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Vessel length and diameter

The length of a vessel is directly proportional to its resistance: the longer the vessel, the greater the resistance and the lower the flow. As with blood volume, this makes intuitive sense, since the increased surface area of the vessel will impede the flow of blood. Likewise, if the vessel is shortened, the resistance will decrease and flow will increase.

The length of our blood vessels increases throughout childhood as we grow, of course, but is unchanging in adults under normal physiological circumstances. Further, the distribution of vessels is not the same in all tissues. Adipose tissue does not have an extensive vascular supply. One pound of adipose tissue contains approximately 200 miles of vessels, whereas skeletal muscle contains more than twice that. Overall, vessels decrease in length only during loss of mass or amputation. An individual weighing 150 pounds has approximately 60,000 miles of vessels in the body. Gaining about 10 pounds adds from 2000 to 4000 miles of vessels, depending upon the nature of the gained tissue. One of the great benefits of weight reduction is the reduced stress to the heart, which does not have to overcome the resistance of as many miles of vessels.

In contrast to length, the diameter of blood vessels changes throughout the body, according to the type of vessel, as we discussed earlier. The diameter of any given vessel may also change frequently throughout the day in response to neural and chemical signals that trigger vasodilation and vasoconstriction. The vascular tone    of the vessel is the contractile state of the smooth muscle and the primary determinant of diameter, and thus of resistance and flow. The effect of vessel diameter on resistance is inverse: Given the same volume of blood, an increased diameter means there is less blood contacting the vessel wall, thus lower friction and lower resistance, subsequently increasing flow. A decreased diameter means more of the blood contacts the vessel wall, and resistance increases, subsequently decreasing flow.

The influence of lumen diameter on resistance is dramatic: A slight increase or decrease in diameter causes a huge decrease or increase in resistance. This is because resistance is inversely proportional to the radius of the blood vessel (one-half of the vessel’s diameter) raised to the fourth power (R = 1/r 4 ). This means, for example, that if an artery or arteriole constricts to one-half of its original radius, the resistance to flow will increase 16 times. And if an artery or arteriole dilates to twice its initial radius, then resistance in the vessel will decrease to 1/16 of its original value and flow will increase 16 times.

The roles of vessel diameter and total area in blood flow and blood pressure

Recall that we classified arterioles as resistance vessels, because given their small lumen, they dramatically slow the flow of blood from arteries. In fact, arterioles are the site of greatest resistance in the entire vascular network. This may seem surprising, given that capillaries have a smaller size. How can this phenomenon be explained?

Questions & Answers

what is amenorrhoea
Adamu Reply
either due to gestational phase or lactational phase amenorrhoea is divided into two namely primary and secondary amenorrhoea ..the gestational phase and lactational phase marks a temporary cease in menstrual flow which is termed secondary amenorrhoea...
Fatukasi
amenorrhoea is simply a stop or cease in menstrual flow..primary amenorrhoea marks menopause
Fatukasi
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loice Reply
50 prefix and surfix
Martha Reply
why arteries deeper than veins?!
Cismaan Reply
arteries colour of blood is deeper than that of vein because its blood contains oxygen which is adhered to haemoglobin(a protein which gives the blood its red color) , while vein contains deoxygenated blood(blood without oxygen)
olusoga
As we know, vein carries used blood to the heart. when we say used blood, we mean to say, blood that its content(oxygen and other nutrients) has been used up.
olusoga
Arteries are deeper b'cuz they need to be protected.......If they are ruptured they cannot form clot and repair themselves.... Moreover, the pressure of blood is too high for the artery to form the clot and repair itself....... Hence, Arteries are deeper than veins........
AMEL
Than u all. Special thanks too AMEL JEELANI.
Cismaan
You're welcome......
AMEL
Thanks all
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mwamba Reply
its located near the vascular pole of the glomurelus also regulate blood pressure and the filtration rate of glomurelus
adam
what are the three methods of data collection used during a community diagnosis
loice
Interviews. Questionnaires and Surveys. Observations.
edna
Describe two early induced responses and what pathogens they affect
olivia Reply
what are pathogens
Priscilla
pathogens are disease-causing agents/organisms
olusoga
pathogen are the causative of disease
Marco
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Priscilla
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Asad
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Asad
What are organelles
RAPHERA Reply
The are little organs found in cells of living things... Eg gogi apparatus
Lombe
what is anatomy
Linda Reply
is the study of the structures of the body and how they relates to each other
Agyemang
Anatomy is the study of the structures of body parts and how they relates to each other
Agyemang
is the study of the structure of the body and how they relates to each other
NAOMI
what are the difference between Pacinian corpuscle and cutaneous vascular plexus?
thivya Reply
what are membranous epithelial tissues
Naa Reply
they are the lining and covering epithelial tissues which cover body surfaces and line cavities... they're grouped into simple and stratified according to the number of layers and squamous, cuboidal and columnar according to their shape
Ophelia
what is an acina
Nuella
acina is known to be the basic functional unit of the lungs .(singular:- acinus) this is where the alveoli(the gaseous exchange site) is found...
Fatukasi
what happens to the unfertilized egg
Wuraola
the study of tissues is called
Scandy Reply
histology
Sirius
microscopic or histology anatomy
Shan
What specific types of biological macromolecules do living things require and why?
Marieland Reply
what is partial pressure?
Tariq Reply
it is the pressure exerted by mixture of gases...
Fatukasi
What is the Important of studying anatomy and philosophy
Michael Reply
because to know the mechanisms of our body
Tariq
to discover the regional structural of human body based on physically and also biochemically.
thivya
how many region do we have in human body
nsofor Reply
head thorax abdomen and many kind of...
Shan
what is principal ponatine nucleas
Tariq
Human body can be divided into different regions on the basis of: 1. Systems: e.g. digestive system, respiratory system, excretory system etc.. 2. Parts: e.g. head, thorax, neck, upper limbs, lower limbs etc..
AMEL
we have 9 region in d human body
ZAINAB

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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