Chap 14 - Cardiac Output, BP, Blood flow

Unfinisheed

What is the primary way HR is regulated?

Through ANS control of SA node:

SNS - Increases HR

PSNS - Lowers HR

The vagus nerve is tonically active, what does this mean for HR?

This means that ACh effects keep resting HR slower than it would be (90-100bpm) without innervation.

In other words, if the ANS did not control resting HR, it would be much faster

Stroke Volume (SV) is regulated by 3 variables:

1) End-diastolic volume (EDV) (if you fill your heart more then it will spit more out)

2) Total peripheral (outside of the heart) resistance (opposition to flow)

3) Contractility of heart

Define “End-diastolic volume”

EDV is sometimes called “preload”

Volume of blood in the ventricles at end of diastole, immediately before they contract

What does an increase in end-diastolic volume (EDV) mean?

results in an increase in stroke volume due to Frank-Starling Law of the Heart

What is total peripheral resistance

Frictional resistance or impedance to blood flow in all of the arteries of the body

What is afterload

If pressure is high in the arteries, then you need to overcome that pressure to get the blood out of the arteries. This can negatively impact ventricular muscle overtime

What is stroke volume inverse to?

Stroke volume (SV) is inversely proportional to peripheral resistance (PR)

• The greater the PR, the lower the SV and vice versa

Define contractility

strength of ventricular contraction of the heart

What increases contractility of the heart

norepinephrine and epinephrine are used by SNS

What are considered as the reservoir or capacitance vessels?

Veins.

They have less smooth muscle and more compliance

What has the lowest pressure?

Veins

Does both the SNS and PSNS have venoconstriction contorl?

No!

SNS controls blood vessel diameter but PSNS has zero control

What has an effect on blood pressure?

Cardiac output: HR, stroke volume, and peripheral resistance

Blood volume

^^^Both have direct affect on blood pressure^^^

How does lymph form?

Forms by fluid coming out at arterial ends of capillaries

How much fluid becomes lymph and how much gets returned?

90% of interstitial fluid returns to the capillaries at the venous end

10% becomes lymph

Define: edema

When there is fluid accumulation in interstitial space

What is the RAAS mechanism

Renin is an enzyme produced in the kidneys and is released when blood pressure (BP) is low.

Renin catalyzes angiotensinogen into angiotensin I

ACE enzyme catalyzes angiotensin I to angiotensin II

What does Angiotensin II stimulate?

Constricts arterioles to elevate blood pressure and stimulate aldosterone release from adrenal cortex

What does ANP do

Has an opposite effect as ADH. It lowers blood volume.

What are considered resistance vessels?

Arterioles are considered resistance vessels because they direct flow to capillary beds

Arterial blood pressure is affected by:

1) Blood volume

2) Total peripheral resistance (in all vessels)

3) Cardiac rate (HR)

Which vessels have the greatest cross-sectional area

Capillaries

How is pulse pressure calculated

pulse pressure = systolic pressure - diastolic pressure

How is mean arterial pressure calculated? (MAP)

Mean arterial pressure = diastolic pressure + 1/3 pulse pressure

Why is MAP (mean arterial pressure) closer to diastolic pressure?

due to heart being in diastole longer than systole

What are baroreceptors?

Sensory receptors that detect changes in blood pressure

Where are the baroreceptors located and where do they report to?

Located in the aortic arch and in the carotid sinuses.

Signal to the cardiac and vasomotor control centers in medulla oblongata

Hypovolemic shock

due to low blood volume

• due to dehydration or hemorrhage

Septic shock

due to sepsis, an abnormal immune response to infection

Anaphylactic shock

Result of sever allergic reaction due to widespread histamine release

What does left side congestive heart failure cause

pulmonary congestion

what does right side congestive heart failure cause

systemic circulation congestion

What is Cardiac Output?

Is the volume of blood pumped per minute by each ventricle.

