Week 1 Review - Abdominal Vascular Anatomy PDF

WEEK 1 REVIEW LECTURE 1: ABDOMINAL VASCULATURE 3 layers of a blood vessel - Tunica adventitia: outermost layer of the vessel that encapsulates the blood vessel in a thin fibrous wall ‣ Vasa vasorum: the tiny veins and arteries that supply the gre...

WEEK 1 REVIEW LECTURE 1: ABDOMINAL VASCULATURE 3 layers of a blood vessel - Tunica adventitia: outermost layer of the vessel that encapsulates the blood vessel in a thin fibrous wall ‣ Vasa vasorum: the tiny veins and arteries that supply the greater blood vessel itself (necessary for muscle) ‣ Nerves - Tunica media: middle, “meaty” layer of the vessel ‣ External elastic membrane: outer layer of the tunica media ‣ Smooth muscle: inner layer and composes most of the tunica media - Tunica intima: innermost layer of the vessel ‣ Internal elastic membrane: outer layer of the tunica intima ‣ Lamina propria: middle layer of smooth muscle and connective tissue ‣ Basement membrane: additional middle layer of the tunica intima ‣ Endothelium: inner layer of of the tunica intima and the overall innermost layer of the greater blood vessel to psoas major Abdominal arteries anterior lateral to the muscle, LT - spine - The abdominal aorta (AO) ‣ Located in the retroperitoneal cavity anterior and left of the IVC and spine  ‣ Originates from the left ventricle of the heart ‣ Posterior to the diaphragm ✴ The diaphragm divides the AO into the descending thoracic AO and descending abdominal AO ‣ Bifurcates (aka splits) at the umbilicus into the right and left iliac arteries ‣ Normally ≤ 3 cm and tapers into a narrower diameter as it descends ✴ Normal iliac arteries are ≤ 1 cm - Branches of the AO arch (located in the thoracic cavity, not in the abdomen) ‣ 1st branch: Right innominate artery/Brachiocephalic trunk ‣ 2nd branch: Left common carotid artery (CCA) 123 ‣ 3rd branch: Left subclavian artery - Branches of the abdominal AO ‣ Celiac trunk: the 1st branch of the abdominal AO ✴ Originates from the anterior AO 1 - 3 cm below the diaphragm ✴ Separates the proximal and distal abdominal AO ✴ 3 branches: Common hepatic artery (CHA): right side of the celiac trunk (aka right side of the seagull sign) ✓ Borders the superior surface of the pancreas head (aka vessel runs parallel and on top of the pancreas towards the liver)  ✓ Low resistance Doppler waveform ✓ Branches: ➡ Gastroduodenal artery ➡ Right gastric artery ➡ Proper hepatic artery (further divided into…) ★ Right and left hepatic arteries ★ Cystic artery (technically a branch of the right hepatic artery) Splenic artery (SA): left side of the celiac trunk (aka left side of the seagull sign) * 4-6 mm in diameter ! ✓ Tortuous in nature (twisted) with numerous branches ✓ Borders the superior surface of the pancreas body and tail (aka vessel runs parallel to and on top of the pancreas towards the spleen) ✓ Low resistance Doppler waveform Left gastric artery: limited visualization with ultrasound due to its very small size celiac before artem teaching and into CHA , LT gastric , SA - Normally 7 mm in diameter Low resistance Doppler waveform in the trunk and branches ✴ Objective: supplies blood to the stomach, liver, spleen, and small intestine  CHA = liver SA = spleen Left gastric = stomach and small intestines ‣ Superior mesenteric artery: the 2nd branch of the abdominal AO ✴ Originates from the anterior AO 1 - 2 cm below the celiac trunk ✴ Runs parallel to the anterior AO (aka vertical) and posterior to the pancreas ✴ Normally 6 mm in diameter ✴ Doppler waveform depends on fasting state Fasting = high resistance = vessels constricted to decrease blood flow Non-fasting = low resistance = vessels dilated to increase blood flow ✴ Objective: supplies blood to the small intestine, cecum, and ascending and transverse colon ‣ Right and left renal arteries: the branches of the abdominal AO that supply the kidneys respectively ✴ Vessels originate from the lateral walls of the AO respectively just below the SMA  Right vessel is longer than the left due to proximity to the right kidney from the AO and the fact that it has to travel around the IVC ✴ Right renal