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Ch. 12 – The Circulatory System

• A.k.a. thecardiovascularsystem

• Blood wasdiscussed in Ch. 11

• Focus of Ch. 12:heart and bloodvessels

The heart

• = the muscularpump of the CVsystem– ~ 100,000

heartbeats/day!• ~ 9000 liters of

blood/day!!

The heart is adouble pump

• Right heart:– Powers pulmonary

circuit– Pumps blood to and

from lungs– Receives blood

from systemiccircuit

• Left heart:– Powers systemic

circuit– Pumps blood to and

from rest of body– Receives blood

from pulmonarycircuit

A quick note onarteries vs. veins

• Definitions:– Arteries carry blood away from

the heart– Veins carry blood towards the

heart• About color:

– While most arteries aresystemic and carry oxygen-richblood (and thus are red), thepulmonary arteries are anotable exception

– While most veins are systemicand carry oxygen-poor blood(and thus are blue), thepulmonary veins are a notableexception

Pulmonary artery

Pulmonary vein

(to systemic circuit)

(from systemic circuit)

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Heart location and pericardium

• Pericardium:fibrous, multi-layered sac (withfluid between thelayers) thatsurrounds,protects, anchors,and lubricates theheart

Heart wall• Surrounded by

pericardium• Lined by thin, smooth

endocardium• Middle, thickest layer

is myocardium(cardiac muscletissue)– Thicker on

left side…why? ● Intercalated discs are

specialized junctions thatelectrically connect cells, allowrhythmic contraction

(Intercalated disc)

Some cardiac anatomy

Papillary muscles

A schematic heart

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Heart valves

• One-way valves; prevent backflow– Open when upstream pressure is higher– Close when downstream pressure is higher

• Closing of valves creates heart sounds (“lub-dup”)• Papillary muscles contract and tense chordae tendineae to prevent AV

valves from opening the wrong way (back into atria) when ventriclescontract

Coronarycirculation

• Feeds blood to themyocardium of theheart

Cardiac cycle= the events of oneheartbeat

Systole = contraction

Diastole = relaxationCardiac conduction system

• Sinoatrial (SA) node (“pacemaker”)spontaneously generates electricalimpulses – sets basic heart rate– No nervous or hormonal input

needed for heart to beat• However, autonomic nervous input

and/or hormonal input needed tochange heart rate ↑ or ↓

• Electrical impulses spread (like awave) cell to cell via intercalateddiscs, causing cardiac muscle tocontract rhythmically

Bundlebranches

His (AV bundle)

Purkinjefibers

down septum

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Electrocardiogram(ECG or EKG)

• = graphical recording of electricalactivity in body fluids (conducted fromheart)– Does not directly record muscle

contraction• ECG waves – record electrical

changes from baseline (0 mV)– P wave = electrical impulse

spreads through atria– QRS complex = electrical

impulse spreads throughventricles

• (Return of atria to restingelectrical state is hidden)

– T wave = ventricles return toresting electrical state

Blood vessels…and you!

Someexamples ofmajor blood

vessels

Maintypesof BVs

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Arteries

• Arteries – carry blood away from the heart– Higher pressure vessels

• Walls have lots of elastin (an elastic protein) towithstand pressure

– Pulse = stretch/recoil of arteries with each heartbeat

– Thick wall compared to lumen size• Walls have lots of smooth muscle that may

vasoconstrict (↓ vessel diameter) or vasodilate (↑vessel diameter) to specifically direct blood flow tocertain locations as needed

– Arterioles = really small arteries

Capillaries• Capillaries – exchange gases,

nutrients, wastes, etc. betweenblood and interstitial fluid– Microscopic, extremely thin-

walled, leaky– Form networks called capillary

beds to increase total surfacearea for exchange (see lowerright picture)

Capillary fluid exchange• Slightly more fluid leaves the capillaries for the tissues than

re-enters the capillaries from the tissues– The excess is returned to the circulation by the lymphatic system

Blood flow throughcapillary beds

• Precapillarysphincters maycontract (vasoconstrict)or relax (vasodilate) toadjust blood flow inresponse to metabolicneeds of differenttissues/organs

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Velocity of blood flow

• Flow slowsdown asbloodspreadsthroughoutcapillarybeds– So more

time forexchange

Veins• Veins – carry bloodtowards the heart– Lower pressure

vessels• So need skeletal muscle

contraction and one-wayvalves (in limbs) toaid venous returnto heart (oftenagainst gravity)

– Thin wallcompared tolumen size

– Venules =really small veins

Bloodpressure (BP)

• Systolic pressure =maximum BP generatedduring ventricularcontraction

• Diastolic pressure =minimum BP at end ofventricular relaxation

• BP typically reported as:

systolic pressure ≈ 120 mm Hgdiastolic pressure 80 mm Hg

• = the force exertedby blood againstthe wall of a vessel

A BVproblem

Some solutions?

Atherosclerosis

Balloon angioplasty

Coronarybypasssurgery

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Lymphatic systemComponents:• Lymph = excess interstitial fluid

that gets absorbed andtransported by…

• Lymphatic vessels = lowpressure tubes that ultimatelyreturn lymph to bloodstream

• Lymphoid tissues and organsthat contain lymphocytes andother supporting cells

General functions:• Return excess interstitial fluid to

bloodstream• Transport products of fat

digestion from small intestine tobloodstream

• Help defend against pathogens(= disease-causing organisms) –more detail in Ch. 13

Lymphatic capillaries• = tiny, low pressure tubes

that drain excess interstitialfluid

• Larger and morepermeable than bloodcapillaries

• Flaplike minivalves helpensure one-way flow

• Drain into largerlymphatic vessels

Flow of lymph• Lymphatic vessels

ultimately return lymphto cardiovascular systemat subclavian veins– Thoracic duct – drains lymph

from most of body, empties intoleft subclavian vein

– Right lymphatic duct – drainslymph from upper rightquadrant of body, empties intoright subclavian vein

• No pump, so lymph movesslowly, in same ways thatvenous blood moves(skeletal muscle contraction,one-way valves, breathing)

• Lymph passes throughlymph nodes on the way(see next slide)

Some lymphoidtissues and organs

Peyer’s patches• Keep bacteria from breaching

the intestinal wall