The Cardiovascular System

1
The Cardiovascular System
2
The Cardiovascular System

• The cardiovascular system consists of 3
  components
• Bloodthe fluid that circulates substances
  throughout the body transports gases, nutrients,
  and wastes also involved in immunity
• Hearta muscular pump that helps move the blood
  through the body
• Blood vesselsarteries, veins, and capillaries
  that are tube-like structures that contain the
  blood and carry it to body cells

3
The Cardiovascular System

• Hematology is the branch of science concerned
  with the study of the blood
• Cardiology is the study of the heart

4
The Heart

• The heart is the pump that circulates blood
  throughout the human body
• Each body cell must receive a constant supply of
  blood at all times
• The heart beats about 100,000 times per day and
  pumps about 3600 gallons of blood per day

5
The Heart (continued)

• The heart is about the same size as a closed fist
• It sits in the thoracic cavity near the midline
  of the body
• It rests on the diaphragm within the mediastinum,
  a mass of tissue that extends from the sternum to
  the vertebral column between the lungs

6
The Heart (continued)

• The apex of the heart is the inferior pointed
  portion, which is directed to the left
• The base is the broad superior portion

7
The Heart (continued)

• Since the heart lies between the vertebral column
  and the sternum, external chest compression can
  be used to force blood out of the heart and into
  circulation
• Cardiopulmonary resuscitation (CPR) keeps
  oxygenated blood circulating in the body when the
  heart suddenly stops beating

8
Membranes of the Heart

• Pericardiumthe membrane that surrounds and
  protects the heart consists of two parts
• Fibrous pericardiumthe superficial portion
• Serous pericardiumconsists of an outer parietal
  layer, which is fused to the fibrous pericardium,
  and an inner visceral layer between these two
  layers is a space called the pericardial cavity
  and a thin film of slippery fluid called
  percardial fluid this fluid reduces friction
  between the membrane layers as the heart moves
  while pumping blood
• Epicardiumone of the layers of the heart wall
  the same as the visceral layer adheres to the
  surface of the heart

9
Layers of the Heart Wall

• Epicardiumthe thin, transparent outer layer of
  the heart wall the same as the visceral layer of
  the serous pericardium
• Myocardiumthe middle muscular layer composed of
  cardiac muscle (a striated, involuntary type of
  muscle tissue) responsible for the pumping
  action of the heart
• Endocardiuma thin layer which lines the chambers
  of the heart and covers the valves continuous
  with the lining of the large blood vessels
  attached to the heart

10
Chambers of the Heart

• The human heart has 4 chambers
• Right atrium
• Left atrium
• Right ventricle
• Left ventricle

11
Chambers of the Heart (continued)

• The atria are the superior chambers the
  ventricles are the inferior chambers
• On the anterior surface of each atrium is a
  pouch-like structure called an auricle the
  auricles allow the atria to hold more blood

12
Sulci

• On the surface of the heart are grooves that
  contain coronary blood vessels and fat
• Coronary sulcusmarks the boundary between the
  atria and the ventricles
• Interventricular sulcus (an anterior and a
  posterior)marks the boundary between the right
  and left ventricles

13
Right Atrium

• Receives blood from 3 main veins the superior
  vena cava, the inferior vena cava, and the
  coronary sinus
• The interatrial septum is a thin partition that
  separates the right atrium from the left
  contains an oval depression called the fossa
  ovalis, a remnant of the foramen ovale, an
  opening in the septum of the fetal heart that
  normally closes soon after birth
• Blood passes from the right atrium into the right
  ventricle through the tricuspid valve, an
  atrioventricular valve

14
Right Ventricle

• Forms most of the anterior surface of the heart
• Trabeculae carneaeridges and folds of the
  myocardium inside the ventricles of the heart
  raised bundles of cardiac muscle fibers
• Papillary musclescone-shaped trabeculae carneae
  which are connected to the tricuspid valve by way
  of tendon-like cords called chordae tendineae
• Interventricular septumseparates the right
  ventricle from the left
• Blood exits the right ventricle through the
  pulmonary semilunar valve and into a large artery
  called the pulmonary trunk this artery divides
  into a right and a left pulmonary artery

15
Left Atrium

• Receives blood from the lungs through four
  pulmonary veins
• Blood passes from the left atrium into the left
  ventricle through the bicuspid (mitral) valve,
  another atrioventricular valve

