veins (alevel help!)

[laurenjane]

hey everyone
im studying biology and sports studies at as level but the two subjects are clashing

my sports textbook says that veins VENOconstrict and VENOdilate to aid venous return but in biology we are told that only arteries vasoconstrict so i asked my biology teacher and she said she had never heard of venoconstriction/dilation and as she specialises in anatomy i am now seriously doubting my sports textbook
please help!!! who is right!!!

also, my sports textbook says that veins have a thicker tunica externa so it can withstand the pressure when the blood pools but in biology arteries and veins have a tunica externa which is the same thickness

please give me the right answers!!
the internet just isnt helping me
thanks in advance :D

[MichaelXY]

I have only seen the term vasoconstrict, not veno (Venoconstrict does show up in dictionary though).

Also with the arteries and veins, think of it this way. The vessels on the sending end (arteries) are under higher pressure than the veins, so it would make sense that the arteries are thicker, I think it is the middle layer not the external. Something like tunica medious or something, cant remember. So bottom line, arteries have to be stronger than vein as they have more pressure.

[mcar]

"Veno-" is a prefix referring to veins. So when the words either constriction or dilation are added after the prefix, it specifically indicates that it's the vein that constricts or dilates.

[Darby]

Veins have no smooth muscle to produce a constriction - it's possible that the constriction produced by surrounding tissues (such as skeletal muscles or dermal tightening) was somehow misconstrued as something the veins were doing.

I should warn you that there's a lot wrong with sports biology (although it seems to be slowly improving) - the research tends to be shoddy, and the background of the writers is often shallow, and there's a lot of bad speculation. If you stay in the field, you'll see "basic" information change almost yearly. And this won't be the last time you run into a contradiction if you stay tapped into basic physiological research.

[Swede]

Venoconstriction is a physiologcal mechanism that exists. Interesting how your teacher isn't aware of this. The majority of your blood exists in your vein system. Sympaticus innervate these vessels and give constriction of them. This accounts for blood shifting from venous compartments into arterial compartments, a mechanism that serves to increase blood pressure and compensate decreased pressure from bleeding, for example.

Another name for veins is capacity vessels. The term "capacity" comes from it's capacity to constrict and deliver more blood to the arterial side of circulation.

[jwalin]

Veins have no smooth muscle to produce a constriction - it's possible that the constriction produced by surrounding tissues (such as skeletal muscles or dermal tightening)

that is a good point you brought to our notice
i just missed that

[Swede]

Indeed, veins do have SMCs in their tunica media! This muscle layer is however not as thick as the SMC-layer in arteries, since arterial vessels have to cope with much higher pressures. In order to constrict a vessel with a BP of 100 mm Hg you need a lot of more smooth muscle cells than if you need to constrict a vessel with a BP of 10 mm Hg.

If you doubt these words, try searching for "constriction of veins" or something on google. Or just read your histology and physiology books.

[Dibear]

Veins have no smooth muscle to produce a constriction - it's possible that the constriction produced by surrounding tissues (such as skeletal muscles or dermal tightening)

that is a good point you brought to our notice
i just missed that

It's not a good point. Sorry.

Veins do have smooth muscle, just not as much as arteries. If you ever get to watch a venous ablation surgery using ultrasound (I used to do ultrasound for these), you'd be likely to see the vein constrict in response to the catheter moving up through the vein. It's a fascinating physiological response, but quite irritating to the people trying to do the surgery.

The veins are also kind of a storage facility for blood. After blood loss, the veins will constrict to compensate for the low volume of blood and the resulting lower blood pressure.