# 20.2 Blood flow, blood pressure, and resistance  (Page 4/34)

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## Cardiac output

Cardiac output is the measurement of blood flow from the heart through the ventricles, and is usually measured in liters per minute. Any factor that causes cardiac output to increase, by elevating heart rate or stroke volume or both, will elevate blood pressure and promote blood flow. These factors include sympathetic stimulation, the catecholamines epinephrine and norepinephrine, thyroid hormones, and increased calcium ion levels. Conversely, any factor that decreases cardiac output, by decreasing heart rate or stroke volume or both, will decrease arterial pressure and blood flow. These factors include parasympathetic stimulation, elevated or decreased potassium ion levels, decreased calcium levels, anoxia, and acidosis.

## Compliance

Compliance is the ability of any compartment to expand to accommodate increased content. A metal pipe, for example, is not compliant, whereas a balloon is. The greater the compliance of an artery, the more effectively it is able to expand to accommodate surges in blood flow without increased resistance or blood pressure. Veins are more compliant than arteries and can expand to hold more blood. When vascular disease causes stiffening of arteries, compliance is reduced and resistance to blood flow is increased. The result is more turbulence, higher pressure within the vessel, and reduced blood flow. This increases the work of the heart.

## A mathematical approach to factors affecting blood flow

Jean Louis Marie Poiseuille was a French physician and physiologist who devised a mathematical equation describing blood flow and its relationship to known parameters. The same equation also applies to engineering studies of the flow of fluids. Although understanding the math behind the relationships among the factors affecting blood flow is not necessary to understand blood flow, it can help solidify an understanding of their relationships. Please note that even if the equation looks intimidating, breaking it down into its components and following the relationships will make these relationships clearer, even if you are weak in math. Focus on the three critical variables: radius (r), vessel length (λ), and viscosity (η).

Poiseuille’s equation:

• π is the Greek letter pi, used to represent the mathematical constant that is the ratio of a circle’s circumference to its diameter. It may commonly be represented as 3.14, although the actual number extends to infinity.
• ΔP represents the difference in pressure.
• r 4 is the radius (one-half of the diameter) of the vessel to the fourth power.
• η is the Greek letter eta and represents the viscosity of the blood.
• λ is the Greek letter lambda and represents the length of a blood vessel.

One of several things this equation allows us to do is calculate the resistance in the vascular system. Normally this value is extremely difficult to measure, but it can be calculated from this known relationship:

If we rearrange this slightly,

Card 5 / 12: For whom would an appreciation of the structural characteristics of the human heart come more easily: an alien who lands on Earth, abducts a human, and dissects his heart, or an anatomy and physiology student performing a dissection of the heart on her very first day of class? Why?
what are regular shaped cells with granules in the cytoplasam
PMNL
Dinu
I need sylubuss of clinical officers book
cholesterol normal value is
less than 200mg/dl
Ashis
100 to159mg/dL
Dinu
Early this wk. I had some "A & P" questions & answers unfortunately didn't save them, Is there any way I can have them back ,so as 2 save them?. Thnx.
Kechi
what are the functions of the female reproductive system
it produces the female egg necessary for reproduction, called the Ova or Oocytes. The system is designed to transport the Ova to the site of fertilization.
Kechi
Female reproductive system was mainly functioned to produce ova(ovum) (female eggs) Into which will be fertilized by male gamete to produce zygote
Omary
absolutely right
nimco
wa qalad nimco rage iska hubi
Khaliil
waxwalba ka fikirbay ubaahantahay
Ahmed
ha wayo jawabtoda wa qabyo nimco wey ku raacdat
Khaliil
ha wayo jawabtoda wa qabyo nimco wey ku raacday
Khaliil
wxayaabaha qaarkood waaa in aan u feejignaano
Ahmed
asc if I try female reproductive system has two function the first is to produce egg cell and the second is to protact and nourish the offspring until birth
Muriidi
what is stercobilinogen
fecal urobilinogen. Created by bacteria in the gut. a chemical that gives feces brown color.
Blayne
next question pls.
Kechi
The rate of diffusion increases if the
stella
Kechi
it's a breaking down of haemoglobin and it's a chemical made by bacteria
Dev
Thnx Dev Raj.
Kechi
yup so any more
Dev
yes I sure do need more "Questions" & "Answers". I'm learning whole lot. Thnx.
Kechi
what is the greatest muscle of the body
gluteus maximus
ABDULLAH
pls!!! more "A&P" questions & answers. Thnx.
Kechi
Gluteus maximus
THE
Describe anatomy of cardiovascular system?
cardiovascular system is a group of organs coming together to perform the circulation of blood. The organs invoked are the heart and the blood vessels with blood being the tissue. The heart is a pump and it pumps oxygenated blood through the systemic circuit and deoxygenated blood through the pulmon
bernard
pulmonary circuit.
bernard
more A&P questions pls. Thnx.
Kechi
If an ANOVA yields a significant F value, you could rely on ________ to test significant differences between group means.
what's ANOVA
Cassandra
analysis of variance
Blayne
plz what you mean with "ANOVA" first
Fatima
anova means analysis of variance, a statistical method in which the variation in a set of observations is divided into distinct components.
Blayne
M value ot test
ABDULLAH
What does it mean by M value ot test?
Orpha
formation of red blood cells
explain why... lower back pain in ovarian cancer
we says that protoplasm is the living part of us How?
is the leaving part of our cellular structure.
Eric
it is the leaving part of our blood cellular structure also
ABDULLAH
what is receptor?
an organ or cell able to respond to light, heat, or other external stimulus and transmit a signal to a sensory nerve.
Jessi
Has anyone taken the first exam?
Sandra
yes
yahye
yes
Allan
hey what is the process after your food is swallowed? how long does it take to get to the stomache until it is released as waste?
that is such a broad question. as you begin to swallow its various doses down the alimentary canal that brings the food into your stomach.then depending on whether it's a protein carbohydrate fat that dictates what function takes place in your stomach. these are all steps of digestion.
Joseph
typo sorry it's peristalsis , wave-like projections that push food down your alimentary canal etc. digestion starts in your mouth ends in your large intestines (colon anus)
Joseph
some of the many processes of digestion include hydrolysis dehydration synthesis denaturation of proteins etc. you have to be more specific.
Joseph
there's many different contributing factors the how long it takes food to convert into waste. remember fats, triglycerides proteins and carbohydrates all breakdown two different monomers and structures. you should be looking up metabolic processes.
Joseph
depending how much fiber you have in your diet dictates how much water is brought to your intestines that has to do with excretion whether fiber is insoluble or soluble. this is an anatomy and physiology app. to simply say the stomach will empty its contents in 2 to 3 hours would do you a disservice
Joseph
can the study of anatomy relate to medical technologies
yes
Khh
absolutely
Jessi
yes...
Sherif
how can I understand micro biology and anatomy better.
Cassandra
yes
Kevin
someone to help me understand glycogeneogenesis
abel
what are the major branches of the aorta?
Kevin
Jessi