Gallifreyan physiology

Gallifreyans, despite being visually indistinguishable from Humans, had a variety of biological differences that set them apart.


 * Most of the known information on Gallifreyans is based on Time Lords, particularly the Doctor. It has been unclear for some time if the terms "Gallifreyan" and "Time Lord" are interchangeable, or if "Time Lord/Lady" is a specific rank within the society, possibly with some specialised abilities. Consequently, the following articles may have some inaccuracies due to these biases.

External appearance
Externally, Gallifreyans were identical to Humans, though they tended to have a mostly Eurasian appearance. Hair and eye colour may be of any colour found among Humans. (TDA: The Last Dodo)


 * The Doctor, especially his Seventh regeneration, appeared to have uncertain eye colours. Whether this was an actual ability of the Gallifreyans to change their eye colours or simply due to others' perception is unknown. (NA: Blood Heat, Legacy)

Resilience
Gallifreyans were, on the whole, extremely tough and resilient. An average Gallifreyan was superior to a Human in their peak. (DWN: Doctor Who and the Terror of the Autons)

Gallifreyans could survive extreme cold (DW: The Seeds of Doom, 42) and extreme heat (DW: The End of the World). They could even survive the subzero temperatures and extremely low pressure of vacuum for around 6 minutes (DW: Four to Doomsday), as well as electric shocks that would be fatal to Humans (DW: World War Three, Evolution of the Daleks). Röntgen radiation affected Gallifreyans so minimally that Gallifreyan children were routinely given radioactive toys in the nursery. They could, at will, absorb very high doses of Röntgen radiation, transform it into a form harmless to Humans, and expel it from their bodies. (DW: Smith and Jones) Radiation of other kinds could be fatal, but even then a Gallifreyan could hold out for a while after receiving these lethal doses. (DW: Planet of the Spiders)

Gallifreyans needed less sleep than Humans do, and can make do with as little as an hour. (DW: The Talons of Weng-Chiang, DWN: The Highlanders)

A severely-injured Gallifreyan would generally slip into a healing coma, and devote all his or her energy to healing the injury. While in the coma, they would appear to be dead. (DW: Inferno, The Doctor's Daughter)

Even without regeneration, Gallifreyans had considerable lifespans. Within one regeneration, Gallifreyans could live for hundreds of years, yet look much younger than a Human of equivalent age. (DW: The Leisure Hive) However, Gallifreyan children and teenagers grew at about the same rate as humans of the same age. (DW: An Unearthly Child, The Sound of Drums)

Senses
Gallifreyans had all the senses of Humans, though theirs were generally superior to those of Humans. Gallifreyans also had extraordinary reflexes and precision timing, literally super-Human. (DWN: Doctor Who and the Terror of the Autons, DW: The End of the World, The Doctor's Daughter)


 * Sight: Gallifreyan eyes were better at seeing in the dark and could gather and enhance available light. (NA: Lucifer Rising)
 * Hearing: Gallifreyans generally had acute hearing. (REF: Doctor Who: The Visual Dictionary)
 * Taste: Using taste, the Doctor was able to identify the blood type of a sample. (DW: The Christmas Invasion, NA: Bad Therapy)
 * Smell: The Gallifreyan sense of smell was equal to their sense of taste. (TDA: Wishing Well) They could do a chemical analysis of the air using their sense of smell. (DWN: Doctor Who and the Carnival of Monsters)

As well as the senses shared with Humans, Gallifreyans had further senses, with at least an undefined Sixth Sense. (TDA: Wishing Well)

Gallifreyans have time related senses and physical attributes; they are able to resist fields of slow time (DW: The Time Monster), notice distortions and jumps in time (DW: Invasion of the Dinosaurs), and perceive all possible time lines (Source?)

Gallifreyans are also able to sense the presence of other Gallifreyans, with the sense being specific enough to allow identification of one another just by sight (though this has been portrayed to varying degrees). This would appear to have some connection to their telepathic and telekinetic abilities. (DW: The Sound of Drums)

Body temperature
Gallifreyans had an internal body temperature of about 60 degrees Fahrenheit (16 degrees Celsius). (REF: Doctor Who: The Visual Dictionary) While recovering from a serious injury, it could drop spontaneously to below-freezing temperatures. (DW: Planet of the Daleks)


 * Oddly, no Humans 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.

The Brain
The Time Lord brain was much more complex than that of a Human brain, not to mention larger. The size differences effectively ruled out brain transplants from a Gallifreyan to a Human. (DW: The Brain of Morbius) They were telepathically linked to one another and were even capable of joining the entire Time Lord intelligence as one. (DW: The Invisible Enemy) The Timewyrm noticed that on a quantum level, the Doctor's brain could receive information from possible futures, possibly without even realizing it consciously. (NA: Timewyrm: Revelation) Time Lords could also separate the hemispheres of their brain, allowing them to multitask easily. (PDA: Island of Death)

Time Lords had an additional lobe to their brain dedicated to mechanical and other bodily functions, freeing up the other lobes for intellectual endeavours. (BFA: Spare Parts)

