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BIOH122Human Biological Science 2
Session 6
Cardiovascular System 4–
Haemodynamics and
Vascular Routes
Bioscience Department
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Session Plan
o Haemodynamics
o Factors affecting blood flow
• Blood pressure
• Vascular resistance
• Venous return
• Velocity of blood flow
o Control of blood pressure
and blood flow
o Checking circulation
• Pulse
• Blood pressure
o Shock and homeostasis
o Vascular routes
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Haemodynamics and Factors
Affecting Blood Flow
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Factors affecting Blood Flow
o Blood flow: The volume of blood that flows through any
tissue in a given time period (in mL/min).
• Total blood flow is cardiac output (CO), the volume of blood that
circulates through systemic (or pulmonary) blood vessels each
minute
Cardiac output = stroke volume x heart rate
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Factors Affecting Blood Flow
o Factors affecting blood flow/circulation
• Pressure differences that drive the blood flow: Blood pressure
• Resistance to blood flow in specific blood vessels: Vascular resistance
• The volume of blood flowing back to the heart through the systemic veins: Venous return
• The speed of blood flow: Velocity of blood flow
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Blood Pressure
o Blood Pressure: the hydrostatic pressure exerted by
blood on the walls of a blood vessels
o Caused by: contraction of the ventricles
• Pressure highest in aorta
– 120 mm Hg during systole and 80 mm Hg during
diastole
• Pressure falls steadily in systemic circulation with
distance from left ventricle
‒ 35 mm Hg entering the capillaries
‒ 0 mm Hg entering the right atrium
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Blood Pressure
o Systolic blood pressure: The highest pressure attained in
arteries during systole
o Diastolic blood pressure: The lowest arterial pressure
during diastole.
o Mean arterial pressure (MAP): The average blood
pressure in arteries, is roughly one-third of the way
between the diastolic and systolic pressures.
MAP = diastolic BP+ 1/3 (systolic BP - diastolic BP)
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Blood Pressureo Factors affecting blood pressure:
• Cardiac output
• Blood volume
• Vascular resistance
• Elasticity of arteries
o Cardiac Output: Increase HR or SV then increase
cardiac output, leads to increase BP
o A decrease in blood volume will decrease BP. Cardiac
response will be to increase HR and SV.
• If decrease in blood volume >10% additional factors
are initiated. eg. Kidneys: Water retention increases
blood pressure
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Vascular Resistance
o Vascular Resistance: The opposition to blood flow due to
friction between blood and the walls of blood vessels
o Increased vascular resistance will increase Blood Pressure
o Factors affecting vascular resistance:
• Size of the blood vessel lumen:
– smaller vessels offer more resistance to blood flow
• Blood viscosity: Thickness of blood
– increase in viscosity increases resistance
• Total blood vessel length:
– the longer the vessel, the greater the resistance to flow
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Vascular Resistance
Systemic vascular resistance (SVR)/ Total peripheral
resistance (TPR):
o Refers to all the vascular resistances offered by systemic
blood vessels.
o Arterioles, capillaries, and venules—contribute the most
resistance.
o SVR mainly controlled by arterioles and therefore blood
pressure and blood flow to particular tissues—by
changing their diameters
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Venous Return
o Venous Return: The volume of blood flowing back to the
heart through the systemic veins, due to the pressure
generated by left ventricular contractions.
o Depends on:
• Pressure difference from venules (16 mm Hg) to right
atrium (0 mm Hg)
‒ if tricuspid valve is leaky then there is a buildup of
blood on the venous side of circulation
• Skeletal muscle pump
• Respiratory pump
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Venous Return
o Skeletal muscle pump:
• Contraction and relaxation of
skeletal muscles
• Opening and closure of
venous valves
o Respiratory pump:
• Diaphragm movement with
breathing
• Changes in thoracic pressure
and abdominal pressure
• Opening and closure of
venous valves
Action of the skeletal muscle pump in
returning blood to the heart
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Velocity of Blood Flow
o Blood flow decreases from the aorta to
arteries, slowest in capillaries and increases
as it returns to the heart.
o The relatively slow rate of flow through
capillaries aids the exchange of materials
between blood and interstitial fluid
o The velocity of blood flow is inversely related to the total cross-sectional
area of blood vessels; Blood flows most slowly where the total cross-sectional area of blood vessels is
the greatest
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Velocity of Blood Flow
o Circulation time is the time required for a drop of blood
to pass from the right atrium, through the pulmonary
circulation, back to the left atrium, through the systemic
circulation down to the foot, and back again to the right
atrium.
o In a resting person, circulation time normally is about 1
minute.
