Bio 219: Cardiovascular System: Blood Vessels, Flow & Pressure

Front 1

arteries

Back 1

conducting vessels
∙ high pressure
∙ thick-walled, muscular & elastic ("pressure reservoir")

Front 2

arterioles

Back 2

resistance vessels
∙ supply capillary beds
∙ smooth muscle in walls → vasoconstriction/vasodilation
∙ regulate local blood flow

Front 3

capillaries

Back 3

exchange vessels
∙ microscopic, very thin walls (endothelium)
∙ permeability of capillary walls: continuous < fenestrated < sinusoid

Front 4

venules

Back 4

small, thin walled
∙ drain capillaries

Front 5

veins

Back 5

low pressure conducting vessels
∙ relatively thin-walled, high compliance/flexibility (:"volume reservoir")
∙ valves assist in one-way flow back to heart

Front 6

Physiology of Circulation:
Blood Pressure

Back 6

∙ Force exerted by blood on the walls of the blood vessels
∙ Expressed I'm millimeters of mercury (mm Hg)
∙ e.g. BP of 120 mm Hg = pressure exerted by column of mercury 120 mm high
∙ All vessels have an associated pressure, however blood pressure typically refers to arterial pressures

Front 7

As we saw with the heart → it is the _____ in BP (__________) that drives blood flow

Back 7

difference: pressure gradient

Front 8

What are the four main factors that affect blood pressure:

Back 8

1) resistance
2) cardiac output
3) vessel elasticity
4) blood volume

resistance and cardiac output are the most important

Front 9

resistance

Back 9

• opposition to flow of blood in vessels
∙ measure of the amount of friction blood encounters
∙ most friction encountered in the systemic circulation is far from heart
∙ therefore referred to as peripheral resistance (PR)

Front 10

Three important sources of resistance are:

Back 10

1) blood viscosity
2) total blood vessel length
3) blood vessel diameter (**most important & changes most frequently)

Front 11

blood viscosity

Back 11

blood thickness of "stickiness"
∙ Viscosity and resistance are directly proportional
∙ ↑ viscosity ↑ resistance
∙ Viscosity does not change often in a healthy person

Front 12

Causes of viscosity

Back 12

∙ dehydration
∙ ↑ EPO production (↑ RBC formation)

Front 13

blood vessel length

Back 13

blood vessel length and resistance are directly proportional
∙ ↑ length ↑ resistance
∙ BV length does not change often in a healthy person

Front 14

Causes of an ↑ length

Back 14

growth of adipose tissue → results in new blood vessel formation and thus an ↑ in total vessel length

Front 15

blood vessel diameter

Back 15

most important
∙ resistance is inversely proportional to BV radius by the 4th power (1/r⁴)
∙ ↓ BV radius ↑↑↑↑↑ resistance
∙ BV diameter does change often in a healthy person

Front 16

causes of an ↓ BV diameter

Back 16

∙ vasoconstriction of vessels
∙ SNS vasomotor fibers release NE
∙ Vasoconstriction hormones Epinephrine, Angiotensin II, ADH

Front 17

Which tube has the LEAST resistance?

Which tube has the GREATEST resistance?

Back 17

LEAST RESISTANCE - 3
GREATEST RESISTANCE - 4

Front 18

Blood encounters resistance when is contacts blood vessel walls
If resistance ↑ blood pressure must ↑ to keep blood moving

Back 18

↑ Viscosity ↑ BV Length and ↓ BV Diameter →→ ↑ Blood Pressure

↓ Viscosity ↓ BV Length and ↑ BV Diameter →→ ↓ Blood Pressure

Front 19

Blood Pressure and Vessel Elasticity
Healthy arteries are elastic (stretch and recoil) as blood moves through them

Back 19

serves as "shock absorbers" to reduce sudden ↑ in BP as blood is forcefully pumped in "waves" from heart to arteries

Front 20

Blood Pressure and Vessel Elasticity
Unhealthy (non-elastic or occluded) arteries cannot expand

Back 20

artery walls therefore experience higher blood pressure & can become damaged

Front 21

Blood Pressure and Blood Volume (BV)
As BV ↑ in vessel, more fluid presses against vessel walls →

Back 21

causing a ↑ BP

Front 22

Blood Pressure and Blood Volume (BV)
As BV ↓, less fluid presses against vessel walls →

Back 22

causing a ↓ BP

Front 23

Blood Pressure and Blood Volume (BV)
Causes of ↑ blood volume

Back 23

↑ salt intake ("H₂O follows salt" into ECF (blood)), overhydration

Front 24

Blood Pressure and Blood Volume (BV)
Causes of ↓ blood volume

Back 24

dehydration, excessive sweating, hemorrhaging

Front 25

Blood Pressure and Cardiac Output
Increasing CO will cause an increase in BP because more pressure is being exerted against vessel walls

