The Cardiovascular System: Blood The Cardiovascular System: Blood Vessels and HemodynamicsVessels and Hemodynamics

A. Anatomy of blood vesselsA. Anatomy of blood vessels 1. Arteries1. Arteries a. Elastic (conducting) arteriesa. Elastic (conducting) arteries b. Muscular (distributing) b. Muscular (distributing) arteriesarteries c. Anastomosesc. Anastomoses 2. Arterioles2. Arterioles 3. Capillaries3. Capillaries 4. Venules4. Venules 5. Veins5. Veins 6. Blood distribution6. Blood distributionB. Capillary exchangeB. Capillary exchange a. Diffusiona. Diffusion b. Vesicular transportb. Vesicular transport c. Bulk flow (filtration and c. Bulk flow (filtration and reabsorption)reabsorption)

C. Hemodynamics: physiology of C. Hemodynamics: physiology of circulationcirculation 1. Velocity of blood flow1. Velocity of blood flow 2. Volume of blood flow2. Volume of blood flow a. Blood pressurea. Blood pressure b. Peripheral resistanceb. Peripheral resistance 3. Venous return3. Venous returnD. Control of blood pressure and blood D. Control of blood pressure and blood

flowflow 1. Cardiovascular center1. Cardiovascular center a. Input to cardiovascular centera. Input to cardiovascular center b. Output from cardiovascular b. Output from cardiovascular centercenter 2. Neural regulation2. Neural regulation a. Baroreceptorsa. Baroreceptors b. Chemoreceptorsb. Chemoreceptors 3. Hormonal regulation3. Hormonal regulation 4. Autoregulation (local control)4. Autoregulation (local control)E. Blood vessel routesE. Blood vessel routes

ArteriesArteries1. lumen1. lumen

2. tunica intima2. tunica intima

a. endotheliuma. endothelium

b. internal elastic laminab. internal elastic lamina

3. tunica media3. tunica media

4. tunica adventitia4. tunica adventitia

Arterial PropertiesArterial Properties

1. elasticity1. elasticity

2. contractility2. contractility

a. vasoconstrictiona. vasoconstriction

b. vasodilationb. vasodilation

Arterial TypesArterial Types1. elastic (conducting)1. elastic (conducting) a. elastina. elastin b. pressure reservoirsb. pressure reservoirs2. muscular (distributing)2. muscular (distributing) a. great contractilitya. great contractility b. blood shuntingb. blood shunting c. anastomosesc. anastomoses d. collateral circulationd. collateral circulation

Muscular Arteries

Muscular Arteries

Elasticarteries

ArteriolesArterioles

1. highest contractility1. highest contractility

2. blood shunting2. blood shunting

Routing of Blood FlowRouting of Blood Flow

CapillariesCapillaries

1. microscopic1. microscopic

2. distribution2. distribution

3. exchange3. exchange

4. simple squamous4. simple squamous

5. precapillary sphincters5. precapillary sphincters

6. vasomotion6. vasomotion

Endothelium basement membrane

Capillary TypesCapillary Types1. continuous1. continuous

2. fenestrated2. fenestrated

3. sinusoids3. sinusoids

Venules and VeinsVenules and Veins1. same basic tunics1. same basic tunics

2. larger lumen2. larger lumen

3. thinner tunica media3. thinner tunica media

4. very distensible4. very distensible

5. valves5. valves

Valve

Blood ReservoirsBlood Reservoirs

Skin, liver, andspleen

Capillary ExchangeCapillary Exchange

1. diffusion1. diffusion2. vesicular transport2. vesicular transport3. bulk flow3. bulk flow a. filtrationa. filtration b. reabsorptionb. reabsorption c. Starling's law of the capillariesc. Starling's law of the capillaries

What is vasomotion?What is vasomotion?

Bulk Flow is Dependent On Bulk Flow is Dependent On Four PressuresFour Pressures

1. blood hydrostatic pressure (BHP = 30 mm Hg-arterial)1. blood hydrostatic pressure (BHP = 30 mm Hg-arterial) (outward force) = 10 mm Hg-venous(outward force) = 10 mm Hg-venous

2. interstitial fluid hydrostatic pressure2. interstitial fluid hydrostatic pressure (IFHP = 0 to -3(suction) mm Hg) (inward force)(IFHP = 0 to -3(suction) mm Hg) (inward force)

3. blood colloid osmotic pressure3. blood colloid osmotic pressure (BCOP = 28 mm Hg) (inward force)(BCOP = 28 mm Hg) (inward force)

4. interstitital fluid osmotic pressure4. interstitital fluid osmotic pressure (IFOP = 8 mm Hg) (outward force)(IFOP = 8 mm Hg) (outward force)

Net Filtration Pressure Net Filtration Pressure (Arterial End)(Arterial End)

