Physiology 31 Lecture
Chapter 15 – Blood Flow & Control of Blood Pressure
I. Overview
A. Blood Vessels
B. Blood Pressure, Resistance, & Flow
C. Capillary Exchange
D. Venous Return & Circulatory Shock
E. Cardiovascular Disease
II. Blood Vessels
A. Circulatory Routes – blood leaving the heart passes through a ____________ route in the
body
1. Blood moves away from the heart to body tissues through __________ to arterioles
to capillaries
2. Blood moves back to the heart from capillaries to venules to _______
B. The walls of arteries & veins are composed of three _____ (layers)
1. Tunica externa (adventitia) - outermost layer, composed of loose fibrous ______ that
anchors the vessel, and provides a passage way for nerves, lymph vessels, and smaller
blood vessels (vasa vasorum)
2. Tunica media - middle layer, composed of smooth _________, collagen and elastic
fibers; smooth muscle contraction = vaso_______________; muscle relaxation =
vaso__________
3. Tunica intima (interna) - innermost layer, of ___________ and a basement
membrane (capillaries consist solely of this layer)
4. The ________ is the central blood-filled space within the vessel.
C. Arteries and arterioles - carry blood (usually ______________) away from the heart.
Three types are
1. Conducting (elastic) arteries (e.g.: ______ & major branches) have many
________ fibers in their smooth muscle, thus expand when BP rises during systole,
then recoil during diastole
2. Distributing (__________) arteries are smaller medium sized arteries, with less
elastic and a thick tunica ________ in relation to their diameters; these distribute
blood to specific organs
3. __________ are even smaller, with little elastic and a relatively thick tunica media;
the smallest of them these only 1-2 layers of smooth muscle over ______thelium
D. _________________ is the process whereby new blood vessels are created
1. Occurs in children as they _______
2. Occurs in adults to repair wounds, for endometrial growth, and in cancerous
_________
3. Mitogenic ________ __________ that promote angiogenesis are
a. Vascular endothelial growth factor (_______) is produced by endothelium
b. ____________ growth factor (FGF)
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4. _____________ that inhibit angiogenesis include
a. ______________, made from the blood protein plasminogen
b. ____________
E. ______________ - narrowest of the blood vessels; the functional units of the circulatory
system
1. Capillary walls are thin, composed of just one layer of ______thelium in a basement
membrane (of CT)
2. It is across capillary walls that ________ (O2 & CO2), nutrients, and wastes are
exchanged with surrounding tissues
3. Blood flow from arteriole to capillary bed is controlled by precapillary
___________--- muscles
a. When sphincters are open, blood flows ____ the capillary bed
b. When sphincters close, blood from arterioles enters _______ directly via
thoroughfare channels
F. Veins - vessels that carry blood (usually ____________________) back toward the heart
1. Capillaries converge to form ______, which converge into veins
2. BP is very _____ in veins & venules (compared to arteries) due to their distance from
the _____, which influences vein structure
a. Veins have thinner walls, with less smooth _________, than arteries
b. Veins _______ more easily than arteries and hold more blood (veins hold about
______ of all the blood in the body)
c. Veins are generally closer to the body ________ than arteries
d. The __________ flow of blood in veins depends mainly upon
1) Skeletal __________ pump: skeletal muscles contract and squeeze associated
veins, pushing blood toward the heart
2) One way venous _______ prevent blood backflow in veins (___________ veins
occur when these valves break down)
3) ___________ pump – during inhalation, the diaphragm contracts, which
decreases intrathoracic pressure and increases intraabdominal pressure, pulling
blood toward the heart
III. Blood Pressure, Resistance, and Flow
A. Blood ______ is the amount of blood moving through an organ, tissue or blood vessel in a
given time (mL/min)
1. ___________ is blood flow per given unit of tissue (mL/min/g), which governs the
speed of O2 and nutrient delivery to the tissue and the speed of waste removal
2. Although total blood flow equals _________ output in a resting person, blood flow and
perfusion vary with the metabolic needs of a tissue (greater metabolic needs 
greater blood flow)
3. Hemo_________, the principles of blood flow, are based mainly on pressure and
resistance [FP/R]
a. The greater the __________ difference (P) between two points, the greater the
flow
b. The greater the _____________ (R), the less the flow.
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4. Poiseuille’s equation describes the relationship between blood pressure, vessel radius,
viscosity, and vessel length on ______ _______:
Blood flow (ΔQ) = πΔP r4
8ηl
ΔP = _________ differences between two ends of a blood vessel
r = blood vessel _________
η = blood ____________; l = blood vessel _________
Which of the above factors would have the greatest effect?
B. Blood _________- force exerted by the blood on inner vessel walls
1. Blood pressure (BP) is much higher in __________ & arterioles than in capillaries,
venules & veins (Why?)
