4.20 Blood Vessels

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4.20 Blood Vessels
2010-11-16 02:25:49
Structure Typers Anastomoses Vasorum Pulmonary Systemic Circulation Disorders Throughout Life

General Characteristics of Blood Vessels and Blood Vessels of the Body
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  1. Structure of Blood Vessels
    • Composed of three layers (tunics):
    • 1. Tunica intima— internal layer, in contact with lumen; composed of simple squamous epithelium (endothelium); forms a smooth surface that minimizes friction of blood moving across them
    • 2. Tunica media—sheets of circularly arranged smooth muscle, with elastin and collagen fibrils in between; thicker in arteries than veins
    • • Contraction causes vasoconstriction
    • • Relaxation causes vasodilation
    • *both regulated by vasomotor nerve fibers of sympathetic nervous system
    • 3. Tunica externa—composed of connective tissue with elastin and collagen fibers; fibers run longitudinally (protects the vessels and anchors it to surrounding structures)

    • Lumen
    • • Central blood-filled space of a vessel
  2. Types of Blood Vessels
    • Arteries—carry blood away from the heart; lumen is small; tunica media is thicker

    • • Capillaries—smallest blood vessels
    • • The site of exchange of molecules between blood and tissue fluid

    • Veins—carry blood toward the heart; lumen is wider; tunica externa is thicker
  3. Types of Arteries
    Elastic Arteries
    Elastic arteries: the largest arteries near the heart

    • Diameters range from 2.5 cm to 1cm; serve as low resistance conduits to smaller arteries

    • Includes the aorta and its major branches

    • Sometimes called conducting arteries

    • High elastin content in tunica media dampens surge of blood pressure
  4. Types of Ateries
    Muscular Arteries
    Muscular (distributing) arteries

    • Lie distal to elastic arteries; supply organs

    • Diameters range from 1 cm to 0.3 mm

    • Includes most named arteries

    • Tunica media is thick, allowing changes in arterial diameter to regulate blood flow to organs
  5. Types of Arteries
    Arterioles are the smallest arteries

    - diameters ranging from 0.3mm to 10um

    - Tunica media contains only one or two layers of smooth muscle cells

    - Larger arterioles have all three tunics plus an internal elastic network in tunica intima
  6. Capillaries
    • Smallest blood vessels – single layer of endothelial cells surrounded by basement membrane

    • Red blood cells pass through single file

    Site-specific functions of capillaries

    • • Lungs—oxygen enters blood, carbon dioxide leaves
    • • Small intestines—receive digested nutrients
    • • Endocrine glands—pick up hormones
    • • Kidneys—remove of nitrogenous wastes

    • Two types of capillary
    • • Continuous—most common ( no pores – occurs in most organs)
    • • Fenestrated—have pores ( small intestine, kidneys)

    • Routes of permeability:
    • 1. direct diffusion through endothelial cell membrane
    • 2. through the intercellular clefts
    • 3. through pinocytotic vesicles that invaginate from the plasma membrane
    • 4. through the fenestrations in fenestrated capillaries

    *blood brain barrier: capillaries are continuous, with tight junctions and no intercellular clefts
  7. Veins
    Conduct blood from capillaries toward the heart

    • Blood pressure is much lower than in arteries, therefore walls are thinner than arteries

    • Smallest veins—called venules

    • Venules join to form veins

    • Tunica externa is the thickest tunic in veins

    • • Some veins have valves formed from tunica intima that prevent backflow
    • - most abundant in limbs, where gravity greatly influences blood flow
    • - contraction of muscles and movement of limbs also aid in blood flow
  8. Vascular Anastomoses/ Vasa Vasorum
    • Vascular Anastomoses: where vessels unite or interconnect; allows multiple pathways for blood flow in the event of vascular blockage, blood can still supply the target tissue along another blood vessel
    • *High in heart, brain, and abdominal organs; low in kidneys, spleen, parts of bone diaphyses, and retina
    • *Veins anastomose more freely than arteries

    Vasa Vasorum: little vessels that supply the outer walls of larger blood vessels
  9. Pulmonary Circulation
    Begins as oxygen-poor blood leaving the right ventricle of the heart via the pulmonary trunk and branches into the right and left pulmonary arteries, each penetrating the medial surface of a lung and dividing into lobar arteries, serving the lobes of the lung (3 in right, 2 in left). The arteries further branch, becoming arterioles and pulmonary capillaries that surround alveoli where gas exchange occurs.

