Positive vs Negative Selection

Positive Selection is when you select something(let it survive, pull it out, whatever) because it has a certain quality.

Negative Selection is when you kill something because it again, has a property of interest.

Sepsis in all its Glory

I won't reproduce all of the information I have read about in this article, but rather mention some highlights. For extra info, you can read from my sources.

Bacteremia

Bacteremia is simply the presence of bacteria in the blood. Is measured by taking a blood sample and attempting to culture out any bacteria. Of course, the blood sample should normally be sterile.

Note that the term bacteremia does not imply the existence of any symptoms.

SIRS – Systemic Inflammatory Response Syndrome

Inflammation is of course a normal and necessary immune response to close off an infection and/or wound, and to being the healing process. However, that inflammation can go wrong and go systemic, hence the terms SIRS. SIRS is a clinical diagnosis, and is diagnosed upon meeting 2 of the following 4 criteria:

• T > 38.5 or T < 35
  
• HR > 90
  
• RR > 20 or PaCO2 < 32 mmHg
  
• WBC < 5000 or WBC > 12,000
  

And when SIRS is deemed to be secondary to a bacterial infection or bacteremia, it is called sepsis. You may notice that this implies that SIRS can be caused by non-bacterial etiologies, and indeed it can, e.g acute pancreatitis.

What is confusing to me are the 4 criteria for SIRS above. They just seem so non-specific to me. Hopefully they will make sense at some point.

Shock

We had a lecture on Shock from Dr. Goldhaber in Block 9. I'm still going with the definition of shock that it is decreased perfusion of organs that leads to organ damage. So shock, or more specifically septic shock in this discussion, is different from SIRS and sepsis. One may even think of shock as a severe outcome of sepsis. References

1. http://www.uptodate.com/contents/sepsis-and-the-systemic-inflammatory-response-syndrome-definitions-epidemiology-and-prognosis

2. http://www.uptodate.com/contents/pathophysiology-of-sepsis

3. http://en.wikipedia.org/wiki/Septic_shock

4. http://en.wikipedia.org/wiki/Bacteremia

Melena vs Hematochezia vs BRBPR

All based on color of stool.

Melena: practically black or 'tarry' stool
BRBPR: just very bright red
Hematochezia:

Wikipedia leads to believe that Hematochezia is different from BRBPR. But one article on UptoDate says hematochezia is "passage of maroon or bright red blood or blood clots per rectum". So these 2 sources of conflicting, and I'm not sure what to think.

References:
1) http://en.wikipedia.org/wiki/Hematochezia
2) http://www.uptodate.com/contents/etiology-of-lower-gastrointestinal-bleeding-in-adults

True or False? Diverticuli Classification

A False Diverticulum is one that in which 2 layers(mucosa & submucosa) penetrate a weakness in the muscular layer. So those 2 layers kind of punch through the muscle, and end up being covered only by serosa.

A True Diverticulum is one in which all 3 layers of the intestinal wall, including the muscular layers, outpouch. So one can argue that the appendix is a true diverticulum.

Note that diverticulosis, false diverticuli are involved. Also, congenitally abnormal diverticuli tend to be of the 'true' type.

Gastritis

Gastritis is one of those topics that bothers me. In fact, almost any –itis disease bothers me. It just seems weird to have an entire disease lying on the existence of inflammation. I still don't quite understand it; in any case, the below is what I've gathered on the subject so far.

Definitions

Gastritis is simply epithelial damage of the stomach mucosa, associated with inflammation found by biopsy. In contrast, gastropathy is the same thing but without the inflammation. Note there has been some confusion around the term, because some endoscopists use the term gastritis to describe changes gross changes they see with the scope. However, one study showed that gross changes by scope are not well associated with presence or absence of inflammation by biopsy.

Classifications

Now as you might imagine, gastritis is a fairly non-specific condition. That is, there exist several disease processes associated with gastritis. As such, there are several ways one might classify gastritis, i.e. by acute vs chronic, etiology(H. pylori vs…TB), specific histological changes (intestinal metaplasia, atrophy, granulomas), etc.

For the med student, it is probably important to know the specific details of each possible disease process.

Signs & Symptoms

First Aid, Goljan Rapid Review, and UpToDate all do not have articles on the signs & symptoms of gastritis. I'm not sure why. Maybe because the symptoms are specific to each disease process associated with gastritis?

Actually, signs& symptoms can be found here: http://emedicine.medscape.com/article/176156-clinical

References:

http://emedicine.medscape.com/article/176156-overview#a0104

http://www.uptodate.com/contents/classification-and-diagnosis-of-gastritis-and-gastropathy?source=see_link

http://www.uptodate.com/contents/acute-and-chronic-gastritis-due-to-helicobacter-pylori?source=search_result&selectedTitle=2~150

Table of Sympathetic Agonists

You should probably know this table by heart

Contraction Alkalosis

Definition: An increase in pH, secondary to a loss of fluid volume.

Mechanism: Fluid loss leads to an activation of the RAAS system. And Angiotensin II activates the Na-H anti-porter in the distal tubule. So more Na+ is being absorbed while H+ is being lost. This helps retain fluid, at the expense of losing H+ ion. So as the body is trying to retain fluid, the pH rises.

Treatment: Simply to treat the underlying fluid loss. The pH should correct on its own

Source: http://en.wikipedia.org/wiki/Contraction_alkalosis
Another source that may be helpful: http://www.usmle-forums.com/usmle-step-1-forum/841-ii-contraction-alkalosis.html

Extra:
Apparently, this can have something to do with Hypo-chloremia. See slide 35 of bk9.wk2.AcidBaseLab