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Home , Blood vessel, Cardiac output, Hemodynamics, Starling equation, Tunica externa, Tunica intima

Over 60,000 Cardiovascular System: Vessels miles of vessels per

Cardiovascular System – Vessels

Blood Vessel :

(branch / diverge / fork)

Elastic Muscular Arteries

Vessel Types: ( 1) Arteries (away from heart) exchange) 2) Capillaries 3) (toward heart)

Veins

(join / merge / converge)

Cardiovascular System – Vessels

Blood Vessel Anatomy:

O2-rich; CO2-poor Pulmonary circuit (short, low pressure loop)

O2-poor; CO2-rich (long, high pressure loop) Systemic circuit

O2-poor; O2-rich; CO2-rich CO2-poor

% / volume not fixed: Function: • Alteration of size 1) Circulate / waste • Alteration of 2) Regulate • Combination of two above

Costanzo (Physiology, 4th ed.) – Figure 4.1

1 Cardiovascular System – Vessels

Blood Vessel Anatomy: Only tunic present in capillaries Vessels composed of distinct tunics :

1) Tunica intima • (simple squamous ) • Connective ( elastic fibers)

2) • / elastic fibers • Regulates pressure / circulation • Sympathetic innervation Lumen Vasa 3) vasorum • Loose fibers • / & blood vessels • Protects / anchors vessel

Vasomotor stimulation = Tunica media relaxation = Tunica externa

Cardiovascular System – Vessels Relative tissue makeup

Blood Vessel Anatomy:

Arteriosclerosis:

Arteries: Hardening / stiffening of arteries

Endothelium

Elastic tissue Elastic Fibrous tissue Fibrous Major groups: muscleSmooth D = Diameter T = Thickness 1) Elastic Arteries (conducting arteries): D: 1.5 cm • Large, thick-walled (near heart) T: 1.0 mm •  [elastic fibers] (pressure reservior)

2) Muscular Arteries (distributing arteries): • Deliver blood to organs D: 6.0 mm T: 1.0 mm •  [smooth muscle] (vasoconstriction)

3) Arterioles: • Control blood into capillaries D: 37.0 m T: 6.0 m • Neural / hormonal / local controls

Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Table 19.1

Cardiovascular System – Vessels Relative tissue makeup

Blood Vessel Anatomy:

Capillaries:

Endothelium

Elastic tissue Elastic

Fibrous tissue Fibrous Smooth muscle Smooth 1) Capillaries: • Location of blood / tissue interface D: 9.0 m T: 1.0 m • Stabilized by (smooth muscle cells)

Types of Capillaries:

A) Continuous 2) Fenestrated 3) Sinusoidal: • Uninterrupted lining • Oval pores present • Holes / clefts present • Found throughout body • Located in high absorption / • Allow passage of large (most common type) filtration regions (e.g., ) molecules (e.g., )

Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Table 19.1 / Figure 19.3

2 Cardiovascular System – Vessels

Blood Vessel Anatomy: Capillaries:

Capillaries do not function independently – Instead they form interweaving networks called beds

Vascular True capillaries Not all capillaries are perfused shunt with blood at all times…

Terminal Postcapillary Precapillary sphincters arteriole • 10 - 100 capillaries / bed • Sphincters control blood flow a) Vascular shunt through capillary bed b) True capillaries Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 19.4

Cardiovascular System – Vessels Relative tissue makeup

Blood Vessel Anatomy:

Leukocyte

Veins: margination

Endothelium

Elastic tissue Elastic Fibrous tissue Fibrous Major groups: muscleSmooth

1) Venules: D: 20.0 m • Formed where capillaries unite T: 1.0 m • Extremely porous

2) Veins (capacitance vessels): D: 5.0 mm • Large lumen; “volume” sink T: 0.5 mm • Low pressure environment

Venous sinuses: Specialized, flattened veins composed only of endothelium; supported by surrounding tissues

Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 19.3 / 19.5

3 Cardiovascular System – Vessels Vascular anastomoses: Blood Vessel Anatomy: Regions where vessels unite, forming interconnections

Heart Heart

Venous anastomoses are common; blockages collateral rarely lead to tissue death Arteriovenous channels Arterial anastomoses provide alternative channels for blood to reach locations • Joints • Abdominal organs •

Retina, spleen, & kidney have Great saphenous limited collateral circulation vein harvest Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 19.2

Cardiovascular System – Vessels Would you want Pathophysiology: Most common form to find this pipe of arteriosclerosis in your house?

