Cardiovascular System - Blood Chapter 17

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Cardiovascular System - BloodChapter 17
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• Blood
• - the only fluid tissue
• Average adult has approximately 5L of blood
• Composed of formed elements and plasma
• Formed elements are cells and cell fragments
• Plasma is liquid portion of blood
• Hematocrit separating blood by centrifugation
  into its formed elements and liquid components
• Erythrocytes (red blood cells) 45
• Plasma nearly 55
• Other cells and platelets less than 1

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• Functions of blood
• 1. Distribution
• A. delivery system for oxygen from the lungs and
  nutrients from the digestive system to all body
  cells.
• B. Transporting metabolic waste products from
  cells to elimination sites.
• C. Transporting hormones from endocrine glands
  to target organs.
• 2. Regulation
• A. Helps maintain proper body temperature and
  distributes heat throughout the body.
• B. Maintains proper pH in body tissues.
• C. Maintains adequate fluid volume in the
  circulatory system.

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• 3. Protection
• A. Preventing blood loss.
• B. Prevents infection with antibodies and
  leukocytes (white blood cells).
• Plasma
• Straw-colored sticky fluid that makes-up about
  55 of blood volume.
• 90 water
• Also contains over 100 dissolved solutes
  including nutrients, gases, hormones, waste
  products, ions, and plasma proteins.
• Plasma proteins are most abundant solutes and are
  mostly produced by the liver
• They are not taken up by cells
• Maintain osmotic pressure of fluids, help to
  carry some nutrients, serve as clotting factors,
  etc.
• Contents constantly adjusted to help maintain
  homeostasis.

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• Formed Elements
• 1. Erythrocytes Red Blood Cells (RBCs)
• Anucleate biconcave discs
• Extremely small size and shape result in huge
  surface area
• Filled (97) with hemoglobin the oxygen
  carrying molecule
• Composed of four polypeptide (protein) chains
  each arranged around a heme group that contains
  an iron atom
• Each molecule of hemoglobin can carry four
  molecules of oxygen
• Oxyhemoglobin when combined with oxygen

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• Lack mitochondria and thus do not use any oxygen
• Useful lifespan is 100-120 days 100 million
  die/minute
• Production of erythrocytes
• General blood cell formation is hematopoiesis or
  hemopoiesis
• Occurs in red bone marrow
• All formed elements arise from hemocytoblasts,
  but they develop differently in response to
  specific hormones and growth factors.
• Erythrocytes are first released into the blood
  stream as reticulocytes (count these to estimate
  RBC production)
• Balance is maintained within narrow limits as too
  few lead to tissue hypoxia while too many make
  the blood too viscous.
• Erythropoietin is the primary hormone (from liver
  and kidneys) that stimulates RBC production in
  response to low oxygen delivery to tissues
• Iron and B-complex vitamins required

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• Disorders due to erythrocytes
• A. Anemias
• - when blood has abnormally low oxygen-carrying
  capacity
• - hemorrhagic, hemolytic, aplastic,
  iron-deficiency, pernicious, abnormal hemoglobin
  (thalassemias and sickle-cell)
• B. Polycythemia
• - abnormal excess of RBCs leading to thick
  blood
• 2. Leukocytes White blood cells (WBCs)
• - only formed elements that are complete cells
• - vary with health
• - crucial in fighting disease
• - can leave circulatory system (diapedesis),
  move by ameboid movement, and use chemotaxis
  to find areas of tissue damage or
  infection.

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• - two main types
• - Granulocytes have specialized granules in
  them
• - phagocytes
• - Agranulocytes lack these granules
• - Lymphocytes most are located in the lymph
  tissues
• - key to immunity
• - T lymphocytes attack virus-infected cells
  and tumor cells directly
• - B lymphocytes produce antibodies
• - Monocytes macrophages present w/ chronic
  infections
• Disorders due to Leukocytes
• A. Leukemias cancerous condition in which WBCs
  proliferate and suppress or impair normal bone
  marrow infection
• B. Mononucleosis viral disease

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• 3. Platelets
• - cell fragments that function in blood clotting
• - stick to damaged blood vessels and form a
  temporary plug
• - release several clotting factors

