5/14/13 Lecture 3 Blood vessels and cardiodynamics
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Transcript 5/14/13 Lecture 3 Blood vessels and cardiodynamics
Cardiodynamics and Blood Vessels
Muse s13 Bio238 Lecture #3
5/16/13
The Conducting System
The Role of Calcium Ions in Cardiac
Contractions
Contraction of a cardiac muscle cell is
produced by an increase in calcium ion
concentration around myofibrils
The Conducting System
The Role of Calcium Ions in Cardiac
Contractions
20% of calcium ions required for a contraction
Calcium ions enter plasma membrane during plateau phase
Arrival of extracellular Ca2+
Triggers release of calcium ion reserves from sarcoplasmic
reticulum
The Conducting System
The Role of Calcium Ions in Cardiac
Contractions
As slow calcium channels close
Intracellular Ca2+ is absorbed by the SR
Or pumped out of cell
Cardiac muscle tissue
Very sensitive to extracellular Ca2+ concentrations
The Conducting System
The Energy for Cardiac Contractions
Aerobic energy of heart
From mitochondrial breakdown of fatty acids and
glucose
Oxygen from circulating hemoglobin
Cardiac muscles store oxygen in myoglobin
The Cardiac Cycle
Phases of the Cardiac Cycle
Within any one chamber
Systole (contraction)
Diastole (relaxation)
The Cardiac Cycle
Figure 20–16 Phases of the Cardiac Cycle
The Cardiac Cycle
Blood Pressure
In any chamber
Rises during systole (ventricular compression) 120
Falls during diastole (vessel elasticity)
60
Blood flows from high to low pressure
Controlled by timing of contractions
Directed by one-way valves - not perfect seals
The Cardiac Cycle
Cardiac Cycle and Heart Rate
At 75 beats per minute
Cardiac cycle lasts about 800 msecs
When heart rate increases
All phases of cardiac cycle shorten, particularly
diastole
The Cardiac Cycle
Figure 20–17 Pressure and Volume Relationships in the Cardiac Cycle
The Cardiac Cycle
Heart Sounds
S1
Loud sounds
Produced by AV valves
S2
Loud sounds
Produced by semilunar valves
S3, S4
Soft sounds
Blood flow into ventricles and atrial contraction
The Cardiac Cycle
Heart Murmur
Sounds produced by regurgitation through
valves
The Cardiac Cycle
Figure 20–18 Heart Sounds
Cardiodynamics
Cardiac Output
CO = HR X SV
CO = cardiac output (mL/min)
HR = heart rate (beats/min)
SV = stroke volume (mL/beat)
Cardiodynamics
Factors Affecting Cardiac Output
Cardiac output
Adjusted by changes in heart rate or stroke volume
Heart rate
Adjusted by autonomic nervous system or hormones
Stroke volume
Adjusted by changing EDV or ESV
Cardiodynamics
Figure 20–20 Factors Affecting Cardiac Output
Cardiodynamics
Factors Affecting the Heart Rate
Autonomic innervation
Cardiac plexuses: innervate heart
Vagus nerves (X): carry parasympathetic preganglionic fibers
to small ganglia in cardiac plexus
Cardiac centers of medulla oblongata:
– cardioacceleratory center controls sympathetic
neurons (increases heart rate)
– cardioinhibitory center controls parasympathetic
neurons (slows heart rate)
Cardiodynamics
Autonomic Innervation
Cardiac reflexes
Cardiac centers monitor:
– blood pressure (baroreceptors)
– arterial oxygen and carbon dioxide levels
(chemoreceptors)
Cardiac centers adjust cardiac activity
Autonomic tone
Dual innervation maintains resting tone by
releasing ACh and NE
Fine adjustments meet needs of other systems
Cardiodynamics
Figure 20–21 Autonomic Innervation of the Heart
Cardiodynamics
Effects on the SA Node
Sympathetic and parasympathetic stimulation
Greatest at SA node (heart rate)
Membrane potential of pacemaker cells
Lower than other cardiac cells
Rate of spontaneous depolarization depends on
