Vessels and Circulation

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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; (beforetransformation)

Transformation :4th through 7th

weeks: some persist,some atrophy

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Right common carotid a ------------------------------.Right subclavian a. --------------------------Brachiocephalic trunk-----------------------------------

4th arches become: Left side: aortic arch Right side: 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

Body RA RV Lungs LA LV Boby

1.Arteries2.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

10“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 2. Muscular 3. Arterioles (then these to capillaries)

Pressure diminishes along the route

1. 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 pressure

Aorta and its branches

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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”

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Arteries continued3. 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

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 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:

1. Brachiocephalic trunk, has 2 branches: Right common carotid a. Right subclavian a.

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

Ligamentum arteriosumconnecting 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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Middle cerebral arteries run through lateral fissures

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* (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

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

Note how it loops around pituitary 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

Intercostal arteries, veins and nerves run just UNDER the ribs

Small bronchial arteries supply the lung structures

*

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Arteries to the abdomen Arise from the abdominal aorta At rest, ½ arterial blood is here! Three single midline branches supply the digestive tube

1. Celiac trunk2. Superior mesenteric artery3. 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

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

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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

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 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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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 coronaryartery 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 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