Chapter 21 the cardiovascular system blood vessels
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Chapter 21: The Cardiovascular System: Blood Vessels. Vessel Structure - General. All vessels same basic structure 3 wall layers (or tunics) Tunica adventitia (externa) - elastic and laminar fibers Tunica media thickest layer elastic fibers and smooth muscle fibers

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Chapter 21: The Cardiovascular System: Blood Vessels

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Chapter 21 the cardiovascular system blood vessels

Chapter 21: The Cardiovascular System: Blood Vessels


Vessel structure general

Vessel Structure - General

  • All vessels same basic structure

  • 3 wall layers (or tunics)

    • Tunica adventitia (externa) - elastic and laminar fibers

    • Tunica media

      • thickest layer

      • elastic fibers and smooth muscle fibers

    • Tunica interna (intima)

      • endothelium – non-stick layer

      • basement membrane

      • internal elastic lamina

  • Lumen - opening


Chapter 21 the cardiovascular system blood vessels

  • Structure/function relationship changes as move through cardiovascular tree

  • Tunic thickness and composition variable throughout cardiovascular tree


Vessel structure elastic arteries

Vessel Structure – Elastic Arteries

  • Elastic (conducting) arteries

    • Near heart

    • Thick walls

    • More elastic fiber, less smooth muscle

    • Lose elasticity with aging


Vessel structure elastic arteries1

Vessel Structure - Elastic Arteries

  • Aorta and elastic arteries

    • Can vasoconstrict or vasodilate

    • Large arteries expand, absorb pressure wave then release it with elastic recoil - Windkessel effect

    • Help to push blood along during diastole

    • With aging have less expansion and recoil


Vessel structure muscular arteries

Vessel Structure – Muscular Arteries

  • Muscular (distributing) arteries

    • Deliver blood to organs

    • More smooth muscle

    • Less elastic fibers


Vessel structure arterioles

Vessel Structure - Arterioles

  • Arterioles

    • Distribution of blood in organs

    • Composition varies depending on position - more muscle, less elasticity nearer heart

    • Regulate flow from arteries to capillaries

      • Flow = ΔP/R

      • vary resistance by changing vessels size

    • Site of blood pressure regulation


Vessel structure capillaries

Vessel Structure - Capillaries

  • Microcirculation connects arteries and veins

  • Found in nearly every tissue in body

    • Higher the metabolic rate, more capillaries in tissue

    • Muscle many caps (>600/mm2)

    • Cartilage none


Vessel structure capillaries1

Vessel Structure - Capillaries

  • Allow exchange of nutrients and wastes between blood and tissue

  • Capillary structure - simple

    • Basal lamina - connective tissue

    • Endothelial cells

  • Structure/function


Flow regulation

Flow Regulation

  • Regulation by vessels with smooth muscle

    • Metarterioles

      • connect arterioles to venules through capillary bed

      • allows flow through capillary bed w/out flow through caps


Flow regulation1

Flow Regulation

  • True capillaries

    • Pre-capillary sphincter

      • ring of smooth muscle

      • open/close to control flow

      • regulated by chemicals

    • Intermittent vasomotion – caps open for flow 5-10X min


Types of capillaries

Types of Capillaries

  • 3 types of capillaries

    • Continuous capillaries

      • continuous endothelial cells except for cleft between cells

      • tight junctions between endothelial cells prevent most things from leaving caps

