Blood vessels
Like the hearts, the major blood vessels are significantly
smaller than those of humans. They do not have to be as large, when the
hearts are smaller; also, since each system covers the entire body, there
are additional vessels in most locations. Where there are not, as with
some peripheral veins, they are not reduced in size.
For each heart, the arteries on the opposite side
of the body follow roughly the same path as those of humans. Arteries on
the same side of the body as the heart are different (see figure 2). Recall
that the second system in a mirror image; both arrangements of vessels
are found on both sides of the body, but the different locations of vulnerable
points reduce the likelihood that both systems will be injured at once.
The aortas are a significant exception. The human
aorta curls tightly over the left bronchus and continues down along the
spine. Time Lord aortas follow a smoother curve, as they cross each
other at the base of the trachea before hooking over the bronchi. This
otherwise very vulnerable point is protected by the sternum and cushioned
by fat.
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Figure 2: Major arteries
This drawing shows only the vessels from the left
heart, except for the aorta and pulmonary arteries from the right heart.
1. Primary carotid artery. This artery
follows the same path as the human carotid artery, and also contains the
baroreceptors the body uses to monitor and regulate blood pressure. On
the left side of the neck, this artery comes from the right heart.
2. Secondary (deep) carotid artery. Beneath
the sternocleidomastoid muscle instead of running along it, this vessel
is finer still than the primary one, though both supply blood to the brain
via the circles of Willis (yes, there are two). No pressure receptors,
but the nerves that monitor oxygen saturation are here, instead of in the
primary carotid artery as with humans.
3. Pulmonary arteries. Note that there
are three branches instead of the four humans have. The branch that follows
the aorta to the other side of the body only takes oxygen from the posterior
lobes of the opposite lung.
4. Coronary arteries. Each heart sends
itself blood, as in humans. Note here that they also serve each other;
vessels from the right heart are shown in darker red.
5. Right spleen and kidney. Humans have
only one spleen, on the left. Note that each spleen only processes blood
from one system. However, both are connected to the single lymphatic system.
The kidneys, however, each filter blood from both cardiovascular systems.
6. Secondary brachial artery, posterior carpal
pulse point. The secondary brachial artery, like the deep carotid,
runs beneath muscle (in this case, the biceps brachii). This drawing is
not clear on the positioning at the elbow; the primary (human analog) artery
is medial, and the secondary artery is lateral. Note that at the wrist,
where the radial and ulnar arteries (split from the primary brachial) pass
at the palmar side, the secondary brachial artery passes behind
the wrist bones. After the thumb branch splits off, the artery passes between
the metacarpals before branching again for the fingers.
7. Femoral arteries. Both are near the
surface at the groin, but they are actually about 2 inches apart, thus
decreasing the risk of damage to both.
8. The arteries at the ankle. On the tibial
(medial) side, the primary (human analog) artery passes in front of the
malleolus, and the secondary passes behind and under. On the fibular (lateral)
side, it is the opposite: primary artery under and behind the ankle bone,
and secondary in front.
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Figure 3: Major veins
Like the artery drawing above, this one shows
primarily the veins of the left heart.
1. Vertebral vein. I felt the need to label
this one although I did not label the vertebral artery above because here
it appears to be between the two jugular veins, when in fact it runs through
the transverse foramen of the cervical vertebrae.
2. Jugular veins. Humans have two jugular
veins on each side: the external, running down the outside of the neck,
and the internal, parallel to the carotid artery along the sternocleidomastoid
muscle. Gallifreyans have both of these, as well as a third that runs parallel
to the deep carotid artery. The more superficial pair return blood to the
opposite heart, while the deep returns it to the near heart.
3. Right subclavian vein.
4. Right superior vena cava. Note that
it is the left subclavian vein that runs into the right vena cava.
This is due to the way the aortae cross, yet paired arteries and veins
are always of the same system.
5. Liver. Slightly smaller than the human
liver to make room for the second spleen (not visible here as it is behind
the liver). Also, each lobe processes blood from only one vascular system.
Note that the splenic veins cross (again, this is due to the crossing of
the aortae). Veins from the digestive system join the splenic veins on
their way to the liver, forming the hepatic portal veins.
6. Pulmonary vein. Three to each heart;
one from the same-side posterior lobes of the lung, one from the same-side
anterior lobe, and one from the opposite side.
7. Left azygous vein. Azygous veins collect
blood from the ribs and intercostal muscles. This is another example where
humans already have a pair of veins, and in the Gallifreyan they are split
between the systems.
8. Left inferior vena cava.
On the veins of the arms: These are almost
entirely analogous to human veins, and are simply split between the two
systems. Like the jugular veins, they are significantly larger than their
attendant arteries. Only the veins of the hands are doubled, possibly because
the smaller diameter affords more protection in a highly used area.