16
Left Ventricle

• Like the right ventricle, the left ventricle
  contains trabeculae carneae, papillary muscles,
  and chordae tendinae, which anchor the bicuspid
  valve
• Blood passes from the left ventricle through the
  aortic semilunar valve into another large artery,
  the aorta
• During fetal life, a temporary blood vessel, the
  ductus arteriosus, shunts blood from the
  pulmonary trunk into the aorta only a small
  amount of blood enters the fetal lungs, which are
  nonfunctioning
• Shortly after birth, the ductus arteriosus
  normally closes, leaving a remnant called the
  ligamentum arteriosum this structure connects
  the aorta and the pulmonary trunk

17
Aorta

• The aorta is the largest artery of the body
• As it exits the left ventricle of the heart, it
  is specifically called the ascending aorta
• It becomes the arch of the aorta as it curves and
  begins to run inferiorly down the body toward the
  legs
• It then becomes the descending aorta, which is
  subdivided into the thoracic aorta and the
  abdominal aorta

18
Myocardial Thickness Variations in the Heart

• The myocardium is relatively thin in the atria,
  but thick in the ventricles
• The walls of the left ventricle are the thickest,
  so this chamber has the greatest pumping ability
• The left ventricle must pump blood to all areas
  of the body

19
Heart Valves

• The function of heart valves is to prevent the
  backward flow of blood
• Valves open and close in response to pressure
  changes as the heart contracts and relaxes
• There are 4 valves in the heart
• Tricuspid valvean atrioventricular valve between
  the right atrium and the right ventricle
• Bicuspid valvean atrioventricular valve between
  the left atrium and the left ventricle
• Pulmonary semilunar valvebetween the right
  ventricle and the pulmonary trunk
• Aortic semilunar valvebetween the left ventricle
  and the aorta

20
Heart Sounds

• The sound of the heartbeat consists of two sounds
  that are loud enough to be heard with a
  stethoscope
• The first sound (lubb) is caused by the closure
  of the atrioventricular valves
• The second sound (dupp) is caused by the
  closure of the closure of the semilunar valves
• A heart murmur is an abnormal heart sound that
  sometimes indicates a valve disorder

21
Circulation of Blood

• The heart pumps blood in two closed pathways with
  each beat
• Systemic circulation--the left ventricle pumps
  oxygenated blood to all areas of the body and
  deoxygenated blood from all areas of the body
  (back to the heart)
• Pulmonary circulationthe right ventricle pumps
  deoxygenated blood to the lungs to pick up oxygen
  and oxygenated blood back to the heart

22
Circulation of Blood (continued)

• Arteries carry blood away from the heart
  arterioles are small arteries
• Veins carry blood toward the heart venules are
  small veins
• Most arteries carry oxygenated blood
• Most veins carry deoxygenated blood
• Capillaries are microscopic blood vessels located
  between arteries and veins these vessels have
  very thin walls through which materials are
  exchanged with the interstitial fluid between
  cells

23
Path of Blood Through the Body

• Left ventricle ? aorta ? arteries (to organs) ?
  arterioles (within tissues) ? capillaries (to
  cells) ? venules (within tissues) ? veins (from
  organs) ? right atrium ? right ventricle ?
  pulmonary trunk ? pulmonary arteries ? pulmonary
  arterioles ? pulmonary capillaries ? pulmonary
  venules ? pulmonary veins ? left atrium ? left
  ventricle

24
Coronary Circulation

• Nutrients cannot diffuse quickly enough from the
  blood within the heart chambers to supply the
  cells that make up the wall of the heart
• The myocardium has its own blood supply
• Coronary arteries branch from the ascending aorta
  and encircle the heart

25
Coronary Circulation (continued)

• The left coronary artery passes inferior to the
  left auricle and divides into the anterior
  interventricular branch (within the anterior
  interventricular sulcus) and the circumflex
  branch (within the coronary sulcus)
• The right coronary artery passes inferior to the
  right auricle and divides into the posterior
  interventricular branch and the marginal branch

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Coronary Circulation (continued)

• Most parts of the body receive blood from
  branches of more than one artery
• If one vessel becomes blocked, another can still
  supply the cells with blood

