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85 Cards in this Set

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arteries
conducting vessels
∙ high pressure
∙ thick-walled, muscular & elastic ("pressure reservoir")
arterioles
resistance vessels
∙ supply capillary beds
∙ smooth muscle in walls → vasoconstriction/vasodilation
∙ regulate local blood flow
capillaries
exchange vessels
∙ microscopic, very thin walls (endothelium)
∙ permeability of capillary walls: continuous < fenestrated < sinusoid
venules
small, thin walled
∙ drain capillaries
veins
low pressure conducting vessels
∙ relatively thin-walled, high compliance/flexibility (:"volume reservoir")
∙ valves assist in one-way flow back to heart
Physiology of Circulation:
Blood Pressure
∙ 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
As we saw with the heart → it is the _____ in BP (__________) that drives blood flow
difference: pressure gradient
What are the four main factors that affect blood pressure:
1) resistance
2) cardiac output
3) vessel elasticity
4) blood volume

resistance and cardiac output are the most important
resistance
• 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)
Three important sources of resistance are:
1) blood viscosity
2) total blood vessel length
3) blood vessel diameter (**most important & changes most frequently)
blood viscosity
blood thickness of "stickiness"
∙ Viscosity and resistance are directly proportional
∙ ↑ viscosity ↑ resistance
∙ Viscosity does not change often in a healthy person
Causes of viscosity
∙ dehydration
∙ ↑ EPO production (↑ RBC formation)
blood vessel length
blood vessel length and resistance are directly proportional
∙ ↑ length ↑ resistance
∙ BV length does not change often in a healthy person
Causes of an ↑ length
growth of adipose tissue → results in new blood vessel formation and thus an ↑ in total vessel length
blood vessel diameter
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
causes of an ↓ BV diameter
∙ vasoconstriction of vessels
∙ SNS vasomotor fibers release NE
∙ Vasoconstriction hormones Epinephrine, Angiotensin II, ADH
Which tube has the LEAST resistance?

Which tube has the GREATEST resistance?
LEAST RESISTANCE - 3
GREATEST RESISTANCE - 4
Blood encounters resistance when is contacts blood vessel walls
If resistance ↑ blood pressure must ↑ to keep blood moving
↑ Viscosity ↑ BV Length and ↓ BV Diameter →→ ↑ Blood Pressure

↓ Viscosity ↓ BV Length and ↑ BV Diameter →→ ↓ Blood Pressure
Blood Pressure and Vessel Elasticity
Healthy arteries are elastic (stretch and recoil) as blood moves through them
serves as "shock absorbers" to reduce sudden ↑ in BP as blood is forcefully pumped in "waves" from heart to arteries
Blood Pressure and Vessel Elasticity
Unhealthy (non-elastic or occluded) arteries cannot expand
artery walls therefore experience higher blood pressure & can become damaged
Blood Pressure and Blood Volume (BV)
As BV ↑ in vessel, more fluid presses against vessel walls →
causing a ↑ BP
Blood Pressure and Blood Volume (BV)
As BV ↓, less fluid presses against vessel walls →
causing a ↓ BP
Blood Pressure and Blood Volume (BV)
Causes of ↑ blood volume
↑ salt intake ("H₂O follows salt" into ECF (blood)), overhydration
Blood Pressure and Blood Volume (BV)
Causes of ↓ blood volume
dehydration, excessive sweating, hemorrhaging
Blood Pressure and Cardiac Output
Increasing CO will cause an increase in BP because more pressure is being exerted against vessel walls
Cardiac Output = Heart Rate x Stroke Volume
Increasing HR or SV will _________ CO and therefore BP
increase
Decreasing HR or SV will _________ CO and therefore BP
decrease
Blood Flow
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
Blood Flow (F) is:
∙ 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
Relationship between blood flow and the pressure gradient (△P)
larger volume of the blood flows through the "vessel" in one minute when a pressure gradient exists
High Blood Flow (F) vs Low Blood Flow (F)
systemic blood pressure
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
Steepest change in blood pressure occurs in ________
arterioles
systolic pressure
pressure exerted on arterial walls during ventricular contraction
diastolic pressure
lowest level of arterial pressure during a ventricular cycle
pulse pressure
the difference between systolic and diastolic pressure
mean arterial pressure (MAP)
pressure that propels blood to tissues
pulse pressure
the difference between systolic and diastolic pressure
MAP =
diastolic pressure + 1/3 pulse pressure

