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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 many classes of drugs do we have?
Jesse Reply
I'm not sure lol
Leti
we have 7classes,e.g stimulant, Cannabis etc
Orpha
scheduled 5...classes stimulants, depressants, hallucinogens, dissociatives, opioids, inhalants and cannabis.
jessica
site of fracture in the kneel
holuwahseun Reply
what is pelvis
Aisha Reply
Complex of bones that connect the trunk and the legs,supports and balance the trunk.
Orpha
What is d most heaviest organ in d body
Abraham Reply
Liver
Akasi
The skin
Akasi
skin
Divya
why skin?
Sam
liver
Anne
water
Mehdi
Heart
Biplob
the brain
lehumo
skin
Emma
skin
jessica
largest internal organ is the liver
jessica
liver is the heaviest organ
Eyyammeh
the liver is the heaviest organs
Khh
What is the meaning? What does it entails to? What are the works of Arthropologists?
Orpha Reply
bones of appendicular skeleton
hemalatha Reply
Fore limbs, hind limbs, pectoral and pelvic girdle
Abraham
Functions of the thoracic cage
Fereh Reply
protect all the organs and tissues from any impact or injury
Javier
It protects the heart other tissues in the chest region
Abraham
why sickle cell carrier people don't get malaria
Boakye Reply
Bcos mosquitoes are not attracted by their blood due to poor oxygen
Abraham
What is the amniotic fluid
bollywood Reply
amniotic fluid is the fluid that is inside the uterus with the baby.
Fati
shielded
Varun
This fluid serves as a cushion for the growing fetus but also serves to facilitate the exchange of nutrients, water, and biochemical products between mother and fetus.
Anne
it also reduces friction during birth as it wets the birth canal during delivery
steve
Amniotic fluid can be taken out by inserting needle to detect birth abnormalities as the foetus cells are present in amniotic fluid. This process is known as amniocentesis.
Biplav
structure of heart and it's function (10 mark )
Priyanka Reply
not possible
Abraham
What is the best book on physiology?
cesar Reply
describe varicocele
malulu
what do you mean by peritoneum
Siba Reply
It is thick covering surrounding the abdomen
Awais
r8
how to become good in Anatomy and physiology
malulu
hi
Milkah
hlo
Wani
What are is the last solution to abdomen pain in pregnant women
Umoru
no it is in kidney
Tantray
Kk
Umoru
structure of heart and it's function
Priyanka
Serous membrane lining the cavity of the abdomen
bollywood
it is four lobs structure and it is triangular in shaped. it 's function pumping the blood
ABDULLAH
explain root of lungs
ABDULLAH
Glomerular pressure -capsule pressure -colloid osmosis pressure
malulu Reply
how to describe mechanism of micturition
malulu
spleen is important?
AKASH Reply
helpful in destruction of rbc
It is imp in storing blood and destruction of microbes and harmful particles
Awais
ty sir
AKASH
K
Umoru
what are the sources of glucose in the body
malulu
describe mechanism of micturition
malulu
Pancreatic hormones with function
mami Reply
Insulin, which helps to regulate our blood sugar levels.
Bb
glucagon which is antagonistic to insulin increase the blood glucose level,. Somatostatin help to regulate the levels of both insulin and glucagon
Ashish
thnks for helping
nimco
thanks
Narendra
what is a lymph node.?
AKASH
lymph nodes are small kidney shaped organs of the lymphatic system.
Trishauna
there are several hundred lymph nodes found mostly throughout the thorax and abdomen of the body with the highest concentrations in the auxiliary (armpit) and inguinal groin regions.
Trishauna

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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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