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Venous system

The pumping action of the heart propels the blood into the arteries, from an area of higher pressure toward an area of lower pressure. If blood is to flow from the veins back into the heart, the pressure in the veins must be greater than the pressure in the atria of the heart. Two factors help maintain this pressure gradient between the veins and the heart. First, the pressure in the atria during diastole is very low, often approaching zero when the atria are relaxed (atrial diastole). Second, two physiologic “pumps” increase pressure in the venous system. The use of the term “pump” implies a physical device that speeds flow. These physiological pumps are less obvious.

Skeletal muscle pump

In many body regions, the pressure within the veins can be increased by the contraction of the surrounding skeletal muscle. This mechanism, known as the skeletal muscle pump    ( [link] ), helps the lower-pressure veins counteract the force of gravity, increasing pressure to move blood back to the heart. As leg muscles contract, for example during walking or running, they exert pressure on nearby veins with their numerous one-way valves. This increased pressure causes blood to flow upward, opening valves superior to the contracting muscles so blood flows through. Simultaneously, valves inferior to the contracting muscles close; thus, blood should not seep back downward toward the feet. Military recruits are trained to flex their legs slightly while standing at attention for prolonged periods. Failure to do so may allow blood to pool in the lower limbs rather than returning to the heart. Consequently, the brain will not receive enough oxygenated blood, and the individual may lose consciousness.

Skeletal muscle pump

The left panel shows the structure of a skeletal muscle vein pump when the muscle is relaxed, and the right panel shows the structure of a skeletal muscle vein pump when the muscle is contracted.
The contraction of skeletal muscles surrounding a vein compresses the blood and increases the pressure in that area. This action forces blood closer to the heart where venous pressure is lower. Note the importance of the one-way valves to assure that blood flows only in the proper direction.

Respiratory pump

The respiratory pump    aids blood flow through the veins of the thorax and abdomen. During inhalation, the volume of the thorax increases, largely through the contraction of the diaphragm, which moves downward and compresses the abdominal cavity. The elevation of the chest caused by the contraction of the external intercostal muscles also contributes to the increased volume of the thorax. The volume increase causes air pressure within the thorax to decrease, allowing us to inhale. Additionally, as air pressure within the thorax drops, blood pressure in the thoracic veins also decreases, falling below the pressure in the abdominal veins. This causes blood to flow along its pressure gradient from veins outside the thorax, where pressure is higher, into the thoracic region, where pressure is now lower. This in turn promotes the return of blood from the thoracic veins to the atria. During exhalation, when air pressure increases within the thoracic cavity, pressure in the thoracic veins increases, speeding blood flow into the heart while valves in the veins prevent blood from flowing backward from the thoracic and abdominal veins.

Questions & Answers

how is speech controlled by the nervous system?
Joseph Reply
The broca's area
Udebuana
chemical level cellular level tissue level organ level organ system level organism
Chidera Reply
Yes Yes because they can perform more than one activity in the body
Chidera
the functional and structural unit of the body
Chidera
A group of 2 or more tissue that come together to perform a specific function
Chidera
A group of organs that work together to perform a specific function or meet the physiological needs of the body
Chidera
It's the highest level of organization
Chidera
2 or more cells coming together to perform a specific function
Chidera
Skeletal muscles can be tetanized but not cardiac muscle.Discuss
Okeke Reply
what is regional anatomy?
Grace Reply
study of structures that contribute to specific body region
charles
what is human anatomy?
Sam
what is grey matter
OJO Reply
What is neuron cell
Dev Reply
neuron cell are the fundamental units of the brain and nervous system responsible for receiving sensory input from the external world, for sending motor commands to muscles and for transforming and relaying the electrical signals at every step in between
Serphine
What is the perfect defination of Life
Dev
What does a word muscles means ?
Abubakar
what is Anatomy
Hannah Reply
because she's not yet at term
Nansi Reply
what is physiology?
Grace Reply
what is physiology
David
Physiology is the study of the functions of the human body
Hannah
am a new one!!
sekela
what is Homeopathy
AHMED
Name three reasons to study anatomy and physiology
Hills Reply
To know more about our body structure and functions this helps us To know disorders easily To get the medicine To appriciate the structure with the system and know that we are unique creatures
Tinbit
Why do we need to study anatomy and physiology
Hills Reply
I want to study human anatomy
Ibrahim
What is anatomy
Christabel Reply
anatomy is the branch of medicine in which we study structure and part of the body
Ansar
The art of studying the different parts of any organized body, to discover their situation, structure, and economy; dissection.
ChristMas
anatomy is the study of structures that make up the body and how they re realated to each other
BRIAN
Anatomy is the study of structures of the body and shape of the body and body parts and their relationship to one another.
Abubakar
what is the importance of anatomy
Emeria Reply
cockroch ka sir katne ke bad o jinda kyu rahta
Anil
it helps us to understand the function of human metabolic system and also who these systems works which system play what role and so on
Nouman
It's help us to know the structure, functions and relationship of the human body
Nansi
it helps us to appreciate how the internal structures works
Damilola
Anatomy opens up to us the structures of the various parts of the human body and correlates them to their specific function respectively
Michael
Anatomy is helps us understand and explore much about human structures
Chuks
systemic anatomy in short
Puja Reply
systemic circulation is the circulation in which heart supplies oxygenated blood to cells of body and takes deoxygenated blood away from body to heart
Ajeet
really?
Puja
yeah
BRIAN
ha ji
Ajeet
well much setisfy
Nouman
hello
Limpo
am new here
Limpo
ok
Emeria
am new here
Sindazi
I'm new as well
Crystal
who ask the question about cockroach cutting head
Nouman
the answer is They have an open circulatory system, which there's much less pressure in.After you cut their heads off very often their necks would seal off just by clotting," he adds. "There's no uncontrolled bleeding.The hardy vermin breathe through spiracles, or little holes in each body se
Nouman
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Sindazi
well it's up-to you how you utilities this
Nouman
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Puja
hello
AKARAJ
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AKARAJ
I think it is helpful
Alfred
Hi
Christabel
hi
Sachin
how do plateletes function in blood clotting
lydia
it's the study of the systems of the body & how they work
Chidera
Please you can say me how to study very easy anatomy book? ?
Juna
hello
Danso
I want to know how to study Anatomy test book
Danso
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Fariha
well conversations
Noor
what are the function of the cell membrane
Elias Reply
the cell membrane helps in allowing and removing substances from the cell. it also aid in protecting the cell and giving it a definite shape.
veezy
The cell membrane is made up of a semipermeable lipid bi-layer which helps to regulate the kind of materials that enters it through active transport and passive diffusion.
Michael

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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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