27
Coronary Circulation (continued)

• After blood passes through coronary arteries, it
  flows into capillaries
• Capillaries supply blood containing oxygen and
  nutrients to cells and receives carbon dioxide
  and wastes from cells
• The blood next moves into coronary veins (or
  cardiac veins)
• Most of the blood drains into the coronary sinus
  (within the coronary sulcus), which empties into
  the right atrium

28
Heart Attacks

• Partial obstruction of blood flow in the coronary
  arteries may cause ischemia (reduced blood flow)
  and hypoxia (reduced oxygen supply)
• Angina pectoris is pain that sometimes
  accompanies myocardial ischemia
• Silent myocardial ischemia is ischemia without
  pain

29
Heart Attacks (continued)

• Myocardial infarction (MI or heart attack) is the
  death of an area of myocardial tissue due to
  complete blockage of a coronary artery blood
  flow to cells beyond the blockage is obstructed,
  so the cells die
• The dead tissue is eventually replaced by scar
  tissue, and the heart muscle loses some of its
  strength

30
Heart Attacks (continued)

• Depending on the size and location of the
  affected area, an MI may disrupt the conduction
  system of the heart and cause sudden death by
  ventricular fibrillation
• Treatment for heart attacks includes use of
  anticlotting medications, angioplasty, or bypass
  surgery
• Heart muscle can remain alive in a resting
  individual if it receives even 10-15 of its
  normal blood supply

31
Cardiac Muscle Tissue

• Cardiac muscle is involunary and striated
• The individual fibers (cells) have
  characteristics similar to skeletal muscle fibers
• Same arrangement of actin, myosin
• Same sarcomere structure as to bands, zones, etc.

32
Cardiac Muscle Tissue (continued)

• Cardiac muscle fibers are shorter in length and
  contain more mitochondria than skeletal muscle
  fibers
• The fibers are branched and separated from one
  another by intercalated discs, which allow the
  fibers to better communicate with one another

33
The Conduction System of the Heart

• The heart contains a network of specialized
  cardiac muscle fibers that are autorhythmic
  (self-excitable)
• Only about 1 of the cardiac muscle fibers have
  this ability
• These fibers repeatedly generate action
  potentials that cause the heart to contractfor
  awhile even when removed from the body

34
The Conduction System of the Heart (continued)

• They act as the pacemaker of the heart by setting
  the rhythm of contraction
• They form a conduction system which enables the
  chambers of the heart to contract in a
  coordinated manner to make the heart an effective
  pump

35
The Conduction System of the Heart (continued)

• There are 5 components to the conduction system
  of the heart
• SA node
• AV node
• AV bundle (Bundle of His)
• Right and left bundle branches
• Purkinje fibers

36
SA Node

• The sinoatrial node (SA node) is a small mass of
  cardiac muscle fibers located in the right atrial
  wall (just below the opening of the superior vena
  cava)
• Serves as the pacemaker of the heart
• Generates an action potential about 100 times per
  minute which propagates throughout both atria and
  causes them to contract
• Acetylcholine released by the parasympathetic
  division of the ANS slows the pace to about 75
  action potentials per minute

37
AV Node

• The atrioventricular node (AV node) is a mass of
  conducting cells located in the interatrial
  septum
• The action potential travels from the SA node to
  the AV node

38
AV Bundle (Bundle of His) and Right and Left
Bundle Branches

• From the AV node, the action potential enters the
  AV bundle (Bundle of His) within the
  interventricular septum
• Next, it moves to the right and left bundle
  branches, which extend from the AV bundle through
  the interventricular septum and toward the apex
  of the heart

39
Purkinjie Fibers

• These large-diameter fibers rapidly conduct the
  action potential from the apex of the heart
  upward to the rest of the ventricular myocardium
• The ventricles contract, and blood moves out of
  the semilunar valves

40
Systole vs. Diastole

• Systole refers to contraction
• Diastole refers to relaxation
• The atria and ventricles contract and relax at
  different times due to the conduction system
  pathway

41
Cardiac Muscle Contraction

• The contraction of cardiac muscle is similar to
  that of skeletal muscle
• The action potential initiated by the SA node
  travels along the conduction system to
  contractile fibers in the atria and ventricles

42
Cardiac Muscle Contraction (continued)

• These muscle fibers have a resting membrane
  potential of about -90 mV
• When stimulated by a threshold-level action
  potential, Na ion influx and depolarization
  occur (to a membrane potential of about 0 mV)

