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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

what are the musles which are found at the forearm
Magembe Reply
Brachioradialis,Flexo capi radialis,Flexor digitorum profundus,Flexor pollicis longus, Extensor digitorum,,Extensor capiradialis longus and brevis.
Titus
where are skeletal muscle located?
Gildas Reply
Are attached at the bone via tendons
Fatuma
what are the bone found into the ear and their function
Justinian Reply
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Nadine Reply
what is anatomy
ORIATO Reply
How can one understands muscles
ORIATO
Human Anatomy:is the study structure of the body
Abba
WHO Discovered Anatomy
Abba Reply
Vesalius
Shikha
what causes the breathing in of air?
Phoka Reply
what is synergist
Flora Reply
hello
Kawsar
working together
Gerhaldish
means connective
Happy
embryonic development of the heart
wamaitha Reply
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Nadine
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Nadine
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Nadine
pharmacology what is it?
Symon
The study of drugs, their chemical and physical properties, their biological and therapeutic effect on the body and also their metabolism within the body and finally how the drug gets excreted from the body.
dr
Study of substances that interact with living systems through chemical processes especially by binding to regulatory molecules and activating or inhibiting body processes
Victor
Roles of cytokines in regulating immune system in the body
Gift Reply
define pharmarcology
HAUWA Reply
pharmacology can be defined as science of drugs and their uses
Lawal
structural mechanism of muscle contraction
warda Reply
descrete body system
Ujunwa Reply
I am paramedic student
Abid
I want to be a doctor but due to poverty I could afforded fees
Abid
there how many systems of the body.?
Phabian Reply
11
Orsine
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Nadine
11
Nadine
what's is reganal anatomy
Sose Reply
it is the study of interrelationships between different organs in a certain region of the body e.g abdomen
Taurai
this helps understand how these different organs work together to serve a particular body region
Taurai

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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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