Atherosclerosis: Formation of (small, patchy thickenings) on wall of vessel; intrude into lumen

1) Endothelium injured 3) Fibrous plaque forms • / • Collagen / fibers deposited around dying or 2) accumulate / oxidize dead foam cells • LDLs collect on tunica intima 4) Plaque becomes unstable Foam cells: • Calcium collects in plaque engorged • Vessel constricts; arterial wall with LDLs; form frays / ulcerates (= )

Link Outcome: : • Myocardial Cholesterol-lowering drugs • • / Stent Bypass

Cardiovascular System – Vessels To stay alive, blood must : be kept moving…

Blood Flow: Volume of blood flowing past a point per given time (ml / min)

The velocity of blood flow is not related to proximity of heart, but depends on the diameter and cross-sectional area of blood vessels

v = Q / A

v = Velocity (cm / sec) Q = Flow (mL / sec) A = Cross-sectional area (cm2)

A = r2

Costanzo (Physiology, 4th ed.) – Figure 4.4

4 Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

Blood Flow: Volume of blood flowing past a point per given time (ml / min)

The velocity of blood flow is not related to proximity of heart, but depends on the diameter and cross-sectional area of blood vessels

v = Q / A Blood velocity is highest in the and lowest in the capillaries Capillaries

Artery Vein

Randall et al. (Eckert Animal Physiology, 5th ed.) – Figure 12.23

Cardiovascular System – Vessels v = Q / A

A man has a cardiac output of 5.5 L / min. The diameter of his aorta is estimated to be 20 mm, and the total cross-sectional area of his systemic capillaries is estimated to be 2500 cm2.

What is the velocity of blood flow in the aorta relative to the velocity of blood flow in the capillaries?

cm3 (1 cm) A = r2 A = (3.14) (10 mm)2 A = 3.14 cm2

(5500 mL) 5.5 L / min 5500 cm3 / min vcapillaries = vaorta = 2500 cm2 3.14 cm2 800x difference

vcapillaries = 2.2 cm / min vaorta = 1752 cm / min

Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

Blood flow through a blood vessel or a series of blood vessels is determined by blood pressure and peripheral resistance

Blood Pressure: per unit area on wall of vessel (mm Hg)

• The magnitude of blood flow is directly proportional to the size of the pressure difference between two ends of a vessel

Blood Flow (Q) = Difference in blood pressure ( P)

• The direction of blood flow is determined by the direction of the pressure gradient

Always moves from high to low pressure

5 Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

Heart generates initial pressure

Vessel resistance generates pressure gradient

Costanzo (Physiology, 4th ed.) – Figure 4.8

Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

Blood flow through a blood vessel or a series of blood vessels is determined by blood pressure and peripheral resistance

Peripheral Resistance: Amount of friction blood encounters passing through vessels (mm Hg / mL / min)

• Blood flow is inversely proportional to resistance encountered in the system

1 Blood Flow (Q) = Peripheral resistance (R)

The major mechanism for changing blood flow in the cardiovascular system is by changing the resistance of blood vessels, particularly the arterioles

Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

(difference in voltage) (current) Difference in blood pressure ( P) Blood Flow (Q) = Peripheral resistance (R) (electrical resistance)

Analogous to Ohm’s Law (V = I x R OR I = V / R)

Q = P / R A man has a renal blood flow of 500 mL / min. The renal atrial pressure R = P / Q is 100 mm Hg and the renal venous pressure is 10 mm Hg. 100 mm Hg – 10 mm Hg R = What is the of 500 mL / min the kidney for this man? R = 0.18 mm Hg / mL / min

6 Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

The factors that determine the resistance of a blood vessel to blood flow are expressed by Poiseuille’s (pwä-zwēz) Law:

Powerful relationship! R = Resistance 8Lη Slight diameter change R = η = of blood equals r4 L = Length large resistance change r = Radius

1) Blood viscosity 2) Vessel Length 3) Vessel Diameter

 viscosity =  resistance  length =  resistance  diameter =  resistance

Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

The total resistance associated with a set of blood vessels also depends on whether the vessels are arranged in series or in parallel

