Transcript blood pressure

PowerPoint® Lecture Slides
prepared by
Betsy C. Brantley
Valencia College
CHAPTER
13
The
Cardiovascular
System: Blood
Vessels and
Circulation
© 2017 Pearson Education, Inc.
Vascular Pathway of Blood Flow (13-1)
• Arteries
• Carry blood away from the heart
• Branch into smaller vessels called arterioles
• Arterioles branch into capillaries
• Capillaries
• Smallest vessels of the venous system
• Where chemical and gaseous exchange occurs
• Drain into venules
• Venules drain into veins
• Return blood to the atria of the heart
Structure of Vessel Walls (13-1)
1. Tunica intima (or tunica interna), the innermost
layer
• Lined by endothelium (epithelial tissue) with basement
membrane
• Surrounded by layer of connective tissue with elastic
fibers
2. Tunica media
• Smooth muscle with loose connective tissue containing
collagen and elastic fibers
• Controls diameter of vessel
3. Tunica externa (or tunica adventitia)
• Sheath of connective tissue around vessel
• May stabilize and anchor vessel to other tissues
Differences in Vessel Structure (13-1)
• Arteries have:
• Smaller lumen than veins
• Thicker tunica media with more elastic fibers and smooth
muscle
• Contraction causes vasoconstriction or decrease in size
of the lumen
• Relaxation causes vasodilation or increase in size of the
lumen
Figure 13-1 A Comparison of a Typical Artery and a Typical Vein.
Elastic Arteries (13-1)
• First type of arteries leaving the heart
• Examples: pulmonary trunk and aorta
• Have more elastic fibers than smooth muscle fibers
• Large, resilient vessels
• Absorb pressure changes readily
• Stretched during systole, elastic fibers recoil during
diastole
• Prevent very high pressure during systole
• Prevent very low pressure during diastole
Muscular Arteries (13-1)
• Also called medium-sized arteries or distribution
arteries
• Examples: external carotid arteries
• Distribute blood to skeletal muscles and internal
organs
• Compared to elastic arteries, tunica media
contains:
• Higher proportion of smooth muscle
• Fewer elastic fibers
Arterioles (13-1)
• Arterioles
• Tunica media has only 1–2 layers of smooth muscle
• Diameter changes in response to various stimuli
• Changing diameter alters blood pressure and flow
Capillaries (13-1)
• Tunica interna only
• Endothelial cells with basement membrane
• Ideal for diffusion between plasma and interstitial
fluid
• Thin walls provide short diffusion distance
• Small diameter slows flow to increase diffusion rate
• Enormous number of capillaries provide huge surface
area for increased diffusion
Figure 13-2 The Structure of the Various Types of Blood Vessels.
Capillary Beds (13-1)
• An interconnected network of capillaries
• Entrance to each capillary is regulated by
precapillary sphincter, a band of smooth muscle
• Relaxation of sphincter allows for increased flow
• Constriction of sphincter decreases flow
• Anastomosis
• A joining of blood vessels
• May form alternate routes for blood flow
Figure 13-3 The Organization of a Capillary Bed.
Veins (13-1)
• Collect blood from tissues and organs and return it
to the heart
• Classified based on internal diameters
• Venules average 20 µm in diameter
• Smaller venules lack a tunica media
• Medium-sized veins range from 2 to 9 mm
• Several smooth muscle layers in tunica media
• Thick tunica externa of elastic and collagen fibers
• Large veins
• Thin tunica media surrounded by thick tunica externa
Vein Features (13-1)
• Relatively thin walls
• Low blood pressure inside
• Medium-sized veins in limbs contain valves
• Folds of tunica interna
• Prevent backflow of blood
• Improve venous return
• Improper functioning valves results in distended vessels
• Examples: varicose veins or hemorrhoids
Valve
closed
Valve opens above
contracting muscle
Valve
closed
Valve closes below
contracting muscle
Figure 13-4 The Function of Valves in the Venous System.