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• Hemostasis
• Stoppage of bleeding
• Three steps
• Vascular spasms
• - constriction of the damaged blood vessel
• Platelet Plug Formation
• - platelets swell, form spiked processes, and
  become sticky
• - stick to exposed fibers of the damaged vessel
  and begin to release clotting factor chemicals
• 3. Coagulation blood clotting
• - Prothrombin activator is formed from certain
  plasma proteins and calcium
• - Prothrombin activator transforms prothrombin
  to the active enzyme thrombin

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• - thrombin catalyzes fibrinogen into insoluble
  fibrin strands which form the structural basis
  for the clot
• Fibrinolysis removes unneeded clots after
  healing
• - cleans out the many small clots that form when
  they shouldnt form

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• Disorders of Hemostasis
• 1. Thromboembolytic conditions
• - a clot that forms in an unbroken blood vessel
  is a thrombus
• - if a thrombus breaks loose and moves within
  the bloodstream it is an embolus
• - cause trouble when they get to a blood vessel
  that is too small for them to pass through and
  they block blood flow
• - caused by conditions which roughen the blood
  vessel endothelium or by slow blood flow
• - aspirin and heparin can decrease risk
• 2. Bleeding disorders
• - when the normal clotting procedure is
  interfered with
• - Platelet deficiency causes spontaneous
  bleeding from small blood vessels throughout the
  body
• - caused by problems in the bone marrow

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• - Impaired liver function can cause excessive
  bleeding because many of the clotting factors
  are produced by the liver
• - Hemophilias genetic bleeding disorders
• - often sex-linked and more common in males
• - treat with injections of the missing factor
• Transfusions
• when blood loss is severe whole blood
  transfusions are given
• Human Blood Groups
• Genetically determined
• Result from certain antigens (proteins) on the
  surface of RBCs
• ABO and Rh blood groups cause strong transfusion
  reactions and are always matched in transfusions
• Agglutination (clumping) of RBCs occurs when
  RBCs with the wrong antigen are transfused into
  another person

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• - when blood types are mixed incorrectly
  antibodies in the recipient plasma cause
  agglutination of the donated RBCs
• - Transfusion reactions can block small blood
  vessels, cause fevers, chills, nausea, vomiting,
  and in severe cases renal failure which can be
  lethal
• - Rh factor is another antigen on the RBCs
• indicates the presence of the antigen

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• Erythroblastosis fetalis is a special case which
  is similar to a transfusion reaction.
• - can happen when an Rh- woman has a second Rh
  child.

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THE HEART
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• The Heart
• Located in the mediastinum of the thoracic
  cavity.
• About the size of your fist
• Surrounded by the double-layered pericardium
  which helps protect it and anchors it to other
  structures
• Pericardial space between the layers allows the
  heart free movement
• Layers of the heart wall
• - epicardium inner layer of the pericardium
  which is tightly attached to outer layer of the
  heart
• - myocardium composed of cardiac muscle which
  actually does the contracting of the heart
• - made of branching fibers which spread the
  impulse between them
• - intercalated discs allow flow of ions from
  fiber to fiber

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• - endocardium inner covering of the heart
  chambers
• Chambers of the heart
• 1. Atria receiving chambers
• - receive the returning blood from the body
  circulation
• - relatively small and thin-walled
• - Right Atrium
• - receives blood from the systemic circulation
• - superior vena cava (precava) from tissues
  above diaphragm
• - inferior vena cava (postcava) from tissues
  below diaphragm
• - coronary sinus collects blood draining from
  the myocardium itself
• - Left Atrium
• - receives blood from the pulmonary circulation
  via the pulmonary veins

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• 2. Ventricles discharging chambers
• - compose most of the mass of the heart
• - walls much thicker and more muscular than the
  atria
• - Right Ventricle pumps blood to pulmonary
  trunk which branches into the pulmonary arteries
  to the lungs
• - Left Ventricle pumps blood to the systemic
  circulation through the aorta
• 3. Valves of the heart
• - unidirectional flaps that impede backflow of
  blood
• - open and close due to blood pressure
  differences on their two sides
• A. Atrioventricular valves control flow between
  the atria and the ventricles
• - chordae tendinae anchor the valve flaps to
  the ventricles and keep the flaps from reversing
  up into the atria when the ventricles contract

