Chapter 19

Question 1

Blood vessels

Answer 1

the delivery system of dynamic structures that begins and ends at heart
– Work with the lymphatic system to circulate fluids

Question 2

Arteries

Answer 2

carry blood away from the heart; oxygenated except for pulmonary circulation and umbilical vessels of the fetus

Question 3

Veins

Answer 3

carry blood toward heart; deoxygenated except for pulmonary circulation and umbilical vessels of fetus

Question 4

Tunica intima

Answer 4

simple squamous epithelium that lines lumen of all vessels

Question 5

Tunica media

Answer 5

Middle layer composed mostly of smooth muscle and sheets of
elastin

Question 6

Vasoconstriction

Answer 6

decreased lumen diameter

Question 7

Vasodilation

Answer 7

increased lumen diameter

Question 8

Vasodilation

Answer 8

increased lumen diameter

Question 9

Tunica externa

Answer 9

Composed mostly of loose collagen fibres that protect and
reinforce wall and anchor it to surrounding structures

Question 10

Elastic arteries

Answer 10

thick-walled with large, low-resistance lumen
 Aorta and its major branches
 Elastin found in tunica media
 Contain substantial smooth muscle, but inactive in vasoconstriction
 Act as pressure reservoirs that expand and recoil as blood is ejected from
heart. Allows for continuous blood flow downstream even between heartbeats

Question 11

Muscular arteries

Answer 11

 Have thickest tunica media with more smooth muscle, but less elastic tissue
 Tunica media sandwiched between elastic membranes

Question 12

Arterioles

Answer 12

 smallest of all arteries
 Larger arterioles contain all three tunics, smaller arterioles are mostly single
layer of smooth muscle surrounding endothelial cells
 Also called resistance arteries because changing diameters change resistance to blood flow

Question 13

Capillaries

Answer 13

Microscopic vessels; diameters so small only single RBC can pass through at a time
* Walls just thin tunica intima
* Functions: exchange of gases, nutrients, wastes, hormones, etc., between blood and
interstitial fluid
* Most capillary endothelial cells are joined by tight junctions with gaps called
intercellular clefts
– Allow passage of fluids and small solutes

Question 14

Continuous capillaries

Answer 14

 Abundant in skin, muscles, lungs, and CNS
– Continuous capillaries of brain are unique
* Form blood brain barrier, totally enclosed with tight
junctions and no intercellular clefts

Question 15

Fenestrated capillary

Answer 15

 Found in areas involved in active filtration (kidneys), absorption (intestines), or endocrine hormone secretion
 Endothelial cells contain Swiss cheese–like pores called fenestrations
– Allow for increased permeability
– Fenestrations usually covered with thin glycoprotein diaphragm

Question 16

Sinusoidal capillaries

Answer 16

 Fewer tight junctions; usually fenestrated with larger intercellular clefts; incomplete basement membranes
– Usually have larger lumens
 Found only in the liver, bone marrow, spleen, and adrenal medulla
 Blood flow is sluggish—allows time for modification of large molecules and blood cells that pass between blood and tissue
 Contain macrophages in lining to capture and destroy foreign invaders

Question 17

Capillary bed

Answer 17

interwoven network of capillaries between arterioles and venules

Question 18

Terminal arteriole

Answer 18

branch off arteriole that
further branches into 10 to 20 capillaries
(exchange vessels) that form capillary bed
– Exchange of gases, nutrients and
wastes from surrounding tissue takes
place in capillaries
* Local chemical conditions and arteriolar
vasomotor nerve fibers regulate amount of
blood entering capillary bed
– Arteriole and terminal arteriole dilated
when blood needed; constricted to
shunt blood away from bed when not
needed

Question 19

Veins

Answer 19

carry blood toward the heart
* Formation begins when capillary
beds unite in postcapillary venules
and merge into larger and larger
veins
* Tunica media is thin, but tunica
externa is thick
– Contain collagen fibers and
elastic networks

Question 20

Venous valves

Answer 20

 Prevent backflow of blood
 Most abundant in veins of limbs

Question 21

Varicose veins

Answer 21

dilated and painful veins due to incompetent (leaky) valves

Question 22

Blood flow

Answer 22

volume of blood flowing through vessel, organ, or entire circulation in given
period
– Measured in ml/min, it is equivalent to cardiac output (CO) for entire vascular system
– Overall is relatively constant when at rest, but at any given moment, varies at
individual organ level, based on needs

Question 23

Blood pressure (BP)

