Module 15: The Cardiovascular System: Blood Vessels and Circulation

Lesson 2: Blood Flow, Blood Pressure, and Resistance

Lưu Lượng Máu, Huyết Áp, Và Kháng Lực

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Dưới đây là danh sách những thuật ngữ Y khoa của module The Cardiovascular System: Blood Vessels and Circulation.
Khái quát được số lượng thuật ngữ sẽ xuất hiện trong bài đọc và nghe sẽ giúp bạn thoải mái tiêu thụ nội dung hơn. Sau khi hoàn thành nội dung đọc và nghe, bạn hãy quay lại đây và luyện tập (practice) để quen dần các thuật ngữ này. Đừng ép bản thân phải nhớ các thuật ngữ này vội vì bạn sẽ gặp và ôn lại danh sách này trong những bài học (lesson) khác của cùng một module.

Medical Terminology: The Cardiovascular System: Blood Vessels and Circulation

abdominal aorta
portion of the aorta inferior to the aortic hiatus and superior to the common iliac arteries
adrenal artery
branch of the abdominal aorta; supplies blood to the adrenal (suprarenal) glands
adrenal vein
drains the adrenal or suprarenal glands that are immediately superior to the kidneys; the right adrenal vein enters the inferior vena cava directly and the left adrenal vein enters the left renal vein
anaphylactic shock
type of shock that follows a severe allergic reaction and results from massive vasodilation
angioblasts
stem cells that give rise to blood vessels
angiogenesis
development of new blood vessels from existing vessels
anterior cerebral artery
arises from the internal carotid artery; supplies the frontal lobe of the cerebrum
anterior communicating artery
anastomosis of the right and left internal carotid arteries; supplies blood to the brain
anterior tibial artery
branches from the popliteal artery; supplies blood to the anterior tibial region; becomes the dorsalis pedis artery
anterior tibial vein
forms from the dorsal venous arch; drains the area near the tibialis anterior muscle and leads to the popliteal vein
aorta
largest artery in the body, originating from the left ventricle and descending to the abdominal region where it bifurcates into the common iliac arteries at the level of the fourth lumbar vertebra; arteries originating from the aorta distribute blood to virtually all tissues of the body
aortic arch
arc that connects the ascending aorta to the descending aorta; ends at the intervertebral disk between the fourth and fifth thoracic vertebrae
aortic hiatus
opening in the diaphragm that allows passage of the thoracic aorta into the abdominal region where it becomes the abdominal aorta
aortic sinuses
small pockets in the ascending aorta near the aortic valve that are the locations of the baroreceptors (stretch receptors) and chemoreceptors that trigger a reflex that aids in the regulation of vascular homeostasis
arterial circle
(also, circle of Willis) anastomosis located at the base of the brain that ensures continual blood supply; formed from branches of the internal carotid and vertebral arteries; supplies blood to the brain
arteriole
(also, resistance vessel) very small artery that leads to a capillary
arteriovenous anastomosis
short vessel connecting an arteriole directly to a venule and bypassing the capillary beds
artery
blood vessel that conducts blood away from the heart; may be a conducting or distributing vessel
ascending aorta
initial portion of the aorta, rising from the left ventricle for a distance of approximately 5 cm
atrial reflex
mechanism for maintaining vascular homeostasis involving atrial baroreceptors: if blood is returning to the right atrium more rapidly than it is being ejected from the left ventricle, the atrial receptors will stimulate the cardiovascular centers to increase sympathetic firing and increase cardiac output until the situation is reversed; the opposite is also true
axillary artery
continuation of the subclavian artery as it penetrates the body wall and enters the axillary region; supplies blood to the region near the head of the humerus (humeral circumflex arteries); the majority of the vessel continues into the brachium and becomes the brachial artery
axillary vein
major vein in the axillary region; drains the upper limb and becomes the subclavian vein
azygos vein
originates in the lumbar region and passes through the diaphragm into the thoracic cavity on the right side of the vertebral column; drains blood from the intercostal veins, esophageal veins, bronchial veins, and other veins draining the mediastinal region; leads to the superior vena cava
basilar artery
formed from the fusion of the two vertebral arteries; sends branches to the cerebellum, brain stem, and the posterior cerebral arteries; the main blood supply to the brain stem
basilic vein
superficial vein of the arm that arises from the palmar venous arches, intersects with the median cubital vein, parallels the ulnar vein, and continues into the upper arm; along with the brachial vein, it leads to the axillary vein
blood colloidal osmotic pressure (BCOP)
pressure exerted by colloids suspended in blood within a vessel; a primary determinant is the presence of plasma proteins
blood flow
movement of blood through a vessel, tissue, or organ that is usually expressed in terms of volume per unit of time
blood hydrostatic pressure
force blood exerts against the walls of a blood vessel or heart chamber
blood islands
masses of developing blood vessels and formed elements from mesodermal cells scattered throughout the embryonic disc
blood pressure
force exerted by the blood against the wall of a vessel or heart chamber; can be described with the more generic term hydrostatic pressure
brachial artery
continuation of the axillary artery in the brachium; supplies blood to much of the brachial region; gives off several smaller branches that provide blood to the posterior surface of the arm in the region of the elbow; bifurcates into the radial and ulnar arteries at the coronoid fossa
brachial vein
deeper vein of the arm that forms from the radial and ulnar veins in the lower arm; leads to the axillary vein
brachiocephalic artery
single vessel located on the right side of the body; the first vessel branching from the aortic arch; gives rise to the right subclavian artery and the right common carotid artery; supplies blood to the head, neck, upper limb, and wall of the thoracic region
brachiocephalic vein
one of a pair of veins that form from a fusion of the external and internal jugular veins and the subclavian vein; subclavian, external and internal jugulars, vertebral, and internal thoracic veins lead to it; drains the upper thoracic region and flows into the superior vena cava
bronchial artery
systemic branch from the aorta that provides oxygenated blood to the lungs in addition to the pulmonary circuit
bronchial vein
drains the systemic circulation from the lungs and leads to the azygos vein
capacitance
ability of a vein to distend and store blood
capacitance vessels
veins
capillary
smallest of blood vessels where physical exchange occurs between the blood and tissue cells surrounded by interstitial fluid
capillary bed
network of 10–100 capillaries connecting arterioles to venules
capillary hydrostatic pressure (CHP)
force blood exerts against a capillary
cardiogenic shock
type of shock that results from the inability of the heart to maintain cardiac output
carotid sinuses
small pockets near the base of the internal carotid arteries that are the locations of the baroreceptors and chemoreceptors that trigger a reflex that aids in the regulation of vascular homeostasis
cavernous sinus
enlarged vein that receives blood from most of the other cerebral veins and the eye socket, and leads to the petrosal sinus
celiac trunk
(also, celiac artery) major branch of the abdominal aorta; gives rise to the left gastric artery, the splenic artery, and the common hepatic artery that forms the hepatic artery to the liver, the right gastric artery to the stomach, and the cystic artery to the gall bladder
cephalic vein
superficial vessel in the upper arm; leads to the axillary vein
cerebrovascular accident (CVA)
blockage of blood flow to the brain; also called a stroke
circle of Willis
