Anatomy Chapter 20-2 PDF Notes

Comparison of companion vessels -​ Companion vessels- lie next to each other -​ Arteries / veins serving same body region -​ Arteries -​ Have thicker tunica media and narrower lumen than veins -​ Have more elastic / collagen fibers (spring back to shape)...

Comparison of companion vessels -​ Companion vessels- lie next to each other -​ Arteries / veins serving same body region -​ Arteries -​ Have thicker tunica media and narrower lumen than veins -​ Have more elastic / collagen fibers (spring back to shape) -​ More resilient / resistant to changes in blood pressure -​ Veins -​ Have thicker tunica externa and larger lumen than arteries -​ Have less elastic / collagen fibers -​ Walls collapses if no blood in vessel -​ Capillaries -​ Contain only tunica intima (no subendothelial layer) -​ Composed of endothelium and basement membrane -​ Thin wall allows for rapid gas and nutrient exchange -​ Arteries branch into smaller vessels extending from heart -​ Decrease in lumen diameter -​ Decrease in elastic fibers -​ Increase in relative amount of smooth muscle -​ 3 basic types of arteries: elastic arteries, muscular arteries, arterioles -​ Elastic (conducting) arteries -​ Largest arteries- diameters from 2.5-1 cm -​ Conduct blood from heart to muscular arteries -​ Have large proportion of elastic fibers allowing stretch / recoil -​ Helps propel blood through arteries during diastole -​ Ex: aorta, pulmonary trunk, common carotid, common iliac arteries -​ Muscular (distributing) arteries -​ Medium size- diameters from 0.3 mm-1 cm -​ Distribute blood to specific body regions -​ Muscle allows vasoconstriction (and dilation) -​ Elastic tissue in 2 layers -​ Internal elastic lamina- b/w tunica intima, tunica media -​ External elastic lamina- b/w tunica media, tunica externa -​ Most named arteries- ex: brachial artery, coronary arteries -​ Arterioles -​ Smallest arteries- diameters of 10 micrometers-0.3 mm -​ Largest arterioles have 3 tunics -​ Smaller arterioles have only thin endothelium and single layer of smooth muscle -​ Smooth muscle usually somewhat constricted -​ Called vasomotor tone -​ Regulated by vasomotor center in brainstem -​ Regulate systemic blood pressure / blood flow Capillaries -​ Small vessels connecting arterioles to venules -​ Average length = 1 mm, diameter = 8-10 micrometers -​ Erythrocytes travel in single file (rouleau) -​ Wall consists of endothelial layer on basement membrane -​ Thin wall and small diameter are optimal for exchange b/w blood / tissue fluid -​ 3 types: continuous, fenestrated, and sinusoid -​ Continuous capillaries -​ Endothelial cells form a continuous lining -​ Tight junctions connect cells but don’t form a complete seal -​ Intercellular clefts are gaps b/w endothelial cells of capillary wall -​ Large particles (cells, proteins) cannot pass, but smaller molecules (glucose) can pass -​ Common: found in muscle, skin, lungs, central NS -​ Fenestrated capillaries -​ Endothelial cells form a continuous lining but cells have fenestrations (pores) -​ Fenestrations allow movement of smaller plasma proteins -​ Found in area where much fluid transport happens -​ Ex: intestine capillaries absorbing nutrients, kidney capillaries filtering blood to form urine -​ Sinusoids -​ Endothelial cells form an incomplete lining with large gaps -​ Basement membrane is incomplete / absent -​ Openings allow transport of large substances (formed elements, large proteins) -​ Found in bone marrow, spleen, some endocrine glands -​ Capillary beds- groups of capillaries functioning together -​ Fed by metarteriole- a vessel branch of an arteriole -​ Proximal part encircled by scattered smooth muscle cells -​ Distal part, thoroughfare channel, has no smooth muscle cells -​ Connects to postcapillary venule, draining bed -​ True capillaries- vessels branching from metarteriole, make up bulk of capillary bed -​ Precapillary sphincter -​ Smooth muscle ring at true capillary origin -​ Sphincter relaxation permits blood to flow into true capillaries -​ Sphincter contraction causes blood