      • most capillaries in body


Types of capillaries1

Types of Capillaries

  • Fenestrated capillaries

    • fenestrations (slits) allow for filtration of small substances

    • glomerular capillaries in kidney


Types of capillaries2

Types of Capillaries

  • Sinusoid capillaries

    • wider gaps between endothelial cells allowing RBC’s to exit the caps

    • found in liver


Vessel structure veins

Vessel Structure - Veins

  • Venules

    • Collect blood from caps carry it to veins

    • Structure changes with position

    • Become more vessel-like (walls) as move from capillaries


Vessel structure veins1

Vessel Structure – Veins

  • Veins

    • Interna thicker than arteries

    • Media thinner, less muscle

    • Externa thick

    • Valves

    • Pressure low

    • High compliance - change volume easily with small change in pressure

    • Varicose veins


Vessel structure histology

Vessel Structure - Histology

  • Very different morphology under light microscopy

  • Tunica media thickness differentiates artery from vein


Chapter 21 the cardiovascular system blood vessels

Artery Vein

Vein Artery


Vessel structure function

Vessel Structure/Function

  • At rest

    • 60% of blood located in veins and venules

    • Serve as reservoirs for blood, “storing” it until needed

    • Particularly veins of abdominal organs, skin

  • ANS regulates volume distribution

    • Vasoconstrict

    • Vasodilate

    • Open areas of circulation to be supplied with blood

      • veins at rest

      • caps during exercise

    • Can “shift” volumes to other areas as needed


Vessel structure function1

Vessel Structure/Function

 0.75 L/min

Rest

CO = 5 L/min


Vessel structure function2

Vessel Structure/Function

CO = 25 L/min

Heavy

Exercise

 20 L/min

 0.75 L/min

Rest

CO = 5 L/min


Physiology of circulation

Physiology of Circulation

  • Flow = ΔP/R

    • or CO = MAP/R

    • MAP - mean arterial pressure

    • Higher pressure to lower pressure with resistance (R) factor

  • Blood pressure

    • Pressure of blood on vessel wall

    • Measurement of pressure of a volume in a space

    • Systole/diastole - 120/80

    • BP falls progressively from aorta to O mm Hg at RA


Regulation of blood flow

Regulation of Blood Flow

  • Resistance - opposition to blood flow from blood and vessel wall friction

  • Factors that affect resistance (R)

    • Viscosity - V R

      • thickness of blood

      • dehydration, polycythemia

    • R proportional to vessel length

      • garden hose vs. straw

      • obesity

    • Vessel diameter

      • changes in diameter affect flow

        • vessel wall drag – blood cells dragging against the wall

        • laminar flow – layers of flow

      • R inverse proportional to radius4

        • decrease in r by 1/2R 16X

        • only important in vessels that can change their size actively


Regulation of pressure resistance

Regulation of Pressure, Resistance

  • Systemic vascular resistance (Total Peripheral Resistance - TPR)

    • All vascular resistance offered by systemic vessels

    • Which vessels change size?

    • Resistance highest in arterioles

    • Largest pressure drop occurs in arterioles

  • Relationship of radius to resistance in arterioles important due to smooth muscle in walls


Systemic blood pressure

Systemic Blood Pressure

  • Arterial Blood Pressure

    • Pulsatile in arteries due to pumping of heart

    • Systolic/diastolic

    • Pulse pressure = systolic (minus) diastolic

      • - Windkessel effect on pulse pressure?

        • - Decreases pulse pressure

      • - What is the effect of hardening of the arteries on pulse pressure?

        • - Increases pulse pressure


Systemic blood pressure1

Systemic Blood Pressure

  • Capillary Blood Pressure

    • Relatively low blood pressure

    • Low pressure good for caps because:

      • caps are fragile - hi pressure tears them up

      • caps are very permeable - hi pressure forces a lot of fluid out


Systemic blood pressure2

Systemic Blood Pressure

  • Venous return

    • Volume of blood flowing back to heart from systemic veins

    • Depends on pressure difference (ΔP) from beginning of venules (16 mmHg) to heart (0 mmHg)

    • Any change in RA pressure changes venous return


Chapter 21 the cardiovascular system blood vessels

  • Help for venous return

    • Skeletal muscle pump

      • muscles squeeze veins

      • force blood back to heart

      • valves prevent back flow

    • Respiratory pump

      • inhaling pulls air into lungs

      • helps to pull blood back into thorax


Velocity of blood flow

Velocity of Blood Flow

  • Velocity of blood flow - inversely related to total cross sectional area (CSA) of vessels

  • Aorta

    • Total CSA 3-5 cm2

    • Velocity 40 cm/sec

  • Capillaries

    • Total CSA 4500-6000 cm2

    • Velocity 0.1 cm/sec

  • Vena Cava

    • Total CSA 14 cm2 in vena cava

    • Velocity 5-20 cm/sec


Vessel structure function3

Vessel Structure - Function

  • Capillary Function

    • Site of exchange between blood and tissues

    • Delivery of nutrients and removal of wastes

    • Slow flow allows time for exchange

  • Mechanisms of nutrient exchange

    • Diffusion - O2, CO2, glucose, AA's, hormones diffuse down [ ] gradients

    • If lipid soluble, can travel through cell

    • If water soluble, between cells


Capillary fluid exchange

Capillary Fluid Exchange

  • Fluid movement

    • Fluid filtered and reabsorbed across capillary wall

    • Starling’s law of the capillaries

  • Forces driving the movement of fluid

    • Hydrostatic pressure capillary (HPc)

    • Hydrostatic pressure interstitial fluid (HPif)

    • Osmotic pressure capillary(OPc)

    • Osmotic pressure interstitial fluid (OPif)

