Chapter 15: Blood Flow and the Control of Blood Pressure Flashcards
closed system
circulatory system
force exerted by blood
pressure
which direction does flow occur?
from high pressure to low pressure
Blood flow to the organs and blood pressure are regulated by ……?
- intrinsic controls
- extrinsic controls
flow =
=ΔP/R
=cardiac output (CO)
ΔP =
mean arterial pressure (MAP)
R=
total peripheral resistance (TPR)
CO=
MAP/TPR
- take blood away from the heart
- Elastic walls and thick layers of vascular smooth muscles
- act as a pressure reservoir
arteries
- take blood back to the heart
- thin walls of vascular smooth muscles
- act as volume reservoir
- valves allow unidirectional blood flow (present in peripheral veins)
veins
site of variable resistance
arterioles
exchange between the blood and cells
capillaries
serve as an expandable volume reservoir
systemic veins
functions as an independent pump
each side of the heart
a pressure reservoir that maintains blood flow during ventricular relaxation
elastic systemic arteries
facilitates exchange
Absence of vascular smooth muscle and elastic tissue reinforcement in capillaries
what do capillaries have that help with exchange?
one cell-thick layer of endothelial cells on basal lamina
Contract and relax in response to local factors
precapillary sphincters
- Intermediate between arterioles and capillaries
- Function as shunts to bypass capillaries
Metarterioles
what happens when precapillary sphincters are relaxed?
blood flows through all capillaries in the bed
what happens if precapillary sphincters constrict?
blood flow bypasses capillaries completely and flows through metarterioles
- Storage site for pressure
- Thick, elastic arterial walls
- Low compliance
- Expand as blood enters arteries during systole
- Recoil during diastole
arteries as a pressure reservoir
is the ease with which a hollow vessel expands
compliance
- in arteries
- Small increase in blood volume causes a large increase in pressure (balloon requires greater effort to inflate)
low compliance
Large increase in blood volume is required to produce a large increase in pressure (balloon expands easily)
high compliance
pushes blood into elastic arteries, causing them to stretch
ventricular contraction
what are the steps of ventricular contraction?
- ventricle contracts
- semilunar valve opens; blood ejected from ventricles flows into the arteries
- aorta and arteries expand and store pressure in elastic walls
how can blood pressure be measured?
- pressure cuff and sphygmomanometer
- uncompressed artery
- Compressed artery
- Turbulent flow produces -Korotkoff sound
- Pressure at first Korotkoff sound = systolic blood pressure
pressure cuff and sphygmomanometer
- flow, no sound
- Pressure when sound disappears = diastolic blood pressure
uncompressed artery
when can the first Korotkoff sounds be heard?
- created by pulsatile blood flow through the compressed artery
- cuff pressure between 80 and 120 mmHG
when is the blood flow silent?
- artery no longer compressed
- cuff pressure <80 mmHg
what is the measured BP shown as?
systolic pressure/diastolic pressure
-example 120/80
SP-DP=
pulse pressure
= diastolic P + 1/3(systolic P – diastolic P)
mean arterial pressure (MAP)
aortic pressure is closer to the minimum pressure twice as long
weighted mean
determines the mean arterial pressure
cardiac output and peripheral resistance
mean arterial pressure is directly proportional to…..?
cardiac output x resistance of arterioles
what are some factors that affect mean arterial pressure?
- blood volume
- effectiveness of the heart as a pump (cardiac output)
- resistance of the system to blood flow
- relative distribution of blood between arterial and venous blood vessels
- resistant vessels
- part of microcirculation
- connect arteries to capillaries or metarterioles
- Contain rings of smooth muscle to regulate radius and, therefore, resistance
arterioles
- provide greatest resistance to blood flow
- greater than 60% of TPR
- resistance is regulated
- largest pressure drop in vasculature
arterioles
alter the contractile state of arteriolar smooth muscle
intrinsic and extrinsic control mechanisms
- include local metabolites
- controlling blood flow to individual capillary beds
intrinsic controls
- control both ANS and hormones
- regulating mean arterial pressure
extrinsic controls
causes vasoconstriction
contraction of smooth muscle (arterioles)
causes vasodilation
relaxation of smooth muscle (arterioles)
what is regulation of blood flow to organs based on?
based on need
how is blood flow to organs regulated?
