Topics related to animals and veterinary medicine
Why some animals do not have gall bladder?
- January 16, 2017 at 17:00 #728
I found in my Zoology book that some animals don’t have gall bladder. In human beings gall bladder performs important functions, like concentrating bile and protecting the intestinal mucosa from the injurious effects of bile salts.
Why it disappeared in those animals in the course of evolution? Does any other organ perform its function in them?
- January 16, 2017 at 17:04 #729
There are many hypotheses behind this.
Animal body contains more fat tissue that leaf or grass. Thus, according to some scientists the requirements of bile to absorb fat is less in herbivores compared to carnivores. So animals with herbivore ancestors lost their gall bladder, while carnivore ancestry helped some animals to retain it. We see tiger, cat, lion have a gall bladder, while horse and most of the deer family lost it. The same reason applies to whales who had a herbivore ancestry and so lack a gall bladder.
Some researchers believe that large body mass may be a reason for this. As increased body mass beyond a certain point is a disadvantage, animals with huge body mass lost their gall bladder. This eliminates the possibility of further weight due to collection of large amount of bile in the gall bladder proportional to their body mass.
Some animals take their food frequently. deer graze on fields and eat grass in small amounts. They require a constant supply of bile to digest their food. So a storage organ is not needed in them.
Bile containing more hydrophobic salts leads to greater chance of formation of gallstones on stasis. So animals who produce proportionately more hydrophobic salts than hydrophilic salts had lost their gall bladder. This is also supported by the discovery that animals undergoing long periods of hibernation either lack a gall bladder or produce more hydrophilic salts (bears go into hibernation and produce cholesterol-7β-hydroxylase, which in case of human beings is cholesterol-7α-hydroxylase). Camels don’t eat or drink for long duration. They also lack gall bladder for the same reason. Other members of camel family also lack the gallbladder.
Lamprey (one of the most primitive member of vertebrata) contains liver and gall bladder like structures in their larval phase. The adult lamprey lose both of this structures.
Invertebrates don’t have gall bladder, this may be due to the absence of liver in them.
Mice have gallbladder, but rats don’t, though they are very related. On investigation into the bile formation mechanism of those two animals it was found that bile secreted from liver is much more concentrated in case of rat compared to mice. But as the bile accumulates into the gallbladder the final bile concentration is more in case of mice. While rats don’t have the concentrating mechanism of gallbladder, the hepatic concentration mechanism perhaps compensate this. Again sphincter of Oddi has a much lesser tone in case of rats than mice leading to a less efficient bile storage mechanism in rats.
Most of these hypotheses have some evidences, while they fail to explain many others. A confirm theory is still unavailable.
- January 18, 2017 at 21:32 #836
- May 9, 2017 at 12:43 #1161
Nice answer…appreciate it.