Thread by @nickmmark, Here’s a #tweetorial about extremes of #physiology that are very much "compatible [...]

Here’s a #tweetorial about extremes of #physiology that are very much "compatible with life".

Case #1. You are called about a critical drop in platelets.
Platelet Count (x10^3/uL)
Previous 475
Current 45

It’s nothing to worry about. This sample came from a ___.

Answer

To avoid VTE while hibernating, squirrels drop their Plt counts 10x! They also

vWF & Factors VIII/IX

Red tailed

have Plt counts ~750 as fawns that drop to ~250 as adults (over yrs)

Stepping on a Lonomia

is a medical emergency. It *CAUSES* thrombocytopenia/DIC!

Answer To avoid VTE while hibernating, squirrels drop their Plt counts 10x! They also vWF & Factors VIII/IXRed tailed have Plt counts ~750 as fawns that drop to ~250 as adults (over yrs)Stepping on a Lonomiais a medical emergency. It *CAUSES* thrombocytopenia/DIC!

Case #2: You get a call from bedside nurse about an abnormal blood pressure:
BP 330/240

You reassure him, that's a totally OK blood pressure because it was measured in a ___.

Answer:

have the highest BP of any extant species, an adaptation to perfuse their

atop 2m necks.

is very viscous (no RBCs, just protein) so their BPs run high for invertebrates (70s/30s) *BUT* they go into CARDIAC ARREST w/ exercise

can develop HTN w/ BPs170s/150s

Answer: have the highest BP of any extant species, an adaptation to perfuse their atop 2m necks.is very viscous (no RBCs, just protein) so their BPs run high for invertebrates (70s/30s) *BUT* they go into CARDIAC ARREST w/ exercisecan develop HTN w/ BPs170s/150s

Bonus answer:

If you think that’s a high BP, long-necked dinosaurs (Barosaurus & Brachiosaurus)

were once thought to have SBP >700mmHg with head raised. This would have required a 1000+ kg heart. More likely it didn’t raise its head but used it to forage while swimming.

Bonus answer: If you think that’s a high BP, long-necked dinosaurs (Barosaurus & Brachiosaurus) were once thought to have SBP >700mmHg with head raised. This would have required a 1000+ kg heart. More likely it didn’t raise its head but used it to forage while swimming.

Point: “normal” BP depends on position. Because humans walk upright our BP must be higher.
This is why orthostatic BP is so useful.

Also, in case you were wondering, taller people *do* have slightly higher BP (in the NHANES dataset at least). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5815765/#!po=32.3529

Associations between height and blood pressure in the United States population

The mechanisms linking short stature with an increase in cardiovascular and cerebrovascular disease risk remain elusive. This study tested the hypothesis that significant associations are present...

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5815765/#!po=32.3529

Case 3: Now you are called by the hematology lab about a critical value on a CBC:
WBC 5
Hb 0
Hct 0
RBC 0
Platelet 150

You tell the lab "It’s cool. Nothing to worry about because the sample came from ____."

Answer:

Icefish (channichthyidae literally means white blood fish) are the only vertebrates w/o hemoglobin

They survive by combining high SV (5x larger heart), big capillaries (low SVR), & increased O2 solubility in the arctic ocean. They also don’t do very much (lower VO2).

Answer: Icefish (channichthyidae literally means white blood fish) are the only vertebrates w/o hemoglobinThey survive by combining high SV (5x larger heart), big capillaries (low SVR), & increased O2 solubility in the arctic ocean. They also don’t do very much (lower VO2).

Other answers:
The

has hemocyanin, an O2 binding metalloprotein w/ Cu instead of Fe

The Opah is the only warm blooded

; it actually uses more O2

The vampire

is adapted to the O2 minimum zone (O2 sat 3%); w/ large gills & O2 avid hemocyanin it extracts >90% of dissolved O2

Turns out FiO2 is pretty important if you don’t have lungs

300 million years ago, insects were *much* bigger. Imagine a dragonfly the size of a seagull (2.5 foot wingspan).
Why? Atmospheric FiO2 was

in the Paleozoic period: 35% compared to 21% today. https://www.eurekalert.org/pub_releases/2006-10/aps-gim100706.php

Giant insects might reign if only there was more oxygen in the air

The delicate lady bug in your garden could be frighteningly large if only there was a greater concentration of oxygen in the air, a new study concludes. The study adds support to the theory that some...

https://www.eurekalert.org/pub_releases/2006-10/aps-gim100706.php

Rarely people survive very low hemoglobin too:
One person survived a Hb of 1.8 g/dL w/o transfusion & another survived Hb of 0.7 g/dL.

Like the animal kingdom examples, this is possible due to

FiO2,

SV,

SVR,

O2 extraction, &

O2 consumption (& also a lot of luck)

Rarely people survive very low hemoglobin too:One person survived a Hb of 1.8 g/dL w/o transfusion & another survived Hb of 0.7 g/dL.Like the animal kingdom examples, this is possible due to FiO2, SV, SVR, O2 extraction, & O2 consumption (& also a lot of luck)

Case 4: Your

just keeps on going off! Now you are getting paged about an abnormal urinalysis result.

Urine Osm 9000
SG > 1.060

That’s expected because it came from a ____.

Answer:

Humans can concentrate our urine to ~1200 mOsm/L
Dolphins reach ~1700 but contrary to belief they can’t drink seawater
Camels reach 2800 mOsm/L but dessert rodents are the champs. Chinchilla go without

for weeks & concentrate urine >7500 mOsm/L. That’s a SG > 1.060!

: Don’t underestimate dehydration in people “found down"
We lose >1.2L/day insensibly (& more if sweating). Life-threatening dehydration occurs w/i DAYS at rest or HOURS with activity

Thanks to @robertpdickson for recommended this great