to bypass capillary bed -​ Vasomotion- cycle of contracting / relaxing of precapillary sphincters -​ At any time, only ¼ of body’s capillary beds are open Veins -​ Venules -​ Smallest veins- diameters of 8-100 micrometers -​ Companion vessels with arterioles -​ Smallest venules are postcapillary venules  -​ Largest venules having all 3 tunics -​ Merge to form veins -​ Small / medium sized veins -​ Companion vessels with muscular arteries -​ Largest veins -​ Travel with elastic arteries -​ Most small, medium, and large veins have numerous valves -​ Prevent blood from pooling in the limbs, ensure flow toward heart -​ Valves made of tunica intima / elastic and collagen fibers -​ Similar structure to heart’s semilunar valves Systemic veins as blood reservoirs -​ Highest percentage of blood at rest -​ Lowest percentage of blood in systemic capillaries -​ Blood can be moved from veins into circulation via vasoconstriction of veins -​ Ex: when more blood needed during exertion -​ Blood can be shifted back into reservoirs via vasodilation -​ Ex: when less blood needed during rest Simple pathway -​ One major artery delivers blood to organ / region -​ An end artery is one that provides only one path for blood to reach an organ / region -​ It branches into smaller arteries that become arterioles -​ Each arteriole feeds into a capillary bed -​ Capillary bed is drained by a venule -​ Venules merge to one major vein -​ Ex: splenic artery delivers blood to spleen, splenic vein drains the organ Alternative pathways -​ Arterial anastomosis (arterial joining) -​ 2 or more arteries converge to supply same region -​ Ex: superior / inferior epigastric arteries supplying abdominal wall -​ If junction is small, the arteries might be functional end arteries -​ Venous anastomosis (more common) -​ 2 or more veins drain same body region -​ Ex: basilic, brachial, and cephalic veins draining upper limb -​ Arteriovenous anastomosis (shunt) -​ Transports blood from artery directly to vein -​ Ex: in fingers, toes, palms, ears -​ Allows areas to be bypassed if body hypothermic -​ Portal system (2 capillary beds in sequence) -​ Path: artery → capillary bed → portal vein → capillary bed → vein -​ Ex: hypothalamo-hypophyseal portal system Lymphatic system -​ Picks up excess fluid not reabsorbed at venous capillary end -​ 15% of fluid not reabsorbed by capillary -​ Filters fluid / returns it to venous circulation Degree of vascularization- extent of vessels in a tissue -​ Metabolically active tissues have high vascularity -​ Ex: brain, skeletal muscle, heart, liver -​ Other structures have little vascularity / are avascular -​ Ex: tendons, ligaments, epithelia, cartilage, cornea, lens of eye Angiogenesis- formation of new vessels -​ Occurs over weeks / months to increase potential perfusion -​ Ex: -​ In skeletal muscle in response to aerobic training -​ In adipose tissue with weight gain -​ In coronary vessels in response to gradual blockage Regression -​ Return of previous state of blood vessels -​ Ex of when vessels regress: -​ In skeletal muscle after individual becomes sedentary -​ In adipose tissue when weight is lost Pulmonary circulation -​ Right ventricle pumps deoxygenated blood to pulmonary trunk -​ Pulmonary trunk splits into lift / right pulmonary arteries -​ Go to corresponding lungs -​ Arteries divide into smaller arteries / arterioles -​ Arterioles branch into pulmonary capillaries -​ Gas exchange occurs in pulmonary capillaries -​ Oxygen from air sacs into blood, carbon dioxide from blood into alveoli -​ Capillaries merge to form venules and then pulmonary veins -​ 2 left / 2 right pulmonary veins carry oxygenated blood to left atrium Characteristics of pulmonary circulation -​ Compared to systemic circulation, pulmonary vessels -​ Have less elastic ct -​ Have wider lumens -​ Are relatively short, since lungs are close to heart -​ Have lower blood pressure -​ Leaves right ventricle with systolic pressure of 15-25 mm Hg -​ Pressure drops to 10 mm Hg in pulmonary capillaries -​ Ensures slow movement and good exchange -​ Blood exits pulmonary capillaries and enter large pulmonary veins -​ As pulmonary veins enter left atrium, blood pressure almost 0 mm Hg General arterial flow out of heart -​ Systemic arteries branch off aorta -​ Oxygenated blood pumped from left ventricle to ascending aorta -​ Left / right coronary arteries -​ Emerge from ascending aorta to supply heart wall -​ Ascending aorta curves left and becomes aortic arch -​ 3 main arterial branches from aortic arch 1.