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Control of Blood Pressure and
Blood Flow
o Controlled by adjusting heart rate, stroke volume,
systemic vascular resistance, and blood volume.
o Through several interconnected negative feedback
mechanisms:
• Cardiovascular centre
• Nervous system
• Hormones
• Auto regulation
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Cardiovascular Center
o The cardiovascular center (CV): A group of neurons in
the medulla oblongata that regulates heart rate,
contractility, and blood vessel diameter
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Cardiovascular Center
o Input to CV from higher brain regions and sensory receptors
(Proprioceptors, baroreceptors and chemoreceptors)
o Output from the CV flows along sympathetic and
parasympathetic fibers.
• Sympathetic impulses along cardio accelerator nerves
increase heart rate and contractility.
• Parasympathetic impulses along vagus nerves decrease
heart rate.
• The sympathetic division also continually sends impulses
to smooth muscle in blood vessel walls via vasomotor
nerves. The result is a moderate state of tonic contraction
or vasoconstriction, called vasomotor tone
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Neural Regulation
of Blood Pressure
o Nervous system: Regulates blood pressure via negative feedback loops of two types of reflexes:
• Baroreceptor reflexes
• Chemoreceptor reflexes
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Neural Regulation of Blood
Pressureo Baroreceptors: Pressure-sensitive sensory neurons located
in the aorta, internal carotid arteries and other large arteries in the neck and chest.
o Function:
• Monitor stretching of the walls of blood vessels and the atria.
• Send impulses to the cardiovascular centre to help regulate blood pressure.
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Neural Regulation of Blood Pressure
• Baroreceptor reflexes:
• The carotid sinus reflex: Maintains normal blood pressure in the brain. Is initiated by baroreceptors in the wall of the carotid sinus.
• The aortic reflex: Maintains with general systemic blood pressure. Initiated by baroreceptors in the wall of the arch of the aorta
• If blood pressure falls →feedback from baroreceptors is decreased → the CV center reduces parasympathetic and increases sympathetic stimulation of the heart →increase in heart rate and force of contraction →increase cardiac output + vasoconstriction → blood pressure increases to the normal level.
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Neural Regulation of Blood
Pressureo Chemoreceptor Reflexes: Sensory receptors that monitor the
chemical composition of blood, located close to the
baroreceptors of the carotid sinus (carotid bodies) and arch of
the aorta (aortic bodies).
o Function:
• Detect changes in blood levels of O2, CO2, and H+
• Hypoxia, hypercapnia or acidosis → stimulates the chemoreceptors
to send impulses to the cardiovascular centre → cardiovascular
center Increases sympathetic stimulation to arterioles and veins →
Vasoconstriction and increase in blood pressure
• Provide input to the respiratory centre in the brain stem to
adjust the rate of breathingchanges breathing rates as well
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Hormonal Regulation of Blood
Pressure
o Hormones: several hormones help regulate blood
pressure and blood flow by altering cardiac output,
changing systemic vascular resistance, or adjusting the
total blood volume:
1. Renin-angiotensin-aldosterone system
• release of renin from renal cells in response to decrease in
Blood volume or decreased blood flow to kidney
• results in formation angiotensin II
– systemic vasoconstriction
– causes release of aldosterone (H2O and Na+
reabsorption)
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Hormonal Regulation of Blood
Pressure2. Epinephrine and norepinephrine
• Released from adrenal medulla in response to sympathetic stimulation of heart through CV
– increases heart rate and force of contraction
– causes vasoconstriction in skin and abdominal organs
– vasodilation in cardiac and skeletal muscle
3. ADH (Antidiuretic hormone)• released from the posterior pituitary in response to dehydration
or decreased blood volume.– causes vasoconstriction
4. ANP (atrial natriuretic peptide) • Released by cells in the atria of the heart when blood pressure
rises– causes vasodilation and a loss of salt and water in the urine
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Auto Regulation
of Blood Pressure
o Auto Regulation: The ability of a tissue to automatically
adjust its own blood flow to match its metabolic demand
for supply of O2 and nutrients and removal of wastes
o Stimuli to cause autoregulatory changes:
1. Physical changes:
– Warming promotes vasodilation, and cooling causes
vasoconstriction.
