Let's study ID: giraffe plumbing (Introduction)

by David Turell , Sunday, June 05, 2022, 16:34 (689 days ago) @ David Turell

More new information:

https://knowablemagazine.org/article/living-world/2021/heads-up-cardiovascular-secrets-...

"Giraffes have sky-high blood pressure because of their sky-high heads that, in adults, rise about six meters above the ground — a long, long way for a heart to pump blood against gravity. To have a blood pressure of 110/70 at the brain — about normal for a large mammal — giraffes need a blood pressure at the heart of about 220/180. It doesn’t faze the giraffes, but a pressure like that would cause all sorts of problems for people, from heart failure to kidney failure to swollen ankles and legs.

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"When cardiologist and evolutionary biologist Barbara Natterson-Horowitz of Harvard and UCLA examined giraffes’ hearts, she and her student found that their left ventricles did get thicker, but without the stiffening, or fibrosis, that would occur in people. The researchers also found that giraffes have mutations in five genes related to fibrosis. In keeping with that find, other researchers who examined the giraffe genome in 2016 found several giraffe-specific gene variants related to cardiovascular development and maintenance of blood pressure and circulation. And in March 2021, another research group reported giraffe-specific variants in genes involved in fibrosis.

"And the giraffe has another trick to avoid heart failure: The electrical rhythm of its heart differs from that of other mammals so that the ventricular-filling phase of the heartbeat is extended, Natterson-Horowitz found. This allows the heart to pump more blood with each stroke, allowing a giraffe to run hard despite its thicker heart muscle.

"People who suffer from hypertension are also prone to annoying swelling in their legs and ankles because the high pressure forces water out of blood vessels and into the tissue. But you only have to look at the slender legs of a giraffe to know that they’ve solved that problem, too.

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"In part, at least, giraffes minimize swelling with the same trick that nurses use on their patients: support stockings. In people, these are tight, elastic leggings that compress the leg tissues and prevent fluid from accumulating. Giraffes accomplish the same thing with a tight wrapping of dense connective tissue. Aalkjær’s team tested the effect of this by injecting a small amount of saline solution beneath the wrapping into the legs of four giraffes that had been anesthetized for other reasons. Successful injection required much more pressure in the lower leg than a comparable injection in the neck, the team found, indicating that the wrapping helped resist leakage.

"Giraffes also have thick-walled arteries near their knees that might act as flow restrictors, Aalkjær and others have found. This could lower the blood pressure in the lower legs, much as a kink in a garden hose causes water pressure to drop beyond the kink. It remains unclear, however, whether giraffes open and close the arteries to regulate lower-leg pressure as needed. “It would be fun to imagine that when the giraffe is standing still out there, it’s closing off that sphincter just beneath the knee,” says Aalkjær. “But we don’t know.”

"When a giraffe raises its head after bending down for a drink, blood pressure to the brain should drop precipitately — a more severe version of the dizziness that many people experience when they stand up suddenly. Why don’t giraffes faint?

"At least part of the answer seems to be that giraffes can buffer these sudden changes in blood pressure. In anesthetized giraffes whose heads could be raised and lowered with ropes and pulleys, Aalkjær has found that blood pools in the big veins of the neck when the head is down. This stores more than a liter of blood, temporarily reducing the amount of blood returning to the heart. With less blood available, the heart generates less pressure with each beat while the head’s down. As the head is raised again, the stored blood rushes suddenly back to the heart, which responds with a vigorous, high-pressure stroke that helps pump blood up to the brain.

"The great height of giraffes poses a problem when they drink: Lowering the head so far should dramatically increase blood pressure to the head. Lifting it again should cause a corresponding drop in cranial blood pressure — an extreme version of what often happens when a person stands up suddenly. Cardiovascular researchers are trying to understand how giraffes minimize this problem." [head up 220/180, head down 300/200 mmHg!]

Comment: we have no idea why giraffes devloped like they are from the standpoint of purposeful development. The giraffe series has a big gap in neck length, just as the whale series has big gaps. It is extremely difficult to imagine chance mutations did this. Fits much better with a designer at work. dhw should recognize they fit into their ecosystem.