    Newly oxygenated blood enters venules and converge into larger veins, largest being the superior and inferior pulmonary veins, which empty into the left atrium

    *Vessels of pulmonary circulation have thinner walls than systemic circulatory vessels, indicating lower pressure (1/6th)
  10. Systemic Circulation
    •Systemic arteries

    •Carry oxygenated blood away from the heart

    •Aorta—largest artery in the body
  11. The Aorta
    • Fetus Structure: Adult Structure
    • Foramen ovale (right atrium to left atrium): Fossa ovalus
    • Ductus ateriosus: Ligamentum arteriosum (interconnects aortic arch and pulmonary trunk)

    • Ascending aorta—arises from the left ventricle
    • Branches—2 coronary arteries that supply the wall of the heart

    • Aortic arch—lies posterior to the manubrium
    • Branches:
    • • Brachiocephalic trunk: ascends to the right towards neck, branching into the right common carotid and right subclavian arteries
    • • Left common carotid
    • • Left subclavian arteries
    • **These three branches supply head, neck, upper limbs and the superior part of the thoracic wall.

    • Descending aorta—continues from the aortic arch, has two parts:
    • Thoracic aorta—in the region of T5–T12; supplies thoracic organs and body wall
    • Abdominal aorta—ends at L4
    • **Divides into right and left common iliac arteries
  12. Blood Supply to the Heart
    Coronary Arteries
    • Functional blood supply
    • • Coronary arteries

    Arise from the aorta

    • Located in the coronary sulcus

    • • Main branches
    • - Left and right coronary arteries

    Coronary arteries – left and right

    Left branches into anterior interventricular

    (supplies anterior walls of both ventricles) and circumflex artery (supplies left atrium and posterior parts of left ventricle)

    Right branches into posterior interventricular and marginal artery. Together they supply right atrium and most of right ventricle.
  13. Blood Supply to the Heart
    Cardiac Veins
    Cardiac veins – carry deoxygenated blood from the heart into right atrium

    Largest cardiac vein – coronary sinus

    Three large tributaries drain into the coronary sinus: great, middle and small cardiac vein
  14. Venae Cavae and Tributaries
    • Superior vena cava
    • • Returns blood from body regions superior to the diaphragm; arises from left and right brachiocephalic veins

    • Inferior vena cava
    • • Returns blood from body regions inferior to the diaphragm; begins at union of the two common iliac veins

    Superior and inferior vena cava join the right atrium

    *the Coronary Sinus also enters the right atrium of the heart
  15. Arteries of the Head and Neck
    • Common carotid artery: Ascend through the neck, lateral to trachea; supply most parts of the head and neck; branch off into internal and external carotid arteries
    • Internal carotid arteries: supply the orbits and most of the cerebrum

    • External carotid arteries: supply most tissues of the head external to the brain and orbit
    • Brachiocephalic trunk: arise from aortic arch; split into right common carotid and right subclavian arteries

    Subclavian artery:

    Vertebral arteries: supply the posterior brain, vertebrae and cervical spinal cord; arise from subclavian arteries at the root of the neck
  16. Veins of the Head and Neck
    Dural Sinuses: (discussed in detail later); join together and drains into the internal jugular vein

    External Jugular vein: a superficial vein unaccompanied by an artery; drain the posterior and lateral scalp and some of the face; empties inferiorly into the subclavian vein

    Internal Jugular vein: drains almost all of the blood from the brain; receives blood from the facial and temporal veins; joins the subclavian vein to form the brachiocephalic vein

    Vertebral vein: do not serve much of the brain; drains only cervical vertebrae, cervical spinal cord, and small muscles in the superior neck

    Brachiocephalic vein: drain into superior vena cava

    Subclavian vein: join with internal and external jugular veins to form brachiocephalic veins; axillary and cephalic veins drain into here

    Superior Vena Cava: brachiocephalic veins join to form superior vena cava
  17. Arteries of the Upper Limbs
    **Arise from Subclavian Artery

    Axillary artery: when the subclavian artery enters the axilla; branches into 4 arteries that supply the muscles of the chest and shoulder

    Brachial artery: when the axial artery continues into the arm; descends medial to humerus; supplies anterior arm muscles; splits into the radial and ulnar arteries

    Radial artery: supplies muscles of lateral anterior forearm and wrist, and thumb and index fingers

    Ulnar artery: supplies muscles that cover the ulnar, splits into interosseous arteries that supply extensor and flexor muscles

    Deep Palmar Arch: lies against the metacarpal bones, where radial and ulnar branches join; branch into digital arteries

    Superficial palmar arch: underlies the skin and fascia of the hand
  18. Veins of the Upper Limbs
    • Deep veins:
    • Follow the paths of companion arteries
    • Have the same names as the companion arteries
    • Most are actually two parallel veins that sandwich their artery

    The deep and superficial palmar veins of the hand empty into the radial and ulnar veins of the forearm, which unite inferior to the elbow to form the brachial vein of the arm. The brachial vein becomes the axillary vein as it reaches the axilla, which becomes the subclavian vein at the first rib.