A) Series resistance:

Sequential arrangement (e.g., pathway within single )

Arteriolar resistance is the greatest which equates to the area with the greatest decrease in pressure

The total resistance is equal to the sum of the individual resistances

Costanzo (Physiology, 4th ed.) – Figure 4.5

Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

The total resistance associated with a set of blood vessels also depends on whether the vessels are arranged in series or in parallel

B) Parallel resistance:

Simultaneous arrangement (e.g., pathway among various circulations)

Adding a new resistance to the circuit causes total resistance to decrease

No loss of pressure in major arteries

Increasing the resistance in one circuit causes total resistance to increase

The total resistance is less than any of the individual resistances

Costanzo (Physiology, 4th ed.) – Figure 4.5

7 Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

Ideally, blood flow in the cardiovascular system is streamlined

1) Laminar Flow: Characterized by parabolic velocity profile • Flow is 0 velocity at wall; maximal at center • Layers of slide past one another Blood ~ 4x Viscosity: more viscous Measure of the resistance to sliding than water between adjacent layers

What would you expect to happen to blood viscosity  viscosity in as vessel diameter decreases? capillaries – Why?

Fahraeus – Lindqvist Effect: () Relative viscosity of blood decreases with Hematocrit decreasing vessel diameter RBCs (< 0.3 mm ~ 1.8x water)

Reduced energy required to drive blood through Plasma Skimming Exit to smaller

Costanzo (Physiology, 4th ed.) – Figure 4.6 vessels

Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

Ideally, blood flow in the cardiovascular system is streamlined

1) Laminar Flow: Characterized by parabolic velocity profile • Flow is 0 velocity at wall; maximal at center • Layers of fluid slide past one another Blood ~ 4x Viscosity: more viscous Measure of the resistance to sliding than water between adjacent layers

2) Turbulent Flow: Blood moves in directions not aligned with axis of blood flow • More pressure required to propel blood • Noisy (stethoscope)

Reynolds Number: Indicator of whether flow will be Thrombi laminar or turbulent

 Re = turbulence (> 2000) Factors affecting : 1) Viscosity ( viscosity =  Reynolds number) 2) Velocity ( velocity =  Reynolds number) Costanzo (Physiology, 4th ed.) – Figure 4.6

Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

The capacitance of a blood vessel describes the volume of blood a vessel can hold at a given pressure

Volume (mL) Compliance = (mL / mm Hg) Pressure (mm Hg) Compliance = slope of line

Compliance is high in veins Unstressed (large blood volumes @ low pressure) volume

Compliance is low in arteries Stressed (low blood volumes @ high pressure) volume

Total = Unstressed volume + Stressed volume

Changes in compliance of the veins cause redistribution of blood between arteries and veins Arterial pressure increases in elderly due to lower compliance • Venoconstriction

Costanzo (Physiology, 4th ed.) – Figure 4.7

8 Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

As noted earlier, blood pressure is not equal throughout system

~ 100 mm Hg 1 High initial pressure: • Large volume of blood entering aorta • Low compliance of 1 aortic wall

Costanzo (Physiology, 4th ed.) – Figure 4.8

Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

Although mean pressure is high and constant, there are pulsations of aortic (and arterial) pressure

Dicrotic notch

Systolic Pressure: Dicrotic notch: Pressure from ventricular contraction Brief period following closure of aortic valve Diastolic Pressure: where pressure drops due to retrograde flow Pressure from ventricular relaxation

Costanzo (Physiology, 4th ed.) – Figure 4.9

Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

Although mean pressure is high and constant, there are pulsations of aortic (and arterial) pressure

Pulse Pressure: Systolic pressure – Diastolic pressure • Reflective of volume

Mean Arterial Pressure: Why is it not Diastolic pressure + 1/3 pressure + 1/2 ?

