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anatomy and physiology mid-term > Chapter 19 > Flashcards

Chapter 19 Flashcards

1
Q

Blood vessels

A

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

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2
Q

Arteries

A

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

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3
Q

Veins

A

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

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4
Q

Tunica intima

A

simple squamous epithelium that lines lumen of all vessels

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5
Q

Tunica media

A

Middle layer composed mostly of smooth muscle and sheets of
elastin

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6
Q

Vasoconstriction

A

decreased lumen diameter

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7
Q

Vasodilation

A

increased lumen diameter

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8
Q

Vasodilation

A

increased lumen diameter

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9
Q

Tunica externa

A

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

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10
Q

Elastic arteries

A

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

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11
Q

Muscular arteries

A

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

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12
Q

Arterioles

A

 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

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13
Q

Capillaries

A

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

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14
Q

Continuous capillaries

A

 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

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15
Q

Fenestrated capillary

A

 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

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16
Q

Sinusoidal capillaries

A

 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

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17
Q

Capillary bed

A

interwoven network of capillaries between arterioles and venules

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18
Q

Terminal arteriole

A

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

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19
Q

Veins

A

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

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20
Q

Venous valves

A

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

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21
Q

Varicose veins

A

dilated and painful veins due to incompetent (leaky) valves

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22
Q

Blood flow

A

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

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23
Q

Blood pressure (BP)

A

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

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24
Q

Resistance (peripheral resistance)

A

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

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25
Blood viscosity
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
26
Total blood vessel length
 The longer the vessel, the greater the resistance encountered
27
Blood vessel diameter
 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
28
Systolic pressure:
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
29
Diastolic pressure
lowest level of aortic pressure when heart is at rest
30
Pulse pressure
difference between systolic and diastolic pressure
31
Pulse
throbbing of arteries due to differences in pulse pressures, which can be felt under skin
32
Mean arterial pressure (MAP)
the pressure that propels blood to tissues – Pulse pressure phases out near end of arterial treeadding diastolic pressure + 1/3 pulse pressure
33
Vital signs
pulse and blood pressure, along with respiratory rate and body temperature
34
Taking a pulse
 Radial pulse (taken at the wrist): most routinely used, but there are other clinically important pulse points
35
Low capillary pressure is desirable because
1. High BP would rupture fragile, thin-walled capillaries 2. Most capillaries are very permeable, so low pressure forces filtrate into interstitial spaces
36
Muscular pump
contraction of skeletal muscles “milks” blood back toward heart; valves prevent backflow
37
Respiratory pump
pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand
38
Respiratory pump
pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand
39
Sympathetic venoconstriction
under sympathetic control, smooth muscles constrict, pushing blood back toward heart
40
Cardiovascular center of medulla
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
41
Baroreceptors
– 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
42
Chemoreceptor reflexes
– 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
43
Influence of higher brain centers
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
44
Adrenal medulla hormones
Epinephrine and norepinephrine from adrenal gland increase CO and vasoconstriction
45
Angiotensin II
stimulates vasoconstriction
46
ADH
high levels can cause vasoconstriction
47
Atrial natriuretic peptide decreases
BP by antagonizing aldosterone, causing decreased blood volume
48
Atrial natriuretic peptide decreases
BP by antagonizing aldosterone, causing decreased blood volume
49
Hypertension
– 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
50
Hypotension
– 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
51
Tissue perfusion: blood flow through body tissues; involved in
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)
52
Extrinsic control
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
53
Intrinsic control
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
54
Autoregulation
local (intrinsic) conditions that regulate blood flow to that area
55
Metabolic controls
– 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
56
Myogenic controls
– 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
57
Four different routes to cross capillary
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
58
Hydrostatic pressures
– 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)
59
Colloid osmotic pressures
– Capillary colloid osmotic pressure (oncotic pressure, OPc)  “Sucking” pressure created by nondiffusible plasma proteins pulling water back in to capillary  Opc 26 mm Hg
60
Hydrostatic-osmotic pressure interactions
– 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
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

anatomy and physiology mid-term (4 decks)

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