Wednesday, April 17, 2013

Kidney Physiology

Great overview

Urine Production Video - Osmotic Gradients

This is kind of fast, but it shows the counter-current diffusion of water and ions from the Nephron loop and vasa recta.


Here's a fun video - why coffee and alcohol make you pee more.

Wednesday, April 10, 2013

Respiration, Oxygen, and Hemoglobin

By decreasing pressure inside the thoracic cavity, we are able to inspire air.  By contracting the diaphragm, intercostal muscles, and others, we increase the size of the thoracic cavity, which in turn lowers the pressure to the point that it is lower than the outside air, causing a pressure gradient so the air rushes into the lungs.  To exhale, it is the opposite- relax the muscles, decrease the space in the cavity, which increases the pressure inside until higher than outside, so the air rushes out to where the pressure is lower.

This video is a good summary.  The embedding doesn't work, so you'll have to click the link instead.  Just left the embed on there for the picture. :)

Partial Pressure
Total Pressure of air can be broken into the partial pressures of all the gases contained in that air.  For instance, if the atmospheric pressure is at 760 mm Hg, and 20% of that is Oxygen gas, 80% Nitrogen gas, then the partial pressure of O2 would be 20% of 760 = 152 mm Hg.  Partial Pressure of N2would be 80% of 760 = 608 mm Hg.
This illustrates how increasing the pressure, as in the B picture, causes more gas to diffuse into the liquid.  A simple way to think about it is just that the higher the partial pressure of that gas, the less space it has to bounce around in the air, so more of it will end up in the liquid.

Here's a long video on partial pressure and gases getting into solution, I didn't watch the entire thing yet but it looks like a good detailed explanation for those who feel they could use more information.

Tuesday, April 9, 2013

Deer Carcass - Determining the Cause of Death

I was wandering around the Dry Canyon area with my boyfriend and we ran across some awesome stuff.  First off, we found a partial skull, which I of course kept, and not far off, we found a mule deer carcass!  There was fur everywhere and even looked as though the animal had been dragged to a more protected area in the bushes, as you can see in this picture:

Here I am next to the carcass, holding the skull

However, it didn't appear that any of the bushes were broken from the animal being dragged in there, and the way the animal was prostrated (particularly the position of the front limbs) didn't seem to indicate dragging but almost rather that it had laid down there.

See my geeking-out face?  Also notice the front limbs curled neatly under the animal.
So, obviously I'm no expert in forensics or animal behavior, but it was fun to try to guess how the animal died and how its body came to be where and in what condition it is.  Did it die of natural causes, and was later ravaged by scavengers who tossed hair to and fro so the surrounding area is littered with it?  Did a predator kill it and drag it out of the way?  Could it even have been a cougar cache at one point?  Let's look at each possibility.

Cougar Cache
There is evidence that could be consistent with dragging a killed animal to a safer place.  However, there is no evidence that any attempt was made to bury or cover it as cougars usually do with their caches, as in these pictures:

There also doesn't seem to be a lot of blood soaked into the fur of the animal as would be expected if it had been killed by a predator.  I would think the neck would be covered with blood if a cougar had brought it down.
Head, neck and open thorax of deer.  Notice lack of blood on fur.
Based on the evidence and that information, my conclusion is it's definitely not a cougar cache.

Another Predator
Perhaps a coyote or even dog brought down the deer?

Died naturally & later scavenged

Wednesday, April 3, 2013

Regulation of Blood Pressure

Blood Pressure is a very important aspect of homeostasis.  So naturally the body has many methods of monitoring and adjusting blood pressure to keep within a range that is functional for life.

Baroreceptor Reflex
Baroreceptors are located in the aortic arch and carotid sinuses (pictured below).  These are mechanoreceptors that respond to stretching of the arteries in response to blood pressure.

When these receptors are stimulated, nervous impulses are sent to the medulla oblongata of the brain where the reflex centers for vasomotor, cardiac, and respiratory are.