Transcript Lecture 19 - Vessels and Circulation

Vessels and Circulation
Some embryology
first
 There are at first six
pairs of aortic
arches
 In fish these are
connected to the
gills
 They undergo a
transformation in
mammals
 Birds use the right
arch of the fourth pair
 Mammals use the
left arch of the
fourth pair
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Ventral (anterior)
view
Full set of arches develops,
but not all present at
the same time; (before
transformation)
Transformation :
4th through 7th
weeks: some persist,
some atrophy
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4th arches become:
Left side: aortic arch
Right side: brachiocephalic trunk
Right common carotid a ------------------------------.
Right subclavian a. -------------------------Brachiocephalic trunk-----------------------------------
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What the aortic
arches become…
Right common carotid a ---------------------------.
Right subclavian a. --------------------------Brachiocephalic trunk-------------------------------
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3 Major types of
blood vessels
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Body
RA
RV
Lungs
LA
LV
Boby
1.Arteries
2.Capillaries
3.Veins
Arteries carry blood away from the heart
-”branch,” “diverge” or “fork”
Veins carry blood toward the heart
-”join”, “merge,” “converge”
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General characteristics of vessels

Three layers (except for the smallest)
1. Tunica intima - AKA intima
2. Tunica media – smooth muscle
3. Tunica externa - AKA adventitia

Lumen is the central blood filled space
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 Intima is endothelium (simple squamous epithelium)
 May have subendothelial layer if 1mm or larger
 Tunica media: layers of circular smooth muscles
 Lamina (layers) of elastin and collagen internal and external
 Thicker in arteries than veins (maintain blood pressure)
Smooth muscle
contraction:
vasoconstriction
Smooth muscle
relaxation:
vasodilation
Sympathetic
vasomotor
nerves of
autonomic
nervous system
regulate
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 Adventitia (t. externa) – longitudinally running
collagen and elastin for strength and recoil
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“muscular” middle sized artery
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Arteries
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Carry blood away from the heart
From big to small, these are the categories:
1. Elastic
2. Muscular
3. Arterioles (then these to capillaries)

Pressure diminishes along the route
1. Elastic arteries: act as conduits
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2.5-1 cm diameter
Expand with surge
of blood from heart
Recoil and continue
the propagation of blood
Elastin is thick in media:
dampens the surge of blood
pressure
Aorta and its branches
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Arteries continued
2. Muscular arteries: act as
distributing arteries
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Middle sized .3mm-1cm
Changes diameter to
differentially regulate flow
to organs as needed
Internal as well as
external elastic lamina
Most of what we see as
“arteries”
Tunica media larger in proportion
to the lumen, thus “muscular” 12
Arteries continued
3. Arterioles
 Smallest: .3mm-10um
 Only larger ones have all 3
layers
 Regulated 2 ways:
 Locally in the tissues
 Sympathetic control
 Systemic blood pressure (the
“BP” we measure) can be
regulated through them
 Send blood into capillaries
Tunica media has only a few
layers of smooth muscle cells
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Capillaries
Heart to arteries to capillaries to veins to heart
 Capillaries are smallest
 8-10um
 Just big enough for single file erythrocytes
 Composed of: single layer of endothelial cells surrounded
by basement membrane
 Universal function
 Oxygen and nutrient delivery to tissues
 CO2 and nitrogenous waste (protein break-down product)
removal
 Some also have tissue specific functions
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Capillaries
There’s a capillary “bed” in almost all tissues
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Capillary permeability
 Direct diffusion through endothelial cell
membranes
 Only O2 and CO2
 Other molecules by various other methods
 Blood brain barrier: complete tight junctions
 Selective transport of necessary molecules
 Lipid soluble agents (like anesthetics) get
through, as do O2 and CO2
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Veins
 Pressure has been lowered so capillaries
can tolerate
 With lower pressure, walls (of veins) can
be thinner
 From smallest to large:
Capillaries to postcapillary venules to venules to
veins
 Veins are larger than arteries, plus
 Tunica externa is thicker
 There is less elastin
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Special features of veins
 Valves
 Prevent backflow
 Most abundant in legs (where
blood has to travel against gravity)
 Muscular contraction
 Aids the return of blood to heart in
conjunction with valves
Mechanical issues…
(really good to know)
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Exercise helps
circulation
(because
muscles
contract and
squeeze blood
back to the
heart)
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Vascular anastomoses
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Vessels communicating with each other
Veins have more than arteries
Form alternative pathways or collateral channels
Protect organs from being supplied by just one
route
 Poor anastomoses & therefore vulnerable: central
artery of retina, kidneys, spleen, bone diaphyses
 Vasa vasorum
 Means vessels of the vessels
 Blood supply to vessel itself
 Smallest vessels don’t need
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Vascular System
(Blood vessels of the body)
 Two circulations
 Systemic
 Pulmonary
 Arteries and veins usually run together
 Often nerves run with them
 Sometimes the systems do not have bilateral
symmetry
 In head and limbs, most are bilaterally symmetrical
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Pulmonary Circulation