– myogenic response:smooth muscle in arteriole walls
contracts more forcefully when it is stretched and relaxes
when stretching lessens
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Auto Regulation
of Blood Pressure
2. Vasodilating and vasoconstricting chemicals:
‒ Vasodilators: K+, H+, lactic acid, and adenosine (from
metabolically active tissues) kinins and histamine (from
tissue trauma or inflammation), nitric oxide (from endothelial
cells)
‒ Vasoconstrictors: thromboxane A2, superoxide radicals,
serotonin (from platelets), and endothelins (from endothelial
cells)
3. Changes in O2 level:
– Systemic vessels dilate in response to low levels of O2
– Pulmonary vessels constrict in response to low levels of O2
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Checking circulation
Shock and Homeostasis
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Checking circulation
o Pulse: is a pressure wave created by alternate
expansion and recoil of an elastic artery after each
systole of the left ventricle
• Normal pulse rate: 70-80 beats/min at rest
– Tachycardia: Pulse rate over 100 beats/min
– Bradycardia: Pulse rate under 60 beat /min
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Checking circulation
o Blood pressure: the pressure in arteries generated by
the left ventricle during systole and the pressure
remaining in the arteries when the ventricle is in diastole.
o Instrument: sphygmomanometer
• Korotkoff sounds: The various sounds that are heard while
taking blood pressure
• Systolic blood pressure: blood pressure on arterial walls just
after ventricular contraction
• Diastolic blood pressure: Blood pressure in arteries during
ventricular relaxation
• Pulse pressure: The difference between systolic and diastolic
‒ normal ratio is 3:2:1 - systolic/diastolic/pulse pressure
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Shock and Homeostasis
o Shock: Failure of the cardiovascular system to deliver
enough O2 and nutrients to meet cellular metabolic
needs.
o Outcomes:
• inadequate perfusion
• cells forced to switch to anaerobic respiration
• lactic acid builds up
• cells and tissues become damaged and die
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Shock and Homeostasis
o Homeostatic Responses to Shock: negative feedback
systems that work to return cardiac output and arterial
blood pressure to normal
o Feedback systems:
• Activation of the renin–angiotensin–aldosterone
system.
• Secretion of antidiuretic hormone
• Activation of the sympathetic division of the ANS.
• Release of local vasodilators
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Disorders: Homeostatic Imbalances
o Hypertension: persistently elevated blood pressure as systolic
blood pressure of 140 mm Hg or greater and diastolic blood
pressure of 90 mm Hg or greater.
o Outcome: damage to the blood vessels, heart, brain, and
kidneys before it causes pain or other noticeable symptoms.
o Management:
• Lifestyle changes: losing weight, limiting alcohol intake, exercising,
reducing sodium intake, maintaining recommended dietary intake of
potassium, calcium, and magnesium, not smoking, and managing
stress.
• Various drugs: diuretics, beta blockers, vasodilators, and calcium
channel blockers have been used to successfully treat
hypertension.
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Disorders: Homeostatic Imbalances
o Primary hypertension: (approximately 90-95% of all
hypertension cases) persistently elevated blood pressure
that cannot be attributed to any particular organic cause.
o Secondary hypertension: (the remaining 5-10% of cases)
has an identifiable underlying cause such as
• obstruction of renal blood flow
• disorders that damage renal tissue,
• hypersecretion of aldosterone
• hypersecretion of epinephrine and norepinephrine by
pheochromocytoma, a tumour of the adrenal gland.
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Aging and the
Cardiovascular System
o General changes in CVS associated with aging
• decreased compliance of the aorta
• reduction in cardiac muscle fiber size
• reduced cardiac output and maximum heart rate
• increase in systolic pressure
o Total cholesterol and LDL increases, HDL decreases
o Increase prevalence of Congestive heart failure,
coronary artery disease and atherosclerosis
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Circulatory Routes
o Circulatory routes for blood flow: The organisation of
blood vessels into routes that deliver blood throughout
the body.
• Systemic circulation:
– coronary circulation
– cerebral circulation
– hepatic portal circulation
• Pulmonary circulation
• Foetal circulation
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Circulatory Routes
o Systemic circulation: from the left side of the heart to the
body and back to the right side of the heart
• Coronary circulation: which supplies the myocardium of the heart
• Cerebral circulation: which supplies the brain
• Hepatic Portal circulation: from the GI tract to the liver
o Pulmonary circulation: from the right-side of the heart to
the lungs and back to the left side of the heart
o Foetal circulation: from the foetal heart through the
umbilical cord to the placenta and back
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Systemic Circulation
o The systemic circulation: carries oxygen and nutrients to
body tissues and removes carbon dioxide and other
wastes and heat from the tissues.
o Oxygenated blood: supplied through systemic arteries
branching from the aorta that arise from left ventricle.
o Deoxygenated blood: returns to the heart through the
systemic veins that drain blood into the superior vena
cava, inferior vena cava, or coronary sinus, which in turn
empty into the right atrium.
