Exam 3 - Cardiac Output, Blood Flow, and Blood Pressure Part #1 Flashcards
cardiac output
- volume of blood pumped per minute by left or right ventricle
- ml/min
- cardiac output = stroke volume (ml/beat) * cardiac rate (beats/min)
- average 5.5 L/min
stroke volume
- volume of blood pumped per beat by each ventricle
- ml/beat
- average is 70-80 ml/beat
mean arterial pressure of systemic circulation vs pulmonary circulation
- systemic:
- 70-105 mmHg
- pulmonary:
- 10-20 mmHg
- cardiac output of right ventricle = cardiac output of left ventricle
- this means pulmonary circulation must have low resistance, low pressure, and high blood flow
total blood volume
- 5.5 L
- each ventricle pumps the equivalent of the total blood volume each minute under resting conditions
norepinephrine from and epinephrine from bind to
receptors in the heart to stimulate the production of
norepinephrine from sympathetic axons and epinephrine from adrenal medulla bind to beta-1-adrenergic receptors in the heart to stimulate the production of cyclic AMP (that then acts on HCN channels and Ca channels of pacemaker cells)
chronotropic effect
- mechanisms that affect the cardiac rate set by the SA node
- those that increase cardiac rate have a positive chronotropic effect
- those that decrease cardiac rate have a negative chronotropic effect
what affect do the sympathetic endings in the musculature of the atria and ventricles have?
increase the strength of contraction and causes a slight decrease in the time spent in systole when the cardiac rate is high
cardiac control center
- coordinates activity of the autonomic innervation of the heart
- found in the medulla oblongata
- affected by higher brain areas and by sensory feedback from baroreceptors (pressure receptors) in the aorta and carotid arteries
- in this way, a fall in BP can produce a reflex increase in HR
three variables that regulate stroke volume
-
end diastolic volume (EDV)
- amount of blood left in the ventricles at the end of diastole (immediately before contraction)
- directly proportional
-
total peripheral resistance in arteries
- inversely proportional
-
contractility of ventricular contraction
- directly proportional
preload
- the workload imposed on the ventricles prior to contraction (EDV)
afterload
- impedance to ejection of blood from ventricle after contraction has begun
- presented by high total peripheral resistance that decreases the stroke volume
ejection fraction
- about 60%
- remains relatively constant over a range of EDV, so that the amount ejected per beat (stroke volume) increases as the EDV increases
- for this to be true, the strength of ventricular conraction must increase as EDV increases
Frank-Starling law of the heart
- an increase in EDV results in increased contraction strength and in increased stroke volume
- intrinsic property of the heart
stretching of myocardial cells during diastole increases the sensitivity of what channels?
-
Ca2+-release channels (ryanodine receptors, RyR2 type) in the sarcoplasmic reticulum
- the greater release of Ca2+ contributes to a stronger contraction
Anrep effect
- the frank-starling mechanism results in an initial rapid increase in contractility when the ventricles are stretched
- this force then gradually increases over the next 10-15 minutes
- this effect appears to be due to increased Ca2+ entering the cytoplasm through the reversal of Na/Ca exchanger
what mechanisms ensure that an increase in EDV intrinsically produces an increase in contraction strength and stroke volume?
- frank-starling mechanism
- increased sensitivity of RyR2 receptors
- anrep effect
how does the frank-starling law explain how the heart can adjust to a rise in total peripheral resistance?
- a rise in peripheral resistance causes a decrease in the stroke volume, so that
- more blood remains in the ventricle and the EDV is greater for the next cycle; as a result,
- the ventricle is stretched to a greater degree in the next cycle and contracts more strongly to eject more blood
why must the rate of blood flow through the pulmonary and systemic circulations be equal?
- to prevent fluid accumulation in the lungs
- to deliver fully oxygenated blood to the body
what is the driving force for the return of blood to the heart?
venous pressure
how much of the total blood volume is located in the veins?
