The Physiology of Circulation Flashcards
pumping action of the heart causes
blood flow
blood flow is measured as the
amount of blood traveling through any organ, tissue, or blood vessel in a given period of time (mL/minute)
velocity of blood flow depends on
cross sectional area through which it flows
blood perfusion describes
the flow of blood through a given volume or mass of tissue per unit of time
the total blood flow in a resting individual is
constant and equal to his or her cardiac output, but blood flow through any particular organ varies from minute to minute as blood gets redirected through different organ systems
hemodynamics are based on
blood pressure and resistance
blood flow is directly proportional to the
difference in pressure between two points
blood flow is inversely proportional to the
resistance it encounters
blood pressure is
the force exerted by blood against the walls of a blood vessel when it encounters resistance as it flows
blood pressure is determined by
cardiac output, blood volume, and resistance
cardiac output is the product of
stroke volume and heart rate
systolic blood pressure occurs during
ventricular contraction
diastolic blood pressure occurs during
ventricular relaxation
pulse pressure is
the difference between the systolic blood pressure and the diastolic blood pressure
mean arterial blood pressure propels blood to
the tissues and measures the stress on blood vessels based upon diastolic pressure and pulse pressure
peripheral resistance describes
the opposition to blood flow because of friction between blood and the walls of the blood vessels
resistance is directly proportional to
blood viscosity
blood viscosity depends on
ratio of erythrocytes to plasma volume and concentration of proteins in blood plasma
any reduction in number of erythrocytes
reduces viscosity, so it decreases resistance
any reduction in concentration of plasma proteins
reduces viscosity, so it decreases resistance
any increase in number of erythrocytes
increases viscosity, so it increases resistance
dehydration increases
blood viscosity, so it increases resistance
resistance is directly proportional to
vessel length
longer blood vessels provide more
friction and greater peripheral resistance
adjusting ____________ has the greatest short term influence on blood flow
BLOOD VESSEL RADIUS
because viscosity is relatively stable and vessel length does not change over short periods of time
vasoconstriction
reduces radius of blood vessel
vasodilation
increases radius of a blood vessel
resistance is inversely proportional to
vessel radius
blood typically exhibits laminar flow by moving
faster near center of a blood vessel due to less friction, and slower near walls of blood vessel due to more friction
decreasing radius of a blood vessel by half increases resistance by
16 times
because of differences in cross-sectional areas
blood flow declines from arteries to capillaries, but increases from capillaries to veins
autoregulation describes
ability of an organ to regulate its own blood supply by varying the resistance of the arterioles in order to meet the metabolic demands for oxygen, nutrients, and waste removal
warming promotes
vasodilation
cooling promotes
vasoconstriction
vasoactive chemicals by platelets, leukocytes, or endothelial cells alter
blood vessel radius
lactic acid, histamines, and nitric oxide are examples of
vasodilators
the cardiovascular center in the medulla oblongata contains a
cardiac center and a vasomotor center, which exerts neural control over blood vessels by transmitting impulses to maintain vasomotor tone
vasomotor tone describes
a state of moderate constriction that varies from organ to organ
baroreflexes are
negative feedback responses to changes in blood pressure that get detected by receptors in aorta and carotid arteries
increase in blood pressure stimulates
baroreflexes, to send signals to vasomotor center to reduce vasomotor tone and cause vasodilation
decrease in blood pressure promotes
vasoconstriction
baroreflexes correct momentary drops in
blood pressure
chemoreflexes are
autonomic responses to changes in pH, oxygen concentration, or carbon dioxide concentration defected by aortic bodies and/or carotid bodies
acidosis, hypoxia, or hypercapnia stimulate
chemoreceptors to cause widespread vasoconstriction to increase blood pressure
hormones influence
blood pressure
angiotensin II is a
vasoconstrictor that raises blood pressure when kidney perfusion is inadequate
angiotensin converting enzyme (ACE) can be
blocked by drugs to reduce angiotensin II levels, which reduces BP
aldosterone promotes
the retention of sodium ions, which promotes water retention and raises BP
antidiuretic hormone (vasopressin) is a
vasoconstrictor released from posterior lobe of pituitary gland, which causes kidneys to conserve water and raise BP
epinephrine and norepinephrine are
vasoconstrictors that raise BP
-they bind to adrenergic receptors on smooth muscle to stimulate contractions
capillary exchange describes
the movement of substances into and out of capillaries
diffusion is
an important exchange mechanism used to move glucose and oxygen between the blood and tissues and to move wastes and carbon dioxide between the tissues and blood
transcytosis occurs when
endothelial cells transport fluid-filled vesicles that contain albumin, fatty acids, or insulin across capillaries
bulk flow is a
passive process by which dissolved substances move from blood into the interstitial fluid by filtration, and from the interstitial fluid into the blood by reabsorption
filtration results from
blood hydrostatic pressure and interstitial fluid osmotic pressure
blood hydrostatic pressure (BHP) is generated by
the hearts pumping action
- is higher at arterial end of capillary bed than at venous end
- because of solutes present in interstitial fluid
interstitial fluid osmotic pressure (IFOP)
draws water out of the capillaries
reabsorption results from
colloid osmotic pressure and interstitial fluid hydrostatic pressure
blood colloid osmotic pressure (BCOP)
draws water into capillaries
interstitial fluid hydrostatic pressure (IFHP)
is negligible
net filtration pressure
NFP= (BHP + IFOP) - (BCOP + IFHP)
BHHP is higher at
arterial end of capillary bed
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BCOP is higher at
the venous end of capillary bed
-there is net inward pressure and fluid moves into capillary from interstitial space
about 85% of the 20 liters of fluid filtered out of the capillaries each day gets
reabsorbed into blood
remaining fluid gets absorbed by the
lymphatic system to prevent fluid from accumulating in tissues, which is then returned to blood
there is a pressure gradient from the venules to the vena cavae that favors
blood flow back to the right atrium, even though blood pressure remains steady at 15 mm Hg and changes very little during the cardiac cycle
gradient will increase when blood volume
increases or when veins dilate
gradient will decrease when veins constrict
or if pressure increases in right atrium due to leaky tricuspid valve
skeletal muscle “pumps” in limbs
squeeze blood out of veins toward the heart
at rest, both valves in a venous segment are
open and blood flows toward heart
muscle contraction compresses the vein which
forces blood through proximal valve
muscle relaxation causes the proximal valve to
close and blood enters venous segment through open distal valve
a thoracic (respiratory) pump
aids in blood flow toward the heart because differences in pressure during inhalation and exhalation “squeeze” in the inferior cava
physical activity increases
venous return because the heart beats faster and harder, blood vessels dilate, muscle contractions increase, and respiratory rate and depth increases
