Circulatory System

1
Circulatory System

• The Delivery of oxygen to the cells of the body
  is a function of blood flow.
• When blood flow is inadequate, good alveolar
  ventilation is of little value.
• The circulatory system is responsible for bring
  freshly oxygenated blood from the lungs to
  various tissues and organs.
• The circulator system consists of blood, the
  heart, and the vascular system.

2
Blood

• Blood consists of numerous specialized cells that
  are suspended in a liquid substance called
  plasma.
• The cells in the plasma include -erythrocytes
  (RBC) -leukocytes (WBC) -thrombocytes
  (platelets)

3
Erythrocytes

• The erythrocytes, also known as the red blood
  cells, constitute the major portion of blood
  cells.
• The percentage of RBCs in relation to the total
  blood volume is known as the hematocrit. -Norma
  l adult male HCT 45 -Normal adult female HCT
  42
• The major constituent of a RBC is hemoglobin,
  which is the primary substance responsible for
  the transport of O2 and CO2

4
Leukocytes

• The primary function of leukocytes is to protect
  the body against the invasion of bacteria and
  other foreign agents.
• Two major groups -polymorphonuclear
  granulocytes neutrophils eosinophils
  basophils -mononuclear of nongranulated
  cells monocytes lymphocytes

5
Leukocytes

• Leukocytes average about 5000 to 9000 cells per
  cubic millimeter of blood.
• People with infections and pneumonias often have
  increased WBC count.
• People receiving chemotherapy or radiation as
  well as HIV patients often have reduced WBC
  counts.

6
Specific Leukocytes

• Neutrophils are the most active cells in response
  to tissue bacterial infections, thus, a high
  neutrophil count suggests a bacterial infection.
• An elevated eosinophil and basophil count may
  indicate an allergic reaction.
• An elevated monocyte count indicates a chronic
  infection.
• Lymphocytes are involved in the production of
  antibodies.

7
Thrombocytes

• Thrombocytes, or blood platelets, are the
  smallest of the formed elements in the plasma.
• Normal platelet count ranges from 250,000 to
  500,000.
• The function of the platelets is to prevent blood
  loss from a traumatized area of the body.
• They do this by activating a substance called
  platelet factor which helps with blood clotting.

8
Plasma

• When all the cells are removed from blood, a
  straw-colored liquid called plasma is left.
• Plasma constitutes about 55 of the total blood
  volume.
• About 90 of plasma consists of water.
• The remaining 10 is composed of proteins,
  electrolytes, respiratory gases, vitamins,
  hormones and waste products.

9
The Heart

• The heart is a hollow, four chambered, muscular
  organ that consists of the upper right and left
  atria and the lower right and left ventricles.
• The atria and the ventricles are separated by
  interatrial and interventicular septums,
  respectively.
• The heart actually functions as two separate
  pumps.

10
Blood Supply of the Heart

• The blood supply that nourishes the heart
  originates directly from the aorta by means of
  two arteries -left coronary
  artery divides into the circumflex and left
  anterior descending artery -Right
  coronary artery
• At rest, the heart receives about 5 percent of
  the total cardiac output.
• Most of the blood delivered to the heart returns
  to the right atrium via the coronary sinus

11
Blood Flow Through Heart

• The right atrium receives blood from the inferior
  and superior vena cava.
• This blood is low in oxygen and high in carbon
  dioxide.
• Blood then flows to the right ventricle through a
  one-way valve called the tricuspid valve which
  lies between the right atrium and right
  ventricle.
• Blood then flows from the right ventricle through
  the pulmonary valve to the pulmonary trunk and
  enters the lungs via the right and left pulmonary
  arteries.

12
Blood Flow Through Heart

• After blood passes through the lungs, it returns
  to the left atrium by way of the pulmonary veins.
• The returning blood is high in O2 and low in CO2.
• Blood then moves through the bicuspid valve and
  into the left ventricle
• The left ventricle pumps blood through the aortic
  valve into the ascending aorta.

13
The Pulmonary and Systemic Vascular Systems

• The vascular network of the circulatory system is
  composed of two major subdivisions - the
  systemic system begins with the aorta and ends
  in the right atrium - the
  pulmonary system begins with the pulmonary
  trunk and ends in the left atrium
• Both systems are composed of arteries,
  arterioles, capillaries, venules, and veins.

14
Neural control of the Vascular System

• The Pulmonary arterioles and most of the
  arterioles in the systemic circulation are
  controlled by sympathetic impulses.
• The vasomotor center, located in the medulla,
  governs the number of sympathetic impulses sent
  to the vascular system.
• The vasomotor center transmits a continual stream
  of sympathetic impulses to the blood vessels,
  maintaining a moderate state of constriction at
  all times called the vasomotor tone.
• Arterial baroreceptors are pressure receptors
  that regulate arterial blood pressure.