43
Cardiac Muscle Contraction (continued)

• In cardiac muscle fibers, depolarization is
  maintained for a short period of time (the
  plateau phase)
• Skeletal muscle fibers do not go through this
  plateau phase

44
Cardiac Muscle Contraction (continued)

• Next, K outflux and repolarization occur
• The membrane potential returns to its resting
  level of -90 mV

45
Cardiac Muscle Contraction (continued)

• As the events of depolarization and
  repolarization occur, Ca2 ion concentration
  increases in the cytoplasm of the cardiac muscle
  fibers
• This is due to Ca2 influx from both interstitial
  fluid and the sarcoplasmic reticulum

46
Cardiac Muscle Contraction (continued)

• Ca2 binds to troponin, and actin myofilaments
  are able to slide past myosin
• The sarcomere shortens
• Contraction of cardiac muscle occurs

47
Cardiac Muscle Contraction (continued)

• The refractory period, the time interval during
  which a second contraction cannot occur, is
  longer in cardiac muscle (about 300 milliseconds)
  than in skeletal muscle (about 5 milliseconds)

48
Electrocardiogram

• As action potentials travel through the heart,
  they create electrical currents that can be
  detected at the body surface
• An electrocardiogram (EKG or ECG) is a recording
  of this activity
• EKGs are used to determine if the conduction
  system of the heart is working normally and if
  the heart is damaged

49
Electrocardiogram (continued)

• A normal EKG record consists of
• P waverepresents atrial depolarization, which
  spreads from the SA node to the AV node this
  causes atrial systole
• QRS complexrepresents ventricular
  depolarization, as the action potential spreads
  from the AV bundle, through the bundle branches
  and Purkinje fibers, and to the myocardium of
  both ventricles this causes ventricular systole
  (and atrial diastole)
• T waverepresents ventricular repolarization
  this causes ventricular diastole

50
The Cardiac Cycle

• A cardiac cycle includes the events associated
  with one heartbeat
• Consists of systole and diastole of the atria and
  systole and diastole of the ventricles
• When the heart rate is 75 beats per minute, a
  cardiac cycle lasts 0.8 seconds

51
Cardiac Output

• Stroke volume (SV) is the volume of blood ejected
  per beat from each ventricle at rest, normal
  stroke volume is 70 mL (a little more than 2
  ounces)
• Cardiac output (CO) is the volume of blood
  ejected from the left ventricle into the aorta
  each minute (or from the right ventricle into the
  pulmonary trunk each minute)
• Heart rate (HR) is the number of heartbeats per
  minute at rest, normal heart rate is 75 beats
  per minute

52
Cardiac Output (continued)

• Cardiac Output Stroke Volume X Heart Rate
• At rest
• CO 70 mL/beat X 75 beats/minute
• 5250 mL/minute
• 5.25 L/minute

53
Cardiac Output (continued)

• Any condition that affects heart rate can also
  affect cardiac output
• Age, gender, physical fitness, body temperature,
  and hormones all influence heart rate
• Tachycardiaan abnormally rapid resting heart
  rate (over 100 beats/minute)
• Bradycardiaa slow resting heart rate (under 50
  beats/minute)

54
Nervous System Control of the Heart

• Nervous system control of the heart originates in
  the cardiovascular center of the medulla
  oblongata
• Based on information it receives, this region of
  the medulla directs the sympathetic and/or
  parasympathetic division of the autonomic nervous
  system to act

55
Nervous System Control of the Heart (continued)

• The heart is innervated by nerves from both
  divisions of the ANS
• Sympathetic stimulation of the heart causes the
  release of norepinephrine NE causes an increase
  in heart rate
• Parasympathetic stimulation (by way of the vagus
  nerve, cranial nerve X) causes the release of
  acetylcholine Ach causes a decrease in heart rate

56
Blood

• Blood is a connective tissue composed of plasma,
  a liquid that contains dissolved substances, and
  formed elements, which are cells and cell
  fragments
• Interstitial fluid is the extracellular fluid
  that bathes body cells (the fluid outside cells)
• Cytoplasm is the intracellular fluid inside cells