Pulmonary trunk branches
 Right and left pulmonary arteries
 Division into lobar arteries
 3 on right
 2 on left
 Smaller and smaller arterioles, into capillaries surrounding alveoli
 Gas exchange

Pulmonary system pressure is only 1/6 of systemic blood pressure
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Pulmonary Circulation
 After gas exchange blood enters venules
 Larger and larger into Superior and Inferior
Pulmonary veins
 Four Pulmonary Veins empty into left atrium
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In lungs
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Systemic Circulation
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Oxygenated blood to body
Leaves LV through Ascending Aorta
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Only branches are the 2 coronary arteries to the heart
Aortic Arch has three arteries branching from it:
1. Brachiocephalic trunk, has 2 branches:
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Right common carotid a.
Right subclavian a.
2. Left common carotid a.
3. Left subclavian a.
Ligamentum arteriosum
connecting to pulmonary a.
remember aortic arches…
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 Descending aorta
 Thoracic aorta
 at T12 becomes
abdominal aorta
 Abdominal aorta
 ends at L4
branching into:
 R & L common
iliac arteries
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 Common
carotids branch:
 Internal carotids
 External carotids
 Subclavian: 3
branches
 Vertebral
arteries
 Thyrocerical
trunk
 Costocervical
trunk
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Head and neck
 Common carotids just
lateral to trachea: feel
 At larynx divides into
internal & external
 External carotid:
supplies head
external to brain and
orbit
 Feel superficial
temporal a.
 Middle meningeal:
vulnerable (branch of
maxillary)
 Internal carotid
 Supply orbits and
most of cerebrum
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Internal carotid a.
 Enters skull
through carotid
canal
 Gives off:
 Ophthalmic artery
 Then divides into
anterior and middle
cerebral arteries
(see next slides):
together they supply
80% of cerebrum
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Angiogram
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arteriogram
 Middle cerebral
arteries run through
lateral fissures
 Anterior cerebral
arteries of each
side, through
anterior
communicating
artery, anastomose
(an anastomosis is a union)
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 R and L vertebral arteries* (from subclavians)
 Ascend through vertebral foramina of C6-C1
transverse processes
 Through foramen magnum into skull
 Join to form one Basilar artery*
*
*
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*
*
 Basilar artery: branches
 Divides into posterior cerebral arteries
 Posterior communicating arteries connect to
middle cerebral arteries
Note how it loops
CIRCLE OF WILLIS
around pituitary
(now called “cerebral arterial circle”)
gland & optic chiasm
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Upper limb
 Subclavian runs
laterally onto 1st rib,
under clavicle
 Enters axilla as
axillary artery
 Sends branches
 Continues as
brachial artery in
upper arm
 Splits into radial &
ulnar arteries
 See hand supply
Feel brachial & radial pulses
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overview
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Thorax
 Anterior intercostals
branch off Internal
thoracic* (branch of
subclavian)
 Posterior
intercostals branch
off Thoracic aorta
*
Small bronchial
arteries supply the
lung structures
Intercostal arteries,
veins and nerves
run just UNDER the
ribs
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Arteries to the abdomen
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Arise from the abdominal aorta
At rest, ½ arterial blood is here!
Three single midline branches supply the digestive tube
1. Celiac trunk
2. Superior mesenteric artery
3. Inferior mesenteric artery
1.
2.
3.
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1. Celiac trunk: divides into 3 right away: left gastric,
splenic & common hepatic (see pic; the latter is
the only which goes off to the right)
2. Superior mesenteric supplies most of intestines
Definition of mesenteries: double layered sheets of peritoneum
that support most organs in the abdominopelvic cavity
1.
2.
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3. Inferior mesenteric supplies distal half of
large intestine
(The 1, 2 and 3 are branches of the abdominal aorta)
1.
2.
3.
Know what these terms mean: phrenic, gastric, hepatic, renal, colic