​ Brachiocephalic trunk a.​ Bifurcates into right common carotid / right subclavian arteries b.​ Right common carotid supplies right side of head / neck c.​ Right subclavian supplies right upper limb and some thoracic structures 2.​ Left common carotid artery a.​ Supplies left side of head / neck 3.​ Left subclavian artery a.​ Supplies left upper limb and some thoracic structures -​ Aortic arch curves inferiorly to become descending thoracic aorta -​ Has several branches supplying thoracic wall and viscera -​ As it passes through diaphragm it becomes the descending abdominal aorta -​ Supplies abdominal wall and organs -​ At level of 4th lumbar vertebra abdominal aorta splits into left and right common iliac arteries -​ Each of these splits into an internal iliac artery (for pelvic structures) and an external iliac artery (for lower limb) General venous return to the heart -​ Blood returns to right atrium by three vessels: superior vena cava, inferior vena cava, and coronary sinus -​ Superior vena cava formed by merger of left and right brachiocephalic veins -​ Drain head, neck, upper limbs, thoracic and abdominal walls -​ Inferior vena cava formed from veins below diaphragm -​ Carries blood from lower limbs, pelvis, perineum, abdominal structures -​ Lies to right of descending abdominal aorta -​ Coronary sinus -​ Drains into right atrium -​ Carries deoxygenated blood from heart myocardium Head and neck- common carotid arteries supply most of the blood -​ Travel parallel to trachea- one on each side -​ Divide into external carotid artery and internal carotid artery -​ External carotid artery supplies structures external to skull -​ Internal carotid artery supplies internal skull structures Additional blood supplied by branches of subclavian artery -​ Vertebral artery (brain) -​ Thyrocervical trunk (thyroid gland, part of neck and shoulder)  -​ Costocervical trunk (deep neck and upper intercostals) -​ Branches of external carotid: -​ Superior thyroid artery (thyroid gland and larynx) -​ Ascending pharyngeal artery (pharynx) -​ Lingual artery (tongue) -​ Facial artery (face) -​ Occipital artery (posterior scalp) -​ Posterior auricular artery (ears and part of scalp) -​ Maxillary artery (teeth, gums, nasal cavity, mastication muscles, meninges) -​ Superficial temporal artery (parotid gland, part of scalp) -​ Internal carotid branches after entering skull -​ Anterior and middle cerebral arteries (brain) -​ Ophthalmic artery (eyes and surrounding structures) -​ Vertebral arteries come off subclavian arteries -​ Travel in transverse foramina of cervical vertebrae -​ Enter skull through foramen magnum -​ Merge to form unpaired basil artery -​ Basilar artery divides into posterior cerebral arteries (posterior cerebrum) -​ Cerebral arterial circle (circle of Willis) -​ Important arterial anastomosis around sella turcica -​ Formed from posterior cerebral, posterior communicating internal carotid arteries, anterior cerebral, and anterior communicating artery -​ Equalizes blood pressure in brain -​ Provides collateral channels if one vessel becomes blocked Head and neck- 3 primary vein: -​ Vertebral vein- empties into subclavian vein -​ External jugular vein- drains superficial head and neck, empties into subclavian vein -​ Internal jugular vein- drains blood from cranial cavity, joins subclavian vein to form brachiocephalic vein Head and neck- cranial cavity -​ Some blood drains to vertebral veins -​ Most blood drains through dural venous sinuses: large modified veins between 2 lawyers of dura mater -​ These sinuses also receive excess csf -​ They drain primarily into internal jugular