artery is often seen superior to the IVC ✴ Left renal artery is more superior than the right This is because the liver, which is very large in size, is on the right side of the body and forces the right kidney to be in a more inferior position than the left ✴ Normally 4 - 5 mm in diameter ✴ Branches into 4 or 5 smaller arteries prior to reaching the hilum of the kidney ✴ Low resistance Doppler waveform Vessels are always dilated because they always require blood ✴ Objective: supplies blood to each kidney respectively ‣ Gonadal arteries: the branches of the abdominal AO that supply the reproductive organs ✴ Difficult to visualize with ultrasound due to small size ✴ Arise from the anterior lateral aspect of the AO, inferior to the renal arteries following the psoas muscle ‣ Inferior mesenteric artery: the last branch of the abdominal AO before it bifurcates into the right and left iliac arteries  ✴ Originates from the anterior lateral side of the AO, 4 cm away from the bifurcation (aka somewhere between the renal vessels and the iliac bifurcation) ✴ Limited visualization on ultrasound due to small size ✴ Normally 3 mm in diameter ✴ High resistance Doppler waveform ✴ Objective: supplies blood to the descending colon, sigmoid colon, and rectum Diaphragmatic crus: a dome-shaped muscular structure that crosses the &TCrusSeei a trV & RTCVs ea. &. midline posterior to the IVC and anterior to the AO - Often mistaken for the right renal artery (RRA)! ‣ The RRA is anterior to the right crus diameter : 11 5 cm Normal Abdominal veins. e - Inferior vena cava (IVC): ‣ Located in the retroperitoneal cavity anterior to the spine, posterior to the intestines and the caudate lobe of the liver, and to the right of the AO ‣ Passes through the diaphragm and terminates in the right atrium of the heart ‣ Formed by convergence of the common iliac veins ‣ Branches of the abdominal IVC: ✴ Hepatic veins: the 1st branches of the IVC from the heart  Located just superior to the renal veins Hepatofugal flow: blood moves away from the liver ✓ Hepatopedal flow: blood moves towards the liver 3 branches: M RT LT ✓ Right branch: drains the right lobe of the liver and divides the right lobe into anterior and posterior portions and right ✓ Middle/intermediate branch: drains the caudate lobe of the liver and divides the caudate lobe into right and left portions ✓ Left branch: drains the left lobe of the liver and divides the left lobe into medial and lateral segments Normally 4 - 7 mm in diameter ✓ Increases in diameter as vessels get closer to the IVC Pulsatile Doppler waveforms Objective: empty blood from the liver into the IVC ✴ Renal veins: the 2nd branches of the IVC from the heart Located just inferior to the renal arteries, with the LRV being longer than the RRV due to proximity ✓ The LRV is seen anterior to the abdominal AO LRV receives blood from gonadal veins and suprarenal veins before terminating into the IVC Normally 4 - 6 mm in diameter  found only arteries - in No pulsatility in Doppler waveforms Objective: drain deoxygenated blood from the kidneys back into the IVC ✴ Superior mesenteric vein (SMV): joins the splenic vein to form the PV Drains the proximal portion of the large intestine and portions of the small intestine Blood flows towards the head posterior to the pancreas neck and anterior to the uncinate process ✴ Splenic vein (SV): joins with the SMV to form the PV Runs along the posterior border of the pancreas Does not drain directly into the IVC ✓ Joins with the inferior mesenteric vein (IMV) first before joining the SMV to form the PV Normally 4 - 6 mm in diameter ✴ Gonadal veins: the next branches of the abdominal IVC after the renal veins Right gonadal vein: located lateral and inferior to the RRV and drains directly into the IVC Left gonadal vein: technically a branch of the LRV, it doesn’t drain directly into the IVC  ✴ Common iliac veins: the lowest branches of the abdominal IVC that splits - The portal venous system ‣ Portal veins wear pajamas! ✴ Appear on a 2D image with hyperechoic borders, which is how we are able to distinguish them from hepatic veins! ‣ Main portal vein (MPV