Ch. 14 Cardiac Output, Blood Flow & Blood Pressure

What is cardiac output?

volume of blood pumped per minute by each ventricle

What is the average resting cardiac rate for an adult?

70 beats per minute

What is stroke volume?

the volume of blood pumped per beat by each ventricle

What is the average stroke volume in an adult?

70-80ml per beat

What is the average Cardiac Output in an adult?

5\.5 L/min

What is the equation to calculate cardiac output?

Cardiac output (ml/min)= Stroke Volume (ml/beat) X cardiac rate (bpm)

True or False: In the complete absence of neural influences, the heart will continue to beat as long as the myocardial cells are alive.

True!

Why in the complete absence of neural influences, will the heart continue to beat as long as the myocardial cells are alive?

due to spontaneous, diastolic depolarization of the pacemaker cells in the SA node

What effect does sympathetic norepinephrine & adrenal norepinephrine have on heart rate?

keeps HCN channels open in pacemaker cells of SA node, increasing heart rate

What effect does parasympathetic acetylcholine have on heart rate?

opens K+ channels, slowing heart rate

How is the activity of the autonomic innervation of the heart coordinated?

by the cardiac control center in the medulla oblongata that is affected by higher brain centers

What is End Diastolic Volume (EDV)?

volume of blood in the ventricles at the end of ventricular diastole

What is End systolic volume (ESV)?

volume of blood in the ventricles at the end of ventricular systole

What is Ejection fraction?

percentage of EDV represented by the SV (SV/EDV)

How do you calculate SV?

SV= EDV-ESV

How do you calculate Cardiac Output?

CO= SV X HR

What is stroke volume regulated by?

end-diastolic volume

total peripheral resistance

contractility

Define preload in the heart

tension on the ventricular walls produced by their filling with the end-diastolic volume of blood

What effect does an increased EDV have on Stroke volume?

stroke volume increases

Define Afterload in the heart

related to the total peripheral resistance & arterial pressure; presents an impedance to the ejection of blood from the ventricles at systole

What is total peripheral resistance?

frictional resistance in the arteries

What is contractility?

strength of a ventricular contraction

When total peripheral resistance increases, stroke volume(?)

decreases; less impedance to blood flow

When contractility increases, stroke volume(?)

Increases

What is the normal ejection fraction?

about 60%

What is the Frank-Starling Law of the heart?

statement describing the relationship between end-diastolic volume & stroke volume of the heart. A greater amount of blood in a ventricle prior to contraction results in greater stretch of the myocardium, and by this means produces a contraction of greater strength

What explains the Frank-Starling Law?

due to decreased myosin & actin overlap but increased actin-myosin interactions allowing more force to be developed & increased sensitivity to Ca2+ in cardiac muscle cells promotes a greater release of Ca2+ resulting in a stronger contraction

What extrinsic factors control contractility of the heart?

Sympathetic norepinephrine / adrenal epinephrine

Parasympathetic acetylcholine

How does Sympathetic norepinephrine / adrenal epinephrine effect the heart?

can increase contractility by making more Ca2+ available to sarcomeres & increase heart rate

How does the Parasympathetic acetylcholine effect the heart?

will decrease heart rate which will increase EDV → increases contraction strength→ increases stroke volume, but not enough for slower rate, so cardiac output decreases

What is an inotropic effect?

something that effects the force of heart contraction

What is a positive inotropic effect?

stronger contraction (Eg. norepinephrine)

What is a negative inotropic effect?

weaker contraction (Eg. acetylcholine)

What is venous return?

return of blood to the heart via veins

EDV is controlled by factors that affect venous return including

total blood volume & venous pressure

True or false: Veins stretch more at a given pressure than arteries

True because they have thinner walls

Veins hold more blood than arteries but maintain (?) pressure

lower

What are the factors of venous return?

the pressure difference between arteries & veins

pressure differences in the venous system

sympathetic nerve activity

skeletal muscle pumps

pressure difference between abdominal & thoracic cavities

What controls the movement of water between the interstitial spaces and the capillaries, affecting blood volume?

Osmotic forces

What is Net filtration pressure?

hydrostatic pressure of the blood in the capillaries minus the hydrostatic pressure of fluid outside the capillaries

Describe the hydrostatic pressure of the interstitial fluid outside the capillaries

opposes filtration

Describe the hydrostatic pressure of the blood in the capillaries

favors filtration; moves out through pores into interstitial space

What is colloid osmotic pressure?

osmotic pressure exerted by plasma proteins that are present as a colloidal suspension; also called oncotic pressure

What favors the movement of fluid into the capillaries?