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• - when ventricles are relaxed these valves are
  open and blood can flow into the ventricles
• B. Semilunar valves
• - prevent backflow of blood into the ventricles
  when the ventricles relax
• - leaking valves are not always severely
  handicapping
• Blood Flow Through the Heart
• - heart acts as a double pump system to two
  distinct circuits
• - Right side is the pulmonary circuit
• - receives oxygen-poor blood and carbon
  dioxide-rich blood
• - enters right atrium which pumps it through
  the tricuspid valve (rt. Atrioventricular
  valve) to the right ventricle which pumps
  blood through the pulmonary semilunar valve
  to the lungs where gas exchange takes place

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• - Left side is the systemic circuit pump
• - left atrium receives oxygen-rich blood from
  the pulmonary vein and pumps it through the
  bicuspid valve (left atrioventricular
  valve) to the left ventricle which pumps blood
  through the aortic semilunar valve to the aorta
  which branches to all parts of the body
• - left ventricle is the largest and strongest
  chamber due to work load

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Blood flow through Heart
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• Blood supply to the heart
• - blood that flows through the heart chambers
  supplies very little of the needs of the heart
• - the two main coronary arteries branch off of
  the aorta as it leaves the heart.
• - heart attacks (myocardial infarctions) are
  caused by occlusion of a coronary artery
• - heart muscle requires 5 of the bodys blood
  supply
• - venous blood returns through the coronary sinus
  which dumps into the right atrium

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Coordination of Heart Beat
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• Heart Beat
• cardiac muscle contraction will occur
  spontaneously (autorhythmic)
• Normally is under nervous system control
• Intrinsic cardiac conduction system is a network
  of noncontractile cardiac fibers which initiate
  and distribute impulses throughout the heart
• Sinoatrial node located in the right atrial wall
  is the normal pacemaker of the heart
• Internodal pathway carries the impulse to the
  atrioventricular node located in the septum
  between the two atria causes a slight
  hesitation in the impulse which allows the atria
  to contract before the ventricles do
• Next to the atrioventricular bundle (bundle of
  His) which branches into the Purkinje fibers
  which carry the impulse throughout the ventricles.

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• - arrhythmias are irregular heart rhythms caused
  by defects in the conduction system
• nervous system control speeds heart rate in
  response to increased body needs for blood
• Electrocardiogram (ECG or EKG) is a graphic
  recording of the electrical changes in the heart
  during a contraction
• P wave caused by depolarization of atria
• QRS complex depolarization of ventricles
• T wave ventricular repolarization

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• Cardiac Cycle
• Systole contraction of the heart chambers
• Diastole relaxation of the heart chambers
• Heart sounds are the sounds of heart valves
  operating
• Heart murmurs are when the blood is not moving
  smoothly through the heart or is moving
  incorrectly through the valves
• Cardiac output
• function of heart rate and stroke volume
• 75/min. x 70 ml/beat 5252 ml/min
  (5.25L)
• Affected by many factors

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• Blood Vessels
• - except for smallest capillaries all blood
  vessel walls are composed of three layers
  surrounding the lumen of the vessel

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• 1. Tunica intima
• - innermost layer which is in contact with the
  blood
• - composed of simple squamous epithelium with
  closely fitting cells which form a slick surface
  with little friction on the blood
• 2. Tunica media
• - layer of circular muscles
• - controlled by sympathetic division of the
  autonomic nervous system
• - vasoconstriction contraction of these
  muscles decreases vessel diameter
• - vasodilation relaxation increases vessel
  diameter
• - very important in control of blood pressure
• 3. Tunica adventitia
• - tough outer layer that protects the blood
  vessel and helps to anchor it to surrounding
  tissues

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• Arteries
• Blood vessels which carry blood away from the
  heart
• Thick walls with small lumens
• Elastic arteries are the large arteries near the
  heart
• Elastin in walls allows them to stretch out and
  push back against the blood to maintain pressure
  between pulses
• Muscular arteries distribute blood to all parts
  of the body
• Arterioles are smallest arteries which control
  blood flow into the capillary beds

