cardiovascular - lecture 2 Flashcards
cardiac output
amount of blood pumped out by each ventricle in 1 minute
cardiac output equals
heart rate (HR) times stroke volume (SV)
stroke volume
volume of blood pumped out by one ventricle with each beat
stroke volume correlates with the force of _________.
contraction
at rest the cardiac output is . . .
5.25 L/min
cardiac index =
cardiac output x body surface area
normal cardiac index is
3 L/min/m2
cardiac output varies directly with _____ and ______.
SV and HR
______ increases when the stroke volume __________.
cardiac output
increases
_____ increases when the heart beats __________.
cardiac output
faster
cardiac reserve
the difference between resting and maximal cardiac output
stroke volume =
EDV - ESV
EDV is affected by . . .
length of ventricular diastole and venous pressure (~120 ml/beat)
ESV is affected by . . .
arterial BP and force of ventricular contraction (~50 ml/beat)
normal SV =
120 ml - 50 ml = 70 ml/beat
three main factors that affect SV:
preload
contractility
afterload
preload
degree to which cardiac muscle cells are stretched just before contraction
relationship between preload and SV called
Frank-Starling law of the heart
changes in preload causes changes in . . .
stroke volume
increased venous return increases the . . .
ventricular filling (end-diastolic volume)
myocytes stretching increase the . . .
sarcomere length
positive inotropic (contractility)
- epinephrine from adrenal medulla
- norepinephrine from sympathetic nerve endings
- promote calcium influx & increased contraction strength
- digoxin, dopamine, isoproterenol, milrinone
negative inotropic agents
- reduction of sympathetic stimulation — reduced contractility
- acidosis, increased extracellular K+, calcium channel blockers
afterload
the pressure that ventricles must overcome to eject blood
major pressure is . . .
back pressure from arterial blood pushing on SL valves
aortic pressure is around . . .
80 mmHg
pulmonary trunk pressure is around . . .
10 mmHg
___________ increases afterload, resulting in increased ___ and reduced ___
hypertension
ESV
SV
afterload is _____________ to the stroke volume
inversely proportional
chronotropic effect
any mechanism that alters cardiac rate
POSITIVE chronotropic effect ___________ HR
increases
NEGATIVE chronotropic effect _________ HR
decreases
heart rate can be regulated by:
autonomic nervous system
chemicals
other factors
_________ or _____________ can activate the sympathetic nervous system
emotional or physical stressors
norepinephrine is released and binds to B1-adrenegric receptors in the heart causing:
- SA node fires more rapidly, increasing HR
- increased contractility
the parasympathetic nervous system _______ sympathetic effects
opposes
acetylcholine ___________ pacemaker cells by opening __________ which slows _____
hyperolarizes
K+ channels
HR
heart at rest exhibits a . . .
vagal tone
parasympathetic is the . . .
dominant influence on heart rate
chemical regulation of heart rate are . . .
hormones
ions
other factors that influence heart rate
age
gender
exercise
body temperature
best indicator of cardiac function is . . .
ejection fraction
ejection fraction is . . .
percentage of blood ejected from ventricles relative to the volume in ventricles before contraction
ejection fraction =
volume ejected / LV end diastolic volume
normal ejection fraction is
60-70%
tachycardia
abnormally fast rate (>100 beats/min)
bradycardia
heart rate slower than 60 beats/min
congestive heart failure (CHF)
progressive condition; cardiac output is so low that blood circulation is inadequate to meet tissue needs
reflects weakened myocardium caused by:
- coronary atherosclerosis
- persistent high blood pressure
- multiple myocardial infarcts
- dilated cardiomyopathy
coronary atherosclerosis
clogged arteries caused by fat buildup; impairs oxygen delivery to cardiac cells
persistent high blood pressure
aortic pressure >90 mmHg causes myocardium to exert more force
what is the most common cause of heart failure ?
persistent high blood pressure
multiple myocardial infarcts
the heart becomes weak as contractile cells are replaced scar tissue
dilated cardiomyopathy:
ventricles stretch and become flabby, and myocardium deteriorates
left sided heart failure results in . . .
pulmonary congestion
right sided heart failure results in . . .
peripheral congestion
pulmonary congestion is . . .
blood backs up in the lungs
peripheral congestion is . . .
blood pools in body organs causing edema
failure of either side ultimately weakens other side which leads to __________.
decompensated
elastic arteries:
thick-walled with large, low-resistance lumen
aorta and its major branch also called __________ arteries because . . .
conducting
they conduct blood from the heart to medium sized vessels
muscular arteries also called ____________ because . . .
distributing
they deliver blood to body organs
arterioles are the _______ of all arteries
smallest
what do arterioles control?
flow into capillary beds via vasodilation and vasoconstriction of smooth muscle
arterioles are also called _________ arteries because . . .
resistance
changing diameters change resistance to blood flow
three types of capillaries
continuous
fenestrated
sinusoidal
where are continuous capillaries found?