57
Functions of Blood

• Transportationblood transports oxygen and
  nutrients to body cells and carbon dioxide and
  wastes from body cells it also transports
  hormones from endocrine glands to body cells
• Regulationblood helps regulate the pH of body
  fluids, the water content of cells, and the
  temperature of the body
• Protectionblood has the ability to clot, which
  prevents its loss it also helps to prevent
  disease by fighting bacteria, viruses, and
  foreign substances

58
Characteristics of Blood

• More viscous than water
• Has a temperature of about 100.4 F
• Has a slightly alkaline pH (7.35-7.45)
• Average volume of blood is 5-6 liters (1.5
  gallons) in adult males and 4-5 liters (1.2
  gallons) in adult females

59
Components of Blood

• Blood is about 45 formed elements and 55 plasma
• Normally, more than 99 of the formed elements
  are red blood cells (erythrocytes) white blood
  cells (leukocytes) and platelets (thrombocytes)
  make up less than 1 of total blood volume

60
Plasma

• When the formed elements are removed from blood,
  a straw-colored liquid is left
• This is plasma, which is about 91.5 water
• The remaining 8.5 consists of plasma proteins
  (7) and other dissolved solute substances
  (1.5), such as electrolytes, nutrients, enzymes,
  hormones, gases, and wastes

61
Plasma Proteins

• Most of the plasma proteins are synthesized in
  the liver by hepatocytes (liver cells)
• These include
• Albuminsmost abundant transport steroid
  hormones and fatty acids
• Globulinsinclude antibodies, which help attack
  viruses and bacteria
• Fibrinogeninvolved in blood clotting

62
Formed Elements

• Erythrocytes (red blood cells)most numerous type
  of blood cell red in color (give blood its red
  color) biconcave disks
• Leukocytes (white blood cells)largest type of
  blood cell pale or colorless normally the least
  numerous type of blood cell 5 main types of WBCs
• Thrombocytes (platelets)cell fragments pale or
  colorless

63
Hematocrit

• The percentage of total blood volume occupied by
  RBCs is called the hematocrit
• Normal hematocrit values
• Adult females38-46 (average of 42) loss of
  blood during menstruation can cause lower values
  than in males
• Adult males40-54 (average of 47) the hormone
  testosterone can indirectly stimulate RBC
  synthesis

64
Formation of Blood Cells

• Hemopoiesisthe process of blood cell production
  occurs in the red bone marrow after birth
• Red bone marrow is located within spongy bone
  tissue spongy bone is present mainly in the
  bones of the axial skeleton, the pectoral and
  pelvic girdles, and the proximal epiphyses of
  long bones such as the humerus and femur

65
Formation of Blood Cells (continued)

• Stem cells are unspecialized cells in the body
  that can divide to produce specialized cells
• Red bone marrow contains stem cells that divide
  and/or develop into several types of immature
  cells before eventually giving rise to mature
  blood cells (blasts are a common type of immature
  blood cell)

66
Formation of Blood Cells (continued)

• Erythropoietina hormone produced and released by
  the kidneys which stimulates red blood cell
  production
• Thrombopoietina hormone produced and released by
  the liver which stimulates platelet formation
• Colony-stimulating factors (CSFs) and
  interleukinshormone-like molecules produced by
  red bone marrow cells stimulate white blood
  cell production

67
Red Blood Cells

• Red blood cells (erythrocytes) contain the
  oxygen-carrying protein hemoglobin in their
  cytoplasm
• Hemoglobin gives blood its red color
• Normal red blood cell counts are
• 5.4 million/µL in adult males
• 4.8 million/µL in adult females
• (one drop of blood is about 50 µL)

68
Red Blood Cells (continued)

• RBCs have a biconcave disc shape and lack a
  nucleus when mature
• Their plasma membranes contain antigens that give
  individuals their ABO and Rh blood types
• Antigens are chemical substances that can cause
  immune responses

69
Red Blood Cells (continued)

• Each RBC contains about 280 million hemoglobin
  molecules
• A hemoglobin molecule consists of
• a protein called globin
• four nonprotein heme pigments
• and four iron ions (Fe2), one attached to each
  heme

70
Red Blood Cells (continued)

• Oxygen is transported by hemoglobin by binding
  with the iron
• Each hemoglobin molecule can bind to four oxygen
  molecules
• Normal hemoglobin values are
• 14-20 g/100 mL in infants
• 12-16 g/100 mL in adult females
• 13.5-18 g/100 mL in adult males

