Wikipedia:Reference desk/Archives/Science/2017 January 16

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January 16

Why is the lymphatic system not symmetric in the body?

Why the lymphatic system is not symmetric in the body? I mean that the right side responsible for the right limb only while the left side responsible for the entire body.(Btw, is it the only system in the body that it is not symmetric or there are additional systems like that?) 93.126.88.30 (talk) 00:41, 16 January 2017 (UTC)

There are many, many systems that are not symmetrical. Try putting a mirror to your face so that you are looking at the left (or right) side of your face replicated - you will hardly recognise yourself. Have a look at the fluctuating asymmetry article. DrChrissy ^(talk) 00:46, 16 January 2017 (UTC)

thank you, but I believe that the lymphatic system is asymmetric prominently as you look at the anatomy of the body. 93.126.88.30 (talk) 01:13, 16 January 2017 (UTC)

the heart isn't symmetric. the lungs aren't symmetric (shape, # of lobes). The spleen, the pancreas, the liver, the stomach, the intestines. The kidneys are only very roughly symmetrical (position, blood supply). The aortic arch. The left and right laryngeal nerves. I see no reason to emphasize the assymetry of the lymphatics more than any one of these. - Nunh-huh 02:09, 16 January 2017 (UTC)

I would guess that the relationship of the right lymphatic duct and left lymphatic duct should be evaluated in a broader context in terms of the asymmetry of great arteries and great veins, but I haven't thought this through. Wnt (talk) 12:36, 16 January 2017 (UTC)

The lymphatic system is initially symmetrical but becomes asymmetrical during the later stages of ontogenesis. Ruslik_Zero 13:19, 16 January 2017 (UTC)

Thanks - figure 33 in that source is especially useful. To quote another source, "The thoracic duct develops during the seventh and eighth week of gestational life from two vessels anterior to the aorta, which become the left and right embryonic thoracic ducts. The left one gives rise to the upper third of the adult thoracic duct while the lower two-thirds of the adult duct arise from the right embryonic thoracic duct."[1] The right thoracic duct retains its outlet, though, and continues to pass lymph from the parts that didn't degenerate or fuse, i.e. bronchomediastinal trunk, subclavian trunk, and jugular trunk ... and in some individuals, the lower lobe of the left lung. Perhaps a closer look at that variation would shed some light into the process. It is striking that all the lymphatic and circulatory structures tend to be variable and to develop such asymmetries, as faithful servants of every variation of the developing body. There's also something of a comic resemblance of these duct outlets to an aspiration vacuum on a laboratory sink - I wonder to what degree the venous flow tends to suck the lymph out... funny thing is, central venous pressure is ~ 3 mm Hg, though jugular venous pressure is presumably often lower from being higher, and also has a relaxation phase. I wonder how congestive heart failure or even some poor sap just being hung upside down at a black site affects the lymphatic system... Wnt (talk) 17:21, 16 January 2017 (UTC)

Nobody has yet mentioned physical and functional asymmetry in the brain - see Brain asymmetry. DrChrissy ^(talk) 22:07, 16 January 2017 (UTC)

More extensive and in-depth discussions of functional brain assymetry asymmetry may be found in our article Lateralization of brain function. One of many examples of functional and structural assymetry asymmetry of the brain in that article is the placement of Broca's Area and Wernicke's Area - both of these are often found only in the left hemisphere. Many functional and structural brain asymmetries are discussed in the article. loupgarous (talk) 00:57, 17 January 2017 (UTC)

It amuses me that the question is about the asymmetry of the lymphatic system and Wnt's links show one blue link for the right side and one red link for the left side. Matt Deres (talk) 15:52, 17 January 2017 (UTC)

That's only because left lymphatic duct should be a redirect to thoracic duct, but isn't wasn't. - Nunh-huh 21:26, 17 January 2017 (UTC)

I couldn't decide what to do with that because the thoracic duct actually includes bits of both left and right; also there's an embryonic left lymphatic duct. But I didn't do anything and you did, so you rightly get the say! Wnt (talk) 23:50, 17 January 2017 (UTC)

@Nunh-huh and Vfrickey: Please! Only your butt can be assymetric. Wnt (talk) 21:56, 17 January 2017 (UTC)

Thanks for the catch, Wnt. That was my brain on antihistamines (I've just edited my remarks with a line through my spelling errors as an acknowledgement of my carelessness). loupgarous (talk) 23:40, 17 January 2017 (UTC)

What is the reason that chewing gum causes to appetite?