15
The Baroreceptor Reflex

• Specialized stretch receptors called
  baroreceptors are locates in the walls of the
  carotid arteries and aorta.
• The baroreceptors regulate arterial blood
  pressure by initiating reflex adjustments to
  deviations in blood pressure.
• The baroreceptors respond instantly to any blood
  pressure change to restore the blood pressure
  toward normal.

16
Other Baroreceptors

• Baroreceptors are also found in the large
  arteries, large veins, pulmonary vessels and the
  cardiac walls.
• By means of these additional receptors, the
  medulla gains a further degree of sensitivity to
  venous, atrial, and ventricular pressures.

17
Pulmonary and Systemic Vascular Pressures

• Three types of pressure are used to study blood
  flow -intravascular is the actual
  blood pressure in the lumen of any vessel at any
  point -transmural is the difference between
  the intravascular pressure of a vessel and the
  pressure surrounding the vessel -driving
  pressure is the difference between the pressure
  at one point in a vessel and the pressure at any
  other point downstream in the vessel.

18
The Cardiac Cycle and B/P

• The arterial blood pressure rises and falls in a
  pattern that corresponds to the phases of the
  cardiac cycle.
• The maximum pressure generated during ventricular
  contraction is the systolic pressure.
• The lowest pressure that remains in the arteries
  prior to the next ventricular contraction is the
  diastolic pressure.
• Normal systemic blood pressure is 120/80 and
  normal pulmonary blood pressure is 25/8.

19
Pulmonary Driving Pressure

• Mean PA pressures are 15 mmHg
• Mean LA pressure is about 5 mmHg
• Thus the pulmonary circulation is a low pressure
  system only requiring 10 mmHg of driving pressure.

20
Blood Volume and BP

• Stroke volume is the amount of blood ejected from
  the left ventricle during systole
• Normal ranges from 40-80mls
• The total volume ejected in a minute is referred
  to as cardiac output.
• Cardiac OutputStroke Volume x HR

21
Distribution of Pulmonary Blood Flow

• In the upright lung, blood flow progressively
  decreases from base to the apex.
• This linear distribution of blood is a function
  of - Gravity - Cardiac Output -
  Pulmonary Vascular Resistance

22
Distribution of Pulmonary Blood Flow

• Zone I Alveolar pressure is greater than
  capillary pressures.
• Zone II- Increasing perfusion.
• Zone III-Constant blood flow.

23
Determinants of Cardiac Output

• CO SV x HR
• Stroke Volume is determined by
• Ventricular preload
• Ventricular afterload
• Myocardial contractility

24
Ventricular Preload

• Preload is the degree that cardiac tissue is
  stretched (filled) prior to systole.
• Increasing preload increases contractility
• To a certain degree increasing preload will
  increase stroke volume and CO.
• VEDP filling pressure meet Frank Starling (Fig
  5-19)

25
Ventricular Afterload

• Afterload is defined as the force against which
  the ventricles must overcome.
• This is determined by the volume and viscosity of
  the blood
• Peripheral vascular resistance.
• The total cross sectional area of the vascular
  space.

26
Myocardial Contractility

• Myocardial contractility is the force generated
  by the myocardium.
• It is the strength of the heart.

27
Distribution of Pulmonary Blood Flow

• In the upright lung, blood flow progressively
  decreases from base to the apex.
• This linear distribution of blood is a function
  of - Gravity - Cardiac Output -
  Pulmonary Vascular Resistance

28
Vascular Resistance

• Circulatory resistance is derived by dividing the
  mean blood pressure by the cardiac output -
  resistance BP / CO
• In general, when the vascular resistance
  increases, the BP increases, thus, BP can be used
  to reflect vascular resistance.
• In the pulmonary system , there are mechanisms
  that change vascular resistance classified as
  either active or passive mechanisms.

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Active Mechanisms

• Active mechanisms that affect vascular resistance
  include -abnormal ABGs decreased PO2
  -pH
  
  -increased PCO2 all increase vascular resistance
  pharmacologic stimulation constrict with
  epinephrine or dopamine. Dilate with O2 and
  aminophylline - pathologic conditions
  pulmonary emboli,sclerosis, emphysema,
  pneumothorax all increase vascular resistance

30
Passive Mechanisms

• The term passive mechanism refers to a secondary
  change in pulmonary vascular resistance that
  occurs in response to another mechanical change.
• Increases in pulmonary artery pressures decrease
  vascular resistance.
• As left atrial pressures increase, pulmonary
  vascular resistance

31
Passive Mechanisms

• During inspiration, alveoli distend and increase
  pulmonary vascular resistance.
• As blood volume increases, pulmonary vascular
  resistance decreases to accommodate the increased
  volume.
• As blood viscosity increases, the pulmonary
  vascular resistance increases. End Chp 5