Notes 23 Circulatory System

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Notes 23 Circulatory System Powered By Docstoc
					           Circulatory System
Most animals have a circulatory system
  including a pumping device – heart
• Open Circulatory System – system may
  have large open spaces (sinuses) where
  definite vessels are absent (mollusks,
  insects) organs are bathed in blood – less
  efficient oxygen delivery
• Closed Circulatory System – blood stays
  enclosed in vessels throughout system
  (earthworms, all vertebrates)
          Circulation in Vertebrates
Closed system consisting of:
• Arteries – carry blood away from the heart – branch into smaller
   vessels called arterioles
• Capillaries – tiny vessels where exchange occurs (walls are only
   one or two cells thick)
• Venules – small vessels that lead away from capillaries – branch
   into the larger
• Veins – vessels that carry blood back to the heart
    – Veins have valves to assist in moving blood up to the heart
       (against gravity) and also depend on squeezing from muscles

William Harvey (1628) – published work marked the beginning
of modern science of Physiology (understanding bodily
processes in terms of chemistry and physics)
     Circulation Pathway in Humans
•    4 chambered heart – 2 separate pumps separated by
     the septum
•    Coronary arteries supply the heart itself with oxygenated
•    Heart Circulation:
1.   Deoxygenated blood returns to heart through superior
     (head, neck, and arms) and inferior (lower body) vena
2.   Right atrium – through tricuspid valve
3.   Right ventricle – through semilunar valve
4.   Pulmonary arteries to lungs – gas exchange takes place
     and blood is oxygenated – blood returns to the heart
     through pulmonary veins
5.   Left atrium through mitral valve (bicuspid) to
6.   Left ventricle through semilunar valve to
7.   Aorta - very large artery carries oxygenated blood to the
Circulation outside of the heart is divided into:
• Pulmonary circulation – pulmonary arteries
  carry deoxy. blood to lungs and pulmonary
  veins carry oxy. blood to heart
• Systemic circulation – aorta, arteries and
  arterioles carry oxg. blood to cells – venules
  and veins carry deoxy. blood back to heart
        Structure of Blood Vessels
Walls composed of three layers:
• Outer connective tissue layer – provides elasticity
• Middle layer of smooth muscle
• Inner layer of connective tissue lined with endothelium
1. Arteries have a thick layer of smooth muscle (very strong
   and elastic – can withstand high pressure)
    – Inner diameter is small
2. Veins are much less elastic (don’t have as much pressure)
    – Smooth muscle layer is thinner and inner diameter is
3. Capillary walls are 1 or 2 cells thick to allow exchange
   between blood and tissues
   Circulation in other Vertebrates
• Four chambered hearts characteristic of birds and
  – High metabolic rates necessitate efficient oxygen
    delivery system (no mixing of oxy. and deoxy. blood)
• Fish have a two chambered heart – systemic
  circulation under very low pressure, blood moves
• Amphibians and reptiles have three chambered
  heart – 2 atria and 1 ventricle
  – Oxy. and deoxy. blood mix in ventricle
  – Reptiles show beginning of development of septum
    (reduces mixing)
          Contraction of the Heart
• Cardiac cells tend to contract naturally
   – Contraction of one heart cell stimulates contraction of
     neighboring cells
• Heartbeat is initiated by the sinoatrial node
   – located in wall of right atrium
• Impulse is carried to ventricles by atrioventricular
  node located on septum between atria
   – Bundle of His – fibers that extend from AV node into
     walls of ventricles
   – Purkinje fibers further branch into all parts of ventricular
• Contraction of atria is initiated by SA node – wave
  of contraction passes through atria to AV node –
  impulse transmitted to ventricles and wave
• Cardiac muscle cells are electrically
  coupled by intercalated disks between
  adjacent cells
                 Cardiac Cycle
• Alternating contraction and relaxation of the heart
• Contraction phase called systole, and relaxation phase
  called diastole
• Heart sounds heard with stethoscope are caused by
  closing of the valves
• Sound pattern is “lub-dup, lub-dup, lub-dup”
• First heart sound (“lub”) created by closing of AV valves
• Second sound (“dup”) created by closing of semilunar
• Heart murmers – occur when valves are damaged and do
  not shut completely, some blood leaks backward resulting
  in a hissing sound
• Electrocardiograms – used to detect electrical changes
  during contraction (can detect abnormalities)
  Blood Pressure and Rate of Flow
• During systole, heart contracts and blood is
  forced into arteries under high pressure
• During diastole, heart relaxes and blood
  pressure falls in arteries
• Blood pressure is measured to record the
  regular cycle of pressure in the arteries as
  the heart contracts
  – Usually measured in upper arm (brachial artery)
    with a sphygmomanometer and stethoscope
  – Average pressure for young adult male is 120
    (systolic)/80 (diastolic)
Blood pressure varies by location in body and
decreases with distance from the heart
• Resulting gradient of pressure causes continuing
  flow of blood – fluids move from regions of high
  pressure to regions of low pressure
• Differences in systolic and diastolic pressures
  diminish with distance from heart
• By the time blood reaches capillaries the flow is
  constant (rather than surging as in the arteries)
• Pressure continually drops through arterioles and
  capillaries, lowest in veins closest to heart
• Rate of flow highest in arteries
• Rate of flow lowest in capillaries
• Increases again in veins
              Capillary Function
• Extremely small in diameter – RBCs pass through single
•Highly branched to
increase total cross –
sectional area
•results in low pressure and
slower flow (more time for
exchange btw blood and
•Large surface area for
exchange and penetration
into all tissues
 Mechanisms for Exchange between Blood
                    and Tissue
• Diffusion
• Materials are picked up by vesicles in cell
  membrane of capillary endothelial cell
  (endocytosis) travel across cell and are
  expelled by exocytosis
• Water and dissolved molecules (not
  proteins) filter through clefts between
  adjacent endothelial cells
Capillary exchange occurs as a result of two
opposing forces:
1. Hydrostatic pressure of blood higher at
   arteriole end than at venule end – tends to
   force materials out of capillary into tissues
2. Osmotic pressure is higher in blood than in
   surrounding tissues (because of
   concentration of proteins in blood) so water
   tends to diffuse back into capillaries
• Blood in capillary bed first unloads
  materials for tissues at the arteriole end
  – Higher hydrostatic pressure (blood pressure)
    favors outflow of materials
• Blood picks up materials for transport at
  venule end where osmotic pressure is
  higher and favors uptake of materials
• Essentially all water that is filtered out at arteriole
  end is reabsorbed at venule end (99%)

