1. Monitoring Circulatory Efficiency
Vital signs: pulse and blood pressure, along with respiratory rate and body temperature
Pulse: pressure wave caused by expansion and recoil of arteries
Radial pulse (taken at the wrist) routinely used
Pressure points where arteries close to body surface
Can be compressed to stop blood flow
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2. Superficial temporal artery
Figure Body sites where the pulse is most easily palpated.
Superficial temporal artery
Facial artery
Common carotid artery
Brachial artery
Radial artery
Femoral artery
Popliteal artery
Posterior tibial
artery
Dorsalis pedis
artery
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3. Measuring Blood Pressure
Systemic arterial BP
Measured indirectly by auscultatory method using a sphygmomanometer
Pressure increased in cuff until it exceeds systolic pressure in brachial artery
Pressure released slowly and examiner listens for sounds of Korotkoff with a stethoscope
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4. Measuring Blood Pressure
Systolic pressure, normally less than 120 mm Hg, is pressure when sounds first occur as blood starts to spurt through artery
Diastolic pressure, normally less than 80 mm Hg, is pressure when sounds disappear because artery no longer constricted; blood flowing freely
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5. Variations in Blood Pressure
Transient elevations occur during changes in posture, physical exertion, emotional upset, fever.
Age, sex, weight, race, mood, and posture may cause BP to vary
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6. Alterations in Blood Pressure
Hypertension: high blood pressure
Sustained elevated arterial pressure of 140/90 or higher
Prehypertension if values elevated but not yet in hypertension range
May be transient adaptations during fever, physical exertion, and emotional upset
Often persistent in obese people
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7. Homeostatic Imbalance: Hypertension
Prolonged hypertension major cause of heart failure, vascular disease, renal failure, and stroke
Heart must work harder  myocardium enlarges, weakens, becomes flabby
Also accelerates atherosclerosis
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8. Primary or Essential Hypertension
90% of hypertensive conditions
No underlying cause identified
Risk factors include heredity, diet, obesity, age, diabetes mellitus, stress, and smoking
No cure but can be controlled
Restrict salt, fat, cholesterol intake
Increase exercise, lose weight, stop smoking
Antihypertensive drugs
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9. Homeostatic Imbalance: Hypertension
Secondary hypertension less common
Due to identifiable disorders including obstructed renal arteries, kidney disease, and endocrine disorders such as hyperthyroidism and Cushing's syndrome
Treatment focuses on correcting underlying cause
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10. Alterations in Blood Pressure
Hypotension: low blood pressure
Blood pressure below 90/60 mm Hg
Usually not a concern
Only if leads to inadequate blood flow to tissues
Often associated with long life and lack of cardiovascular illness
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11. Homeostatic Imbalance: Hypotension
Orthostatic hypotension: temporary low BP and dizziness when suddenly rising from sitting or reclining position
Chronic hypotension: hint of poor nutrition and warning sign for Addison's disease or hypothyroidism
Acute hypotension: important sign of circulatory shock; threat for surgical patients and those in ICU
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12. Blood Flow Through Body Tissues
Tissue perfusion involved in
Delivery of O2 and nutrients to, and removal of wastes from, tissue cells
Gas exchange (lungs)
Absorption of nutrients (digestive tract)
Urine formation (kidneys)
Rate of flow is precisely right amount to provide proper function
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13. Figure 19.13 Distribution of blood flow at rest and during strenuous exercise.
750
750
Brain
750
12,500
Heart
250
Skeletal
muscles
1200
Skin
500
Kidneys
1100
Abdomen
1400
1900
Other
600
Total blood
flow at rest
5800 ml/min
600
600
400
Total blood flow during
strenuous exercise
17,500 ml/min
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14. Changes as travels through systemic circulation
Velocity of Blood Flow
Changes as travels through systemic circulation
Inversely related to total cross-sectional area
Fastest in aorta; slowest in capillaries; increases in veins
Slow capillary flow allows adequate time for exchange between blood and tissues
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15. Relative cross- sectional area of different vessels
Figure Blood flow velocity and total cross-sectional area of vessels.
