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.

First day: Baby goes to school

Teacher started with the syllabus for the semester. Fantastic teacher doing her Ph.D. Mrs Deepali! Done her 3 years MSc from Solapur . She adds that guys don’t do that particular coarse because of its duration.

She started with very basic like Atoms, elements, moving on to measurement, I will be posting only the things I found new or interesting.

pH value: Normal blood pH is between 7.35 to 7.45. Water is at 7 (neutral), below that gets acidic and above Alkaline. pH is defined as the negative logarithm of the hydrogen ion concentration. I couldn’t understand so told her that any solvent would not contain ANY free ions. It should be all neutral. She took the example of H20 (water). She said it is H+ and OH- and added that it will need an hour’s explanation kept for future. I also couldn’t understand why water has a pH of 7 when it is neutral. I think the answer is it’s just a nomenclature. When the blood pH goes below 7.4 it is called Alkalosis and over it is Acidosis.

Enzymes are catalysts. I asked if hormones are enzymes. She said hormones are just the messenger. They will ask the organs to secrete enzymes. She said enzymes are very important and hence Vitamins are important. I couldn’t understand the link so I asked. She said Vitamins stick with enzymes and are actually co-enzymes.


For example if AH2 is oxidized to form H2, then an enzyme and a co-enzyme is needed for the reaction. The co-enzyme is nothing but a Vitamin, in this case “FAD”. It forms FADH2. This FADH2 is used by ETC electron Transport Chain. Somewhere along the line which I forgot (how much can one learn in one day!) that two Hydrogen atoms are released back in the form of two protons and two electrons. The electron move in the ETC of the IMM (inner microbial membrane) this movement allows the creation of three channels from which protons move out. The center part contains a bunch of protons surrounded by an impermeable membrane. The electrons move around and are later joined by the protons (from the pair of Hydrogen atom: two electron and proton)



FAD stands for flavin adenine dinucleotide and is the co-enzyme. FAD stands for flavin adenine dinucleotide and is the co-enzyme (I forgot the name of the Enzyme). Nothing much was talked about FAD except that it came from the Vitamin Niacin (in that particular flowchart). I asked if that is the Vitamin in rice, she replied saying that was Thiamine and not Niacin (I wonder if Niacin is in Aspirin or the cholesterol reducing medication).



After oxidation the H2 atoms generated are split into 2 protons and 2 electrons. The 2 protons go right inside the impermeable membrane while the electron move outwards joining later with the protons and oxygen to form water (bio water? Water made by our body). I asked if this water is used as sweat. She said not always. The movements of the electrons open three channels through which the protons move out. To maintain equilibrium the protons need to be put back in. This is done with forcefully and is called PMF proton motive force!



The topic in syllabus was how the body maintains its blood pH value near 7. She said that for example in a diabetic patient, I interrupted saying the glucose level in the blood increases. She said we are not talking about glucose level. I said “Insulin?” She then explain how insulin opens the channel to allow glucose in. When in starvation, there is no glucose hence fat is converted into glucose. I asked which channel open/which hormone is needed for the fat channel to open. She answered that the cell membranes allow the oil/fat without the need of any such “channels”/triggers (passive transfer). I asked is it like leather allowing “oil” (I should have said water but she got the jest). Things become hazy here maybe because its time to sleep so I will just scribble. Glucose produced by the body using its own protein (eating itself) is used only for life saving organs like Brain (or heart?). A byproduct of this metabolism is extra ions(?). I said if that is why Anna’s ketones level increased. She exclaimed "YES"! I asked if it was possible to keep the glucose level so high if he was starving for so many days. There is some khichadi which I don’t want to dig too deep because as the teacher also said it was for a good cause ;) Somethings are better left unsaid.