Resting membrane potential
Rate of depolarization
ACh (parasympathetic stimulation)
Slows the heart
NE (sympathetic stimulation)
Speeds the heart
Cardiodynamics
Figure 20–22 Autonomic Regulation of Pacemaker Function
Cardiodynamics
Hormonal Effects on Heart Rate
Increase heart rate (by sympathetic
stimulation of SA node)
Epinephrine (E)
Norepinephrine (NE)
Thyroid hormone
Cardiodynamics
Factors Affecting the Stroke Volume
The EDV: amount of blood a ventricle contains at the
end of diastole
Filling time:
– duration of ventricular diastole
Venous return:
– rate of blood flow during ventricular diastole
Cardiodynamics
The Frank–Starling Principle
As EDV increases, stroke volume increases
Physical Limits
Ventricular expansion is limited by
Myocardial connective tissue
The cardiac (fibrous) skeleton
The pericardial sac
Cardiodynamics
End-Systolic Volume (ESV)
The amount of blood that remains in the
ventricle at the end of ventricular systole is
the ESV
Cardiodynamics
Effects of Autonomic Activity on Contractility
Sympathetic stimulation
NE released by postganglionic fibers of cardiac nerves
Epinephrine and NE released by suprarenal (adrenal)
medullae
Causes ventricles to contract with more force
Increases ejection fraction and decreases ESV
Cardiodynamics
Effects of Autonomic Activity on
Contractility
Parasympathetic activity
Acetylcholine released by vagus nerves
Reduces force of cardiac contractions
Cardiodynamics
Hormones
Many hormones affect heart contraction
Pharmaceutical drugs mimic hormone actions
Stimulate or block beta receptors
Affect calcium ions (e.g., calcium channel
blockers)
Cardiodynamics
Heart Rate Control Factors
Autonomic nervous system
Sympathetic and parasympathetic
Circulating hormones
Venous return and stretch receptors
Cardiac Reserve
The difference between resting and maximal cardiac output
Cardiodynamics
Figure 20–24 A Summary of the Factors Affecting Cardiac Output
Classes of Blood Vessels
Arteries
Carry blood away from heart
Arterioles
Are smallest branches of arteries
Capillaries
Are smallest blood vessels
Location of exchange between blood and interstitial fluid
Venules
Collect blood from capillaries
Veins
Return blood to heart
Blood Vessels
The Largest Blood Vessels
Attach to heart
Pulmonary trunk
Carries blood from right ventricle
To pulmonary circulation
Aorta
Carries blood from left ventricle
To systemic circulation
Blood Vessels
The Smallest Blood Vessels
Capillaries
Have small diameter and thin walls
Chemicals and gases diffuse across walls
Blood Vessels
The Structure of Vessel Walls
Walls have three layers:
Tunica intima
Tunica media
Tunica externa
Blood Vessels
The Tunica Intima
Is the innermost layer
Includes
The endothelial lining
Connective tissue layer
Internal elastic membrane:
– in arteries, is a layer of elastic fibers in outer margin of
tunica intima
Blood Vessels
The Tunica Media
Is the middle layer
Contains concentric sheets of smooth muscle in loose
connective tissue
Binds to inner and outer layers
External elastic membrane of the tunica media
Separates tunica media from tunica externa
Blood Vessels
The Tunica Externa
Is outer layer
Contains connective tissue sheath
Anchors vessel to adjacent tissues in arteries
Contain collagen
Elastic fibers
In veins
Contains elastic fibers
Smooth muscle cells
Vasa vasorum (“vessels of vessels”)
Small arteries and veins
In walls of large arteries and veins
Supply cells of tunica media and tunica externa
Blood Vessels
Figure 21–1 Comparisons of a Typical Artery and a Typical Vein.
Blood Vessels
Figure 21–1 Comparisons of a Typical Artery and a Typical Vein.