Relative cross-
sectional area of
different vessels
of the vascular bed
5000
Total area
(cm2) of the
vascular
bed
4000
3000
2000
1000 50 40
Velocity of
blood flow
(cm/s) 30 20 10
Aorta
Veins
Arteries
Arterioles
Venules
Capillaries
Venae cavae
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16. Organs regulate own blood flow by varying resistance of own arterioles
Autoregulation
Automatic adjustment of blood flow to each tissue relative to its varying requirements
Controlled intrinsically by modifying diameter of local arterioles feeding capillaries
Independent of MAP, which is controlled as needed to maintain constant pressure
Organs regulate own blood flow by varying resistance of own arterioles
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17. Two types of autoregulation
Metabolic controls
Myogenic controls
Both determine final autoregulatory response
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18. Metabolic Controls
Vasodilation of arterioles and relaxation of precapillary sphincters occur in response to
Declining tissue O2
Substances from metabolically active tissues (H+, K+, adenosine, and prostaglandins) and inflammatory chemicals
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19. Endothelins released from endothelium are potent vasoconstrictors
Metabolic Controls
Effects
Relaxation of vascular smooth muscle
Release of NO (powerful vasodilator) by endothelial cells
Endothelins released from endothelium are potent vasoconstrictors
NO and endothelins balanced unless blood flow inadequate, then NO wins
Inflammatory chemicals also cause vasodilation
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20. Vascular smooth muscle responds to stretch
Myogenic Controls
Myogenic responses keep tissue perfusion constant despite most fluctuations in systemic pressure
Vascular smooth muscle responds to stretch
Passive stretch (increased intravascular pressure) promotes increased tone and vasoconstriction
Reduced stretch promotes vasodilation and increases blood flow to the tissue
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21. Figure Intrinsic and extrinsic control of arteriolar smooth muscle in the systemic circulation.
Vasodilators
Metabolic O2
CO2 H+ K+
• Prostaglandins
• Adenosine
• Nitric oxide
Neuronal
Sympathetic tone
Hormonal
• Atrial natriuretic
peptide
Extrinsic mechanisms
Intrinsic mechanisms
(autoregulation)
Vasoconstrictors
• Neuronal or hormonal controls
• Maintain mean arterial pressure
(MAP)
• Redistribute blood during exercise
and thermoregulation
• Metabolic or myogenic controls
• Distribute blood flow to individual
organs and tissues as needed
Myogenic
Neuronal
• Stretch
Sympathetic tone
Metabolic
Hormonal
• Endothelins
• Angiotensin II
• Antidiuretic hormone
• Epinephrine
• Norepinephrine
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22. Long-term Autoregulation
Occurs when short-term autoregulation cannot meet tissue nutrient requirements
Angiogenesis
Number of vessels to region increases and existing vessels enlarge
Common in heart when coronary vessel occluded, or throughout body in people in high-altitude areas
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23. Blood Flow: Skeletal Muscles
Varies with fiber type and activity
At rest, myogenic and general neural mechanisms predominate - maintain ~ 1L /minute
During muscle activity
Active or exercise hyperemia - blood flow increases in direct proportion to metabolic activity
Local controls override sympathetic vasoconstriction
Muscle blood flow can increase 10
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24. Blood Flow: Brain
Blood flow to brain constant as neurons intolerant of ischemia; averages 750 ml/min
Metabolic controls
Decreased pH of increased carbon dioxide cause marked vasodilation
Myogenic controls
Decreased MAP causes cerebral vessels to dilate
Increased MAP causes cerebral vessels to constrict
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25. Brain vulnerable under extreme systemic pressure changes
Blood Flow: Brain
Brain vulnerable under extreme systemic pressure changes
MAP below 60 mm Hg can cause syncope (fainting)
MAP above 160 can result in cerebral edema
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26. Blood flow through skin
Blood Flow: Skin
Blood flow through skin
Supplies nutrients to cells (autoregulation in response to O2 need)
Helps regulate body temperature (neurally controlled) – primary function
Provides a blood reservoir (neurally controlled)
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27. Blood Flow: Skin
Blood flow to venous plexuses below skin surface regulates body temperature
Varies from 50 ml/min to 2500 ml/min, depending on body temperature
Controlled by sympathetic nervous system reflexes initiated by temperature receptors and central nervous system
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28. Temperature Regulation
As temperature rises (e.g., heat exposure, fever, vigorous exercise)
Hypothalamic signals reduce vasomotor stimulation of skin vessels 