71
Red Blood Cells (continued)

• Hemoglobin also transports about 23 of the total
  carbon dioxide carried in the blood
• CO2 is a waste product of metabolism

72
Red Blood Cells (continued)

• The life span of a red blood cell is about 120
  days
• Dead and/or damaged RBCs are removed from the
  blood and destroyed by cells in the spleen and
  liver
• The products that make up RBCs are recycled

73
White Blood Cells

• White blood cells (leukocytes) have nuclei and do
  not contain hemoglobin
• Most live only a few days, but some can live
  several months or years
• Normal white blood cell count is 5,000-10,000/ µL
  
• The general function of WBCs is to fight foreign
  microbes
• An increase in WBC count usually indicates
  inflammation or infection

74
White Blood Cells (continued)

• There are 5 main types of WBCs
• Neutrophils
• Lymphocytes
• Monocytes
• Eosinophils
• Basophils

75
Neutrophils

• 60-70 of all WBCs
• Function in phagocytosis of bacteria
  (ingest/engulf)
• First WBC type to respond to infection by
  bacteria

76
Lymphocytes

• 20-25 of all WBCs
• Only 2 of lymphocytes are circulating in the
  blood at a given time the rest are in lymphatic
  fluid and organs such as the skin, lungs, lymph
  nodes, and spleen
• Include B cells, T cells, and natural killer
  cells
• Mediate immune responses
• B cells develop into plasma cells and secrete
  antibodies, proteins that combine with antigens
  to destroy them particularly effective against
  bacteria
• T cells and natural killer cells attack viruses,
  bacteria, fungi, cancer cells, and transplanted
  tissues

77
Monocytes

• 3-8 of all WBCs
• Largest type of WBC
• Take longer to arrive at an infection site, but
  arrive in larger numbers and destroy more
  microbes
• Transported by the blood into tissues, where
  these cells enlarge and become macrophages
• Macrophages function in phagocytosis to clean up
  after infection

78
Eosinophils

• 2-4 of all WBCs
• Function in phagocytosis and destroy certain
  parasitic worms
• Release enzymes that combat the effects of
  inflammation

79
Basophils

• 0.5-1 of all WBCs
• Involved in allergic reactions and inflammatory
  responses
• These cells release histamine when cells are
  injured

80
Platelets

• Platelets (thrombocytes) are tiny cell fragments
  that lack a nucleus
• Each of these cells consists of a small amount of
  cytoplasm enclosed by a plasma membrane
• Platelets help stop blood loss from damaged
  vessels by forming a platelet plug they also
  promote blood clotting
• They live only about 5-9 days
• Normal platelet count is 150,000-400,000/ µL

81
Hemostasis

• Hemostasis is the series of 3 steps that stop
  bleeding
• Vascular spasmthe smooth muscles in the walls of
  damaged arteries contract to reduce blood loss
  for up to several hours
• Platelet plug formationplatelets undergo changes
  that make them stick together and plug a hole in
  a blood vessel
• Blood clottingthe coagulation of blood and
  formation of a thrombus, or clot

82
Hemostasis (continued)

• As blood clots, it thickens and separates
• Serum is blood plasma minus clotting proteins
• The clot is a gel-like mass of insoluble protein
  fibers (fibrin) and trapped formed elements

83
Hemostasis (continued)

• Clotting involves many factors
• The major factors include
• Calcium ions (Ca2) necessary to form the
  enzyme prothrombinase
• Prothrombin, a plasma protein formed by the
  liver prothrombinase converts prothrombin into
  the enzyme thrombin
• Fibrinogen, another plasma protein formed by the
  liver thrombin converts fibrinogen into fibrin
• Vitamin Krequired for the synthesis of some of
  the other clotting factors produced by bacteria
  that normally inhabit the large intestine

84
Fibrinolysis

• Fibrinolysisdissolving of a clot
• The body has the ability to dissolve unnecessary
  clots
• Plasmin is an enzyme in blood plasma that, once
  activated, dissolves/digests the clot
• In addition, blood contains anticoagulants (ex.
  heparin) that prevent clots from forming

85
Blood Vessels

• There are 5 main types of blood vessels
• Arteriescarry blood away from the heart to other
  organs
• Arteriolessmall arteries that deliver blood to
  capillaries
• Capillariesmicroscopic blood vessels located
  between arterioles and venules
• Venulessmall veins that collect blood from
  capillaries
• Veinscarry blood from organs back to the heart