NFP = outward forces - inward forcesNFP = outward forces - inward forces = (BHP + IFOP) - (BCOP + IFHP)= (BHP + IFOP) - (BCOP + IFHP) = (30 + 8) - (28 + 0)= (30 + 8) - (28 + 0) = (38) - (28)= (38) - (28) = +10 mm Hg= +10 mm HgIf IFHP was (-3) then NFP = 13 mm HgIf IFHP was (-3) then NFP = 13 mm Hg

net flow of fluid is? out of the capillarynet flow of fluid is? out of the capillary (filtration)(filtration)

Net Filtration Pressure- Venous Net Filtration Pressure- Venous EndEnd

NFP = outward forces - inward forcesNFP = outward forces - inward forces = (BHP + IFOP) - (BCOP + IFHP)= (BHP + IFOP) - (BCOP + IFHP) = (10 + 8) - (28 + 0)= (10 + 8) - (28 + 0) = (18) - (28)= (18) - (28) = -10 mm Hg= -10 mm Hg

If IFHP was (-3) then NFP = -7 mm HgIf IFHP was (-3) then NFP = -7 mm Hg

net flow of fluid is? into of the capillarynet flow of fluid is? into of the capillary (reabsorption)(reabsorption)

The Forces of Capillary Filtration The Forces of Capillary Filtration and Absorptionand Absorption

Capillary ExchangeCapillary Exchange

Hemodynamics

Blood flow (ml/min)Perfusion (ml/min/g)Blood flow velocity (mm/sec)Cross-sectional area (cm2)

total cross sectional area

velocity

art

erio

les

(40

cm

2)

vein

s (

80

cm

2)

ven

ae

ca

vae

(8

cm

2 )

If total cross-sectional area then velocity (aorta to capillaries)

venu

les

(250

cm

2 )

If total cross-sectional area then velocity (capillaries to venae cavae) Relationship between blood flow velocity and total

cross-sectional area of the vascular tree

Flow α ∆Pressure Resistance

art

erie

s (2

0 c

m2 )

capillaries (2500 cm2)

12

00

mm

/se

c

15

mm

/se

c

0.4

mm

/se

c

5 m

m/s

ec

80

mm

/se

c (I

VC

)

Blood PressureBlood Pressure

1. What is blood pressure?1. What is blood pressure?

2. direct determinants of BP2. direct determinants of BP

a. cardiac output a. cardiac output

b. blood volume b. blood volume

c. peripheral resistancec. peripheral resistance

Volume of Blood FlowVolume of Blood Flow

CO = SV x HRCO = SV x HR = 5.25 L/min (the volume of blood circulating= 5.25 L/min (the volume of blood circulating through systemic or pulmonary through systemic or pulmonary vessels each minute)vessels each minute)

Two other factors influence cardiac output:Two other factors influence cardiac output: 1) blood pressure1) blood pressure 2) resistance (opposition)2) resistance (opposition)

CO = CO = mean arterial blood pressure (MABP)mean arterial blood pressure (MABP) resistance (R)resistance (R)

Resistance (Opposition to Flow)Resistance (Opposition to Flow)

1. blood viscosity1. blood viscosity

2. total blood vessel length2. total blood vessel length

3. blood vessel radius3. blood vessel radius

Systemic vascular resistance (SVR)Systemic vascular resistance (SVR)(total peripheral resistance (TPR)(total peripheral resistance (TPR) 1. major function of arterioles1. major function of arterioles2. vasodilation 2. vasodilation vsvs vasocontriction vasocontriction a. Blood flow is proportional to the fourth power of a. Blood flow is proportional to the fourth power of vessel radius.vessel radius. r = 1 mm r4 = 1r = 1 mm r4 = 144 = 1 flow = 1 mm/sec = 1 flow = 1 mm/sec r = 2 mm r4 = 2r = 2 mm r4 = 244 = 16 flow = 16 mm/sec = 16 flow = 16 mm/sec r = 3 mm r4 = 3r = 3 mm r4 = 344 = 81 flow = 81 mm/sec = 81 flow = 81 mm/sec

b. Therefore, a 3-fold change in resistance exerts b. Therefore, a 3-fold change in resistance exerts an an 81-fold change in velocity.81-fold change in velocity.