or PV): originates from the junction of the SMV and SV, posterior to the pancreas and just to the right of the midline ✴ Bifurcates at the porta hepatis into right and left portal veins ✴ Normally < 13 mm in diameter & portal triad = proper hepatic Common art. bile duct + PV + ‣ Right portal vein (RPV): runs centrally and horizontally in the right lobe of the liver ✴ Bifurcates into anterior and posterior branches that divide the right lobe of the liver into anterior and posterior segments ✴ Larger than the left portal vein ‣ Left portal vein (LPV): runs in the left lobe of the liver ✴ Branches divide the left lobe of the liver into medial and lateral segments RT 6 mm, must R/O appendicitis ✴ Sonographic appearance of the appendix SAG = finger-like projection TRV = bullseye  burearea sac lesser liver lesser entum stomach pancreas duodenum transverse color greatertum  supracolic transverse compartment color descending color ascending colon infracolic compartment LT paracolic gutter RT paracolic gutter  fimbrial utems ovary anterior cul-de-sac rectum urinary bladder posterior cul-de-sac public is symphys vaginalal space a o anus wrethra  WEEK 4 REVIEW THE THYROID Thyroid: an endocrine gland consisting of two lateral lobes and a connecting isthmus between the lobes - Anatomy of the thyroid and neck ‣ Directional terms ✴ Thyroid lies within the inferior portion of the neck ✴ Thyroid lies anterior to the trachea ✴ Trachea is medial to both thyroid lobes ✴ Common carotid arteries (CCA) and internal jugular veins (IJV) lie posterior and lateral to the thyroid ✴ Esophagus is LT lateral to the trachea and LT thyroid lobe Most often seen while scanning in TRV ‣ Muscles of the neck ✴ Strap muscles: group of muscles within the neck Sternohyoid (SH): located anterior and lateral within the neck adjacent to the OH Sternothyroid (ST): located closest to the thyroid Omohyoid (OH): located anterior and lateral within the neck adjacent to the SH  Sternocleidomastoid (SCM): located most anterior and lateral within the neck The longus colli muscle, esophagus, and neurovascular bundle are located posterior to the thyroid ✓ CCA, IJV, and vagus nerve are located posterolateral to the thyroid ‣ Dimensions ✴ Length = 4-6 cm ✴ A/P = 2-3 cm ✴ Width = 1.5-2 cm ✴ Isthmus A/P = 2-6 mm (most narrow portion of the thyroid, always measured A/P) - Physiology of the thyroid ‣ Major role in growth and development in the endocrine system ‣ Regulates metabolism by synthesis, storage, and secretion of thyroid hormones ✴ Triiodothyronin (T3): regulates metabolic rate ✴ Thyroxine (T4): regulates metabolic rate ✴ Calcitonin: lowers blood calcium levels by promoting uptake of calcium by bones, kidneys, and intestines More a primary function of the parathyroid than the thyroid  ✴ Thyroid-stimulating hormone (TSH): produced by the pituitary gland and regulates T3 and T4 - Sonographic appearance of the thyroid ‣ Homogeneous with medium-level echoes similar to the liver and testes ‣ Hyperechoic to the surrounding muscles and vasculature ‣ Most to least echogenic (brightest to darkest) = thyroid > muscles > blood vessels - Normal variants of the thyroid ‣ Pyramidal lobe: an accessory lobe usually on the LT lobe of the thyroid ✴ 10-40% of the population ✴ A superior extension from the isthmus to the hyoid bone Parathyroid: small, encapsulated, oval glands attached to the posterior surfaces of the lateral lobes of the thyroid gland - Most people have 4 parathyroid glands - Location ‣ Parathyroids are located posterior to the thyroid ‣ Parathyroids are located anterior to the longus colli muscle ‣ Superior parathyroid glands: located more posterior and medial ‣ Inferior parathyroid glands: located more anterior and may be imbedded in the thyroid tissue - Dimensions  ‣ Length = 5-7 mm ‣ A/P = 1-2 mm ‣ Width = 3-4 mm - Physiology of the parathyroids ‣ Maintains homeostasis of blood calcium by secreting parathyroid hormone ✴ Parathyroid hormone (PTH): hormone that triggers bones to release calcium back into the bloodstream when levels are too low - Sonographic appearance of the parathyroid ‣ May be seen in young patients but