Answer 23

force per unit area exerted on wall of blood vessel by blood
– Expressed in mm Hg
– Measured as systemic arterial BP in large arteries near heart
– Pressure gradient provides driving force that keeps blood moving from higher- to lower-pressure area

Question 24

Resistance (peripheral resistance)

Answer 24

opposition to flow
– Measurement of amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation
– Three important sources of resistance: Blood viscosity, Total blood vessel length, Blood vessel diameter

Question 25

Blood viscosity

Answer 25

The thickness or “stickiness” of blood due to formed elements and plasma proteins
– The greater the viscosity, the less easily molecules are able to slide past each other

Question 26

Total blood vessel length

Answer 26

 The longer the vessel, the greater the resistance encountered

Question 27

Blood vessel diameter

Answer 27

 Has greatest influence on resistance
 Viscosity and blood vessel length are relatively constant
 Fluid close to walls moves more slowly than in middle of tube (called laminar flow)
 Resistance varies inversely with fourth power of vessel radius
– If radius increases, resistance decreases, and vice-versa
– Example: if radius is doubled, resistance drops to 1/16 as much

Question 28

Systolic pressure:

Answer 28

pressure exerted in aorta during ventricular contraction
– Left ventricle pumps blood into aorta, imparting kinetic energy that stretches aorta
– Averages 120 mm Hg in normal adult

Question 29

Diastolic pressure

Answer 29

lowest level of aortic pressure when heart is at rest

Question 30

Pulse pressure

Answer 30

difference between systolic and diastolic pressure

Question 31

Pulse

Answer 31

throbbing of arteries due to differences in pulse pressures, which can be felt under skin

Question 32

Mean arterial pressure (MAP)

Answer 32

the pressure that propels blood to tissues
– Pulse pressure phases out near end of arterial treeadding diastolic pressure + 1/3 pulse pressure

Question 33

Vital signs

Answer 33

pulse and blood
pressure, along with respiratory
rate and body temperature

Question 34

Taking a pulse

Answer 34

 Radial pulse (taken at the
wrist): most routinely used,
but there are other clinically
important pulse points

Question 35

Low capillary pressure is desirable because

Answer 35

1. High BP would rupture fragile, thin-walled capillaries
2. Most capillaries are very permeable, so low pressure forces filtrate into interstitial spaces

Question 36

Muscular pump

Answer 36

contraction of skeletal muscles
“milks” blood back toward heart;
valves prevent backflow

Question 37

Respiratory pump

Answer 37

pressure changes during
breathing move blood toward heart
by squeezing abdominal veins as thoracic veins
expand

Question 38

Respiratory pump

Answer 38

pressure changes during
breathing move blood toward heart
by squeezing abdominal veins as thoracic veins
expand

Question 39

Sympathetic venoconstriction

Answer 39

under sympathetic control, smooth muscles constrict, pushing blood back toward heart

Question 40

Cardiovascular center of medulla

Answer 40

composed of clusters of sympathetic neurons in medulla
 Consists of:
– Cardiac centers: cardioinhibitory and cardioacceleratory
centers
– Vasomotor center: sends steady impulses via sympathetic
efferents called vasomotor fibers to blood vessels
– Cause continuous moderate constriction called vasomotor
tone

Question 41

Baroreceptors

Answer 41

– Located in carotid sinuses, aortic arch, and walls of large arteries of neck and thorax
– If MAP is high:
 Increased blood pressure stimulates baroreceptors to stimulates the cardioinhibitory center
 Results in decreased blood pressure due to reduced cardiac output and vasodilation

Question 42

Chemoreceptor reflexes

Answer 42

– Aortic arch and large arteries of neck detect increase in CO2, or drop in pH or O2
– Cause increased blood pressure by:
 Signaling cardioacceleratory center to increase CO
 Signaling vasomotor center to increase vasoconstriction

Question 43

Influence of higher brain centers

Answer 43

Influence of higher brain centers
– Reflexes that regulate BP are found in medulla
– Hypothalamus and cerebral cortex can modify arterial pressure via relays to medulla
– Hypothalamus increases blood pressure during stress
– Hypothalamus mediates redistribution of blood flow during exercise and changes in body temperature

Question 44

Adrenal medulla hormones

Answer 44

Epinephrine and norepinephrine from adrenal gland increase CO and vasoconstriction