2. Arterial BP can be measured with a _________manometer and a stethoscope
3. Normal adult BP is about ____/____, where 120 mm Hg is the systolic pressure and
80 mm Hg is the diastolic pressure
a. Systolic pressure is created by blood flow through arteries during ventricular
___________
b. Diastolic pressure is a measurement of arterial pressure during ventricular
___________
c. The difference between the systolic & diastolic pressures is the ________
pressure
d. _______ arterial pressure (MAP) is the “average” pressure in the _________
during the cardiac cycle
1) Calculated by: [MAP = diastolic pressure + 1/3 _______ pressure]
2) MAP is the _______ that propels the blood to the tissues during the cardiac
cycle
4. _______________ is an elevated BP, dangerous because of the damage to heart and
other vital organs due to weakening of small blood vessels in the organs
C. Expansion and contraction of elastic arteries during systole and diastole reduces the
_________ pressure and eases the strain on smaller arteries.
D. Factors affecting blood __________ and flow are cardiac output, blood volume, and
peripheral resistance
1. As cardiac output increases, blood flow and blood pressure ___________ (What
factors influence cardiac output?)
2. As blood volume increases, blood flow and pressure _________
3. Peripheral ______________ is affected by 3 major factors
a. Blood ___________ – the thickness or “stickiness” of blood; more viscosity =
greater resistance = higher BP
b. Total blood vessel _________ – longer vessels have greater resistance. As we gain
weight, blood vessel length increases, leading to increased BP
c. Blood vessel ____________ (vasodilation = larger diameter; vasoconstriction =
smaller diameter)
1) The narrower the vessel, the greater the __________ of the blood against the
vessel walls, causing slower blood flow
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2) In wider vessels, blood near the wall moves slowly, but blood in the middle
moves rapidly (laminar flow); less resistance = _________ blood flow
3) Blood vessel ________ changes have the greatest effect on resistance (as width
increases, resistance decreases), and thus on blood flow
4) Blood flow is fastest in the ______ and its branches (higher pressure), and
slowest in _____________ (lowest pressure)
E. __________ of blood pressure and blood flow is controlled mainly by local, neural, and
hormonal control of vessel constriction and dilation (__________)
1. Local control involves myogenic ______regulation, the ability of smooth muscle to
regulate its own state of contraction.
a. Short term local vasomotion is stimulated by vasoactive chemicals; (e.g.,
histamine, serotonin, and nitric oxide ________ vessels)
b. When arterioles _________ due to high BP, Ca2+ channels in smooth muscle cells
open, resulting in vasoconstriction and a decrease in blood flow
c. Long term autoregulation can be achieved by angio________, the growth of new
blood vessels (e.g., in coronary arteries)
2. Neural control of blood vessels is based on the vasomotor center in the ________
oblongata, which integrates baroreflexes, chemoreflexes, and the medullary ischemic
reflex
a. _____receptors in the aorta and carotid arteries sense changes in blood ______ and
signal the medulla to restore homeostasis
b. ______receptors in the aorta and carotid arteries sense changes in pH, O2, and CO2
and signal the medulla
1) Low O2, high CO2 and H+ cause vaso____________, which increases BP and
blood flow to lungs for increased gas exchange
c. The medullary ________ reflex involves a decrease in blood flow to the brain; the
vasomotor center responds by sending ___________ signals to the heart and blood
vessels
1) Heart rate and contraction force __________
2) Blood vessels vaso__________
3) All increase blood ______________ and flow to the brain
3. Hormonal control involves the following ___________:
a. _______________ II – vasoconstricts vessels and raises BP
b. ____________ – “salt retaining hormone” that promotes Na+ retention by kidneys
and in the blood vessels; water flows into the blood, ___________ blood volume and
pressure
c. Antiduretic hormone (____) also promotes water retention, as well as
vasoconstriction
d. Atrial natriuretic peptide (____), secreted by the heart, causes increased Na+
excretion by kidneys and vasodilation, which _____________ BP
e. _____________ & Norepinephrine
1) Cause vaso__________ in vessels of skeletal muscle, liver, and coronary arteries
(due to β2 receptors), ___________ blood flow during exercise
2) Cause vaso____________ in other vessels, such as those to the ____ tract (due to
α receptors), decreasing blood flow
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4. Vasomotion can _______ blood flow from organs with less need to organs with more
need at a given time (e.g., from intestines to skeletal muscle during exercise)
IV. Capillary ___________ – the movement of water and solutes across capillary walls to and
from surrounding tissues
A. Substances pass between the blood stream and ________ fluid via
1. Intercellular ________ between endothelial cells (paracellular)
2. Fenestrations (_______) within fenestrated capillaries
3. Endothelial cell ___________ (transendothelial)
B. ___________ mechanisms include diffusion, trancytosis, filtration, and absorption
1. ______________ is the movement of substances from high concentration to a lower
concentration.
