Download Blood Flow

Lab Lecture #3
Circulatory system
1/20/10
Monitoring Circulatory Efficiency
• Vital signs: pulse and blood pressure, along
with respiratory rate and body temperature
• Pulse: pressure wave caused by the
expansion and recoil of arteries
• Radial pulse (taken at the wrist) routinely used
Measuring Blood Pressure
• Systemic arterial BP
• Measured indirectly by the auscultatory
method using a sphygmomanometer
• Pressure is increased in the cuff until it
exceeds systolic pressure in the brachial artery
Measuring Blood Pressure
• Pressure is released slowly and the examiner
listens for sounds of Korotkoff with a
stethoscope
• Sounds first occur as blood starts to spurt
through the artery (systolic pressure, normally
110–140 mm Hg)
• Sounds disappear when the artery is no
longer constricted and blood is flowing freely
(diastolic pressure, normally 70–80 mm Hg)
Variations in Blood Pressure
• Blood pressure cycles over a 24-hour period
• BP peaks in the morning due to levels of
hormones
• Age, sex, weight, race, mood, and posture
may vary BP
Alterations in Blood Pressure
• Hypotension: low blood pressure
• Systolic pressure below 100 mm Hg
• Often associated with long life and lack of
cardiovascular illness
Homeostatic Imbalance: Hypotension
• Orthostatic hypotension: temporary low BP
and dizziness when suddenly rising from a
sitting or reclining position
• Chronic hypotension: hint of poor nutrition and
warning sign for Addison’s disease or
hypothyroidism
• Acute hypotension: important sign of
circulatory shock
Alterations in Blood Pressure
• Hypertension: high blood pressure
• Sustained elevated arterial pressure of 140/90
or higher
• May be transient adaptations during fever,
physical exertion, and emotional upset
• Often persistent in obese people
Homeostatic Imbalance: Hypertension
• Prolonged hypertension is a major cause of
heart failure, vascular disease, renal failure,
and stroke
• Primary or essential hypertension
• 90% of hypertensive conditions
• Due to several risk factors including heredity,
diet, obesity, age, stress, diabetes mellitus,
and smoking
Homeostatic Imbalance: Hypertension
• Secondary hypertension is less common
• Due to identifiable disorders, including kidney
disease, arteriosclerosis, and endocrine
disorders such as hyperthyroidism and
Cushing’s syndrome
Blood Flow Through Body Tissues
• Blood flow (tissue perfusion) is involved in
• Delivery of O2 and nutrients to, and removal of
wastes from, tissue cells
• Gas exchange (lungs)
• Absorption of nutrients (digestive tract)
• Urine formation (kidneys)
• Rate of flow is precisely the right amount to
provide for proper function
Brain
Heart
Skeletal
muscles
Skin
Kidney
Abdomen
Other
Total blood
flow at rest
5800 ml/min
Total blood flow during strenuous
exercise 17,500 ml/min
Figure 19.13
Velocity of Blood Flow
• Changes as it travels through the systemic
circulation
• Is inversely related to the total cross-sectional
area
• Is fastest in the aorta, slowest in the
capillaries, increases again in veins
• Slow capillary flow allows adequate time for
exchange between blood and tissues
Relative crosssectional area of
different vessels
of the vascular bed
Total area
(cm2) of the
vascular
bed
Velocity of
blood flow
(cm/s)
Figure 19.14
Autoregulation
• Automatic adjustment of blood flow to each
tissue in proportion to its requirements at any
given point in time
• Is controlled intrinsically by modifying the
diameter of local arterioles feeding the
capillaries
• Is independent of MAP, which is controlled as
needed to maintain constant pressure
Autoregulation
•
Two types of autoregulation
1. Metabolic
2. Myogenic
Metabolic Controls
• Vasodilation of arterioles and relaxation of
precapillary sphincters occur in response to
• Declining tissue O2
• Substances from metabolically active tissues
(H+, K+, adenosine, and prostaglandins) and
inflammatory chemicals
Metabolic Controls
• Effects
• Relaxation of vascular smooth muscle
• Release of NO from vascular endothelial cells
• NO is the major factor causing vasodilation
• Vasoconstriction is due to sympathetic
stimulation and endothelins
Myogenic Controls
• Myogenic responses of vascular smooth
muscle keep tissue perfusion constant despite
most fluctuations in systemic pressure
• Passive stretch (increased intravascular
