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    Physiology
    Normal physiological values[64]:330
    Body temperature 38.6 °C (101.5 °F)
    Heart rate 120–140 beats per minute
    Breathing rate 16–40 breaths per minute


    Thermograph
    Cats are familiar and easily kept animals, and their physiology has been particularly well studied; it generally resembles those of other carnivorous mammals, but displays several unusual features probably attributable to cats' descent from desert-dwelling species.[33] For instance, cats are able to tolerate quite high temperatures: Humans generally start to feel uncomfortable when their skin temperature passes about 38 °C (100 °F), but cats show no discomfort until their skin reaches around 52 °C (126 °F),[56]:46 and can tolerate temperatures of up to 56 °C (133 °F) if they have access to water.[65]


    Cats conserve heat by reducing the flow of blood to their skin and lose heat by evaporation through their mouths. Cats have minimal ability to sweat, with glands located primarily in their paw pads,[66] and pant for heat relief only at very high temperatures[67] (but may also pant when stressed). A cat's body temperature does not vary throughout the day; this is part of cats' general lack of circadian rhythms and may reflect their tendency to be active both during the day and at night.[68]:1 Cats' feces are comparatively dry and their urine is highly concentrated, both of which are adaptations to allow cats to retain as much water as possible.[33] Their kidneys are so efficient, they can survive on a diet consisting only of meat, with no additional water,[69] and can even rehydrate by drinking seawater.[68]:29[70]


    Cats are obligate carnivores: their physiology has evolved to efficiently process meat, and they have difficulty digesting plant matter.[33] In contrast to omnivores such as rats, which only require about 4% protein in their diet, about 20% of a cat's diet must be protein.[33] Cats are unusually dependent on a constant supply of the amino acid arginine, and a diet lacking arginine causes marked weight loss and can be rapidly fatal.[71] Another unusual feature is that the cat cannot produce taurine, with taurine deficiency causing macular degeneration, wherein the cat's retina slowly degenerates, causing irreversible blindness.[33] Since cats tend to eat all of their prey, they obtain minerals by digesting animal bones, and a diet composed only of meat may cause calcium deficiency.[33]


    A cat's gastrointestinal tract is adapted to meat eating, being much shorter than that of omnivores and having low levels of several of the digestive enzymes needed to digest carbohydrates.[72] These traits severely limit the cat's ability to digest and use plant-derived nutrients, as well as certain fatty acids.[72] Despite the cat's meat-oriented physiology, several vegetarian or vegan cat foods have been marketed that are supplemented with chemically synthesized taurine and other nutrients, in attempts to produce a complete diet. However, some of these products still fail to provide all the nutrients cats require,[73] and diets containing no animal products pose the risk of causing severe nutritional deficiencies.[74]


    Cats do eat grass occasionally. A proposed explanation is that cats use grass as a source of folic acid. Another proposed explanation is that it is used to supply dietary fiber.[75]


    Senses
    Main article: Cat senses


    Reflection of camera flash from the tapetum lucidum
    Cats have excellent night vision and can see at only one-sixth the light level required for human vision.[56]:43 This is partly the result of cat eyes having a tapetum lucidum, which reflects any light that passes through the retina back into the eye, thereby increasing the eye's sensitivity to dim light.[76] Another adaptation to dim light is the large pupils of cats' eyes. Unlike some big cats, such as tigers, domestic cats have slit pupils.[77] These slit pupils can focus bright light without chromatic aberration, and are needed since the domestic cat's pupils are much larger, relative to their eyes, than the pupils of the big cats.[77] Indeed, at low light levels a cat's pupils will expand to cover most of the exposed surface of its eyes.[78] However, domestic cats have rather poor color vision and (like most nonprimate mammals) have only two types of cones, optimized for sensitivity to blue and yellowish green; they have limited ability to distinguish between red and green.[79] A 1993 paper reported a response to middle wavelengths from a system other than the rods which might be due to a third type of cone. However, this appears to be an adaptation to low light levels rather than representing true trichromatic vision.[80]


    Cats have excellent hearing and can detect an extremely broad range of frequencies. They can hear higher-pitched sounds than either dogs or humans, detecting frequencies from 55 Hz to 79,000 Hz, a range of 10.5 octaves, while humans and dogs both have ranges of about 9 octaves.[81][82] Cats can hear ultrasound, which is important in hunting [83] because many species of rodents make ultrasonic calls.[84] However, they do not communicate using ultrasound like rodents do. Cats' hearing is also sensitive and among the best of any mammal,[81] being most acute in the range of 500 Hz to 32 kHz.[85] This sensitivity is further enhanced by the cat's large movable outer ears (their pinnae), which both amplify sounds and help detect the direction of a noise.[83]



    Cats' whiskers are highly sensitive to touch.
    Cats have an acute sense of smell, due in part to their well-developed olfactory bulb and a large surface of olfactory mucosa, about 5.8 cm2 (0.90 in2) in area, which is about twice that of humans.[86] Cats are sensitive to pheromones such as 3-mercapto-3-methylbutan-1-ol,[87] which they use to communicate through urine spraying and marking with scent glands.[88] Many cats also respond strongly to plants that contain nepetalactone, especially catnip, as they can detect that substance at less than one part per billion.[89] About 70—80% of cats are affected by nepetalactone.[90] This response is also produced by other plants, such as silver vine (Actinidia polygama) and the herb valerian; it may be caused by the smell of these plants mimicking a pheromone and stimulating cats' social or sexual behaviors.[91]


    Cats have relatively few taste buds compared to humans. Domestic and wild cats share a gene mutation that keeps their sweet taste buds from binding to sugary molecules, leaving them with no ability to taste sweetness.[92] Their taste buds instead respond to amino acids, bitter tastes, and acids.[93]


    To aid with navigation and sensation, cats have dozens of movable whiskers (vibrissae) over their bodies, especially their faces. These provide information on the width of gaps and on the location of objects in the dark, both by touching objects directly and by sensing air currents; they also trigger protective blink reflexes to protect the eyes from damage.[56]:47