Costanzo (Physiology, 4th ed.) – Figure 4.9

9 Cardiovascular System – Vessels

Pathophysiology:

Several pathologic conditions alter the arterial pressure curve in a predictable way

Arteriosclerosis:

 compliance =  systolic pressure C = V / P

Aortic :

=  systolic pressure Costanzo (Physiology, 4th ed.) – Figure 4.10

Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

As noted earlier, blood pressure is not equal throughout system Pulsations in large arteries greater than aorta ~ 100 ~ 100 • Pressure wave travels faster than blood 2 mm Hg mm Hg • Pressure waves reflected at branch points Pressure remains high: • High elastic recoil of walls • Pressure reservoir 1 2

Costanzo (Physiology, 4th ed.) – Figure 4.8

Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving…

As noted earlier, blood pressure is not equal throughout system

~ 100 ~ 100 ~ 50 ~ 20 ~ 4 2 mm Hg mm Hg mm Hg mm Hg mm Hg Pressure remains high: Largest Profile similar in • High elastic recoil of drop pulmonary system artery walls but with much lower • Pressure reservoir pressures (25 / 8) Energy 1 2 consumed 3 to overcome Dramatic drop in pressure: frictional • High resistance to flow 4 3 4 Pressure continues to drop: • Frictional resistance to flow • Filtration of fluid out of Blood return assisted by: capillaries • Large lumen ( resistance) • Valves

Costanzo (Physiology, 4th ed.) – Figure 4.8 • Muscular pumps

10 Cardiovascular System – Vessels

Blood Pressure Regulation:

Mean arterial pressure (Pa) is the driving force for blood flow, and must be maintained at a high, constant level

Difference in blood pressure ( P) Blood Flow (Q) = Peripheral resistance (R)

Mean Arterial Pressure (P ) = Cardiac Output (Q) x Peripheral a Resistance (R)

Note: Cardiovascular System – Vessels Equation deceptively simple; Blood Pressure Regulation: in reality, cardiac output and peripheral resistance are not independent of each other Factors Affecting Blood Pressure:

Blood Volume * ( Blood Volume =  BP)

Mean Arterial Pressure (P ) = Cardiac Output (Q) x Peripheral a Resistance (R)

Cardiac Output * Vessel Diameter * ( CO =  BP) ( D =  R =  BP)

Blood Viscosity ( V =  R =  BP) Pa is regulated by two major systems that work via negative feedback to maintain ~ 100 mm Hg Vessel Length ( L =  R =  BP)

Vessel Elasticity ( VE =  R =  BP) * Variables that can be readily manipulated

Cardiovascular System – Vessels

Blood Pressure Regulation: System 1

Baroreceptor mechanisms are fast, neurally mediated reflexes that attempt

to keep Pa constant via changes in cardiac output and vessel diameter

Baroreceptors:

Function: • Mechanoreceptors (respond to stretch) •  Pa =  stretch =  firing rate •  Pa =  stretch =  firing rate

While sensitive to absolute level of pressure, they are most sensitive rates of changes in pressure

Location:

• Carotid sinus (increase / decrease in Pa) • Glossopharyngeal (IX)

• Aortic arch (increase in Pa) • (X)

Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 18.4 / 19.22

11 Cardiovascular System – Vessels

Blood Pressure Regulation:

Baroreceptor mechanisms are fast, neurally mediated reflexes that attempt

to keep Pa constant via changes in cardiac output and vessel diameter

 Pa (+) (+)

(integration center; medulla) (-) (+)

cardiovascular centers in medulla

Decrease in Increase in HR / contractility (+) (-) (-) (-) (-) vessel diameter ( CO) ( PR)

Costanzo (Physiology, 4th ed.) – Figure 4.31

Cardiovascular System – Vessels : Blood Pressure Regulation: Expiring against a closed glottis; used to test integrity of baroreceptor reflex

Baroreceptor mechanisms are fast, neurally mediated reflexes that attempt

to keep Pa constant via changes in cardiac output and vessel diameter

 Pa (-)

(integration center; medulla) (+) (-)

cardiovascular centers in medulla

Increase in Decrease in HR / contractility (-) (+) (+) (+) (+) vessel diameter ( CO) ( PR)

Costanzo (Physiology, 4th ed.) – Figure 4.31

Cardiovascular System – Vessels

Blood Pressure Regulation: System 2

Renin- II-aldosterone system is a slow, hormonally mediated

response to keep Pa constant via changes in blood volume

Detected by mechanoreceptors in Released by juxtaglomerular cells (kidney) Decapeptide; no biological activity

(Produced by liver) ( / kidneys)

Costanzo (Physiology, 4th ed.) – Figure 4.33

12 Cardiovascular System – Vessels

Blood Pressure Regulation:

Renin-angiotensin II-aldosterone system is a slow, hormonally mediated

response to keep Pa constant via changes in blood volume

(adrenal cortex) (kidney) (hypothalamus) (blood vessels)

 Blood Volume

Costanzo (Physiology, 4th ed.) – Figure 4.33

Cardiovascular System – Vessels

Blood Pressure Regulation:

Additional mechanisms aid in regulating mean arterial pressure

A) Peripheral chemoreceptors C) Antidiuretic (ADH) (carotid bodies / aortic arch) (posterior pituitary)

• Respond to  P with vasoconstriction O2 and increased aka

B) Central chemoreceptors (medulla oblongata) • Respond to an  serum osmolarity and a  in blood pressure • Respond to primarily to  P and  pH CO2 • Triggers vasoconstriction (V1 receptors) Brain becomes ischemic D) Atrial natriuretic peptide (ANP)  P and  pH CO2 (atria) Increased sympathetic outflow

BIG RED BUTTON

Intense arteriolar vasoconstriction in peripheral capillary beds • Respond to an  in blood pressure

Redirects blood • Triggers vasodilation and  H2O excretion to brain

Cardiovascular System – Vessels

Microcirculation: Functions of the arterioles, capillaries, lymphatic vessels, and veins

Heart Exchange across capillary wall:

( soluble) (water soluble)

O2 / CO2 Solutes

Directly through Aqueous clefts endothelium between cells

• Simple drives exchange of gases and solutes • Fluid transfer across membrane occurs via osmosis

• Hydrostatic pressure Starling • Osmotic pressure forces

Microcirculation

Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 19.2

13 Cardiovascular System – Vessels

Microcirculation:

Fluid movement across a capillary wall is driven by the Starling pressures across the wall

capillary Starling equation:

P  J = K [(P – P) – ( – )] c c v f c i c i Kf interstitial fluid

Pi i Jv = Fluid movement (mL / min)

Kf = Hydraulic conductance (mL / min  mm Hg) Water permeability of capillary wall (structural property)

Pc = Capillary hydrostatic pressure (mm Hg) Capillary fluid pressure

Pi = Interstitial hydrostatic pressure (mm Hg) Interstitial fluid pressure

c = Capillary osmotic pressure (mm Hg) Capillary osmotic pressure (due to [])

i = Interstitial osmotic pressure (mm Hg) Interstitial osmotic pressure (due to [protein])

Direction of fluid movement (Jv) may be into or out of capillary Filtration = Net fluid movement is out of capillary and into interstitial fluid ((+) number) Absorption = Net fluid movement is into capillary and out of interstitial fluid ((-) number)

Cardiovascular System – Vessels

In a skeletal muscle of an individual, the following Starling pressures were measured:

Pc = 30 mm Hg

Pi = 1 mm Hg Kf = 0.5 mL / min  mm Hg c = 26 mm Hg

i = 3 mm Hg What is the direction and magnitude of fluid movement across this capillary?

Jv = Kf [(Pc – Pi) – (c – i)]

Jv = 0.5 [(30 – 1) – (26 – 3)]

Jv = 0.5 [29 – 23]

Jv = 0.5 (6) Jv = 3 mL / min (filtration)

Cardiovascular System – Vessels

In a skeletal muscle of an individual, the following Starling pressures were measured:

Pc = 30 mm Hg

Pi = 1 mm Hg Kf = 0.5 mL / min  mm Hg c = 26 mm Hg

i = 3 mm Hg What is the direction and magnitude of fluid movement across this capillary?

Jv = 0.5 (6) Pc = +30 c = -26 +6 Jv = 3 mL / min (filtration)

Pi = -1 c = +3

14 Cardiovascular System – Vessels

Microcirculation:

Fluid movement across a capillary wall is not equal along the length of a capillary

Arterial end

+10 Pc = +35 c = -26 Pc = +17 c = -26 -8

Venous end

Pi = 0 c = +1 Pi = 0 c = +1

Jv = 0.5 (2) What happens to the fluid not returned to the capillary? Jv = 1 mL / min (net filtration)

Randall et al. (Eckert Animal Physiology, 5th ed.) – Figure 12.37

Cardiovascular System – Vessels

Microcirculation:

Lymphoid system returns excess fluid to bloodstream

Additional Functions: • Produce / maintain / distribute lymphocytes  Lymph node biopsy • Distributes / nutrients / waste products