abundant in skin, muscles, lungs and CNS
where are fenestrated capillaries found?
areas involved in active filtration (kidney), absorption (intestines), or endocrine hormone secretion
where are sinusoidal capillaries found?
only in the liver, bone marrow, spleen, and adrenal medulla
** blood flow is sluggish
what do sinusiodal capillaries allow?
large molecules and even cells to pass across their walls
** most permeable
capillary bed are made up of what?
terminal arteriole
postcapillary venule
capillary bed is
an interwoven network of capillaries between the arterioles and venule
terminal arteriole is
exchange of gases, nutrients, and wastes from surrounding tissue takes place in capillaries
what regulates the amount of blood entering the capillary bed ?
local chemical conditions and arteriolar vasomotor nerve fibers
arteriole and terminal arteriole dilated when ____________
blood needed
capillary bes of intestinal mesenteries:
- vascular shunt
- precapillary sphincter
vascular shunt
channel that directly connects arteriole with venule (bypasses true capillaries)
precapillary sphincters
acts as valve regulating blood flow into the capillary bed
what makes veins a good storage vessel?
large lumen and thin walls
veins are called ____________ because . . .
capacitance vessels
they contain up to 65% of the blood supply
venous valves prevent what ?
backflow of blood
where are venous valves most abundant ?
veins of limbs
what are venous sinuses?
flattened veins with extremely thin walls
where are venous sinuses located?
coronary sinus of the heart and dural sinuses of the brain
varicose veins
dilated and painful veins due to incompetent (leaky) valves
what can cause varicose veins?
elevated venous pressure
- prolonged standing in one position
- obesity
- pregnancy
what percentage of adults are affected by varicose veins?
15%
blood flow
volume of blood flowing through a vessel, organ, or entire circulation in a given period
blood pressure
force per unit area exerted on the wall of blood vessels by blood
pressure gradient provides what ?
a driving force that keeps blood from moving from higher to lower pressure areas
resistance (peripheral resistance):
opposition flow
measurement of the amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation
three important sources of resistance:
blood viscosity
total blood vessel length
blood vessel diameter
blood viscosity is the . . .
thickness or “stickiness” of blood due to formed elements and plasma proteins
the greater the viscosity . . .
the less easily molecules an slide past each other
increased viscosity equals
increased resistance
total blood vessel length is
the longer the vessel, the greater the resistance encountered
what has the GREATEST influence on resistance?
blood vessel diameter
what is laminar flow?
fluid close to walls move more slowly than in the middle of the tube
if radius increases then . . .
resistance decreases (and vice-versa)
small-diameter arteriole are major determinants of . . .
peripheral resistance
laminar flow is disrupted and becomes _____________ which is . . .
turbulent flow
an irregular flow that causes increased resistance
blood flow is ______________ to a blood pressure gradient
directly proportional
blood flow is ______________ to peripheral resistance
inversely proportional
peripheral resistance is more important in influencing local blood flow because . . .
it is easily changed by altering blood vessel diameter
systemic blood pressure is highest in . . .
aorta
where does systemic blood pressure have its steepest drop?
arterioles
arterial blood pressure is determined by two factors:
- elasticity of arteries close to the heart
- volume of blood forced into them at anytime
blood pressure near heart is . . .
pulsatile
systolic pressure
pressure exerted in the aorta during ventricular contraction
diastolic pressure
lowest level of aortic pressure when the heart is at rest
pulse pressure
difference between systolic and diastolic pressure
pulse
throbbing of arteries due to differences in pulse pressures
mean arterial pressure (MAP)
pressure that propels blood to tissues
** heart spends more time in diastole
pulse pressure and MAP both decline with . . .
increasing distance from heart
factors aiding venous return
- muscular pump
- respiratory pump
- sympathetic venoconstriction
muscle pump
contraction of skeletal muscles “milks” blood back toward the heart; valves prevent backflow
respiratory pump
pressure changes during breathing move blood toward the heart by squeezing abdominal veins as thoracic veins expand
sympathetic venoconstriction
under sympathetic control, smooth muscles constrict, pushing blood back toward heart
capillary blood pressure
35 mmHg (beginning) - 17 mmHg (end)
venous blood pressure
changes little during the cardiac cycle
~ 15 mmHg
if a VEIN is cut . . .
low pressure of the venous system causes blood to flow out smoothly
if the ARTERY is cut . . .
blood spurts out because of higher pressure
3 main factors regulate BP:
cardiac output
peripheral resistance
blood volume
blood pressure (MAP) is _____________ to CO and PR
directly porportional
CO =
SV x HR
MAP =
CO x R
or
SV x HR x R
short-term MAP regulation
alters BP by changing PR and CO
short-term MAP regulation is done through . . .
neural controls
hormonal controls
Goal of short-term regulation
maintain MAP by altering blood vessel diameter AND altering blood distribution in response to various organ demands
long-term MAP regulation
alters BP by changing blood volume via the kidneys
long-term MAP regulation is done through . . .
