regulation of cardiac output and blood pressure

human anatomy and physiology lecture 13

cardiac output

volume of blood pumped by the heart every minute

flow

movement of blood through the blood vessels

blood pressure

pressure exerted by circulating blood on blood vessel walls

factors effecting blood pressure

• cardiac output

• volume of blood

• viscosity of blood

• vasoconstriction / vasodilation

stroke volume

volume ejected from each ventricle during systole, end diastolic volume - end systolic volume

heart rate

number of cardiac cycles per minute

preload

degree of stretching of the ventricular muscle during diastole, affects the ability of muscle cells to produce tension and is directly proportional to EDV

contractility

forcefulness of contraction of individual ventricular muscle fibers due to permeability of the cardiac muscle to ions, can be altered by neurotransmitters and hormones

afterload (arterial pressure)

pressure that must be exceeded by the ventricle before blood can be ejected from the ventricle

filling time

length of diastole, dependent on heartrate

factors that influence venous return

• filling time

• pressure gradient in venous circuit

• valves

• respiratory pump

• muscular pump

pressure gradient in venous circuit

due to the size of vessels increasing as they approach the heart

valves in venous circuit

prevent backflow of blood

regulation of the heart

• autoregulation

• neural mechanisms

• endocrine mechanisms

autoregulation of the heart

intrinsic, causes immediate, localized homeostatic adjustments

neural regulation of the heart

extrinsic, respond quickly to changes at specific sites

endocrine regulation of the heart

extrinsic, direct long-term changes

Frank-Starling law

• stroke volume is controlled by the EDV

• the more the heart is stretched during diastole, the stronger it contracts during the following systole

• heart adapts its output to match its input

congestive heart failure

inability of the heart to pump blood efficiently, refers to fluid build up

pulmonary congestion

congestive failure of the left ventricle, left ventricle can’t keep up with the right ventricle

consequences of pulmonary congestion

• blood can’t return from lungs

• lungs become congested with blood

• no reabsorption

• net movement of fluid is into the lung tissue

• pulmonary edema

• person suffocates to death

peripheral congestion

congestive failure of the right ventricle, right ventricle can’t keep up with left ventricle

consequences of peripheral congestion

• blood can’t return from systemic circulation

• body organs become engorged with blood

• net movement of fluid is into the peripheral tissue

• edema in extremities inferior to heart (feet, ankles, fingers)

role of acetylcholine in autonomic tone of heart

• secreted by parasympathetic nervous system to reduce heart rate following a stressful situation

• acts to increase K⁺ efflux out of cell, causing a decreased rate of firing

• can be persistently activated during grief and depression

role of norepinephrine in autonomic tone of heart

• secreted by sympathetic nervous system to increase heart rate in response to emotional or physical stress

• enhances contractility

• acts to increase Na⁺ influx into cell, resulting in an increased rate of firing

control centers in the medulla oblongata

• cardioinhibitory → parasympathetic

• cardioacceleratory → sympathetic

• vasoconstrictor → sympathetic

chronotropic effect

affecting heart rate

autonomic resting heart rate

• resting autonomic tone of the cardioinhibitory center of the medulla oblongata

• parasympathetic extrinsic control

• neurotransmitter: acetylcholine

• involves: long preganglionic neurons, short postganglionic neurons

• muscarinic cholinergic receptors on autorhythmic conductive cells

maintenance of autonomic resting heart rate

• cardioinhibitory center of the medulla oblongata stimulates parasympathetic neurons to secrete acetylcholine on the heart’s autorhythmic cells

• acetylcholine causes efflux of K⁺ on SA and AV nodes

• causes hyperpolarization in the cells, increasing time it takes to reach activation threshold

baroreceptor reflex to high blood pressure

• high blood pressure activates the cardioinhibitory center of the medulla oblongata

• parasympathetic extrinsic control

• neurotransmitter: acetylcholine

• involves: long preganglionic neurons, short postganglionic neurons

• muscarinic cholinergic receptors on autorhythmic cardiac muscle cells

carotid bodies

bifurcation of the common carotid artery (supplies head and neck with oxygenated blood)

aortic bodies

arch of aorta (largest artery in the body originating from left ventricle of the heart and supplies the rest of the body)

sensory cranial nerve

signals from the carotid and aortic bodies to the control centers in the medulla oblongata

result of baroreceptor reflex to high blood pressure

decreased cardiac output and vasodilation

extrinsic increase of contractility

• norepinephrine acts on myocardial cells, leading to a greater influx of Ca²⁺

• increases the degree and duration of contraction

• more Ca²⁺ means more Ca²⁺ induced chemically-gated Ca²⁺ channels on the sarcoplasmic reticulum to release more Ca²⁺

• increases calcium in the cytoplasm

• calcium allows myosin-actin crossbridge to form

• more crossbridge increases the degree of contractions and duration of contractions

• increases stroke volume

functional characteristics of cardiac muscle tissue

• automaticity

  • contraction without neural stimulation

  • controlled by pacemaker cells

  • effected by acetylcholine and norepinephrine

• variable contraction tension

  • controlled by β1 adrenergic receptors via signal transduction and calcium channels

bainbridge atrial reflex

• increased venous return, leads to the ventricles to be filled and backflow into the atria

• atrial stretching activates cardioacceleratory center of medulla oblongata

• sympathetic extrinsic control → mechanoreceptors in atrial walls

• neurotransmitter: norepinephrine and epinephrine

• involves: short preganglionic neurons, long postganglionic neurons

• β1 adrenergic receptor on SA node, AV node, and ventricular cardiac muscles

baroreceptor reflex to low blood pressure

• low blood pressure activates cardioacceleratory center of medulla oblongata

• sympathetic extrinsic control

• neurotransmitter: norepinephrine and epinephrine

• involves: short preganglionic neurons, long postganglionic neurons

• β1 adrenergic receptor

result of baroreceptor reflex to low blood pressure

increased cardiac output and vasoconstriction

extrinsic control of heart in response to blood gasses

• chemoreceptors detect low O₂, high CO₂, and low pH in blood, activating cardioacceleratory center of medulla oblongata

• sympathetic extrinsic control

• neurotransmitter: norepinephrine and epinephrine

• involves: short preganglionic neurons, long postganglionic neurons

• β1 adrenergic receptor

result of extrinsic control of heart in response to blood gasses

increased cardiac output and vasoconstriction

effected by stimulation of the cardioinhibitory center by the parasympathetic nervous system

autorhythmic cells of the SA and AV nodes

effected by stimulation of the cardioacceleratory center by the sympathetic nervous system

autorhythmic cells of the SA and AV nodes and contractile cells

effected by the stimulation of the vasomotor center by the sympathetic nervous system

smooth muscle around blood vessels