(also, arterial circle) anastomosis located at the base of the brain that ensures continual blood supply; formed from branches of the internal carotid and vertebral arteries; supplies blood to the brain
circulatory shock
also simply called shock; a life-threatening medical condition in which the circulatory system is unable to supply enough blood flow to provide adequate oxygen and other nutrients to the tissues to maintain cellular metabolism
common carotid artery
right common carotid artery arises from the brachiocephalic artery, and the left common carotid arises from the aortic arch; gives rise to the external and internal carotid arteries; supplies the respective sides of the head and neck
common hepatic artery
branch of the celiac trunk that forms the hepatic artery, the right gastric artery, and the cystic artery
common iliac artery
branch of the aorta that leads to the internal and external iliac arteries
common iliac vein
one of a pair of veins that flows into the inferior vena cava at the level of L5; the left common iliac vein drains the sacral region; divides into external and internal iliac veins near the inferior portion of the sacroiliac joint
compliance
degree to which a blood vessel can stretch as opposed to being rigid
continuous capillary
most common type of capillary, found in virtually all tissues except epithelia and cartilage; contains very small gaps in the endothelial lining that permit exchange
cystic artery
branch of the common hepatic artery; supplies blood to the gall bladder
deep femoral artery
branch of the femoral artery; gives rise to the lateral circumflex arteries
deep femoral vein
drains blood from the deeper portions of the thigh and leads to the femoral vein
descending aorta
portion of the aorta that continues downward past the end of the aortic arch; subdivided into the thoracic aorta and the abdominal aorta
diastolic pressure
lower number recorded when measuring arterial blood pressure; represents the minimal value corresponding to the pressure that remains during ventricular relaxation
digital arteries
formed from the superficial and deep palmar arches; supply blood to the digits
digital veins
drain the digits and feed into the palmar arches of the hand and dorsal venous arch of the foot
dorsal arch
(also, arcuate arch) formed from the anastomosis of the dorsalis pedis artery and medial and plantar arteries; branches supply the distal portions of the foot and digits
dorsal venous arch
drains blood from digital veins and vessels on the superior surface of the foot
dorsalis pedis artery
forms from the anterior tibial artery; branches repeatedly to supply blood to the tarsal and dorsal regions of the foot
ductus arteriosus
shunt in the fetal pulmonary trunk that diverts oxygenated blood back to the aorta
ductus venosus
shunt that causes oxygenated blood to bypass the fetal liver on its way to the inferior vena cava
elastic artery
(also, conducting artery) artery with abundant elastic fibers located closer to the heart, which maintains the pressure gradient and conducts blood to smaller branches
esophageal artery
branch of the thoracic aorta; supplies blood to the esophagus
esophageal vein
drains the inferior portions of the esophagus and leads to the azygos vein
external carotid artery
arises from the common carotid artery; supplies blood to numerous structures within the face, lower jaw, neck, esophagus, and larynx
external elastic membrane
membrane composed of elastic fibers that separates the tunica media from the tunica externa; seen in larger arteries
external iliac artery
branch of the common iliac artery that leaves the body cavity and becomes a femoral artery; supplies blood to the lower limbs
external iliac vein
formed when the femoral vein passes into the body cavity; drains the legs and leads to the common iliac vein
external jugular vein
one of a pair of major veins located in the superficial neck region that drains blood from the more superficial portions of the head, scalp, and cranial regions, and leads to the subclavian vein
femoral artery
continuation of the external iliac artery after it passes through the body cavity; divides into several smaller branches, the lateral deep femoral artery, and the genicular artery; becomes the popliteal artery as it passes posterior to the knee
femoral circumflex vein
forms a loop around the femur just inferior to the trochanters; drains blood from the areas around the head and neck of the femur; leads to the femoral vein
femoral vein
drains the upper leg; receives blood from the great saphenous vein, the deep femoral vein, and the femoral circumflex vein; becomes the external iliac vein when it crosses the body wall
fenestrated capillary
type of capillary with pores or fenestrations in the endothelium that allow for rapid passage of certain small materials
fibular vein
drains the muscles and integument near the fibula and leads to the popliteal vein
filtration
in the cardiovascular system, the movement of material from a capillary into the interstitial fluid, moving from an area of higher pressure to lower pressure
foramen ovale
shunt that directly connects the right and left atria and helps to divert oxygenated blood from the fetal pulmonary circuit
genicular artery
branch of the femoral artery; supplies blood to the region of the knee
gonadal artery
branch of the abdominal aorta; supplies blood to the gonads or reproductive organs; also described as ovarian arteries or testicular arteries, depending upon the sex of the individual
gonadal vein
generic term for a vein draining a reproductive organ; may be either an ovarian vein or a testicular vein, depending on the sex of the individual
great cerebral vein
receives most of the smaller vessels from the inferior cerebral veins and leads to the straight sinus
great saphenous vein
prominent surface vessel located on the medial surface of the leg and thigh; drains the superficial portions of these areas and leads to the femoral vein
hemangioblasts
embryonic stem cells that appear in the mesoderm and give rise to both angioblasts and pluripotent stem cells
hemiazygos vein
smaller vein complementary to the azygos vein; drains the esophageal veins from the esophagus and the left intercostal veins, and leads to the brachiocephalic vein via the superior intercostal vein
hepatic artery proper
branch of the common hepatic artery; supplies systemic blood to the liver
hepatic portal system
specialized circulatory pathway that carries blood from digestive organs to the liver for processing before being sent to the systemic circulation
hepatic vein
drains systemic blood from the liver and flows into the inferior vena cava
hypertension
chronic and persistent blood pressure measurements of 140/90 mm Hg or above
hypervolemia
abnormally high levels of fluid and blood within the body
hypovolemia
abnormally low levels of fluid and blood within the body
hypovolemic shock
type of circulatory shock caused by excessive loss of blood volume due to hemorrhage or possibly dehydration
hypoxia
lack of oxygen supply to the tissues
inferior mesenteric artery
branch of the abdominal aorta; supplies blood to the distal segment of the large intestine and rectum
inferior phrenic artery
branch of the abdominal aorta; supplies blood to the inferior surface of the diaphragm
inferior vena cava
large systemic vein that drains blood from areas largely inferior to the diaphragm; empties into the right atrium
intercostal artery
branch of the thoracic aorta; supplies blood to the muscles of the thoracic cavity and vertebral column
intercostal vein
drains the muscles of the thoracic wall and leads to the azygos vein
internal carotid artery
arises from the common carotid artery and begins with the carotid sinus; goes through the carotid canal of the temporal bone to the base of the brain; combines with branches of the vertebral artery forming the arterial circle; supplies blood to the brain
internal elastic membrane
membrane composed of elastic fibers that separates the tunica intima from the tunica media; seen in larger arteries
internal iliac artery
branch from the common iliac arteries; supplies blood to the urinary bladder, walls of the pelvis, external genitalia, and the medial portion of the femoral region; in females, also provide blood to the uterus and vagina
