# 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,

what is stumac
What is phagocytosis
Phagocytosis, process by which certain living cells called phagocyte
what are the six types of connective tissues
describe the structure of the liver
what is specific name for spinal cord
what is the best description for skeletal muscular
Stanley
what is the best description for skeletal muscular
Stanley
costs of bones of skeleton, their joint s and voluntary
grace
what are examples of long bones
grace
example of long bones will be the femur tibia and humerus and even radius
Nina
so basically long bones are mostly in you hands and feets
Nina
skeletal muscular are voluntary and are attached to the bone by tendon which help maintain the posture and position of the body and it also protects internal organs in the abdominal region
Nina
The specific name for spinal cord is coccygeal segment
Sandra
Smallest unit of life
cell
The cell is the smallest structural and functional unit of living organisms, which can exist on its own. Therefore, it is sometimes called the building block of life. Some organisms, such as bacteria or yeast, are unicellular—consisting only of a single cell—while others, for instance, mammalians, a
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Describe the complications of fracture
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response of neurons against sodium ion Chanel
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The resting membrane potential of a neuron is about -70 mV (mV=millivolt) - this means that the inside of the neuron is 70 mV less than the outside. At rest, there are relatively more sodium ions outside the neuron and more potassium ions inside that neuron.
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are groups of specialized cell that perform they same activity
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a group of specialized cells of the same structure and function
Malenga
a group of specialized cells that have the same structure and perform the same function
Cantiago
what is meant by control center?
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is the study of the structure of the body and their relationship to each refers to the shapes iyo sizes
If water touches hydrophobic tail, what will happen as negative effect?
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is the study of structural of the human body and their function
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What is the function of the Trachea
Samuel
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In biology, a blastomere is a type of cell produced by cleavage (cell division) of the zygote after fertilization and is an essential part of blastula formation.
what is cell
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Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. ... Cells have many parts, each with a different
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cell is a membrane bound unit that contains the fundamentals molecules of life
Sushma
A1
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movement,reproduction, excretion, respiration ,growth ,nutrition, response to external stimuli.
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Which muscle of the gluteal region originates from lumber spine? a. Gluteus medius b. Psoas major c. Iliacus d. Gluteus maximus
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what is the functional unit of kidneys
nephron is the functional unit of kidney
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Maryam Riaz sister option. d. gluteus maximus
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nephron is the functional unit of kidney
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d
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Ihsan
what is cell
Shilpa
cell is the smallest unit of life
Maryam
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Shilpa
Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. ... Cells have many parts, each with a different
function
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type structure function origin insertion action of muscles
get anatomyka app
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Raghvendra
oxygn amount in our body
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