On the veins of the legs: Here, there are
several extras, though not a complete doubling as with the cerebral veins.
Veins of the feet are doubled, and in the ankle, they cross the bones in
the same locations as their attendant arteries. |
Capillaries
Although both vascular systems bring blood to
the entire body, not every small area is served by both. Rather, capillary
beds from each system alternate, but they are small enough that the neighboring
beds could compensate if necessary.
Blood composition
The red cell count is noticeably higher than in
most humans; it is comparable to those who live at high altitudes. Under
normal conditions, white cell count is similar, but it can change very
rapidly in the face of infection.
Physiology
Results of blood loss
Unless both vascular systems were damaged, even
severe blood loss would not kill a Time Lord. The second system could supply
enough oxygen and nutrients to keep all organs alive, though not up to
optimum functioning. Loss of as little as a pint of blood (the amount humans
donate in my time) from either system can produce symptoms, from giddiness
with a small loss, through reduced function of all organs, possibly progressing
as far as coma if loss is very high.
The lymphatic system will work to correct an imbalance
between the two vascular systems. Fluid balance is corrected quite readily,
though replacement of lost cells takes longer. White cells are returned
to the damaged system more quickly because extra ones are stored in the
lymphatic vessels when not needed. Red cells are more difficult; they must
be replaced by new ones just as in humans.
Protection of peripheral arteries
Because there are more points at which arteries
approach the surface, one might think they are more vulnerable to damage.
However, they are protected in several ways. First, they are significantly
smaller in diameter and thus not only present a smaller target but also
lose less blood if cut. Second, as in humans, veins run parallel and slightly
superficial to many arteries, but this is even more significant in Time
Lords because most veins are so much larger than the arteries. Third, there
are actually sphincters proximal to the pulse points which will close in
response to damage, minimizing (though not completely stopping) blood flow
through the wound.
With some exceptions, the veins do not have these
same protective factors. Those of the head, hands, and feet are doubled
and therefore smaller, providing some protection relative to humans.
Hemoglobin
Gel electrophoresis suggests four-part hemoglobin
molecules as in humans. It also suggests that 50% of the components are
alpha-chains. However, beta-chains do not make up the entire remaining
50% as they do in adult humans; only 45% are beta-chains. I believe the
remaining 5% are gamma-chains, which would mean that Time Lords retain
(and maintain, since red cells are replaced every few months) 10%
of their fetal hemoglobin (humans retain none, under normal circumstances).
Fetal hemoglobin has a much higher affinity for oxygen - necessary to be
able to take the oxygen from mother's blood, but problematic in free-living
organisms because it does not readily give up the oxygen to the tissues
unless they are in distress. This likely aids a respiratory
adaptation I will discuss later, and it may explain the need for more red
cells (so that the same amount of oxygen is always available to the tissues).
Vital signs
As I mentioned above, the heart rate is higher
than in humans. Also, the two heart rates are not synchronized, and thus
electronic monitoring devices will likely read the rate as twice what it
actually is. This is the reason I unintentionally killed the Time Lord
who would later become my friend; we used defibrillation to treat non-existent
tachycardia and instead stopped his hearts.
The pulse can be measured by auscultation of one
heart at a time, and by palpation of arteries. Despite the increased number
of surface pulse points, there are fewer readable ones than in humans because
the arteries are so much smaller. Only the femoral and external carotid
arteries are consistently palpable. Those with a light touch and sensitive
fingers may be able to detect the pulse at the radial, ulnar, and posterior
carpal sites, as well as the temporal arteries (one along the base of the
temple, the other about one inch higher). Those with a heavier touch will
not be able to feel these by hand because the pressure they need would
obliterate the pulse.
Most pulse points analogous to humans as well
as other places the arteries approach the surface can be read with a Doppler.
Deeper sites, such as the popliteal, can not be read at all.
Blood pressure tends to be comparable to that
of healthy humans. Although the arteries are smaller and thus more susceptible
to tension, the cardiac output is proportionally decreased.
Blood pressure can be measured by auscultation
of the brachial arteries as in humans. However, it is essential to place
the stethoscope carefully so only the medial artery can be heard. Testing
the left arm will give the blood pressure from the right heart, and vice
versa. Generally, they would be the same, unless one vascular system were
damaged.
Temperature tends to be slightly higher than human
(about 37.5 C) due to a higher basal metabolic rate.
Resuscitation
CPR compressions are quite obviously impossible,
but I believe that defibrillation would work, assuming that a) the pads
were placed correctly to affect only one heart, b) the heart was in either
ventricular fibrillation or true tachycardia, and c) the subject did not
regenerate before you could get the pads in place and deliver a shock.
Index by system
Cardiovascular - Respiratory
- Genetics - Life
Cycle