Warm blood flushes into capillary beds 
Heat radiates from skin
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29. Temperature Regulation
Sweat also causes vasodilation via bradykinin in perspiration
Bradykinin stimulates NO release
As temperature decreases, blood is shunted to deeper, more vital organs
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30. Pulmonary circuit unusual
Blood Flow: Lungs
Pulmonary circuit unusual
Pathway short
Arteries/arterioles more like veins/venules (thin walled, with large lumens)
Arterial resistance and pressure are low (24/10 mm Hg)
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31. Autoregulatory mechanism opposite that in most tissues
Blood Flow: Lungs
Autoregulatory mechanism opposite that in most tissues
Low O2 levels cause vasoconstriction; high levels promote vasodilation
Allows blood flow to O2-rich areas of lung
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32. During ventricular systole
Blood Flow: Heart
During ventricular systole
Coronary vessels are compressed
Myocardial blood flow ceases
Stored myoglobin supplies sufficient oxygen
During diastole high aortic pressure forces blood through coronary circulation
At rest ~ 250 ml/min; control probably myogenic
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33. During strenuous exercise
Blood Flow: Heart
During strenuous exercise
Coronary vessels dilate in response to local accumulation of vasodilators
Blood flow may increase three to four times
Important–cardiac cells use 65% of O2 delivered so increased blood flow provides more O2
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34. Blood Flow Through Capillaries
Vasomotion
Slow, intermittent flow
Reflects on/off opening and closing of precapillary sphincters
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35. Capillary Exchange of Respiratory Gases and Nutrients
Diffusion down concentration gradients
O2 and nutrients from blood to tissues
CO2 and metabolic wastes from tissues to blood
Lipid-soluble molecules diffuse directly through endothelial membranes
Water-soluble solutes pass through clefts and fenestrations
Larger molecules, such as proteins, are actively transported in pinocytotic vesicles or caveolae
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36. Pinocytotic vesicles Red blood cell in lumen Endothelial cell
Figure Capillary transport mechanisms. (1 of 2)
Pinocytotic
vesicles
Red blood
cell in lumen
Endothelial
cell
Fenestration
(pore)
Endothelial
cell nucleus
Basement
membrane
Tight
junction
Intercellular
cleft
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37. fenestrations (water-soluble substances) 3 Basement membrane
Figure Capillary transport mechanisms. (2 of 2)
Lumen
Caveolae
Pinocytotic
vesicles
Endothelial
fenestration
(pore)
Intercellular
cleft
Transport
via vesicles
or caveolae
(large
substances) 4
Movement
through
fenestrations (water-soluble
substances) 3
Basement
membrane
Movement
through
intercellular
clefts (water-
soluble
substances) 2
Diffusion
through
membrane
(lipid-soluble
substances) 1
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38. Fluid Movements: Bulk Flow
Fluid leaves capillaries at arterial end; most returns to blood at venous end
Extremely important in determining relative fluid volumes in blood and interstitial space
Direction and amount of fluid flow depend on two opposing forces: hydrostatic and colloid osmotic pressures
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39. Hydrostatic Pressures
Capillary hydrostatic pressure (HPc) (capillary blood pressure)
Tends to force fluids through capillary walls
Greater at arterial end (35 mm Hg) of bed than at venule end (17 mm Hg)
Interstitial fluid hydrostatic pressure (HPif)
Pressure that would push fluid into vessel
Usually assumed to be zero because of lymphatic vessels
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40. Colloid Osmotic Pressures
Capillary colloid osmotic pressure (oncotic pressure) (OPc)
Created by nondiffusible plasma proteins, which draw water toward themselves
~26 mm Hg
Interstitial fluid osmotic pressure (OPif)
Low (~1 mm Hg) due to low protein content
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41. NFP—comprises all forces acting on capillary bed
Hydrostatic-osmotic Pressure Interactions: Net Filtration Pressure (NFP)
NFP—comprises all forces acting on capillary bed
NFP = (HPc—HPif)—(OPc—OPif)
Net fluid flow out at arterial end
Net fluid flow in at venous end
More leaves than is returned
Excess fluid returned to blood via lymphatic system
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42. Figure Bulk fluid flow across capillary walls causes continuous mixing of fluid between the plasma and the interstitial fluid compartments, and maintains the interstitial environment. (1 of 5)
The big picture
Fluid filters from capillaries at their arteriolar
end and flows through the interstitial space.
Most is reabsorbed at the venous end.
Arteriole
Fluid moves through
the interstitial space.
