the heart and circulation transportation- oxygen and carbon dioxide red blood cells
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The heart and circulation Transportation- oxygen and carbon dioxide red blood cells Regulation-hormones, temperature Protection- against blood loss (clotting); infection (immune system). Components of the circulatory system Cardiovascular system- heart and blood vessels - PowerPoint PPT PresentationTRANSCRIPT
The heart and circulation
Transportation- oxygen and carbon dioxidered blood cells
Regulation-hormones, temperature
Protection- against blood loss (clotting);infection (immune system)
Components of the circulatory system
Cardiovascular system- heart and blood vessels
Lymphatic system- lymph nodes, lymphaticvessels
Electrical activity of the heart
Myocardial cells beat automatically
Action potential is usually originated insinoatrial node
Spontaneous depolarization (pacemaker potential)diffusion of calcium through slow channels
threshold- fast calcium channels open, voltageregulated sodium channels open
repolarization produced through diffusion of potassium
Electrocardiogram
Conduction of electrical potentials through heart
P wave- atrial depolarization
QRS- ventricular depolarizationbeginning of systole
T wave- repolarization of the ventriclesbeginning of diastole
Regulation of cardiac rate
Rhythm is set by the SA node
Sympathetic nervesepinephrine and norepinephrinestimulate opening of calcium and sodiumchannels; increase cardiac rate
Parasympathetic (vagus) nervesacetylcholine promotes opening of potassiumchannels; reduces cardiac rate
Heart muscle cannot sustain contraction
Long refractory periods- heart cannot be stimulated until it has relaxed fromprevious contraction
Arrhythmias- something affects the cardiaccycle; treatment depends on what it is
Fast Na channel blockersSlow Ca channel blockers-adrenergic receptor blockers
Arrhythmias
Bradycardia- slow rate (less than 60 bpm)Tachycardia- fast rate (more than 100 bpm)
Can occur normally; is abnormal if rateincreases during rest (ectopic pacemakers)
Flutters- extremely rapid contractions
Fibrillation- different groups of fibers are activatedso coordinated pumping of chambers is notpossible
Blood vessels- arteries and veins
Arteries, arterioles, capillaries
Veins and venules
Arteries are more muscular
Veins have valves
Veins
Veins can expand to accommodate increasingamounts of blood; arteries can’t
Venous pressure is low compared to arterial pressure
Blood flow through veins is facilitated by:contraction of skeletal musclesvalves that prevent backflow
Atherosclerosis
Damage to endothelium
“Fatty streaks” (macrophages and lymphocytes)
Fibrous plaques
High blood cholesterol, LDL contribute toatherosclerosis
HDL also help transport cholesterol, but donot contribute to atherosclerosis
Lymphatic system
Fluid transportfrom tissues
Fat transport from intestines
Immune response
Regulation of cardiac activity
Cardiac output
Blood flow
Blood pressure
Cardiac output= stroke volume X cardiac rate
(ml/min) (ml/beat) (beats/min)
At 70 beats/min and 80 ml/beat, this comes toabout 5.5 liters per minute—
Equivalent to the total blood volume
Stroke volume regulated by
End-diastolic volumeamount of blood in ventricles before theybegin to contractincreases stroke volume
Total peripheral resistance to blood flow inthe arteriesthe higher the resistance, higher pressureheart compensates by beating morestrongly
Contraction strength of ventricle; proportionalto stroke volume
Exercise reduces vagus inhibition and increasessympathetic nerve activity
Cardiac control center in medulla oblongatacoordinates this activity
This in turn is regulated by higher brain activityand pressure (baroreceptors) in aorta andcarotid arteries
Venous return
At rest, most of the blood is in the veinsveins can “give” more and hold moreblood than arteries; venous pressureis much lower (2 mm Hg vs. 90-100 mm Hgmean arterial pressure)
Venous pressure determines rate of blood returnto the heart
Blood volume
Extracellular fluid distributed betweenblood plasma and interstitial fluid
Affected by:forces acting at capillaries (to drawfluid out of or into them)
overall balance of water loss and gain
(lymphatic system)
Regulation of blood volume by kidneys
Filtration of blood- almost all of filtrate isreabsorbed by the kidneys
(out of daily production of ca. 180L of filtrate,only about 1.5 L actually excreted)
Various hormones acting on, or produced by,the kidneys
(to be discussed later, but think about: whatcauses fluid to be retained or lost?)