internal iliac vein
drains the pelvic organs and integument; formed from several smaller veins in the region; leads to the common iliac vein
internal jugular vein
one of a pair of major veins located in the neck region that passes through the jugular foramen and canal, flows parallel to the common carotid artery that is more or less its counterpart; primarily drains blood from the brain, receives the superficial facial vein, and empties into the subclavian vein
internal thoracic artery
(also, mammary artery) arises from the subclavian artery; supplies blood to the thymus, pericardium of the heart, and the anterior chest wall
internal thoracic vein
(also, internal mammary vein) drains the anterior surface of the chest wall and leads to the brachiocephalic vein
interstitial fluid colloidal osmotic pressure (IFCOP)
pressure exerted by the colloids within the interstitial fluid
interstitial fluid hydrostatic pressure (IFHP)
force exerted by the fluid in the tissue spaces
ischemia
insufficient blood flow to the tissues
Korotkoff sounds
noises created by turbulent blood flow through the vessels
lateral circumflex artery
branch of the deep femoral artery; supplies blood to the deep muscles of the thigh and the ventral and lateral regions of the integument
lateral plantar artery
arises from the bifurcation of the posterior tibial arteries; supplies blood to the lateral plantar surfaces of the foot
left gastric artery
branch of the celiac trunk; supplies blood to the stomach
lumbar arteries
branches of the abdominal aorta; supply blood to the lumbar region, the abdominal wall, and spinal cord
lumbar veins
drain the lumbar portion of the abdominal wall and spinal cord; the superior lumbar veins drain into the azygos vein on the right or the hemiazygos vein on the left; blood from these vessels is returned to the superior vena cava rather than the inferior vena cava
lumen
interior of a tubular structure such as a blood vessel or a portion of the alimentary canal through which blood, chyme, or other substances travel
maxillary vein
drains blood from the maxillary region and leads to the external jugular vein
mean arterial pressure (MAP)
average driving force of blood to the tissues; approximated by taking diastolic pressure and adding 1/3 of pulse pressure
medial plantar artery
arises from the bifurcation of the posterior tibial arteries; supplies blood to the medial plantar surfaces of the foot
median antebrachial vein
vein that parallels the ulnar vein but is more medial in location; intertwines with the palmar venous arches
median cubital vein
superficial vessel located in the antecubital region that links the cephalic vein to the basilic vein in the form of a v; a frequent site for a blood draw
median sacral artery
continuation of the aorta into the sacrum
mediastinal artery
branch of the thoracic aorta; supplies blood to the mediastinum
metarteriole
short vessel arising from a terminal arteriole that branches to supply a capillary bed
microcirculation
blood flow through the capillaries
middle cerebral artery
another branch of the internal carotid artery; supplies blood to the temporal and parietal lobes of the cerebrum
middle sacral vein
drains the sacral region and leads to the left common iliac vein
muscular artery
(also, distributing artery) artery with abundant smooth muscle in the tunica media that branches to distribute blood to the arteriole network
myogenic response
constriction or dilation in the walls of arterioles in response to pressures related to blood flow; reduces high blood flow or increases low blood flow to help maintain consistent flow to the capillary network
nervi vasorum
small nerve fibers found in arteries and veins that trigger contraction of the smooth muscle in their walls
net filtration pressure (NFP)
force driving fluid out of the capillary and into the tissue spaces; equal to the difference of the capillary hydrostatic pressure and the blood colloidal osmotic pressure
neurogenic shock
type of shock that occurs with cranial or high spinal injuries that damage the cardiovascular centers in the medulla oblongata or the nervous fibers originating from this region
obstructive shock
type of shock that occurs when a significant portion of the vascular system is blocked
occipital sinus
enlarged vein that drains the occipital region near the falx cerebelli and flows into the left and right transverse sinuses, and also into the vertebral veins
ophthalmic artery
branch of the internal carotid artery; supplies blood to the eyes
ovarian artery
branch of the abdominal aorta; supplies blood to the ovary, uterine (Fallopian) tube, and uterus
ovarian vein
drains the ovary; the right ovarian vein leads to the inferior vena cava and the left ovarian vein leads to the left renal vein
palmar arches
superficial and deep arches formed from anastomoses of the radial and ulnar arteries; supply blood to the hand and digital arteries
palmar venous arches
drain the hand and digits, and feed into the radial and ulnar veins
parietal branches
(also, somatic branches) group of arterial branches of the thoracic aorta; includes those that supply blood to the thoracic cavity, vertebral column, and the superior surface of the diaphragm
perfusion
distribution of blood into the capillaries so the tissues can be supplied
pericardial artery
branch of the thoracic aorta; supplies blood to the pericardium
petrosal sinus
enlarged vein that receives blood from the cavernous sinus and flows into the internal jugular vein
phrenic vein
drains the diaphragm; the right phrenic vein flows into the inferior vena cava and the left phrenic vein leads to the left renal vein
plantar arch
formed from the anastomosis of the dorsalis pedis artery and medial and plantar arteries; branches supply the distal portions of the foot and digits
plantar veins
drain the foot and lead to the plantar venous arch
plantar venous arch
formed from the plantar veins; leads to the anterior and posterior tibial veins through anastomoses
popliteal artery
continuation of the femoral artery posterior to the knee; branches into the anterior and posterior tibial arteries
popliteal vein
continuation of the femoral vein behind the knee; drains the region behind the knee and forms from the fusion of the fibular and anterior and posterior tibial veins
posterior cerebral artery
branch of the basilar artery that forms a portion of the posterior segment of the arterial circle; supplies blood to the posterior portion of the cerebrum and brain stem
posterior communicating artery
branch of the posterior cerebral artery that forms part of the posterior portion of the arterial circle; supplies blood to the brain
posterior tibial artery
branch from the popliteal artery that gives rise to the fibular or peroneal artery; supplies blood to the posterior tibial region
posterior tibial vein
forms from the dorsal venous arch; drains the area near the posterior surface of the tibia and leads to the popliteal vein
precapillary sphincters
circular rings of smooth muscle that surround the entrance to a capillary and regulate blood flow into that capillary
pulmonary artery
one of two branches, left and right, that divides off from the pulmonary trunk and leads to smaller arterioles and eventually to the pulmonary capillaries
pulmonary circuit
system of blood vessels that provide gas exchange via a network of arteries, veins, and capillaries that run from the heart, through the body, and back to the lungs
pulmonary trunk
single large vessel exiting the right ventricle that divides to form the right and left pulmonary arteries
pulmonary veins
two sets of paired vessels, one pair on each side, that are formed from the small venules leading away from the pulmonary capillaries that flow into the left atrium
pulse
alternating expansion and recoil of an artery as blood moves through the vessel; an indicator of heart rate
pulse pressure
difference between the systolic and diastolic pressures
radial artery
formed at the bifurcation of the brachial artery; parallels the radius; gives off smaller branches until it reaches the carpal region where it fuses with the ulnar artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region