For all capillary beds,
20 L of fluid is filtered
out per day—almost 7
times the total plasma
volume!
Net filtration pressure (NFP) determines the
direction of fluid movement. Two kinds of
pressure drive fluid flow:
Hydrostatic pressure (HP)
Osmotic pressure (OP)
• Due to fluid pressing against a
boundary
• Due to nondiffusible solutes that
cannot cross the boundary
• HP “pushes” fluid across the
boundary
• OP “pulls” fluid across the
boundary
• In blood vessels, is due to blood
pressure
• In blood vessels, is due to
plasma proteins
Piston
17 L of fluid per
day is reabsorbed
into the capillaries
at the venous end.
Solute
molecules
(proteins)
About 3 L per day
of fluid (and any
leaked proteins) are
removed by the
lymphatic system
(see Chapter 20).
Boundary
Boundary
“Pushes”
“Pulls”
Lymphatic
capillary
Venule
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43. How do the pressures drive fluid flow across a capillary?
Figure Bulk fluid flow across capillary walls causes continuous mixing of fluid between the plasma and the interstitial fluid compartments, and maintains the interstitial environment. (4 of 5)
How do the pressures drive fluid flow across a capillary?
Net filtration occurs at the arteriolar end of a capillary.
Capillary
Boundary
(capillary wall)
Interstitial fluid
Hydrostatic pressure in capillary “pushes” fluid out of capillary.
HPc = 35 mm Hg
To determine the pressure driving the fluid out of the capillary at any given point, we calculate the net filtration pressure (NFP)––the outward pressures (HPc and OPif) minus the inward pressures
(HPif and OPc). So,
Osmotic pressure in capillary “pulls” fluid
into capillary.
OPc = 26 mm Hg
Hydrostatic pressure in
interstitial fluid “pushes” fluid into capillary.
HPif = 0 mm Hg
NFP
= (HPc + OPif) – (HPif + OPc)
= (35 + 1) – (0 + 26)
= 10 mm Hg (net outward
pressure)
OPif = 1 mm Hg
Osmotic pressure in interstitial fluid “pulls” fluid out
of capillary.
As a result, fluid moves from the capillary into the interstitial space.
NFP = 10 mm Hg
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44. Again, we calculate the NFP:
Figure Bulk fluid flow across capillary walls causes continuous mixing of fluid between the plasma and the interstitial fluid compartments, and maintains the interstitial environment. (5 of 5)
Net reabsorption occurs at the venous end of a capillary.
Capillary
Boundary
(capillary wall)
Interstitial fluid
Hydrostatic pressure in capillary
“pushes” fluid out of capillary.
The pressure has dropped
because of resistance encountered
along the capillaries.
HPc = 17 mm Hg
Osmotic pressure in capillary “pulls” fluid into capillary.
OPc = 26 mm Hg
Again, we calculate the NFP:
NFP
= (HPc + OPif) – (HPif + OPc)
= (17 + 1) – (0 + 26)
= –8 mm Hg (net inward
pressure)
Hydrostatic pressure in interstitial fluid “pushes” fluid into capillary.
HPif = 0 mm Hg
OPif = 1 mm Hg
Osmotic pressure in interstitial fluid “pulls” fluid out of capillary.
Notice that the NFP at the venous end is a negative number. This means that reabsorption, not filtration, is occurring and so fluid moves from the interstitial space into the capillary.
NFP= –8 mm Hg
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45. Results in inadequate blood flow to meet tissue needs
Circulatory Shock
Any condition in which
Blood vessels inadequately filled
Blood cannot circulate normally
Results in inadequate blood flow to meet tissue needs
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46. Hypovolemic shock: results from large-scale blood loss
Circulatory Shock
Hypovolemic shock: results from large-scale blood loss
Vascular shock: results from extreme vasodilation and decreased peripheral resistance
Cardiogenic shock results when an inefficient heart cannot sustain adequate circulation
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47. Figure 19.18 Events and signs of hypovolemic shock.
