Circulatory SystemVessels

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Circulatory System-Vessels

• Ch. 15 continued

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Circulatory routes

• Simply put heartarteriesarterioles
  capillariesvenulesveinsheart
• In a portal system blood passes through two
  consecutive capillary networks before returning
  to the heart
• An anastomosis is a point where two veins or
  arteries merge with each other
• Venous anastomosis provide alternative routes of
  drainage from an organ, so blockage of a vein is
  seldom life threatening
• Arterial anastomosis is where two arteries merge
  and provide collateral (alternate) routes of
  blood supply

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Vessel Wall

• 3 layers
• Tunica externa (tunica adventitia)-outermost
  layer, loose connective tissue, anchors vessels
• Tunica media-middle, thickest layer, smooth
  muscle, collagen, and maybe elastic tissue
• Tunica interna (or intima)-inner layer, exposed
  to blood, endothelium is selectively permeable

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Arteries

• Arteries are more muscular than veins
• 3 types
• Conducting or elastic arteries-largest, expand
  when ventricles contract (aorta is example)
• Distributing or muscular arteries-distribute
  blood to specific organs (brachial artery is
  example)
• Resistance or small arteries-vary in location and
  number, smallest are arterioles

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Capillaries

• Functional units of the cardiovascular system
• Contain thin layer of endothelium designed for
  diffusion (tunica interna)
• Location for the exchange of gases
• Few located in tendons, ligaments, and none in
  cartilage, epithelium, and cornea and lens of eye
• Organized into capillary beds which increase the
  total surface area and slows blood flow

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Types of Capillaries

• Continuous capillaries -occur in most tissue,
  endothelium forms uninterrupted tube, contain
  narrow intercellular clefts which allow small
  solutes like glucose through
• Fenestrated capillaries -have fenestrations
  (filtration pores) that allow for the rapid
  passage of small molecules, especially important
  in organs like the kidney that are designed for
  rapid absorption and filtration

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Types of capillaries cont.

• Sinusoids or discontinuous capillaries are wider,
  larger vessels with little or no basement
  membrane. These are designed to move bigger
  molecules and are located in the bone marrow,
  anterior pituitary, parathyroid glands, adrenal
  glands, spleen, and liver

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Veins and venules

• Venules are small veins that connect to
  capillaries
• Venous sinuses- are veins with very thin walls,
  large lumens, and no smooth muscle (coronary
  sinus, dural sinus)
• Veins have a much lower blood pressure than
  arteries (usually about 10 mmHg)
• Veins have thinner walls and collapse when empty

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Veins continued

• Veins can expand to accommodate more blood than
  arteries (considered to be blood reservoirs)
• Upward flow of blood depends in part on the
  massage action of skeletal muscle and on the
  presence of one way venous valves that keep blood
  from dropping down again when muscle relaxes
• These valves are not present in small veins and
  very large veins, veins of the ventral body
  cavity, and veins of the brain
• Varicose veins are caused by pooling of the blood
  and stretching of the vein

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Blood pressure

• Two pressures are recorded using a
  sphygmomanometer
• systolic pressure is the peak arterial BP
  attained during ventricular systole
• Diastolic pressure is the minimum arterial BP
  between heartbeats
• Written as a ratio systolic over diastolic or
  120/80 for example
• Difference between systolic and diastolic
  pressure is called pulse pressure, which is a
  measure of stress on the small arteries

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Arterial pulse

• Can palpate the pulse at
• Temporal artery, facial artery, carotid artery,
  brachial artery, radial artery, femoral artery,
  popliteal artery, posterior tibial artery, and
  dorsalis pedis artery

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Pulse points
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Medical conditions

• Hypertension-higher than 140/90
• May weaken small arteries and cause aneurisms
• Hypotension-lower than normal, may be caused by
  blood loss, dehydration, anemia
• Deep vein thrombosis- blood clot in a veinmost
  common place is the calf and femoral region
• Hemorrhoids -varicose veins of rectum

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Regulation of BP

• 1. Autoregulation -ability of tissues to regulate
  their own blood supply
• 2. Blood platelets, endothelial cells, and
  perivascular tissue secrete vasoactive chemicals
  that stimulate vasomotion
• These include bradykinin, and histamine, and
  prostaglandins that stimulate vasodilation during
  trauma, inflammation, and exercise
• 3. If a tissues blood supply is cut off then
  restored, it exhibits reactive hyperemia-an
  increase above the normal flow, probably due to
  increased metabolites (wastes)

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Regulation continued

• 4. Angiogenesis -growth of new blood vessels
• Seen in regrowth of uterine lining after
  menstrual period, the development of capillaries
  in the muscles of well conditioned athletes, and
  the growth of arterial bypasses around
  obstructions in the coronary circulation