radial vein
parallels the radius and radial artery; arises from the palmar venous arches and leads to the brachial vein
reabsorption
in the cardiovascular system, the movement of material from the interstitial fluid into the capillaries
renal artery
branch of the abdominal aorta; supplies each kidney
renal vein
largest vein entering the inferior vena cava; drains the kidneys and leads to the inferior vena cava
resistance
any condition or parameter that slows or counteracts the flow of blood
respiratory pump
increase in the volume of the thorax during inhalation that decreases air pressure, enabling venous blood to flow into the thoracic region, then exhalation increases pressure, moving blood into the atria
right gastric artery
branch of the common hepatic artery; supplies blood to the stomach
sepsis
(also, septicemia) organismal-level inflammatory response to a massive infection
septic shock
(also, blood poisoning) type of shock that follows a massive infection resulting in organism-wide inflammation
sigmoid sinuses
enlarged veins that receive blood from the transverse sinuses; flow through the jugular foramen and into the internal jugular vein
sinusoid capillary
rarest type of capillary, which has extremely large intercellular gaps in the basement membrane in addition to clefts and fenestrations; found in areas such as the bone marrow and liver where passage of large molecules occurs
skeletal muscle pump
effect on increasing blood pressure within veins by compression of the vessel caused by the contraction of nearby skeletal muscle
small saphenous vein
located on the lateral surface of the leg; drains blood from the superficial regions of the lower leg and foot, and leads to the popliteal vein
sphygmomanometer
blood pressure cuff attached to a device that measures blood pressure
splenic artery
branch of the celiac trunk; supplies blood to the spleen
straight sinus
enlarged vein that drains blood from the brain; receives most of the blood from the great cerebral vein and flows into the left or right transverse sinus
subclavian artery
right subclavian arises from the brachiocephalic artery, whereas the left subclavian artery arises from the aortic arch; gives rise to the internal thoracic, vertebral, and thyrocervical arteries; supplies blood to the arms, chest, shoulders, back, and central nervous system
subclavian vein
located deep in the thoracic cavity; becomes the axillary vein as it enters the axillary region; drains the axillary and smaller local veins near the scapular region; leads to the brachiocephalic vein
subscapular vein
drains blood from the subscapular region and leads to the axillary vein
superior mesenteric artery
branch of the abdominal aorta; supplies blood to the small intestine (duodenum, jejunum, and ileum), the pancreas, and a majority of the large intestine
superior phrenic artery
branch of the thoracic aorta; supplies blood to the superior surface of the diaphragm
superior sagittal sinus
enlarged vein located midsagittally between the meningeal and periosteal layers of the dura mater within the falx cerebri; receives most of the blood drained from the superior surface of the cerebrum and leads to the inferior jugular vein and the vertebral vein
superior vena cava
large systemic vein; drains blood from most areas superior to the diaphragm; empties into the right atrium
systolic pressure
larger number recorded when measuring arterial blood pressure; represents the maximum value following ventricular contraction
temporal vein
drains blood from the temporal region and leads to the external jugular vein
testicular artery
branch of the abdominal aorta; will ultimately travel outside the body cavity to the testes and form one component of the spermatic cord
testicular vein
drains the testes and forms part of the spermatic cord; the right testicular vein empties directly into the inferior vena cava and the left testicular vein empties into the left renal vein
thoracic aorta
portion of the descending aorta superior to the aortic hiatus
thoroughfare channel
continuation of the metarteriole that enables blood to bypass a capillary bed and flow directly into a venule, creating a vascular shunt
thyrocervical artery
arises from the subclavian artery; supplies blood to the thyroid, the cervical region, the upper back, and shoulder
transient ischemic attack (TIA)
temporary loss of neurological function caused by a brief interruption in blood flow; also known as a mini-stroke
transverse sinuses
pair of enlarged veins near the lambdoid suture that drain the occipital, sagittal, and straight sinuses, and leads to the sigmoid sinuses
trunk
large vessel that gives rise to smaller vessels
tunica externa
(also, tunica adventitia) outermost layer or tunic of a vessel (except capillaries)
tunica intima
(also, tunica interna) innermost lining or tunic of a vessel
tunica media
middle layer or tunic of a vessel (except capillaries)
ulnar artery
formed at the bifurcation of the brachial artery; parallels the ulna; gives off smaller branches until it reaches the carpal region where it fuses with the radial artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region
ulnar vein
parallels the ulna and ulnar artery; arises from the palmar venous arches and leads to the brachial vein
umbilical arteries
pair of vessels that runs within the umbilical cord and carries fetal blood low in oxygen and high in waste to the placenta for exchange with maternal blood
umbilical vein
single vessel that originates in the placenta and runs within the umbilical cord, carrying oxygen- and nutrient-rich blood to the fetal heart
vasa vasorum
small blood vessels located within the walls or tunics of larger vessels that supply nourishment to and remove wastes from the cells of the vessels
vascular shock
type of shock that occurs when arterioles lose their normal muscular tone and dilate dramatically
vascular shunt
continuation of the metarteriole and thoroughfare channel that allows blood to bypass the capillary beds to flow directly from the arterial to the venous circulation
vascular tone
contractile state of smooth muscle in a blood vessel
vascular tubes
rudimentary blood vessels in a developing fetus
vasoconstriction
constriction of the smooth muscle of a blood vessel, resulting in a decreased vascular diameter
vasodilation
relaxation of the smooth muscle in the wall of a blood vessel, resulting in an increased vascular diameter
vasomotion
irregular, pulsating flow of blood through capillaries and related structures
vein
blood vessel that conducts blood toward the heart
venous reserve
volume of blood contained within systemic veins in the integument, bone marrow, and liver that can be returned to the heart for circulation, if needed
venule
small vessel leading from the capillaries to veins
vertebral artery
arises from the subclavian artery and passes through the vertebral foramen through the foramen magnum to the brain; joins with the internal carotid artery to form the arterial circle; supplies blood to the brain and spinal cord
vertebral vein
arises from the base of the brain and the cervical region of the spinal cord; passes through the intervertebral foramina in the cervical vertebrae; drains smaller veins from the cranium, spinal cord, and vertebrae, and leads to the brachiocephalic vein; counterpart of the vertebral artery
visceral branches
branches of the descending aorta that supply blood to the viscera
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Blood flow refers to the movement of blood through a vessel, tissue, or organ, and is usually expressed in terms of volume of blood per unit of time. It is initiated by the contraction of the ventricles of the heart. Ventricular contraction ejects blood into the major arteries, resulting in flow from regions of higher pressure to regions of lower pressure, as blood encounters smaller arteries and arterioles, then capillaries, then the venules and veins of the venous system. This section discusses a number of critical variables that contribute to blood flow throughout the body. It also discusses the factors that impede or slow blood flow, a phenomenon known as resistance.