Initial stimulus
Physiological response
Signs and symptoms
Result
Acute bleeding (or other events that reduce
blood volume) leads to:
1. Inadequate tissue perfusion
resulting in O2 and nutrients to cells
2. Anaerobic metabolism by cells, so lactic
acid accumulates
3. Movement of interstitial fluid into blood,
so tissues dehydrate
Chemoreceptors activated
(by in blood pH)
Baroreceptor firing reduced
(by blood volume and pressure)
Hypothalamus activated
(by blood pressure)
Brain
Major effect
Minor effect
Respiratory centers
activated
Cardioacceleratory and
vasomotor centers activated
Sympathetic nervous
system activated
ADH
released
Neurons
depressed
by pH
Intense vasoconstriction
(only heart and brain spared)
Heart rate
Central
nervous system
depressed
Renal blood flow
Kidneys
Adrenal
cortex
Renin released
Angiotensin II
produced in blood
Aldosterone
released
Kidneys retain
salt and water
Water
retention
Rate and
depth of
breathing
Tachycardia;
weak, thready
pulse
Skin becomes
cold, clammy,
and cyanotic
Urine output
Thirst
Restlessness
(early sign)
Coma
(late sign)
CO2 blown
off; blood
pH rises
Blood pressure maintained;
if fluid volume continues to
decrease, BP ultimately
drops. BP is a late sign.
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48. Circulatory Pathways: Blood Vessels of the Body
Two main circulations
Pulmonary circulation: short loop that runs from heart to lungs and back to heart
Systemic circulation: long loop to all parts of body and back to heart
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49. Pulmonary capillaries of the R. lung Pulmonary capillaries of the
Figure 19.19a Pulmonary circulation.
Pulmonary
capillaries
of the
R. lung
Pulmonary
capillaries
of the
L. lung
R. pulmonary
artery
L. pulmonary
artery To
systemic
circulation
Pulmonary
trunk
R. pulmonary veins
From
systemic circulation RA LA
L. pulmonary
veins RV LV
Schematic flowchart.
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50. Figure 19.19 Pulmonary circulation.
capillaries
of the
R. lung
Pulmonary
capillaries
of the
L. lung
R. pulmonary
artery
L. pulmonary
artery
Pulmonary
trunk To
systemic
circulation
R. pulmonary veins
From
systemic circulation RA LA
L. pulmonary
veins RV LV
Schematic flowchart.
Left pulmonary
artery
Air-filled
alveolus
of lung
Aortic arch
Pulmonary trunk
Right pulmonary
artery
Three lobar arteries
to right lung
Pulmonary
capillary
Gas exchange
Two lobar arteries
to left lung
Pulmonary
veins
Pulmonary
veins
Right
atrium
Left atrium
Right
ventricle
Left
ventricle
Illustration. The pulmonary arterial system is shown in blue to indicate that the blood it carries is oxygen-poor.
The pulmonary venous drainage is shown in red to indicate that the blood it transports is oxygen-rich.
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51. Figure 19.20 Schematic flowchart showing an overview of the systemic circulation.
Common
carotid arteries
to head and
subclavian
arteries to
upper limbs
Capillary beds of
head and
upper limbs
Superior
vena cava
Aortic
arch
Aorta RA LA RV LV
Azygos
system
Thoracic
aorta
Venous
drainage
Arterial
blood
Inferior
vena
cava
Capillary beds of
mediastinal structures
and thorax walls
Diaphragm
Abdominal
aorta
Capillary beds of
digestive viscera,
spleen, pancreas,
kidneys
Inferior
vena
cava
Capillary beds of
gonads, pelvis, and
lower limbs
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52. Differences Between Arteries and Veins
Delivery
Blood pumped into single systemic artery—the aorta
Blood returns via superior and interior venae cavae and the coronary sinus
Location
Deep, and protected by tissues
Both deep and superficial
Pathways
Fairly distinct
Numerous interconnections
Supply/drainage
Predictable supply
Usually similar to arteries, except dural sinuses and hepatic portal circulation
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53. Developmental Aspects
Endothelial lining arises from mesodermal cells in blood islands
Blood islands form rudimentary vascular tubes, guided by cues
Vascular endothelial growth factor determines whether vessel becomes artery or vein
The heart pumps blood by the 4th week of development
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54. Developmental Aspects
Fetal shunts (foramen ovale and ductus arteriosus) bypass nonfunctional lungs
Ductus venosus bypasses liver
Umbilical vein and arteries circulate blood to and from placenta
Congenital vascular problems rare
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55. Developmental Aspects
Vessel formation occurs
To support body growth
For wound healing
To rebuild vessels lost during menstrual cycles
With aging, varicose veins, atherosclerosis, and increased blood pressure may arise
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