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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

mention two processes of bone formation
Ngopiro Reply
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Ngopiro
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Justine Reply
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Justine Reply
bones and structures
Nkechi Reply
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Cb
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Cb
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patrick
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King
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Mwasiti Reply
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Mwasiti Reply
Heart Blood Blood Vessel
Md
what are the components of the bone
Ngopiro
what is Hodgkin's disease
Mwasiti Reply
What is anatomy
Munira Reply
anatomy is a study of physical and structural functions of human body parts
Mohd
is the study of structure of the body and physical relationship involve between the body system
Mwasiti
is the study of structure of the body and physical relationship involve between the body system
Mwasiti
why simple columnar support peristalisis
Camilius Reply
why when sex of an individual is determined by y chromosome found in male therefore why there is many women than male
pamfili Reply
I'm not sure if I fully understand your question.
are you sure it is more
samir
i don't remember what I said.
I'm not sure if I fully understand your question.
roughly taking a lead.
samir
Muscle of mastication
JIMOH Reply
what is anatomy
Akanle
Sorry....it's the study of human body and it's functions.
Irene
Anatomy is the study of human organs
Kity
what is serum protein?
Salum
what is anatomy
Akanle
Anatomy is the study of human organs
Kity
Who is a bovin
Kity
Who is a bovin
Kity
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Kity
pls does broken bones get healed
Desmond
yes
Belinda
how
Desmond
by surgery or medication
Desmond
Medication
Irene
why do a bovin not menstruate unlike women?
patrick
Why do you ask tough questions I'm in JHS 3
Kity
Anatomy is the study of structure of the human body
Belinda
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Belinda
medication
Belinda
yes
Belinda
animals within that group include cows as well as others.
ihope that was helpful
aaa,kity.bovin is a terminology used by veteranians to refer a cow.for dogs its carnine,cats it's ferline...etc
patrick
i believe if you look up the classification of Bovin , it tell clarify more for you.
ihope that was helpful
i don't think my first message about taxonomy sent
i don't think my first message about taxonomy sent
difference between seminiferous tubules and ejaculatory duct
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Musibi
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Kity
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what is azygous vein
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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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