Resistance to blood flow
Related to pressure difference between the endsof the vessel
Inversely related to resistance of blood flow through vessel
In body, vasodilation in one organ system mightbe offset by vasoconstriction in another
Regulation of blood flow
Sympathetic nervous systemoverall, increase in cardiac output and inperipheral resistance
vasoconstriction in arterioles of visceraand skin
vasodilation in skeletal muscles(depends on receptors)
Parasympathetic- vasodilation effect confinedto GI, genitalia, salivary glands
Paracrine regulation, e.g., inflammationlocalized vasoconstriction, dilation
Intrinsic (autoregulation)myogenic- response to changes in bloodpressure (constrict to protect bloodvessels, dilate to improve blood flow)
metabolic-oxygen, carbon dioxide levelslocal vasodilation
Regulation of blood flow to the heart
Alpha and beta adrenergic receptors(constriction and dilation; norepinephrineand epinephrine)
Also intrinsic regulationincreased metabolic rate- oxygen need,accumulation of carbon dioxide, etc.smooth muscle stimulated to cause
relaxation and dilation
How are aerobic requirements of heart met?
Lots of capillariesMyoglobin releases oxygen during systole
(blood flow is reduced at that time)capacity for aerobic respiration:extra mitochondria, enzymes
Blockages in blood supply are corrected byangioplasty, bypass, etc.
Total increased blood flowmore to muscles, less to skin and viscera
Overall flow to brain is about the same
Mainly due to increased cardiac rate
With conditioning, stroke volume alsoincreases
Blood flow to brain
Intrinsic mechanisms maintain constant flowmyogenic responses to changes in bloodpressuresensitive to CO2 levels in arterial blood
metabolic responses- local vasodilation
Blood flow to skin is highly sensitive to actionof sympathetic nervous systemtemperature sensitive
Blood pressure
Blood flow resistance highest in arteriolesFlow rate lowest in capillaries
Blood pressure can be raised by:vasoconstriction of arteriolesincrease in cardiac output
(higher cardiac rate or stroke volume)
Various factors can affect these: kidneys,sympathetic nervous system, etc.
Pressure receptors (baroreceptors)
Action potentials will increase or decreaseas pressure rises or falls
Baroreceptor reflex activated when bloodpressure rises or falls. Activated when a person changes position
Vasomotor control centers- constriction/dilation
Cardiac control centers- cardiac rate
Blood pressure also regulated by:
Atrial stretch receptorsADH releaseRenin-angiotensin-aldosteroneANF
Measurement of blood pressuresphygmomanometer
Systolic/diastolic pressure, e.g., 120/80exercise tends to raise systolic morechanging position tends to affect diastolic
Pulse pressure: systolic- diastolicreflects stroke volumedrops in dehydration or blood loss
Pulse rate reflects cardiac rateMean arterial pressure= diastolic + 1/3 pulse
pressure (indicator of peripheral resistance)
Pathophysiology of cardiovascular system
HypertensionSecondary- results from known diseases
(table 14.10)processes that affect blood flow; damageto tissue that results in release ofvasoactive chemicals; damage to sympa-thetic nervous system, etc.
Essential- accounts for most cases of hypertension
Increased total peripheral resistance
Low renin secretion?High salt intake?Stress?
Inability of kidneys to regulation salt and waterexcretion?
Consequences of high blood pressure
Can damage cerebral blood vessels and leadto stroke
Causes heart to work harder (harder to eject blood if peripheral resistance is high)
Contributes to atherosclerosis
Treatments are many and varieddiet, diuretics, various receptor blockers
Shock due to loss of blood flowhypovolemic- blood LOSS
septic- blood-borne infection; nitric oxideformation might be the culprit(vasodilator)
anaphylactic- severe allergic reaction(histamine)
cardiogenic- infarction causes extensivedamage to heart muscle
Congestive heart failure- cardiac output isinadequatecauses: heart disease, hypertension,electrolyte imbalance
Digitalis increases contractility of heart muscle
Diuretics lower blood volume
Nitroglycerin is a vasodilator
Make heart work more efficiently; reduce stresson heart
Summary
Cardiac output can be regulated byautonomic nervous systemstroke volumevenous return (blood volume andefficiency of veins)
Blood flow to different parts of body isadjustable depending on need
Blood pressure is regulated by cardiacrate, blood volume and total peripheralresistance. High or low pressure isassociated with disease.