Vessels and Circulation

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Some embryology

▪ There are at first six pairs of aortic arches

▪ In fish these are connected to the gills

▪ They undergo a transformation to form the great arteries ▪ Birds use the right

arch of the fourth pair as the main artery

▪ Mammals use the left arch of the fourth pair to become the main artery of the body, the aorta

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Full set of arches develops, but not all present at the same time; (before transformation)

Transformation : 4th through 7th

weeks: some persist, some atrophy

Fetal development (anterior view)

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Right common carotid a. !Brachiocephalic trunk

4th ARCHES BECOME: Left: aortic arch Right: brachiocephalic trunk

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What the aortic arches become…

Right common carotid a. !Brachiocephalic trunk

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3 Major types of blood vessels

▪ 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: endothelium (simple squamous epithelium) May have subendothelial layer if 1mm or

larger

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▪ 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 & elastin for strength & recoil

11“muscular” middle sized artery

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ARTERIES

▪ Carry blood away from the heart ▪ From big to small, these are the

categories: 1. Elastic arteries 2. Muscular arteries 3. Arterioles (then these to capillaries)

!▪ Pressure diminishes along the route

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1. ELASTIC ARTERIES ▪ Act as conduits ▪ Are the largest ▪ (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 ▪ Includes the Aorta and its

branches

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2. MUSCULAR ARTERIES ▪ Act as distributing

arteries ▪ Middle sized 1cm-.3 mm ▪ 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”

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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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CAPILLARIESHeart 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

single layer of endothelial cells surrounded by basement membrane

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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 in diameter 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

▪ 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 Circuit ▪ Pulmonary Circuit !

▪ 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

[means both arteries and veins]

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PULMONARY CIRCULATION

▪ Pulmonary trunk branches:

▪ Right and left pulmonary arteries (are blue: deoxygenated) ▪ 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 venules eventually become

Superior and Inferior Pulmonary veins (red) ▪Four Pulmonary Veins empty into left atrium

27GAS EXCHANGE

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In lungsAlveolus

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SYSTEMIC CIRCULATIONOxygenated blood is sent to the body Leaves LV through Ascending Aorta

Only branches of ascending aorta are the 2 coronary arteries to the heart, right & left coronary arteries (not shown in the pic here)

Aortic Arch has three arteries branching from it: 1. Brachiocephalic trunk, which has 2 branches:

▪ Right common carotid a. ▪ Right subclavian a.

2. Left common carotid a. 3. Left subclavian a.

!Ligamentum arteriosum- scarred connection to pulmonary a.

!remember aortic arches…

1 2 3

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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

Before talking about the arteries to the head and neck we will finish the course of the aorta after it arches

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!▪ Common carotids

branch: ▪ Internal carotids ▪ External carotids

▪ Subclavian: 3 branches off of it before it goes into the armpit as the axillary artery 1. Vertebral arteries 2. Thyrocerical trunk 3. Costocervical

trunk

123

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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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The middle meningeal artery runs through the foramen spinosum onto the inner surface of the skull, supplying it and the dura; it is vulnerable to trauma because of the thinness of the temporal bone here

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Internal carotid artery▪ 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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▪ Middle cerebral arteries run through lateral fissures of brain

▪ Anterior cerebral arteries of each side, through anterior communicating artery, anastomose

(an anastomosis is a union)

arteriogram

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▪ R and L vertebral arteries* (1st branches of 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

CIRCLE OF WILLIS(now called “cerebral arterial circle”)

Note how it loops around pituitary gland & optic chiasm

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Upper limb▪ Subclavian artery-

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* (a branch of subclavian)

▪ Posterior intercostals branch off Thoracic aorta !

!! Intercostal arteries,

veins and nerves run just UNDER the ribs

*

Note: the internal thoracic artery is used in coronary artery bypass grafting

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Arteries to abdomen arise from 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

1.

2.

Definition of mesenteries: double layered sheets of peritoneum that support most organs in the abdominopelvic cavity

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3. Inferior mesenteric supplies distal half of large intestine

2.

3.

1.

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

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

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Arteries to the abdomen, continued▪ Paired branches off the abdominal

aorta supply adrenal glands, kidneys, gonads and abdominal body wall

supply diaphragm

3.

supply adrenals

to kidney

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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 rest of lower limbs

(External iliac becomes the Femoral artery after it crosses under the Inguinal Ligament)

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▪ External iliac a. passes under inguinal ligament becoming Femoral artery

▪ At back of knee femoral becomes popliteal artery, and branches:

feel dorslis pedis & posterior tibial pulses

Femoral a.

Aorta

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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 join subclavian v. to form brachiocephalic veins (unlike arteries

there is one on each side) ▪ External jugulars – drain some of scalp & face

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Vein overview

Azygos system drains the thorax:

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

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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 portal vein with hepatic 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 vein empties into the splenic vein

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*

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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

(same info with different pic)

Tributaries of hepatic portal vein: -superior mesenteric vein -splenic vein -inferior mesenteric vein

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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

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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 after conception

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[called Fossa ovalis now]

[called Ligamentum arteriosus now]

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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