a. Small, __________ molecules (O2, CO2), H2O, and _______ soluble molecules
(steroids) can diffuse freely through capillary walls
b. __________ diffuses out of the blood stream into surrounding tissues
c. _____ and wastes diffuse from tissues into the blood stream
d. In the lungs, O2 and CO2 diffuse in the __________ directions
e. Lipid insoluble molecules, such as ________, and electrolytes must pass through
membrane channels, fenestrations, or intercellular clefts of capillaries
2. ____________ involves endocytosis and exocytosis of larger molecules, such as fatty
acids, proteins, and some hormones, across capillary endothelial walls
3. ______________ & absorption take place via bulk flow
a. ________ flow is the mass movement of fluid between the blood and interstitial
fluid due to hydrostatic and osmotic pressure (net pressure = hydrostatic pressure
– colloid osmotic pressure)
b. ___________ - Fluid is forced out of capillaries at the arterial end of a capillary via
higher blood (hydrostatic) pressure than surrounding tissues
c. ___________ – Fluid is drawn back into capillaries at the venous end of a capillary
via colloid __________ pressure, because blood has higher osmolarity than
tissues, due to plasma proteins
d. About 15% of tissue fluid is absorbed by the ___________ system and returned to
the bloodstream
e. Overall, the volume of fluid __________ into the blood is almost as large as the
volume _______ out (Starling’s Law)
e. Fluid exchange ________ from place to place in the body and from moment to
moment
1) Some capillaries engage solely in __________ (e.g., kidney glomeruli)
2) Some capillaries participate solely in _____________ (e.g., lung alveolar
capillaries)
3) Absorption dominates in ___________ tissues in which precapillary sphincters
are constricted and BP is low in capillaries
4) Filtration dominates in ___________ tissues in which precapillary sphincters
are open and capillary blood flow and pressure increase
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C. _________ is an accumulation of excess tissue fluid resulting from increased capillary
filtration, reduced reabsorption, or obstructed lymphatic drainage
1. Increased capillary _____________can result from increases in capillary ____ or
permeability due to poor venous return, water retention, an increase in interstitial
proteins
2. Reduced capillary _________ can result from hypoproteinemia (low plasma ______
concentration), as in Kwashiokor syndrome
3. Obstructed ______________ drainage can occur with certain diseases, advanced age,
and surgical removal of lymph nodes
4. Severe edema can lead to circulatory ________, due to low BP, impaired O2 delivery
and waste removal, and tissue necrosis
V. Venous Return & Circulatory Shock
A. Venous __________ is the flow of blood back to the heart, and is achieved by 5
mechanisms
1. ___________ gradient – movement of blood from higher pressure vessels (i.e.,
venules) to lower pressure vessels (veins).
2. ________ – blood from head and neck flows “downhill” to heart
3. Skeletal __________ pump – limb veins are surrounded by muscles that squeeze
blood upward as they contract and relax
4. __________ pump – inspiration flattens the diaphragm, causing a decrease in thoracic
pressure and increasing abdominal pressure, which pulls blood upward
5. Cardiac ___________ – expansion of the artial space during ventricular systole
creates suction that draws blood into the atria
B. Venous Return & Exercise
1. Exercise ___________ venous return because the vessels dilate, the thoracic and
skeletal muscle pumps work harder, and cardiac output is elevated
2. Inactivity allows blood to accumulate in low points in the body (venous pooling). It
can result in ____________ (fainting) if too much blood flows away from the brain
C. Circulatory _______ occurs when cardiac output is not sufficient to meet the body’s
metabolic needs. Two major categories are
1. ______________ shock – caused by inadequate pumping of the heart, usually due to
myocardial infarction
2. Low ____________ return (LVR) shock – caused by too little blood returned to the
heart. Three types of LVR are
a. ______________ shock most common, produced by a loss of blood volume due to
bleeding or dehydration
b. __________ venous return shock due to tumor or aneurysm
c. Venous __________ (vascular) shock occurs when a body has a normal blood
volume, but blood pools in the limbs due to prolonged sitting, standing, or
widespread vasodilation
d. _________ shock and anaphylactic shock both result from general vasodilation
and increased capillary permeability, combining hypovolemia and venous pooling
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VI. Blood Vessel Disorders
A. Arterio____________ (hardening of the arteries) - thickening and loss of elasticity of
arterial walls
B. ________sclerosis - most common type of arteriosclerosis; the arterial tunica intima
thickens with atherosclerotic __________ that narrow and can eventually block the artery
lumen, causing
1. Cerebrovascular Accident (_____) - Stroke if an artery to the brain is blocked
2. Myocardial _____________ if a coronary artery is blocked
C. An _______________ is a bulge in an artery or vein that puts the vessel at risk of
rupturing
1. May result from a congenital defect, _______________, or arteriosclerosis
2. Usually occurs in the abdominal _________ and arteries of the brain & kidneys