Blood Vessels
Differences between Arteries and Veins
Arteries and veins run side by side
Arteries have thicker walls and higher blood pressure
Collapsed artery has small, round lumen (internal
space)
Vein has a large, flat lumen
Vein lining contracts, artery lining does not
Artery lining folds
Arteries more elastic
Veins have valves
Structure and Function of Arteries
Arteries and Pressure
Elasticity allows arteries to absorb pressure waves
that come with each heartbeat
Contractility
Arteries change diameter
Controlled by sympathetic division of ANS
Vasoconstriction:
– the contraction of arterial smooth muscle by the ANS
Vasodilatation:
– the relaxation of arterial smooth muscle
– enlarging the lumen
Structure and Function of Arteries
Vasoconstriction and Vasodilation
Affect
Afterload on heart
Peripheral blood pressure
Capillary blood flow
Structure and Function of Arteries
Arteries
From heart to capillaries, arteries change
From elastic arteries
To muscular arteries
To arterioles
Structure and Function of Arteries
Elastic Arteries
Also called conducting arteries
Large vessels (e.g., pulmonary trunk and
aorta)
Tunica media has many elastic fibers and few
muscle cells
Elasticity evens out pulse force
Structure and Function of Arteries
Muscular Arteries
Also called distribution arteries
Are medium sized (most arteries)
Tunica media has many muscle cells
Structure and Function of Arteries
Arterioles
Are small
Have little or no tunica externa
Have thin or incomplete tunica media
Artery Diameter
Small muscular arteries and arterioles
Change with sympathetic or endocrine stimulation
Constricted arteries oppose blood flow
– resistance (R):
» resistance vessels: arterioles
Structure and Function of Arteries
Aneurysm
A bulge in an arterial wall
Is caused by weak spot in elastic fibers
Pressure may rupture vessel
Structure and Function of Arteries
Figure 21–2 Histological Structure of Blood Vessels
Structure and Function of Arteries
Figure 21–3 A Plaque within an Artery
Atherosclerosis
Hardening of the arteries. -Cholesterol
rich fatty plaques stick to side walls of
artery and fill with calcium.
When they burst can lead to inflammation
which occludes the artery.
White blood cells can build up here and
contribute to inflammatory response
atherosclerosis
Structure and Function of Capillaries
Capillaries
Are smallest vessels with thin walls
Microscopic capillary networks permeate all active
tissues
Capillary function
Location of all exchange functions of cardiovascular system
Materials diffuse between blood and interstitial fluid
Structure and Function of Capillaries
Capillary Structure
Endothelial tube, inside thin basal lamina
No tunica media
No tunica externa
Diameter is similar to red blood cell
Structure and Function of Capillaries
Fenestrated Capillaries
Have pores in endothelial lining
Permit rapid exchange of water and larger solutes
between plasma and interstitial fluid
Are found in
Choroid plexus
Endocrine organs
Kidneys
Intestinal tract
Structure and Function of Capillaries
Figure 21–4 Capillary Structure
Structure and Function of Capillaries
Figure 21–4 Capillary Structure
Structure and Function of Capillaries
Capillary Sphincter
Guards entrance to each capillary
Opens and closes, causing capillary blood to
flow in pulses
Structure and Function of Capillaries
Vasomotion
Contraction and relaxation cycle of capillary
sphincters
Causes blood flow in capillary beds to
constantly change routes
Structure and Function of Veins
Veins
Collect blood from capillaries in tissues and organs
Return blood to heart
Are larger in diameter than arteries
Have thinner walls than arteries
Have lower blood pressure
Structure and Function of Veins
Vein Categories
Venules
Very small veins
Collect blood from capillaries
Medium-sized veins
Thin tunica media and few smooth muscle cells
Tunica externa with longitudinal bundles of elastic fibers
Large veins
Have all three tunica layers
Thick tunica externa
Thin tunica media
Structure and Function of Veins
Venous Valves
Folds of tunica intima
Prevent blood from flowing backward
Compression pushes blood toward heart
Structure and Function of Veins
Figure 21–6 The Function of Valves in the Venous System
Blood Vessels
The Distribution of Blood
Heart, arteries, and capillaries
30–35% of blood volume
Venous system
60–65%:
– 1/3 of venous blood is in the large venous networks of the liver,
bone marrow, and skin
Blood Vessels
Figure 21–7 The Distribution of Blood in the Cardiovascular
System
Hemorrhage!