Colloid osmotic pressure

What are Starling Forces?

combination of hydrostatic pressure & oncotic pressure that predicts movement of fluid across capillary membranes

What is Edema?

excessive accumulation of interstitial fluid

What might Edema result from?

High arterial pressure

Venous obstruction

Leakage of plasma proteins into interstitial space

Myxedema

decreased plasma protein concentration

Obstruction of lymphatic drainage

What is the role of the sympathetic nervous system in regulation of Blood volume by the kidneys?

kidney arterioles dilate, increasing blood flow & increases urine production that will decrease blood volume

What is ADH?

Antidiuretic hormone that acts to stimulate water reabsorption resulting in increased blood volume

Where is ADH produced?

The hypothalamus

Where is ADH secreted from?

The posterior pituitary

What stimulates ADH secretion?

Osmoreceptors detect increased plasma osmolality

What causes plasma osmolality to increase?

dehydration or excessive salt intake

What is Aldosterone?

a steroid hormone secreted by the adrenal cortex

What is the function of aldosterone?

Stimulates reabsorption of salt & water in kidneys

How is the release of Aldosterone triggered?

secreted by the adrenal cortex indirectly when blood volume & pressure are reduced

Does Aldosterone change blood osmolality?

No because both salt & water are involved

When blood pressure is low, cells in the kidneys secrete the enzyme (?)

Renin

Angiotensinogen is converted to (?) by Renin

Angiotensin I

Angiotensin I is converted to Angiotensin II by

ACE Enzyme

What is Atrial Natriuretic Peptide?

a polypeptide hormone produced by the atria of the heart when stretch is detected from high volume or increased venous return

What does ANP do?

promotes salt & water excretion in urine in response to increased blood volume

inhibits ADH secretion

antagonist of Aldosterone

Blood flows from a region of (?) to (?)

higher pressure → lower pressure

True or false: Cardiac output is distributed unequally to different organs due to unequal resistance to blood flow through the organs

True..

Rate of blood flow is proportional to

differences in pressure

Higher blood pressure = (?) blood flow

Faster

Lower blood pressure = (?) blood flow

slower

What is the relationship between the rate of blood flow to the frictional resistance to blood flow within the vessels?

inversely proportional

The greater the resistance the (?) the blood flow

slower

The (?) the blood vessel the greater the resistance

longer

The more narrow the blood vessel the (?) the resistance

the greater

What are the most important factors in blood flow

What is the sum of all vascular resistance in systemic circulation?

Total peripheral resistance

Can a change in resistance within one organ affect another? Why?

No because blood flow to organs runs parallel to each other

Vasodilation in a large organ may affect total peripheral resistance in what way?

Decrease total peripheral resistance & mean arterial pressure

True or False: Blood flow is restricted during systole?

True; myoglobin in cardiac tissue stores oxygen during diastole to be released in systole

Can the brain tolerate variation in blood flow?

No cerebral flow is relatively constant

Unless mean arterial pressure becomes very high there is (?) sympathetic control of blood flow to the brain

little

At high blood pressure in cerebral flow what occurs to prevent damage & stroke?

vasoconstriction occurs

What is blood pressure affected by?

An increase in

Vasoconstriction of arterioles raises blood pressure where in the arteries?

Upstream

Why is capillary blood pressure low?

because of the large total cross-sectional area

Why is artery blood pressure high?

small total cross-sectional area

What are barorececeptors?

stretch receptors located in the aortic arch & carotid sinuses that detect changes in blood pressure

What effect does an increase in blood pressure have on baroreceptors?

stretches the receptors which increases action potentials to cardiac control centers in the medulla

Is the baroreceptor reflex more sensitive to drops in pressure or increases in pressure?

Drops in BP

What is pulse pressure?

The difference between blood pressure at systole & at diastole; reflection of stroke volume

What is the mean arterial pressure?

average pressure in the arteries in one cardiac cycle

How do you calculate mean arterial pressure?

diastolic pressure + 1/3 pulse pressure

What forces drive blood into the capillaries?

the difference between mean arterial pressure & venous pressure

What is hypertension?

High blood pressure

What is essential hypertension?

can be a result of a complex & poorly understood process

What is secondary hypertension?

a symptom of another disease, such as kidney disease

Most people with hypertension fall into which category?

essential hypertension

What can cause essential hypertension?

increased salt intake/decreased kidney filtering ability

increased sympathetic nerve activity

responses to paracrine regulators

increased total peripheral resistance

How can hypertension be treated?

lifestyle modifications

diuretics

Beta blockers

ACE inhibitors

What can occur when cardiac output is not sufficient to maintain the blood flow required by the body?

congestive heart failure

What causes congestive heart failure?

myocardial infarction, congenital defects, hypertension, aortic valve stenosis, or disturbances in electrolyte levels