As noted earlier, hydrostatic pressure is the force exerted by a fluid due to gravitational pull, usually against the wall of the container in which it is located. One form of hydrostatic pressure is blood pressure, the force exerted by blood upon the walls of the blood vessels or the chambers of the heart. Blood pressure may be measured in capillaries and veins, as well as the vessels of the pulmonary circulation; however, the term blood pressure without any specific descriptors typically refers to systemic arterial blood pressure—that is, the pressure of blood flowing in the arteries of the systemic circulation. In clinical practice, this pressure is measured in mm Hg and is usually obtained using the brachial artery of the arm.
Arterial blood pressure in the larger vessels consists of several distinct components (Figure 1): systolic and diastolic pressures, pulse pressure, and mean arterial pressure.

A. Systolic and Diastolic Pressures

When systemic arterial blood pressure is measured, it is recorded as a ratio of two numbers (e.g., 120/80 is a normal adult blood pressure), expressed as systolic pressure over diastolic pressure. The systolic pressure is the higher value (typically around 120 mm Hg) and reflects the arterial pressure resulting from the ejection of blood during ventricular contraction, or systole. The diastolic pressure is the lower value (usually about 80 mm Hg) and represents the arterial pressure of blood during ventricular relaxation, or diastole.

B. Pulse Pressure

As shown in Figure 1, the difference between the systolic pressure and the diastolic pressure is the pulse pressure. For example, an individual with a systolic pressure of 120 mm Hg and a diastolic pressure of 80 mm Hg would have a pulse pressure of 40 mmHg.

Generally, a pulse pressure should be at least 25 percent of the systolic pressure. A pulse pressure below this level is described as low or narrow. This may occur, for example, in patients with a low stroke volume, which may be seen in congestive heart failure, stenosis of the aortic valve, or significant blood loss following trauma. In contrast, a high or wide pulse pressure is common in healthy people following strenuous exercise, when their resting pulse pressure of 30–40 mm Hg may increase temporarily to 100 mm Hg as stroke volume increases. A persistently high pulse pressure at or above 100 mm Hg may indicate excessive resistance in the arteries and can be caused by a variety of disorders. Chronic high resting pulse pressures can degrade the heart, brain, and kidneys, and warrant medical treatment.

