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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. Ventral (anterior) view.

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some embryology first
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
ventral anterior view
Ventral (anterior) view

Transformation :

4th through 7th

weeks: some persist,

some atrophy

Full set of arches develops,

but not all present at

the same time; (before



4th arches become:

Left side: aortic arch

Right side: brachiocephalic trunk

Right common carotid a ------------------------------.

Right subclavian a. --------------------------

Brachiocephalic trunk-----------------------------------

what the aortic arches become
What the aortic arches become…

Right common carotid a ---------------------------.

Right subclavian a. ---------------------------

Brachiocephalic trunk-------------------------------

3 major types of blood vessels
3 Major types of blood vessels
  • Body
  • RA
  • RV
  • Lungs
  • LA
  • LV
  • Boby
  • Arteries
  • Capillaries
  • Veins

Arteries carry blood away from the heart

-”branch,” “diverge” or “fork”

Veins carry blood toward the heart

-”join”, “merge,” “converge”

general characteristics of vessels
General characteristics of vessels
  • Three layers (except for the smallest)
    • Tunica intima - AKA intima
    • Tunica media – smooth muscle
    • Tunica externa - AKA adventitia
  • Lumen is the central blood filled space
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

  • 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
  • Elastic arteries: act as conduits
    • 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


    • Aorta and its branches
arteries continued
Arteries continued

2. Muscular arteries: act as distributing arteries

  • 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”

arteries continued13
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


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

There’s a capillary “bed” in almost all tissues

capillary permeability
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
  • 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
special features of veins
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)

vascular anastomoses
Vascular anastomoses
  • 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
vascular system blood vessels of the body
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
pulmonary circulation
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
pulmonary circulation24
Pulmonary Circulation
  • After gas exchange blood enters venules
  • Larger and larger into Superior and Inferior Pulmonary veins
  • Four Pulmonary Veins empty into left atrium
systemic circulation
Systemic Circulation
  • Oxygenated blood to body
  • Leaves LV through Ascending Aorta
    • Only branches are the 2 coronary arteries to the heart
  • Aortic Arch has three arteries branching from it:
    • Brachiocephalic trunk, has 2 branches:
      • Right common carotid a.
      • Right subclavian a.
    • Left common carotid a.
    • Left subclavian a.

Ligamentum arteriosum

connecting to pulmonary a.

remember aortic arches…

Descending aorta
    • Thoracic aorta
      • at T12 becomes abdominal aorta
    • Abdominal aorta
      • ends at L4 branching into:
      • R & L common iliac arteries
Common carotids branch:
    • Internal carotids
    • External carotids
  • Subclavian: 3 branches
    • Vertebral arteries
    • Thyrocerical trunk
    • Costocervical trunk
head and neck
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
internal carotid a
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



  • Middle cerebral arteries run through lateral fissures
  • Anterior cerebral arteries of each side, through anterior communicating artery, anastomose

(an anastomosis is a union)

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*





Basilar artery: branches
    • Divides into posterior cerebral arteries
  • Posterior communicating arteries connect to middle cerebral arteries


Note how it loops around pituitary gland & optic chiasm

(now called “cerebral arterial circle”)

upper limb
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

  • Anterior intercostals branch off Internal thoracic*(branch of subclavian)
  • Posterior intercostals branch off Thoracic aorta

Intercostal arteries, veins and nerves run just UNDER the ribs


Small bronchial arteries supply the lung structures

arteries to the abdomen
Arteries to the abdomen
  • Arise from the abdominal aorta
  • At rest, ½ arterial blood is here!
  • Three single midline branches supply the digestive tube
    • Celiac trunk
    • Superior mesenteric artery
    • Inferior mesenteric artery




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)
  • Superior mesenteric supplies most of intestines

Definition of mesenteries: double layered sheets of peritoneum

that support most organs in the abdominopelvic cavity




(The 1, 2 and 3 are branches of the abdominal aorta)

3. Inferior mesenteric supplies distal half of large intestine




Know what these terms mean: phrenic, gastric, hepatic, renal, colic

arteries to the abdomen46
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


Abdominal aorta branches into Common iliacs at L4; these branch into
    • Internal iliacs to pelvic organs, perineum, buttocks, medial thighs
    • External iliacs: to 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

systemic veins
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
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 Jugularvein
      • Exits skull through jugular foramen
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
vein overview
Vein overview

Note that unlike the arteries, the veins have a brachiocephalic on the right and left sides

Azygos system drains the thorax:

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)

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
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

kind of confusing
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




(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
Leg veins
  • Names similar to arteries
  • Femoral becomes external iliac after crossing under inguinal ligament
  • External iliac joins with internal iliac to form common iliac vein

_________used for grafting in coronary

artery bypass grafts: is the longest vein in the body

fetal circulation
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
some diseases
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