Maintaining Adequate Blood Flow (13-2)
• Normally, blood flow equals cardiac output (CO)
• Increased CO leads to increased flow through capillaries
• Decreased CO leads to reduced flow
• Blood flow also influenced by pressure and
resistance
• Increased pressure increases flow
• Increased resistance decreases flow
Pressure (13-2)
• Liquids exert hydrostatic pressure in all directions
• Liquid flows from higher pressure to lower pressure
• Pressure gradient is difference in pressure from one end
of a vessel to the other
• Flow rate is directly proportional to pressure gradient
Circulatory Pressure (13-2)
• Circulatory pressure
• Largest pressure gradient
• Difference between pressure at base of aorta and
entrance to right atrium
• Divided into three components
1. Arterial pressure is blood pressure
2. Capillary pressure
3. Venous pressure
Resistance (13-2)
• Any force that opposes movement
• Sources of this resistance include:
• Vascular resistance
• The longer the vessel, the higher the resistance
• The smaller the diameter, the greater the resistance
• Viscosity
• Turbulence
• Caused by variance in flow speed
• Slow flow near the walls of vessels, faster flow in center
Blood Pressure (13-2)
• Arterial pressure fluctuates
• Systolic pressure
• Peak pressure measured during ventricular contraction
• Diastolic pressure
• Minimum pressure at the end of ventricular relaxation
• Blood pressure recorded as systolic over diastolic
(e.g., 120/80 mm Hg)
• Pulse is rhythmic alternating changes in pressures
• Pulse pressure is the difference between systolic
and diastolic pressures
Figure 13-5 Pressures within the Systemic Circuit.
Systolic
120
Pulse
pressure
100
80
Blood
pressure
(mm Hg)
0
Venae cavae
Large veins
Venules
Capillaries
Arterioles
Muscular arteries
20
Aorta
40
Elastic arteries
60
Medium-sized veins
Diastolic
Capillary Pressures (13-2)
• Pressure of blood within a capillary bed
• Drops from 35 to 18 mm Hg along capillary length
• Capillaries are permeable to ions, nutrients,
wastes, gases, and water
• Capillary pressures cause filtration of water and
solutes out of bloodstream and into tissues
• Some materials reabsorbed into capillaries
• Remainder picked up by lymphatic vessels
Four Functions of Capillary Exchange (13-2)
1. Maintains constant communication between
plasma and interstitial fluid
2. Speeds distribution of nutrients, hormones, and
gases
3. Assists in transport of insoluble molecules
4. Flushes bacterial toxins and other chemicals to
lymphatic tissues for body defense and immune
response
Mechanisms of Capillary Exchange (13-2)
• Diffusion
• Movement of ions or molecules from area of high
concentration to area of low concentration
• Filtration
• Movement of solute due to “push” of water or hydrostatic
pressure down fluid pressure gradients
• Water is filtered out of capillary by fluid or hydrostatic
pressures
• Reabsorption
• Water is reabsorbed into capillary by osmosis
• Movement due to osmotic pressure
Forces across Capillary Walls (13-2)
• Capillary hydrostatic pressure (CHP)
• High at arterial end, low at venous end
• Tends to push water out of plasma into tissues at arterial
end, favoring filtration
• Blood osmotic pressure (BOP)
• Higher than osmotic pressure in interstitial fluid
• Due to dissolved proteins
• Constant along length of capillary
• As CHP drops over length of capillary, BOP remains the
same, favoring reabsorption at venous end
Figure 13-6 Forces Acting across Capillary Walls.