Skeletal structure
Gallifreyan skeletal structure was identical to Human skeletal structure, with the exception of the rib cage: Gallifreyans had 26 ribs, two more than Humans. (NA: Blood Heat)

Circulatory system
Gallifreyan blood was different in composition from Human blood, as well as darker in colour and with a slight orange tinge to it. (DW: The Two Doctors, NA: The Left-Handed Hummingbird) The differences were readily apparent under a microscope. (DW: Spearhead from Space, The Invisible Enemy, Doctor Who: The TV Movie) It was highly adaptive, with regenerative properties. (TDA: The Art of Destruction) It didn't have the same A and B types as Human blood (i.e., the A and B antibodies were not present), the extra-cellular matrix was incompatible with Earth-based life and the structure of hemoglobin was different. (TDA: The Art of Destruction, DW: The Invisible Enemy, EDA: Placebo Effect)

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 emerged with a single heart and gained their second only after their first regeneration. (MA: The Man in the Velvet Mask) Those of Newblood houses sprang from the Looms with two hearts from the outset. (NA: Christmas on a Rational Planet) A Gallifreyan could survive with only one heart, should the other be punctured or destroyed, though he or she would be weakened greatly. (MA: Managra, EDA: The Adventuress of Henrietta Street, DW:The Shakespeare Code) Even if all the blood were removed from one cardiovascular system, the Gallifreyan could still survive. (DW: Smith and Jones) A Gallifreyan in total cardiac arrest would need CPR on both hearts. (DW: Smith and Jones)

Gallifreyans could, with training, gain conscious control over their hearts, enabling them to stop their hearts and feign death, (DW: Destiny of the Daleks) and could slow them down significantly (DW: Terror of the Zygons, TDA: Wishing Well). A dual cardiovascular system being more efficient, Gallifreyans had a resting pulse of as few as 10 beats per minute. (DW: Spearhead from Space) Under stress, the hearts' rate could seem dangerously fast and irregular to human doctors. (DW: Doctor Who: The Movie) Two pulses could be detected in the wrist. (DW: The Five Doctors, Time and the Rani)

Respiratory system
In order to use their two hearts, Gallifryans had an advanced respiratory system. Instead of large lungs, they had a series of pulmonary tubes parallel to the lymphatic system. This made them positively buoyant, allowing them to swim with ease. (PDA: Island of Death) They could also survive longer without much oxygen, past the point where a Human would be unconscious. (DW: The Ark in Space, The Two Doctors, Smith and Jones, NA: Legacy) Despite this, Gallifreyans (especially frailer individuals) could be affected by altitude sickness. (DWN: Marco Polo)

Like most aspects of Gallifreyan physiology, the respiratory system was largely under conscious control. Gallifreyans could, at will, enter a trance state which reduced the need for oxygen. (DW: Terror of the Zygons, Four to Doomsday) Gallifreyans also had a respiratory bypass system, which allowed them to survive strangulation. (DW: Pyramids of Mars, NA:Human Nature)

Gallifreyans were immune to the effect of helium gas, which could make Human voices sound high-pitched and squeaky (though this is implied to be a learned technique rather than an innate ability). (DW: The Robots of Death)

Other Organs
The Gallifreyans had two livers. (EDA: Halflife) They also had several organs which had no analogue in Humans. (EDA: Placebo Effect)

Biochemistry
On the whole, Gallifreyan biochemistry seems to have been quite similar to Human biochemistry: they could eat anything Humans could and could breathe in the atmosphere of Earth. (NA: The Left-Handed Hummingbird)

Gallifreyan biochemistry, like many other aspects of Gallifreyan physiology, was subject to the conscious control of the individual. For example, a Gallifreyan was able to counteract the negative properties of Psilocybin by modifying the chemicals into something harmless, though the techniques were not foolproof and drug overdoses were still possible. NA: The Left-Handed Hummingbird) Similarly, though Gallifreyans were susceptible to the intoxicating effects of alcohol, they could easily shrug off the effects when they needed to. (PDA: The Quantum Archangel, DW: The Girl in the Fireplace) As with Humans, however, excessive consumption could produce a hangover. (BBCR: Slipback)

Some Human medicines seem to have worked on Gallifreyans as well as Humans: some sleep-inducing drugs or toxic gases, for example. (DW: The Brain of Morbius) Anaesthetic gases of the type commonly administered before surgery, however, did not work well on Gallifreyans; a much greater quantity of anaesthetic must be administered, and even then it may not work completely. (DW:Doctor Who: The TV Movie) Finally, some Human medicines could be toxic to Gallifreyans. The Doctor claimed that single tablet of aspirin might kill him; this was offered as an example of his metabolic differences from humans. (DW:The Mind of Evil)

Gallifreyans were as susceptible to Humans to the devastating effect of spectrox poisoning; spectrox toxaemia proceeded at roughly the same rate in both species, though a Gallifreyan, being tougher, would not succumb as quickly. (DW:The Caves of Androzani) They could counteract cyanide poisoning, given a number of ingredients (ginger beer, salt (from anchovies, as pure salt is "too salty"), walnuts) and a physical or mental shock, but only if done very soon after the cyanide is ingested. (DW:The Unicorn and the Wasp)