86
Arteries

• Carry blood away from the heart through the
  hollow lumen
• Have 3 layers in their walls
• Tunica internainnermost coat contains a lining
  of endothelium, a basement membrane, and an
  internal elastic layer
• Tunica mediamiddle coat and thickest layer
  consists of elastic fibers and circular smooth
  muscle fibers
• Tunica externaouter coat composed of elastic
  and collagen fibers

87
Arteries (continued)

• Increased sympathetic stimulation (from the ANS)
  causes vasoconstriction as smooth muscle in the
  tunica media contracts this decreases the
  diameter of the lumen of an artery
• Decreased sympathetic stimulation causes
  vasodilation as the smooth muscle relaxes this
  increases the diameter of the lumen

88
Capillaries

• Blood flows from arterioles to venules through
  capillaries
• These vessels are found near almost every cell of
  the body
• Their main function involves the exchange of
  nutrients and oxygen with wastes and CO2 between
  the blood and tissue cells through interstitial
  fluid

89
Capillaries (continued)

• The walls of capillaries are composed of only a
  layer of endothelium and a basement membrane
  they have no tunica media or tunica externa
• Capillaries form extensive branching networks

90
Veins

• Carry blood toward the heart
• Have the same 3 layers in their walls as
  arteries tunica interna, tunica media, and
  tunica externa
• The layers are thinner in veins the walls have
  less muscle and fewer elastic fibers

91
Veins (continued)

• The lumens of veins are larger than in arteries
• Veins appear somewhat flattened as compared to
  arteries
• Veins have valves to prevent the backward flow of
  blood
• About 64 of an individuals blood volume in in
  veins and venules while at rest these vessels
  are called blood reservoirs

92
Venous Return

• The volume of blood that flows back to the heart
  (into the right atrium) through the systemic
  veins is called venous return
• Several factors affect venous return
• the pumping action of the heart
• milking by the alternating contraction and
  relaxation of skeletal muscles in the legs
• respiratory pumping caused by movement of the
  diaphragm during breathing

93
Blood Pressure

• The pressure exerted by blood on the walls of a
  vessel is called blood pressure
• Blood pressure is highest in the aorta it
  gradually decreases as the blood flows into
  arterioles, capillaries, venules, and veins

94
Velocity of Blood Flow

• The velocity of blood flow is greatest in large
  arteries and slows as the blood moves into
  smaller-diameter vessels (arterioles and
  capillaries)
• Blood flows slowest in capillaries, allowing time
  for exchange of materials between the blood and
  body cells
• As the blood travels back toward the heart, it
  flows faster as it moves into vessels with larger
  lumen diameters
• It takes about 1 minute for a drop of blood to
  travel through the body while an individual is at
  rest

95
Blood Pressure (continued)

• Many factors effect blood pressure
• Heart rate
• Blood volume
• Size of the lumen of a blood vessel
• Blood viscosity (thickness)
• Blood vessel length
• Stress
• Drugs
• Body position
• Body temperature
• Body size/obesity
• Diet and exercise
• Smoking

96
Blood Pressure (continued)

• The human body has ways to adjust blood pressure
  as needed
• The cardiovascular center in the medulla
  oblongata helps regulate heart rate, stroke
  volume, force of contraction of the heart, and
  blood vessel diameter (vasoconstriction and
  vasodilation) this region of the brain receives
  input from higher brain regions and from sensory
  receptors
• Hormones also help regulate blood pressure in
  various ways (ex. Epinephrine and norepinephrine
  are released by the adrenal glands in response to
  sympathetic stimulation)

97
Blood Pressure (continued)

• There are 3 main types of sensory receptors
• Proprioceptorsmonitor body movements and
  position
• Baroreceptorsmonitor changes in pressure and
  stretch in the walls of blood vessels located
  primarily in the aorta (ascending and arch
  portions) and the internal carotid arteries
• Chemoreceptorsmonitor the concentration of
  various chemicals in the blood located near the
  baroreceptors in the aorta and internal carotid
  arteries detect changes in levels of O2, CO2,
  and hydrogen ions (H)