C. Mean Arterial Pressure

Mean arterial pressure (MAP) represents the “average” pressure of blood in the arteries, that is, the average force driving blood into vessels that serve the tissues. Mean is a statistical concept and is calculated by taking the sum of the values divided by the number of values. Although complicated to measure directly and complicated to calculate, MAP can be approximated by adding the diastolic pressure to one-third of the pulse pressure or systolic pressure minus the diastolic pressure:

MAP = diastolic BP + (systolic BP-diastolic BP)/3
or
MAP = diastolic BP + (pulse pressure)/3.

In Figure 1, this value is approximately 80 + (120−80)/3, or 93.33. Normally, the MAP falls within the range of 70–110 mm Hg. If the value falls below 60 mm Hg for an extended time, blood pressure will not be high enough to ensure circulation to and through the tissues, which results in ischemia, or insufficient blood flow. A condition called hypoxia, inadequate oxygenation of tissues, commonly accompanies ischemia. The term hypoxemia refers to low levels of oxygen in systemic arterial blood. Neurons are especially sensitive to hypoxia and may die or be damaged if blood flow and oxygen supplies are not quickly restored.
After blood is ejected from the heart, elastic fibers in the arteries help maintain a high-pressure gradient as they expand to accommodate the blood, then recoil. This expansion and recoiling effect, known as the pulse, can be palpated manually or measured electronically. Although the effect diminishes over distance from the heart, elements of the systolic and diastolic components of the pulse are still evident down to the level of the arterioles.

Because pulse indicates heart rate, it is measured clinically to provide clues to a patient’s state of health. It is recorded as beats per minute. Both the rate and the strength of the pulse are important clinically. A high or irregular pulse rate can be caused by physical activity or other temporary factors, but it may also indicate a heart condition. The pulse strength indicates the strength of ventricular contraction and cardiac output. If the pulse is strong, then systolic pressure is high. If it is weak, systolic pressure has fallen, and medical intervention may be warranted.

Pulse can be palpated manually by placing the tips of the fingers across an artery that runs close to the body surface and pressing lightly. While this procedure is normally performed using the radial artery in the wrist or the common carotid artery in the neck, any superficial artery that can be palpated may be used (Figure 2). Common sites to find a pulse include temporal and facial arteries in the head, brachial arteries in the upper arm, femoral arteries in the thigh, popliteal arteries behind the knees, posterior tibial arteries near the medial tarsal regions, and dorsalis pedis arteries in the feet. A variety of commercial electronic devices are also available to measure pulse.
Blood pressure is one of the critical parameters measured on virtually every patient in every healthcare setting. The technique used today was developed more than 100 years ago by a pioneering Russian physician, Dr. Nikolai Korotkoff. Turbulent blood flow through the vessels can be heard as a soft ticking while measuring blood pressure; these sounds are known as Korotkoff sounds. The technique of measuring blood pressure requires the use of a sphygmomanometer (a blood pressure cuff attached to a measuring device) and a stethoscope. The technique is as follows:

  • The clinician wraps an inflatable cuff tightly around the patient’s arm at about the level of the heart.
  • The clinician squeezes a rubber pump to inject air into the cuff, raising pressure around the artery and temporarily cutting off blood flow into the patient’s arm.
  • The clinician places the stethoscope on the patient’s antecubital region and, while gradually allowing air within the cuff to escape, listens for the Korotkoff sounds.

Although there are five recognized Korotkoff sounds, only two are normally recorded. Initially, no sounds are heard since there is no blood flow through the vessels, but as air pressure drops, the cuff relaxes, and blood flow returns to the arm. As shown in Figure 3, the first sound heard through the stethoscope—the first Korotkoff sound—indicates systolic pressure. As more air is released from the cuff, blood is able to flow freely through the brachial artery and all sounds disappear. The point at which the last sound is heard is recorded as the patient’s diastolic pressure.

The majority of hospitals and clinics have automated equipment for measuring blood pressure that work on the same principles. An even more recent innovation is a small instrument that wraps around a patient’s wrist. The patient then holds the wrist over the heart while the device measures blood flow and records pressure.
Five variables influence blood flow and blood pressure:

  • Cardiac output.
  • Compliance.
  • Volume of the blood.
  • Viscosity of the blood.
  • Blood vessel length and diameter.

Recall that blood moves from higher pressure to lower pressure. It is pumped from the heart into the arteries at high pressure. If you increase pressure in the arteries (afterload), and cardiac function does not compensate, blood flow will actually decrease. In the venous system, the opposite relationship is true. Increased pressure in the veins does not decrease flow as it does in arteries, but actually increases flow. Since pressure in the veins is normally relatively low, for blood to flow back into the heart, the pressure in the atria during atrial diastole must be even lower. It normally approaches zero, except when the atria contract (see Figure 1).

A. Cardiac Output

Cardiac output is the measurement of blood flow from the heart through the ventricles, and is usually measured in liters per minute. Any factor that causes cardiac output to increase, by elevating heart rate or stroke volume or both, will elevate blood pressure and promote blood flow. These factors include sympathetic stimulation, the catecholamines epinephrine and norepinephrine, thyroid hormones, and increased calcium ion levels. Conversely, any factor that decreases cardiac output, by decreasing heart rate or stroke volume or both, will decrease arterial pressure and blood flow. These factors include parasympathetic stimulation, elevated or decreased potassium ion levels, decreased calcium levels, anoxia, and acidosis.

B. Compliance

Compliance is the ability of any compartment to expand to accommodate increased content. A metal pipe, for example, is not compliant, whereas a balloon is. The greater the compliance of an artery, the more effectively it is able to expand to accommodate surges in blood flow without increased resistance or blood pressure. Veins are more compliant than arteries and can expand to hold more blood. When vascular disease causes stiffening of arteries, compliance is reduced and resistance to blood flow is increased. The result is more turbulence, higher pressure within the vessel, and reduced blood flow. This increases the work of the heart.

