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By the end of this section, you will be able to:
  • Describe the system of blood flow through the body
  • Describe how blood pressure is regulated

Blood pressure (BP) is the pressure exerted by blood on the walls of a blood vessel that helps to push blood through the body. Systolic blood pressure measures the amount of pressure that blood exerts on vessels while the heart is beating. The optimal systolic blood pressure is 120 mmHg. Diastolic blood pressure measures the pressure in the vessels between heartbeats. The optimal diastolic blood pressure is 80 mmHg. Many factors can affect blood pressure, such as hormones, stress, exercise, eating, sitting, and standing. Blood flow through the body is regulated by the size of blood vessels, by the action of smooth muscle, by one-way valves, and by the fluid pressure of the blood itself.

How blood flows through the body

Blood is pushed through the body by the action of the pumping heart. With each rhythmic pump, blood is pushed under high pressure and velocity away from the heart, initially along the main artery, the aorta. In the aorta, the blood travels at 30 cm/sec. As blood moves into the arteries, arterioles, and ultimately to the capillary beds, the rate of movement slows dramatically to about 0.026 cm/sec, one-thousand times slower than the rate of movement in the aorta. While the diameter of each individual arteriole and capillary is far narrower than the diameter of the aorta, and according to the law of continuity, fluid should travel faster through a narrower diameter tube, the rate is actually slower due to the overall diameter of all the combined capillaries being far greater than the diameter of the individual aorta.

The slow rate of travel through the capillary beds, which reach almost every cell in the body, assists with gas and nutrient exchange and also promotes the diffusion of fluid into the interstitial space. After the blood has passed through the capillary beds to the venules, veins, and finally to the main venae cavae, the rate of flow increases again but is still much slower than the initial rate in the aorta. Blood primarily moves in the veins by the rhythmic movement of smooth muscle in the vessel wall and by the action of the skeletal muscle as the body moves. Because most veins must move blood against the pull of gravity, blood is prevented from flowing backward in the veins by one-way valves. Because skeletal muscle contraction aids in venous blood flow, it is important to get up and move frequently after long periods of sitting so that blood will not pool in the extremities.

Blood flow through the capillary beds is regulated depending on the body’s needs and is directed by nerve and hormone signals. For example, after a large meal, most of the blood is diverted to the stomach by vasodilation of vessels of the digestive system and vasoconstriction of other vessels. During exercise, blood is diverted to the skeletal muscles through vasodilation while blood to the digestive system would be lessened through vasoconstriction. The blood entering some capillary beds is controlled by small muscles, called precapillary sphincters, illustrated in [link] . If the sphincters are open, the blood will flow into the associated branches of the capillary blood. If all of the sphincters are closed, then the blood will flow directly from the arteriole to the venule through the thoroughfare channel (see [link] ). These muscles allow the body to precisely control when capillary beds receive blood flow. At any given moment only about 5-10% of our capillary beds actually have blood flowing through them.

Questions & Answers

state any one specialized animal cell and it's function
Pascal Reply
sperm cell: Fertilization
Can DNA and RNA be praticalized
Oyewale Reply
you can make models of them and show how they replicate
what is dentition
Tisa Reply
Study of teeths and their functions
what are the function
it's not teeths. teeth is plural as well as singular noun. the function of the teeth is to cut and grind food for easier swallowing and for increasing the surface area if the fish as the substrate in which digestive enzymes work
dentition is not the study of teeth but the arrangement of teeth in the mouth of species or individuals
what are the two types of teeth
Function of probosis
Adeola Reply
why do we study biology?
where biology began
What are chromesome
Talkmore Reply
condensed DNA wrapped with histone
what is chromosome?
Royd Reply
How can a person who has been in the vascular disease repairs his or her DNA
Rabson Reply
i need its explanation sir..pls provid na...🙁
Shaf Reply
Of wat
explanation for wat
Of war na so dat I can provide
Is d process which food is converted into substance dat can be utilize by d body
the meaning of disgestion
Charity Reply
because they are considered to be proteins ..lipids,fats, and nucleic acids
Geeta Reply
what is osmosis
Festus Reply
Is the movement of solvent molecules from the region of a higher concentration to the region of lower concentration
It is the movement of solvent from the region of lower concentration to the region of higher concentration through a semi-permeable membrane.
and diffusion
it is the movement of water molecules fro region of higher conc. to the region of lower conc.thro a semi-permeable membrane.
Diffusion is the movement of solute molecules from a region of higher concentration to a region of lower concentration.
osmosis is the movement of water molecule from the region higher water potential to a region of lower water potential
what is the function of Nerve cell?
Hello Everyone!! Any good study app recommendations?
For which subject
Hello everyone!! I want to be sure does exoskeleton consist of endoskeleton? plz help right nw
Try this one and also biology Olevels
Hey, I'm completely new to biology. I'm computer science graduate but I want to learn Neuroscience from scratch. So I have decided to study this book as my entry point to the field. is this book good for a complete beginner in the field?
Adeetya Reply
Yes it can help since u ar a beginner
Thanks for the clarification.
WhAt are the differences between prokaryotic cell and eukaryotic cell
oluwapelumi Reply
Prokaryotic cell is a single celled organism that do not have membrane -bound nuclei.
prokaryotes also lack other cell organelles whereas eukaryotes possess an organized nucleus with nuclear envelope and also they have complex locomotory and cytoskeletal structures
genetic material is found in cytoplasm in prokaryotic cell while in eukaryotes genetic material is found in nucleus
What cells are the basic unit of life?

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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