I'm looking for the physiological reason why chewing gum is a trigger for hunger? 93.126.88.30 (talk) 01:07, 16 January 2017 (UTC)

Googling "chewing gum is a trigger for hunger" returns several sites that claim that the production of saliva triggers the digestive system into thinking that there is food to be digested, making you hungrier. Rojomoke (talk) 03:26, 16 January 2017 (UTC)

I'll vouch for that. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:36, 16 January 2017 (UTC)

Also, the taste of sweetness, whether sugar or a substitute, may cause the body to anticipate digestion and release insulin, leading to lower blood sugar and hence hunger. A good test to distinguish this from the other reason would be to chew a type of gum with no sweetener. StuRat (talk) 07:37, 16 January 2017 (UTC)

According to early advertisements for Doublemint gum, ("double-strength" peppermint) stimulates salivation, aiding digestion -- not to mention soothing throats and mouths, quenching thirst, promote weight loss, slow tooth decay, make the day go by faster, soothe the tired and the nervous, have more fun, make you more attractive to the opposite sex, ... [2] 107.15.152.93 (talk) 12:16, 16 January 2017 (UTC)

...And who can forget this immortal quote: "I'm the Court Jester, and Wrigley's is the Court 'Digester'"[3] 107.15.152.93 (talk) 12:16, 16 January 2017 (UTC)

Lower sex drive during the daytime,higher sex drive at night

Do people have a lower sex drive during the daytime, and a higher sex drive during the night?Uncle dan is home (talk) 18:53, 16 January 2017 (UTC)

Nocturnal penile tumescence ("morning wood") and nocturnal clitoral tumescence seem to support that idea. From an evolutionary POV, before artificial lighting, there wasn't much else one could do to ensure the survival of one's genes at night, in the dark, other than sleep, so this was a good time for mating, while daylight hours were precious, and every minute needed to be spent hunting, gathering, making tools, scouting, etc. (After the discovery of fire, it was possible to do some things by firelight, but there's also a cost to that, such as the time taken to gather, break up, and dry the wood and the effort to light it, so it might be better to save the dry wood for emergencies, like cold or animal attacks, than keep the fire going all night long, every night.) StuRat (talk) 19:12, 16 January 2017 (UTC)

The overlapping articles Libido and Sexual desire list many contributory factors but do not claim a causative correlation with a person's Circadian rhythm. One's particular social demands and opportunities, which are very different for modern or prehistoric man, shape opportunities to act on or think about hormonal drives. Blooteuth (talk) 21:52, 16 January 2017 (UTC)

NPT and NCT are known to be signs of REM sleep: if you have any references to support their correlation with "higher sex drive during the night", StuRat, please provide them.

Likewise, your remarks about an evolutionary connection to prehistoric life activities sound superficially plausible – not surprising, since you're evidently reasonably intelligent and broadly knowledgable – but without references to or citations of any scholarly investigation into the subject, or obvious pointers to subjects that others can follow up, they are no more than your personal musings. Scientific references on the Science Refdesk, please. {The poster formerly known as 87.81.230.195} 2.122.62.241 (talk) 10:55, 17 January 2017 (UTC)

Yes, StuRat's proposed explanation sounds a lot like a just-so story, and is contradicted by the linked articles, which state that they have nothing to do with libido, but are physiological phenomena resulting from changes in brain activity during sleep. Penile or clitoral erections can occur without sexual arousal. --47.138.163.230 (talk) 01:40, 18 January 2017 (UTC)

If you mean the articles I linked to, they do not "state that they have nothing to do with libido". The first article states "REM sleep may allow testosterone-related excitatory actions to manifest as NPT", which sure sounds like they are describing sexual arousal. StuRat (talk) 03:05, 18 January 2017 (UTC)

Physio-chemically, excitation is not the same as psycho-sexual arousal. μηδείς (talk) 16:47, 18 January 2017 (UTC)

There's also nocturnal emission. Are we also going to argue that this has nothing to do with sexual arousal ? StuRat (talk) 22:44, 18 January 2017 (UTC)

I am not arguing anything. "Testosterone-related excitatory actions" refers to excitation of neurons as mediated by testosterone, as per the link I provided. This is an event on the electrochemical level that uses a word you mistakenly apply to macrophysiology. Excitation here doesn't mean excitement. Now, I am not denying that erections are caused by the effects of certain types of neural activity, but you are equivocating by equating excitation with arousal. A 400-level course in organismic physiology will clarify this. μηδείς (talk) 02:13, 19 January 2017 (UTC)

Orgasmic physiology would be even better, if there were such a course. {The poster formerly known as 87.81.230.195} 94.12.94.189 (talk) 14:45, 19 January 2017 (UTC)

My understanding (and experience) of nocturnal emissions is that they're mostly to do with ridding the body of surplus seminal fluid, which is continually produced and which would otherwise leak inconveniently. Any associated perception of sexual arousal (such as a sexually themed dream) is surely a result rather than a cause, just as one may, for example, dream of a fire engine when the alarm clock goes off.

To return closer to the OP's question. I suggest that there may be element of psychological association involved, in that (a) people usually remove their (daytime) clothing to sleep (and may sleep nude) and (b) those that are sexually active will more often be so at night/in bed for cultural reasons. {The poster formerly known as 87.81.230.195} 94.12.94.189 (talk) 14:56, 19 January 2017 (UTC)

Sex drive depends on the time of day.[4]. 92.2.72.206 (talk) 17:18, 19 January 2017 (UTC)