When large amounts of blood is lost in a short time
Class II haemorrhage (15–30% total blood volume)
Blood Vessels
Capacitance of a Blood Vessel
The ability to stretch
Relationship between blood volume and blood
pressure
Veins (capacitance vessels) stretch more
than arteries
Blood Vessels
Venous Response to Blood Loss
Vasomotor centers stimulate sympathetic
nerves
Systemic veins constrict (venoconstriction)
Veins in liver, skin, and lungs redistribute venous
reserve
Pressure and Resistance
Figure 21–8 An Overview of Cardiovascular Physiology
Pressure and Resistance
Pressure (P)
The heart generates P to overcome resistance
Absolute pressure is less important than pressure
gradient
The Pressure Gradient (P)
Circulatory pressure = pressure gradient
The difference between
Pressure at the heart
And pressure at peripheral capillary beds
Pressure and Resistance
Force (F)
Is proportional to the pressure difference (P)
Divided by R
Pressure and Resistance
Measuring Pressure
Blood pressure (BP)
Arterial pressure (mm Hg)
Capillary hydrostatic pressure (CHP)
Pressure within the capillary beds
Venous pressure
Pressure in the venous system
Pressure and Resistance
Viscosity
R caused by molecules and suspended
materials in a liquid
Whole blood viscosity is about four times that
of water
Pressure and Resistance
Turbulence
Swirling action that disturbs smooth flow of
liquid
Occurs in heart chambers and great vessels
Atherosclerotic plaques cause abnormal
turbulence
Pressure and Resistance
Pressure and Resistance
Pressure and Resistance
Pressure and Resistance
Figure 21–12 Forces Acting across Capillary Walls
Cardiovascular Regulation
Tissue Perfusion
Blood flow through the tissues
Carries O2 and nutrients to tissues and organs
Carries CO2 and wastes away
Is affected by
Cardiac output
Peripheral resistance
Blood pressure
Cardiovascular Regulation
Cardiovascular regulation changes blood
flow to a specific area
At an appropriate time
In the right area
Without changing blood pressure and blood
flow to vital organs
Cardiovascular Regulation
Figure 21–13 Short-Term and Long-Term Cardiovascular Responses
Cardiovascular Regulation
Controlling Cardiac Output and Blood Pressure
Autoregulation
Causes immediate, localized homeostatic adjustments
Neural mechanisms
Respond quickly to changes at specific sites
Endocrine mechanisms
Direct long-term changes
Cardiovascular Regulation
Autoregulation of Blood Flow within Tissues
Adjusted by peripheral resistance while cardiac
output stays the same
Local vasodilators:
– accelerate blood flow at tissue level
» low O2 or high CO2 levels
» low pH (acids)
» nitric oxide (NO)
» high K+ or H+ concentrations
» chemicals released by inflammation (histamine)
» elevated local temperature
Cardiovascular Regulation
Vasomotor Tone
Produced by constant action of sympathetic
vasoconstrictor nerves
Cardiovascular Regulation
Reflex Control of Cardiovascular Function
Cardiovascular centers monitor arterial blood
Baroreceptor reflexes:
– respond to changes in blood pressure
Chemoreceptor reflexes:
– respond to changes in chemical composition, particularly
pH and dissolved gases
Cardiovascular Regulation
Baroreceptor Reflexes
Stretch receptors in walls of
Carotid sinuses: maintain blood flow to brain
Aortic sinuses: monitor start of systemic circuit
Right atrium: monitors end of systemic circuit
When blood pressure rises, CV centers
Decrease cardiac output
Cause peripheral vasodilation
When blood pressure falls, CV centers
Increase cardiac output
Cause peripheral vasoconstriction
Cardiovascular Regulation