pressure) promotes increased tone and
vasoconstriction
• Reduced stretch promotes vasodilation and
increases blood flow to the tissue
Intrinsic mechanisms
(autoregulation)
• Distribute blood flow to individual
organs and tissues as needed
Extrinsic mechanisms
• Maintain mean arterial pressure (MAP)
• Redistribute blood during exercise and
thermoregulation
Amounts of:
Sympathetic
pH
O2
Metabolic
a Receptors
b Receptors
controls
Amounts of:
Nerves
Epinephrine,
norepinephrine
CO2
K+
Angiotensin II
Hormones
Prostaglandins
Adenosine
Nitric oxide
Endothelins
Myogenic
controls
Stretch
Antidiuretic
hormone (ADH)
Atrial
natriuretic
peptide (ANP)
Dilates
Constricts
Figure 19.15
Long-Term Autoregulation
• Angiogenesis
• Occurs when short-term autoregulation cannot
meet tissue nutrient requirements
• The number of vessels to a region increases
and existing vessels enlarge
• Common in the heart when a coronary vessel
is occluded, or throughout the body in people
in high-altitude areas
Blood Flow: Skeletal Muscles
• At rest, myogenic and general neural
mechanisms predominate
• During muscle activity
• Blood flow increases in direct proportion to the
metabolic activity (active or exercise hyperemia)
• Local controls override sympathetic
vasoconstriction
• Muscle blood flow can increase 10 or more
during physical activity
Blood Flow: Brain
• Blood flow to the brain is constant, as neurons
are intolerant of ischemia
• Metabolic controls
• Declines in pH, and increased carbon dioxide
cause marked vasodilation
• Myogenic controls
• Decreases in MAP cause cerebral vessels to
dilate
• Increases in MAP cause cerebral vessels to
constrict
Blood Flow: Brain
• The brain is vulnerable under extreme
systemic pressure changes
• MAP below 60 mm Hg can cause syncope
(fainting)
• MAP above 160 can result in cerebral edema
Blood Flow: Skin
• Blood flow through the skin
• Supplies nutrients to cells (autoregulation in
response to O2 need)
• Helps maintain body temperature (neurally
controlled)
• Provides a blood reservoir (neurally controlled)
Arteriole
Venule
Interstitial fluid
Net HP—Net OP
(35—0)—(26—1)
Net
HP
35
mm
Capillary
Net
OP
25
mm
NFP (net filtration pressure)
is 10 mm Hg; fluid moves out
Net HP—Net OP
(17—0)—(26—1)
Net
HP
17
mm
Net
OP
25
mm
NFP is ~8 mm Hg;
fluid moves in
HP = hydrostatic pressure
• Due to fluid pressing against a wall
• “Pushes”
• In capillary (HPc)
• Pushes fluid out of capillary
• 35 mm Hg at arterial end and
17 mm Hg at venous end of
capillary in this example
• In interstitial fluid (HPif)
• Pushes fluid into capillary
• 0 mm Hg in this example
OP = osmotic pressure
• Due to presence of nondiffusible
solutes (e.g., plasma proteins)
• “Sucks”
• In capillary (OPc)
• Pulls fluid into capillary
• 26 mm Hg in this example
• In interstitial fluid (OPif)
• Pulls fluid out of capillary
• 1 mm Hg in this example
Figure 19.17
Circulatory Shock
• Hypovolemic shock: results from large-scale
blood loss
• Vascular shock: results from extreme
vasodilation and decreased peripheral
resistance
• Cardiogenic shock results when an inefficient
heart cannot sustain adequate circulation
Acute bleeding (or other events that cause
blood volume loss) leads to:
1. Inadequate tissue perfusion
resulting in O2 and nutrients to cells
2. Anaerobic metabolism by cells, so lactic
acid accumulates
3. Movement of interstitial fluid into blood,
so tissues dehydrate
Chemoreceptors activated
(by in blood pH)
Major effect
Baroreceptor firing reduced
(by blood volume and pressure)
Initial stimulus
Physiological response
Signs and symptoms
Result
Hypothalamus activated
(by pH and blood pressure)
Brain
Minor effect
Activation of
respiratory centers
Cardioacceleratory and
vasomotor centers activated
Heart rate
Sympathetic nervous
system activated
Neurons
depressed
by pH
ADH
released
Intense vasoconstriction
(only heart and brain spared)
Central
nervous system
depressed
Kidney
Renal blood flow
Adrenal
cortex
Renin released
Angiotensin II
produced in blood
Aldosterone
released
Rate and
depth of
breathing
CO2 blown
off; blood
pH rises
Tachycardia,
weak, thready
pulse
Skin becomes
cold, clammy,
and cyanotic
Kidneys retain
salt and water
Water
retention
Urine output
Thirst
Restlessness
(early sign)
Coma
(late sign)
Blood pressure maintained;
if fluid volume continues to
decrease, BP ultimately
drops. BP is a late sign.