renal controls
two main neural mechanisms control peripheral resistance
- altering blood vessel diameter, which alters resistance
- can alter blood distribution to organs in response to specific demands
neural controls operate via ___________ that involve . . .
reflex arcs
baroreceptors
chemoreceptors / high brain centers
baroreceptors
pressure-sensitive mechanoreceptors that respond to changes in arterial pressure & stretch
baroreceptor reflexes are located in
carotid sinuses, aortic arch, and walls of large arteries of neck & thorax
if MAP is high:
- inhibits vasomotor and cardioacceleratory centers
- stimulates cardioinhibitory center
- results in decreased blood pressure through 2 mechanisms (vasodilation & decreased cardiac output)
what are the 2 mechanisms that decrease blood pressure?
- vasodilation
- decreased cardiac output
vasodilation
decreased output from the vasomotor center causes dilation
arteriolar vasodilation
reduces peripheral resistance (MAP falls)
venodilation
shifts blood to venous reservoirs, decreasing venous return and CO
decreased cardiac output
impulses to cardiac centers inhibit sympathetic activity and stimulate parasympathetic
if MAP is low:
reflex vasoconstriction is initiated that increases CO and BP
carotid sinus reflex
baroreceptors that monitor BP to ensure enough blood to the brain
aortic reflex
maintainsBP in the systemic circuit
chemoreceptor reflexes are located in . . . and they detect . . .
aortic arch and large arteries of neck
increase in CO2 or drop in pH or O2
chemoreceptor reflexes cause increased blood pressure by:
- signaling cardioacceleratory center to increase CO2
- signaling vasmotor center to increase vasoconstriction
influence of higher brain centers
- relfexes that regulate BP are found in medulla
- hypothalamus & cerebral cortex can modify arterial pressure via relays to medulla
- hypothalamus increases blood pressure during stress
- hypothalamus mediates redistribution of blood flow during exercise and changes in body temperature
cardiovascular center
composed of clusters of sympathetic neurons in the medulla
cardiovascular center consists of :
- cardiac center
- vasomotor center
cardiovascular center receives inputs from . . .
baroreceptors
chemoreceptors
higher brain centers
input to cardiovascular center from higher brain centers:
cerebral cortex, limbic system, & hypothalamus
input to cardiovascular center from proprioceptors:
monitor joint movements
input to cardiovascular center from baroreceptors:
monitor blood pressure
input to cardiovascular center from chemoreceptors:
monitor blood acidity
output to effectors - heart:
decreased rate (from vagus)
increased rate (from cardiac accelerator nerves)
output to effectors - blood vessels:
vasoconstriction (from vasomotor nerves)
hormones regular BP in short term via __________________________ or long term via ___________________________.
changes in peripheral resistance
changes in blood volume
hormonal controls
adrenal medulla hormones
angiotensin II
ADH
atrial natriuretic peptide
angiostensin II
stimulates vasoconstriction
ADH
high levels can cause vasoconstriction
atrial natriuretic peptide
decreases BP by antagonizing aldosterone, causing decreased blood volume
kidneys regulate arterial blood pressure by:
- direct renal mechanism
- indirect renal mechanism
direct renal mechanism
alters blood volume independently of hormones
increased BP/blood volume =
elimination of more urine, thus reducing BP
decreased BP/blood volume =
kidneys to conserve water, and BP rises
indirect mechanism
decreased arterial blood pressure causes the release of renin from the kidneys
angiotensin II acts in four ways to stabilize arterial BP and ECF:
- causes ADH release from the posterior pituitary
- triggers hypothalamic thirst center to drink more water
- acts as a potent vasoconstrictor, directly increasing blood pressure
GOAL of blood pressure regulation is to keep blood pressure high enough to . . . but not so high that . . .
provide adequate tissue perfusion
blood vessels are damaged
homeostatic imbalances in blood pressure
hypertension
primary hypertension
secondary hypertension
hypotension
circulatory shock
prolonged hypertension is a major cause of
heart failure, vascular disease, renal failure, and stroke
primary hypertension is ______ of hypertensive conditions
90%
primary hypertension risk factors
heredity
diet
obesity
age
diabetes mellitus
stress
smoking
secondary hypertension is __________ and is due to . . .
less common
identifiable disorders including obstructed renal arteries, kidney disease, and endocrine disorders
hypotension is low pressure below . . .
90/60 mmHg
orthostatic hypotension
temporary low BP and dizziness when suddenly rising from sitting or reclining position
chronic hypotension
a hint of poor nutrition and warning sign for Addison’s disease or hypothyroidism
acute hypotension
an important sign of circulatory shock
circulatory shock
condition where blood vessels inadequately fill and cannot circulate blood normally
hypovolemic shock
results from large-scale blood loss
vascular shock
results from extreme vasodilation and decreased peripheral resistance
cardiogenic shock
results when an inefficient heart cannot sustain adequate circulation