  •Extent of blood supply to
  tissues depends on degree
  of dilation or constriction of
  capillary sphincters

  •Capillaries are not all open
  at same time – dilation
  occurs when blood supply
  to tissues in necessary
  (dilation occurs in
  capillaries of small intestine
  after meal)
                     Lymphatic System
•   System of vessels that returns the other 1% of fluid in tissues
    back to the blood
•   Consists of lymph veins and capillaries
•   Three main functions:
1. Extensive system of lymph capillaries throughout tissues that
    pick up fluids (lymph) and proteins – transfer to lymph veins
    that eventually empty fluids and proteins into veins of blood
    circulatory system
2. Picks up fats absorbed by small intestine
3. Plays important role in immune system
    Lymph nodes located along major lymph vessels made up
       of connective tissue
    Nodes filter lymph and remove dead cells from immune
       response to infection
    Nodes harbor phagocytic cells and produce some white
       blood cells
•   Lymph is moved by pressure from contraction of skeletal
    muscles – backflow is prevented by one-way valves
                   Composition of Blood
1.    Plasma – liquid matrix constituting 50 – 60% of whole
      blood plasma is 90% water with a variety of dissolved
     • 0.9% - inorganic cations (Na+, Ca+2, K+, Mg+2) and
          organic anions (Cl-, HCO3-)
          concentrations are kept relatively stable to maintain
             homeostasis (even slight shifts in concentration can
             cause dysfunction or cell death)
2.    7 – 9% - plasma proteins (fibrinogen, albumins, and
      globulins – important for osmotic pressure in plasma, help
      to transport substances, blood clotting)
3.    Organic nutrients (glucose, fats, phospholipids, amino
      acids, lactic acid, cholesterol)
4.    Nitrogenous wastes – urea, ammonia and uric acid
5.    Hormones – regulatory chemicals
6.    3 gases found in small amounts – nitrogen, oxygen and
      carbon dioxide
             Composition of Blood
Cells found in blood:
1. White blood cells – leukocytes
   • Five major types: monocytes, neutrophils, basophils,
        eosinophils, and lymphocytes
   • Fight infections
   • Monocytes and neutrophils are phagocytes
   • Eosinophils fight infection against parasites
   • Basophils release histamine – causes vasodilation
        (increases blood flow to injured site) – part of
        inflammatory response
   • Lymphocytes – B cells and T cells – part of specific
        immune response resulting from exposure to an antigen
        (foreign substance in body)
        B cells produce antibodies (globulin proteins) to
            destroy antigen – specifically fight antigen that
            stimulates production
           Composition of Blood
2. Red Blood Cells – erythrocytes
  •   Biconcave, disc-shaped, lack nuclei
  •   Approx 5 million/mm3 of blood
  •   Live approx 120 days – destroyed by liver and
  •   Formed in red bone marrow (in long bones,
      skull, ribs, and pelvis)
  •   Filled with hemoglobin (carries oxygen, gives
      red color)
  •Some animals (mollusks and
  arthropods) have hemocyanin –
  contains Cu instead of Fe –
  dissolved in plasma not in cells
• Whole blood – blood as it is in the
  circulatory system
• Blood plasma – whole blood without
  formed elements
• Blood serum – plasma without fibrinogen
                Blood Clotting
• Fibrinogen comes out of solution and converts to
  fibrin (forms a hard lump or clot)

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