not normally seen in adults  Thyroid trachea Sternohyoid Strap omonyoid parathyroid muscles Sternothyroid Sternocleido- mastoid internal jugular vein common esophagus carotid artery spine THE FEMALE PELVIS Anatomy of the female pelvis - Located in the RT/LT iliac regions and the hypogastric region - Linea terminalis: circular line that separates the true and false pelvis ‣ False/Major/Greater pelvis: the more superior pelvic cavity that extends from the iliac crest to the linea terminalis ‣ True/Minor/Lesser pelvis: the more posterior and inferior pelvic cavity that extends from the linea terminalis to the pelvic diaphragm ✴ Pelvic inlet: region from the pubic bone to the sacrum ✴ Pelvic outlet: region from the ischial tuberosities to the coccyx - Pelvic girdle: the bones that comprise the pelvis ‣ Sacrum ‣ Coccyx ‣ Innominate bones: bilateral fusion of 3 bones ✴ Ilium ✴ Ishium ✴ Pubis - Muscles of the pelvis ‣ False pelvis ✴ Iliopsoas ✴ Rectus abdominus  ✴ Iliacus ‣ True pelvis ✴ Obturator internus ✴ Piriformis ✴ Pelvic diaphragm Levator ani (set of muscle that elevate the anus) ✓ Pubococcygeus ✓ Puborectalis ✓ Iliococcygeus Coccygeus - Ligaments of the pelvis ‣ Broad ligament: double folds of peritoneum but not a true ligament, more like a drape of tissue ✴ Contains the fallopian tube, round ligament, ovarian ligament, vessels, and nerves of the uterus and ovaries ‣ Uterine ligaments: sits within the broad ligament ✴ Contains the round ligament, cardinal ligament, and uterosacral ligament ‣ Ovarian ligaments: part of the broad ligament ✴ Contains the infundibulopelvic ligament, ovarian ligament, and mesovarium ligament - Blood supply of the female pelvis ‣ Uterine blood vessels ✴ Uterine artery (from the internal iliac/hypogastric artery) and branches Vaginal artery Arcuate artery Radial artery ✓ Further branches into spiral arteries (these slough off during menstruation) Straight artery ‣ Vaginal blood vessels ✴ Vaginal artery (branch of the uterine artery) ‣ Ovarian blood vessels ✴ Uterine artery ✴ Ovarian artery (branch of the uterine artery) - Potential spaces of the female pelvis ‣ Anterior cul-de-sac/Morison’s pouch/Vesicouterine pouch: located between the anterior uterus and bladder ‣ Posterior cul-de-sac/Pouch of Douglas/Rectouterine pouch: located between the uterus and rectum ✴ Most dependent portion of the peritoneal cavity  ‣ Space of Retzius/Prevesical space/Retropubic space: located between the anterior bladder wall and the pubic symphysis - Organs of the female pelvis ‣ Vagina: extends from the external genitalia to the cervix of the uterus ✴ Size: 7-10 cm ✴ Fornices: pockets around the base of the cervix Anterior fornix Lateral fornix Posterior fornix ✴ 3 layers of the vagina Mucosal lining: innermost layer Muscle wall: middle layer of thin, smooth muscle Adventitia: outermost layer ✴ Sonographic appearance of the vagina Isoechoic to the uterus with a central linear echogenic stripe ‣ Uterus: a pear-shaped, muscular, hollow organ that nourishes the developing fetus during pregnancy ✴ 3 layers of the uterus Endometrium: innermost, mucosal layer of the uterus ✓ Superficial/Functional layer: increases in size during the menstrual cycle and sloughs off during menstruation  ✓ Deep/Basal layer: composed of the stroma and mucosa and is not affected by the menstrual cycle Myometrium: the middle layer of the uterus composed of smooth muscle Serosa: outermost peritoneal membrane of the uterus ✴ 4 sections of the uterus Fundus: widest, most superior portion of the uterus Body/Corpus: largest portion of the uterus Isthmus: constricted portion of the uterus that joins the cervix (aka where the body narrows before turning into the cervix) Cervix: lower cylindrical portion of the uterus that opens into the vaginal canal ✓ External os: opens into the vagina ✓ Internal os: opens into the uterus ✴ Sonographic appearance of the uterus Hypoechoic to the surrounding bowel Smooth outer contour ✴ Uterine dimensions Uterus size varies with age and parity (aka number of births) ✓ Pre-pubertal dimensions = 1-3 cm x 0.5-1 cm x 0.5-1 cm ✓ Post-pubertal dimensions  ➡ Nulliparous (no