Cats under the microscope


Cats. They’ll push your glass off the table, get you to open the window just to look outside some more, and recognise your voice but pretend they didn’t hear. Yet, the little despots rule the internet – and the couch. This International Cat Day, take your obsession with cats to a new level by learning about their physiology: how their bodies work.

How does cats’ hunter vision work?

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Cats have a broader visual field than us, spanning about 200 degrees instead of 180, however they can only see objects 20 feet away, whereas we can see over 100 feet away. While our eyes are chock full of cone cells that specialise in detail and colour, cats’ are packed with rod cells specialised for dim light and night-vision. Because they have more rod cells, they can track quicker movements. This might explain why they find laser pointers so fascinating. While we see the laser darting from one spot to the next, a cat would see its path along the way.

Why do cats cause allergies?

Do cats have you reaching for tissues?  They are a common cause of allergy: an overreaction of our immune system, which triggers mechanisms designed to fight infection (like a runny nose, itching and swelling) in response to harmless substances. Cat allergies are mostly triggered by two major allergen proteins. The most reactive one, Fel d 1, triggers reactions in more than half of cat allergy sufferers. It is found in cats’ saliva and waste, but is also produced by their skin cells. Another protein, Fel d 4, is similar to what triggers allergies to horses, dogs, guinea pigs and rabbits. Allergens in cats’ saliva end up on their fur when they groom themselves. It is the fur they shed, along with dead skin cells, which flies around and ends up on surfaces, carpets… and in the noses of allergic people! But there is hope yet for allergic cat lovers.  Allergen-specific immunotherapy, an ‘allergy vaccine’ of sorts, aims to train the immune system to stop overreacting to harmless allergens, by introducing it in small doses at first, and increasing them little by little. To avoid the risk of a dangerous allergic reaction during the process, scientists are developing molecules that look enough like the allergens to train the immune system, without the power to trigger an allergic reaction. In the meantime, allergic cat lovers might be tempted by claims of hypoallergenic animals. While some cats may naturally produce lower levels of allergens, this varies from cat to cat and no breed has been proven ‘hypoallergenic.’ Opting for a short-haired or bald cat breed may limit allergy risk because they won’t shed as much fur, but better keep those anti histamines close – cats have no notion of personal space!

How do cats purr?

What makes the purr distinctive from other cat vocalizations is that it is produced continually, while the cat breathes in and out. In contrast, a meow is only produced when breathing out, like when we speak. The purr sound is produced in the larynx – the voice box. Cats with a paralysed larynx can’t purr, and purring returns with their voice, after healing. In the larynx, the vocal folds oscillate to create the purring sound as inspired or expired air passes through.

Because it is created by a different mechanism than voice, purring can occur at the same time as a meow, hence the purr-cry that cats use to manipulate us when they want to be fed. And house cats are not the only ones to purr. Purring has been recorded in most felines, except for panther-like species: Lion, Leopard, Jaguar, Tiger, Snow Leopard and Clouded Leopard. As lovely as it is, a cat purring at the vet’s (if only!) may prevent them from hearing properly during auscultation. There’s an easy fix for it, just turn on a tap nearby!

What determines calico fur patterns?

The fur pattern of a calico or tortoiseshell cat all boils down to genetics, and specifically the X chromosome.

Tortoiseshell cat

To understand how, we need to take a short detour into sex chromosomes. X and Y chromosomes, the two that determine sex, were not created equal; Y chromosomes have very few genes, whereas X chromosomes have hundreds. And while males only have one of the large X chromosomes, females have two. Double the chromosomes, double the proteins, right? Not quite, because producing double the amount of proteins from the X chromosome would be toxic. To make up for this imbalance, females shut down one of the X’s when the fertilised egg starts dividing. The gene for fur colour is on the X chromosome in calico cats. When the black fur gene is inactivated, the cell creates orange fur instead. The X chromosome that’s inactivated is randomly chosen in each cell. This means certain parts of the fur will be black and others will be red.

 

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