Figure 21–14 Baroreceptor Reflexes of the Carotid and Aortic Sinuses
Cardiovascular Regulation
Hormones and Cardiovascular Regulation
Hormones have short-term and long-term
effects on cardiovascular regulation
For example, E and NE from suprarenal
medullae stimulate cardiac output and
peripheral vasoconstriction
Cardiovascular Regulation
Antidiuretic Hormone (ADH)
Released by neurohypophysis (posterior lobe of
pituitary)
Elevates blood pressure
Reduces water loss at kidneys
ADH responds to
Low blood volume
High plasma osmotic concentration
Circulating angiotensin II
Cardiovascular Regulation
Angiotensin II
Responds to fall in renal blood pressure
Stimulates
Aldosterone production
ADH production
Thirst
Cardiac output
Peripheral vasoconstriction
Cardiovascular Regulation
Erythropoietin (EPO)
Released at kidneys
Responds to low blood pressure, low O2
content in blood
Stimulates red blood cell production
Cardiovascular Regulation
Natriuretic Peptides
Atrial natriuretic peptide (ANP)
Produced by cells in right atrium
Brain natriuretic peptide (BNP)
Produced by ventricular muscle cells
Respond to excessive diastolic stretching
Lower blood volume and blood pressure
Reduce stress on heart
Cardiovascular Regulation
Figure 21–16a The Hormonal Regulation of Blood Pressure and Blood
Volume.
Cardiovascular Regulation
Figure 21–16b The Hormonal Regulation of Blood Pressure and Blood
Volume.
Cardiovascular Adaptation
Cardiovascular Adaptation
Short-Term Elevation of Blood Pressure
Carotid and aortic reflexes
Increase cardiac output (increasing heart rate)
Cause peripheral vasoconstriction
Sympathetic nervous system
Triggers hypothalamus
Further constricts arterioles
Venoconstriction improves venous return
Cardiovascular Adaptation
Short-Term Elevation of Blood Pressure
Hormonal effects
Increase cardiac output
Increase peripheral vasoconstriction (E, NE,
ADH, angiotensin II)
Cardiovascular Adaptation
Long-Term Restoration of Blood Volume
Recall of fluids from interstitial spaces
Aldosterone and ADH promote fluid retention
and reabsorption
Thirst increases
Erythropoietin stimulates red blood cell
production
Cardiovascular Adaptation
Blood Flow to the Brain
Is top priority
Brain has high oxygen demand
When peripheral vessels constrict, cerebral
vessels dilate, normalizing blood flow
Cardiovascular Adaptation
Stroke
Also called cerebrovascular accident (CVA)
Blockage or rupture in a cerebral artery
Stops blood flow
Cardiovascular Adaptation
Heart Attack
A blockage of coronary blood flow
Can cause
Angina (chest pain)
Tissue damage
Heart failure
Death
Cardiovascular Adaptation
Blood Flow to the Lungs
Regulated by O2 levels in alveoli
High O2 content
Vessels dilate
Low O2 content
Vessels constrict
The Systemic Circuit
Figure 21–20 An Overview of the Major Systemic Arteries
The Systemic Circuit
Figure 21–24a Major Arteries of the Trunk
Aging and the Cardiovascular System
Three Age-Related Changes in Blood
Decreased hematocrit
Peripheral blockage by blood clot (thrombus)
Pooling of blood in legs
Due to venous valve deterioration
Aging and the Cardiovascular System
Five Age-Related Changes in the Heart
Reduced maximum cardiac output
Changes in nodal and conducting cells
Reduced elasticity of cardiac (fibrous) skeleton
Progressive atherosclerosis
Replacement of damaged cardiac muscle cells by
scar tissue
Aging and the Cardiovascular System
Three Age-Related Changes in Blood Vessels
Arteries become less elastic
Pressure change can cause aneurysm
Calcium deposits on vessel walls
Can cause stroke or infarction
Thrombi can form
At atherosclerotic plaques