live births) = 6-8 cm x 3-5 cm x 3-5 cm ➡ Multiparous (at least one live birth) = 8-10 cm x 5-7 cm x 5-7 cm ✓ Post-menopausal dimensions = 3-5 cm x 2-3 cm x 2-3 cm ➡ Significant decrease in size returning to a similar shape to a pre-pubertal uterus Cervical length = ≥3 cm Endometrial thickness varies depending on the stage of the menstrual cycle ✓ Pre-menopausal = 18-20 mm ✓ Post-menopausal = 4 mm ✴ Positions of the uterus Anteverted: position of the uterus in which the body and fundus are tilted anteriorly ✓ Fundus points anteriorly ✓ Most common position of the uterus Anteflexed: position of the uterus in which the body and fundus are bent anteriorly ✓ Fundus points anteriorly Retroverted: position of the uterus in which the body and fundus are tilted posteriorly  ✓ Fundus points superiorly Retroflexed: position of the uterus in which the body and fundus are bent posteriorly ✓ Fundus points posteriorly Levoversion: position of the uterus in which the body and fundus are tilted to the left side of the body Dextroversion: position of the uterus in which the body and fundus are tilted to the right side of the body ‣ Fallopian tubes: coiled muscular tubes that direct mature ovum from the ovaries to the uterus via peristalsis ✴ Dimensions Length = 7-12 cm Diameter = 3 mm ✴ 4 sections of the fallopian tube Interstitial: narrowest portion of the tube enclosed by the uterus at the cornua ✓ Worst possible location for an ectopic pregnancy Isthmus: the short, straight section of the tube Ampulla: widest and longest section of the tube ✓ Location of fertilization  Infundibulum: funnel-shaped portion of the tube that opens into the peritoneal cavity ✓ Fimbriae: projections that direct ovum into the tube ‣ Ovaries: a pair of almond-shaped organs that form ova (aka eggs) ✴ Dimensions Pre-pubertal = 3 cc Post-pubertal = 3.5-5 cm x 1.5 cm (or 3.2-5.1 cc) Post-menopausal = 2 cm x 1 cm x 0.5 cm (or 1.3 cc) ✴ 2 layers of the ovary Cortex: the outer functional layer of the ovary containing follicles Medulla: the inner layer of the ovary containing blood vessels ✴ Location Ovaries are normally lateral to the uterus Ovaries are sometimes superiolateral to the uterus Ovaries are anterior and medial to the ureters and internal iliac arteries (aka somewhere between the uterus and pelvic vessels/ muscles)  sacrum fassets Nurs lineaanal is THE MALE PELVIS Anatomy of the male pelvis - Scrotum: a pouch of skin continuous with the abdomen that supports the testes ‣ Contains the testicles, epididymis, and the proximal portion of the vas Deferens ‣ Median raphe: externally divides the scrotum into right and left portions ‣ Tunica dartos: internally divides the scrotum into left and right sacs ‣ Cremaster muscle: suspends each testicle and raises/lowers them to create ideal temperature for spermatogenesis ‣ Tunica vaginalis: outer covering of the testicle, surrounds the tunica albuginea ‣ Tunica albuginea: inner covering of the testicle, surrounded by the tunica vaginalis - Testicles: a pair of organs where sperm is produced ‣ Location/Orientation ✴ Divided into sections called lobules which each contain 1-3 seminiferous tubules ✴ Joined at the mediastinum to form the rete testis Empties into the efferent ducts, which empty into the epididymis ‣ Vascularity  ✴ RT gonadal vein branches directly from the IVC ✴ LT gonadal vein branches from the LT renal vein ✴ RT and LT gonadal arteries branch directly from the AO ‣ Dimensions ✴ Length = 3-5 cm ✴ A/P measurement = 2-3 cm ✴ Width = 2-3 cm ‣ Sonographic appearance of the testes ✴ Homogenous, medium-level echoes ✴ Mediastinum is highly echogenic along the long axis of the testes ✴ A bit of anechoic fluid is found between the layers of the tunica vaginalis ‣ Normal variants of the testes ✴ Appendix epididymis: an extension/flap coming off of the epididymis ✴ Appendix testes: an accessory small piece of testicular tissue - Epididymis: an organ that lies along the posterolateral aspect of each testicle ‣ Divided into the head, body, and tail ✴ Epididymis head: the superior aspect of the testicle and the largest part of the epididymis  ✴ Epididymis body: runs along