    • Superficial veins
    • • Visible beneath the skin; larger than deep veins
    • • Frequently form anastomese
    • • Median cubital vein is used to obtain blood or administer IV fluids

    The dorsal venous network (veins on dorsal side of hand) drains superiorly into the cephalic vein, which extends anterolaterally (anterior and lateral) all the way up to join the axillary vein.

    The basilic vein arises from the medial aspect of the hand's dorsal venous network and ascends posteriomedially along the forearm and anteromedially along the arm, joining the brachial vein to become the axillary vein.

    The median cubital vein connects the basilic and cephalic veins along the inner elbow
  19. Arteries of the Abdomen
    Celiac Trunk: supplies the visceral in the superior part of the abdominal cavity; emerges from aorta at T12, divides into left gastric, splenic, and common hepatic arteries

    Left Gastric artery: runs superiorly and to the left, to junction of stomach and esophagus, extends along the lesser curvature of the stomach

    Splenic artery: runs horizontally and to the left, posterior to the stomach to enter the spleen; also supplies pancreas

    Common Hepatic artery: the only branch of the celiac trunk that runs to the right; branches into the hepatic artery proper supplying the liver, the right gastric artery supplying the lesser curvature of the stomach, and the gastroduodenal artery supplying the greater curvature of the stomach, duodenum, and pancreas

    Superior mesenteric artery: serves most of the intestines; arises from the abdominal aorta behind the pancreas

    Renal arteries: stems from the sides of the aorta; paired arteries to the kidneys, aids in removing nitrogenous wastes

    Gonadal arteries: paired arteries to the gonads; branch from aorta at L2, in between superior and inferior mesenteric arteries

    Inferior mesenteric artery: the final major branch of the abdominal aorta; serves distal half of large intestine
  20. Veins of the Abdomen
    All drain into the inferior vena cava

    Hepatic veins: exit the liver superiorly and empty into the inferior vena cava; carry all the blood that originated in the digestive organs from the hepatic portal system

    Hepatic Portal vein: large vein that delivers nutrients to the liver to be processed, and then passes the nutrients to the hepatic veins and vena cava.

    - Superior mesenteric vein: ascends to the right of superior mesenteric artery; drains the entire small intestine, half of the large intestine, and some of the stomach

    - Inferior mesenteric vein: ascends along posterior abdominal wall; drains organs supplied by inferior mesenteric artery (distal region of colon and rectum); empties into splenic vein

    - Splenic vein: microbes escaping the spleen are carried to the liver for distruction; runs horizontally, posterior to the stomach and pancreas; joins the superior mesenteric vein to form hepatic portal vein

    Renal vein: drain the kidneys
  21. Arteries of the Lower Limb
    Common iliac artery: aorta split from the level of L4, supply the inferior part of the anterior abdominal wall, pelvic organs, and lower limbs

    External iliac artery: carry blood to the lower limbs; originates from common iliac arteries, branches slightly to anterior abdominal wall; becomes femoral artery as it enters the leg

    Internal iliac artery: supply the pelvic walls, pelvic viscera, buttocks, medial thighs, and perineum

    Femoral artery: descends vertically, medial to the femur; supplies thigh muscles

    Popliteal artery: inferior continuation of the femoral artery; split inferiorly to form anterior and posterior tibial arteries

    Anterior tibial artery: runs through anterior muscular compartment of the leg; supplies extensor muscles; becomes the dorsalis pedis artery at the ankle, and the arcuate atery at the base of the metatarsals, which branch off to form metatarsal arteries

    Posterior tibial artery: descends through posteromedial part of the leg, deep to the soleus muscle; branches into fibular artery; supplies the flexor muscles

    Fibular artery: descends medially along the fibula; helps supply the flexor muscles
  22. Veins of the Pelvis and Lower Limbs
    • Deep veins
    • • Share the name of the accompanying artery
    • - Arising from the plantar veins, the posterior tibial vein ascends deep in the calf and receives the fibular vein. The anterior tibial vein, which is the superior continuation of the dorsalis pedis vein of the foot, ascends to and unites with the posterior tibial vein to form the popliteal vein. This in turn becomes the femoral vein, which drains the thigh. The femoral vein continues superiorly and becomes the external iliac vein, uniting with the internal iliac vein in the pelvis to form the common iliac vein.

    • Superficial veins; both arise from the dorsal venous arch (metatarsal veins drain into arch)
    • Great saphenous vein empties into the femoral vein; longest vein in the body
    • Small saphenous vein empties into the popliteal vein; posterior to the knee
  23. Dural Sinuses
    • Most veins of the brain drain into dural sinuses – series of channels,
    • lie between the two layers of dura matter in the brain.
  24. The Hepatic Portal System
    • A specialized part of the vascular circuit

    • Picks up digested nutrients - Blood is drained from the digestive viscera, spleen and pancreas and delivered to liver via hepatic portal vein.

    • Delivers nutrients to the liver for processing

    • The liver in turn is drained by hepatic veins that enter the inferior venacava.