  • Net filtration pressure (NFP) is a sum of all


Capillary fluid exchange1

Capillary Fluid Exchange

  • On average 85% of fluid filtered at arteriole end is reabsorbed at venular end


Maintaining blood pressure short term mechanisms cns

Maintaining Blood Pressure - Short Term Mechanisms - CNS

  • Neural Control - Cardiac centers in medulla

    • Vasomotor center

      • medullary area dedicated to control of blood vessels

      • sends sympathetic output to blood vessels

        • Vasoconstricts or vasodilates as needed

        • tone - normal amount of vasoconstriction or vasodilation

        • can vary tone which varies delivery of blood

      • receives input from different sources

        • baroreceptors

        • chemoreceptors


Maintaining blood pressure short term mechanisms cns reflexes

Maintaining Blood Pressure – Short term mechanisms – CNS reflexes

  • Baroreceptor initiated reflex

    • Located at carotid sinus and aortic arch

    • Monitor changes in blood pressure

    • Regulate activity of Sympathetic Nervous System (vascular tone)


Maintaining blood pressure short term mechanisms cns reflexes1

Maintaining Blood Pressure – Short term mechanisms – CNS reflexes

  • Chemoreceptor initiated reflexes

    • Carotid bodies, aortic bodies

    • Monitors changes in chemicals (O2, CO2, [H+])

    •  CO2,  H+, O2 (stresses) result in  sympathetic activity and  BP


Maintaining blood pressure short term mechanisms cns reflexes2

Maintaining Blood Pressure – Short term mechanisms – CNS reflexes

  • Influence of Higher Brain Centers (areas above medulla) - Cortex and Hypothalamus

    • Not involved in minute to minute regulation

    • Influence vasomotor center depending on conditions

      • public speaking

      • temperature regulation


Maintaining blood pressure short term mechanisms hormones

Maintaining Blood Pressure - Short Term Mechanisms - Hormones

  • Renin - Angiotensin - Aldosterone

    • Renin

      • enzyme from kidney

      • results in formation of Angiotensin II (AII)

    • AII

      • vasoconstrictor

      • stimulates ADH, thirst

      • stimulates aldosterone - Na+ reabsorption

    • Why/how would these things affect blood pressure?


Maintaining blood pressure short term mechanisms hormones1

Maintaining Blood Pressure - Short Term Mechanisms - Hormones

  • Adrenal medulla - Epi and Norepi

    •  CO (HR,  SV)

    • Constrict abdominal, cutaneous arterioles/venules

    • Dilate cardiac, skeletal muscle beds

  • Why/how would this affect blood pressure?


Maintaining blood pressure short term mechanisms hormones2

Maintaining Blood Pressure -Short Term Mechanisms - Hormones

  • Antidiuretic Hormone (ADH)

    • Osmoreceptors in hypothalamus

    • Retains fluid (inhibited by alcohol)

    • Vasoconstriction at high levels

  • Why/how would this affect blood pressure?


Maintaining blood pressure short term mechanisms hormones3

Maintaining Blood Pressure -Short Term Mechanisms - Hormones

  • ANP (atrial natriuretic peptide)

    • Released from atrial cells in response to BP

    • Vasodilator, Na+ and water loss, opposes Aldosterone

  • Why/how would this affect blood pressure?


Maintaining blood pressure long term regulation

Maintaining Blood Pressure - Long Term Regulation

  • Renal mechanism

    • Volume in a space

    • Regulate space in the short term – we just talked about it!

      • nervous control

      • hormones

    • Regulate volume in the long term

    • The kidneys!

      •  BP,  urine flow to  BP

      •  BP,  urine flow to  BP


Control of blood flow

Control of Blood Flow

  • Autoregulation (local control) - local automatic adjustment of blood flow to match tissue needs

    • Physical changes

      • Warming -  vasodilation

      • Cooling -  vasoconstriction

    • Chemical changes - metabolic products

      • Vasodilators

      • Vasoconstrictors

  • Myogenic control

    • smooth muscle controls resistance

    •  stretch  contraction,  stretch  relaxation


Blood flow in special areas

Blood Flow in Special Areas

  • Skeletal Muscle

    • Wide variability in amount of flow

    • Sympathetic regulation from brain in response to level of activity

      • α receptors - vasoconstrict

      • β receptors - vasodilate

    • Metabolic regulation in tissue

      • low O2 vasodilate to increase flow

      • hi O2 vasoconstrict to decrease flow

  • Brain

    • Very little variability in flow

    • Stores few nutrients so flow must be maintained!

    • Metabolic regulation


Blood flow in special areas1

Blood Flow in Special Areas

  • Skin

    • Supplies nutrients, aids in temperature regulation, provides a blood reservoir

    • Metabolic and sympathetic regulation

  • Lungs

    • Low pressure (25/10), low resistance

    • Flow regulated by O2 availability in the lungs

      • hi O2 vasodilate to increase flow – opposite to muscle

      • low O2 vasoconstrict to decrease flow – opposite to muscle

  • Heart

    • Variable flow depending on activity

    • Metabolic and sympathetic regulation


Regulation of blood pressure

Regulation of Blood Pressure

CO = MAP/R

MAP = CO x R


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