Return to
circulation
3.6 L/day flows
into lymphatic
vessels
Tissue cells
Arteriole
Venule
Reabsorption
20.4 L/day
Filtration
24 L/day
35
mm
Hg
25
mm
Hg
CHP > BOP
Fluid forced
out of capillary
25
mm
Hg
25
mm
Hg
CHP = BOP
No net
movement
of fluid
18
25
mm mm
Hg Hg
BOP > CHP
Fluid moves
into capillary
KEY
CHP (Capillary
hydrostatic pressure)
BOP (Blood
osmotic pressure)
Venous Pressure (13-2)
• Gradient is low compared to arterial system
• Large veins provide low resistance, ensuring
increase in flow despite low pressure
• Two factors help blood flow overcome gravity when
standing
• Muscular compression pushes on outside of veins
• Venous valves prevent backflow
• Respiratory pump results from changes in thoracic
pressures during inhalation
Autoregulation of Perfusion (13-3)
• Adjustments in blood flow made by precapillary
sphincters
• Automatic, immediate, local changes in response to
changing tissue conditions
• Vasodilators
• Factors that promote dilation of precapillary sphincters
and increased blood flow
• Low O2 or pH, high CO2, histamine, nitric oxide (NO)
• Vasoconstrictors
• Factors that stimulate constriction of precapillary
sphincters and decreased blood flow
• If homeostasis not restored, neural and endocrine
processes activated
Neural Control of Blood Pressure and
Perfusion (13-3)
• Cardiovascular center in the medulla oblongata
• Responds to changes in arterial pressure or blood gas
levels to maintain adequate blood flow
• Cardiac center contains:
• Cardioacceleratory center that increases cardiac output
• Cardioinhibitory center that reduces cardiac output
• Vasomotor center
• Controls diameter of arterioles and peripheral resistance
• Controls venoconstriction (constriction of
peripheral veins)
Reflexes for Neural Processes (13-3)
• Two types of reflexes involved in adjusting cardiac
output and peripheral resistance to maintain tissue
perfusion
• Both regulated by negative feedback
• Baroreceptor reflexes
• Respond to changes in blood pressure
• Chemoreceptor reflexes
• Respond to changes in chemical composition
Baroreceptor Reflexes (13-3)
• Baroreceptors monitor degree of stretch in walls of
expandable organs (including blood vessels)
• Carotid sinuses
• Expanded chambers near bases of internal carotid arteries
of the neck
• Very sensitive to ensure adequate blood flow to the brain
• Aortic sinuses
• Located in pockets in walls of ascending aorta
• Aortic reflex adjusts blood flow through systemic circuit
Baroreceptor Reflex Process (13-3)
• Increased blood pressure
• Increases output from baroreceptors
• Inhibits cardioacceleratory center
• Stimulates cardioinhibitory center
• Inhibits vasomotor center
• Results are:
• Decreased cardiac output
• Widespread peripheral vasodilation
• Opposite process occurs with decreased blood
pressure
Figure 13-8 The Baroreceptor Reflexes of the Carotid and Aortic Sinuses.
Effector
Baroreceptors
stimulated
Medulla oblongata
Decreased
Result
• Cardioinhibitory
cardiac output
in
center stimulated
• Cardioacceleratory
center inhibited
• Vasomotor center Results in Vasodilation
inhibited
Receptors
Baroreceptors in
aortic and carotid
sinuses
Reduced blood pressure
Homeostasis
DISTURBED BY
INCREASING
RESTORED
STIMULUS
blood pressure
DECREASING
NORMAL RANGE OF BLOOD PRESSURE
RESTORED
STIMULUS
DECREASING
blood pressure
HOMEOSTASIS
Homeostasis
DISTURBED BY
Homeostasis
RESTORED BY
blood pressure
Homeostasis
RESTORED BY
INCREASING
blood pressure
Receptors
Baroreceptors in
aortic and carotid
sinuses
Increased blood pressure
Effector
Medulla oblongata
Baroreceptors
inhibited
• Vasomotor center
stimulated
• Cardioacceleratory
center stimulated
• Cardioinhibitory
center inhibited
Results in
Result
in
Vasoconstriction
Increased
cardiac output
Chemoreceptor Reflexes (13-3)
• Receptors are:
• Sensitive to changes in carbon dioxide, oxygen, and pH in
blood and cerebrospinal fluid
• Located in carotid and aortic bodies, medulla oblongata
• Receptors are activated by:
• Decrease in pH
• Decrease in plasma O2
• Increase in plasma CO2
• Receptors stimulate cardioacceleratory and vasomotor
centers
• Result is increase in arteriolar constriction and blood flow
• Respiratory centers also activated to increase respiratory rate
Figure 13-9 The Chemoreceptor Reflexes.
