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 Transformation : 4th through 7th weeks: some persist, some atrophy Full set of arches develops, but not all present at the same time; (before transformation)

Right side: brachiocephalic trunk 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… Right common carotid a ---------------------------. Right subclavian a. --------------------------- Brachiocephalic trunk-------------------------------

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 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

Adventitia (t. externa) – longitudinally running collagen and elastin for strength and recoil

“muscular” middle sized artery

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 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

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 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

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

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

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

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

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)

Exercise helps circulation (because muscles contract and squeeze blood back to the heart)

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) 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 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 Circulation After gas exchange blood enters venules Larger and larger into Superior and Inferior Pulmonary veins Four Pulmonary Veins empty into left atrium

In lungs

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 Abdominal 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 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. 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

Angiogram

Middle cerebral arteries run through lateral fissures arteriogram 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 CIRCLE OF WILLIS Note how it loops around pituitary gland & optic chiasm (now called “cerebral arterial circle”)

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

overview

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

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 1. 2. 3.

Superior mesenteric supplies most of intestines 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 1. 2.

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

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.

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

review

review

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 Jugular vein 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 Azygos system drains the thorax: 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… 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 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 Atherosclerotic cardiovascular disease Affecting veins 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