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Arteries to the abdomen
 Paired branches off the abdominal aorta
supply adrenal glands, kidneys, gonads
and abdominal body wall
supply
diaphragm
supply
adrenals
to kidney
3.
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 Abdominal aorta
branches into
Common iliacs at
L4; these branch
into
 Internal iliacs to
pelvic organs,
perineum,
buttocks, medial
thighs
 External iliacs: to
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rest of lower limbs
 External iliac
passes under
inguinal ligament
becoming Femoral
artery
 At back of knee
femoral becomes
popliteal artery,
and branches
Feel dorslis pedis &
posterior tibial
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review
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review
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Systemic Veins
 3 major vessels enter Right Atrium:
 SVC (superior vena cava)
 IVC (inferior vena cava)
 Coronary sinus
 Many veins are very superficial (unlike
arteries)
 Venous plexuses (networks of anastomoses
and parallel veins) are very common
 Head and hepatic portal systems are unusual
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 Dural sinuses
 Drain the veins of
the brain
 Cavernous sinuses
 Carotid arteries and
some cranial nerves
run within them
 Dangerous if trauma
 Come together as
sigmoid sinus –
becomes Internal
Jugular vein
 Exits skull through
jugular foramen
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 Internal jugular veins
 Drain most of blood from brain
 Run lateral to internal then common carotid
 At base of neck joins subclavian v. to form brachiocephalic v.
 External jugulars – drain some of scalp & face
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Vein
overview
Note that unlike the arteries, the veins
have a brachiocephalic on the right
and left sides
Azygos system
drains the thorax:
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 Deep veins of
upper limbs follow
arteries, most of
them double to
one artery
 Superficial veins:
see pic
 Blood drawn from
median cubital
vein in antecubital
fossa
(look at)
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 Tributaries of IVC: note asymmetry
 Left gonadal and suprarenal veins drain into left renal
vein
 On right they drain directly into IVC
 Right and left hepatic veins enter superior part of IVC
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 Hepatic portal system
 Picks up digested nutrients from stomach & intestines and delivers them
to liver for processing and storage
 Storage of nutrients
 Detoxification of toxins, drugs, etc.
 Two capillary beds
 Route: artery to capillaries of gut to hepatic portal vein to liver’s
capillaries to hepatic vein to IVC
Don’t confuse hepatic vein with hepatic portal vein
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Kind of confusing…
Superior mesenteric
and splenic veins join
to form hepatic
portal vein, which
goes up into liver
Inferior mesenteric
empties into the
splenic vein
*
*
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(same info with different pic)
Tributaries of hepatic
portal vein:
-superior mesenteric vein
-splenic vein
-inferior mesenteric vein
 Hepatic portal system
 Picks up digested nutrients from stomach & intestines
and delivers them to liver for processing and storage
 Storage of nutrients
 Detoxification of toxins, drugs, etc.
 Two capillary beds
 Route: artery to capillaries of gut to hepatic portal
vein to liver’s capillaries to hepatic vein to IVC
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Leg veins
 Names similar to
arteries
 Femoral becomes
external iliac after
crossing under
inguinal ligament
_________used for grafting in coronary
artery bypass grafts: is the
longest vein in the body
 External iliac joins
with internal iliac to
form common iliac
vein
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Fetal
Circulation
 The one umbilical
vein brings blood
which has been to
the placenta for
oxygenation (by gas
diffusion from mom’s
blood)
 The pair of umbilical
arteries (branches
from baby’s internal
iliac arteries) carry
blood to placenta to
pick up oxygen and
nutrients
 Fetal heart starts
beating at 21 days
post conception
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Some Diseases
 Atherosclerotic cardiovascular disease
 Cerebrovascular disease – affects brain, strokes
 Coronary artery disease (CAD) – arteries of heart
 Peripheral vascular disease (PVD) – arterial
 Affecting veins
 Chronic venous insufficiency – venous = veins
 Deep venous thrombosis (DVT)
 Aneurysms
 Portal hypertension
 Hypertension
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