Mechanisms of Venous ReturnMechanisms of Venous Return

1. decreasing x-sec area1. decreasing x-sec area

2. venous valves2. venous valves

3. muscle pumps3. muscle pumps

4. respiratory pump4. respiratory pump

Control of Blood Pressure and Control of Blood Pressure and Blood FlowBlood Flow

The cardiovascular center (CVC) consists The cardiovascular center (CVC) consists of three groups of neurons:of three groups of neurons:

1. cardioacceleratory neurons1. cardioacceleratory neurons

2. cardioinhibitory neurons2. cardioinhibitory neurons

3. vasomotor neurons3. vasomotor neurons

CVC Input CVC Input

1. input1. input

a. higher brain centersa. higher brain centers

b. baroreceptorsb. baroreceptors

c. chemoreceptorsc. chemoreceptors

Nervous Input to Medullary Nervous Input to Medullary Cardiovascular CenterCardiovascular Center

higher brain cerebral cortex limbic system hypothalamus

medullaoblongata

baroreceptors(blood pressure)

chemoreceptors (O2, H+, CO2)

CVC Output CVC Output

2. output2. output

a. vagus (X) nervea. vagus (X) nerve

b. sympathetic neuronsb. sympathetic neurons

(1) heart(1) heart

(2) arterioles(2) arterioles

Nervous Output From Medullary Nervous Output From Medullary Cardiovascular CenterCardiovascular Center

heart(decrease rate)

heart (increase rateand contractility)

Medulla oblongata

blood vessels (vasoconstriction and vasodilation)

cardiac accelerator nerves (sympathetic)

vasomotor nerves (sympathetic)

vagus nerve (X)

Neural Control of the Heart Reflexes

carotid sinus and aortic sinus reflexesright atrial (Bainbridge) reflex

Reflexes activate the Vasomotor center – results in vasoconstriction/vasodilation of arteriolesBaroreflexes and chemoreflexes

Medullary ischemic reflexcarotid sinus baroreceptorssensory fibers in c.n. IX

aortic sinus baroreceptors

SA nodeAV node

parasympathetic fibers in c.n. X

sympathetic fibers in spinal nerves

cerebrum

hypothalamus

cardiovascular center in medulla

spinal cord

Baroreceptor ReflexBaroreceptor Reflex

Chemoreceptor ReflexChemoreceptor Reflex

Negative Feedback of Neural Control

CONTROLLED CONDITION

a stimulus or stress disrupts homeostasis by causing a decrease in blood pressure

RECEPTOR

RETURN TO HOMEOSTASIS

EFFECTORS

CONTROL CENTER

baroreceptors in carotid and aortic sinuses are stretched less, resulting in decreased

rate of nerve impulses to the cardiovascular center

1. increased sympathetic output via cardioacceleratory center2. decreased parasympathetic output from cardioinhibitory center

1. contractility = stroke volume2. heart rate therefore cardiac output

3. vasoconstriction = resistance

increased blood pressure

Hormonal RegulationHormonal Regulation1. epinephrine and norepinephrine1. epinephrine and norepinephrinepotent vasoconstrictor increased resistance increased BPincreased HR + increased SV = increased CO increased BP

2. antidiuretic hormone2. antidiuretic hormoneincreases water retention by kidneys increased blood volume increased BP

3. angiotensin II3. angiotensin IIpotent vasoconstrictor increased resistance increased BP

4. aldosterone4. aldosteronepromotes sodium retention by kidneysincreased water retention increased blood volume increased BP

5. atrial natriuretic peptide5. atrial natriuretic peptidedecreases sodium retention by kidneysdecreased water retention decreased blood volume decreased BP

AutoregulationAutoregulationAbility of tissues to regulate their own blood supplyMetabolic theory of autoregulation

Inadequate perfusion =A. Decreased O2 vasodilationB. Increased wastes (CO2, H+, K+, adenosine) vasodilation

Adequate perfusion again = vasoconstriction

Vasoactive Chemicals- secreted by platelets, endothelial cells, perivascular tissues with trauma - Examples include Histamine, prostaglandins, bradykinin stimulate vasodilation

Reactive hyperemia

Summary of Blood Pressure Controldecreased blood pressure

leads to

decreased activity of baroreceptors in carotid and aortic sinuses

leads to

decreased nervous input to cardioinhibitory center

leads to

increased activity of the:1.cardioacceleratory center2.vasomotor center

leads to

increased sympathetic output from spinal cord

norepinephrine secretion causes

increased blood pressure

increased stroke volumeincreased heart rate

leads to leads to

increased vasoconstriction

leads to

increased cardiac output

leads to

increased resistance

leads to

negative feedback

increased activity

increased activity

decreased activity

Blood Vessel Routes Blood Vessel Routes (see Handout)(see Handout)

Beginning of the AortaBeginning of the Aorta

Arterial Supply Head and NeckArterial Supply Head and Neck

Arterial Circle of the Brain- Circle Arterial Circle of the Brain- Circle of Willisof Willis

Arterial Supply to the Upper ArmArterial Supply to the Upper Arm

Arterial Supply to the ThoraxArterial Supply to the Thorax

Arterial Supply to the AbdomenArterial Supply to the Abdomen

Arterial Supply to the Pelvic Arterial Supply to the Pelvic Region and Lower LimbRegion and Lower Limb