<< Chapter < Page Chapter >> Page >

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 does a saggital plane look like and a frontal plane
susan Reply
saggital plane divides left and right.. frontal plane divides front and back.. I'm trying to upload a picture but idk how.
Pipiena
tnx sis
Angella
what is a neurones?
Angella Reply
how many systems are there in human
Angella
What is ovulation
Joy Reply
Ovulation is release of mature ovum from ovary
AMEL
what is physiology
Firdaus Reply
The study of how e body systems or structures function and interrelate with each other
Prettygal
what is the composition of the ground substance?
Nana Reply
large carbohydrates and proteins which is known as acid mucopolysacchrides
adam
thanks👍
Nana
you guy welcome
adam
Hi guys am new here
Nji
how does the negative feedback helps in maintaining body temperature at its normal range
dzreke
I need good sites that I can test myself on chapters 1,3,4,5. I have an exam tomorrow
Ana
please can you kindly share your questions here after the exams please
dzreke
What causes the banding pattern seen in the muscle fibril under the electron microscope
Nji
what organelles controls protein synthesis?
Katie Reply
Ribosome
AMEL
hmm...the ribosomes?
Fatukasi
ribosome
adam
Ribosome
Opara
Ribosome
Saifkhan
ribosome
DR
ribosome
ELIZABETH
are ribisomes made in the rRNA?
Lola
nop they are produced by cells of Nucleolus
adam
Is there anything about nerve and muscle physiology?
AMEL Reply
how many types of epithelial tissues do we have
Benedicta Reply
Epithelial tissues are grouped in two ways.. ●Based on the number of layers.(Simple and stratified ) ●Based of their shapes(Squamous,Cuboidal and columnar) Also we can have a combination of the two,say,simple Squamous
Prince
awww thanks dearie😊😊😊💖
Benedicta
describe the function and structure of blood
Belindah Reply
It has four main components: plasma, red blood cells, white blood cells, and platelets. Blood has many different functions, including: transporting oxygen and nutrients to the lungs and tissues.
Arlena
well answered arlena.. #thumbs up#
Fatukasi
have u some prepared MCQs on CNS and Special senses physiology?
dr
Anyone got the human heart labelled diagram
Sawmtei
you can download from Google... I don't think it's possible to share docs or files here
Fatukasi
ok thanks
Sawmtei
you're welcome..
Fatukasi
thanks
dr
Thank you
Drs
what's an easy way of knowing the different structures of tissues what they do and where their found
Lola
are you know function of the blood?
Drs
to carry nutrients to parts of the body
Lola
well Lola the easiest way is to attributes the tissues based on their funcs(especially those with similar funcs)..you can create your own mnemonics that will help you rmba em..and the a random reading.. it helps you retain em better
Fatukasi
and try random reading*
Fatukasi
ok thanks
Lola
funtction of WBCs
DR
bone tissue
Waqar
Blood is a fluid connective tissue made up of blood cells suspended in plasma, which is the fluid part of blood. The cell include erthrocytes, leukocytes and thrombocytes. Blood is responsible for transportation of substances around e body eg hormones oxygen and substances
Prettygal
Blood is responsible for defence... As it acts as a defense mechanism against microbes through action of leukocytes which destroy any foreign substances
Prettygal
identy the vein and arteries of coronary circulation
abdifatah Reply
to be a nurse a doctor or just to understand the body
Drew Reply
what is the basic part of life
Drew
cell remains the basic unit of life...
Fatukasi
A cell is the basic part of life
Angella
The coronary arteries branches off of what
Ada Reply
gh
Asad
rephrase your question
Fatukasi
Discuss Active Myosin contraction theory
Xavier Reply
What is dissected?
Jc Reply
It is a minute and detailed analysis.."dissection"rather..
Kabwe
what is the net charge on both atoms of hydrogen and helium?
Brianna Reply
hii
Shubham
hii
Maddy
Muche kuch bhi samaz me nhi aa rha he
Shubham
kya samaj nahii Aa raha hai
Maddy

Get the best Anatomy & Physiology course in your pocket!





Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Anatomy & Physiology' conversation and receive update notifications?

Ask