Circulatory system is composed of:
1. heart
2. blood vessels
3. blood
Functions of the circulatory system
1. transport essential materials (oxygen, fuel molecules, hormones, etc) throughout the body to cells where they are needed to collect waste materials (carbon dioxide, lactic acid, urea, etc) generated by the body's metabolic activity.
Circulatory system is divided in 2 sections
a. pulmonary circuit - blood vessels going to and from lungs
b, systemic circuit - blood vessels going to and from the rest of tissues of the body
Heart
4 chamber, muscular pump which propels blood through the blood vessels
Atria
the 2 upper chambers of the heart.
Ventricles
the 2 lower chambers
Right ventricle
pumps blood through the pulmonary circuit
Left ventricle
pumps blood through the systemic circuit
Wall of right ventricle vs wall of left ventricle
wall of left ventricle is thicker than wall of right ventricle because the systemic circulation is a much higher pressure system than the pulmonary circulation
Septum
divides the left and right sides of the heart -> 2 pumps.
The direction of blood flow through the heart is controlled by
unidirectional valves
Heart Murmur
valve is damaged or does not close properly -> blood regurgitates, causing a noise
The heart muscle (myocardium)
is a specialized type of muscle - cardiac muscle
Unlike skeletal muscle, all of the fibers or cells in cardiac muscles are
anatomically interconnected - functional syncytium. When one fiber contracts, all fibers contract.
The fibers of the atria are separate from
the fibers of the ventricles
Conduction system of the heart
the heart's inherent contractile rhythm originates in an area of specialized tissue located in the posterior wall of the right atrium
the S-A node
normal pacemaker of the heart
Pathway of conduction of the wave of depolarization (cardiac impulse) across heart:
antrial muscle fibers -> A-V bundle ->left and right bundle brances -> Purkinjie fibers which travels throughout the ventricular myocardium -> simultaneous contractionof the left and right ventricles.
The wave of depolarization is delayed in A-V node for approximately 0.10 seconds in order to...
to give the atria time to contract the empty their contents into the ventricles.
Electrocardiography
records the wave of depolarization as it passes across the heart using electrodes on the surface of the body
Components of a normal EKG wavefor:
P wave- atrial waveform
QRS wave - ventricular depolarization
T wave - ventricular repolarization
Arrhythmia
an irregularity in the rhythm of the heartbeat
Diagnosing arrhythmias
look at heart rate, amplitude and shapes of the components of the EKG waveform, and time travels.
Examples of arrhythmias
a. atrial - tachycardia
b. nodal - second and third degree heart blocks
c. ventricular - premature ventricle contraction (PVC), ventricular tachycardia, ventricular fibrillation.
Blood supply to the heart
the heart muscle is supplied by 2 maor arteries that originate from the aorta just above the aortic valve - left coronary artery and right coronary artery. The large beins of the heart converge and empty into the right atrium.
Since cardiac muscle is highly dependent on aerobic metabolism,
it has a rich blood supply. At rest, normal blood flow to the myocardium is about 5% of the total cardiac output.
Blood vessels:
1. arteries
2. capillaries
3. venules
4. veins
5. valves
Arteries
blood vessels that carry blood away from the heart. They range in size from the aorta which is about 25 mm in diameter in man to those about 0.5 mm.
Going from large arteries -> medium-sized arteries -> small arteries -> arterioles
there is less elastic tissue in the wall of the artery and more smooth muscle
Arterioles
arteries under 0.5 mm in diameter. By constricting or relaxing the thick layer of smooth muscle in the walls of arterioles, blood flow can be increased or decreased to various capillaries.
Arteries and arterioles constitute the high pressure part of the c
Capillaries
very tiny (10 microns diameter), thin-walled vessels. This is the site of exchange of nutrients and gases between the blood and tissues.