Since diastole lasts longer than systole, MAP is not simply the average of systolic and diastolic pressure
Blood Pressure (MAP Regulation)
Maintaining blood flow is vital for proper organ function

tissue perfusion -
blood flow through tissues
To ensure blood flow to all tissues, body regulates/maintains homeostasis of:
cardiac output, resistance, and blood volume
What are the two types of MAP regulation?
short term controls and long term controls
MAP Regulation
short term controls
mediated by:
a) nervous system
b) hormones
• counteract moment-to-moment fluctuations in blood pressure by altering Resistance
• can also affect Cardiac Output
MAP Regulation
long term controls
mediated by:
a) renal mechanisms
regulate Blood Volume
b) additional hormonal mechanisms
• regulate Blood Volume
Brain Centers (Medulla Oblongata) for ____ term control of MAP
short
Vasomotor center
in medulla oblongata regulates diameter of blood vessels (resistance)
• transmits impulses via SNS fibers that innervate smooth muscle (tunica media) of arteries (esp. arterioles)
Vasomotor tone
arterioles are almost always in state of moderate constriction; varies by location/organ
↑ SNS activity =
vasoconstriction
↓ SNS activity =
vasodilation
Baroreceptors
• monitors changes in BP
• stretch receptors in walls of: carotid sinuses, aortic arch, right atrium
Baroreceptor Reflexes
Vascular Center Control
Baroreceptor Reflexes
When blood pressure rises, Vascular centers:
decrease cardiac output
cause peripheral vasodilation
Baroreceptor Reflexes
When blood pressure falls, Vascular centers:
increase cardiac output
cause peripheral vasoconstriction
What hormones increase MAP?
vasopressin (ADH), Anglotensin II, and Adrenal medulla hormones
Vasopressin (ADH)
causes vasoconstriction in most tissues
Anglotensin III
causes vasoconstriction
Adrenal medulla hormones
epinephrine & norepinephrine cause vasoconstriction in most tissues and ↑ CO
What hormones decrease MAP?
Atrial natriuretic peptide (ANP) & Brain natriuretic peptide (BNP)
Atrial natriuretic peptide (ANP) & Brain natriuretic peptide (BNP)
cause vasodilation (and other LONG TERM mechanisms)
Long-Term Mechanisms: Renal Regulation
Kidneys act directly and indirectly to maintain long-term blood pressure by altering blood volume (rather than peripheral resistance):
1) Direct renal mechanism
2) Indirect renal mechanism
Long-Term Mechanisms: Renal Regulation
Direct renal mechanism
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)
Long-Term Mechanisms: Renal Regulation
Indirect renal mechanism
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)
An _____ in BV raises MAP (because of a greater fluid load in the vascular system); _____ BV causes fall in MAP
increase: decrease
Long-Term Mechanisms: Additional Hormonal Mechanisms

Renal mechanism
stimulates release of hormones to regulate blood volume
• angiotensin II, ADH, aldosterone
Long-Term Mechanisms: Additional Hormonal Mechanisms

Additional hormones regulate blood volume:
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
Capillary Exchange
• exchange occurs between blood plasma and interstitial fluid
• vital for maintaining homeostasis

nutrients, wastes, signaling molecules are exchanged via diffusion
diffusion
movement of ions or molecules from high to low concentration (down concentration gradient)
________ is also exchanged in slightly more complex manner
Fluid
Two forces at work during capillary exchange of fluids
Hydrostatic pressure & Osmotic Pressure
Hydrostatic Pressure
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
Osmotic Pressure (OP)
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
Colloid Osmotic Pressure
created by presence of large molecules (e.g. plasma proteins) that can't move across membrane
• protein molecules "pull" water toward them (encourage osmosis)
At arterial end of capillary →
fluid moves out of capillary into interstitial fluid (filtration)
At venous end of capillary →
fluid moves into capillary out of interstitial fluid (reabsorption)
The Transition Point:
Between filtration and reabsorption
—closer to venous end than arterial end
Therefore → capillaries filter more than reabsorb
Excess fluid enter lymphatic vessels
Fluid Recycling
Water continuously moves out of capillaries, and back into bloodstream via the lymphatic system
Fetal Circulation
• Embryonic lungs and digestive tract nonfunctional
• Respiratory functions and nutrition provided by placenta
Fetal Circulation

Blood flows to the placenta:
through pair of umbilical arteries
-arise from internal iliac arteries and enter umbilical cord
Fetal Circulation

Blood returns from placenta:
in a single umbilical vein
-drains into ductus venosus
Fetal Circulation

Ductus venosus:
empties into inferior vena cava
What are the two fetal pulmonary circulation bypasses?
foramen ovale and ductus arteriosus
Foramen ovale
• interatrial opening
• covered by valve-like flap
• directs blood from right to left atrium
Ductus arteriosus
• short vessel
• connects pulmonary and aortic trunks
Cardiovascular Changes at Birth
• Pulmonary vessels expand
• Reduced resistance allows blood flow
• Rising O₂ causes ductus arteriosus constriction
• Rising left atrium pressure closes foramen ovale
NFP =
Net Filtration Pressure