-by varying resistance
organ blood flow=MAP/organ resistance
what is the Vascular smooth muscle response to four factors:
- metabolic activity
- changes in blood flow
- stretch of arteriolar smooth muscle
- local chemical messengers
what do changes associated with increased metabolic activity cause?
vasodilation
what do changes associated with decreased metabolic activity cause?
vasoconstriction
increased blood flow in response to increased metabolic activity
active hyperemia
- O2 is delivered as fast as it is consumed
- CO2 is removed as fast as it is produced
steady state
- O2 is consumed faster than it is delivered
- CO2 is produced faster than it is removed
increased metabolic rate (active hyperemia)
act on arteriolar
smooth muscle to promote vasodilation
The decreased oxygen concentration and increased
carbon dioxide concentration
promotes increased blood flow, which
increases oxygen delivery to cells and carbon dioxide
removal from cells
vasodilation
matches blood flow to increased metabolism
active hyperemia
increased blood flow in response to a previous reduction in blood flow
reactive hyperemia
- Metabolites increase and oxygen decreases
- Vasodilation
blockage of blood flow to tissues (reactive hyperemia)
- Increased blood flow due to low resistance
- Metabolites removed, oxygen delivered
occurs when blockage is released (reactive hyperemia)
follows a period of decreased blood flow
reactive hyperemia
change in vascular resistance in response to stretch of blood vessels in the absence of external factors
myogenic response
- Increased pressure in arteriole stretches arteriole wall
- Stretch of vascular smooth muscle induces contraction of vascular smooth muscle—inherent property of smooth muscle
- Vasoconstriction decreases blood flow
- Purpose: keep blood flow constant (autoregulate)
myogenic autoregulation
happens because of changes in perfusion pressure
myogenic response
depends on total peripheral resistance (TPR)
mean arterial pressure
depends on radius of arterioles
total peripheral resistance (TPR)
- regulated by extrinsic mechanisms to control mean arterial pressure
- sympathetic activity
- hormones
radius of arterioles
- Sympathetic innervation of smooth muscle of arterioles
- Norepinephrine binds to α adrenergic receptors
- Produces vasoconstriction
- Increases TPR
- Increases MAP
Sympathetic control of arteriolar radius
controlled by tonic release of norepinephrine
arteriole diameter
as signal rate increases…..?
the blood vessels constricts
as the signal rate decreases…..?
the blood vessel dilates
what hormones are involved in hormone control?
- epinephrine
- vasopressin (ADH)
- angiotensin II
released from adrenal medulla
epinephrine
- Secreted by posterior pituitary
- Increases water reabsorption by kidneys
- Vasoconstriction
vasopressin (ADH)
- Vasoconstriction
- Increases TPR
angiotensin II
how is mean arterial pressure regulated?
- neural control of MAP
- negative feedback loops
baroreceptors
detector for negative feedback loops (of MAP)
cardiovascular centers in the brainstem
integration center (of MAP)
autonomic nervous system
controllers (of MAP)
heart and blood vessels
effectors (of MAP)
- pressure receptors
- sometimes called stretch receptors
- Respond to stretching due to pressure changes in arteries
baroreceptors
- sinoaortic receptors
- aortic arch
- carotid sinuses
arterial baroreceptors
exchange materials across thin capillary walls
plasma and cells
related to metabolic activity of cells
capillary density
- have the thinnest walls
- Single layer of flattened endothelial cells
- Supported by basal lamina
capillaries
what are the kinds of capillaries?
- continuous
- fenestrated
do not have typical capillaries but rather sinusoids
Bone marrow, liver, and spleen
occurs by paracellular pathway or endothelial transport
Exchange between plasma and interstitial fluid
move by diffusion, depending on lipid solubility and concentration gradient
small dissolved solutes and gases
move mostly by vesicular transport
larger solutes and proteins
transported by transcytosis
large molecules and selected proteins in most capillaries
- most common capillaries
- small gaps between endothelial cells
- allow small water soluble molecules to move through
continuous capillaries
- Large gaps between endothelial cells forming pores or fenestrations (windows)
- Allow proteins, and in some cases blood cells, to move through
fenestrated capillaries
have leaky junctions
continuous capillaries
may fuse to create temporary channels
some vesicles
have large pores
fenestrated capillaries
Mass movement as a result of hydrostatic or osmotic pressure gradients
bulk flow
- fluid movement out of capillaries
- caused by hydrostatic pressure
- net filtration at arterial end
filtration
- fluid movement into capillaries
- Net absorption at venous end
- Caused by colloid osmotic pressure (due to proteins)
absorption
forces fluid out of the capillary
hydrostatic pressure
net pressure=
hydrostatic pressure-colloid osmotic pressure
indicates filtration
positive net pressure
indicates absorption
negative net pressure
pulls fluid into the capillary
colloid osmotic pressure of proteins within the capillary
what is the net average of fluid that filters out of the capillaries?
3L/day
picked up by the lymph vessels and returned to the circulation
excess of water and solutes that filter out of the capillary
- Return fluid and proteins to circulatory system
- Pick up fat absorbed and transferring it to circulatory system
- Serve as filter for pathogens
lymphatic system
what are the two main causes of edema?
- Inadequate drainage of lymph
- Filtration far greater than absorption
- Increase in hydrostatic pressure
- Decrease in plasma protein concentration
- Increase in interstitial proteins
Filtration far greater than absorption
