Ch 14 Cardiac Output, Blood Flow, and Blood Pressure

Cardiac output

The volume of blood pumped each minute by each ventricle (CO = stroke volume × heart rate)

Stroke volume

Amount of blood pumped per beat by one ventricle

Heart rate

Number of heartbeats per minute

Average cardiac output

~5,500 mL/min in a healthy adult

SA node

Primary pacemaker of the heart that initiates spontaneous depolarization

HCN channels

Channels in SA node that allow Na+ influx during pacemaker potential

Positive chronotropic effect

Increase in heart rate

Negative chronotropic effect

Decrease in heart rate

Sympathetic stimulation (heart)

Increases heart rate via norepinephrine/epinephrine

Parasympathetic stimulation (heart)

Decreases heart rate via acetylcholine

Medulla oblongata cardiac center

Brain region that regulates heart rate via autonomic input

End diastolic volume (EDV)

Volume of blood in ventricles at end of diastole (preload)

Afterload

Resistance the heart must overcome to eject blood (total peripheral resistance)

Contractility

Strength of ventricular contraction

Ejection fraction

Percentage of EDV ejected (~60%)

Frank-Starling law

More EDV → stronger contraction → increased stroke volume

Myocardial stretch

Increases contraction strength due to increased fiber length

Anrep effect

Increased contractility due to sustained increased afterload

Venous return

Volume of blood returning to the heart

Veins

High compliance vessels that store most blood volume

Capacitance vessels

Veins that hold ~2/3 of blood volume

Total blood volume

Total amount of blood in circulation

Interstitial fluid

Fluid between cells in tissues

Plasma

Fluid portion of blood

Net filtration pressure

Force driving fluid out of capillaries

Oncotic pressure

Osmotic pressure due to plasma proteins pulling fluid into capillaries

Starling forces

Balance of hydrostatic and oncotic pressures controlling fluid movement

Edema

Excess fluid accumulation in interstitial spaces

Filariasis

Parasitic infection causing lymphatic blockage and elephantiasis

Glomeruli

Kidney capillaries where filtration begins

ADH (vasopressin)

Hormone that increases water reabsorption in kidneys

Osmoreceptors

Sense plasma osmolarity and regulate ADH release

Aldosterone

Hormone that increases Na+ and water reabsorption

Renin

Enzyme released by kidneys to activate RAAS

Angiotensin II

Vasoconstrictor that increases blood pressure and stimulates aldosterone

ACE

Enzyme that converts angiotensin I to angiotensin II

ANP

Hormone that increases salt and water excretion to reduce blood volume

Hypertension

High blood pressure above normal range

Primary hypertension

High blood pressure with no identifiable cause

Secondary hypertension

High blood pressure due to another disease

Essential hypertension

Common form caused by multiple interacting factors

Atherosclerosis

Buildup of plaque in arteries

Stroke

Brain damage caused by interrupted blood flow

Beta blockers

Drugs that reduce heart rate and cardiac output

ACE inhibitors

Drugs that block formation of angiotensin II

ARBs

Drugs that block angiotensin II receptors

Preeclampsia

Pregnancy disorder involving hypertension and organ damage

Proteinuria

Excess protein in urine

Circulatory shock

Inadequate blood flow/oxygen delivery to tissues

Hypovolemic shock

Shock caused by low blood volume

Septic shock

Shock caused by infection-induced vasodilation

Anaphylactic shock

Severe allergic reaction causing vasodilation

Neurogenic shock

Shock caused by loss of sympathetic control

Cardiogenic shock

Shock caused by heart failure

Congestive heart failure (CHF)

Inability of heart to maintain adequate cardiac output

Left-sided heart failure

Causes pulmonary congestion and shortness of breath

Right-sided heart failure

Causes systemic edema and congestion

Digitalis

Drug that increases cardiac contractility

Diuretics

Increase urine output to reduce blood volume

Baroreceptors

Sense blood pressure changes and trigger reflexes

Baroreceptor reflex

Homeostatic response to stabilize blood pressure

Skeletal muscle pump

Assists venous return during movement

Respiratory pump

Pressure changes during breathing that aid venous return

Hypertrophy

Enlargement of heart muscle due to increased workload