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Biology 232
Human Anatomy and Physiology
Chapter 21 Lecture Outline
CARDIOVASCULAR SYSTEM – BLOOD VESSELS
Arteries – muscular, elastic vessels: carry blood away from the heart
Arterioles – smaller branches of arteries
Capillaries – tiny, thin-walled vessels; site of exchange of substances between
blood and tissues
Venules – small branches which merge to form veins
Veins – large, relatively thin-walled vessels; carry blood to the heart
(vasa vasorum – vasculature of large vessels)
Systemic Circuit
arteries carry oxygenated blood away from heart
veins carry deoxygenated blood to the heart
Pulmonary Circuit
arteries carry deoxygenated blood away from heart
veins carry oxygenated blood to the heart
ARTERIES
3 layers (tunics):
tunica interna (intima) – inner layer
endothelium – simple squamous epithelium
basement membrane
internal elastic membrane – elastic connective tissue
tunica media – middle layer; usually thickest
circular smooth muscle cells and elastic fibers
tunica externa – outer layer
connective tissue with elastic and collagen fibers
contains nerve endings (and blood vessels)
elastic fibers allow arteries to stretch, then recoil to original size
smooth muscle allows changes in vessel diameter
vasoconstriction – decreased diameter
vasodilation – increased diameter
Elastic Arteries – largest diameter, closest to heart
(aorta and its main branches, pulmonary trunk and arteries)
higher proportion of elastic fibers in tunica media
fewer smooth muscle fibers
pressure reservoirs
stretch to accommodate surge of blood from heart
store mechanical energy to recoil and move blood forward
conducting arteries – conduct blood from heart to arterial branches
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Muscular Arteries – medium diameter
higher proportion of muscle; fewer elastic fibers
distributing arteries – distribute blood to different body regions
eg. brachial arteries to arms, femoral arteries to legs
Arterioles – small diameter branches in tissues
deliver blood to capillaries
have decreasing amounts of muscle and connective tissue as they get
closer to capillaries
smallest are endothelium with a few muscle fibers
resistance vessels – control resistance (opposition to blood flow)
resistance is due to friction between blood and vessel walls
smaller vessel = greater resistance
regulate resistance by vasoconstriction and vasodilation
CAPILLARIES – microscopic vessels
endothelial layer + basement membrane
no tunica media (muscle) or tunica externa
exchange vessels – site of diffusion of materials between blood and tissues
found in most tissues; number depends on metabolic needs of tissue
branch extensively – large surface area for exchange
capillary bed – 10-100 capillaries supplying a tissue region
metarteriole/ thoroughfare channel
direct path from arteriole to venule
forms a capillary bypass
precapillary sphincters – regulate blood flow into capillaries or
thoroughfare channel
alternately open and close based on needs of tissue
Types of Capillaries:
continuous capillaries – least permeable; found in most tissues
intercellular gaps – spaces between endothelial cells
water, small solutes, lipid-soluble materials can cross through
fenestrated capillaries – more permeable
intercellular gaps +
fenestrations – pores in endothelial cells
found at sites of filtration, absorption, and secretion
kidneys, choroid plexuses of brain, ciliary processes
also in small intestine, endocrine glands
sinusoids – large, most permeable
large intercellular gaps
large fenestrations
incomplete basement membranes
found at sites for protein and cellular exchange
red bone marrow, spleen, liver
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Venules
carry blood from capillaries to veins
very thin-walled near capillaries – site of some exchange
muscle and connective tissue in walls increases as they get farther from capillaries
VEINS
3 tunics:
tunica interna
endothelium
basement membrane
(no internal elastic lamina)
tunica media
thin muscle layer with few elastic fibers
tunica externa – thickest layer
collagen and elastic fibers
allow some stretching, but easily damaged by high pressure
valves – one-way cusps that prevent backflow of blood
pressure in veins is too low to keep blood flowing against gravity
varicose veins – dilated veins due to leaky valves
Collateral Circulation – alternate pathway for blood flow in a region if one vessel
becomes blocked
anastamoses – connections between arteries/arterioles supplying adjacent
regions (also occur in veins and venules)
end artery – artery that doesn’t anastamose
infarction – death of tissue due to blockage of an end artery
myocardial infarction = heart attack (heart muscle dies)
HEMODYNAMICS – forces involved in circulating blood
blood flow – volume of blood passing through a tissue/minute
total blood flow = cardiac output(CO)
factors affecting blood flow:
pressure difference – greater difference = greater flow
vascular resistance – greater resistance = less flow
Vascular Resistance (R) – opposition to flow due to friction between blood
and vessel wall
depends on:
1) diameter of vessel lumen
R is inversely proportional to diameter4