Back 25

Cardiac Output = Heart Rate x Stroke Volume

Front 26

Increasing HR or SV will _________ CO and therefore BP

Back 26

increase

Front 27

Decreasing HR or SV will _________ CO and therefore BP

Back 27

decrease

Front 28

Blood Flow

Back 28

volume (not speed) of blood flowing through a vessel, organ, or entire circulation in a given period of time:
∙ measured in ml per minute
∙ equivalent to cardiac output (CO) when considering entire CV system
∙ relatively constant when at rest
∙ varies widely through individual organs

Front 29

Blood Flow (F) is:

Back 29

∙ directly proportionally to the difference in blood pressure (△P) between two points in the circulation
∙ inversely proportional to the resistance of the vessel connecting those 2 points

Front 30

Relationship between blood flow and the pressure gradient (△P)

Back 30

larger volume of the blood flows through the "vessel" in one minute when a pressure gradient exists

Front 31

High Blood Flow (F) vs Low Blood Flow (F)

Back 31

Front 32

systemic blood pressure

Back 32

pumping action of heart generates blood flow through vessels along a pressure gradient (always moving from higher to lower pressure areas)
• pressure = highest in aorta (100mm Hg)
• declines throughout length of pathway
• pressure = 0 mm Hg in right atrium

Steepest change in blood pressure occurs in arterioles

Front 33

Steepest change in blood pressure occurs in ________

Back 33

arterioles

Front 34

systolic pressure

Back 34

pressure exerted on arterial walls during ventricular contraction

Front 35

diastolic pressure

Back 35

lowest level of arterial pressure during a ventricular cycle

Front 36

pulse pressure

Back 36

the difference between systolic and diastolic pressure

Front 37

mean arterial pressure (MAP)

Back 37

pressure that propels blood to tissues

Front 38

pulse pressure

Back 38

the difference between systolic and diastolic pressure

Front 39

MAP =

Back 39

diastolic pressure + 1/3 pulse pressure

Since diastole lasts longer than systole, MAP is not simply the average of systolic and diastolic pressure

Front 40

Blood Pressure (MAP Regulation)
Maintaining blood flow is vital for proper organ function

tissue perfusion -

Back 40

blood flow through tissues

Front 41

To ensure blood flow to all tissues, body regulates/maintains homeostasis of:

Back 41

cardiac output, resistance, and blood volume

Front 42

What are the two types of MAP regulation?

Back 42

short term controls and long term controls

Front 43

MAP Regulation
short term controls

Back 43

mediated by:
a) nervous system
b) hormones
• counteract moment-to-moment fluctuations in blood pressure by altering Resistance
• can also affect Cardiac Output

Front 44

MAP Regulation
long term controls

Back 44

mediated by:
a) renal mechanisms
regulate Blood Volume
b) additional hormonal mechanisms
• regulate Blood Volume

Front 45

Brain Centers (Medulla Oblongata) for ____ term control of MAP

Back 45

short

Front 46

Vasomotor center

Back 46

in medulla oblongata regulates diameter of blood vessels (resistance)
• transmits impulses via SNS fibers that innervate smooth muscle (tunica media) of arteries (esp. arterioles)

Front 47

Vasomotor tone

Back 47

arterioles are almost always in state of moderate constriction; varies by location/organ

Front 48

↑ SNS activity =

Back 48

vasoconstriction

Front 49

↓ SNS activity =

Back 49

vasodilation

Front 50

Baroreceptors

Back 50

• monitors changes in BP
• stretch receptors in walls of: carotid sinuses, aortic arch, right atrium

Front 51

Baroreceptor Reflexes

Back 51

Vascular Center Control

Front 52

Baroreceptor Reflexes
When blood pressure rises, Vascular centers:

Back 52

decrease cardiac output
cause peripheral vasodilation

Front 53

Baroreceptor Reflexes
When blood pressure falls, Vascular centers:

Back 53

increase cardiac output
cause peripheral vasoconstriction

Front 54

What hormones increase MAP?

Back 54

vasopressin (ADH), Anglotensin II, and Adrenal medulla hormones

Front 55

Vasopressin (ADH)

Back 55

causes vasoconstriction in most tissues

Front 56

Anglotensin III

Back 56

causes vasoconstriction

Front 57

Adrenal medulla hormones

Back 57

epinephrine & norepinephrine cause vasoconstriction in most tissues and ↑ CO

Front 58

What hormones decrease MAP?

