chapter 3 - · pdf filevelocity of blood flow o circulation time is the time required for a...

© Endeavour College of Natural Health endeavour.edu.au

BIOH122Human Biological Science 2

Session 6

Cardiovascular System 4–

Haemodynamics and

Vascular Routes

Bioscience Department

© Endeavour College of Natural Health endeavour.edu.au 2

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


Haemodynamics and Factors

Affecting Blood Flow


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


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


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


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)


Blood Pressure


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


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


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


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


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


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


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.


Control of Blood Pressure and

Blood Flow


Factors that Increase Blood Pressure


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


Cardiovascular Center

o The cardiovascular center (CV): A group of neurons in

the medulla oblongata that regulates heart rate,

contractility, and blood vessel diameter


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


Neural Regulation

of Blood Pressure

o Nervous system: Regulates blood pressure via negative feedback loops of two types of reflexes:

• Baroreceptor reflexes

• Chemoreceptor reflexes


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.


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.


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


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)


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


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


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


Checking circulation

Shock and Homeostasis



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



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



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



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


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.


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.


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


Circulatory Routes


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


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


Circulatory Routes


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.


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


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


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


Circle of Willis


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


Descending Aorta

o Descending

Aorta:

• Thoracic aorta

• Abdominal aorta


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


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


Abdominal Aorta


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


Visceral Branches of Abdominal Aorta


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


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


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


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


Major Systemic Veins


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


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


Arterial Supply and Venous Drainage of Liver


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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