half the diameter = 16X the resistance
twice the diameter = 1/16 the resistance
regulated by vasoconstriction and vasodilation
arteriosclerosis
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2) blood viscosity
thicker blood = increased resistance
depends mainly on ratio of blood cells to plasma
(plasma proteins have a lesser effect on viscosity)
dehydration
polycythemia (increased RBCs)
3) blood vessel length
longer blood vessel = greater resistance
obesity
Blood Pressure – hydrostatic pressure of blood on the walls of an artery;
pressure delivering blood to tissue capillaries
sphygmomanometer – used to measure systemic blood pressure
brachial artery
systolic pressure – highest arterial pressure (120mmHg)
produced by left ventricular systole
diastolic pressure – lowest arterial pressure (80mmHg)
during ventricular diastole; maintained by elastic rebound
in arteries and arterioles
pulse – waves of pressure through arteries and arterioles
pulse pressure = systolic BP – diastolic BP (40mmHg)
disappears in capillaries
Mean Arterial Pressure (MAP) – average pressure in arteries
MAP = diastolic BP + 1/3(pulse pressure)
100mmHg at aorta
decreases farther from heart
Capillary pressure – pressure in capillaries
35mmHg at beginning of capillaries
18mmHg at end of capillaries
Venous pressure – pressure in veins
18mmHg to 2mmHg at R atrium
Blood Flow Rate (Velocity)
rate is determined by blood pressure and total cross-sectional area of vessels
Arteries – very high pressure = rapid flow
Arterioles – decreasing pressure = decreasing velocity
Capillaries – low pressure and very large cross-sectional area
very slow flow – allows time for exchange
Veins – low pressure, but decreasing cross-sectional area
flow rate increases, but is still slow
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Venous Return
low pressure difference is barely enough to overcome gravity
(18mmHg – 2mmHg)
syncope – fainting due to insufficient blood to brain
Aids to Venous Return:
valves – one-way
skeletal muscle pump – contraction of limb muscles compresses vein;
“milks” blood through vein with help of valves
respiratory pump
diaphragm moves downward during inhalation
pressure in abdominal cavity increases
pressure in thoracic cavity decreases
venous blood flows from high pressure in abdominal vessels
to low pressure in throracic vessels
veins and venules serve as blood reservoirs (capacitance vessels)
expand easily to contain slow-flowing blood (esp. liver, skin, marrow)
contain 60% of blood volume at rest
venoconstriction returns more blood to the heart when needed
eg. hemorrhage, exercise
venodilation occurs at rest
CAPILLARY EXCHANGE – purpose of cardiovascular system
Diffusion – solutes exchanged from high concentration to low concentration
diffusion from blood into cells – oxygen, nutrients, hormones
diffusion from cells into blood – carbon dioxide, wastes, hormones
diffusion occurs through intracellular gaps, fenestrations, ion channels,
through cell membranes (lipid-soluble materials)
plasma proteins and blood cells only diffuse through sinusoids
Bulk Flow – pressure driven movement of fluid across a porous membrane
(water and solutes small enough to fit through pores)
FILTRATION – bulk flow from blood  interstitial fluid
REABSORPTION – bulk flow from interstitial fluid  blood
Pressures That Promote Filtration:
capillary hydrostatic pressure (CHP)
physical pressure due to blood pressure
pushes fluid out of capillaries
interstitial colloid osmotic pressure (ICOP) – very low
osmotic pressure due to interstitial proteins
pulls fluid out of capillaries
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Pressures That Promote Reabsorption:
blood colloid osmotic pressure (BCOP)
osmotic pressure due to plasma proteins
pulls fluid into capillaries
interstitial hydrostatic pressure (IHP) – near zero
physical pressure of fluid in interstitial space
pushes fluid into capillaries
Net Filtration Pressure (NFP) – indicates net fluid movement
NFP = (CHP - IHP) – (BCOP - ICOP)
positive NFP – filtration occurs
negative NFP – reabsorption occurs
85% of filtered fluid is reabsorbed
excess returned to blood by lymphatic system
edema – tissue swelling due to filtration exceeding reabsorption
REGULATION OF BLOOD PRESSURE AND BLOOD FLOW
tissue perfusion – amount of blood being supplied to tissues; must supply needs
of tissues for oxygen and nutrients, and removal of wastes
blood pressure depends on:
cardiac output
heart rate
stroke volume – preload, contractility, afterload
vascular resistance
AUTOREGULATION OF CAPILLARY BEDS
based on metabolic needs of tissues
release of local factors that cause dilation or constriction of arterioles
and precapillary sphincters
vasodilators
< oxygen, > carbon dioxide
metabolic by-products
potassium, hydrogen ions, lactic acid, adenosine
trauma, allergy – histamine from basophils and mast cells
nitric oxide from endothelial cells
> tissue temperature
vasoconstrictors
tissue trauma
platelets – prostaglandins, thromboxanes
endothelial cells – endothelins
NEURAL REGULATION
Cardiovascular Center – medulla
cardiac center - regulates cardiac output see chapter 20
heart rate
contractility