Figure 19.18
R. external
carotid artery
R. axillary
R. internal
carotid artery
R. vertebral
R. common carotid
– right side of head and neck
R. subclavian
– neck and
R. upper limb
Brachiocephalic
– head, neck, and
R. upper limb
Arteries of
R. upper
limb
L. external
carotid artery
L. internal
carotid artery
L. common carotid
– left side of head and neck
L. vertebral
L. subclavian
– neck and L.
upper limb
Aortic arch
L. axillary
Arteries of
L. upper
limb
Ascending aorta
– L. ventricle to sternal angle
Thoracic aorta T5 – T12 (diaphragm)
L. and R. coronary
arteries
L. ventricle of heart
Parietal branches
Visceral branches
Mediastinal
– posterior
mediastinum
Esophageal
– esophagus
Bronchial
– lungs and
bronchi
Pericardial
– pericardium
Posterior intercostals
– intercostal muscles, spinal
cord, vertebrae, pleurae, skin
Superior phrenics
– posterior and superior
diaphragm
Diaphragm
Abdominal aorta T12 (diaphragm) – L4
Parietal branches
Visceral branches
Gonadal
– testes or
ovaries
Suprarenal
– adrenal
glands
and
Renal
– kidneys
Superior
and inferior
mesenterics
– small
intestine
– colon
Celiac trunk
– liver
– gallbladder
– spleen
– stomach
– esophagus
– duodenum
R. common iliac
– pelvis and R. lower limb
Arteries of R. lower limb
Inferior phrenics
– inferior diaphragm
Lumbars
– posterior
abdominal
wall
Median sacral
– sacrum
– coccyx
L. common iliac
– pelvis and L. lower limb
(a) Schematic flowchart
Arteries of L. lower limb
Figure 19.21a
Arteries of the head and trunk
Internal carotid artery
External carotid artery
Common carotid arteries
Vertebral artery
Subclavian artery
Brachiocephalic trunk
Aortic arch
Ascending aorta
Coronary artery
Thoracic aorta (above
diaphragm)
Celiac trunk
Abdominal aorta
Superior mesenteric artery
Renal artery
Gonadal artery
Common iliac artery
Inferior mesenteric artery
Internal iliac artery
(b) Illustration, anterior
view
Arteries that supply
the upper limb
Subclavian artery
Axillary artery
Brachial artery
Radial artery
Ulnar artery
Deep palmar arch
Superficial palmar arch
Digital arteries
Arteries that supply
the lower limb
External iliac artery
Femoral artery
Popliteal artery
Anterior tibial artery
Posterior tibial artery
Arcuate artery
Figure 19.21b
Ophthalmic artery
Basilar artery
Vertebral artery
Internal
carotid artery
External
carotid artery
Common
carotid artery
Thyrocervical
trunk
Costocervical
trunk
Subclavian
artery
Axillary
artery
Branches of
the external
carotid artery
• Superficial
temporal artery
• Maxillary artery
• Occipital artery
• Facial artery
• Lingual artery
• Superior thyroid
artery
Larynx
Thyroid gland
(overlying trachea)
Clavicle (cut)
Brachiocephalic
trunk
Internal thoracic
artery
(b) Arteries of the head and neck, right aspect
Figure 19.22b
Anterior
Frontal lobe
Optic chiasma
Cerebral arterial
circle
(circle of Willis)
• Anterior
communicating
artery
• Anterior
cerebral artery
• Posterior
communicating
artery
• Posterior
cerebral artery
Basilar artery
Middle
cerebral
artery
Internal
carotid
artery
Mammillary
body
Temporal
lobe
Pons
Occipital lobe
Vertebral artery
Cerebellum
Posterior
(d) Major arteries serving the brain (inferior view, right side
of cerebellum and part of right temporal lobe removed)
Figure 19.22d
Vertebral artery
Thyrocervical trunk
Suprascapular artery
Costocervical trunk
Thoracoacromial artery
Axillary artery
Posterior circumflex
humeral artery
Anterior circumflex
humeral artery
Subscapular artery
Brachial artery
Deep artery of arm
Common
interosseous
artery
Common carotid
arteries
Left subclavian artery
Right subclavian artery
Brachiocephalic trunk
Posterior intercostal
arteries
Anterior intercostal
artery
Internal thoracic artery
Descending aorta
Lateral thoracic artery
Radial artery
Ulnar artery
Deep palmar arch
Superficial palmar arch
Digital arteries
(b) Illustration, anterior view
Figure 19.23b
Liver (cut)
Inferior vena cava
Diaphragm
Esophagus
Celiac trunk
Common hepatic
artery
Hepatic artery
proper
Gastroduodenal
artery
Right gastric artery
Gallbladder
Left gastric
artery
Stomach
Splenic artery
Pancreas
(major portion lies
posterior to stomach)
Right
gastroepiploic
artery
Superior
mesenteric
mesenteric
Duodenum
Abdominal aorta
Left
gastroepiploic
artery
Spleen
(b) The celiac trunk and its major branches. The left half of the liver has been removed.