C. A Mathematical Approach to Factors Affecting Blood Flow

Jean Louis Marie Poiseuille was a French physician and physiologist who devised a mathematical equation describing blood flow and its relationship to known parameters. The same equation also applies to engineering studies of the flow of fluids. Although understanding the math behind the relationships among the factors affecting blood flow is not necessary to understand blood flow, it can help solidify an understanding of their relationships. Please note that even if the equation looks intimidating, breaking it down into its components and following the relationships will make these relationships clearer, even if you are weak in math. Focus on the three critical variables: radius (r), vessel length (λ), and viscosity (η).

Poiseuille’s equation: Blood flow = πΔPr^4/8ηλ

  • π is the Greek letter pi, used to represent the mathematical constant that is the ratio of a circle’s circumference to its diameter. It may commonly be represented as 3.14, although the actual number extends to infinity.
  • ΔP represents the difference in pressure.
  • r4 is the radius (one-half of the diameter) of the vessel to the fourth power.
  • η is the Greek letter eta and represents the viscosity of the blood.
  • λ is the Greek letter lambda and represents the length of a blood vessel.

One of several things this equation allows us to do is calculate the resistance in the vascular system. Normally this value is extremely difficult to measure, but it can be calculated from this known relationship:

Blood flow = ΔP/Resistance.

If we rearrange this slightly:

Resistance = ΔP/Blood flow.

Then by substituting Pouseille’s equation for blood flow:

Resistance = 8ηλ/πr^4.

By examining this equation, you can see that there are only three variables: viscosity, vessel length, and radius, since 8 and π are both constants. The important thing to remember is this: Two of these variables, viscosity and vessel length, will change slowly in the body. Only one of these factors, the radius, can be changed rapidly by vasoconstriction and vasodilation, thus dramatically impacting resistance and flow. Further, small changes in the radius will greatly affect flow, since it is raised to the fourth power in the equation.

We have briefly considered how cardiac output and blood volume impact blood flow and pressure; the next step is to see how the other variables (contraction, vessel length, and viscosity) articulate with Pouseille’s equation and what they can teach us about the impact on blood flow.

D. Blood Volume

The relationship between blood volume, blood pressure, and blood flow is intuitively obvious. Water may merely trickle along a creek bed in a dry season, but rush quickly and under great pressure after a heavy rain. Similarly, as blood volume decreases, pressure and flow decrease. As blood volume increases, pressure and flow increase.

Under normal circumstances, blood volume varies little. Low blood volume, called hypovolemia, may be caused by bleeding, dehydration, vomiting, severe burns, or some medications used to treat hypertension. It is important to recognize that other regulatory mechanisms in the body are so effective at maintaining blood pressure that an individual may be asymptomatic until 10–20 percent of the blood volume has been lost. Treatment typically includes intravenous fluid replacement.

Hypervolemia, excessive fluid volume, may be caused by retention of water and sodium, as seen in patients with heart failure, liver cirrhosis, some forms of kidney disease, hyperaldosteronism, and some glucocorticoid steroid treatments. Restoring homeostasis in these patients depends upon reversing the condition that triggered the hypervolemia.

E. Blood Viscosity

Viscosity is the thickness of fluids that affects their ability to flow. Clean water, for example, is less viscous than mud. The viscosity of blood is directly proportional to resistance and inversely proportional to flow; therefore, any condition that causes viscosity to increase will also increase resistance and decrease flow. For example, imagine sipping milk, then a milkshake, through the same size straw. You experience more resistance and therefore less flow from the milkshake. Conversely, any condition that causes viscosity to decrease (such as when the milkshake melts) will decrease resistance and increase flow.

Normally the viscosity of blood does not change over short periods of time. The two primary determinants of blood viscosity are the formed elements and plasma proteins. Since the vast majority of formed elements are erythrocytes, any condition affecting erythropoiesis, such as polycythemia or anemia, can alter viscosity. Since most plasma proteins are produced by the liver, any condition affecting liver function can also change the viscosity slightly and therefore alter blood flow. Liver abnormalities such as hepatitis, cirrhosis, alcohol damage, and drug toxicities result in decreased levels of plasma proteins, which decrease blood viscosity. While leukocytes and platelets are normally a small component of the formed elements, there are some rare conditions in which severe overproduction can impact viscosity as well.

F. Vessel Length and Diameter

The length of a vessel is directly proportional to its resistance: the longer the vessel, the greater the resistance and the lower the flow. As with blood volume, this makes intuitive sense, since the increased surface area of the vessel will impede the flow of blood. Likewise, if the vessel is shortened, the resistance will decrease and flow will increase.

The length of our blood vessels increases throughout childhood as we grow, of course, but is unchanging in adults under normal physiological circumstances. Further, the distribution of vessels is not the same in all tissues. Adipose tissue does not have an extensive vascular supply. One pound of adipose tissue contains approximately 200 miles of vessels, whereas skeletal muscle contains more than twice that. Overall, vessels decrease in length only during loss of mass or amputation. An individual weighing 150 pounds has approximately 60,000 miles of vessels in the body. Gaining about 10 pounds adds from 2000 to 4000 miles of vessels, depending upon the nature of the gained tissue. One of the great benefits of weight reduction is the reduced stress to the heart, which does not have to overcome the resistance of as many miles of vessels.

In contrast to length, the diameter of blood vessels changes throughout the body, according to the type of vessel, as we discussed earlier. The diameter of any given vessel may also change frequently throughout the day in response to neural and chemical signals that trigger vasodilation and vasoconstriction. The vascular tone of the vessel is the contractile state of the smooth muscle and the primary determinant of diameter, and thus of resistance and flow. The effect of vessel diameter on resistance is inverse: Given the same volume of blood, an increased diameter means there is less blood contacting the vessel wall, thus lower friction and lower resistance, subsequently increasing flow. A decreased diameter means more of the blood contacts the vessel wall, and resistance increases, subsequently decreasing flow.