the posterior aspect of the testicle ✴ Epididymis tail: the smaller, inferior portion of the epididymis ‣ Ductus epididymis: the single convoluted tube that makes up the epididymis ✴ Size: 6-7 cm ✴ Turns into the vas Deferens, which turns into the ejaculatory duct ‣ Sonographic appearance of the epididymis ✴ Head is posterior and superior to the testicle ✴ Isoechoic/Hyperechoic to the testicle - Spermatic cord: runs from the scrotum through the inguinal canal ‣ Contains the vas Deferens, testicular arteries, pampiniform plexus, lymphatics, nerves, and cremaster muscle fibers - Seminal vesicle: paired glands that join with the vas Deferens to form the ejaculatory duct ‣ Location/Orientation ✴ Vesicles lie posterior and inferior to the bladder ✴ Vesicles lie posterior and superior to the prostate ‣ Ejaculatory duct: travels through the prostate and empties into the prostatic urethra  urinary bladder pubisassis rectum vas seminalnicles Deferens prostate in bulbouretha urethra penis analinter testis epididymis scrotum  ret is wasterens epididym pidid unic nea epididymists a seminifers turicaginalis  epididymis efferent ducts tunica vaginalis seminiferous tubules Deferen tunica adventifia lobule testis VASCULARITY Lower extremity vasculature - Arteries ‣ Divided into 3 systems ✴ Aortoiliac (aka inflow): area from the iliac bifurcation to the inguinal ligament that supplies the buttocks, pelvis and thighs Distal abdominal AO, CIA, EIA, IIA/hypogastric artery ✴ Femoropopliteal (aka outflow): area from the inguinal ligament to the trifurcation of the popliteal artery that supplies the thighs CFA, deep FA, superficial FA, popliteal artery Most common site of atherosclerosis ✴ Tibioperoneal (aka runoff): area from the end of the popliteal artery (aka the tibialperoneal trunk) to the ankle that supplies the calves and feet Peroneal artery, ATA, PTA ‣ Arteries lie lateral to veins ‣ Order of lower extremity arteries: aorta (AO), common iliac arteries (CIA), external iliac and internal iliac arteries (EIA and IIA), common femoral artery (CFA), deep femoral and superficial femoral arteries (DFA and SFA), popliteal artery (POP), anterior tibial and posterior tibial arteries (ATA and PTA).  - Veins ‣ 3 types of veins ✴ Deep veins CIV, EIV, IIV ✴ Superficial veins CFV, GSV, FV, DFV n e - longestveini > ✴ Perforating veins: connect the deep and superficial venous systems ‣ There are two veins for every one artery ‣ Order of lower extremity veins: inferior vena cava (IVC), common iliac veins (CIV), external iliac and internal iliac veins (EIV and IIV), common femoral vein (CFV), great saphenous vein (GSV), femoral vein and deep femoral vein (FV and DFV), popliteal vein (POP), peroneal vein (PV), anterior tibial and posterior tibial veins (ATV and PTV) Upper extremity vasculature - Arteries ‣ Order of upper extremity arteries: subclavian artery, axillary artery, brachial artery, ulnar artery (pinkie side), radial artery (thumb side) - Veins ‣ Deep veins ✴ Order of upper extremity deep veins: subclavian vein, axillary vein, brachial veins, ulnar vein (pinkie side), radial vein (thumb side)  ‣ Superficial veins ✴ Order of upper extremity superficial veins: axillary vein, cephalic vein, basilic vein Cerebrovascularity - 3 main branches of the AO arch ‣ Brachiocephalic trunk/Innominate artery ✴ Branches into the RT common carotid artery (RCCA) and RT subclavian ✴ Branches into RT external carotid and RT internal carotid ‣ LT common carotid artery (LCCA) ✴ Branches into LT external carotid and LT internal carotid ‣ LT subclavian artery - Common carotid arteries ‣ Located medial to the jugular veins and lateral to the thyroid Internal carotids External carotids Posterior/Lateral to ECCAs Anterior/Medial to ICCAs Larger Smaller No visible branches Branches Low resistance waveforms High resistance waveforms Supplies brain and eyes Supplies face, neck, and scalp - Vertebral arteries  ‣ Pass through the cervical vertebrae to supply blood to the posterior aspect of the brain - Circle of Willis: collateral pathway in the brain (aka if there is a blockage in one branch, blood can still get to the brain)