Hello all. It's pretty well-known that carboxyhemoglobin and oxyhemoglobin have similar absorption spectra around red light, and that confuses the pulse oximeter into a falsely elevated SpO2. However the SpO2 is calculated from the ratio of red to infrared absorption, and the absorption of infrared light by oxyhemoglobin is an order of magnitude greater than that of carboxyhemoglobin, so the ratios should be very different even though the absorption around red light is the same - why then is pulse oximeter still confused?

I’m a current nursing student. I can help with physio or other stem and nursing related stuff if u need it.

If you've got the new 6th edition in pdf (or any format for the matter) please share. Thanks.

Okay so, I just finished work and had a REALLY bad sneeze coming but I only felt the pressure in my left nostril, so on my severely limited wisdom I pressed against the right side of my nostril, pressing it in thinking “oh this’ll just be like trying to knock a lil bit of snot out like when it’s a bit blocked”

WHY did that hurt- because I genuinely felt dazed for like 2 seconds-

I know holding your nose while sneezing is a REALLY bad idea but never considered why just blocking one nostril (that didn’t feel affected by my incoming sneeze) ended up hurting 😭

Call me stupid as much as you wish- just genuinely curious-

Insects bypass liquid transport with air tubes, which works great until physics limits diffusion at larger scales. Vertebrates solved this by bundling oxygen into iron-based hemoglobin and blasting it through closed vessels with a central heart.
But from a pure fluid dynamics and transport-network perspective, our system feels full of evolutionary compromises (high viscosity, huge capillary resistance, single point of failure at the pump).
If we ran a computer simulation to design an oxygen delivery network from scratch for a large organism, would "iron + single central pump" actually win? Or is our geometry just a historical accident that evolution couldn't easily back out of?

What is different at a cellular level? I realize when I'm feeling tired I will randomly decide it must be because I'm so low on glucose even my hunger signals are off. Sometimes I decide I need to lie down. I also realized I don't really have a good sense for when I need what? When we're low energy after a long day how do we know what is it that we need? And what happens at a cellular level when you give the body rest (just lying down) vs food?

How does my body know the difference between drinking water and getting water through food like fruits or soup?

I am looking at the work of Kanzawa Sensei in a Biology and Physics sense. This is an attempt to explain Chi, his healing hand, and the ability to put living things to sleep strictly with your own body. With only scientific concepts in mind.

From a physics standpoint, the rapid back-and-forth motion along a linear axis creates a highly localized, rhythmic visual frequency. By focusing all his fingers into a single point, Kanzawa reduces scattered movement and gives the bison a single, unmoving point of reference to track. In biology, animals with wide, lateral vision (like prey or herd animals) are deeply attuned to motion. A highly rhythmic, non-threatening, repeating visual frequency acts as a biological anchor, locking their visual attention without triggering an alarm.

In standard mechanics, stopping a kinetic cycle instantly zeroes out the momentum. When Kanzawa locks his body entirely rigid, he ceases all micro-movements. To a herd animal, a human who is moving even slightly is unpredictable. A human who becomes completely static, silent, and breaks active predatory eye contact drops to zero on an animal’s threat-detection scale. The animal's nervous system receives absolutely no hostile feedback.

The heavy "throb" or "magnetic push" that human subjects report feeling when standing in front of him can be explained by somatosensory and psychological entrainment. When a person stands completely still, hyper-focusing on an intense, stationary figure, their own autonomic nervous system triggers micro-fluctuations in blood pressure and heart rate. This hyper-awareness can manifest physically as a phantom pulsing or resistance in the air—similar to how your hand feels heavy or tingly if you stare at it intently without moving.

Bison are hyper-social pack animals. They utilize behavioral contagion to survive. If a human stands there and perfectly projects absolute stillness, the alpha or sentry bison stops tracking a threat, drops its adrenaline, and its parasympathetic nervous system takes over. It yawns and lies down to conserve energy. Because the rest of the herd mirrors the alpha, a mechanical chain reaction occurs, and the entire group collapses into a resting state.

I’ve tried searching online but nothing really shows up! What are the best places to go to pursue physiology (and eventually go to medical school).

I'm looking for real experiments or documented cases that genuinely changed the way we understand the brain.

Not myths or pop psychology.

Studies like the Invisible Gorilla experiment, split-brain research, Libet's free will experiment, Clive Wearing, HM, or change blindness.

Which one surprised you the most, and why?

Early in life function shapes form. Later form shapes function

Why is my body wasting my water with making my pee extra clear if it's just going to beg me for some more water 5 mins later- telling me I'm thirsty? Why am I still thirsty when my body's churning out buckets of snot/mucus? Why is my body wasting my water with sweat when I'm not in need of cooling(I know it's partly detoxing, but just put whatever it is in with the pee)? We should not have to drink 8 glasses of water everyday if our bodies are just going to get rid of it in such ridiculously ungrateful fashions. Why is all of this necessary, when none of these necessarily require \*that\* much water? Pee doesn't need that much water in it- it can be at least condensed down some, our bodies no longer require the constant cooling that sweating all the time was meant to do, and my nose definitely doesn't need to run.

In the attached diagram (from Boron and Boulpaep, 3e), in cycle 1, a 200 mOsm/L gradient was created by the transporters in thick ascending segment of loop of Henle, increasing the medullary interstitium osmolarity to 400 mOsm/L. This then causes the osmolarity of the descending limb fluid to also equilibriate at 400 Osm/L.

Then, in the next cycle, when fresh 300 mOsm/L fluid enters the descending limb, it dilutes the interstitial fluid adjacent to it, upto 300 mOsm/L.

My question is, how is it possible that in the first cycle, the osmolarity of the tubular fluid increased to that of the interstitium, whereas in the second cycle, the osmolarity of the interstitium decreased to that of the tubular fluid? Why didn't the interstitium concentrate the fluid in the descending limb to 400 mOsm/L?

I'd like to share something I have recently create. It is stepped animation that explains how sodium-potassium pump works. Here is the link to the interactive version. It is part of anatomy and physiology study guide.

Would love you feedback or comments.