veins Thoracic and abdominal walls -​ Internal thoracic artery (anterior thoracic wall and mammary gland) -​ Emerges from subclavian artery -​ Branches include 6 anterior intercostal arteries (intercostal spaces) -​ Branches include musculophrenic artery -​ Divides into anterior intercostal arteries 7-9 -​ Becomes superior epigastric (superior abdominal wall) -​ Inferior epigastric artery (inferior abdominal wall)  -​ A branch of external iliac -​ Anastomoses with superior epigastric artery -​ Supreme intercostal artery -​ A branch of costocervical trunk -​ Branches into first and second posterior intercostal arteries -​ Posterior intercostal arteries 3-11 branch off thoracic aorta -​ All posterior intercostal arteries anastomose with anterior intercostal arteries -​ Lumbar arteries (posterolateral abdominal wall) -​ 5 pairs branch off abdominal aorta -​ Median sacral artery (sacrum and coccyx) -​ Unpaired artery extending from bifurcation of aorta in pelvis -​ Internal thoracic vein -​ Receives blood from anterior intercostal veins -​ Receives blood from musculophrenic and superior epigastric veins -​ Drains into brachiocephalic vein -​ Inferior epigastric vein -​ Merges with external iliac vein -​ First and second posterior intercostal veins -​ Merge with supreme intercostal vein -​ Drains into brachiocephalic vein -​ Azygos system of veins receives blood from lumbar and posterior intercostal veins -​ Hemiazygos and accessory hemiazygos veins (drain left side veins) -​ Azygos veins (drains right side veins and hemiazygos veins) -​ Drains into superior vena cava Thoracic organs -​ Lungs -​ Bronchial arteries- supply bronchi and bronchioles -​ Tiny branches off descending thoracic aorta -​ Bronchial veins -​ Drain into azygos and pulmonary veins -​ Esophagus -​ Esophageal arteries -​ Several small branches off descending thoracic aorta -​ Esophageal branches- also emerge off left gastric artery -​ Esophageal veins -​ Drain into azygos or left gastric vein -​ Diaphragm -​ Superior phrenic arteries -​ Pair emerging from descending thoracic aorta -​ Inferior phrenic arteries -​ Pair emerging from descending abdominal aorta -​ Musculophrenic arteries and pericardiacophrenic arteries -​ Arise from internal thoracic artery  -​ Superior phrenic and inferior phrenic artery -​ Drain to inferior vena cava -​ Musculophrenic vein -​ Drains to internal thoracic veins Gastrointestinal tract -​ Arterial supply comes from abdominal aorta -​ 3 unpaired arteries serve GI tract: -​ Celiac trunk -​ Located just inferior to diaphragm -​ Has 3 branches: -​ Left gastric artery (part of stomach, esophagus) -​ Splenic artery (spleen, part of stomach and pancreas) -​ Common hepatic artery- 2 main branches -​ Hepatic artery proper (liver, gallbladder, part of stomach) -​ Gastroduodenal artery (part of stomach, duodenum, pancreas) -​ Superior mesenteric artery -​ Located immediately inferior to celiac trunk -​ Branches: -​ Intestinal arteries (jejunum and ileum) -​ Middle colic artery (most of transverse colon) -​ Right colic arty (ascending colon) -​ Ileocolic artery (ileum, cecum, appendix) -​ Inferior mesenteric artery -​ Located just above bifurcation of aorta -​ Branches: -​ Left colic artery (distal transverse colon, descending colon) -​ Sigmoid arteries (part of descending colon and sigmoid colon) -​ Superior rectal artery (rectum) -​ Venous return: the hepatic portal system -​ Blood from digestive organs is sent to liver -​ Digested nutrients processed and harmful agents absorbed by liver -​ Digestive system blood comes from 3 main veins that drain into the hepatic portal vein -​ Splenic vein- horizontally positioned -​ Inferior mesenteric vein- vertically positioned -​ Superior mesenteric vein- vertically positioned on right side of body -​ Hepatic portal vein flows into liver sinusoids -​ Blood leaves liver by hepatic veins that drain into inferior vena cava Posterior abdominal organs -​ A middle suprarenal artery- supplies each adrenal gland -​ A renal artery supplies each kidney -​ A gonadal artery supplies each gonad  -​ All 3 of the above branch off descending aorta and are drained by veins with same name as arteries Pelvis and perineum -​ Right and left common iliacs divide into internal and external iliac arteries -​ Internal iliac artery is primary arterial supply to pelvic region and has several branches: -​ Superior gluteal artery (gluteus medius and minimus) -​ Inferior gluteal artery (gluteus maximus) -​ Superior vesical artery (bladder) -​ Middle rectal artery (rectum) -​ Vaginal and uterine artery (vagina and uterus) -​ Internal pudendal artery (anal canal and perineum) -​ Obturator artery (medial thigh muscles) -​ Medial umbilical ligaments are remnants of fetal umbilical arteries -​ Venous drainage -​ Pelvic and perineal veins have same name as supplying arteries -​ They merge with internal iliac vein, which merges with common iliac vein Upper limb -​ Subclavian artery -​ Left subclavian artery comes off aortic arch -​ Right subclavian artery comes off brachiocephalic trunk -​ Axillary artery (axilla, chest wall, shoulder, humerus) -​ Continuation of subclavian after vessel passes beyond first rib -​ Renamed as brachial artery once it passes beyond teres major -​ Deep brachial artery -​ Branch of brachial artery supplying blood to most arm muscles -​ Radial and ulnar arteries -​ Divisions of brachial artery supplying forearm and wrist -​ Anastomose and form 2 arterial arches -​ Deep palmar arch (primarily from radial) -​ Superficial palmar arch (primarily from ulnar) -​ Digital arteries emerging from arches to supply fingers -​ Superficial venous drainage -​ Highly variable among individuals -​ Dorsal venous network (arch) on hand dorsum -​ Drains into medial basilic vein and lateral cephalic vein -​ Drain into axillary vein -​ Median cubital vein -​ Connects cephalic and basilic veins in cubital region -​ Common site for venipuncture -​ Deep venous drainage -​ Digital veins and superficial palmar venous arches -​ Drain into radial and ulnar veins running parallel to arteries  -​ Brachial veins travel with brachial artery -​ Formed with merger of radial and ulnar veins -​ Axillary vein -​ Forms from brachial veins and basilic vein -​ Renamed the subclavian vein at lateral border of first rib -​ Merges with internal jugular to form brachiocephalic vein Lower limb -​ External iliac artery is main supply -​ Starts as branch of common iliac -​ Renamed femoral artery as it passes the inguinal ligament -​ Deep femoral artery (hip joint, many thigh muscles) -​ Branches off femoral artery, travels posteromedially -​ Popliteal artery (supplies knee joint and regional muscles) -​ Continuation of femoral artery in popliteal fossa -​ Divides into anterior and posterior tibial arteries -​ Anterior tibial artery (anterior leg) -​ Becomes dorsalis pedis artery as it crosses ankle -​ Posterior tibial artery (posterior leg) -​ Extends a branch, fibular artery (lateral leg) -​ Medial and lateral plantar arteries (plantar side of foot) -​ Continuation of posterior tibial artery -​ Plantar arterial arch of foot -​ Forms from merger of dorsalis pedis and a branch of lateral plantar artery -​ Digital arteries (toes) -​ Extend from plantar arch Superficial veins of lower limbs -​ Dorsal venous arch on dorsum of foot -​ Drains to great and small saphenous veins -​ Great saphenous vein -​ Originates in medial ankle -​ Extends along medial surface of entire lower limb -​ Drains into femoral vein -​ Small saphenous vein -​ Extends adjacent to lateral ankle -​ Travels along posterior calf -​ Drains into popliteal vein Deep veins of the lower limb (paired in each limb) -​ Medial and lateral plantar veins -​ Drain digital veins and deep veins of foot -​ Posterior tibial veins -​ Drain medial and lateral plantar veins, fibular veins -​ Anterior tibial veins -​ Drain deep veins of foot and ankle -​ Popliteal vein -​ Formed from merger of anterior and posterior tibial veins -​ Renamed femoral vein in anterior thigh -​ Renamed external iliac vein superior to inguinal ligament -​ Common iliac vein -​ Forms from merged external and internal iliac veins