two-thirds
capacitance vessels
veins (have a higher compliance)
resistance vessels
arteries
mean venous pressure vs mean arterial pressure
- mean venous pressure is 2 mmHg
- mean arterial pressure is 90-100 mmHg
venous pressure in venules vs junction of venae cavae with the right atrium
- venules is 10 mmHg
- venae cavae is 2-6 mmHg
things that promote venous return to the heart
- pressure difference between venules and junction of venae cavae with right atrium
- sympathetic nerve activity
- stimulates smooth muscle contraction in venous walls and reduces compliance
- skeletal muscle pump
- respiratory pump
blood pressure vs osmotic forces (effects on blood volume)
- blood pressure promotes the formation of interstitial fluid from plasma
- osmotic forces draw water from the tissues into the vascular system
net filtration pressure
- equal to the hydrostatic pressure of blood in capillaries minus the hydrostatic pressure of tissue fluid outside capillaries, which opposes filtration
colloid osmotic pressure
- the osmotic pressure exerted by proteins
- the colloid osmotic pressure of plasma is much greater than the colloid osmotic pressure of interstitial fluid (due to restricted filtration of proteins through capillary pores)
oncotic pressure
- difference between colloid osmotic pressure of plasma and interstitial fluid
- essentially equal to the colloid osmotic pressure of plasma, since the colloid pressure of interstitial fluid is low enough to be neglected
- 25 mmHg
- favors movement of water into the capillaries
starling forces
opposing forces that affect the distribution of fluid across the capillary
hydrostatic pressure at arteriolar end of systemic capillaries vs venular end
- arteriolar end 37 mmHg
- venular end 17 mmHg
(edit)
- positive value at the arteriolar end indicates that the starling forces that favor the filtration of fluid out of the capillary predominate
- negative value at the venular end indicates that the net starling forces favor the return of fluid to the capillary
% of filtrate returned directly to the blood capillaries?
how does the remaining filtrate return to the blood?
- 85-90% of filtrate is returned directly to the blood capillaries
- remaining 10-15% is returned to the blood by way of the lymphatic system
what does edema result from?
-
high arterial blood pressure
- this increases capillary pressure and causes excessive filtration
- venous obstruction
-
leakage of plasma proteins into interstitial fluid
- causes reduced osmotic flow of water into capillaries
- occurs during inflammation and allergic reactions as a result of increased capillary permeability
-
myxedema
- excessive production of a particular glycoprotein (mucin) in the extracellular matrix caused by hypothyroidism
-
decreased plasma protein concentration
- as a result of liver disease or kidney disease
-
obstruction of the lymphatic drainage
- in elephantiasis or surgery
glomeruli
capillaries that filtrate plasma to form urine
atrial natriuretic peptide
hormone secreted by the atria that increases the excretion of salt and water in the urine, thereby working to lower blood volume
aldosterone
- steroid hormone secreted by the adrenal cortex
- stimulates the reabsorption of salt by the kidneys
- “salt-retaining hormone”
- increases blood volume, but does not produce a change in plasma osmolality
renin-angiotensin-aldosterone system (edit)
extrinsic regulation of blood flow
control by autonomic nervous system and endocrine system
vasoconstriction in fight-or-flight
- adrenergic sympathetic fibers (those that release norepinephrine) active alpha-adrenergic receptors to cause vasoconstriction in the digestive tract, kidneys, and skin
vasodilation in fight-or-flight
- arterioles in skeletal muscles receive cholinergic sympathetic fibers, which release acetylcholine
- this causes vasodilation
- vasodilation in skeletal muscles is also produced by epinephrine secreted by the adrenal medulla which stimulates beta-adrenergic receptors
parasympathetic innervation of blood vessels is limited to…
- digestive system
- external genitalia
- salivary glands
paracrine regulators
molecules produced by one tissue that help to regulate another tissue of the same organ
autoregulation
refers to the ability of some organs (i.e. brain and kidneys) to utilize intrinsic control mechanisms to maintain a relatively constant blood flow despite wide fluctations in blood pressure
myogenic control mechanisms
- type of intrinsic mechanism
-
direct responses by the vascular smooth muscle to changes in pressure
- a decrease in arterial pressure causes cerebral vessels to dilate
- high blood pressure causes cerebral vessels to constrict
localized chemical conditions that promote vasodilation
- decreased oxygen concentrations
- increased carbon dioxide concentrations
- decrease tissue pH
- release of K and paracrine regulations
reactive hyperemia
- when constriction is removed and blood flow resumes, the metabolic products that have accumulated cause vasodilation
- the tissue thus appears red
- metabolic control mechanism
active hyperemia
- increase in blood flow to skeletal muscles and other organs as a result of increased metabolism
- this increased blood flow can wash out the vasodilator metabolites, so that blood flow can fall to pre-exercise levels
- metabolic control mechanism