Question 45

Angiotensin II

Answer 45

stimulates vasoconstriction

Question 46

ADH

Answer 46

high levels can cause vasoconstriction

Question 47

Atrial natriuretic peptide decreases

Answer 47

BP by antagonizing aldosterone, causing decreased
blood volume

Question 48

Atrial natriuretic peptide decreases

Answer 48

BP by antagonizing aldosterone, causing decreased
blood volume

Question 49

Hypertension

Answer 49

– Sustained elevated arterial pressure of 140/90 mm Hg or higher
– Prolonged hypertension is major cause of heart failure, vascular disease, renal
failure, and stroke
 Heart must work harder; myocardium enlarges, weakens, and becomes flabby
 Also accelerates atherosclerosis

Question 50

Hypotension

Answer 50

– Low blood pressure below 90/60 mm Hg
– Usually not a concern unless it causes inadequate blood flow to tissues
– Often associated with long life and lack of cardiovascular illness

Question 51

Tissue perfusion: blood flow through body tissues; involved in

Answer 51

1. Delivery of O2 and nutrients to, and removal of wastes from, tissue cells
2. Gas exchange (lungs)
3. Absorption of nutrients (digestive tract)
4. Urine formation (kidneys)

Question 52

Extrinsic control

Answer 52

sympathetic nervous system and hormones control blood flow through whole body
 Act on arteriolar smooth muscle to reduce flow to regions that need it the least

Question 53

Intrinsic control

Answer 53

Autoregulation (local) control of blood flow: blood flow is
adjusted locally to meet specific tissue’s requirements
 Local arterioles that feed capillaries can undergo a modification of their diameters
 Organs regulate own blood flow by varying resistance of own arterioles

Question 54

Autoregulation

Answer 54

local (intrinsic) conditions that regulate blood flow to that area

Question 55

Metabolic controls

Answer 55

– Increase in tissue metabolic activities results in:
 Declining levels of O2
 Increasing levels of metabolic products
-Cause:
 release of nitric oxide (NO), a powerful vasodilator, by endothelial cells
 direct relaxation of arterioles and relaxation of precapillary sphincters

Question 56

Myogenic controls

Answer 56

– local vascular smooth muscle responds to changes in MAP to keep perfusion constant to
avoid damage to tissue
 Passive stretch: increased MAP stretches vessel wall more than normal
– Smooth muscle responds by constricting, causing decreased blood flow to tissue
 Reduced stretch: decreased MAP causes less stretch than normal
– Smooth muscle responds by dilating, causing increased blood flow to tissue

Question 57

Four different routes to cross capillary

Answer 57

1. Diffuse directly through endothelial
   membranes
    Example: lipid-soluble molecules such as
   respiratory gases
2. Pass through clefts
    Example: water-soluble solutes
3. Pass through fenestrations
    Example: water-soluble solutes
4. Active transport via pinocytotic vesicles or
   caveolae
    Example: larger molecules, such as
   proteins

Question 58

Hydrostatic pressures

Answer 58

– Hydrostatic pressure (HP): force exerted by fluid pressing against wall
 Capillary hydrostatic pressure (HPc): capillary blood pressure that tends to force
fluids through capillary walls
– Greater at arterial end (35 mm Hg) of bed than at venule end (17 mm Hg)

Question 59

Colloid osmotic pressures

Answer 59

– Capillary colloid osmotic pressure (oncotic pressure, OPc)
 “Sucking” pressure created by nondiffusible plasma proteins pulling water back in to
capillary
 Opc 26 mm Hg

Question 60

Hydrostatic-osmotic pressure interactions

Answer 60

– Net filtration pressure (NFP): comprises all forces acting on capillary bed
 NFP = (HPc + OPif) − (HPif + OPc)
– Net fluid flow out at arterial end (filtration)
– Net fluid flow in at venous end (reabsorption)
– More fluid leaves at arterial end than is returned at venous end
 Excess interstitial fluid is returned to blood via lymphatic system

Question 61

Edema: abnormal increase in amount of interstitial fluid
* Caused by either an increase in outward pressure (driving fluid out of the capillaries) or
a decrease in inward pressure
1. An increase in capillary hydrostatic pressure accelerates fluid loss from blood
 Could result from incompetent venous valves, localized blood vessel
blockage, congestive heart failure, or high blood volume
2. An increase in interstitial fluid osmotic pressure can result from an inflammatory
response
 Inflammation increases capillary permeability and allows proteins to leak into
interstitial fluid
 Causes large amounts of fluid to be pulled into interstitial space
3. A decrease in capillary colloid osmotic pressure hinders fluid return to blood
 Can be caused by hypoproteinemia, low levels of plasma proteins caused
by malnutrition, liver disease, or glomerulonephritis (loss of plasma proteins
from kidneys)
4. A decreased drainage of interstitial fluid through
lymphatic vessels that have been blocked by disease or surgically removed