CO = HR x SV

Cardiac rate =

Cardiac rate = heart rate (HR) = beats per minute

~ average resting rate is 70bpm

Stroke volume =

Stroke volume (SV) = volume of blood pumped

What are the mechanisms that affect heart rate called

Chronotropic effects.

The primary way HR is regulated is through ANS control of SA node.

Does spontaneous depolarization occure at the SA node?

Yes! When HCN channels open, allowing Na+ in

What affects does PSNS and SNS have on pacemaker cells?

SNS depolarizes the pacemaker cells faster

PSNS slows depolarization of pacemaker cells due to hyperpolarization

What SNS hormones are used on the pacemaker cells and what do they do?

Norepinephrine and adrenal epinephrine keep HCN and Ca2+ channels open,

increasing heart rate

What PSNS hormones are used on the pacemaker cells and what do they do?

Parasympathetic ACh from vagus nerve opens K+ channels, slowing heart rate

What is necessary in order to eject blood?

Pressure generated in a ventricle when it contracts must be greater than the pressure in the arteries (blood will only flow from high to low pressure)

What is ejection fraction

Fraction (%) of the blood in each ventricle that is ejected per contraction.

What is frank starling’s law?

Increase in End Diastolic Volume (EDV) = Increase in Pre load = Increase in Stroke Volume (SV) = More forceful contraction

What increases contractility?

Positive inotropic effects:

• Norepinephrine from sympathetic nerve endings

• Epinephrine from adrenal medulla

When a person starts to exercise, venous return increases due to:

• the skeletal muscle pump and sympathetic venoconstriction

• Blood will move into other vessels during exercise

What are considered resistance vessels

Arteries because they do not stretch as much when they fill

What factors affect venous return

• Veins have the lowest pressure

• Breathing

• Venoconstriction due to sympathetic stimulation

• Skeletal muscle pump

  • Valves in veins preventing backflow

  • Muscles pushing on veins in limbs

Explain how lymph flows

Net out at arterial end

Net in at venous end

10% of interstitial fluid becomes lymph, flows towards the heart

Edema can result from: (list at least 3)

1. High arterial blood pressure (too much filtration from capillaries)

2. Obstruction of lymphatic drainage

3. Venous obstruction

Blood volume and urine volume are linked, explain this

The kidneys filter blood to create urine

• If too much urine is produced, then blood volume is reduced

• If not enough urine is produced, then blood volume is increased

What does your body do when there is low venous return?

Body releases ADH and renin (RAAS activated)

These two mechanisms work together to elevate blood volume and blood pressure

What does ADH do?

ADH increases blood volume and decreases urine volume in the kidneys.

If dehydration or high salt ingestion is noticed, ADH will be released to help us retain water in the kidneys. Less urine produced so more blood volume.

When is renin produced?

It is produced in the kidneys when blood pressure is low.

What does RAAS do?

Helps to elevate blood volume and thus blood pressure.

• Renin catalyzes the activation of angiotensiogen into angiotensin I

• ACE enzyme catalyzes the change from angiotensin I to angiotensin II

• Angiotensin II constricts arterioles to elevate blood pressure and stimulates aldosterone release from the adrenal cortex

• Aldosterone stimulates Na+ retention in kidneys

What does aldosterone do

Stimulates Na+ retention in kidneys

What happens when there is too much venous return

Body responds by releasing ANP and less ADH

• less ADH means more urine production

Blood flow is….

Inversely related to diameter

More resistance leads to less blood flow

What vessels have the most and least pressure

Arteries must have the highest pressure

Veins must have the LOWEST pressure

This must occur in order for blood to flow through the system.

Arterial blood pressure is affected by…

Blood volume

Total peripheral resistance (in all vessels)

Cardiac rate (HR)

Arterial BP is proportional to CO x PR

Why is it significate that the capillaries have the highest cross sectional area?

It reduces velocity and pressure significantly

When reading blood pressure what is the average and what do the number represent?

Average: 120/80

Systolic / diastolic pressure

What maintains blood pressure?

The barorecepotor reflex