Effector
Medulla oblongata
Respiratory centers
stimulated
Chemoreceptors
stimulated
Receptors
Homeostasis
DISTURBED BY
INCREASING
CO2 Levels
and
DECREASING
pH and O2 levels
Chemoreceptors in
carotid and aortic
bodies and
medulla oblongata
STIMULUS
• Cardioacceleratory
center stimulated
• Cardioinhibitory
center inhibited
• Vasomotor center
stimulated
Result in
Result
in
Results in
Respiratory rate increases
Increased cardiac
output and blood
pressure
Vasoconstriction
Increased pH and O2
levels, and decreased
CO2 levels
RESTORED
HOMEOSTASIS
NORMAL pH, O2, AND CO2 LEVELS IN BLOOD AND CSF
Homeostasis
RESTORED BY
DECREASING
CO2 Levels
and
INCREASING
pH and O2 levels
Hormones and Cardiovascular Regulation (13-3)
• Short-term
• Epinephrine (E) and norepinephrine (NE) stimulate
cardiac output and peripheral vasoconstriction
• Long-term
• Antidiuretic hormone (ADH), angiotensin II,
erythropoietin (EPO)
• Raise BP when too low
• Atrial natriuretic peptide (ANP)
• Lowers BP when too high
Figure 13-10a The Hormonal Regulation of Blood Pressure and Blood Volume.
Increased Na+ loss in urine
Increased water loss in urine
Releases
atrial natriuretic
peptide (ANP)
Receptor
Effectors
Kidneys and
blood vessels
Response
to ANP
Reduced thirst
Inhibition of ADH, aldosterone,
epinephrine, and
norepinephrine release
Peripheral vasodilation
Cardiac muscle
cells
(right atrium)
Decreased blood
pressure and volume
Homeostasis
DISTURBED BY
INCREASING
blood pressure
and volume
STIMULUS
RESTORED
HOMEOSTASIS
NORMAL BLOOD PRESSURE AND VOLUME
Homeostasis
RESTORED BY
DECREASING
blood pressure
and volume
Figure 13-10b The Hormonal Regulation of Blood Pressure and Blood Volume.
HOMEOSTASIS
NORMAL BLOOD PRESSURE AND VOLUME
Homeostasis
DISTURBED BY
DECREASING
blood pressure
and volume
RESTORED
STIMULUS
Short-term
effects
Long-term
effects
Combined Short-Term
and Long-Term Effects
Receptors
Receptors
Increased blood
pressure
Baroreceptors
Kidneys
Increased blood
volume
Endocrine Response
of Kidneys
Sympathetic
activation and
release of
adrenal hormones
E and NE
Erythropoietin (EPO)
is released
Increased red blood
cell formation
Renin release leads to
angiotensin II activation
Angiotensin II Effects
Antidiuretic hormone
(ADH) released
Aldosterone secreted
Thirst stimulated
Effectors
Heart and
blood vessels
Respond
with
Increased cardiac
output and peripheral
vasoconstriction
Homeostasis
RESTORED BY
INCREASING
blood pressure
and volume
Circuits of the Cardiovascular System (13-5)
• Cardiovascular system divided into:
• Pulmonary circuit
• Arteries and veins transporting blood between heart and
lungs
• Begins at right ventricle; ends at left atrium
• Systemic circuit
• Arteries and veins transporting blood to and from all other
organs and tissues
• Begins at the left ventricle; ends at right atrium
Figure 13-11 An Overview of the Pattern of Circulation.
The Pulmonary Circuit (13-6)
• Blood exits right ventricle through pulmonary
trunk
• Branches into left and right pulmonary arteries
• These arteries carry deoxygenated blood
• Enter lungs and branch repeatedly
• Smallest pulmonary arterioles provide blood to capillary
networks surrounding small air pockets, or alveoli
• Thin walls of alveoli allow gas exchange between
alveolar capillaries and inhaled air
• Oxygenated blood returns to left atrium through left
and right pulmonary veins (two from each lung)
Figure 13-12 The Pulmonary Circuit.