The influence of lumen diameter on resistance is dramatic: A slight increase or decrease in diameter causes a huge decrease or increase in resistance. This is because resistance is inversely proportional to the radius of the blood vessel (one-half of the vessel’s diameter) raised to the fourth power (R = 1/r4). This means, for example, that if an artery or arteriole constricts to one-half of its original radius, the resistance to flow will increase 16 times. And if an artery or arteriole dilates to twice its initial radius, then resistance in the vessel will decrease to 1/16 of its original value and flow will increase 16 times.

G. The Roles of Vessel Diameter and Total Area in Blood Flow and Blood Pressure

Recall that we classified arterioles as resistance vessels, because given their small lumen, they dramatically slow the flow of blood from arteries. In fact, arterioles are the site of greatest resistance in the entire vascular network. This may seem surprising, given that capillaries have a smaller size. How can this phenomenon be explained? Figure 4 compares vessel diameter, total cross-sectional area, average blood pressure, and blood velocity through the systemic vessels. Notice in parts (a) and (b) that the total cross-sectional area of the body’s capillary beds is far greater than any other type of vessel. Although the diameter of an individual capillary is significantly smaller than the diameter of an arteriole, there are vastly more capillaries in the body than there are other types of blood vessels. Part (c) shows that blood pressure drops unevenly as blood travels from arteries to arterioles, capillaries, venules, and veins, and encounters greater resistance. However, the site of the most precipitous drop, and the site of greatest resistance, is the arterioles. This explains why vasodilation and vasoconstriction of arterioles play more significant roles in regulating blood pressure than do the vasodilation and vasoconstriction of other vessels.

Part (d) shows that the velocity (speed) of blood flow decreases dramatically as the blood moves from arteries to arterioles to capillaries. This slow flow rate allows more time for exchange processes to occur. As blood flows through the veins, the rate of velocity increases, as blood is returned to the heart.
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.

A. 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 (Figure 5), 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.

B. 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.

C. Pressure Relationships in the Venous System

Although vessel diameter increases from the smaller venules to the larger veins and eventually to the venae cavae (singular = vena cava), the total cross-sectional area actually decreases (see Figure 4a and 4b). The individual veins are larger in diameter than the venules, but their total number is much lower, so their total cross-sectional area is also lower.

Also notice that, as blood moves from venules to veins, the average blood pressure drops (see Figure 4c), but the blood velocity actually increases (see Figure 4d). This pressure gradient drives blood back toward the heart. Again, the presence of one-way valves and the skeletal muscle and respiratory pumps contribute to this increased flow. Since approximately 64 percent of the total blood volume resides in systemic veins, any action that increases the flow of blood through the veins will increase venous return to the heart. Maintaining vascular tone within the veins prevents the veins from merely distending, dampening the flow of blood, and as you will see, vasoconstriction actually enhances the flow.

D. The Role of Venoconstriction in Resistance, Blood Pressure, and Flow

As previously discussed, vasoconstriction of an artery or arteriole decreases the radius, increasing resistance and pressure, but decreasing flow. Venoconstriction, on the other hand, has a very different outcome. The walls of veins are thin but irregular; thus, when the smooth muscle in those walls constricts, the lumen becomes more rounded. The more rounded the lumen, the less surface area the blood encounters, and the less resistance the vessel offers. Vasoconstriction increases pressure within a vein as it does in an artery, but in veins, the increased pressure increases flow. Recall that the pressure in the atria, into which the venous blood will flow, is very low, approaching zero for at least part of the relaxation phase of the cardiac cycle. Thus, venoconstriction increases the return of blood to the heart. Another way of stating this is that venoconstriction increases the preload or stretch of the cardiac muscle and increases contraction.

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at openstax.org.

The graph shows the components of blood pressure throughout the blood vessels, including systolic, diastolic, mean arterial, and pulse pressures.

The pulse is most readily measured at the radial artery, but can be measured at any of the pulse points shown.

When pressure in a sphygmomanometer cuff is released, a clinician can hear the Korotkoff sounds. In this graph, a blood pressure tracing is aligned to a measurement of systolic and diastolic pressures.

The relationships among blood vessels that can be compared include (a) vessel diameter, (b) total cross-sectional area, (c) average blood pressure, and (d) velocity of blood flow.

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.

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Dưới đây là video và các luyện tập (practice) của bài này. Nghe là một kĩ năng khó, đặc biệt là khi chúng ta chưa quen nội dung và chưa có nhạy cảm ngôn ngữ. Nhưng cứ đi thật chậm và đừng bỏ cuộc.
Xem video và cảm nhận nội dung bài. Bạn có thể thả trôi, cảm nhận dòng chảy ngôn ngữ và không nhất thiết phải hiểu toàn bộ bài. Bên dưới là script để bạn khái quát nội dụng và tra từ mới.
Script:
  1. Blood flow is the movement of blood through a vessel, tissue, or organ.
  2. The slowing or blocking of blood flow is called resistance.
  3. Blood pressure is the force that blood exerts upon the walls of the blood vessels or chambers of the heart.
  4. The components of blood pressure include systolic pressure, which results from ventricular contraction, and diastolic pressure, which results from ventricular relaxation.
  5. Pulse pressure is the difference between systolic and diastolic measures, and mean arterial pressure is the “average” pressure of blood in the arterial system, driving blood into the tissues.
  6. Pulse, the expansion and recoiling of an artery, reflects the heartbeat.
  7. The variables affecting blood flow and blood pressure in the systemic circulation are cardiac output, compliance, blood volume, blood viscosity, and the length and diameter of the blood vessels.
  8. In the arterial system, vasodilation and vasoconstriction of the arterioles is a significant factor in systemic blood pressure.
  9. Slight vasodilation greatly decreases resistance and increases flow, whereas slight vasoconstriction greatly increases resistance and decreases flow.
  10. In the arterial system, as resistance increases, blood pressure increases and flow decreases.
  11. In the venous system, constriction increases blood pressure as it does in arteries.
  12. The increasing pressure helps to return blood to the heart.
  13. In addition, constriction causes the vessel lumen to become more rounded, decreasing resistance and increasing blood flow.
  14. Venoconstriction, while less important than arterial vasoconstriction, works with the skeletal muscle pump, the respiratory pump, and their valves to promote venous return to the heart.
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