Back 58

Atrial natriuretic peptide (ANP) & Brain natriuretic peptide (BNP)

Front 59

Atrial natriuretic peptide (ANP) & Brain natriuretic peptide (BNP)

Back 59

cause vasodilation (and other LONG TERM mechanisms)

Front 60

Long-Term Mechanisms: Renal Regulation
Kidneys act directly and indirectly to maintain long-term blood pressure by altering blood volume (rather than peripheral resistance):

Back 60

1) Direct renal mechanism
2) Indirect renal mechanism

Front 61

Long-Term Mechanisms: Renal Regulation
Direct renal mechanism

Back 61

alters BV by altering filtration rate
**without use of hormones

BV or MAP rises
↓
rate that fluid from bloodstream is filtered at kidneys rises (= more urine production)

BV or MAP falls
↓
rate that fluid from bloodstream is filtered at kidneys falls (= less urine production)

Front 62

Long-Term Mechanisms: Renal Regulation
Indirect renal mechanism

Back 62

involves renin-angiotensin mechanism

MAP falls
↓
Renin (enzyme) released from kidneys
↓
Triggers enzymatic cascade that produces angiotensin II
↓
Angiotensin II - vasoconstrictor & stimulates aldosterone & ADH release
↓
aldosterone enhances Na+ reabsorption at kidneys ("H₂O follows") & ADH ↑ H₂O reabsorption at kidneys (both decrease urine production)

Front 63

An _____ in BV raises MAP (because of a greater fluid load in the vascular system); _____ BV causes fall in MAP

Back 63

increase: decrease

Front 64

Long-Term Mechanisms: Additional Hormonal Mechanisms

Renal mechanism

Back 64

stimulates release of hormones to regulate blood volume
• angiotensin II, ADH, aldosterone

Front 65

Long-Term Mechanisms: Additional Hormonal Mechanisms

Additional hormones regulate blood volume:

Back 65

1) ANP/BNP
• Reduce Blood Volume
∙ increase Na+ excretion at kidneys
∙ block release of ADH, aldosterone, epinephrine, and norephinephrine
∙ reduce thirst
∙ promote water loss at kidneys (↑ urine production)
2) EPO
• Increase Blood Volume
∙ stimulate RBC production → ↑ volume

Front 66

Capillary Exchange

Back 66

• exchange occurs between blood plasma and interstitial fluid
• vital for maintaining homeostasis

nutrients, wastes, signaling molecules are exchanged via diffusion

Front 67

diffusion

Back 67

movement of ions or molecules from high to low concentration (down concentration gradient)

Front 68

________ is also exchanged in slightly more complex manner

Back 68

Fluid

Front 69

Two forces at work during capillary exchange of fluids

Back 69

Hydrostatic pressure & Osmotic Pressure

Front 70

Hydrostatic Pressure

Back 70

force exerted by fluid pressing against a wall

in capillaries = Capillary Hydrostatic Pressure (HPc)
~ capillary blood pressure (pressure of blood against wall)
Force fluids OUT of capillary

in interstitial fluid = Interstitial Hydrostatic Pressure (HPif)
Force fluids INTO capillary

Front 71

Osmotic Pressure (OP)

Back 71

of a solution is force of osmotic water movement

in capillaries = Capillary Colloid Osmotic Pressure (OPc) abundant plasma proteins (albumins) create OPc
Force fluids INTO capillary

in interstitial fluid = Interstitial Osmotic Pressure (OPif)
Force fluids OUT of capillary

Front 72

Colloid Osmotic Pressure

Back 72

created by presence of large molecules (e.g. plasma proteins) that can't move across membrane
• protein molecules "pull" water toward them (encourage osmosis)

Front 73

At arterial end of capillary →

Back 73

fluid moves out of capillary into interstitial fluid (filtration)

Front 74

At venous end of capillary →

Back 74

fluid moves into capillary out of interstitial fluid (reabsorption)

Front 75

The Transition Point:

Back 75

Between filtration and reabsorption
—closer to venous end than arterial end
Therefore → capillaries filter more than reabsorb
Excess fluid enter lymphatic vessels

Front 76

Fluid Recycling

Back 76

Water continuously moves out of capillaries, and back into bloodstream via the lymphatic system

Front 77

Fetal Circulation

Back 77

• Embryonic lungs and digestive tract nonfunctional
• Respiratory functions and nutrition provided by placenta

Front 78

Fetal Circulation

Blood flows to the placenta:

Back 78

through pair of umbilical arteries
-arise from internal iliac arteries and enter umbilical cord

Front 79

Fetal Circulation

Blood returns from placenta:

Back 79

in a single umbilical vein
-drains into ductus venosus

Front 80

Fetal Circulation

Ductus venosus:

Back 80

empties into inferior vena cava

Front 81

What are the two fetal pulmonary circulation bypasses?

Back 81

foramen ovale and ductus arteriosus

Front 82

Foramen ovale

Back 82

• interatrial opening
• covered by valve-like flap
• directs blood from right to left atrium

Front 83

Ductus arteriosus

Back 83

• short vessel
• connects pulmonary and aortic trunks

Front 84

Cardiovascular Changes at Birth

Back 84

• Pulmonary vessels expand
• Reduced resistance allows blood flow
• Rising O₂ causes ductus arteriosus constriction
• Rising left atrium pressure closes foramen ovale

Front 85

NFP =

Back 85

Net Filtration Pressure