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Aorta and its Branches
o Aorta: The largest artery
of the body
o Branches of Aorta:
• Ascending aorta
• Arch of aorta
• Descending aorta: Thoracic aorta
Abdominal aorta
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Ascending Aorta and Arch
o Ascending aorta:
• Right and left coronary
arteries
o Arch of aorta:
• Brachiocephalic trunk Right common carotid
artery
Right subclavian artery
• Left common carotid
artery
• Left subclavian artery
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Subclavian Branches
o Subclavian arteries: pass superior to the 1st rib
• Vertebral artery: supplies blood to the Circle of Willis on the base of the brain
• Axillary artery: in the armpit
• Brachial artery: in the arm
• Radial and Ulnar branches: in the forearm
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Common Carotid Branches
o Common Carotid arteries: passes superiorly into neck to supply structures in head
• External carotid arteries: supplies structures external to the skull as branches of maxillary and superficial temporal branches
• Internal carotid arteries: (contribute to the Circle of Willis) supply eyeballs and parts of brain
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Descending Aorta
o Descending
Aorta:
• Thoracic aorta
• Abdominal aorta
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Thoracic Aorta
o Thoracic aorta: a continuation of the arch of the aorta
o It begins at the level of the fourth and fifth thoracic intervertebral disc.
• Branches of Thoracic aorta:• Visceral branches: to viscera,
• Parietal branches: to body wall structures
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Abdominal Aorta
o Abdominal Aorta: continuation of the thoracic aorta after
it passes through the diaphragm
o It begins at the aortic hiatus in the diaphragm
o Branches of Abdominal Aorta:
• Visceral branches
• Parietal branches
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Visceral Branches off
Abdominal Aortao Unpaired Visceral Branches:
o Coeliac artery is first branch inferior to diaphragm
• left gastric artery, splenic artery, common hepatic artery
o Superior mesenteric artery lies in mesentery
• pancreaticoduodenal, jejunal, ileocolic, ascending and middle colic arteries
o Inferior mesenteric artery
• descending colon, sigmoid colon and rectal arteries
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Common Iliac
Arteries
o Common Iliac Arteries: The
abdominal aorta ends by
dividing into the right and
left common iliac arteries at
4th lumbar vertebrae
• External iliac arteries supply
lower extremity
• Internal iliac arteries supply
pelvic viscera
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Arteries of the Lower Extremity
o External iliac artery
become femoral
artery when it passes
under the inguinal
ligament and into the
thigh
o Femoral artery
becomes popliteal
artery behind the
knee
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Veins of the Systemic Circulation
o Drains blood from the entire
body and returns it to the
right side of the heart
o Deep veins: parallel the
arteries in the region
o Superficial veins: are found
just beneath the skin
o All venous blood drains to
either superior or inferior
vena cava, or the coronary
sinus
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Major Systemic Veins
o Major Systemic Veins: empty into the right atrium of the
heart
• Superior vena cava drains the head and upper
extremities
• Inferior vena cava drains the abdomen, pelvis and
lower limbs
• Coronary sinus is a large vein draining the heart
muscle back into the heart
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Hepatic Portal Circulation
o Hepatic portal system:
o A subdivision of systemic circulation
o Carries blood between two capillary networks, from
capillaries of the gastrointestinal tract to sinusoids of the
liver.
o Formed by union of splenic, superior mesenteric and
hepatic veins
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Hepatic Portal System
o Function:
o Collects blood from the
veins of the pancreas,
spleen, stomach,
intestines, and gallbladder
and directs it into the
hepatic portal vein of the
liver before it returns to the
heart.
o Enables nutrient utilization
and blood detoxification by
the liver
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Arterial Supply and Venous Drainage of Liver
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Readings and Resources
o Tortora, GJ & Derrickson, B 2014. Principles of Anatomy and Physiology, 14th edn, Wiley.
o Harris, P, Nagy, S & Vardaxis, N 2010, Mosby’s Dictionary of Medicine, Nursing and Health Professions, 2nd edn, Mosby Elsevier.
o Guyton, AC & Hall, JE 2011, Textbook of Medical Physiology, 12th edn, Saunders Elsevier.
o Marieb, EN & Hoehn, K 2010, Human Anatomy and Physiology, 8th edn, Benjamin Cummings Pearson.
o Moore, KL, Dalley, AF & Agur, AMR 2010, Clinically Orientated Anatomy, 6th edn, Lippincott, Williams & Wilkins.
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