Lymph nodes filter fluids (99% purified) Flow of Lymph:

• Originate as pockets • Large diameters / thin walls • One-way valves (external)

Lymphatic ducts Lymphatic Trunks

Lymphatic capillaries Lymphatic vessels Collecting Vessels

One-way valves (internal) Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 20.1

Cardiovascular System – Vessels

Microcirculation: • Lymph from right side of • Lymph from left side of Flow of Lymph: body above diaphragm head, neck, and

Thoracic Duct: • Begins inferior to diaphragm • Empties into left

Right Lymphatic Duct: • Empties into right subclavian vein

Cisterna chyli: Chamber that collects lymph from , , and lower limbs Similar to Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 20.2

15 Cardiovascular System – Vessels

Pathophysiology:

Edema (swelling) results from an increase in interstitial fluid volume Forms when the volume of fluids filtered out of the capillaries exceeds the ability of the lymphatics to return it to circulation

Elephantiasis Jv = Kf [(Pc – Pi) – (c – i)]

Causes: 1) Increased capillary hydrostatic pressure • Arteriole dilation • •

2) Decreased capillary osmotic pressure • Severe liver failure (limited protein synthesis) • Protein malnutrition 4) Impaired lymphatic drainage • Prolonged standing 3) Increased hydraulic conductance • Removal / irradiation of lymph nodes • Severe • Parasitic infection • (leaky vessels)

Cardiovascular System – Vessels

Special Circulations:

Blood flow is variable between one organ and another, depending on the overall demands of each

Interorgan differences in blood flow results from differences in vascular resistance

Blood flow to specific organs can increase or decrease depending on metabolic demands

What about the lungs? Changes in blood flow to an individual organ are achieved by altering arteriolar resistance

Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 19.13

Cardiovascular System – Vessels

Special Circulations:

The mechanisms that regulate blood flow are categorized as local (intrinsic) control and neural / hormonal (extrinsic) control

Local controls are most important mechanism for regulating 1) Local control: coronary, cerebral, skeletal muscle, pulmonary, and renal circulation A) • Maintenance of constant blood flow in face of changing arterial pressure

Myogenic Hypothesis: Q = P / R When is stretched, it contracts

 BP =  BP =  smooth muscle stretch = vasoconstriction

ALTERNATIVELY

 BP =  BP =  smooth muscle stretch = vasodilation

16 Cardiovascular System – Vessels

Special Circulations:

The mechanisms that regulate blood flow are categorized as local (intrinsic) control and neural / hormonal (extrinsic) control

Local controls are most important mechanism for regulating 1) Local control: coronary, cerebral, skeletal muscle, pulmonary, and renal circulation B) Active hyperemia • Blood flow to an organ is proportional to its metabolic activity

C) Reactive hyperemia (Repayment of ‘debt’) • Blood flow to an organ is increased in response to a period of decreased blood flow

Vasodilator metabolites

Metabolic Hypothesis:

O delivery to a tissue is matched + + + + 2 CO2 H K lactate CO2 H K lactate to O consumption by altering Back to resting… 2 O Fluid arteriole resistance 2

Tissues Tissues Tissues

Cardiovascular System – Vessels

Special Circulations:

The mechanisms that regulate blood flow are categorized as local (intrinsic) control and neural / hormonal (extrinsic) control

2) Neuronal / Hormonal controls: Neuronal / hormonal controls are most important mechanism for maintaining circulation A) Neuronal • Sympathetic innervation of vascular smooth muscle

B) Hormonal

Histamine Serotonin • arteriodilator; venoconstrictor • local vasoconstriction • local vasodilators / vasoconstrictors

•  Pc = local

Bradykinin • arteriodilator; venoconstrictor

•  Pc = local edema

Cardiovascular System – Vessels

Pathophysiology:

Circulatory refers to any condition in which the blood vessels are inadequately filled

A) B) Vascular Shock C) Large-scale blood loss Abnormal expansion of Heart malfunctions vascular beds due Thready pulse to extreme vasodilation

(  HR;extreme vasoconstriciton)

• Acute hemorrage • Myocardial • Severe vomiting / diarrhea • Anaphylaxis (allergies) • Extensive • Failure of ANS regulation • Septicemia (bacteria)

17