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vasomotor center – regulates vascular resistance
sympathetic vasomotor neurons
maintain vasomotor tone in arterioles
stimulate contraction of tunica media
controls diameter of muscular arteries and arterioles
< diameter = > resistance = > BP
causes venoconstriction – increases venous return to heart
> preload = > CO = > BP
baroreceptor reflexes
stretch receptors in aortic sinus and carotid sinus
send impulses to CV center
low BP = increased sympathetic vasomotor tone
increased vasoconstriction & venconstriction
high BP = decreased sympathetic vasomotor tone
vasodilation and venodilation
chemoreceptor reflexes – detect levels of oxygen, carbon dioxide and
hydrogen ions
chemoreceptors in carotid bodies, aortic body
send impulses to CV center
increase sympathetic vasomotor tone due to:
low oxygen, high carbon dioxide or hydrogen ions
HORMONAL REGULATION
1) RAA system – stimulated by decreased blood flow to kidneys
angiotensin II – vasoconstriction (thirst, >CO)
aldosterone – kidneys retain sodium and water
increases blood volume
increases BP
2) ADH (vasopressin) – stimulated by dehydration or angiotensin II
vasoconstriction
kidneys retain water – increases blood volume
increases BP
3) erythropoietin – stimulated by hypoxia or < BP
increases formation of RBCs = increases blood volume
increases BP
4) adrenal medulla – sympathetic response
5) atrial natriuretic peptide (ANP) – stimulated by atrial stretching
vasodilation
blocks mechanisms that increase BP
decreases BP
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Shock – cardiovascular system fails to deliver adequate oxygen and nutrients to meet
cellular needs
4 Types:
hypovolemic shock – low blood volume
hemorrhage
dehydration – diarrhea, vomiting, sweating
diabetes – excessive urine production
cardiogenic shock – poor heart function
heart attack, valve problems, arrhythmias
vascular shock – decreased vascular resistance
anaphylactic shock – allergy vasodilators
neurogenic shock – CV center dysfunction (head trauma)
septic shock – bacterial toxins
obstructive shock – blockage of blood flow
pulmonary thromboembolism
signs and symptoms of shock
low BP – systolic <90mmHg
rapid HR
weak, rapid pulse
cool, pale, clammy skin and nausea (sympathetic effects)
impaired mental state
reduced urination and increased thirst
low plasma pH (lactic acid)
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SYSTEMIC ARTERIES
Ascending aorta
R & L coronary arteries – heart
Aortic Arch
Brachiocephalic trunk (right) – arm and head
R common carotid – head and neck
R internal carotid – brain
R external carotid – head
R subclavian
R vertebral – brain
R internal thoracic – ribs and chest
R axillary – shoulder
R brachial – arm
R radial – forearm and hand
R ulnar – forearm and hand
L common carotid – same branches as R
L subclavian – same branches as R
Descending Aorta:
Thoracic Aorta
R & L posterior intercostals – intercostal muscles, spine
Abdominal Aorta
Celiac trunk
L gastric – stomach and esophagus
Splenic – spleen, pancreas, stomach
Common hepatic – liver, stomach, duodenum
Superior mesenteric – small and large intestines
R & L renal – kidneys
R & L ovarian or testicular – gonads
Inferior mesenteric – large intestine
R & L common iliac
R & L internal iliac – pelvis, buttocks, genitals
R & L external iliac – abdominal wall, leg
R & L femoral – thigh
R & L popliteal – knee
R & L anterior tibial – crus and foot
R & L posterior tibial – crus and foot
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SYSTEMIC VEINS
Superior Vena Cava
Azygos – chest wall
R & L intercostals - ribs
R & L brachiocephalic
R & L internal jugular – brain
R & L vertebral – cervical spine
R & L subclavian
R & L external jugular – head and neck
R & L axillary – shoulder
R & L cephalic – lateral arm (superficial)
R & L brachial – arm
R & L radial – forearm and hand
R & L ulnar – forearm and hand
R & L basilic – medial arm (superficial)
R & L median cubital – anterior elbow
Inferior Vena Cava
R & L hepatic – liver
Hepatic Portal System (veincapillariesvein)
Hepatic portal vein
Superior mesenteric – small and large intestine
Splenic – spleen, pancreas, stomach
Inferior mesenteric – large intestine
L gastric – stomach
R & L renal – kidneys
R & L ovarian or testicular – gonads (L comes off L renal)
R & L common iliac
R & L internal iliac – pelvic region
R & L external iliac – leg
R & L femoral – thigh
R & L great saphenous – medial leg (superficial)
R & L popliteal – knee
R & L anterior tibial – crus and foot
R & L posterior tibial – crus and foot
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PULMONARY CIRCUIT
Pulmonary Trunk
R & L pulmonary arteries
Pulmonary capillaries
R & L pulmonary veins
FETAL CIRCULATION
VENOUS CIRCULATION:
Umbilical vein (from placenta - oxygenated)
some blood – Hepatic portal system
most blood – Ductus venosus (bypasses liver)
Inferior vena cava
HEART:
Foramen ovale (fossa ovalis when closed)
R atrium  L atrium
ARTERIAL CIRCULATION:
Ductus arteriosus (ligamentum arteriosum when closed)
pulmonary trunk  aorta
R & L internal iliac
R & L umbilical arteries  placenta
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