All other organs of the circulatory system exist
only to serve the capillary beds
Capillaries in human body
-surface area= 6000 sq. meters
-60,000 miles long
-mass - twice the size of liver
Venules
small vessels which conduct venous blood from capillaries to veins
Veins
vessels that convey blood toward the heart
Vein vs artery
veins are of greater diameter, but thinner-walled than arteries with which they travel. there are both; superficial and deep veins
Veins also have
smooth muscle in their walls which allow them to change their diameter
The venules and the veins contsitute
the low pressure part of the circulatory system
Valves
found in those veins which carry blood against the force of gravity, especially in the vein of the legs
Mechanism involved in return of blood to heart;
a. pressure difference between left ventricle and right atrium - 120 - 3 = 117 mm Hg driving pressure
b. skeletal muscle pump - active muscles squeeze the veins and push the blood towards the heart
c. respiratory pump - decreased pressure in thoracic cavi
Blood
composed of specialized cells (red blood cells, white blood cells and platelets) suspended in a liquid plasma, makes up 50-60 %of blood by volume
blood volume of average adult with normal body composition
is 8% of body mass
Blood volume is greater for
larger, more endurance trained, and altitude acclimitized people
Plasma
composed of 90% water and 10 % solutes
Red blood cells (eukaryotes)
-biconcave dises about 7 mivros in diameter
-in human blood - 5-6 million RBC per cubic millimeter of blood
-hemocrit - the ratio of the volume of blood cells to the total volume of blood expressed as a percentage, 45 - 47% in males
-RBC's are continually
Hemoglobin
transports oxygen and carbion dioxide, iron containing protein which reversibly binds with oxygen
Normal values for hemoglobin
Men: 14-16 grams per 100 ml blood
Women: 12-14 grams per 100 ml blood
Gas exchange and transport
2 sites of gas exchange in the body
1. Alveolar-capillary membrane in lung:
- net diffusion of O2 from alveoli ? blood
- net diffusion of CO2 from blood ? alveoli
2. Tissue-capillary membrance in tissues:
- net diffusion of O2 from blood ? tissue
- net diffusion of CO2 from tissue ? blood
partial pressure of gases in a gas mixture
Partial pressure of a gas - the pressure of a gas in a gas mixture is dependent on:
(1) the total (barometric) pressure, and
(2) the fractional concentration of that gas
For example at sea level, the total pressure of all dry ambient (atmospheric) air gases
equals 760 mm Hg which equals barometric pressure
Composition of dry ambient air at sea level:
Gas Concentration Partial Pressure
O2 20.93% .2093 X 760 = 159.2mmHg
N2 79.04% .7904 X 760 = 600.7 mmHg
C O2 0.03% .0003 X 760 = 0.1 mmHg
100.00% 760.0 mmHg
The most important factor determining gas exchange is
the partial pressure gradients of the gases involved
Partial pressure of gases in a liquid (blood)
Henry's Law - the amount of gas that dissolves in a fluid is a function of two factors:
(1) The pressure of the gas above the fluid, which is given by the gas concentration
times the barometric pressure
(2) The solubility coefficient of the gas - CO2 is 2
Lung diffusing capacity
diffusing capacity for oxygen - the bolume of oxygen that crosses the alveolar-capillary membrane per minute per millimeter mercury pressure between the alveolar air and pulmonary capillary blood
Besides partial pressure gradients, diffusing capacity can be affected by other factors
1. The thickness of the respiratory membrane - length of the diffusion path. Diffusing capacity is decreased in restrictive lung diseases such as pulmonary fibrosis or pneumonia.
2. The number of red blood cells or their hemoglobin concentration or both
3
Diffusing capacity can increase up to 3 times resting values during heavy aerobic exercise. Mechanism:
1. Increased lung volumes during exercise ? increased surface area for diffusion
2. Opening up of more capillaries in the lung and greater volume of blood flowing
through the lung.
Transport of oxygen by blood
98% of the oxygen in the blood is carried in red blood cells in chemical combination
with hemoglobin. The other 2% is dissolved in plasma.
Hb + O2 ? HbO2.
O2 carrying capacity of hemoglobin - one gram of hemoglobin becomes saturated with O2 when it combin
For instance:
Therefore if hemoglobin concentration equals 15.0 grams per 100 ml of blood, the O2 carrying capacity of the blood would be 15.0 X 1.34 = 20.1 ml of O2 per 100 ml of
blood.
Percent saturation of hemoglobin with O2 (%SO2)
relates the amount of O2 actually
combined with hemoglobin to the maximum O2 capacity of hemoglobin
Arterial blood at rest at sea level (PB = 760 mmHg):
Hemoglobin is 97.5% saturated with O2 - 97.5% X 20.1 = 19.5 ml O2 per 100 ml blood
Venous blood at rest at sea level:
Hemoglobin is 75% saturated with 02 - 75% X 20.1 = 15.1 ml O2 per 100 ml blood
Arteriovenous oxygen difference = 19.5 - 15.1 = 4.4 ml O2
Hemoglobin acts as a tissue oxygen buffer system
The level of alveolar oxygen may
vary greatly, from 60 to more than 500 mm Hg, and still the PO2 in the tissue doesn't vary more than a few mm Hg from normal.
Blood
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