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Neural control

• Vasomotor center of the medulla oblongata exerts
  sympathetic control over blood vessels throughout
  the body
• Vasomotor center is the integrating center for 3
  autonomic reflexes
• 1. baroreflexes- autonomic, negative feedback
  response to change in blood pressure, occur in
  all large arteries above the heart (aortic arch
  has most)
• Short term regulation of BP

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Neural control continued

• 2. chemoreflex-autonomic response to change in
  blood chemistry (pH, oxygen and carbon dioxide
  concentration)
• Initiated by chemoreceptors within aortic body
  and carotid body found in aortic arch, subclavian
  arteries, and external carotid arteries
• Adjust respiration to changes in blood chemistry
  and can stimulate vasomotion

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Neural control continued

• 3. Medullary ischemic reflex-autonomic response
  to insufficient perfusion of the brainstem
• Within seconds of insufficient perfusion the
  cardiac and vasomotor centers of the medulla send
  sympathetic signals to the heart and blood
  vessels to increase heart rate and force of
  contraction and causes widespread
  vasoconstriction which increases blood pressure

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Hormonal control

• Angiotensin II is one of the most important
  vasoactive hormones
• Liver produces angiotensinogen and secretes it
  into blood
• Low blood pressure causes kidney to secrete
  renin, which converts angiotensinogen to
  angiotensin I
• Angiotensin-converting enzyme in the lung (ACE)
  converts angiotensin I to angiotensin II
• This is a vasoconstrictor that raises blood
  pressure

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Paths of Circulation

• Pulmonary circulation-begins with pulmonary
  trunkpulmonary arteries---lobar arteries in
  lungs----capillary beds---venules---veins---pulmon
  ary veins---left atrium
• Systemic circulation-blood flow to rest of body,
  often named for location
• http//www.wisc-online.com/objects/index_tj.asp?ob
  jIDAP12704

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Pulmonary circuit
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Systemic circuit

• composed of vessels that lead from the heart to
  all body parts (except the lungs) and back to the
  heart
• includes the aorta and its branches
• includes the system of veins that return blood
  to the right atrium

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Branches of Aorta

• Ascending aorta- arises from the left ventricle
• Branches into coronary arteries which supply the
  heart muscle
• Aortic arch gives off 3 branches
  brachiocephalic trunk, left common carotid
  artery, left subclavian artery
• brachiocephalic trunk which splits into right
  common carotid artery (supplies right side of
  head and neck), and right subclavian artery
  (supplies right upper limb and some of thorax)
• Descending aorta -passes downward behind the
  heart, called thoracic aorta above the diaphragm
  and abdominal aorta below it. It ends when it
  forks into left and right common iliac arteries

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Arteries to Head and Neck and Brain

• Branches of subclavian and common carotid
  arteries supply neck, head, and brain
• Vertebral arteries arise from subclavian arteries
  and supply vertebrae and their ligaments and
  muscles
• Vertebral arteries unite to form basilar artery
  in brain, and terminates by branching into two
  posterior cerebral arteries (these help form
  Circle of Willis) http//science.nhmccd.edu/biol/c
  ardio/willis.htm

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Circle of Willis
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Carotid arteries

• Left and right common carotid arteries ascend
  deeply in neck and divide into external and
  internal carotid arteries
• External carotid artery gives off branches that
  supply neck, face, jaw, scalp, and base of skull
• Internal carotid artery follows a deep pathway to
  the base of the skull and enters cranial cavity
  and provides a major blood supply to the brain

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Arteries to head, neck, brain
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Arteries of Shoulder and Upper Limb

• Subclavian artery continues into limb and becomes
  the axillary artery (supplies axilla, and chest
  wall)
• Axillary artery becomes the brachial artery
  (humerus to elbow)
• Brachial artery gives rise to deep brachial
  artery which supplies triceps muscle
• Brachial artery divides at elbow into ulnar
  artery and radial artery
• http//mywebpages.comcast.net/wnor/lesson4arteries
  ofarm.htm

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Arteries to upper extremity
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Arteries to Thoracic and Abdominal wall

• Subclavian artery branches into internal thoracic
  artery which gives off two branches called
  anterior intercostal arteries
• Posterior intercostal arteries arise from
  thoracic aorta
• Branches from internal thoracic artery and
  external iliac arteries supply anterior abdominal
  wall
• Paired vessels from abdominal aorta (phrenic and
  lumbar arteries) supply posterior and lateral
  abd. wall

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Arteries to Pelvis and Lower Limb

• Abdominal aorta divides into common iliac
  arteries at pelvic brim
• This divides into internal iliac artery (pelvic
  muscle, viscera, gluteal muscles, and external
  genitalia)
• Also divide into external iliac artery which is
  the main blood supply to the lower extremity

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Lower limb continued

• External iliac artery becomes the femoral artery
• Femoral branches into popliteal artery (behind
  knee)
• Popliteal artery divides into anterior and
  posterior tibial artery
• Anterior tibial artery becomes the dorsalis pedis
  artery which supplies the instep and toes

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Arteries to lower extremity
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continued

• Posterior tibial artery descends beneath the calf
  muscle
• Largest branch from posterior tibial artery is
  the fibular artery which travels along the fibula
• Obviously I havent put all the arteries on here.
  However, most are obvious so if you see them on a
  test it should be easy to figure out.(splenic
  artery supplies spleen, gastric artery-stomach,
  renal artery-kidney, common hepatic artery-liver)
• The gastric, common hepatic, and splenic arteries
  are part of the celiac trunk.

