion is simplification of complex food so that the nutrition can be absorbed. 99% of the mechanism or function of the body are based on negative feedback. The CO2 is released by each cells is transported to the heart which then send it to the lungs and its then expelled out. Skeletal system is used by the body to transfer itself to a congenial environment (if it’s too hot or cold), it allows to move towards food/water.