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• Capillaries
• - smallest blood vessels in which exchange takes
  place between the blood and tissues
• - walls are one cell thick
• - some have continuous walls others have pores
  that allow materials through
• - capillary beds are alternately filled with
  blood or by-passed depending on the opening or
  closing of precapillary sphincters

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• Veins
• - capillaries fuse to form venules which begin to
  carry blood back to the heart
• - venules fuse to form veins
• - thinner walls and more open lumens than
  arteries
• - normally contain about 65 of total blood
  volume
• - because blood in veins is under low pressure
  they often contain valves to control the backflow
  of blood
• - varicose veins are caused by stretching of the
  veins above these valves
• - blood is often moved through veins by
  contraction of surrounding skeletal muscles

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• Blood Flow, Blood Pressure, and Resistance
• - blood must continuously flow to all body
  tissues to perform its vital functions
• - Blood flow actual volume of blood flowing
  through an organ or the entire circulation in a
  given amount of time
• - in totality cardiac output but varies
  within certain organs at different times
• - Blood Pressure force per unit area on the
  wall of a blood vessel by the blood contained
  within it
• - Resistance opposition to blood flow through a
  vessel a measure of the friction on the blood.
  Affected by three main factors
• 1. blood viscosity internal resistance to flow
• 2. total blood vessel length longer vessels
  create greater resistance
• 3. blood vessel diameter most important factor
  in controlling peripheral resistance constantly
  changing

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• Blood Pressure
• - normally measured in large systemic arteries
• - affected by amount of blood entering the
  arteries and the amount leaving the arteries at
  any time

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• - because blood entering varies with the heart
  beat while blood leaving is essentially constant
  the pressure is felt as a pulse

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• - Systolic pressure pressure peak caused by the
  contraction of the left ventricle
• - Diastolic pressure lowest pressure when the
  ventricles are relaxed and the elastic arteries
  are recoiling from the pulse
• - pressure decreases the further you get from the
  heart
• - low pressure in most capillaries is desirable
• - blood pressure in veins is too low to keep
  blood flowing so muscle contractions in
  surrounding tissues move the blood
• - blood pressure is an overall function of
  cardiac output, peripheral resistance, and blood
  volume
• - changes in any one of these will be
  compensated for to maintain constant pressure
• - blood pressure is measured using a
  sphygmomanometer which is used to cut-off blood
  flow and then allow flow to slowly return

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• - blood pressure is measured using a
  sphygmomanometer which is used to cut-off blood
  flow and then allow flow to slowly return
• - systolic pressure is read when blood flow
  returns through the artery
• - diastolic pressure is read when no further
  resistance is being offered to blood flow

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• Fetal Circulation
• - mother and childs blood does not mix, but is
  in close proximity at placenta
• - chorionic villi from the chorion surrounding
  the embryo/fetus penetrate into the uterine
  lining
• - blood vessels in the umbilical cord belong to
  fetal circulation
• - within the circulation of the fetus several
  things are different than in the adult
• 1. Ductus arteriosus redirects blood from lungs
  to aorta
• 2. Ductus venosus returns blood from umbilical
  cord to fetus
• 3. Umbilical arteries branch from internal
  iliac arteries (in legs) to umbilical cord and
  placenta
• 4. Foramen ovale allows blood to flow from
  right atrium to left atrium instead of right
  ventricle (decreases blood going to fetal lungs)
• - all of these must close at birth

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• Diseases and disorders of the Cardiovascular
  System
• 1. Hypotension low blood pressure
• 2. Hypertension high blood pressure
• - common in obese people due to greater total
  length of blood vessels
• - chronic hypertension is often a result of
  increased peripheral resistance
• - often caused by atherosclerosis
• - primary hypertension has no discernable cause
  but is affected by diet, obesity, age, race,
  heredity, stress, smoking

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• 3. Circulatory Shock
• - most often caused by blood loss
• 4. Heart attack
• - caused by blockage of the coronary arteries