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Abdominal aorta and major branches
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Venous system

• Returns blood to heart after gas, nutrients, and
  wastes are exchanged between blood and body cells
• The veins from all systemic areas of the body
  merge into either the superior vena cava or
  inferior vena cava

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Veins of Head, Neck, and Brain

• External jugular veins drain blood from face,
  scalp, and superficial areas of neck
• Empty into the right and left subclavian veins at
  base of neck
• Internal jugular veins drain brain, parts of face
  and neck and join subclavian veins
• Union of internal jugular vein and subclavian
  veins forms the brachiocephalic veins on each
  side
• These merge in mediastinum and give rise to
  superior vena cava

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Veins from upper limb and shoulder

• Main vessels of superficial network are basilic
  vein and cephalic vein
• Basilic vein ascends along medial side of arm
  until it joins the brachial vein. They both unite
  to form the axillary vein
• Cephalic vein ascends along the lateral side of
  the arm and joins the axillary vein at the
  shoulder. This forms the subclavian vein
• A median cubital vein is located at the bend of
  the elbow and is used in venipuncture

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Deep veins of arm

• Deep veins parallel arteries and are given the
  same names
• Radial vein, ulnar vein, brachial vein, and
  axillary vein
• http//mywebpages.comcast.net/wnor/lesson4veinsofa
  rm.htm

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Veins of the abdominal and thoracic walls

• Veins from abdominal viscera originate in
  capillary networks of stomach, intestines,
  pancreas, and spleen and carry blood into the
  hepatic portal vein to the liver
• From there blood enters hepatic sinusoids
• Tributaries of this hepatic portal system
  include right and left gastric veins (stomach),
  superior mesenteric vein (small intestine,
  ascending and transverse colon), splenic vein
  (spleen), inferior mesenteric vein (descending
  colon, sigmoid colon, rectum)
• After entering hepatic sinusoids the blood
  travels into hepatic veins then into inferior
  vena cava

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Hepatic Portal System

• Functions to filter deoxygenated but NUTRIENT
  RICH blood received from digestive system to get
  rid of toxins and bacteria BEFORE it is
  distributed to rest of body
• Liver receives venous blood from digestive organs
  via portal vein
• Portal vein divides into 2 branches (left and
  right) which enter liver
• These keep branching until they form the hepatic
  sinusoids within the lobes of the liver
• The hepatic sinusoids unite to form the hepatic
  veins which exit the liver and enter the inferior
  vena cava

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Hepatic portal vein
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Veins that drain abdominal viscera
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Veins from lower limb and pelvis

• Deep veins of leg have names that correspond to
  arteries they accompany
• These include anterior and posterior tibial veins
• At knee these merge to form popliteal vein
• This continues through thigh as the femoral vein,
  which becomes the external iliac vein

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Major veins
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Lower limb continued

• Superficial veins of foot, leg, thigh connect to
  form a complex network beneath the skin and drain
  into 2 major trunks the great and small
  saphenous veins
• Small saphenous vein passes upward behind lateral
  malleolus and eventually joins the popliteal vein
• The great saphenous vein is the longest vein in
  the body. It passes along the medial side of the
  leg and thigh and eventually joins the femoral
  vein (use this one in coronary bypass surgery)

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Continued

• Vessels leading to internal iliac vein drain the
  reproductive organs, urinary, and digestive
• Internal iliac veins originate deep in pelvis and
  ascend to unite with the right and left iliac
  veins to form common iliac veins
• These merge to produce the inferior vena cava at
  the 5th lumbar vertebra

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Veins that drain the lower extremity
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Fetal circulation

• Oxygenated blood enters umbilical VEIN and blood
  and enters ductus venosus to move toward inferior
  vena cava
• Oxygenated blood in ductus venosus mixes with
  deoxygenated blood in inferior vena cava
• Blood from both vena cavae empty into right
  atrium
• Most blood goes through foramen ovale into the
  left atrium
• Most blood enters left ventricle then out into
  body
• Deoxygenated blood returns to mom via 2 umbilical
  ARTERIES

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Practice!

• http//media.pearsoncmg.com/bc/bc_marieb_ehap_8/ac
  tivities/chapter11/Act11E.html