Aortic arch
Ascending aorta
Pulmonary trunk
Superior vena cava
Left lung
Right lung
Left pulmonary
arteries
Right pulmonary
arteries
Left pulmonary
veins
Right pulmonary
veins
Alveolus
Capillary
O2
Inferior vena cava
Descending aorta
CO2
The Systemic Circuit (13-7)
• Supplies oxygenated blood to all parts of the body
not in the pulmonary circuit
• Oxygenated blood leaves left ventricle through
aorta
• Returns deoxygenated blood to right atrium
through superior and inferior venae cavae and
coronary sinus
• Contains about 84 percent of total blood volume
The Aorta (13-7)
• Aorta is the first systemic vessel and largest artery
• Ascending aorta
• Begins at aortic semilunar valve
• Left and right coronary arteries branch off near base
• Aortic arch curves across superior surface
of heart
• Descending aorta drops down through
mediastinum
Three Elastic Arteries of the Aortic Arch (13-7)
1. Brachiocephalic trunk
• Branches to form right common carotid artery and right
subclavian artery
2. Left common carotid
3. Left subclavian
Figure 13-14 Arteries of the Chest and Upper Limb.
The Carotid Arteries (13-7)
• Common carotid arteries ascend up into the neck
and divide into:
• External carotid artery
• Supplies pharynx, esophagus, larynx, and face
• Can be palpated on either side of the windpipe
• Internal carotid artery
• Enters skull, supplies brain
© 2017 Pearson Education, Inc.
Anterior cerebral
Middle cerebral
Cerebral arterial
circle
Posterior
cerebral
Basilar
Branches of the
External Carotid
Superficial
temporal
Maxillary
Occipital
Facial
Internal carotid
External
carotid
Carotid sinus
Vertebral
Thyrocervical
trunk
Common carotid
Subclavian
Internal
thoracic
Brachiocephalic
trunk
Second rib
a The general circulation pattern of arteries supplying the neck
and superficial structures of the head
Figure 13-15a Arteries of the Neck, Head, and Brain.
Blood Supply to the Brain (13-7)
• Supplied by both the internal carotid arteries and
vertebral arteries
• Vertebral arteries ascend within transverse
foramina of cervical vertebrae, enter skull and fuse
to form one basilar artery
• Cerebral arterial circle, or circle of Willis
• Ring-shaped anastomosis encircling the infundibulum of
the pituitary
• Interconnects internal carotids and basilar arteries
Figure 13-15b Arteries of the Neck, Head, and Brain.
Cerebral Arterial Circle
Anterior
communicating
Anterior
cerebral
Anterior cerebral
Internal
carotid (cut)
Posterior
communicating
Middle
cerebral
Posterior cerebral
Posterior
cerebral
Basilar
Vertebral
b The arterial supply to the brain
Iliac Arteries (13-7)
• Abdominal aorta divides into the:
• Common iliac arteries carrying blood to pelvis
and lower limbs
• Each common iliac artery divides into:
• Internal iliac artery
• Supplies pelvis
• External iliac artery
• Supplies lower limbs
Figure 13-16a Major Arteries of the Trunk.
The Superior Vena Cava (13-7)
• Superior vena cava (SVC)
• Receives blood from:
• Head and neck
• Upper limbs, shoulders, and chest
Venous Return from Head and Neck (13-7)
• Small veins in brain drain into dural sinuses
• Largest is superior sagittal sinus
• Dural sinuses drain into internal jugular veins
• External jugular veins
• Drain blood from superficial head and neck
• Vertebral veins
• Drain blood from cervical spinal cord and posterior skull
• Descend within transverse foramina of cervical vertebrae
Figure 13-17 Major Veins of the Head and Neck.
Superior
sagittal sinus
Temporal
Great cerebral
Maxillary
Dural sinuses
Facial
Vertebral
External jugular
Internal jugular
Right
subclavian
Clavicle
Right brachiocephalic
Left brachiocephalic
Superior vena cava
Internal thoracic
Inferior Vena Cava (13-7)
• Inferior vena cava (IVC)
• Collects most of the blood from organs inferior to
diaphragm
Figure 13-18 The Venous Drainage of the Abdomen and Chest.