Figure 19.24b
Hiatus (opening)
for inferior
vena cava
Hiatus (opening)
for esophagus
Adrenal
(suprarenal)
gland
Kidney
Celiac trunk
Abdominal aorta
Lumbar arteries
Ureter
Median sacral
artery
Diaphragm
Inferior
phrenic artery
Middle
suprarenal
artery
Renal artery
Superior
mesenteric
artery
Gonadal
(testicular or
ovarian) artery
Inferior
mesenteric
artery
Common
iliac artery
(c) Major branches of the abdominal aorta.
Figure 19.24c
Popliteal artery
Anterior tibial artery
Posterior tibial
artery
Lateral plantar
artery
Medial plantar
artery
Fibular artery
Dorsalis pedis artery
(from top of foot)
Plantar arch
(c) Posterior view
Figure 19.25c
Common iliac artery
Internal iliac artery
Superior gluteal artery
External iliac artery
Deep artery of thigh
Lateral circumflex
femoral artery
Medial circumflex
femoral artery
Obturator artery
Femoral artery
Adductor hiatus
Popliteal artery
Anterior tibial artery
Posterior tibial artery
Fibular artery
Dorsalis pedis artery
Arcuate artery
Dorsal metatarsal
arteries
(b) Anterior view
Figure 19.25b
Veins of the head and trunk
Dural venous sinuses
External jugular vein
Vertebral vein
Internal jugular vein
Right and left
brachiocephalic veins
Superior vena cava
Great cardiac vein
Hepatic veins
Splenic vein
Hepatic portal vein
Renal vein
Veins that drain
the upper limb
Subclavian vein
Axillary vein
Cephalic vein
Brachial vein
Basilic vein
Median cubital vein
Ulnar vein
Radial vein
Digital veins
Veins that drain
the lower limb
Superior mesenteric
vein
Inferior vena cava
Inferior mesenteric vein
External iliac vein
Common iliac vein
Popliteal vein
Internal iliac vein
Posterior tibial vein
Femoral vein
Great saphenous vein
Anterior tibial vein
(b) Illustration, anterior
view. The vessels of the
pulmonary circulation
are not shown.
Small saphenous vein
Dorsal venous arch
Dorsal metatarsal veins
Figure 19.26b
Brachiocephalic veins
Right subclavian vein
Axillary vein
Brachial vein
Cephalic vein
Basilic vein
Median cubital vein
Internal jugular vein
External jugular vein
Left subclavian vein
Superior vena cava
Azygos vein
Accessory hemiazygos
vein
Hemiazygos vein
Posterior intercostals
Inferior vena cava
Ascending lumbar vein
Median antebrachial
vein
Cephalic vein
Basilic vein
Radial vein
Ulnar vein
Deep palmar venous arch
Superficial palmar venous arch
Digital veins
(b) Anterior view
Figure 19.28b
Hepatic veins
Inferior vena cava
Right suprarenal
vein
Right gonadal
vein
Inferior phrenic
vein
Left suprarenal
vein
Renal veins
Left ascending
lumbar vein
Lumbar veins
Left gonadal vein
Common iliac
vein
Internal iliac vein
External iliac
vein
(b) Tributaries of the inferior vena cava. Venous drainage
of abdominal organs not drained by the hepatic portal vein.
Figure 19.29b
Inferior vena cava
(not part of hepatic
portal system)
Hepatic veins
Liver
Hepatic portal
vein
Small intestine
Gastric veins
Spleen
Inferior vena cava
Splenic vein
Right gastroepiploic
vein
Inferior
mesenteric vein
Superior
mesenteric vein
Large intestine
Rectum
(c) The hepatic portal circulation.
Figure 19.29c
Common iliac vein
Internal iliac vein
External iliac vein
Inguinal ligament
Femoral vein
Great saphenous
vein (superficial)
Popliteal vein
Small saphenous
vein
Fibular vein
Anterior tibial vein
Dorsalis pedis vein
Dorsal venous arch
Dorsal metatarsal
veins
(b) Anterior view
Figure 19.30b
Superficial temporal
vein
Occipital vein
Posterior
auricular vein
External
jugular vein
Ophthalmic vein
Facial vein
Vertebral vein
Internal jugular
vein
Superior and middle
thyroid veins
Brachiocephalic
vein
Subclavian vein
Superior
vena cava
(b) Veins of the head and neck, right superficial aspect
Figure 19.27b
Superior sagittal
sinus
Falx cerebri
Inferior sagittal
sinus
Cavernous
sinus
Straight sinus
Confluence
of sinuses
Transverse
sinuses
Sigmoid sinus
Jugular foramen
Right internal
jugular vein
(c) Dural venous sinuses of the brain
Figure 19.27c