98
Blood Pressure (continued)

• Output from the cardiovascular center travels
  along both sympathetic and parasympathetic
  neurons of the autonomic nervous system
• An increase in sympathetic stimulation results in
  an increase in heart rate and contractility
• A decrease in sympathetic stimulation results in
  a decrease in heart rate and contractility

99
Blood Pressure (continued)

• Parasympathetic stimulation, by way of cranial
  nerve X (vagus nerve), decreases heart rate
• The cardiovascular center also sends impulses to
  smooth muscle in blood vessel walls by way of
  vasomotor nerves, which cause vasoconstriction or
  vasodilation

100
Measuring Blood Pressure

• Blood pressure is usually measured in the
  brachial artery in the left arm using a device
  called a sphygmomanometer
• Normal blood pressure should be less than 120 mm
  Hg/ 80 mm Hg
• The top number represents the systolic pressure
  (the force of blood against the walls of the
  artery just after contraction of the left
  ventricle) the bottom number represents the
  diastolic pressure (the force of blood against
  the walls of the artery as the left ventricle
  relaxes)

101
Hepatic Portal Circulation

• The hepatic portal vein carries blood from one
  capillary network (in the GI organs and spleen)
  to another (in the liver)
• After an individual eats, the hepatic portal vein
  carries blood that is full of nutrients absorbed
  from the GI tract to the liver before the
  nutrients pass into the general circulation
• In addition, harmful substances such as alcohol
  can be detoxified

102
Hepatic Portal Circulation (continued)

• The liver also receives blood from the hepatic
  artery, which branches from the celiac trunk
  artery
• Blood leaves the liver through the hepatic veins,
  which drain into the inferior vena cava

103
Fetal Circulation

• The circulatory system of a fetus contains
  special features that allow the fetus to exchange
  materials with its mother
• The lungs (and kidneys and GI organs) do not
  begin to function until birth, so a fetus gets O2
  and nutrients from and eliminates CO2 and wastes
  into maternal blood

104
Fetal Circulation (continued)

• The exchange of materials between fetal and
  maternal circulations occurs through the placenta
• The placenta forms in the mothers uterus and
  attaches to the fetus by the umbilical cord
• Capillaries from the umbilical cord and from the
  uterus come in very close contact with one
  another exchange of substances occurs between
  the vessels
• Normally, there is no mixing of maternal and
  fetal blood

105
Fetal Circulation (continued)

• Two umbilical arteries (within the umbilical
  cord) carry deoxygenated blood from the fetus to
  the placenta
• These blood vessels are branches of the internal
  iliac arteries of the fetus
• The umbilical arteries pick up O2 and nutrients
  and give up CO2 and wastes

106
Fetal Circulation (continued)

• Oxygenated blood returns from the placenta by way
  of a single umbilical vein
• This vein carries blood toward the liver of the
  fetus, where it divides into two branches
• Some blood flows through the branch that joins
  the hepatic portal vein and enters the liver

107
Fetal Circulation (continued)

• Most of the blood flows into the other branch,
  called the ductus venosus, which drains into the
  inferior vena cava
• In the inferior vena cava, oxygenated blood from
  the ductus venosus mixes with deoxygenated blood
• This mixed blood enters the right atrium, along
  with deoxygenated blood from the superior vena
  cava

108
Fetal Circulation (continued)

• Most of the fetal blood does not pass from the
  right ventricle to the lungs (as it does after
  birth), but it passes through the foramen ovale,
  an opening in the interatrial septum
• This opening carries blood from the right atrium
  to the left atrium

109
Fetal Circulation (continued)

• Some of the fetal blood does pass into the right
  ventricle, though, and on into the pulmonary
  trunk
• From the pulmonary trunk, this blood travels
  through the ductus arteriosus, a vessel that
  connects the pulmonary trunk with the aorta
• Little fetal blood ever reaches the
  nonfunctioning lungs

110
Fetal Circulation (continued)

• The blood in the aorta is carried to all fetal
  tissues through systemic circulation
• The blood that reaches the internal iliac
  arteries travels into the umbilical arteries and
  on to the placenta

111
Fetal Circulation (continued)

• Shortly after birth, the foramen ovale closes to
  become the fossa ovalis, a depression in the
  interatrial septum complete closure usually
  occurs within one year
• The ductus arteriosus closes and becomes the
  ligamentum arteriosum after several months