Gallifreyan physiology

The Gallifreyans, despite looking similar to Humans, have a variety of biological differences that set them apart.


 * Most of the known information of the Gallifreyans is based on the Time Lords, particularly the Doctor. Consequently, the following articles may have some inaccuracies due to these biases.

External anatomy
Externally, Gallifreyans are identical to Humans. However, whereas the Humans of Earth have a diverse range of ethnicities, Gallifreyans tend to have a mostly Eurasian appearance.

Resilience
Gallifreyans are generally tough and resilient, being able to survive extreme cold (DW: The Seeds of Doom, 42) and extreme heat (DW: The End of the World). They could survive the subzero temperatures of vacuum for around 6 minutes (DW: Four to Doomsday) as well electric shocks that would be fatal to Humans (DW: World War Three, Evolution of the Daleks). They can also survive and absorb very high doses of Röntgen radiation, although it was vital to expel the radiation afterwards, although the process of expulsion did cause an itch in the area where the radiation was expelled from, such as from a foot into a shoe. (DW: Smith and Jones). Despite this, radiation of other kinds can be fatal, but even then a Gallifreyan can hold out for a while after receiving these lethal doses. (DW: Planet of the Spiders)

Body temperature
Gallifreyans have a mean body temperature of 60 degrees on the Earth Fahrenheit scale (16 degrees Celsius). (DW: Spearhead from Space, Doctor Who: The Visual Dictionary)


 * Oddly, no Humans have pointed out the differences in temperatures by touch. This might mean that this is a core temperature, whereas their skin temperature is closer to those of a Human.

Senses
Gallifreyans have better senses then a Human. Using taste, the Doctor was able to identify the blood type of a sample. (DW: The Christmas Invasion, NA: Bad Therapy) Gallifreyan eyes are better at seeing in the dark and can gather and enhance available light. (NA: Lucifer Rising) Their sense of hearing is also better than a Human. (Doctor Who: The Visual Dictionary)

The Brain

 * For differences between Time Lord and Human brains see Time Lord anatomy. Some of these differences may also apply to the difference between the brains of Humans and ordinary Gallifreyans, as well.

Circulatory system
Gallifreyan blood is different in composition then a Human's, though similar in colour. (DW: Spearhead from Space, The Invisible Enemy) It is highly adaptive with regenerative properties. (TDA: The Art of Destruction) It doesn't have the same A and B types and the extra-cellular matrix is incompatible with Earth-based life. (TDA: The Art of Destruction, DW: ''The Invisible Enemy')


 * Whether this regenerative properties means that it can repair from damage or that it regenerates is unknown.

Dual cardiovascular system
Gallifreyans naturally born before the time of Rassilon and Pythia had two hearts (NA: Cat's Cradle: Time's Crucible, Lungbarrow).

Oldbood Gallifreyans Loomed after the Pythia's curse of sterility, emerge with a single heart and gain their second only after their first regeneration (MA: The Man in the Velvet Mask). Those of Newblood houses spring from the Looms with two hearts from the outset (NA: Christmas on a Rational Planet). "One for casual, one for best," as Romana once joked. (source?) Time Lords can survive with only one heart, should the other be punctured or destroyed, though they will be weakened greatly (MA: Managra, EDA: The Adventuress of Henrietta Street). Even if all the blood is removed from one cardiovascular system, the Time Lord can still survive (DW: Smith and Jones).

Romana could stop her hearts at will and feign death (DW: Destiny of the Daleks). They only have a resting heart-beat of 10 (DW: Spearhead from Space).

Respiratory system
In order to use these two hearts, the Time Lords require advanced respiratory system. Instead of large lungs, they have a series of pulmonary tubes parallel to the lymphatic system. This makes them positively buoyant, which allows them to swim with ease. (PDA: Island of Death) This also means they can place themselves in a trance state which reduces the need for oxygen. (DW: Terror of the Zygons, Four to Doomsday) Gallifreyans are immune to the effect of helium gas, which can make Human voices sound high-pitched and squeaky. (DW: The Robots of Death)

Gallifreyan also have a respiratory bypass system, which allows them to survive strangulation (DW: Pyramids of Mars). It also means that they can survive longer without much oxygen, past the point where a Human would be unconscious. (DW: The Ark in Space, Smith and Jones)


 * The Doctor found himself susceptible to drowning and strangulation on one occasion, but then that took place in the Matrix, which had different physical laws and conditions. (DW: The Deadly Assassin)

Miscellaneous informations

 * Gallifreyans are susceptible to the intoxicating effects of alcohol, but they can easily shrug off the effects when they must. (PDA: The Quantum Archangel, DW: The Girl in the Fireplace) Contradicting this, the Doctor had a hangover after some alcoholic over-indulgence. (BBCR: Slipback)


 * On one occasion, the Doctor may not have sobered up quickly but have only feigned drunkenness in the first place, in order to trick the Clockwork Droids. (DW: The Girl in the Fireplace)


 * The Doctor was susceptible to certain toxic gases and sleep-inducing drug, though not more so than a Human in the same position. (DW: The Brain of Morbius). The fifth incarnation of the Doctor had an allergy to gases in the praxis range of the spectrum. (DW: The Caves of Androzani)


 * We do not know if all incarnations of the Doctor had this problem or just some of them, or what exact effect the allergy had on him.


 * Time Lords have 26 ribs, as opposed to the 24 in Humans. (NA: Blood Heat)